Terminal device and method

Abstract

The embodiments of the present disclosure relate to a method, an apparatus, and a computer-readable medium for communication. The method includes: in a first terminal device, transmitting a data transmission corresponding to a Hybrid Automatic Repeat Request (HARQ) feedback opportunity to a second terminal device; detecting HARQ feedback information associated with the data transmission from the second terminal device on the plurality of HARQ feedback opportunities; determining whether a radio link failure criterion is met based on at least a scaling factor and a detection result; and determining an occurrence of a radio link failure on a sidelink channel between the first terminal device and the second terminal device according to a determination that the radio link failure criterion is met. By considering the effect of LBT, unnecessary radio link failure procedures can be avoided.

Description

[Technical field]

[0001] FIELD Embodiments of the present disclosure relate generally to the field of telecommunications, and more particularly to a method, apparatus, and computer-readable medium for sidelink communications. [Background technology]

[0002] Sidelink in unlicensed spectrum or band (SL-U) is one of the main themes of the 3rd Generation Partnership Project (3GPP) Release 18. The SL-U scheme should be based 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 the terminal device transmitting the sidelink data transmission on resources for a feedback channel called physical sidelink feedback channel (PSFCH). From the transmitting UE's perspective, the PSFCH reception opportunity may not always be valid or available for Listen Before Talk (LBT). For example, it may be occupied by other UEs within the same radio access technology (RAT) or from other RATs. Therefore, there may be multiple PSFCH reception opportunities associated with one PSFCH transmission (e.g., HARQ feedback information) in SL-U. If there is no PSFCH transmission on a certain number of PSFCH reception opportunities, the Tx UE may indicate HARQ-based sidelink radio link failure (RLF) detection. Therefore, the SL-U RLF detection procedure needs to be enhanced to take into account the impact of LBT. Summary of the Invention [Problem to be solved by the invention]

[0003] Generally, the exemplary embodiments of the present disclosure provide a communication method, apparatus, and computer-readable medium. [Means for solving the problem]

[0004] In a first aspect, a communication method is provided, the method including: in a first terminal device, transmitting a data transmission corresponding to a Hybrid Automatic Repeat Request (HARQ) feedback opportunity to a second terminal device, detecting HARQ feedback information associated with the data transmission from the second terminal device on the plurality of HARQ feedback opportunities, determining whether a radio link failure criterion is met based on at least a scaling factor and a detection result, and determining an occurrence of a radio link failure on a sidelink channel between the first terminal device and the second terminal device according to a determination that the radio link failure criterion is met.

[0005] In a second aspect, a method of communication is provided, the method including: transmitting, in a first terminal device, a data transmission corresponding to a Hybrid Automatic Repeat Request (HARQ) feedback opportunity to a second terminal device, detecting HARQ feedback information associated with the data transmission from the second terminal device on the plurality of HARQ feedback opportunities, and determining, when the HARQ feedback information is detected on one of the plurality of HARQ feedback opportunities, that there is no other HARQ feedback information detected on remaining ones of the plurality of HARQ feedback opportunities.

[0006] In a third aspect, a method of communication is provided, comprising: in a first terminal device, transmitting to a second terminal device a data transmission corresponding to a Hybrid Automatic Repeat Request (HARQ) feedback opportunity, detecting HARQ feedback information associated with the data transmission from the second terminal device on the plurality of HARQ feedback opportunities, determining whether a radio link failure criterion is met based on the detection result and a discontinuous transmission (DTX) timer, and determining an occurrence of a radio link failure on a sidelink channel between the first terminal device and the second terminal device according to a determination that the radio link failure criterion is met.

[0007] In a fourth aspect, there is provided a terminal device, the terminal device comprising a processor configured to execute the method according to the first aspect.

[0008] In a fifth aspect, there is provided a terminal device, the terminal device comprising a processor configured to execute the method according to the second aspect.

[0009] In a sixth aspect, there is provided a terminal device, the terminal device comprising a processor configured to execute the method according to the third aspect.

[0010] In a seventh aspect, there is provided a computer readable medium storing instructions which, when executed on at least one processor of an apparatus, cause the apparatus to perform a method according to the first aspect.

[0011] In an eighth aspect, there is provided a computer readable medium storing instructions which, when executed on at least one processor of an apparatus, cause the apparatus to perform a method according to the second aspect.

[0012] In a ninth aspect, there is provided a computer readable medium having stored thereon instructions which, when executed on at least one processor of an apparatus, cause the apparatus to perform a method according to the third aspect.

[0013] It should be understood that this summary is not intended to identify key or essential features of the embodiments of the present disclosure, nor to limit the scope of the present disclosure. Other features of the present disclosure will be readily apparent from the following description. [Brief description of the drawings]

[0014] The above and other objects, features and advantages of the present disclosure will become more apparent from the following detailed description of several embodiments of the present disclosure in the accompanying drawings.

[0015] [Figure 1] 2 is a schematic diagram of multiple PSFCH reception opportunities allocated to a PSSCH transmission;

[0016] [Diagram 2] FIG. 1 illustrates an exemplary communications network in which embodiments of the present disclosure may be implemented.

[0017] [Diagram 3] FIG. 2 is a schematic diagram of an example sidelink resource allocation in accordance with some embodiments of the present disclosure.

[0018] [Figure 4] FIG. 2 illustrates a signaling flow for communication in accordance with some embodiments of the present disclosure.

[0019] [Diagram 5] 1 is a flowchart of an exemplary method for communication according to an embodiment of the present disclosure.

[0020] [Figure 6] FIG. 2 illustrates a signaling flow for communication in accordance with some embodiments of the present disclosure.

[0021] [Figure 7] 1 is a flowchart of an exemplary method for communication according to an embodiment of the present disclosure.

[0022] [Figure 8] FIG. 2 illustrates a signaling flow for communication in accordance with some embodiments of the present disclosure.

[0023] [Figure 9] 1 is a flowchart of an exemplary method for communication according to an embodiment of the present disclosure.

[0024] [Figure 10] FIG. 1 is a schematic block diagram of an apparatus suitable for implementing embodiments of the present disclosure.

[0025] In the drawings, the same or similar reference numbers represent the same or similar elements. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] The principles of the present disclosure will now be described with reference to some exemplary embodiments. It should be understood that these embodiments are provided for illustrative purposes only, to assist those skilled in the art in understanding and implementing the present disclosure, and do not imply any limitations on the scope of the present disclosure. The disclosure described herein can be implemented in various ways different from those described below.

[0027] In the following description and claims, unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure pertains.

[0028] As used herein, the term "terminal device" refers to any device having wireless or wired communication capabilities. Examples of terminal devices include User Equipment (UE), personal computers, desktops, mobile phones, cellular phones, smartphones, personal digital assistants (PDAs), portable computers, tablets, wearable devices, Internet of Things (IoT) devices, Ultra-Reliable Low Latency Communication (URLLC) devices, Internet of Everything (IoE) devices, machine type communication (MTC) devices, vehicle-mounted devices for V2X communications where X means pedestrian, vehicle, or infrastructure / network, devices for integrated access and integrated access and backhaul (IAB), Small Data Transmission (SDT), Multicast and Broadcast Services (MBS), positioning, dynamic / flexible duplication in commercial networks, reduced capability (RedCap), High Altitude Platforms (HAP) including satellites and Unmanned Aircraft Systems (UAS). These include, but are not limited to, satellite-mounted vehicles or airborne vehicles in a non-terrestrial network (NTN) including the ICT Platform, extended reality (XR) devices including different types of reality such as augmented reality (AR), mixed reality (MR), and virtual reality (VR), unmanned aerial vehicles (UAVs), which are aircraft without a human pilot and are commonly referred to as drones, devices on high speed trains (HSTs), image acquisition devices such as digital cameras, sensor game devices, music storage and playback devices, or Internet appliances that enable wireless or wired Internet access and browsing.The "Terminal Equipment" may further have "Multicast / Broadcast" capabilities to support public safety and mission critical V2X applications, transparent IPv4 / IPv6 multicast distribution, IPTV, Smart TV, wireless services, over-the-air software distribution, group communication and IoT applications. It may also incorporate one or more Subscriber Identity Modules (SIMs), known as multi-SIMs. The term "Terminal Equipment" may be used interchangeably with UE, mobile station, subscriber station, mobile terminal, user terminal, or wireless device.

[0029] The terminal device or network device may have the capability of artificial intelligence (AI) or machine learning. Generally, it includes a model trained from a large amount of data collected for a specific function and can be used to predict some information.

[0030] The terminal device or network device may operate on several frequency ranges, such as FR1 (410 MHz-7125 MHz), FR2 (24.25 GHz-71 GHz), frequency bands greater than 100 GHz, and Tera Hertz (THz). It can also operate on licensed / unlicensed / shared spectrum. The terminal device may have two or more connections with the network device under Multi-Radio Dual Connectivity (MR-DC) application scenarios. The terminal device or network device can operate in full duplex, flexible duplex, and cross division duplex modes.

[0031] The network device may have a function of network energy saving, Self-Organizing Networks (SON) / Minimization of Drive Test (MDT). The terminal may have a function of power saving.

[0032] The term "network device" refers to a device capable of providing or hosting a cell or coverage in which a terminal device can communicate. Examples of network devices include, but are not limited to, a Node B (NodeB or NB), an evolved Node B (eNodeB or eNB), a next generation Node B (gNB), a transmit / receive point (TRP), a remote radio unit (RRU), a radio head (RH), a remote radio head (RRH), an IAB node, a femto node, a pico node, a reconfigurable intelligent surface (RIS), a low power node such as a network controlled repeater, etc.

[0033] Sidelink communication provides several advantages, including reducing data transmission load on the core network, system resource consumption, transmission power consumption and network operation costs, saving radio spectrum resources and improving the spectrum efficiency of the cellular wireless communication system. In a sidelink communication system, sidelink resources are used to transmit data or information between terminal devices (e.g., UEs). Depending on application scenarios, types of services, etc., sidelink communication schemes include, but are not limited to, device-to-device (D2D) communication, vehicle-to-everything (V2X) communication, etc.

[0034] V2X communication enables vehicles to communicate with other vehicles (i.e., vehicle-to-vehicle (V2V) communication), infrastructure (i.e., vehicle-to-infrastructure (V2I) communication), wireless networks (i.e., vehicle-to-network (V2N) communication), pedestrians (i.e., vehicle-to-pedestrian (V2P) communication), and even with the owner's home (i.e., vehicle-to-home (V2H) communication). Examples of infrastructure include roadside devices such as traffic lights and toll booths. V2X communication can be used in a wide range of situations, including accident prevention, safety, convenience, traffic efficiency, and accident-free driving, and will ultimately lead to autonomous and self-driving vehicles.

[0035] In a sidelink communication system, a UE that transmits a data transmission (e.g., a PSSCH transmission) may be referred to as a Tx UE, and another 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 a SL-U scenario, multiple PSFCH reception opportunities may be reserved for one data transmission. FIG. 1 is a schematic diagram of multiple PSFCH reception opportunities allocated 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 the transmission opportunity, e.g., slots #n+2, #n+4, and #n+6, are assigned for PSSCH transmission, where the number of transmission opportunities is 3 and the PSFCH period is 2 slots. Since the transmission opportunity is utilized by the Rx UE to report HARQ feedback information, in the following, the transmission opportunity may be referred to as a HARQ feedback opportunity. From the perspective of a Tx UE, a transmission opportunity corresponds to a PSFCH receiving opportunity or a PSFCH opportunity, i.e., the Tx UE is more likely to receive the HARQ feedback information on a PSFCH receiving opportunity.

[0036] However, Rx UEs may not always be able to utilize transmission opportunities due to LBT failure. According to the conventional HARQ-based RLF detection mechanism, if there is no HARQ feedback information on a certain number of consecutive PSFCH reception opportunities, the Tx UE will treat those absent PSFCH reception opportunities as discontinuous transmission (DTX) and indicate that sidelink RLF is detected. In this case, the Tx UE may release the data radio bearer (DRB) of this destination (i.e., the Rx UE). This leads to unnecessary interruptions and delays in communication.

[0037] To solve the above problems and other potential problems, a solution for sidelink RLF detection has been proposed. According to embodiments of the present disclosure, the effect of LBT is taken into account, and therefore unnecessary RLF procedures are avoided. Additionally, a scaling factor is provided to scale the threshold associated with triggering sidelink DTX detection. This solution can improve service continuity and reduce communication interruptions and delays.

[0038] 2 is a schematic diagram of an exemplary communication network 200 in which an embodiment of the present disclosure may 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.

[0039] The first terminal device 210 and the second terminal device 220 may communicate with each other via a sidelink channel by a unified air interface, e.g., a PC5 interface. In some exemplary embodiments, the sidelink communication between the first terminal device 210 and the second terminal device 220 may be performed on an 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 RATs. Before transmitting any data, the terminal device 210 and / or the second terminal device 220 monitors the sidelink channel based on the LBT mechanism. If the sidelink channel is not occupied, the terminal device 210 and / or the second terminal device 220 transmits data on the sidelink channel.

[0040] The terminal devices 210 and 220 may use resources in a sidelink resource pool for sidelink communication. The sidelink resource pool includes resources in the time and frequency domain that are either dedicated to sidelink communication or shared by sidelink communication and the cellular link. The sidelink resource pool may include multiple slots and resource blocks (RBs), where all or a portion of the symbols in a slot can be used for sidelink transmission.

[0041] 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 embodiment, the direction from the network device 230 to the first terminal device 210 and / or the second terminal device 220 is referred to as the downlink or DL. The direction from the first terminal device 210 and / or the second terminal device 220 to the network device 230 is referred to as the uplink or UL.

[0042] It should be understood that the number of devices in Figure 2 is given for illustrative purposes and does not imply any limitations to the present disclosure. Communications network 200 may include any suitable number of network devices and / or terminal devices suitable for implementing embodiments of the present disclosure.

[0043] Communications in communication system 200 may be achieved according to any suitable communications protocol, including, but not limited to, a cellular communications protocol, such as a first generation (1G), second generation (2G), 2.5G, 2.75G, third generation (3G), fourth generation (4G), 4.5G, fifth generation (5G) communications protocol, 5.5G, 5G-Advanced networks, or sixth generation (6G) networks, a wireless local area network communications protocol, such as the Institute for Electrical and Electronics Engineers (IEEE) 802.11, and / or any other protocol now known or developed in the future. Further, the communications may utilize any suitable wireless communication technology, including, but not limited to, Code Division Multiple Access (CDMA), Frequency Division Multiple Access (FDMA), Time Division Multiple Access (TDMA), Frequency Division Duplexer (FDD), Time Division Duplexer (TDD), Multiple Input Multiple Output (MIMO), Orthogonal Frequency Division Multiple Access (OFDMA), and / or any other technology now known or developed in the future.

[0044] Hereinafter, the principles and implementations of the present disclosure will be described in detail with reference to Figures 3 to 7. Figure 3 is a schematic diagram of an exemplary sidelink resource allocation scheme 300 according to some embodiments of the present disclosure. For illustrative purposes, the scheme 300 will be described with reference to Figure 2. As shown in Figure 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., a PSSCH / PSCCH resource. Thus, the second terminal device 220 reports HARQ feedback information associated with the data transmission on feedback resources corresponding to a number of slots #n+2, #n+4... #n+2K, e.g., on a PSFCH.

[0045] As mentioned above, multiple transmission opportunities for HARQ feedback information associated with one data transmission may be allocated. For example, for an Rx UE, there may be K transmission opportunities for HARQ feedback information. Therefore, there should be K PSFCH reception opportunities for a 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 opportunities for the first terminal device 210 include slots #n+2, #n+4... #n+2K.

[0046] It should be understood that the sidelink resource allocation scheme 300 is given for illustrative purposes and does not pose any limitation to the present disclosure. In practice, different PSFCH periods and more or fewer PSFCH reception opportunities may be used for sidelink communications.

[0047] To avoid unnecessary RLF procedures by DTX, an enhanced SL-U RLF detection mechanism is provided. Reference is now made to FIG. 4, which illustrates a signaling flow for communication according to some embodiments of the present disclosure. For illustrative purposes, a process 400 is described with reference to FIG. 2 and FIG. 3. The process 400 may involve a first terminal device 210 functioning as a Tx UE, a second terminal device 220 functioning as an Rx UE, and a network device 230.

[0048] The first terminal device 210 transmits a data transmission to the second terminal device 220 in slot #n (402). According to the resource allocation scheme 300, the data transmission corresponds to K HARQ feedback opportunities in slots #n+2, #n+4... #n+2K. The data transmission may be, for example, a PSSCH / PSCCH transmission.

[0049] In some exemplary embodiments, the value of K may be set or pre-set by network device 230. In this case, network device 230 may indicate the value of K to first terminal device 210 and second terminal device 220.

[0050] Additionally or alternatively, the value of K may be determined, for example, by a scheduling module of the Tx UE, i.e., the first terminal device 210. If the network device 230 has already preset the value of K, the first terminal device 210 may still determine a different value for K that is smaller than the value preset by the network device 230. The first terminal device 210 may indicate the value of K to the second terminal device 220.

[0051] In some other exemplary embodiments, the value of K may be determined by either the first terminal device 210 or the second terminal device 220 based on the priority of data transmission (e.g., ProSe per packet priority), the priority of the service transmitted via the data transmission, the delay requirement of HARQ feedback, etc. 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 or rule, e.g., a metric or rule regarding the priority of data transmission, the priority of the service transmitted via the data transmission, the delay requirement of HARQ feedback, etc. Therefore, there is no need to exchange the value of K between them.

[0052] The second terminal device 220 may generate HARQ feedback information indicating whether the data transmission was successfully received by the second terminal device 220 (404), or may generate HARQ feedback information indicating that the data transmission was successfully received by the second terminal device 220 (404). Before transmitting the HARQ feedback information, the second terminal device 220 may determine whether a sidelink feedback channel, i.e., a PSFCH, is available (406). For example, the second terminal device 220 may perform an LBT procedure on slots #n+2, #n+4... #n+2K, and determine whether to transmit HARQ feedback information based on the result of the LBT.

[0053] Thus, the first terminal device 210 detects HARQ feedback information from the second terminal device 220 on K HARQ feedback opportunities corresponding to slots #n+2, #n+4 . . . #n+2K (408).

[0054] Then, the first terminal device 210 determines whether an RLF criterion is met based on the scaling factor and the detection result (410). The RLF criterion is defined to indicate whether HARQ DTX is detected, and will be described in detail later.

[0055] The scaling factor M may be associated with the number of HARQ feedback opportunities K. For example, the value of the scaling factor M may be equal to the value of K.

[0056] Alternatively, the scaling factor M may be predefined in the 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 opportunities for a single data transmission. Predefining or (pre)configuring the scaling factor M reduces signaling overhead.

[0057] In some exemplary embodiments in which the scaling factor M is predefined or preconfigured, the first terminal device 210 may always apply the scaling factor M when determining whether the RLF criterion is met.

[0058] In some exemplary embodiments in which the scaling factor M is predefined or preconfigured, the first terminal device 210 may apply the scaling factor M in determining whether the RLF criteria are met when the first terminal device 210 (i.e., Tx UE) operates on an unlicensed band or carrier. In other words, when the first terminal device 210 operates on a licensed band, the scaling factor M is not applied and the first terminal device 210 may apply a conventional threshold to determine whether the RLF criteria are met.

[0059] In some exemplary embodiments, a list of candidate values ​​for the scaling factor M may be predefined or preset, and the first terminal device 210 may select one of the candidate values ​​based on the following rules:

[0060] As an example, a predefined or preset list of candidate values ​​for the scaling factor M is mapped to the number of PSFCH reception opportunities K, as shown in Table 1. [Table 1]

[0061] As another example, a predefined or preset list of candidate values ​​for the scaling factor M may be associated with a channel busy ratio (CBR), as shown in Table 2. [Table 2]

[0062] As yet another example, a predefined or preset list of candidate values ​​for the scaling factor M may be associated with a priority of the PSSCH or a priority of a service or packet transmitted over the PSSCH. Table 3 shows an example relationship between a list of candidate values ​​for the scaling factor M and a priority of the PSSCH. [Table 3]

[0063] When multiple candidate values ​​of the scaling factor M are defined or (pre)defined, a Tx UE in sidelink communication can flexibly adjust the value of the scaling factor M to timely adapt to current channel conditions or service requirements.

[0064] Returning to FIG. 4, if the RLF criteria are met, the first terminal device 210 determines the 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 referred to as a sidelink channel to a specific destination, i.e., the second terminal device 220. Thus, the first terminal device 210 determining the 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 that an RLF has been detected for the destination, i.e., the second terminal device 220. In this case, the MAC layer of the first terminal device 210 may indicate the HARQ-based sidelink RLF to the 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 (412).

[0065] In some example embodiments, the RLF criteria may be defined as follows: if no HARQ feedback information is detected on any of the K HARQ feedback opportunities, the first terminal device 210 may increment a value of a consecutive DTX counter associated with the sidelink channel, i.e. increment numConsecutiveDTX by 1; If the value of the consecutive DTX counter reaches a maximum consecutive DTX counter value, 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 a HARQ-based sidelink RLF to the RRC and release the DRB of the destination, i.e., the second terminal device 220. If the HARQ feedback information is detected on any of the K HARQ feedback opportunities, first terminal device 210 may determine that the radio link failure criterion is not met. In this case, first terminal device 210 may reinitialize the value of numConsecutiveDTX to zero.

[0066] In the above embodiment, the scaling factor M is equal to the number K, and the trigger for incrementing the value of numConsecutiveDTX is delayed. In this way, unnecessary RLF procedures can be avoided.

[0067] The following table shows exemplary sidelink RLF related actions for a Tx UE, for example performed by the first terminal device 210: [Table 4]

[0068] Alternatively, in some example embodiments, the RLF criterion may be defined as follows: A threshold for a consecutive DTX counter (e.g., numConsecutiveDTX) associated with a sidelink channel is determined based on a scaling factor M and a maximum value of the consecutive DTX counter (e.g., sl-maxNumConsecutiveDTX). Thus, the threshold is denoted by M*sl-maxNumConsecutiveDTX. If the HARQ feedback information is not detected on one of the K HARQ feedback opportunities, the first terminal device 210 may increment a value of a consecutive DTX counter. 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, the MAC layer of the first terminal device 210 may indicate the HARQ-based sidelink RLF to the 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 the K HARQ feedback opportunities, first terminal device 210 may determine that the radio link failure criterion is not met. In this case, first terminal device 210 may reinitialize the value of numConsecutiveDTX to zero.

[0069] In the above embodiment, compared to the conventional HARQ based sidelink RLF detection scheme, the threshold for identifying RLF is scaled with M. The scaling factor M may be related to the number K or may be predefined or (pre)configured. In this way, unnecessary RLF procedures can be avoided.

[0070] The following table shows exemplary sidelink RLF related actions for a Tx UE, for example performed by the first terminal device 210: [Table 5]

[0071] Alternatively, in some example embodiments, the RLF criterion may be defined as follows: If no HARQ feedback information is detected on the K HARQ feedback opportunities, the first terminal device 210 may increment a consecutive DTX counter associated with the sidelink channel, e.g. increment numConsecutiveDTX by 1, and may start a DTX timer (e.g. timerDTX) if the DTX timer is not running. The DTX timer is provided to ensure that the delay due to HARQ DTX detection is tolerable. The first terminal device 210 is i) the value of the consecutive DTX counter reaches the maximum consecutive DTX counter value, e.g., sl-maxNumConsecutiveDTX; ii) The value of the DTX timer reaches the maximum DTX timer value (e.g., maxValueTimerDTX), or iii) the DTX timer expires; If one of the following is satisfied, then it may be determined that the RLF criteria is satisfied. In any of the above cases, the 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 opportunities, 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 reinitialize the value of numConsecutiveDTX to zero. Additionally, in this case, the first terminal device 210 may stop the DTX timer. Alternatively, in this case, the first terminal device 210 may restart the DTX timer. Thus, for example, for an RLF criterion where the value of the DTX timer reaches the maximum value of the DTX timer, starting the DTX timer means setting the DTX timer to an initial value, for example, 0 or 1, and restarting the DTX timer means setting the DTX timer to an initial value, for example, 0 or 1. As another example, for the RLF criterion, starting the DTX timer means setting the DTX timer to a maximum value, and restarting the DTX timer also means setting the DTX timer to a maximum value.

[0072] The following table shows exemplary sidelink RLF related actions for a Tx UE, for example performed by the first terminal device 210: [Table 6]

[0073] Alternatively, in some example embodiments, the RLF criterion may be defined as follows: ● A threshold for a consecutive DTX counter associated with a sidelink channel (e.g. numConsecutiveDTX) is determined based on the maximum value of the consecutive DTX counter (e.g. sl-maxNumConsecutiveDTX) and possibly a scaling factor M. Thus, the threshold may be represented by sl-maxNumConsecutiveDTX if M is not used, or M*sl-maxNumConsecutiveDTX if M is used. The determined threshold may be configured via a traditional IE, i.e. SL-ConfigCommonNR-r16 in SIB12, or a new IE (e.g. a new format SIB dedicated for SL-U). If no HARQ feedback information is detected on one of the K HARQ feedback opportunities, the first terminal device 210 may increment the value of the consecutive DTX counter, e.g., increment numConsecutiveDTX by 1, and at the same time start the DTX timer if it is not running. The DTX timer is provided to ensure that the delay is tolerable. The first terminal device 210 is i) the value of the continuous DTX counter reaches the threshold; ii) The value of the DTX timer reaches the maximum DTX timer value (e.g., maxValueTimerDTX), or iii) the DTX timer expires; If one of the following is satisfied, then it may be determined that the RLF criteria is satisfied. In any of the above cases, the first terminal device 210 may indicate a HARQ-based sidelink RLF to the 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 opportunities, first terminal device 210 may determine that the radio link failure criterion is not met. In this case, first terminal device 210 may reinitialize the value of numConsecutiveDTX to zero. Additionally, first terminal device 210 may stop the DTX timer in this case. Alternatively, first terminal device 210 may restart the DTX timer in this case.

[0074] In the above embodiment, the scaling factor M may be related to the number K or may be predefined or (pre)set.

[0075] The following table shows exemplary sidelink RLF related actions for a Tx UE, for example performed by the first terminal device 210: [Table 7]

[0076] Alternatively, in some example embodiments, the RLF criterion may be defined as follows: ● If no HARQ feedback information is detected on any of the K HARQ feedback opportunities, the first terminal device 210 may increment the value of a consecutive DTX counter associated with the sidelink channel, for example incrementing numConsecutiveDTX by 1, while starting or restarting a DTX timer provided to ensure that the delay is acceptable. The first terminal device 210 is i) the value of the consecutive DTX counter reaches the maximum consecutive DTX counter value, e.g., sl-maxNumConsecutiveDTX; ii) The value of the DTX timer reaches the maximum DTX timer value (e.g., maxValueTimerDTX), or iii) the DTX timer expires; If one of the following is satisfied, then it may be determined that the RLF criteria is satisfied. In any of the above cases, the first terminal device 210 may indicate a HARQ-based sidelink RLF to the 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 opportunities, first terminal device 210 may determine that RLF is not satisfied. In this case, first terminal device 210 may reinitialize the value of numConsecutiveDTX to zero. Additionally, first terminal device 210 may stop the DTX timer in this case. Alternatively, first terminal device 210 may restart the DTX timer in this case.

[0077] The following table shows exemplary sidelink RLF related actions for a Tx UE, for example performed by the first terminal device 210: [Table 8]

[0078] Alternatively, in some example embodiments, the RLF criterion may be defined as follows: ● A threshold for a consecutive DTX counter associated with a sidelink channel (e.g. numConsecutiveDTX) is determined based on the maximum value of the consecutive DTX counter (e.g. sl-maxNumConsecutiveDTX) and possibly the number of HARQ feedback opportunities (i.e. the value of M). Thus, the threshold may be represented by sl-maxNumConsecutiveDTX if M is not used, or M*sl-maxNumConsecutiveDTX if M is used. The determined threshold may be configured via a conventional IE, i.e. SL-ConfigCommonNR-r16 in SIB12, or a new IE (e.g. a new format SIB dedicated for SL-U). ● If no HARQ feedback information is detected on one of the K HARQ feedback opportunities, the first terminal device 210 may increment the value of the consecutive DTX counter, for example incrementing numConsecutiveDTX by 1, and at the same time start or restart a DTX timer provided to ensure that the delay is acceptable. The first terminal device 210 is i) the value of the continuous DTX counter reaches the threshold; ii) The value of the DTX timer reaches the maximum DTX timer value (e.g., maxValueTimerDTX), or iii) the DTX timer expires; If one of the following is satisfied, then it may be determined that the RLF criteria is satisfied. In any of the above cases, the first terminal device 210 may indicate a HARQ-based sidelink RLF to the 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 opportunities, first terminal device 210 may determine that RLF is not satisfied. In this case, first terminal device 210 may reinitialize the value of numConsecutiveDTX to zero. Additionally, first terminal device 210 may stop the DTX timer in this case. Alternatively, first terminal device 210 may restart the DTX timer in this case.

[0079] The following table shows exemplary sidelink RLF related actions for a Tx UE, for example performed by the first terminal device 210: [Table 9]

[0080] In some exemplary embodiments, parameters of the DTX timer, such as the time interval of the DTX timer, maxValueTimerDTX, etc., may be set or modified by the gNB (e.g., network device 230) or the Tx UE (e.g., first terminal device 210).

[0081] In some other embodiments, the DTX timer parameters and maxValueTimerDTX may be set via a system message, such as a SIB12 containing a new IE containing the DTX timer parameters, or a SIB in a new format specific to SL-U.

[0082] An example of a legacy system message (e.g., SIB12) containing the new IE is shown below. SL-ConfigCommonNR-r18 ::= SEQUENCE { sl-MaxNumConsecutiveDTX-r18 ENUMERATED {n1, n2, n3, n4, n6, n8, n16, n32, n64, n128} OPTIONAL, --Need R }

[0083] An example of a new SIB for SL-U is shown below. SL-ConfigCommonNR-r18 ::= SEQUENCE { sl-MaxNumConsecutiveDTX-r18 ENUMERATED {n1, n2, n3, n4, n6, n8, n16, n32, n64, n128} OPTIONAL, --Need R }

[0084] In the above example, the field sl-MaxNumConsecutiveDTX indicates the maximum number of consecutive HARQ DTX before triggering a sidelink RLF, where the value n1 corresponds to 1, the value n2 corresponds to 2, and so on. A new IE is introduced to provide values ​​for sl-MaxNumConsecutiveDTX that are larger than in the current release of the 3GPP specifications (e.g., Release 17), e.g., n64 and n128 are added to the new IE.

[0085] According to an exemplary embodiment, an enhanced sidelink RLF detection mechanism is provided, in which the effect of LBT is taken into account, so that unnecessary radio link failure procedures can be avoided. In particular, the trigger of HARQ DTX detection can be adapted to different channel conditions, service requirements, and application scenarios by adjusting the scaling factor. Thus, service continuity can be guaranteed and communication delay can be reduced.

[0086] 5 is a flow chart of an example method 500 for communication according to an embodiment of the present disclosure. In some embodiments, the method 500 may be implemented in a Tx UE in sidelink communication, such as the first terminal device 210 as shown in FIG. 2. For illustrative purposes, the method 500 will be described as being performed by the first terminal device 210 with reference to FIG. 2 without loss of generality.

[0087] At 510, first terminal device 210 transmits a data transmission corresponding to multiple HARQ feedback opportunities to second terminal device 220. The number of the multiple HARQ feedback opportunities may be represented by K.

[0088] At 520, first terminal device 210 detects HARQ feedback information from second terminal device 220 on the multiple HARQ feedback opportunities. The HARQ feedback information is associated with a data transmission.

[0089] At 530, the first terminal device 210 determines whether an RLF criterion is met based on at least the scaling factor and the detection result. The RLF criterion may be defined to indicate whether a HARQ DTX is detected. A scaling factor M, denoted by M, may be provided to scale a threshold associated with triggering sidelink DTX detection.

[0090] In some example embodiments, a scaling factor M is associated with the number of the plurality of HARQ feedback opportunities, i.e., K. For example, the value of M may be equal to the value of K. If no HARQ feedback information is detected in the plurality of HARQ feedback opportunities, 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 consecutive DTX counter value (e.g., sl-maxNumConsecutiveDTX), first terminal device 210 may determine that the RLF criterion is met.

[0091] In some example embodiments, the first terminal device 210 may determine a consecutive DTX counter threshold associated with a sidelink channel based on a 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 the HARQ feedback information is not detected on one of the multiple HARQ feedback opportunities, 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 determine that the RLF criterion is met.

[0092] In some example embodiments, a scaling factor M may be associated with the number K of the plurality of HARQ feedback opportunities. Specifically, if no HARQ feedback information is detected on the plurality of HARQ feedback opportunities, the first terminal device 210 may increment a value of a continuous DTX counter associated with a sidelink channel and may start a DTX timer if it is not running. ● The value of the consecutive DTX counter reaches the maximum consecutive DTX counter value (e.g., sl-maxNumConsecutive) DTX. - The DTX timer value reaches the maximum DTX timer value, or - The DTX timer expires, If one of the following is satisfied, the first terminal device 210 may determine that the RLF criteria is satisfied.

[0093] In some example embodiments, the first terminal device 210 may determine a threshold for a continuous DTX counter associated with a sidelink channel based on a scaling factor and a maximum value of the continuous DTX counter. If no HARQ feedback information is detected on one of the HARQ feedback opportunities, the first terminal device 210 may increment the value of the continuous DTX counter and start the DTX timer if it is not running. ● The value of the continuous DTX counter reaches a threshold. - The DTX timer value reaches the maximum DTX timer value, or - The DTX timer expires, If one of the following is satisfied, the first terminal device 210 may determine that the RLF criteria is satisfied.

[0094] In some example embodiments, a scaling factor M may be associated with the number K of HARQ feedback opportunities. If no HARQ feedback information is detected on the multiple HARQ feedback opportunities, the first terminal device 210 may start or restart a DTX timer while incrementing a value of a continuous DTX counter associated with a sidelink channel. ● The value of the continuous DTX counter reaches the maximum value DTX of the continuous DTX counter. - The DTX timer value reaches the maximum DTX timer value, or - The DTX timer expires, If one of the following is satisfied, the first terminal device 210 may determine that the RLF criteria is satisfied.

[0095] In some example embodiments, the first terminal device 210 may determine a threshold for a consecutive DTX counter associated with a sidelink channel based on a 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 HARQ feedback opportunities, the first terminal device 210 may increment the value of the consecutive DTX counter while simultaneously starting or restarting a DTX timer. ● The value of the continuous DTX counter reaches a threshold. - The DTX timer value reaches the maximum DTX timer value, or - The DTX timer expires, If one of the following is satisfied, the first terminal device 210 may determine that the RLF criteria is satisfied.

[0096] At least one of the maximum value of the continuous DTX counter, the time interval and the maximum value of the DTX timer may be indicated via a system message. In some exemplary embodiments, the first terminal device 210 may receive an SIB indicating the maximum value of the continuous DTX counter. The SIB may be dedicated to SL-U communication. Alternatively, the SIB may include an IE dedicated to the continuous DTX counter associated with SL-U communication.

[0097] In some embodiments, the first terminal device 210 may receive an SIB indicating the time interval and maximum value of the DTX timer and the maximum value of the continuous discontinuous transmission counter. The SIB may be dedicated to SL-U communication. Alternatively, the SIB may include an IE dedicated to the continuous DTX counter associated with SL-U communication.

[0098] The scaling factor M may be indicated by a network device 230 serving the first terminal device 210. In some exemplary embodiments, the first terminal device 210 may receive an indication of the scaling factor M from the network device 230.

[0099] In some example embodiments, first terminal device 210 may receive an indication of a number (e.g., K) of HARQ feedback opportunities associated with a data transmission from a network device serving first terminal device 210, i.e., network device 230. First terminal device 210 may determine a scaling factor M based on the number K of HARQ feedback opportunities and at least one of a delay requirement or a priority of the data transmission.

[0100] In some example embodiments, the scaling factor M may be determined by one of first terminal device 210 or second terminal device 220 based on at least one of a delay requirement or a priority of the data transmission.

[0101] In some example embodiments, the first terminal device 210 may determine a CBR for the sidelink channel. The first terminal device 210 may select a value for the scaling factor M from a list of candidate values ​​for the scaling factor M based on the CBR. The list of candidate values ​​may be preconfigured by the network device 230 or predefined, for example, within a relevant specification or standard.

[0102] In some example embodiments, first terminal device 210 may determine the number of the plurality of HARQ feedback opportunities, i.e., K. First terminal device 210 may select a value for scaling factor M from a list of candidate values ​​for scaling factor M based on the number K. The list of candidate values ​​may be pre-configured by network device 230 or pre-defined, for example, within a relevant specification or standard.

[0103] In some exemplary embodiments, the scaling factor may be preconfigured by the network device 230 or may be predefined, for example, within a relevant specification or standard. If the first terminal device 230 operates on an unlicensed spectrum, the first terminal device 210 may apply the scaling factor M in determining whether the radio link failure criteria are met.

[0104] If the RLF criteria are met, at 540, the first terminal device 210 determines the occurrence of an RLF on the sidelink channel between the first terminal device 210 and the second terminal device 220.

[0105] In some example embodiments, if the HARQ feedback information is detected on at least one of the multiple HARQ feedback opportunities, first terminal device 210 may determine that the RLF criterion is not met. If the RLF criterion is not met, first terminal device 210 may reinitialize the value of a continuous DTX counter.

[0106] In some example embodiments where the RLF criteria are not met, the first terminal device 210 may stop the DTX timer.

[0107] To further reduce delay in sidelink communication, another enhanced SL-U RLF detection mechanism is provided and described in relation to FIG. 6.

[0108] 6 is a diagram illustrating a signaling flow for communication according to some embodiments of the present disclosure. For illustrative purposes, the process 600 is described with reference to FIG. 2 and FIG. 3. The process 600 may involve a first terminal device 210 functioning as a Tx UE, a second terminal device 220 functioning as an Rx UE, and a network device 230.

[0109] The first terminal device 210 transmits a data transmission to the second terminal device 220 in slot #n (602). According to the resource allocation scheme 300, the data transmission corresponds to K HARQ feedback opportunities in slots #n+2, #n+4... #n+2K. The data transmission may be, for example, a PSSCH / PSCCH transmission.

[0110] Similar to process 400, the value of K may be set or pre-configured by network device 230, or may be determined, for example, by a scheduling module of first terminal device 210. Additionally or alternatively, the value of K may be determined by either first terminal device 210 or second terminal device 220 based on the priority of the data transmission, the priority of the service transmitted via the data transmission, the delay requirement of HARQ feedback, etc. For brevity, similar settings or operations are not repeated in detail.

[0111] The second terminal device 220 may generate HARQ feedback information indicating whether the data transmission was successfully received by the second terminal device 220 or indicating that the data transmission was successfully received by the second terminal device 220 (604). Before transmitting the HARQ feedback information, the second terminal device 220 may determine whether a sidelink feedback channel, i.e., a PSFCH, is available (606). For example, the second terminal device 220 may perform an LBT procedure on slots #n+2, #n+4... #n+2K and determine whether to transmit HARQ feedback information based on the result of the LBT.

[0112] Thus, the first terminal device 210 detects HARQ feedback information from the second terminal device 220 on at least some of the multiple HARQ feedback opportunities corresponding to slots #n+2, #n+4 . . . #n+2K (608).

[0113] When the HARQ feedback information is detected on one of the multiple HARQ feedback opportunities, the first terminal device 210 determines that there is no other HARQ feedback information to be detected on the remaining ones of the multiple HARQ feedback opportunities (610). In other words, when HARQ feedback information is detected on any one of the PSFCH reception opportunities for one PSSCH, the first terminal device 210 does not expect HARQ DTX to be detected on the remaining PSFCH reception opportunities for the same PSSCH. In this case, the TX UE does not need to perform DTX detection on the remaining PSFCH reception opportunities for the same PSSCH.

[0114] In some example embodiments, first terminal device 210 and second terminal device 220 may operate according to process 600 if the network indicates that the HARQ feedback information is permitted to be transmitted only on the first PSFCH reception opportunity immediately following a successful LBT. Additionally, in these embodiments, second terminal device 220 may not transmit HARQ-ACKs on remaining PSFCH reception opportunities for the same PSSCH. This may depend on channel status, service requirements for delay, etc. For example, if the network determines that the current channel status is sufficiently good, the network may transmit such an indication to first terminal device 210 and second terminal device 220.

[0115] In some exemplary embodiments, when the HARQ feedback information is detected on one of the multiple HARQ feedback opportunities, the first terminal device 210 may reinitialize the value of a continuous DTX counter associated with a sidelink channel between the first terminal device 210 and the second terminal device 220.

[0116] Also, if the HARQ feedback information is not detected on one of the multiple HARQ feedback opportunities, the first terminal device 210 may increment a value of a consecutive DTX counter. If the value of the consecutive DTX counter reaches a maximum consecutive DTX counter value, the first terminal device 210 may determine the occurrence of an RLF on the sidelink channel.

[0117] In some exemplary embodiments, maxValueTimerDTX may be set via a system message, e.g., SIB12, which includes a new IE containing the parameters of the DTX timer, or a new format SIB specific to SL-U. Exemplary formats of conventional system messages (e.g., SIB12) including the new IE and new SIB have already been discussed in the description of process 400 and will not be repeated for brevity.

[0118] According to an embodiment of the present disclosure, when the HARQ feedback information is detected, the Tx UE will not attempt to receive the HARQ-ACK. Therefore, the Rx UE can also avoid repeatedly transmitting the HARQ-ACK on the PSFCH. Compared with the conventional sidelink RLF detection mechanism, the proposed solution has less communication delay and can avoid unnecessary RLF procedures.

[0119] 7 is a flow chart of an example method 700 for communication according to an embodiment of the present disclosure. In some embodiments, the method 700 may be implemented in a Tx UE in sidelink communication, such as the first terminal device 210 as shown in FIG. 2. For illustrative purposes, the method 700 will be described as being performed by the first terminal device 210 with reference to FIG. 2 without loss of generality.

[0120] At 710, first terminal device 210 transmits, to second terminal device 220, a data transmission corresponding to multiple HARQ feedback opportunities.

[0121] At 720, first terminal device 210 detects HARQ feedback information from second terminal device 220 on the multiple HARQ feedback opportunities. The HARQ feedback information is associated with a data transmission.

[0122] At 730, when the HARQ feedback information is detected on one of the multiple HARQ feedback opportunities, the first terminal device 210 determines that there is no other HARQ feedback information detected on the remaining ones of the multiple HARQ feedback opportunities.

[0123] In some example embodiments, if no HARQ feedback information is detected on one of the HARQ feedback opportunities, first terminal device 210 may increment a value of a continuous DTX counter associated with a sidelink channel between first terminal device 210 and second terminal device 220. If the value of the continuous DTX counter reaches a maximum continuous DTX counter value, first terminal device 210 may determine an occurrence of RLF on the sidelink channel.

[0124] In some example embodiments, when the HARQ feedback information is detected on one of the multiple HARQ feedback opportunities, first terminal device 210 may reinitialize a value of a consecutive DTX counter.

[0125] In some example embodiments, the maximum value of the continuous DTX counter may be indicated in a system message. In these embodiments, the first terminal device 210 may receive a SIB indicating the maximum value of the continuous DTX counter. The SIB may be a new SIB dedicated to SL-U communication, or the SIB may be a conventional SIB (e.g., SIB 12) that includes an IE dedicated to the continuous DTX counter associated with SL-U communication.

[0126] In order to reduce delay in sidelink communication, another enhanced SL-U RLF detection mechanism is provided and described in relation to FIG. 8.

[0127] 8 illustrates a signaling flow for communication according to some embodiments of the present disclosure. For illustrative purposes, the process 800 is described with reference to FIG. 2 and FIG. 3. The process 800 may involve a first terminal device 210 functioning as a Tx UE, a second terminal device 220 functioning as an Rx UE, and a network device 230.

[0128] The first terminal device 210 transmits a data transmission to the second terminal device 220 in slot #n (802). According to the resource allocation scheme 300, the data transmission corresponds to K HARQ feedback opportunities in slots #n+2, #n+4... #n+2K. The data transmission may be, for example, a PSSCH / PSCCH transmission.

[0129] Similar to processes 400 and 600, the value of K may be set or pre-configured by network device 230, or may be determined, for example, by a scheduling module of first terminal device 210. Additionally or alternatively, the value of K may be determined by either first terminal device 210 or second terminal device 220 based on the priority of the data transmission, the priority of the service transmitted via the data transmission, the delay requirement of HARQ feedback, etc. For brevity, similar settings or operations are not repeated in detail.

[0130] The second terminal device 220 may generate HARQ feedback information indicating whether the data transmission was successfully received by the second terminal device 220 (804). Before transmitting the HARQ feedback information, the second terminal device 220 may determine whether a sidelink feedback channel, i.e., a PSFCH, is available (806). For example, the second terminal device 220 may perform an LBT procedure on slots #n+2, #n+4... #n+2K and determine whether to transmit HARQ feedback information based on the results of the LBT.

[0131] Thus, the first terminal device 210 detects HARQ feedback information from the second terminal device 220 on the multiple HARQ feedback opportunities corresponding to slots #n+2, #n+4 . . . #n+2K (808).

[0132] Then, the first terminal device 210 determines whether the RLF criterion is met based on the DTX timer and the detection result (810). The DTX timer is provided to ensure that the delay due to HARQ DTX detection is tolerable. The RLF criterion is defined to indicate whether HARQ DTX is detected or not, and will be described in detail later.

[0133] The parameters of the DTX timer may be indicated in a system message. In some exemplary embodiments, the first terminal device 210 may receive an SIB indicating the time interval (e.g., TimerDTX) and maximum value (e.g., maxValueTimerDTX) of the DTX timer. The SIB may be dedicated to SL-U communication. Alternatively, the SIB may include an IE dedicated to a continuous DTX counter associated with SL-U communication.

[0134] In some example embodiments, the RLF criteria may be defined as follows: ● If no HARQ feedback information is detected on one of the K HARQ feedback opportunities, or on each HARQ feedback opportunity, the first terminal device 210 may increment the value of a consecutive DTX counter associated with the sidelink channel, for example incrementing numConsecutiveDTX by 1, and at the same time start the DTX timer if it is not running. The first terminal device 210 is i) the value of the consecutive DTX counter reaches the maximum consecutive DTX counter value, e.g., sl-maxNumConsecutiveDTX; ii) The value of the DTX timer reaches the maximum DTX timer value (e.g., maxValueTimerDTX), or iii) the DTX timer expires; If one of the following is satisfied, then it may be determined that the RLF criteria is satisfied. In any of the above cases, the first terminal device 210 may indicate a HARQ-based sidelink RLF to the RRC and release the DRB of the destination, i.e., the second terminal device 220. ● Otherwise, if HARQ feedback information is detected on any or each of the K HARQ feedback opportunities, first terminal device 210 may determine that RLF is not satisfied. In this case, first terminal device 210 may reinitialize the value of numConsecutiveDTX to zero. Additionally, first terminal device 210 may stop the DTX timer in this case. Alternatively, first terminal device 210 may restart the DTX timer in this case.

[0135] 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 a scaling factor M described in relation to Fig. 3 to the maximum value of the consecutive DTX counter. As an example, the threshold value of the consecutive DTX counter may be determined to be M*sl-maxNumConsecutiveDTX.

[0136] The following table shows exemplary sidelink RLF related actions for a Tx UE, for example performed by the first terminal device 210: [Table 10]

[0137] Alternatively, in some example embodiments, the RLF criterion may be defined as follows: ● If HARQ feedback information is not detected on one of the K HARQ feedback opportunities or on each HARQ feedback opportunity, the first terminal device 210 may increment the value of the consecutive DTX counter, for example incrementing numConsecutiveDTX by 1, and at the same time start or restart a DTX timer provided to ensure that the delay is acceptable. The first terminal device 210 is i) the value of the Continuous DTX Counter reaches the Maximum Continuous DTX Counter value; ii) The value of the DTX timer reaches the maximum DTX timer value (e.g., maxValueTimerDTX), or iii) the DTX timer expires; If one of the following is satisfied, then it may be determined that the RLF criteria is satisfied. In any of the above cases, the first terminal device 210 may indicate a HARQ-based sidelink RLF to the RRC and release the DRB of the destination, i.e., the second terminal device 220. ● Otherwise, if HARQ feedback information is detected on any or each of the K HARQ feedback opportunities, first terminal device 210 may determine that RLF is not satisfied. In this case, first terminal device 210 may reinitialize the value of numConsecutiveDTX to zero. Additionally, first terminal device 210 may stop the DTX timer in this case. Alternatively, first terminal device 210 may restart the DTX timer in this case.

[0138] 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 a scaling factor M described in relation to Fig. 3 to the maximum value of the consecutive DTX counter. As an example, the threshold value of the consecutive DTX counter may be determined to be M*sl-maxNumConsecutiveDTX.

[0139] The following table shows exemplary sidelink RLF related actions for a Tx UE, for example performed by the first terminal device 210: [Table 11]

[0140] 9 is a flow chart of an example method 900 for communication according to an embodiment of the present disclosure. In some embodiments, the method 900 may be implemented in a Tx UE in sidelink communication, such as the first terminal device 210 as shown in FIG. 2. For illustrative purposes, the method 900 will be described as being performed by the first terminal device 210 with reference to FIG. 2 without loss of generality.

[0141] At 910, first terminal device 210 transmits, to second terminal device 220, a data transmission corresponding to multiple HARQ feedback opportunities.

[0142] At 920, first terminal device 210 detects HARQ feedback information from second terminal device 220 on the multiple HARQ feedback opportunities. The HARQ feedback information is associated with a data transmission.

[0143] At 930, the first terminal device 210 determines whether the RLF criteria are met based on the detection result and the DTX timer.

[0144] In some example embodiments, if no HARQ feedback information is detected on one of the multiple HARQ feedback opportunities, the first terminal device 210 may increment the value of a continuous DTX counter associated with the sidelink channel and may start the DTX timer if it is not running. ● The value of the continuous DTX counter reaches the maximum value DTX of the continuous DTX counter. - The DTX timer value reaches the maximum DTX timer value, or - The DTX timer expires, If one of the following is satisfied, the first terminal device 210 may determine that the RLF criteria is satisfied.

[0145] In these embodiments, the first terminal device 210 may determine a consecutive DTX counter threshold associated with the sidelink channel based on the scaling factor M and the maximum consecutive DTX counter value. ● The value of the continuous DTX counter reaches the maximum value DTX of the continuous DTX counter. - The DTX timer value reaches the maximum DTX timer value, or - The DTX timer expires, If one of the following is satisfied, the first terminal device 210 may determine that the RLF criteria is satisfied.

[0146] In some example embodiments, a scaling factor M may be provided to scale a threshold associated with triggering sidelink DTX detection. The scaling factor M may be associated with the number of HARQ feedback occasions or may be predefined or (pre)configured.

[0147] In these embodiments, the first terminal device 210 may determine a consecutive DTX counter threshold associated with a sidelink channel based on a scaling factor M and a maximum consecutive DTX counter value. As an example, the consecutive DTX counter threshold may be determined to be M*sl-maxNumConsecutiveDTX. If no HARQ feedback information is detected on one of the HARQ feedback opportunities, the first terminal device 210 may increment the value of the consecutive DTX counter and start the DTX timer if it is not running. ● The value of the continuous DTX counter reaches a threshold. - The DTX timer value reaches the maximum DTX timer value, or - The DTX timer expires, If one of the following is satisfied, the first terminal device 210 may determine that the RLF criteria is satisfied.

[0148] Alternatively, in these embodiments, the first terminal device 210 may determine a consecutive DTX counter threshold associated with the sidelink channel based on the scaling factor M and a maximum consecutive DTX counter value. As an example, the consecutive DTX counter threshold may be determined to be M*sl-maxNumConsecutiveDTX. If no HARQ feedback information is detected on one of the HARQ feedback opportunities, the first terminal device 210 may increment the value of the consecutive DTX counter and simultaneously start or restart the DTX timer. ● The value of the continuous DTX counter reaches a threshold. - The DTX timer value reaches the maximum DTX timer value, or - The DTX timer expires, If one of the following is satisfied, the first terminal device 210 may determine that the RLF criteria is satisfied.

[0149] In some example embodiments, the first terminal device 210 may determine a CBR for the sidelink channel. The first terminal device 210 may select a value for the scaling factor M from a list of candidate values ​​for the scaling factor M based on the CBR. The list of candidate values ​​may be preconfigured by the network device 230 or predefined, for example, within a relevant specification or standard.

[0150] In some example embodiments, first terminal device 210 may determine the number of the plurality of HARQ feedback opportunities, i.e., K. First terminal device 210 may select a value for scaling factor M from a list of candidate values ​​for scaling factor M based on the number K. The list of candidate values ​​may be pre-configured by network device 230 or pre-defined, for example, within a relevant specification or standard.

[0151] In some exemplary embodiments, the scaling factor M may be preconfigured by the network device 230 or may be predefined, for example, within a relevant specification or standard. If the first terminal device 230 operates on an unlicensed spectrum, the first terminal device 210 may apply the scaling factor M in determining whether the radio link failure criteria are met.

[0152] At least one of the time interval and maximum value of the DTX timer and the maximum value of the continuous DTX counter may be indicated via a system message. In some exemplary embodiments, the first terminal device 210 may receive an SIB indicating the maximum value of the continuous DTX counter. The SIB may be dedicated to SL-U communication. Alternatively, the SIB may include an IE dedicated to the continuous DTX counter associated with SL-U communication.

[0153] In some embodiments, the first terminal device 210 may receive an SIB indicating the time interval and maximum value of the DTX timer and the maximum value of the continuous discontinuous transmission counter. The SIB may be dedicated to SL-U communication. Alternatively, the SIB may include an IE dedicated to the continuous DTX counter associated with SL-U communication.

[0154] If the RLF criteria are met, at 940, the first terminal device 210 determines the occurrence of an RLF on the sidelink channel between the first terminal device 210 and the second terminal device 220.

[0155] In some example embodiments, if at least one HARQ feedback information is detected on the multiple HARQ feedback opportunities, first terminal device 210 may determine that the RLF criterion is not met, in which case first terminal device 210 may reinitialize the value of the consecutive DTX counter.

[0156] In some example embodiments, when the HARQ feedback information is detected on one of the multiple HARQ feedback opportunities, the first terminal device 210 may determine that there is no other HARQ feedback information detected on the remaining ones of the multiple HARQ feedback opportunities.

[0157] In some example embodiments where the RLF criteria are not met, the first terminal device 210 may stop the DTX timer.

[0158] 10 is a schematic block diagram of an apparatus 1000 suitable for implementing an embodiment of the present disclosure. The apparatus 1000 may be considered as another exemplary implementation of the first terminal device 210 or the second terminal device 220 shown in FIG. 2. Thus, the apparatus 1000 may be implemented in the terminal device 210 or 220 or as at least a part thereof.

[0159] As shown, the device 1000 comprises 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 portion of a program 1030. The TX / RX 1040 is used for bidirectional communication. The TX / RX 1040 has at least one antenna to facilitate communication, although the terminal device or network device mentioned herein may actually have multiple antennas. The communication interface may represent any interface required for communication with other network elements, such as an X2 interface for bidirectional communication between eNBs, an S1 interface for communication between a mobility management entity (MME) / serving gateway (S-GW) and an eNB, an Un interface for communication between an eNB and a relay node (RN), or an Uu interface for communication between an eNB and a terminal device.

[0160] The program 1030 is assumed to include program instructions that, when executed by the associated processor 1010, enable the device 1000 to operate according to embodiments of the present disclosure, as described herein with reference to Figures 3-9. The embodiments of the present disclosure 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, the combination of the processor 1010 and the memory 1020 may form a processing means 1050 suitable for implementing various embodiments of the present disclosure.

[0161] The memory 1020 may be of any type suitable for a local technology network and may be implemented using any suitable data storage technology, such as, by way of non-limiting example, non-transitory computer-readable storage media, semiconductor-based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory. Although only one memory 1020 is shown in the device 1000, there may be several physically different memory modules in the device 1000. The processor 1010 may be of any type suitable for a local technology network and may include, by way of non-limiting example, one or more of a general purpose computer, a special purpose computer, a microprocessor, a digital signal processor (DSP) and a processor based on a multi-core processor architecture. The device 1000 may have multiple processors, for example application specific integrated circuit chips time-slaved to a clock that synchronizes the main processor.

[0162] In some exemplary embodiments, a first terminal device comprises a circuit configured to: transmit a data transmission corresponding to a Hybrid Automatic Repeat Request (HARQ) feedback opportunity to a second terminal device; detect HARQ feedback information associated with the data transmission from the second terminal device on the plurality of HARQ feedback opportunities; determine whether a radio link failure criterion is met based on at least a scaling factor and a detection result; and determine an occurrence of a radio link failure on a sidelink channel between the first terminal device and the second terminal device according to a determination that the radio link failure criterion is met.

[0163] In some exemplary embodiments, the scaling factor is associated with a number of the plurality of HARQ feedback opportunities, and the circuitry may be configured to: increment a value of a continuous discontinuous transmission (DTX) counter associated with the sidelink channel according to a determination that no HARQ feedback information has been detected on the plurality of HARQ feedback opportunities; and to determine that the radio link failure criterion is met according to a determination that a value of the continuous DTX counter has reached a maximum value of the continuous DTX counter.

[0164] In some exemplary embodiments, the circuitry may be configured to determine a threshold for a discontinuous transmission (DTX) counter associated with the sidelink channel based on the scaling factor and a maximum value of the continuous DTX counter, increment a value of the continuous DTX counter according to a determination that no HARQ feedback information is detected on one of the plurality of HARQ feedback opportunities, and determine that the radio link failure criterion is met according to a determination that a value of the continuous DTX counter has reached the threshold.

[0165] In some exemplary embodiments, the scaling factor is associated with a number of the plurality of HARQ feedback opportunities, and the circuitry may be configured to: increment a value of a continuous discontinuous transmission (DTX) counter associated with the sidelink channel according to a determination that no HARQ feedback information has been detected on the plurality of HARQ feedback opportunities, and simultaneously start the DTX timer if it is not running, and determine that the radio link failure criterion is met according to a determination that one of: a value of the continuous DTX counter has reached a maximum value of the continuous DTX counter, a value of the DTX timer has reached a maximum value of the DTX timer, or the DTX timer has expired.

[0166] In some exemplary embodiments, the circuitry determining whether the radio link failure criterion is met includes determining a threshold of a continuous discontinuous transmission (DTX) counter associated with the sidelink channel based on the scaling factor and a maximum value of the continuous DTX counter; and incrementing a value of the continuous DTX counter according to a determination that no HARQ feedback information has been detected on one of the plurality of HARQ feedback opportunities, while starting the DTX timer if it is not running; and determining that the radio link failure criterion is met according to a determination that one of: a value of the continuous DTX counter has reached the threshold, a value of the DTX timer has reached a maximum value of the DTX timer, or the DTX timer has expired.

[0167] In some exemplary embodiments, the multiple time periods are indicated in a radio resource control message from the second network device or in a message received on a side control channel.

[0168] In some exemplary embodiments, the scaling factor is associated with a number of the plurality of HARQ feedback opportunities, and the circuitry may be configured to: increment a value of a continuous discontinuous transmission (DTX) counter associated with the sidelink channel in accordance with a determination that no HARQ feedback information has been detected on the plurality of HARQ feedback opportunities, while simultaneously starting or restarting a DTX timer, and to determine that the radio link failure criterion is met in accordance with a determination that one of: a value of the continuous DTX counter has reached a maximum value of the continuous DTX counter, a value of the DTX timer has reached a maximum value of the DTX timer, or the DTX timer has expired.

[0169] In some exemplary embodiments, the circuitry may be configured to: determine a threshold for a continuous discontinuous transmission (DTX) counter associated with the sidelink channel based on the scaling factor and a maximum value of the continuous DTX counter; increment a value of the continuous DTX counter while starting or restarting a DTX timer according to a determination that no HARQ feedback information has been detected on one of the plurality of HARQ feedback opportunities; and determine that the radio link failure criterion is met according to a determination that one of: a value of the continuous DTX counter has reached the threshold, a value of the DTX timer has reached a maximum value of the DTX timer, or the DTX timer has expired.

[0170] In some exemplary embodiments, the circuitry may be configured to determine that the radio link failure criterion is not met in accordance with a determination that at least one HARQ feedback information has been detected, and to reinitialize a value of the continuous DTX counter in accordance with a determination that the radio link failure criterion is not met.

[0171] In some exemplary embodiments, the circuitry may be further configured to stop the DTX timer following a determination that the radio link failure criterion is not met.

[0172] In some exemplary embodiments, the circuitry may be further configured to receive a system information block (SIB) indicating a maximum value of the continuous DTX counter, the SIB being dedicated to sidelink unlicensed communication or the SIB including an information element dedicated to the continuous DTX counter associated with sidelink unlicensed communication.

[0173] In some exemplary embodiments, the circuitry may be further configured to receive a system information block (SIB) indicating a time interval and a maximum value of the DTX timer and a maximum value of the consecutive discontinuous transmission counter, the SIB being dedicated to sidelink unlicensed communication or the SIB including an information element dedicated to the consecutive discontinuous transmission counter associated with sidelink unlicensed communication.

[0174] In some exemplary embodiments, the circuitry may be further configured to receive an indication of the scaling factor from a network device serving the first terminal device.

[0175] In some exemplary embodiments, the circuitry may be further configured to receive an indication of a number of HARQ feedback opportunities associated with the data transmission from a network device serving the first terminal device, and to determine the scaling factor based on the number of HARQ feedback opportunities and at least one of a delay requirement or a priority of the data transmission.

[0176] In some exemplary 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 delay requirement or a priority of the data transmission.

[0177] In some exemplary embodiments, the circuitry may be further configured to determine a channel busy ratio (CBR) of the sidelink channel and to select a value for the scaling factor from a list of candidate values ​​for the scaling factor based on the CBR, the list of candidate values ​​being pre-configured or pre-defined by a network device.

[0178] In some exemplary embodiments, the circuitry may be further configured to determine a number of the plurality of HARQ feedback opportunities and, based on the number, select a value for the scaling factor from a list of candidate values ​​for the scaling factor, the list of candidate values ​​being pre-configured or pre-defined by a network device.

[0179] In some exemplary embodiments, the scaling factor may be pre-set or pre-defined by a network device, and the circuitry may be further configured to apply the scaling factor in determining whether the radio link failure criterion is satisfied pursuant to a determination that the first terminal device is operating in an unlicensed band.

[0180] In some exemplary embodiments, a first terminal device comprises a circuit configured to transmit a data transmission corresponding to a Hybrid Automatic Repeat Request (HARQ) feedback opportunity to a second terminal device, detect HARQ feedback information associated with the data transmission from the second terminal device on the plurality of HARQ feedback opportunities, and determine that when the HARQ feedback information is detected on one of the plurality of HARQ feedback opportunities, there is no other HARQ feedback information detected on remaining ones of the plurality of HARQ feedback opportunities.

[0181] In some exemplary embodiments, the circuitry may be further configured to increment a value of a discontinuous transmission (DTX) counter associated with a sidelink channel between the first terminal device and the second terminal device in accordance with a determination that no HARQ feedback information was detected on one of the plurality of HARQ feedback opportunities, and to determine an occurrence of a radio link failure on the sidelink channel in accordance with a determination that a value of the continuous DTX counter has reached a maximum value of the continuous DTX counter.

[0182] In some exemplary embodiments, the circuitry may be further configured to reinitialize a value of the continuous DTX counter when the HARQ feedback information is detected on one of the plurality of HARQ feedback opportunities.

[0183] In some exemplary embodiments, the circuitry may be further configured to receive a system information block (SIB) indicating a maximum value of the continuous DTX counter, the SIB being dedicated to sidelink unlicensed communication or the SIB including an information element dedicated to the continuous DTX counter associated with sidelink unlicensed communication.

[0184] In some exemplary embodiments, a first terminal device comprises a circuit configured to transmit a data transmission corresponding to a Hybrid Automatic Repeat Request (HARQ) feedback opportunity to a second terminal device, detect HARQ feedback information associated with the data transmission from the second terminal device on the plurality of HARQ feedback opportunities, determine whether a radio link failure criterion is met based on the detection result and a discontinuous transmission (DTX) timer, and determine an occurrence of a radio link failure on a sidelink channel between the first terminal device and the second terminal device according to a determination that the radio link failure criterion is met.

[0185] In some exemplary embodiments, the circuitry may be configured to increment a value of a continuous DTX counter associated with the sidelink channel according to a determination that no HARQ feedback information has been detected on one of the plurality of HARQ feedback opportunities, and simultaneously start the DTX timer if the DTX timer is not running, and determine that the radio link failure criterion is met according to a determination that one of the following is met: a value of the continuous DTX counter has reached a maximum value of the continuous DTX counter, a value of the DTX timer has reached a maximum value of the DTX timer, or the DTX timer has expired.

[0186] In some exemplary embodiments, the circuitry may be configured to increment a value of a continuous DTX counter associated with the sidelink channel in accordance with a determination that no HARQ feedback information has been detected on one of the plurality of HARQ feedback opportunities, and to simultaneously start or restart a DTX timer and determine that the radio link failure criterion is met in accordance with a determination that one of the following is met: a value of the continuous DTX counter has reached a maximum value of the continuous DTX counter, a value of the DTX timer has reached a maximum value of the DTX timer, or the DTX timer has expired.

[0187] In some exemplary embodiments, the circuitry may be configured to determine that the radio link failure criterion is not met in accordance with a determination that at least one HARQ feedback information has been detected, and to reinitialize a value of the continuous DTX counter in accordance with a determination that the radio link failure criterion is not met.

[0188] In some exemplary embodiments, the circuitry may be further configured to stop the DTX timer following a determination that the radio link failure criterion is not met.

[0189] In some exemplary embodiments, the circuitry may be further configured to receive a system information block (SIB) indicating a time interval and a maximum value of the DTX timer and a maximum value of the consecutive discontinuous transmission counter, the SIB being dedicated to sidelink unlicensed communication or the SIB including an information element dedicated to the consecutive discontinuous transmission counter associated with sidelink unlicensed communication.

[0190] In some example embodiments, the circuitry may be further configured to determine that when the HARQ feedback information is detected on one of the plurality of HARQ feedback opportunities, no other HARQ feedback information is detected on remaining ones of the plurality of HARQ feedback opportunities.

[0191] In some exemplary embodiments, the circuitry may be configured to: determine a threshold for a continuous discontinuous transmission (DTX) counter associated with the sidelink channel based on a scaling factor and a maximum value of the continuous DTX counter; increment a value of the continuous DTX counter according to a determination that no HARQ feedback information has been detected on one of the plurality of HARQ feedback opportunities; and, simultaneously, start the DTX timer if it is not running; and determine that the radio link failure criterion is met according to a determination that one of: a value of the continuous DTX counter has reached the threshold, a value of the DTX timer has reached a maximum value of the DTX timer, or the DTX timer has expired.

[0192] In some exemplary embodiments, the circuitry may be configured to determine a threshold for a continuous discontinuous transmission (DTX) counter associated with the sidelink channel based on a scaling factor and a maximum value of the continuous DTX counter, increment a value of the continuous DTX counter and simultaneously start or restart a DTX timer according to a determination that no HARQ feedback information has been detected on one of the plurality of HARQ feedback opportunities, and determine that the radio link failure criterion is met according to a determination that one of: a value of the continuous DTX counter has reached the threshold, a value of the DTX timer has reached a maximum value of the DTX timer, or the DTX timer has expired.

[0193] In some example embodiments, a scaling factor is associated with the number of the multiple HARQ feedback opportunities.

[0194] In some exemplary embodiments, the circuitry may be further configured to determine a channel busy ratio (CBR) of the sidelink channel and to select a value for the scaling factor from a list of candidate values ​​for the scaling factor based on the CBR, the list of candidate values ​​being pre-configured or pre-defined by a network device.

[0195] In some exemplary embodiments, the circuitry may be further configured to determine a number of the plurality of HARQ feedback opportunities and, based on the number, select a value for the scaling factor from a list of candidate values ​​for the scaling factor, the list of candidate values ​​being pre-configured or pre-defined by a network device.

[0196] In some exemplary embodiments, the scaling factor may be pre-set or pre-defined by a network device, and the circuitry may be further configured to determine that the scaling factor is applied in accordance with a determination that the first terminal device operates in an unlicensed band.

[0197] The term "circuitry" as used herein may refer to a hardware circuit and / or a combination of a hardware circuit and software. For example, a circuit may be a combination of analog and / or digital hardware circuitry and software / firmware. As yet another example, a circuit may be any portion of a hardware processor having software, including a digital signal processor, software, and one or more memories, that cooperate to cause a device, such as a terminal device or a network device, to perform various functions. In yet another example, a circuit may be a hardware circuit and / or a processor, such as a microprocessor or a portion thereof, that requires software / firmware for operation, but the software may not be present if not required for operation. As used herein, the term "circuitry" also includes an implementation of only a hardware circuit or one or more processors, or a portion of a hardware circuit or one or more processors and its (or their) associated software and / or firmware.

[0198] Overall, 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 that may be executed by a controller, microprocessor, or other computing device. Although various aspects of the embodiments of the present disclosure have been illustrated and described using block diagrams, flow charts, or some other pictorial representations, it should be understood that the blocks, devices, systems, techniques, or methods described herein may be implemented, by way of non-limiting examples, in hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing device, or any combination thereof.

[0199] 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 instructions included in a program module, that execute in a device on a target real or virtual processor to perform the process or method described above with reference to Figures 2, 5, and 7-11. Generally, program modules include routines, programs, libraries, objects, classes, components, data structures, etc. that perform particular tasks or implement particular abstract data types. In various embodiments, the functionality of the program modules may be combined or split between program modules as appropriate. The machine-executable instructions of the program modules may be executed in local or distributed devices. In a distributed device, the program modules may be located in both local and remote storage media.

[0200] Program codes for carrying out the 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, a special purpose computer, or other programmable data processing device, and when executed by the processor or controller, the program code causes the functions / operations specified in the flowcharts and / or block diagrams to be implemented. The program code may run entirely on the machine, partially on the machine, as a separate software package, partially on the machine and partially on a remote machine, or entirely on a remote machine or server.

[0201] The above program code may be implemented on a machine-readable medium, which may be any tangible medium that can contain or store a program used by or associated with an instruction execution system, device, or apparatus. The machine-readable medium may be a machine-readable signal medium or a machine-readable storage medium. The machine-readable medium may include, but is not limited to, an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, device, or apparatus, or any suitable combination of the aforementioned media. More specific examples of the machine-readable storage medium may include an electrical connection having one or more wires, a portable computer disk, 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 disk read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the aforementioned.

[0202] It should be noted that although operations have been described in a particular order, it should not be understood that such operations need to be performed in the particular order shown, or in any sequential order, or that all of the operations described must be performed in order to achieve desired results. In some cases, multitasking and parallel processing may be advantageous. Similarly, although some specific implementation details are included in the above discussion, these should not be construed as limitations on the scope of the disclosure, but rather as descriptions of features that may be specific to certain embodiments. Some features described in the context of individual embodiments may be realized in combination in a single embodiment. Conversely, various features described in the context of a single embodiment may be implemented separately in multiple embodiments or in any suitable subcombination.

[0203] Although the present disclosure has been described in language specific to structural features and / or methodological acts, it should be understood that the present disclosure, as 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

1. 1. A method of communication comprising: In the first terminal device, transmitting a data transmission corresponding to a plurality of Hybrid Automatic Repeat Request (HARQ) feedback opportunities to a second terminal device; Detecting HARQ feedback information associated with the data transmission from the second terminal device on the plurality of HARQ feedback opportunities; determining whether a radio link failure criterion is met based at least on the scaling factor and the detection result; determining, in accordance with a determination that the radio link failure criterion is satisfied, an occurrence of a radio link failure on a sidelink channel between the first terminal device and the second terminal device; The method includes:

2. the scaling factor being related to a number of the plurality of HARQ feedback opportunities; Determining whether the radio link failure criterion is satisfied comprises: incrementing a value of a discontinuous transmission (DTX) counter associated with the sidelink channel according to a determination that no HARQ feedback information has been detected on the plurality of HARQ feedback opportunities; and determining that the radio link failure criterion is met in accordance with a determination that the value of the consecutive DTX counter has reached the consecutive DTX counter maximum value; 2. The method of claim 1, comprising:

3. Determining whether the radio link failure criterion is satisfied comprises: determining a threshold for a discontinuous transmission (DTX) counter associated with the sidelink channel based on the scaling factor and a maximum value of the continuous DTX counter; incrementing a value of the consecutive DTX counter in accordance with a determination that no HARQ feedback information was detected on one of the plurality of HARQ feedback opportunities; determining that the radio link failure criterion is met in accordance with a determination that the value of the consecutive DTX counter has reached the threshold; 2. The method of claim 1, comprising:

4. the scaling factor being related to a number of the plurality of HARQ feedback opportunities; Determining whether the radio link failure criterion is satisfied comprises: incrementing a value of a discontinuous transmission (DTX) counter associated with the sidelink channel according to a determination that no HARQ feedback information has been detected on the plurality of HARQ feedback opportunities and starting a DTX timer if the DTX timer is not running. the value of the consecutive DTX counter has reached a maximum value of the consecutive DTX counter; the value of the DTX timer has reached the maximum value of the DTX timer; or that the DTX timer has expired; determining that the radio link failure criterion is met in accordance with a determination that one of the following criteria is met:

2. The method of claim 1, comprising:

5. Determining whether the radio link failure criterion is satisfied comprises: determining a threshold for a discontinuous transmission (DTX) counter associated with the sidelink channel based on the scaling factor and a maximum value of the continuous DTX counter; incrementing a value of the consecutive DTX counter and starting a DTX timer if the DTX timer is not running according to a determination that no HARQ feedback information was detected on one of the plurality of HARQ feedback opportunities; the value of the consecutive DTX counter reaches the threshold; the value of the DTX timer has reached the maximum value of the DTX timer; or that the DTX timer has expired; determining that the radio link failure criterion is met in accordance with a determination that one of the following criteria is met:

2. The method of claim 1, comprising:

6. the scaling factor being related to a number of the plurality of HARQ feedback opportunities; Determining whether the radio link failure criterion is satisfied comprises: incrementing a value of a discontinuous transmission (DTX) counter associated with the sidelink channel and starting or restarting a DTX timer according to a determination that no HARQ feedback information has been detected on the plurality of HARQ feedback opportunities. the value of the consecutive DTX counter has reached a maximum value of the consecutive DTX counter; the value of the DTX timer has reached the maximum value of the DTX timer; or that the DTX timer has expired; determining that the radio link failure criterion is met in accordance with a determination that one of the following criteria is met:

2. The method of claim 1, comprising:

7. Determining whether the radio link failure criterion is satisfied comprises: determining a threshold for a discontinuous transmission (DTX) counter associated with the sidelink channel based on the scaling factor and a maximum value of the continuous DTX counter; incrementing a value of the consecutive DTX counter and starting or restarting a DTX timer according to a determination that no HARQ feedback information was detected on one of the plurality of HARQ feedback opportunities; the value of the consecutive DTX counter reaches the threshold; the value of the DTX timer has reached the maximum value of the DTX timer; or that the DTX timer has expired; determining that the radio link failure criterion is met in accordance with a determination that one of the following criteria is met:

2. The method of claim 1, comprising:

8. Determining whether the radio link failure criterion is satisfied comprises: determining that the radio link failure criterion is not met in accordance with determining that at least one HARQ feedback information has been detected; reinitializing a value of the consecutive DTX counter in accordance with a determination that the radio link failure criterion is not satisfied; The method according to any one of claims 2 to 7, comprising:

9. stopping the DTX timer in accordance with a determination that the radio link failure criterion is not met; The method according to any one of claims 4 to 7, further comprising:

10. receiving a system information block (SIB) indicating a maximum value of the consecutive DTX counter; the SIB is dedicated to sidelink unlicensed communications, or The SIB includes an information element dedicated to the consecutive DTX counter associated with sidelink unlicensed communication. The method according to claim 2 or 3.

11. receiving a system information block (SIB) indicating a time interval and a maximum value of the DTX timer and a maximum value of the consecutive DTX counter; the SIB is dedicated to sidelink unlicensed communications, or The SIB includes an information element dedicated to the consecutive DTX counter associated with sidelink unlicensed communication. The method according to any one of claims 4 to 7.

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

13. receiving an indication of a number of HARQ feedback opportunities associated with the data transmission from a network device serving the first terminal device; determining the scaling factor based on at least one of a number of HARQ feedback opportunities and a delay requirement or a priority of the data transmission; The method of claim 1 further comprising:

14. The scaling factor is determined by one of the first terminal device or the second terminal device based on at least one of a delay requirement or a priority of the data transmission. The method of claim 1.

15. determining a channel busy ratio (CBR) of the sidelink channel; and selecting a value for the scaling factor from a list of candidate values ​​for the scaling factor based on the CBR; The list of candidate values ​​is pre-configured or pre-defined by the network device. The method of claim 1.

16. determining a number of the plurality of HARQ feedback opportunities; and selecting a value for the scaling factor from a list of candidate values ​​for the scaling factor based on the number; The list of candidate values ​​is pre-configured or pre-defined by the network device. The method of claim 1.

17. the scaling factor is pre-configured or pre-defined by the network device; The method comprises: determining the scaling factor to be applied in accordance with a determination that the first terminal device operates in an unlicensed spectrum; The method of claim 1 further comprising:

18. A processor configured to carry out the method according to any one of claims 1 to 17. Terminal device.

19. storing instructions which, when executed on at least one processor of a device, cause said device to carry out a method according to any one of claims 1 to 17; Computer-readable medium.

Images