WO2023173437A1

WO2023173437A1 - Method, device and computer readable medium for communications

Info

Publication number: WO2023173437A1
Application number: PCT/CN2022/081808
Authority: WO
Inventors: Gang Wang; Zhaobang MIAO
Original assignee: Nec Corporation
Priority date: 2022-03-18
Filing date: 2022-03-18
Publication date: 2023-09-21

Abstract

Embodiments of the present disclosure relate to method, device and computer readable media for communications. A method comprises: transmitting, at a first terminal device and to a second terminal device, a data transmission corresponding to a plurality of Hybrid Automatic Repeat Request, HARQ, feedback occasions; detecting HARQ feedback information from the second terminal device on the plurality of HARQ feedback occasions, the HARQ feedback information being associated with the data transmission; determining whether a radio link failure criterion is met based at least in part on a scaling factor and a detection result; and in accordance with a determination that the radio link failure criterion is met, determining an occurrence of radio link failure on a sidelink channel between the first terminal device and the second terminal device. By taking the influence of LBT into consideration, unnecessary radio link failure procedure can be avoided.

Description

METHOD, DEVICE AND COMPUTER READABLE MEDIUM FOR COMMUNICATIONS

TECHNICAL FIELD

Embodiments of the present disclosure generally relate to the field of telecommunication, and in particular, to a method, device and computer readable media for sidelink communication.

BACKGROUND

Sidelink in unlicensed spectrum or band (SL-U) is one of the key topics in Release 18 of the 3rd Generation Partnership Project (3GPP) . The scheme of SL-U should base on New Radio (NR) sidelink and NR-U. Sidelink Hybrid Automatic Repeat Request (HARQ) feedback information associated with a sidelink data transmission should be reported to a terminal device that transmits the sidelink data transmission on a resource for a feedback channel, which may be referred to as physical sidelink feedback channel (PSFCH) . From the perspective of transmitting (Tx) UE, PSFCH reception occasion may not be always effective or available due to listen before talk (LBT) failure. For example, it may be occupied by other UE in the same radio access technology (RAT) or from other RAT. Hence, there could be multiple PSFCH reception occasions associated with one PSFCH transmission (e.g., the HARQ feedback information) in SL-U. In a case where PSFCH transmission is absent on a certain number of PSFCH reception occasions, Tx UE may indicate a HARQ-based sidelink radio link failure (RLF) detection. Therefore, the SL-U RLF detection procedure needs to be enhanced by taking the influence of LBT into consideration.

SUMMARY

In general, example embodiments of the present disclosure provide methods, devices and computer readable media for communications.

In a first aspect, there is provided a method for communications. The method comprises: transmitting, at a first terminal device and to a second terminal device, a data transmission corresponding to a plurality of Hybrid Automatic Repeat Request, HARQ, feedback occasions; detecting HARQ feedback information from the second terminal device on the plurality of HARQ feedback occasions, the HARQ feedback information being associated with the data transmission; determining whether a radio link failure criterion is met based at least in part on a scaling factor and a detection result; and in accordance with a determination that the radio link failure criterion is met, determining an occurrence of radio link failure on a sidelink channel between the first terminal device and the second terminal device.

In a second aspect, there is provided a method for communications. The method comprises: transmitting, at a first terminal device and to a second terminal device, a data transmission corresponding to a plurality of Hybrid Automatic Repeat Request, HARQ, feedback occasions; detecting HARQ feedback information from the second terminal device on the plurality of HARQ feedback occasions, the HARQ feedback information being associated with the data transmission; and once the HARQ feedback information is detected on one of the plurality of HARQ feedback occasions, determining that no further HARQ feedback information is to be detected on the rest of the plurality of HARQ feedback occasions.

In a third aspect, there is provided a method for communications. The method comprises: transmitting, at a first terminal device and to a second terminal device, a data transmission corresponding to a plurality of Hybrid Automatic Repeat Request, HARQ, feedback occasions; detecting HARQ feedback information from the second terminal device on the plurality of HARQ feedback occasions, the HARQ feedback information being associated with the data transmission; determining whether a radio link failure criterion is met based on a detection result and a discontinuous transmission, DTX, timer; and in accordance with a determination that the radio link failure criterion is met, determining an occurrence of radio link failure on a sidelink channel between the first terminal device and the second terminal device.

In a fourth aspect, there is provided a terminal device. The terminal device comprises a processor configured to perform the method according to the first aspect.

In a fifth aspect, there is provided a terminal device. The terminal device comprises a processor configured to perform the method according to the second aspect.

In a sixth aspect, there is provided a terminal device. The terminal device comprises a processor configured to perform the method according to the third aspect.

In a seventh aspect, there is provided a computer readable medium having instructions stored thereon. The instructions, when executed on at least one processor of a device, cause the device to perform the method according to the first aspect.

In an eight aspect, there is provided a computer readable medium having instructions stored thereon. The instructions, when executed on at least one processor of a device, cause the device to perform the method according to the second aspect.

In a ninth aspect, there is provided a computer readable medium having instructions stored thereon. The instructions, when executed on at least one processor of a device, cause the device to perform the method according to the third aspect.

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

Through the more detailed description of some embodiments of the present disclosure in the accompanying drawings, the above and other objects, features and advantages of the present disclosure will become more apparent, wherein:

Fig. 1 illustrates a schematic diagram of multiple PSFCH reception occasions assigned to a PSSCH transmission;

Fig. 2 illustrates an example communication network in which implementations of the present disclosure can be implemented;

Fig. 3 illustrates a schematic diagram of an example sidelink resource allocation according to some embodiments of the present disclosure;

Fig. 4 illustrates a signaling flow for communications according to some embodiments of the present disclosure;

Fig. 5 illustrates a flowchart of an example method for communications in accordance with an embodiment of the present disclosure;

Fig. 6 illustrates a signaling flow for communications according to some embodiments of the present disclosure;

Fig. 7 illustrates a flowchart of an example method for communications in accordance with an embodiment of the present disclosure;

Fig. 8 illustrates a signaling flow for communications according to some embodiments of the present disclosure;

Fig. 9 illustrates a flowchart of an example method for communications in accordance with an embodiment of the present disclosure;

Fig. 10 is a simplified block diagram of a device that is suitable for implementing embodiments of the present disclosure.

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

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 limitations 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.

As used herein, the term ‘terminal device’ refers to any device having wireless or wired communication capabilities. Examples of the terminal device include, but not limited to, user equipment (UE) , personal computers, desktops, mobile phones, cellular phones, smart phones, personal digital assistants (PDAs) , portable computers, tablets, wearable devices, internet of things (IoT) devices, Ultra-reliable and Low Latency Communications (URLLC) devices, Internet of Everything (IoE) devices, machine type communication (MTC) devices, device on vehicle for V2X communication where X means pedestrian, vehicle, or infrastructure/network, devices for Integrated Access and Backhaul (IAB) , Small Data Transmission (SDT) , mobility, Multicast and Broadcast Services (MBS) , positioning, dynamic/flexible duplex in commercial networks, reduced capability (RedCap) , Space borne vehicles or Air borne vehicles in Non-terrestrial networks (NTN) including Satellites and High Altitude Platforms (HAPs) encompassing Unmanned Aircraft Systems (UAS) , eXtended Reality (XR) devices including different types of realities such as Augmented Reality (AR) , Mixed Reality (MR) and Virtual Reality (VR) , the unmanned aerial vehicle (UAV) commonly known as a drone which is an aircraft without any human pilot, devices on high speed train (HST) , or image capture devices such as digital cameras, sensors, gaming devices, music storage and playback appliances, or Internet appliances enabling wireless or wired Internet access and browsing and the like. The ‘terminal device’ can further have ‘multicast/broadcast’ feature, to support public safety and mission critical, V2X applications, transparent IPv4/IPv6 multicast delivery, IPTV, smart TV, radio services, software delivery over wireless, group communications and IoT applications. It may also incorporate one or multiple Subscriber Identity Module (SIM) as known as Multi-SIM. The term “terminal device” can be used interchangeably with a UE, a mobile station, a subscriber station, a mobile terminal, a user terminal or a wireless device.

The terminal device or the network device may have Artificial intelligence (AI) or Machine learning capability. It generally includes a model which has been trained from numerous collected data for a specific function, and can be used to predict some information.

The terminal or the network device may work on several frequency ranges, e.g., FR1 (410 MHz –7125 MHz) , FR2 (24.25GHz to 71GHz) , frequency band larger than 100GHz as well as Tera Hertz (THz) . It can further work on licensed/unlicensed/shared spectrum. The terminal device may have more than one connection with the network devices under Multi-Radio Dual Connectivity (MR-DC) application scenario. The terminal device or the network device can work on full duplex, flexible duplex and cross division duplex modes.

The network device may have the function of network energy saving, Self-Organising Networks (SON) /Minimization of Drive Tests (MDT) . The terminal may have the function of power saving.

The term “network device” refers to a device which is capable of providing or hosting a cell or coverage where terminal devices can communicate. Examples of a network device include, but not limited to, a Node B (NodeB or NB) , an evolved NodeB (eNodeB or eNB) , a next generation NodeB (gNB) , a transmission reception point (TRP) , a remote radio unit (RRU) , a radio head (RH) , a remote radio head (RRH) , an IAB node, a low power node such as a femto node, a pico node, a reconfigurable intelligent surface (RIS) , Network-controlled Repeaters, and the like.

Sidelink communication provides several advantages, including reducing data transmission load on a core network, system resource consumption, transmission power consumption, and network operation costs, saving wireless spectrum resources, and increasing spectrum efficiency of a cellular wireless communication system. In a sidelink communication system, sidelink resources are used to transmit data or information between terminal devices (e.g., UE) . According to application scenarios, service types, etc., a sidelink communication manner includes but is not limited to device to device (D2D) communication, Vehicle-to-Everything (V2X) communication, etc.

V2X communication enables vehicles to communicate with other vehicles (i.e. Vehicle-to-Vehicle (V2V) communication) , with infrastructure (i.e. Vehicle-to-Infrastructure (V2I) , with wireless networks (i.e. Vehicle-to-Network (V2N) communication) , with pedestrians (i.e. Vehicle-to-Pedestrian (V2P) communication) , and even with the owner's home (i.e. Vehicle-to-Home (V2H) ) . Examples of infrastructure include roadside units such as traffic lights, toll gates and the like. V2X communication can be used in a wide range of scenarios, including in accident prevention and safety, convenience, traffic efficiency and clean driving, and ultimately in relation to autonomous or self-driving vehicles.

In the sidelink communication system, a UE that transmits a data transmission (e.g., PSSCH transmission) may be referred to as a Tx UE, while the other UE that receives the data transmission and attempts to report HARQ feedback information associated with the data transmission may be referred to as a receiving (Rx) UE. In SL-U scenario, multiple PSFCH reception occasions may be reserved for a single data transmission. Fig. 1 illustrates a schematic diagram of multiple PSFCH reception occasions assigned to a Physical Sidelink Shared Channel (PSSCH) transmission. As shown in Fig. 1, a PSSCH transmission is transmitted on slot #n, and candidate PSFCH resources on transmission opportunities, e.g., slots #n+2, #n+4, and #n+6 are allocated for the PSSCH transmission, where the number of transmission opportunities is 3, and a PSFCH period is 2 slots. The transmission opportunities are to be used by Rx UE for reporting the HARQ feedback information, thus hereinafter, the transmission opportunities may be also referred to as HARQ feedback occasions. From the perspective of Tx UE, the transmission opportunities correspond to PSFCH reception occasions or PSFCH occasions. That is, Tx UE is likely to receive the HARQ feedback information on the PSFCH reception occasions.

However, Rx UE may not always be able to take the transmission opportunities due to LBT failure. According to the legacy HARQ-based RLF detection mechanism, if HARQ feedback information is absent on a certain number of consecutive PSFCH reception occasions, Tx UE will treat those absent PSFCH reception occasions as discontinuous transmission (DTX) , and indicate that sidelink RLF is detected. In this case, Tx UE may then release a data radio bearer (DRB) of this destination (i.e., Rx UE) . This would lead to an unnecessary interruption and communication delay.

In order to solve above problems or other potential problems, solutions for sidelink RLF detection are proposed. According to embodiments of the present disclosure, the influence of LBT is taken into consideration so that unnecessary RLF procedure is avoided. In addition, a scaling factor is provided for scaling a threshold that is associated with a trigger of sidelink DTX detection. The solutions can improve the service continuity and reduce communication interruption and delay.

Fig. 2 illustrates a schematic diagram of an example communication network 200 in which embodiments of the present disclosure can be implemented. As shown in Fig. 2, the communication network 200 includes a first terminal device 210, a second terminal device 220, and a network device 230.

The first terminal device 210 and the second terminal device 220 may communicate with each other via sidelink channel through the Unified Air Interface, e.g., PC5 interface. In some example embodiments, the sidelink communication between the first terminal device 210 and the second terminal device 220 may be performed over unlicensed band, which may be referred to as SL-U. The unlicensed band may be shared with other terminal devices in the same RAT or from other RAT. Before transmitting any data, the terminal device 210 and/or the second terminal device 220 monitors the sidelink channel based on LBT mechanism. If the sidelink channel is unoccupied, the terminal device 210 and/or the second terminal device 220 then transmit the data on the sidelink channel.

The

terminal devices

210 and 220 may use resources in a sidelink resource pool for sidelink communication. The sidelink resource pool includes resources in time domain and frequency domain, which are the resources dedicated to the sidelink communication, or shared by the sidelink communication and a cellular link. The resources may contain multiple slots and resource blocks (RBs) , and all or part of the symbols in a slot can be used for sidelink transmission.

The network device 230 (e.g., a gNB in NR) may communicate with the first terminal device 210 and/or the second terminal device 220. In the context of the example embodiments, the direction from the network device 230 to the first terminal device 210 and/or the second terminal device 220 refers to downlink or DL. The direction from the first terminal device 210 and/or the second terminal device 220 to the network device 230 refers to uplink or UL.

It is to be understood that the number of devices in Fig. 2 is given for the purpose of illustration without suggesting any limitations to the present disclosure. The communication network 200 may include any suitable number of network devices and/or terminal devices adapted for implementing implementations of the present disclosure.

Communications in the communication system 200 may be implemented according to any proper communication protocol (s) , comprising, but not limited to, cellular communication protocols of the first generation (1G) , the second generation (2G) , 2.5G, 2.75G, the third generation (3G) , the fourth generation (4G) , 4.5G, the fifth generation (5G) communication protocols, 5.5G, 5G-Advanced networks, or the sixth generation (6G) networks, wireless local network communication protocols such as Institute for Electrical and Electronics Engineers (IEEE) 802.11 and the like, and/or any other protocols currently known or to be developed in the future. Moreover, the communication may utilize any proper wireless communication technology, comprising but not limited to: Code Divided Multiple Address (CDMA) , Frequency Divided Multiple Address (FDMA) , Time Divided Multiple Address (TDMA) , Frequency Divided Duplexer (FDD) , Time Divided Duplexer (TDD) , Multiple-Input Multiple-Output (MIMO) , Orthogonal Frequency Divided Multiple Access (OFDMA) and/or any other technologies currently known or to be developed in the future.

Principle and implementations of the present disclosure will be described in detail below with reference to FIG. 3 to FIG. 7. Fig. 3 illustrates a schematic diagram of an example sidelink resource allocation scheme 300 according to some embodiments of the present disclosure. For the purpose of discussion, the scheme 300 will be described with reference to Fig. 2. As shown in Fig. 3, the first terminal device 210 transmits a data transmission to the second terminal device 220 on a sidelink resource corresponding to slot #n, e.g., PSSCH/PSCCH resource. Accordingly, the second terminal device 220 reports HARQ feedback information associated with the data transmission on feedback resources corresponding to a plurality of slots #n+2, #n+4…#n+2K, for example, over PSFCH.

As previously mentioned, multiple transmission opportunities for HARQ feedback information associated with a single data transmission may be assigned. For example, for the Rx UE, there may be K transmission opportunities for HARQ feedback information. Accordingly, there should be K PSFCH reception occasions for the Tx UE. In the example of Fig. 3, K is the number of transmission opportunities for the second terminal device 220, and the PSFCH reception occasions for the first terminal device 210 includes slots #n+2, #n+4…#n+2K.

It should be understood that the sidelink resource allocation scheme 300 is given for illustrative purpose without any limitations of the present disclosure. In practice, different PSFCH period and more or less PSFCH reception occasions can be used for sidelink communication.

In order to avoid unnecessary RLF procedure due to DTX, there is provided an enhanced SL-U RLF detection mechanism. Now reference is made to Fig. 4, which illustrates a signaling flow for communications according to some embodiments of the present disclosure. For the purpose of discussion, the process 400 will be described with reference to Fig. 2 and Fig. 3. The process 400 may involve the first terminal device 210 that acts as Tx UE, the second terminal device 220 that acts as Rx UE, and the network device 230.

The first terminal device 210 transmits 402 a data transmission to the second terminal device 220 at slot #n. According to the resource allocation scheme 300, the data transmission corresponds to K HARQ feedback occasions, which are in slots #n+2, #n+4…#n+2K. The data transmission may be, for example, the PSSCH/PSCCH transmission.

In some example embodiments, a value of K may be configured or preconfigured by the network device 230. In this case, the network device 230 may indicate the value of K to the first terminal device 210 and the second terminal device 220.

Additionally or alternatively, the value of K may be decided by, for example, a scheduling module of Tx UE, i.e., the first terminal device 210. In a case where the network device 230 has preconfigured with a value of K, the first terminal device 210 may still determine a different value that is smaller than the one preconfigured by the network device 230 for K. The first terminal device 210 may indicate the value of K to the second terminal device 220.

In some other example embodiments, the value of K may be determined based on a priority of the data transmission (for example, ProSe Per-Packet Priority) , a priority of the service transmitted via the data transmission, latency requirement of HARQ feedback, etc., by either the first terminal device 210 or the second terminal device 220. In this case, the determined value of K is indicated from one to the other. Alternatively, both the first terminal device 210 and the second terminal device 220 may determine the value of K based on the same metric (s) or rule (s) , for example, metric (s) or rule (s) related to a priority of the data transmission, a priority of the service transmitted via the data transmission, latency requirement of HARQ feedback, etc.. Thus there is no need to exchange the value of K between them.

The second terminal device 220 may generate 404 HARQ feedback information indicative of whether the data transmission has been successfully received by the second terminal device 220 or generate 404 HARQ feedback information indicating that the data transmission has been successfully received by the second terminal device 220. Before transmitting the HARQ feedback information, the second terminal device 220 may determine 406 whether the sidelink feedback channel, i.e., PSFCH, is available. For example, the second terminal device 220 may perform LBT procedure on slots #n+2, #n+4…#n+2K, and determine whether to transmit the HARQ feedback information based on a result of LBT.

Accordingly, the first terminal device 210 detects 408 the HARQ feedback information from the second terminal device 220 on K HARQ feedback occasions corresponding to slots #n+2, #n+4…#n+2K.

The first terminal device 210 then determines 410 whether a RLF criterion is met based on a scaling factor and a detection result. The RLF criterion is defined to indicate if HARQ DTX is detected, which will be discussed in details later.

A scaling factor M may be associated with the number of HARQ feedback occasions, K. For example, a value of the scaling factor M may be equal to the value of K.

Alternatively, the scaling factor M may be predefined in relevant specification or (pre-) configured by the network device 230. In this case, the scaling factor M is independent of the number K of HARQ feedback occasions for a single data transmission. By predefining or (pre-) configuring scaling factor M, signaling overhead is reduced.

In some example embodiments where the scaling factor M is predefined or preconfigured, the first terminal device 210 may always apply the scaling factor M in determining whether the RLF criterion is met.

In some example embodiments where the scaling factor M is predefined or preconfigured, the first terminal device 210 may apply the scaling factor M in determining whether the RLF criterion is met, upon the first terminal device 210 (i.e., the Tx UE) operates on an unlicensed band or carrier. In other words, if the first terminal device 210 operates on a licensed band, the scaling factor M would not be applied, and the first terminal device 210 may apply a legacy threshold for determining whether the RLF criterion is met.

In some example embodiments, a list of candidate values of the scaling factor M may be predefined or preconfigured, and the first terminal device 210 may select one of the candidate values based on the following rules.

By way of example, the predefined or preconfigured list of candidate values of the scaling factor M is mapped to the number of PSFCH reception occasion K, as shown in Table 1.

Table 1. Mapping from a list of candidate values of M to K.

The number of PSFCH reception

Scaling factor M

occasion K
4	2
8	3

By way of another example, the predefined or preconfigured list of candidate values of the scaling factor M may be associated with a channel busy ratio (CBR) , as shown in Table 2.

Table 2. Relationship between a list of candidate values of M with CBR.

CBR	Scaling factor M
0<= CBR <= 0.3	2
0.3< CBR <= 0.6	3
0.6< CBR <= 0.8	4
0.8< CBR <= 0.1	5

By way of still another example, the predefined or preconfigured list of candidate values of the scaling factor M may be associated with a priority of PSSCH or a priority of service or packet transmitted via PSSCH. Table 3 shows an example relationship between the list of candidate values of scaling factor M with the priority of PSSCH.

Table 3. Relationship between a list of candidate values of M with priority of PSSCH.

The priority of PSSCH	Scaling factor M
1	2
2	3

When multiple candidate values of scaling factor M is defined or (pre-) configured, Tx UE of sidelink communication is able to flexibly adjust the value of scaling factor M to adapt to the current channel state or the service requirement in time.

Back to Fig. 4, if the RLF criterion is met, the first terminal device 210 determines an occurrence of RLF on the sidelink channel between the first terminal device 210 and the second terminal device 220. The sidelink channel between the first terminal device 210 and the second terminal device 220 may be also referred to as a sidelink channel to a specific destination, i.e., the second terminal device 220. Thus, the first terminal device 210 determines an occurrence of RLF on the sidelink channel between the first terminal device 210 and the second terminal device 220 means that the first terminal device 210 determines RLF is detected for the destination, i.e., the second terminal device 220. In this case, MAC layer of the first terminal device 210 may indicate HARQ-based sidelink RLF to RRC (i.e., the RRC layer of the first terminal device 210) , and release 412 the DRB of the destination, i.e., the second terminal device 220.

In some example embodiments, the RLF criterion may be defined as follows:

● If no HARQ feedback information is detected on all of the K HARQ feedback occasions, the first terminal device 210 may increment a value of a consecutive DTX counter associated with the sidelink channel, i.e., the numConsecutiveDTX is incremented by 1; and

● if the value of the consecutive DTX counter reaches a maximum value of the consecutive DTX counter, e.g., sl-maxNumConsecutiveDTX, the first terminal device 210 may determine that the RLF criterion is met. In this case, the first terminal device 210 may indicate the HARQ-based sidelink RLF to RRC, and release the DRB of the destination, i.e., the second terminal device 220.

● Otherwise, if HARQ feedback information is detected on any of the K HARQ feedback occasions, the first terminal device 210 may determine that the radio link failure criterion is not met. In this case, the first terminal device 210 may re-initialize the value of numConsecutiveDTX to zero.

In the above embodiments, the scaling factor M is equal to the number K, and a trigger for incrementing the value of numConsecutiveDTX is delayed. In this way, unnecessary RLF procedure can be avoided.

The following table shows example sidelink RLF related actions of Tx UE, such as performed by the first terminal device 210:

Alternatively, in some example embodiments, the RLF criterion may be defined as follows:

● a threshold of a consecutive DTX counter associated with the sidelink channel (e.g., the numConsecutive DTX) is determined based on the scaling factor M and a maximum value of the consecutive DTX counter (e.g., sl-maxNumConsecutiveDTX) . Accordingly, the threshold is denoted by M*sl-maxNumConsecutiveDTX.

● If no HARQ feedback information is detected on one of the K HARQ feedback occasions, the first terminal device 210 may increment a value of the consecutive DTX counter; and

● If the value of the consecutive DTX counter reaches the threshold (e.g., M*sl-maxNumConsecutiveDTX) , the first terminal device 210 may determine that the RLF criterion is met. In this case, MAC layer of the first terminal device 210 may indicate the HARQ-based sidelink RLF to RRC (i.e., the RRC layer of the first terminal device 210) , and release the DRB of the destination, i.e., the second terminal device 220.

● Otherwise, if the HARQ feedback information is detected on K HARQ feedback occasions, the first terminal device 210 may determine that the radio link failure criterion is not met. In this case, the first terminal device 210 may re-initialize the value of numConsecutiveDTX to zero.

In the above embodiments, the threshold for identifying the RLF is scaled by M, as compared with the legacy HARQ-based sidelink RLF detection scheme. The scaling factor M may be associated with the number K, or alternatively predefined or (pre-) configured. In this way, unnecessary RLF procedure can be avoided.

● If no HARQ feedback information is detected on the K HARQ feedback occasions, the first terminal device 210 may increment the value of the consecutive DTX counter associated with the sidelink channel, for example, the numConsecutiveDTX is incremented by 1, and start a DTX timer (e.g., timerDTX) if the DTX timer is not running. The DTX timer is provided to ensure the delay due to HARQ DTX detection is acceptable.

● The first terminal device 210 may determine that the RLF criterion is met, if one of the following is met:

i) the value of the consecutive DTX counter reaches a maximum value of the consecutive DTX counter, e.g., sl-maxNumConsecutiveDTX.

ii) a value of the DTX timer reaches a maximum value of the DTX timer (e.g., maxValueTimerDTX) , or

iii) the DTX timer expires.

In any of the above cases, MAC layer of the first terminal device 210 may indicate the HARQ-based sidelink RLF to RRC (i.e., the RRC layer of the first terminal device 210) , and release the DRB of the destination, i.e., the second terminal device 220.

● Otherwise, if HARQ feedback information is detected on any of the K HARQ feedback occasions, the first terminal device 210 may determine that the radio link failure criterion is not met. In this case, the first terminal device 210 may re-initialize the value of numConsecutiveDTX to zero. Additionally, the first terminal device 210 may stop the DTX timer in this case. Alternatively, the first terminal device 210 may restart the DTX timer in this case. For example, for the RLF criterion that a value of the DTX timer reaches a maximum value of the DTX timer, to start the DTX timer means to set the DTX timer to the initial value, such as 0 or 1, and to restart the DTX timer means to set the DTX timer to the initial value, such as 0 or 1 accordingly. As another example, for the RLF criterion that, to start the DTX timer means to set the DTX timer to the maximum value and to restart the DTX timer means to set the DTX timer to the maximum value too.

● a threshold of a consecutive DTX counter associated with the sidelink channel (e.g., the numConsecutive DTX) is determined based on a maximum value of the consecutive DTX counter (e.g., sl-maxNumConsecutiveDTX) and optionally the scaling factor M. Accordingly, the threshold may be denoted by sl-maxNumConsecutiveDTX if M is not used, or by M*sl-maxNumConsecutiveDTX if M is used. The determined threshold may be configured via legacy IE, i.e., IE SL-ConfigCommonNR-r16 in SIB12 or a new IE (e.g., a SIB in a new format dedicated for SL-U) .

● If no HARQ feedback information is detected on one of the K HARQ feedback occasions, the first terminal device 210 may increment a value of the consecutive DTX counter, for example, the numConsecutiveDTX is incremented by 1, while start a DTX timer if the DTX timer is not running. The DTX timer is provided to ensure the delay is acceptable.

i) the value of the consecutive DTX counter reaches the threshold,

iii) the DTX timer expires.

In any of the above cases, the first terminal device 210 may indicate the HARQ-based sidelink RLF to RRC, and release the DRB of the destination, i.e., the second terminal device 220.

● Otherwise, if HARQ feedback information is detected on any of the K HARQ feedback occasions, the first terminal device 210 may determine that the radio link failure criterion is not met. In this case, the first terminal device 210 may re-initialize the value of numConsecutiveDTX to zero. Additionally, the first terminal device 210 may stop the DTX timer in this case. Alternatively, the first terminal device 210 may restart the DTX timer in this case.

In the above embodiments, the scaling factor M may be associated with the number K, or alternatively predefined or (pre-) configured.

● If no HARQ feedback information is detected on all of the K HARQ feedback occasions, the first terminal device 210 may increment the value of the consecutive DTX counter associated with the sidelink channel, for example, the numConsecutiveDTX is incremented by 1, while start or restart a DTX timer that is provided to ensure the delay is acceptable.

iii) the DTX timer expires.

● Otherwise, if HARQ feedback information is detected on any of the K HARQ feedback occasions, the first terminal device 210 may determine that the RLF criterion is not met. In this case, the first terminal device 210 may re-initialize the value of numConsecutiveDTX to zero.. Additionally, the first terminal device 210 may stop the DTX timer in this case. Alternatively, the first terminal device 210 may restart the DTX timer in this case.

● a threshold of a consecutive DTX counter associated with the sidelink channel (e.g., the numConsecutive DTX) is determined based on a maximum value of the consecutive DTX counter (e.g., sl-maxNumConsecutiveDTX) and optionally the number of HARQ feedback occasions (e.g., the value of M) . Accordingly, the threshold may be denoted by sl-maxNumConsecutiveDTX if M is not used, or by M*sl-maxNumConsecutiveDTX if M is used. The determined threshold may be configured via legacy IE, i.e., IE SL-ConfigCommonNR-r16 in SIB12 or a new IE (e.g., a SIB in a new format dedicated for SL-U) .

● If no HARQ feedback information is detected on one of the K HARQ feedback occasions, the first terminal device 210 may increment a value of the consecutive DTX counter, for example, the numConsecutiveDTX is incremented by 1, while start or restart a DTX timer that is provided to ensure the delay is acceptable.

i) the value of the consecutive DTX counter reaches the threshold.

iii) the DTX timer expires.

● Otherwise, if HARQ feedback information is detected on any of the K HARQ feedback occasions, the first terminal device 210 may determine that the RLF criterion is not met. In this case, the first terminal device 210 may re-initialize the value of numConsecutiveDTX to zero. Additionally, the first terminal device 210 may stop the DTX timer in this case. Alternatively, the first terminal device 210 may restart the DTX timer in this case.

In some example embodiments, parameters of the DTX timer, such as duration of the DTX timer, the maxValueTimerDTX, etc., may be configured or modified by a gNB (e.g., the network device 230) or Tx UE (e.g., the first terminal device 210) .

In some other embodiments, the parameters of the DTX timer and the maxValueTimerDTX may be configured via a system message, for example, SIB12 which includes a new IE containing the parameters of the DTX timer, or alternatively, a SIB in a new format dedicated for SL-U.

An example of the legacy system message (e.g., SIB12) including a new IE is shown below.

An example of a new SIB for SL-U is shown below.

In the above examples, the field of sl-MaxNumConsecutiveDTX indicates the maximum number of consecutive HARQ DTX before triggering sidelink RLF, the value n1 corresponds to 1, the value n2 corresponds to 2, and so on. The new IE is introduced to provide larger values for sl-MaxNumConsecutiveDTX than current release of 3GPP specification (e.g., release17) , for example, the n64 and n128 are added in the new IE.

According to the example embodiments, there is provided an enhanced sidelink RLF detection mechanism. In this mechanism, the influence of LBT is taken into consideration, thus unnecessary radio link failure procedure can be avoided. In particular, by adjusting a scaling factor, the trigger of HARQ DTX detection can be adapted to various channel states, service requirements, and application scenarios. In this way, the service continuity can be guaranteed and the communication delay can be reduced.

Fig. 5 illustrates a flowchart of an example method 500 for communications in accordance with an embodiment of the present disclosure. In some embodiments, the method 500 can be implemented at Tx UE in sidelink communication, for example, the first terminal device 210 as shown in Fig. 2. For the purpose of discussion, the method 500 will be described with reference to Fig. 2 as performed by the first terminal device 210 without loss of generality.

At 510, the first terminal device 210 transmits to the second terminal device 220 a data transmission corresponding to a plurality of HARQ feedback occasions. The number of the plurality of HARQ feedback occasions may be denoted by K.

At 520, the first terminal device 210 detects HARQ feedback information from the second terminal device 220 on the plurality of HARQ feedback occasions. The HARQ feedback information is associated with the data transmission.

At 530, the first terminal device 210 determines whether a RLF criterion is met based at least in part on a scaling factor and a detection result. The RLF criterion may be defined to indicate if HARQ DTX is detected. The scaling factor, denoted by M, may be provided for scaling a threshold that is associated with a trigger of sidelink DTX detection.

In some example embodiments, the scaling factor M is associated with the number of the plurality of HARQ feedback occasions, i.e., K. For example, the value of M may be equal to the value of K. If no HARQ feedback information is detected on the plurality of HARQ feedback occasions, the first terminal device 210 may increment a value of a consecutive DTX counter associated with the sidelink channel. If the value of the consecutive DTX counter reaches a maximum value of the consecutive DTX counter (e.g., sl-maxNumConsecutiveDTX) , the first terminal device 210 may determine that the RLF criterion is met.

In some example embodiments, the first terminal device 210 may determine a threshold of a consecutive DTX counter associated with the sidelink channel based on the scaling factor M and a maximum value of the consecutive DTX counter. For example, the threshold may be determined to be M*sl-maxNumConsecutiveDTX. If no HARQ feedback information is detected on one of the plurality of HARQ feedback occasions, the first terminal device 210 may increment a value of the consecutive DTX counter. If the value of the consecutive DTX counter reaches the threshold, the first terminal device 210 may then determine that the RLF criterion is met.

In some example embodiments, the scaling factor M may be associated with the number of the plurality of HARQ feedback occasions, K. In particular, if no HARQ feedback information is detected on the plurality of HARQ feedback occasions, the first terminal device 210 may increment a value of a consecutive DTX counter associated with the sidelink channel, while start a DTX timer if the DTX timer is not running. In a case where one of the following is met, the first terminal device 210 may determine that the RLF criterion is met:

● the value of the consecutive DTX counter reaches a maximum value of the consecutive DTX counter (e.g., sl-maxNumConsecutiveDTX )

● a value of the DTX timer reaches a maximum value of the DTX timer, or

● the DTX timer expires.

In some example embodiments, the first terminal device 210 may determine a threshold of a consecutive DTX counter associated with the sidelink channel based on the scaling factor and a maximum value of the consecutive DTX counter. If no HARQ feedback information is detected on one of the plurality of HARQ feedback occasions, the first terminal device 210 may increment a value of the consecutive DTX counter, while start a DTX timer if the DTX timer is not running. In a case where one of the following is met, the first terminal device 210 may determine that the RLF criterion is met:

● the value of the consecutive DTX counter reaches the threshold,

● a value of the DTX timer reaches a maximum value of the DTX timer, or

● the DTX timer expires.

In some example embodiments, the scaling factor M may be associated with the number of the plurality of HARQ feedback occasions, K. If no HARQ feedback information is detected on the plurality of HARQ feedback occasions, the first terminal device 210 may increment a value of a consecutive DTX counter associated with the sidelink channel, while start or restart a DTX timer. In a case where one of the following is met, the first terminal device 210 may determine that the RLF criterion is met:

● the value of the consecutive DTX counter reaches a maximum value of the consecutive DTX counter,

● a value of the DTX timer reaches a maximum value of the DTX timer, or

● the DTX timer expires.

In some example embodiments, the first terminal device 210 may determine a threshold of a consecutive DTX counter associated with the sidelink channel based on the scaling factor M and a maximum value of the consecutive DTX counter. For example, the threshold may be determined to be M*sl-maxNumConsecutiveDTX. If no HARQ feedback information is detected on one of the plurality of HARQ feedback occasions, the first terminal device 210 may increment a value of the consecutive DTX counter, while start or restart a DTX timer. In a case where one of the following is met, the first terminal device 210 may determine that the RLF criterion is met:

● the value of the consecutive DTX counter reaches the threshold,

● a value of the DTX timer reaches a maximum value of the DTX timer, or

● the DTX timer expires.

At least one of the maximum value of the consecutive DTX counter, and a duration and the maximum value of the DTX timer may be indicated via a system message. In some example embodiments, the first terminal device 210 may receive a SIB indicative of the maximum value of the consecutive DTX counter. The SIB may be dedicated to SL-U communication. Alternatively, the SIB may include an IE dedicated to the consecutive DTX counter associated with SL-U communication.

In some example embodiments, the first terminal device 210 may receive a SIB indicative of a duration and the maximum value of the DTX timer and the maximum value of the consecutive discontinuous transmission counter. The SIB may be dedicated to SL-U communication. Alternatively, the SIB may include an IE dedicated to the consecutive DTX counter associated with SL-U communication.

The scaling factor M may be indicated by a network device 230 that serves the first terminal device 210. In some example embodiments, the first terminal device 210 may receive an indication of the scaling factor M from the network device 230.

In some example embodiments, the first terminal device 210 may receive an indication of a number of HARQ feedback occasions associated with the data transmission (e.g., K) from a network device that serves the first terminal device 210, i.e., the network device 230. The first terminal device 210 may determine the scaling factor M based on the number of HARQ feedback occasions K and at least one of a latency requirement or a priority of the data transmission.

In some example embodiments, the scaling factor M may be determined by one of the first terminal device 210 or the second terminal device 220 based on at least one of a latency requirement or a priority of the data transmission.

In some example embodiments, the first terminal device 210 may determine a CBR of the sidelink channel. The first terminal device 210 may then select a value of the scaling factor M from a list of candidate values of the scaling factor M based on the CBR. The list of candidate values may be preconfigured by the network device 230 or predefined, e.g., in relevant specifications or standards.

In some example embodiments, the first terminal device 210 may determine the number of the plurality of HARQ feedback occasions, i.e., K. The first terminal device 210 may then select a value of the scaling factor M from a list of candidate values of the scaling factor M based on the number K. The list of candidate values may be preconfigured by the network device 230 or predefined, e.g., in relevant specifications or standards.

In some example embodiments, the scaling factor is preconfigured by the network device 230 or predefined, e.g., in relevant specifications or standards. If the first terminal device 230 operates on an unlicensed band, the first terminal device 210 may apply the scaling factor M in determining whether the radio link failure criterion is met.

If the RLF criterion is met, at 540, the first terminal device 210 determines an occurrence of RLF on a sidelink channel between the first terminal device 210 and the second terminal device 220.

In some example embodiments, if the HARQ feedback information is detected on at least one of the plurality of HARQ feedback occasions, the first terminal device 210 may determine that the RLF criterion is not met. In a case where the RLF criterion is not met, the first terminal device 210 may reinitialize the value of the consecutive DTX counter.

In some example embodiments where the RLF criterion is not met, the first terminal device 210 may stop the DTX timer.

In order to further reduce delay in sidelink communication, another enhanced SL-U RLF detection mechanism is provided, which will be described in connection with Fig. 6.

Fig. 6 illustrates a signaling flow for communications according to some embodiments of the present disclosure. For the purpose of discussion, the process 600 will be described with reference to Fig. 2 and Fig. 3. The process 600 may involve the first terminal device 210 that acts as Tx UE, the second terminal device 220 that acts as Rx UE, and the network device 230.

The first terminal device 210 transmits 602 a data transmission to the second terminal device 220 at slot #n. According to the resource allocation scheme 300, the data transmission corresponds to K HARQ feedback occasions, which are in slots #n+2, #n+4…#n+2K. The data transmission may be, for example, the PSSCH/PSCCH transmission.

Similar to process 400, the value of K may be configured or preconfigured by the network device 230, or alternatively, decided by, for example, a scheduling module of the first terminal device 210. Additionally or alternatively, the value of K may be determined based on a priority of the data transmission, a priority of the service transmitted via the data transmission, latency requirement of HARQ feedback, etc., by either the first terminal device 210 or the second terminal device 220. Similar configurations or operations are not repeated with details for brevity.

The second terminal device 220 may generate 604 HARQ feedback information indicative of whether the data transmission has been successfully received by the second terminal device 220 or indicative of the data transmission has been successfully received by the second terminal device 220. Before transmitting the HARQ feedback information, the second terminal device 220 may determine 606 whether the sidelink feedback channel, i.e., PSFCH, is available. For example, the second terminal device 220 may perform LBT procedure on slots #n+2, #n+4…#n+2K, and determine whether to transmit the HARQ feedback information based on a result of LBT.

Accordingly, the first terminal device 210 detects 608 the HARQ feedback information from the second terminal device 220 on at least part of the plurality of HARQ feedback occasions corresponding to slots #n+2, #n+4…#n+2K.

Once the HARQ feedback information is detected on one of the plurality of HARQ feedback occasions, the first terminal device 210 determines 610 that no further HARQ feedback information is to be detected on the rest of the plurality of HARQ feedback occasion. In other words, if HARQ feedback information is detected on any one of PSFCH reception occasions for one PSSCH, the first terminal device 210 does not expect HARQ DTX to be detected on the rest of the PSFCH reception occasions for the same PSSCH. In this case, TX UE has no need to preform DTX detection on the remaining PSFCH reception occasion (s) for the same PSSCH.

In some example embodiments, if the network indicates that the HARQ feedback information is only allowed to be transmitted on the first PSFCH reception occasion right after the successful LBT, the first terminal device 210 and the second terminal device 220 may operate based on process 600. Additionally, in these embodiments, the second terminal device 220 may not transmit HARQ-ACK on the remaining PSFCH reception occasion (s) for the same PSSCH. This may depend on the channel status, service requirements of delay and so on. For example, if the network determines that the current channel status is good enough, it may transmit such indication to the first terminal device 210 and the second terminal device 220.

In some example embodiments, upon the HARQ feedback information is detected on one of the plurality of HARQ feedback occasions, the first terminal device 210 may reinitialize the value of a consecutive DTX counter associated with a sidelink channel between the first terminal device 210 and the second terminal device 220.

Otherwise, if no HARQ feedback information is detected on one of the plurality of HARQ feedback occasions, the first terminal device 210 may increment a value of the consecutive DTX counter. If the value of the consecutive DTX counter reaches a maximum value of the consecutive DTX counter, the first terminal device 210 may then determine an occurrence of RLF on the sidelink channel.

In some example embodiments, the maxValueTimerDTX may be configured via a system message, for example, SIB12 which includes a new IE containing the parameters of the DTX timer, or alternatively, a SIB in a new format dedicated for SL-U. The example formats of the legacy system message (e.g., SIB12) including a new IE and the new SIB has been discussed in the description of process 400, and thus not repeated for brevity.

According to the example embodiments of the present disclosure, once HARQ feedback information is detected, the Tx UE will no more attempt to receive HARQ-ACK. Accordingly, the Rx UE may also avoid repeatedly transmitting the HARQ-ACK on PSFCH. As compared with the legacy sidelink RLF detection mechanism, the proposed solution leads to less communication delay and can avoid unnecessary RLF procedure.

Fig. 7 illustrates a flowchart of an example method 700 for communications in accordance with an embodiment of the present disclosure. In some embodiments, the method 700 can be implemented at Tx UE in sidelink communication, for example, the first terminal device 210 as shown in Fig. 2. For the purpose of discussion, the method 700 will be described with reference to Fig. 2 as performed by the first terminal device 210 without loss of generality.

At 710, the first terminal device 210 transmits to the second terminal device 220 a data transmission corresponding to a plurality of HARQ feedback occasions.

At 720, the first terminal device 210 detects for HARQ feedback information from the second terminal device 220 on the plurality of HARQ feedback occasions. The HARQ feedback information is associated with the data transmission.

Once the HARQ feedback information is detected on one of the plurality of HARQ feedback occasions at 730, the first terminal device 210 determines that no further HARQ feedback information is to be detected on the rest of the plurality of HARQ feedback occasions.

In some example embodiments, if no HARQ feedback information is detected on one of the plurality of HARQ feedback occasions, the first terminal device 210 may increment a value of a consecutive DTX counter associated with a sidelink channel between the first terminal device 210 and the second terminal device 220. In a case where the value of the consecutive DTX counter reaches a maximum value of the consecutive DTX counter, the first terminal device 210 may determine an occurrence of RLF on the sidelink channel.

In some example embodiments, once the HARQ feedback information is detected on one of the plurality of HARQ feedback occasions, the first terminal device 210 may reinitialize the value of the consecutive DTX counter.

In some example embodiments, the maximum value of the consecutive DTX counter may be indicated in a system message. In these embodiments, the first terminal device 210 may receive a SIB indicative of the maximum value of the consecutive DTX counter. The SIB may be a new SIB dedicated to a SL-U communication, or alternatively, the SIB may be a legacy SIB (e.g., SIB12) that comprises an IE dedicated to the consecutive DTX counter associated with SL-U communication.

In order to reduce delay in sidelink communication, another enhanced SL-U RLF detection mechanism is provided, which will be described in connection with Fig. 8.

Fig. 8 illustrates a signaling flow for communications according to some embodiments of the present disclosure. For the purpose of discussion, the process 800 will be described with reference to Fig. 2 and Fig. 3. The process 800 may involve the first terminal device 210 that acts as Tx UE, the second terminal device 220 that acts as Rx UE, and the network device 230.

The first terminal device 210 transmits 802 a data transmission to the second terminal device 220 at slot #n. According to the resource allocation scheme 300, the data transmission corresponds to K HARQ feedback occasions, which are in slots #n+2, #n+4…#n+2K. The data transmission may be, for example, the PSSCH/PSCCH transmission.

Similar to

processes

400 and 600, the value of K may be configured or preconfigured by the network device 230, or alternatively, decided by, for example, a scheduling module of the first terminal device 210. Additionally or alternatively, the value of K may be determined based on a priority of the data transmission, a priority of the service transmitted via the data transmission, latency requirement of HARQ feedback, etc., by either the first terminal device 210 or the second terminal device 220. Similar configurations or operations are not repeated with details for brevity.

The second terminal device 220 may generate 804 HARQ feedback information indicative of whether the data transmission has been successfully received by the second terminal device 220. Before transmitting the HARQ feedback information, the second terminal device 220 may determine 806 whether the sidelink feedback channel, i.e., PSFCH, is available. For example, the second terminal device 220 may perform LBT procedure on slots #n+2, #n+4…#n+2K, and determine whether to transmit the HARQ feedback information based on a result of LBT.

Accordingly, the first terminal device 210 detects 808 the HARQ feedback information from the second terminal device 220 on the plurality of HARQ feedback occasions corresponding to slots #n+2, #n+4…#n+2K.

The first terminal device 210 then determines 810 whether a RLF criterion is met based on a DTX timer and a detection result. The DTX timer is provided to ensure the delay due to HARQ DTX detection is acceptable. The RLF criterion is defined to indicate if HARQ DTX is detected, which will be discussed in details later.

Parameters of the DTX timer may be indicated in a system message. In some example embodiments, the first terminal device 210 may receive a SIB indicative of duration (e.g., TimerDTX) and the maximum value of the DTX timer (e.g., maxValueTimerDTX) . The SIB may be dedicated to SL-U communication. Alternatively, the SIB may include an IE dedicated to the consecutive DTX counter associated with SL-U communication.

In some example embodiments, the RLF criterion may be defined as follows:

● If no HARQ feedback information is detected on one of the K HARQ feedback occasions or each HARQ feedback occasion, the first terminal device 210 may increment a value of a consecutive DTX counter associated with the sidelink channel, for example, the numConsecutiveDTX is incremented by 1, while start the DTX timer if it is not running.

iii) the DTX timer expires.

● Otherwise, if HARQ feedback information is detected on any of the K HARQ feedback occasions or each HARQ feedback occasion, the first terminal device 210 may determine that the RLF criterion is not met. In this case, the first terminal device 210 may re-initialize the value of numConsecutiveDTX to zero. Additionally, the first terminal device 210 may stop the DTX timer in this case. Alternatively, the first terminal device 210 may restart the DTX timer in this case.

Additionally or alternatively, instead of comparing the value of the consecutive DTX counter with the maximum value of the consecutive DTX counter, the first terminal device 210 may further apply the scaling factor M as discussed in connection with Fig. 3 on the maximum value of the consecutive DTX counter. By way of example, a threshold of a consecutive DTX counter may be determined to be M*sl-maxNumConsecutiveDTX.

● If no HARQ feedback information is detected on one of the K HARQ feedback occasions or each HARQ feedback occasion, the first terminal device 210 may increment a value of the consecutive DTX counter, for example, the numConsecutiveDTX is incremented by 1, while start or restart a DTX timer that is provided to ensure the delay is acceptable.

i) the value of the consecutive DTX counter reaches a maximum value of the consecutive DTX counter,

iii) the DTX timer expires.

Fig. 9 illustrates a flowchart of an example method 900 for communications in accordance with an embodiment of the present disclosure. In some embodiments, the method 900 can be implemented at Tx UE in sidelink communication, for example, the first terminal device 210 as shown in Fig. 2. For the purpose of discussion, the method 900 will be described with reference to Fig. 2 as performed by the first terminal device 210 without loss of generality.

At 910, the first terminal device 210 transmits to the second terminal device 220 a data transmission corresponding to a plurality of HARQ feedback occasions.

At 920, the first terminal device 210 detects for HARQ feedback information from the second terminal device 220 on the plurality of HARQ feedback occasions. The HARQ feedback information is associated with the data transmission.

At 930, the first terminal device 210 determines whether a RLF criterion is met based on a detection result and a DTX timer.

In some example embodiments, if no HARQ feedback information is detected on one of the plurality of HARQ feedback occasions, the first terminal device 210 may increment a value of a consecutive DTX counter associated with the sidelink channel, while start the DTX timer if the DTX timer is not running. In a case where one of the following is met, the first terminal device 210 may determine that the RLF criterion is met:

● a value of the DTX timer reaches a maximum value of the DTX timer, or

● the DTX timer expires.

In some example embodiments, if no HARQ feedback information is detected on one of the plurality of HARQ feedback occasions or each HARQ feedback occasion, the first terminal device 210 may increment a value of a consecutive DTX counter associated with the sidelink channel, while start or restart the DTX timer if the DTX timer. In a case where one of the following is met, the first terminal device 210 may determine that the RLF criterion is met:

● a value of the DTX timer reaches a maximum value of the DTX timer, or

● the DTX timer expires.

In some example embodiments, a scaling factor M may be provided for scaling a threshold that is associated with a trigger of sidelink DTX detection. The scaling factor M may be associated with the number of the plurality of HARQ feedback occasions, or alternatively, predefined or (pre-) configured.

In these embodiments, the first terminal device 210 may determine a threshold of a consecutive DTX counter associated with the sidelink channel based on the scaling factor M and a maximum value of the consecutive DTX counter. By way of example, a threshold of a consecutive DTX counter may be determined to be M*sl-maxNumConsecutiveDTX. If no HARQ feedback information is detected on one of the plurality of HARQ feedback occasions, the first terminal device 210 may increment a value of the consecutive DTX counter, while start the DTX timer if the DTX timer is not running. In a case where one of the following is met, the first terminal device 210 may determine that the RLF criterion is met:

● the value of the consecutive DTX counter reaches the threshold,

● a value of the DTX timer reaches a maximum value of the DTX timer, or

● the DTX timer expires.

Alternatively, in these embodiments, the first terminal device 210 may determine a threshold of a consecutive DTX counter associated with the sidelink channel based on the scaling factor M and a maximum value of the consecutive DTX counter. By way of example, a threshold of a consecutive DTX counter may be determined to be M*sl-maxNumConsecutiveDTX. If no HARQ feedback information is detected on one of the plurality of HARQ feedback occasions, the first terminal device 210 may increment a value of the consecutive DTX counter, while start or restart the DTX timer. In a case where one of the following is met, the first terminal device 210 may determine that the RLF criterion is met:

● the value of the consecutive DTX counter reaches the threshold,

● a value of the DTX timer reaches a maximum value of the DTX timer, or

● the DTX timer expires.

In some example embodiments, the scaling factor M is preconfigured by the network device 230 or predefined, e.g., in relevant specifications or standards. If the first terminal device 230 operates on an unlicensed band, the first terminal device 210 may apply the scaling factor M in determining whether the radio link failure criterion is met.

At least one of the duration and the maximum value of the DTX timer and the maximum value of the consecutive DTX counter may be indicated via a system message. In some example embodiments, the first terminal device 210 may receive a SIB indicative of the maximum value of the consecutive DTX counter. The SIB may be dedicated to SL-U communication. Alternatively, the SIB may include an IE dedicated to the consecutive DTX counter associated with SL-U communication.

If the RLF criterion is met, at 940, the first terminal device 210 determines an occurrence of RLF on a sidelink channel between the first terminal device 210 and the second terminal device 220.

In some example embodiments, if at least one HARQ feedback information is detected on the plurality of HARQ feedback occasions, the first terminal device 210 may determine that the RLF criterion is not met. In this case, the first terminal device 210 may reinitialize the value of the consecutive DTX counter.

In some example embodiments, once the HARQ feedback information is detected on one of the plurality of HARQ feedback occasions, the first terminal device 210 may determine that no further HARQ feedback information is to be detected on the rest of the plurality of HARQ feedback occasions.

Fig. 10 is a simplified block diagram of a device 1000 that is suitable for implementing embodiments of the present disclosure. The device 1000 can be considered as a further example implementation of the first terminal device 210 or the second terminal device 220 as shown in Fig. 2. Accordingly, the device 1000 can be implemented at or as at least a part of the

terminal device

210 or 220.

As shown, the device 1000 includes a processor 1010, a memory 1020 coupled to the processor 1010, a suitable transmitter (TX) and receiver (RX) 1040 coupled to the processor 1010, and a communication interface coupled to the TX/RX 1040. The memory 1020 stores at least a part of a program 1030. The TX/RX 1040 is for bidirectional communications. The TX/RX 1040 has at least one antenna to facilitate communication, though in practice the terminal device or the network device as mentioned in this application may have several ones. The communication interface may represent any interface that is necessary for communication with other network elements, such as X2 interface for bidirectional communications between eNBs, S1 interface for communication between a Mobility Management Entity (MME) /Serving Gateway (S-GW) and the eNB, Un interface for communication between the eNB and a relay node (RN) , or Uu interface for communication between the eNB and a terminal device.

The program 1030 is assumed to include program instructions that, when executed by the associated processor 1010, enable the device 1000 to operate in accordance with the embodiments of the present disclosure, as discussed herein with reference to Fig. 3 to 9. The embodiments herein may be implemented by computer software executable by the processor 1010 of the device 1000, or by hardware, or by a combination of software and hardware. The processor 1010 may be configured to implement various embodiments of the present disclosure. Furthermore, a combination of the processor 1010 and memory 1020 may form processing means 1050 adapted to implement various embodiments of the present disclosure.

The memory 1020 may be of any type suitable to the local technical network and may be implemented using any suitable data storage technology, such as a non-transitory computer readable storage medium, semiconductor-based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory, as non-limiting examples. While only one memory 1020 is shown in the device 1000, there may be several physically distinct memory modules in the device 1000. The processor 1010 may be of any type suitable to the local technical network, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multicore processor architecture, as non-limiting examples. The device 1000 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.

In some example embodiments, a first terminal device comprises circuitry configured to: transmit, to a second terminal device, a data transmission corresponding to a plurality of Hybrid Automatic Repeat Request (HARQ) feedback occasions; detect HARQ feedback information from the second terminal device on the plurality of HARQ feedback occasions, the HARQ feedback information being associated with the data transmission; determine whether a radio link failure criterion is met based at least in part on a scaling factor and a detection result; and in accordance with a determination that the radio link failure criterion is met, determine an occurrence of radio link failure on a sidelink channel between the first terminal device and the second terminal device.

In some example embodiments, the scaling factor is associated with the number of the plurality of HARQ feedback occasions, and the circuitry may be configured to: in accordance with a determination that no HARQ feedback information is detected on the plurality of HARQ feedback occasions, increment a value of a consecutive discontinuous transmission (DTX) counter associated with the sidelink channel; and in accordance with a determination that the value of the consecutive DTX counter reaches a maximum value of the consecutive DTX counter, determine that the radio link failure criterion is met.

In some example embodiments, the circuitry may be configured to: determine a threshold of a consecutive discontinuous transmission (DTX) counter associated with the sidelink channel based on the scaling factor and a maximum value of the consecutive DTX counter; in accordance with a determination that no HARQ feedback information is detected on one of the plurality of HARQ feedback occasions, incrementing a value of the consecutive DTX counter; and in accordance with a determination that the value of the consecutive DTX counter reaches the threshold, determine that the radio link failure criterion is met.

In some example embodiments, the scaling factor is associated with the number of the plurality of HARQ feedback occasions, and the circuitry may be configured to: in accordance with a determination that no HARQ feedback information is detected on the plurality of HARQ feedback occasions, increment a value of a consecutive discontinuous transmission, DTX, counter associated with the sidelink channel, while starting a DTX timer if the DTX timer is not running; and in accordance with a determination that one of the following is met, determine that the radio link failure criterion is met: the value of the consecutive DTX counter reaches a maximum value of the consecutive DTX counter, a value of the DTX timer reaches a maximum value of the DTX timer, or the DTX timer expire.

In some example embodiments, the circuitry may be configured to: determining whether the radio link failure criterion is met comprises: determine a threshold of a consecutive discontinuous transmission, DTX, counter associated with the sidelink channel based on the scaling factor and a maximum value of the consecutive DTX counter; in accordance with a determination that no HARQ feedback information is detected on one of the plurality of HARQ feedback occasions, increment a value of the consecutive DTX counter, while start a DTX timer if the DTX timer is not running; and in accordance with a determination that one of the following is met, determine that the radio link failure criterion is met: the value of the consecutive DTX counter reaches the threshold, a value of the DTX timer reaches a maximum value of the DTX timer, or the DTX timer expires.

In some example embodiments, the plurality of periods is indicated in a radio resource control message from the second network device or a message received on a side control channel.

In some example embodiments, the scaling factor is associated with the number of the plurality of HARQ feedback occasions, and the circuitry may be configured to: in accordance with a determination that no HARQ feedback information is detected on the plurality of HARQ feedback occasions, increment a value of a consecutive discontinuous transmission (DTX) counter associated with the sidelink channel, while starting or restarting a DTX timer; and in accordance with a determination that one of the following is met, determine that the radio link failure criterion is met: the value of the consecutive DTX counter reaches a maximum value of the consecutive DTX counter, a value of the DTX timer reaches a maximum value of the DTX timer, or the DTX timer expires.

In some example embodiments, the circuitry may be configured to: determine a threshold of a consecutive discontinuous transmission (DTX) counter associated with the sidelink channel based on the scaling factor and a maximum value of the consecutive DTX counter; in accordance with a determination that no HARQ feedback information is detected on one of the plurality of HARQ feedback occasions, increment a value of the consecutive DTX counter, while start or restart a DTX timer; and in accordance with a determination that one of the following is met, determine that the radio link failure criterion is met: the value of the consecutive DTX counter reaches the threshold, a value of the DTX timer reaches a maximum value of the DTX timer, or the DTX timer expires.

In some example embodiments, the circuitry may be configured to: in accordance with a determination that at least one HARQ feedback information is detected, determine that the radio link failure criterion is not met; and in accordance with a determination that the radio link failure criterion is not met, reinitialize the value of the consecutive DTX counter.

In some example embodiments, the circuitry may be further configured to: in accordance with a determination that the radio link failure criterion is not met, stop the DTX time.

In some example embodiments, the circuitry may be further configured to: receive a system information block, SIB, indicative of the maximum value of the consecutive DTX counter, wherein the SIB is dedicated to a sidelink unlicensed communication, or wherein the SIB comprises an information element dedicated to the consecutive DTX counter associated with sidelink unlicensed communication.

In some example embodiments, the circuitry may be further configured to: receive a system information block, SIB, indicative of a duration and the maximum value of the DTX timer and the maximum value of the consecutive discontinuous transmission counter, wherein the SIB is dedicated to a sidelink unlicensed communication, or wherein the SIB comprises an information element dedicated to the consecutive discontinuous transmission counter associated with sidelink unlicensed communication.

In some example embodiments, the circuitry may be further configured to: receive, from a network device serving the first terminal device, an indication of the scaling factor.

In some example embodiments, the circuitry may be further configured to: receive, from a network device serving the first terminal device, an indication of a number of HARQ feedback occasions associated with the data transmission; and determine the scaling factor based on the number of HARQ feedback occasions and at least one of a latency requirement or a priority of the data transmission.

In some example embodiments, the scaling factor is determined by one of the first terminal device or the second terminal device based on at least one of a latency requirement or a priority of the data transmission.

In some example embodiments, the circuitry may be further configured to: determine a channel busy ratio, CBR, of the sidelink channel; and select, based on the CBR, a value of the scaling factor from a list of candidate values of the scaling factor, the list of candidate values being preconfigured by a network device or predefined.

In some example embodiments, the circuitry may be further configured to: determine the number of the plurality of HARQ feedback occasions; and select, based on the number, a value of the scaling factor from a list of candidate values of the scaling factor, the list of candidate values being preconfigured by a network device or predefined.

In some example embodiments, the scaling factor is preconfigured by a network device or predefined, and the circuitry may be further configured to: in accordance with a determination that the first terminal device operates on an unlicensed band, apply the scaling factor in determining whether the radio link failure criterion is met.

In some example embodiments, a first terminal device comprises circuitry configured to: transmit, to a second terminal device, a data transmission corresponding to a plurality of Hybrid Automatic Repeat Request (HARQ) feedback occasions; detect HARQ feedback information from the second terminal device on the plurality of HARQ feedback occasions, the HARQ feedback information being associated with the data transmission; and once the HARQ feedback information is detected on one of the plurality of HARQ feedback occasions, determine that no further HARQ feedback information is to be detected on the rest of the plurality of HARQ feedback occasions.

In some example embodiments, the circuitry may be further configured to: in accordance with a determination that no HARQ feedback information is detected on one of the plurality of HARQ feedback occasions, increment a value of a consecutive discontinuous transmission (DTX) counter associated with a sidelink channel between the first terminal device and the second terminal device; and in accordance with a determination that a value of the consecutive DTX counter reaches a maximum value of the consecutive DTX counter, determine an occurrence of radio link failure on the sidelink channel.

In some example embodiments, the circuitry may be further configured to: once the HARQ feedback information is detected on one of the plurality of HARQ feedback occasions, reinitialize the value of the consecutive DTX counter.

In some example embodiments, a first terminal device comprises circuitry configured to: transmit, to a second terminal device, a data transmission corresponding to a plurality of Hybrid Automatic Repeat Request (HARQ) feedback occasions; detect HARQ feedback information from the second terminal device on the plurality of HARQ feedback occasions, the HARQ feedback information being associated with the data transmission; determine whether a radio link failure criterion is met based on a detection result and a discontinuous transmission, DTX, timer; and in accordance with a determination that the radio link failure criterion is met, determine an occurrence of radio link failure on a sidelink channel between the first terminal device and the second terminal device.

In some example embodiments, the circuitry may be configured to: in accordance with a determination that no HARQ feedback information is detected on one of the plurality of HARQ feedback occasions, increment a value of a consecutive DTX counter associated with the sidelink channel, while starting the DTX timer if the DTX timer is not running; and in accordance with a determination that one of the following is met, determine that the radio link failure criterion is met: the value of the consecutive DTX counter reaches a maximum value of the consecutive DTX counter, a value of the DTX timer reaches a maximum value of the DTX timer, or the DTX timer expires.

In some example embodiments, the circuitry may be configured to: in accordance with a determination that no HARQ feedback information is detected on one of the plurality of HARQ feedback occasions, increment a value of a consecutive DTX counter associated with the sidelink channel, while start or restart the DTX timer; and in accordance with a determination that one of the following is met, determine that the radio link failure criterion is met: the value of the consecutive DTX counter reaches a maximum value of the consecutive DTX counter, a value of the DTX timer reaches a maximum value of the DTX timer, or the DTX timer expires.

In some example embodiments, the circuitry may be further configured to: in accordance with a determination that the radio link failure criterion is not met, stop the DTX timer.

In some example embodiments, the circuitry may be further configured to: once the HARQ feedback information is detected on one of the plurality of HARQ feedback occasions, determine that no further HARQ feedback information is to be detected on the rest of the plurality of HARQ feedback occasions.

In some example embodiments, the circuitry may be configured to: determine a threshold of a consecutive discontinuous transmission (DTX) counter associated with the sidelink channel based on a scaling factor and a maximum value of the consecutive DTX counter; in accordance with a determination that no HARQ feedback information is detected on one of the plurality of HARQ feedback occasions, increment a value of the consecutive DTX counter, while starting a DTX timer if the DTX timer is not running; and in accordance with a determination that one of the following is met, determine that the radio link failure criterion is met: the value of the consecutive DTX counter reaches the threshold, a value of the DTX timer reaches a maximum value of the DTX timer, or the DTX timer expires.

In some example embodiments, the circuitry may be configured to: determine a threshold of a consecutive discontinuous transmission (DTX) counter associated with the sidelink channel based on a scaling factor and a maximum value of the consecutive DTX counter; in accordance with a determination that no HARQ feedback information is detected on one of the plurality of HARQ feedback occasions, increment a value of the consecutive DTX counter, while starting or restarting the DTX timer; and in accordance with a determination that one of the following is met, determine that the radio link failure criterion is met: the value of the consecutive DTX counter reaches the threshold, a value of the DTX timer reaches a maximum value of the DTX timer, or the DTX timer expires.

In some example embodiments, the scaling factor is associated with the number of the plurality of HARQ feedback occasions.

In some example embodiments, the circuitry may be further configured to: determine a channel busy ratio (CBR) of the sidelink channel; and select, based on the CBR, a value of the scaling factor from a list of candidate values of the scaling factor, the list of candidate values being preconfigured by a network device or predefined.

In some example embodiments, the scaling factor is preconfigured by a network device or predefined, and the circuitry may be further configured to: in accordance with a determination that the first terminal device operates on an unlicensed band, determine the scaling factor to be applied.

The term “circuitry” used herein may refer to hardware circuits and/or combinations of hardware circuits and software. For example, the circuitry may be a combination of analog and/or digital hardware circuits with software/firmware. As a further example, the circuitry may be any portions of hardware processors with software including digital signal processor (s) , software, and memory (ies) that work together to cause an apparatus, such as a terminal device or a network device, to perform various functions. In a still further example, the circuitry may be hardware circuits and or processors, such as a microprocessor or a portion of a microprocessor, that requires software/firmware for operation, but the software may not be present when it is not needed for operation. As used herein, the term circuitry also covers an implementation of merely a hardware circuit or processor (s) or a portion of a hardware circuit or processor (s) and its (or their) accompanying software and/or firmware.

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 representation, it will be appreciated that the blocks, apparatus, systems, techniques or methods 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 process or method as described above with reference to FIGs. 2, 5 and 7 to 11. 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.

The above program code may be embodied on a machine readable medium, which may be any tangible medium that may contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device. The machine readable medium may be a machine readable signal medium or a machine readable storage medium. A machine 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 machine 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 language 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 method for communications, comprising:

transmitting, at a first terminal device and to a second terminal device, a data transmission corresponding to a plurality of Hybrid Automatic Repeat Request, HARQ, feedback occasions;

detecting HARQ feedback information from the second terminal device on the plurality of HARQ feedback occasions, the HARQ feedback information being associated with the data transmission;

determining whether a radio link failure criterion is met based at least in part on a scaling factor and a detection result; and

in accordance with a determination that the radio link failure criterion is met, determining an occurrence of radio link failure on a sidelink channel between the first terminal device and the second terminal device.
The method of claim 1, wherein the scaling factor is associated with the number of the plurality of HARQ feedback occasions, and wherein determining whether the radio link failure criterion is met comprises:

in accordance with a determination that no HARQ feedback information is detected on the plurality of HARQ feedback occasions, incrementing a value of a consecutive discontinuous transmission, DTX, counter associated with the sidelink channel; and

in accordance with a determination that the value of the consecutive DTX counter reaches a maximum value of the consecutive DTX counter, determining that the radio link failure criterion is met.
The method of claim 1, wherein determining whether the radio link failure criterion is met comprises:

determining a threshold of a consecutive discontinuous transmission, DTX, counter associated with the sidelink channel based on the scaling factor and a maximum value of the consecutive DTX counter;

in accordance with a determination that no HARQ feedback information is detected on one of the plurality of HARQ feedback occasions, incrementing a value of the consecutive DTX counter;

in accordance with a determination that the value of the consecutive DTX counter reaches the threshold, determining that the radio link failure criterion is met.
The method of claim 1, wherein the scaling factor is associated with the number of the plurality of HARQ feedback occasions, and wherein determining whether the radio link failure criterion is met comprises:

in accordance with a determination that no HARQ feedback information is detected on the plurality of HARQ feedback occasions, incrementing a value of a consecutive discontinuous transmission, DTX, counter associated with the sidelink channel, and starting a DTX timer if the DTX timer is not running; and

in accordance with a determination that one of the following is met, determining that the radio link failure criterion is met:

the value of the consecutive DTX counter reaches a maximum value of the consecutive DTX counter,

a value of the DTX timer reaches a maximum value of the DTX timer, or

the DTX timer expires.
The method of claim 1, wherein determining whether the radio link failure criterion is met comprises:

determining a threshold of a consecutive discontinuous transmission, DTX, counter associated with the sidelink channel based on the scaling factor and a maximum value of the consecutive DTX counter;

in accordance with a determination that no HARQ feedback information is detected on one of the plurality of HARQ feedback occasions, incrementing a value of the consecutive DTX counter, and starting a DTX timer if the DTX timer is not running; and

in accordance with a determination that one of the following is met, determining that the radio link failure criterion is met:

the value of the consecutive DTX counter reaches the threshold,

a value of the DTX timer reaches a maximum value of the DTX timer, or

the DTX timer expires.
The method of claim 1, wherein the scaling factor is associated with the number of the plurality of HARQ feedback occasions, and wherein determining whether the radio link failure criterion is met comprises:

in accordance with a determination that no HARQ feedback information is detected on the plurality of HARQ feedback occasions, incrementing a value of a consecutive discontinuous transmission, DTX, counter associated with the sidelink channel, and starting or restarting a DTX timer; and

in accordance with a determination that one of the following is met, determining that the radio link failure criterion is met:

the value of the consecutive DTX counter reaches a maximum value of the consecutive DTX counter,

a value of the DTX timer reaches a maximum value of the DTX timer, or

the DTX timer expires.
The method of claim 1, wherein determining whether the radio link failure criterion is met comprises:

determining a threshold of a consecutive discontinuous transmission, DTX, counter associated with the sidelink channel based on the scaling factor and a maximum value of the consecutive DTX counter;

in accordance with a determination that no HARQ feedback information is detected on one of the plurality of HARQ feedback occasions, incrementing a value of the consecutive DTX counter, and starting or restarting a DTX timer; and

in accordance with a determination that one of the following is met, determining that the radio link failure criterion is met:

the value of the consecutive DTX counter reaches the threshold,

a value of the DTX timer reaches a maximum value of the DTX timer, or

the DTX timer expires.
The method of any of claims 2 to 7 wherein determining whether the radio link failure criterion is met comprises:

in accordance with a determination that at least one HARQ feedback information is detected, determining that the radio link failure criterion is not met; and

in accordance with a determination that the radio link failure criterion is not met, reinitializing the value of the consecutive DTX counter.
The method of any of claims 4 to 7, further comprising:

in accordance with a determination that the radio link failure criterion is not met, stopping the DTX timer.
The method of claim 2 or 3, further comprising:

receiving a system information block, SIB, indicative of the maximum value of the consecutive DTX counter,

wherein the SIB is dedicated to a sidelink unlicensed communication, or

wherein the SIB comprises an information element dedicated to the consecutive DTX counter associated with sidelink unlicensed communication.
The method of any of claims 4 to 7, further comprising:

receiving a system information block, SIB, indicative of a duration and the maximum value of the DTX timer and the maximum value of the consecutive discontinuous transmission counter,

wherein the SIB is dedicated to a sidelink unlicensed communication, or

wherein the SIB comprises an information element dedicated to the consecutive discontinuous transmission counter associated with sidelink unlicensed communication.
The method of claim 1, further comprising:

receiving, from a network device serving the first terminal device, an indication of the scaling factor.
The method of claim 1, further comprising:

receiving, from a network device serving the first terminal device, an indication of a number of HARQ feedback occasions associated with the data transmission; and

determining the scaling factor based on the number of HARQ feedback occasions and at least one of a latency requirement or a priority of the data transmission.
The method of claim 1, wherein the scaling factor is determined by one of the first terminal device or the second terminal device based on at least one of a latency requirement or a priority of the data transmission.
The method of claim 1, further comprising:

determining a channel busy ratio, CBR, of the sidelink channel; and

selecting, based on the CBR, a value of the scaling factor from a list of candidate values of the scaling factor, the list of candidate values being preconfigured by a network device or predefined.
The method of claim 1, further comprising:

determining the number of the plurality of HARQ feedback occasions; and

selecting, based on the number, a value of the scaling factor from a list of candidate values of the scaling factor, the list of candidate values being preconfigured by a network device or predefined.
The method of claim 1, wherein the scaling factor is preconfigured by a network device or predefined, and the method further comprises:

in accordance with a determination that the first terminal device operates on an unlicensed band, determining the scaling factor to be applied.
A terminal device, comprising:

a processor configured to perform the method according to any of claims 1-17.
A computer readable medium having instructions stored thereon, the instructions, when executed on at least one processor of a device, causing the device to carry out the method according to any of claims 1-17.