Method and apparatus for radio link management in sidelink communication

Abstract

The present invention relates to a method and apparatus for radio link management in sidelink communication. An operation method of a first terminal in a communication system supporting sidelink communication can include transmitting one or more sidelink data to a second terminal, performing a monitoring operation to receive one or more hybrid automatic repeat request (HARQ) responses for the one or more sidelink data from the second terminal, declaring that a radio link failure (RLF) occurs in a radio link between the first terminal and the second terminal when the one or more HARQ responses indicate a discontinuous transmission (DTX).

Description

[0001] This application is a divisional application of Chinese PCT patent application No. 202010886277.4, entitled "Method and apparatus for wireless link management in sidelink communication", filed on August 28, 2020.

[0002] Cross-references to related applications This application claims priority to U.S. Provisional Patent Application No. 62 / 894,169, filed August 30, 2019, with the United States Patent and Trademark Office and Korean Patent Application No. 10-2020-0079361, filed June 29, 2020, with the Korean Intellectual Property Office, the entire contents of which are incorporated herein by reference. Technical Field

[0003] This invention relates generally to sidelink communication technology, and more specifically, to technology for detecting radio link failures (RLF) in the sidelink. Background Technology

[0004] Various systems have been developed for processing wireless data, such as fourth-generation (4G) communication systems (e.g., Long Term Evolution (LTE) or LTE-Advanced (LTE-A)) and fifth-generation (5G) communication systems (e.g., New Radio (NR)). Fifth-generation (5G) communication systems use higher frequency bands than 4G systems. 5G communication systems support enhanced mobile broadband (eMBB) communication, ultra-reliable and low-latency communication (URLLC), massive machine-type communication (mMTC), and more.

[0005] 4G and 5G communication systems support vehicle-to-everything (V2X) communication. V2X communication supported in cellular communication systems (e.g., 4G, 5G, etc.) can be referred to as "cellular-V2X (C-V2X) communication." V2X communication (e.g., C-V2X communication) can include: vehicle-to-vehicle (V2V) communication, vehicle-to-infrastructure (V2I) communication, vehicle-to-pedestrian (V2P) communication, vehicle-to-network (V2N) communication, etc.

[0006] In cellular communication systems, V2X communication (e.g., C-V2X communication) can be performed based on "sidelink" communication technologies (e.g., Proximity-Based Service (ProSe) communication technology, Device-to-Device (D2D) communication technology, etc.). For example, a sidelink channel can be established for vehicles participating in V2V communication, and the sidelink channel can be used to perform communication between vehicles. Sidelink communication can be performed using configured licensed (CG) resources. CG resources can be configured periodically, and periodic data (e.g., periodic sidelink data) can be sent using CG resources.

[0007] On the other hand, in sidelink communication, radio link failures (RLFs) may occur depending on the state of the radio link, changes in the distance between terminals, etc., and an RLF detection method that takes into account the characteristics of sidelink communication is needed. Furthermore, when an RLF occurs, a method for restoring the radio link used for sidelink communication is required. Summary of the Invention

[0008] Therefore, exemplary embodiments of the present invention provide a method and apparatus for detecting radio link failures (RLF) in sidelink communication.

[0009] According to an exemplary embodiment of the present invention, an operation method of a first terminal in a communication system supporting sidelink communication may include: sending one or more sidelink data to a second terminal; performing a monitoring operation to receive one or more Hybrid Automatic Repeat Request (HARQ) responses to the one or more sidelink data from the second terminal; and declaring a radio link failure (RLF) in the radio link between the first terminal and the second terminal when one or more HARQ responses indicate discontinuous transmission (DTX).

[0010] One or more sidelink data can be sent to the second terminal using semi-static scheduling (SPS) resources, configured authorization (CG) resources, or resources scheduled by sidelink control information (SCI).

[0011] RLF can be declared when the number of one or more HARQ responses indicating DTX is greater than or equal to a preset threshold.

[0012] An RLF can be declared when one or more HARQ responses indicating DTX are received within a predetermined time period.

[0013] An RLF can be declared when one or more HARQ responses indicating DTX are received within a predetermined time period, and the number of such HARQ responses indicating DTX is greater than or equal to a preset threshold.

[0014] When one or more HARQ responses are negative acknowledgments (NACK) and the NACK is set to indicate DTX, the one or more HARQ responses can be determined to indicate DTX.

[0015] The operation method may further include: receiving configuration information from the base station, including one or more information elements for declaring an RLF.

[0016] The operation method may further include: sending information indicating a declaration of RLF to the base station.

[0017] The operation method may further include: when an RLF is declared, performing an operation to release the sidelink resources configured for the radio link.

[0018] Furthermore, according to an exemplary embodiment of the present invention, an operation method of a first terminal in a communication system supporting sidelink communication may include: sending one or more sidelink data to a second terminal; performing a monitoring operation to receive one or more Hybrid Automatic Repeat Request (HARQ) responses to the one or more sidelink data from the second terminal; and declaring a radio link failure (RLF) when no HARQ response is received.

[0019] When the number of one or more HARQ responses that the first terminal has not received is equal to or greater than a preset threshold, an RLF can be declared.

[0020] The one or more HARQ responses can be consecutive HARQ responses.

[0021] When the number of one or more HARQ responses that the first terminal does not receive within a predetermined time period is equal to or greater than a preset threshold, an RLF can be declared.

[0022] The operation method may further include: receiving configuration information from the base station, including one or more information elements for declaring an RLF.

[0023] The configuration information may include a preset threshold, which is a comparison standard for the number of the one or more HARQ responses.

[0024] The operation method may further include: sending information indicating a declaration of RLF to the base station.

[0025] The operation method may further include: when an RLF is declared, performing an operation to release the sidelink resources configured for the radio link.

[0026] Furthermore, according to an exemplary embodiment of the present invention, the operation method of a base station in a communication system supporting sidelink communication may include: sending configuration information including one or more information elements for declaring a radio link failure (RLF) on the sidelink to one or more terminals; receiving information indicating that an RLF has been declared from a first terminal among one or more terminals; and releasing sidelink resources configured for the radio link associated with the RLF.

[0027] The operation method may further include: reconfiguring the sidelink resources used for the wireless link; and sending the configuration information of the reconfigured sidelink resources to the first terminal.

[0028] The configuration information may include information indicating the number of RLF-HARQ (RLF-HARQ) responses, and an RLF may be declared on the first terminal when the first terminal receives at least one HARQ response indicating discontinuous transmission (DTX) and the number of the at least one HARQ response is equal to or greater than the number of RLF-HARQ responses.

[0029] The configuration information may include information indicating the RLF time period, and when the first terminal receives a HARQ response indicating DTX within the RLF time period, the first terminal may declare the RLF.

[0030] The configuration information may include information indicating a Channel Busy Rate (RLF-CBR) threshold, and an RLF may be declared on the first terminal when the CBR measured at the first terminal is equal to or greater than the RLF-CBR threshold.

[0031] According to an exemplary embodiment of the present invention, the base station can send parameters related to an RLF (Relative Link Failure) to the terminal, and the terminal can determine whether an RLF has occurred on the side link based on the parameters related to the RLF. When an RLF is declared, the side link resources configured for the radio link associated with the corresponding RLF can be released, and the side link resources used for the radio link can be reconfigured. Therefore, the RLF detection process for the side link can be effectively performed in the communication system, and the release and / or reconfiguration process of side link resources can be effectively performed based on the RLF detection. That is, the performance of the communication system supporting side link communication can be improved. Attached Figure Description

[0032] Exemplary embodiments of the present invention will become more apparent from a detailed description of them with reference to the accompanying drawings, in which: Figure 1 This is a conceptual diagram illustrating a V2X communication scenario according to an exemplary embodiment of the present invention; Figure 2 This is a conceptual diagram illustrating a cellular communication system according to an exemplary embodiment of the present invention; Figure 3 This is a conceptual diagram illustrating a communication node constituting a cellular communication system according to an exemplary embodiment of the present invention; Figure 4 This is a block diagram illustrating the user plane protocol stack of a UE performing sidelink communication according to an exemplary embodiment of the present invention; Figure 5 This is a block diagram illustrating the control plane protocol stack of a UE performing sidelink communication according to an exemplary embodiment of the present invention; Figure 6 This is a block diagram illustrating the control plane protocol stack of a UE performing sidelink communication according to an exemplary embodiment of the present invention; Figure 7 This is a sequence diagram illustrating a first exemplary embodiment of a method for RLF detection and wireless link recovery in a communication system supporting sidelink communication; Figure 8 This is a sequence diagram illustrating a second exemplary embodiment of a method for RLF detection and wireless link recovery in a communication system supporting sidelink communication; Figure 9 This is a sequence diagram illustrating a third exemplary embodiment of a method for RLF detection and radio link recovery in a communication system supporting sidelink communication; and Figure 10 This is a sequence diagram illustrating a fourth exemplary embodiment of a method for RLF detection and wireless link recovery in a communication system supporting sidelink communication.

[0033] It should be understood that the accompanying drawings referenced above are not necessarily drawn to scale, but are schematic simplifications to illustrate various features to demonstrate the basic principles of the invention. Specific design features of the invention (including, for example, specific dimensions, orientations, positions, and shapes) will be determined in part by the specific environment in which it will be applied and used. Detailed Implementation

[0034] It should be understood that the term "vehicle" or "of a vehicle" or other similar terms as used herein generally include motor vehicles, such as passenger vehicles including sport utility vehicles (SUVs), buses, trucks, various commercial vehicles, vessels including various boats and ships, aircraft, etc., and includes hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen-powered vehicles, and other alternative fuel vehicles (e.g., vehicles derived from non-fossil fuels). As mentioned herein, a hybrid vehicle is a vehicle with two or more power sources, such as both gasoline and electric power.

[0035] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the invention. As used herein, the singular forms “an,” “a,” and “the” are intended to equally include the plural forms unless the context explicitly indicates that the plural forms are excluded. It will also be further understood that when the terms “comprising” and / or “including” are used in this specification, they indicate the presence of the stated feature, value, step, operation, element, and / or component, but do not exclude the presence or addition of one or more other features, values, steps, operations, elements, components, and / or groups thereof. As used herein, the term “and / or” includes any and all combinations of one or more related enumerations. Throughout the specification, unless explicitly described to the contrary, the word “comprising” and variations such as “including” or “including” will be understood to include the stated elements but not exclude any other elements. Furthermore, the terms “unit,” “device,” “component,” and “module” described in the specification mean a unit for performing at least one function and operation, and can be implemented by hardware components or software components and combinations thereof.

[0036] Furthermore, the control logic of the present invention can be implemented as a non-volatile computer-readable medium, which is a computer-readable medium comprising executable program instructions that run by a processor or controller. Examples of computer-readable media include, but are not limited to, ROM, RAM, optical disc (CD)-ROM, magnetic tape, floppy disk, flash memory drive, smart card, and optical data storage device. The computer-readable medium can also be distributed across a network-connected computer system, such that the computer-readable medium is stored and executed in a distributed manner, for example, via a telematics server or a controller area network (CAN).

[0037] This document discloses exemplary embodiments of the present invention. However, the specific structural and functional details disclosed herein are for the purpose of describing exemplary embodiments of the invention only. Therefore, embodiments of the invention may be implemented in many alternative forms and should not be construed as limited to the embodiments set forth herein.

[0038] Accordingly, while the invention can have various modifications and alternatives, specific embodiments thereof are shown by way of example in the accompanying drawings and will be described in detail herein. However, it should be understood that the invention is not intended to be limited to the specific forms disclosed; rather, it should encompass all modifications, equivalents, and alternatives within the spirit and scope of the invention. Throughout the description of the drawings, the same reference numerals denote the same elements.

[0039] It is understood that while the terms first, second, etc., may be used herein to describe various elements, these elements should not be limited by these terms. These terms are used only to distinguish one element from another. For example, a first element may be referred to as a second element, and similarly, a second element may be referred to as a first element, without departing from the scope of the invention. As used herein, the term "and / or" includes any and all combinations of one or more of the related enumerations.

[0040] It should be understood that when an element is described as "connected" or "linked" to another element, it can be directly connected or linked to the other element, or there may be an intervening element. Conversely, when an element is described as "directly connected" or "directly linked" to another element, there is no intervening element. Other terms used to describe the relationship between elements should be interpreted in a similar manner (i.e., "between" and "directly between," "adjacent" and "directly adjacent," etc.).

[0041] Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains. It will be further understood that terms (e.g., terms as defined in commonly used dictionaries) should be interpreted as having the same meaning as they do in the context of the prior art, and should not be interpreted in an idealized or overly formal sense unless explicitly defined herein.

[0042] Furthermore, it should be understood that one or more of the following methods or aspects thereof can be operated by at least one control unit. The terms "control unit" or "controller" can refer to a hardware device including a memory and a processor. The memory is configured to store program instructions, and the processor is specifically programmed to execute the program instructions to perform one or more processes further described below. As described herein, a control unit can control the operation of units, modules, components, etc. Furthermore, as will be appreciated by those skilled in the art, it should be understood that the following methods can be performed by a device including a control unit (e.g., a communication node) in combination with one or more other components.

[0043] In the following description, exemplary embodiments of the invention will be described in more detail with reference to the accompanying drawings. For ease of overall understanding in describing the invention, the same parts in the drawings are denoted by the same reference numerals, and repeated descriptions thereof will be omitted.

[0044] Figure 1 This is a conceptual diagram illustrating a V2X communication scenario. (For example...) Figure 1As shown, V2X communication can include vehicle-to-vehicle (V2V) communication, vehicle-to-infrastructure (V2I) communication, vehicle-to-pedestrian (V2P) communication, vehicle-to-network (V2N) communication, etc. V2X communication can be supported by a cellular communication system (e.g., cellular communication system 140), and the V2X communication supported by cellular communication system 140 can be referred to as "cellular-V2X (C-V2X) communication." Here, cellular communication system 140 can include 4G communication systems (e.g., LTE communication systems or LTE-A communication systems), 5G communication systems (e.g., NR communication systems), etc.

[0045] V2V communication can include communication between a first vehicle 100 (e.g., a communication node located in vehicle 100 (e.g., the first vehicle)) and a second vehicle 110 (e.g., a communication node located in vehicle 110 (e.g., the second vehicle)). Various driving information, such as speed, direction of travel, time, and location, can be exchanged between vehicles 100 and 110 via V2V communication. For example, autonomous driving (e.g., platooning) can be supported based on the driving information exchanged via V2V communication. V2V communication supported in the cellular communication system 140 can be performed based on "sidelink" communication technologies (e.g., proximity-based services (ProSe) and D2D communication technologies). Specifically, communication between vehicles 100 and 110 can be performed using at least one sidelink channel established between vehicles 100 and 110.

[0046] V2I communication can include communication between a first vehicle 100 (e.g., a communication node located in vehicle 100) and roadside infrastructure (e.g., a roadside unit (RSU)) 120. Infrastructure 120 may also include traffic lights or streetlights located on the roadside. For example, when performing V2I communication, communication can occur between a communication node located in the first vehicle 100 and a communication node located in a traffic light. Traffic information and driving information can be exchanged between the first vehicle 100 and infrastructure 120 via V2I communication. V2I communication supported in the cellular communication system 140 can also be performed based on sidelink communication technologies (e.g., ProSe and D2D communication technologies). Specifically, communication between vehicle 100 and infrastructure 120 can be performed using at least one sidelink channel established between vehicle 100 and infrastructure 120.

[0047] V2P communication can include communication between a first vehicle 100 (e.g., a communication node located within the vehicle 100) and a person 130 (e.g., a communication node carried by the person 130). Driving information of the first vehicle 100 and movement information of the person 130, such as speed, direction of travel, time, and location, can be exchanged between the vehicle 100 and the person 130 via V2P communication. By detecting hazardous situations based on the acquired driving and movement information, the communication node located in the vehicle 100 or the communication node carried by the person 130 can be configured to generate an alarm indicating a hazard. V2P communication supported in the cellular communication system 140 can be performed based on sidelink communication technologies (e.g., ProSe and D2D communication technologies). Specifically, communication between the communication node located in the vehicle 100 and the communication node carried by the person 130 can be performed using at least one sidelink channel established between the communication nodes.

[0048] V2N communication can be communication between a first vehicle 100 (e.g., a communication node located in vehicle 100) and a server connected via a cellular communication system 140. V2N communication can be performed based on 4G communication technologies (e.g., LTE or LTE-A) or 5G communication technologies (e.g., NR). Furthermore, V2N communication can be performed based on wireless access (WAVE) communication technologies in a vehicle environment, or wireless local area network (WLAN) communication technologies as defined in IEEE 802.11, or wireless personal area network (WPAN) communication technologies as defined in IEEE 802.15.

[0049] Meanwhile, the cellular communication system 140 that supports V2X communication can be configured as follows.

[0050] Figure 2 This is a conceptual diagram illustrating an exemplary implementation of a cellular communication system. (Example:) Figure 2 As shown, a cellular communication system may include an access network and a core network. The access network may include base station 210, relay station 220, and user equipment (UE) 231 to 236. UE 231 to 236 may include: located at... Figure 1 The communication nodes in vehicles 100 and 110, located Figure 1 The communication nodes in the infrastructure 120 and the Figure 1 The core network may include: a Serving Gateway (S-GW) 250, a Packet Data Network (PDN) Gateway (P-GW) 260, and a Mobility Management Entity (MME) 270, etc., carried by the person 130.

[0051] When a cellular communication system supports 5G communication technology, the core network may include: User Plane Function (UPF) 250, Session Management Function (SMF) 260, and Access and Mobility Management Function (AMF) 270, etc. Alternatively, when the cellular communication system operates in non-standalone (NSA) mode, the core network consisting of S-GW 250, P-GW 260, and MME 270 can support both 5G and 4G communication technologies, or the core network consisting of UPF 250, SMF 260, and AMF 270 can support both 4G and 5G communication technologies.

[0052] Furthermore, when a cellular communication system supports network slicing technology, the core network can be divided into multiple logical network slices. For example, network slices that support V2X communication can be configured (e.g., V2V network slices, V2I network slices, V2P network slices, V2N network slices, etc.), and V2X communication can be supported through V2X network slices configured in the core network.

[0053] Communication nodes in cellular communication systems (e.g., base stations, relay stations, UEs, S-GWs, P-GWs, MMEs, UPFs, SMFs, AMFs, etc.) can be configured to communicate using at least one of the following technologies: Code Division Multiple Access (CDMA), Time Division Multiple Access (TDMA), Frequency Division Multiple Access (FDMA), Orthogonal Frequency Division Multiplexing (OFDM), Filtered OFDM, Single Carrier FDMA (SC-FDMA), Non-Orthogonal Multiple Access (NOMA), Generalized Frequency Division Multiplexing (GFDM), Filter Bank Multicarrier (FBMC), Universal Filtered Multicarrier (UFMC), and Space Division Multiple Access (SDMA).

[0054] The communication nodes of the cellular communication system (e.g., base stations, relay stations, UEs, S-GWs, P-GWs, MMEs, UPFs, SMFs, AMFs, etc.) can be configured as follows.

[0055] Figure 3 This is a conceptual diagram illustrating an exemplary implementation of a communication node constituting a cellular communication system. (As shown) Figure 3 As shown, the communication node 300 may include at least one processor 310, a memory 320, and a transceiver 330 connected to a network for communication. Furthermore, the communication node 300 may further include an input interface device 340, an output interface device 350, and a storage device 360, etc. Each component included in the communication node 300 can be configured to communicate with each other when connected via a bus 370.

[0056] However, each component included in communication node 300 can be connected to processor 310 via a separate interface or a separate bus instead of the common bus 370. For example, processor 310 can be connected to at least one of memory 320, transceiver 330, input interface device 340, output interface device 350, and storage device 360 ​​via a dedicated interface.

[0057] Processor 310 may be configured to execute at least one instruction stored in at least one of memory 320 and storage device 360. Processor 310 may refer to a central processing unit (CPU), graphics processing unit (GPU), or dedicated processor on which methods according to exemplary embodiments of the present invention are performed. Each of memory 320 and storage device 360 ​​may include at least one of volatile storage medium and non-volatile storage medium. For example, memory 320 may include at least one of read-only memory (ROM) and random access memory (RAM).

[0058] Refer again Figure 2 In the communication system, base station 210 can form a macro cell or a cell and can connect to the core network via ideal backhaul or non-ideal backhaul. Base station 210 can be configured to transmit signals received from the core network to UEs 231 to 236 and relay station 220, and to transmit signals received from UEs 231 to 236 and relay station 220 to the core network. UEs 231, 232, 234, 235, and 236 can belong to the cell coverage area of ​​base station 210. UEs 231, 232, 234, 235, and 236 can connect to base station 210 by performing a connection establishment procedure. UEs 231, 232, 234, 235, and 236 can be configured to communicate with base station 210 after connecting to it.

[0059] Relay station 220 can connect to base station 210 and relay communication between base station 210 and UEs 233 and 234. That is, relay station 220 can be configured to transmit signals received from base station 210 to UEs 233 and 234, and vice versa. UE 234 can be within the cell coverage area of ​​both base station 210 and relay station 220, and UE 233 can be within the cell coverage area of ​​relay station 220. That is, UE 233 can be located outside the cell coverage area of ​​base station 210. UEs 233 and 234 can connect to relay station 220 by performing a connection establishment procedure. UEs 233 and 234 can be configured to communicate with relay station 220 after connecting to it.

[0060] Base station 210 and relay station 220 can support multiple-input multiple-output (MIMO) technologies (e.g., single-user (SU)-MIMO, multi-user (MU)-MIMO, massive MIMO, etc.), coordinated multipoint (CoMP) communication technologies, carrier aggregation (CA) communication technologies, unlicensed band communication technologies (e.g., licensed assisted access (LAA), enhanced LAA (eLAA), etc.), and sidelink communication technologies (e.g., ProSe communication technologies, D2D communication technologies). UEs 231, 232, 235, and 236 can perform operations corresponding to base station 210 and operations supported by base station 210. UEs 233 and 234 can be configured to perform operations corresponding to relay station 220 and operations supported by relay station 220.

[0061] Specifically, base station 210 can refer to Node B (NB), Evolved Node B (eNB), Base Transceiver Station (BTS), Radio Remote Header (RRH), Transmitter Receiver Point (TRP), Radio Unit (RU), Roadside Unit (RSU), Radio Transceiver, Access Point, Access Node, etc. Relay station 220 can refer to small base station, relay node, etc. Each of UEs 231 to 236 can refer to terminal, access terminal, mobile terminal, station, user station, mobile station, portable user station, node, equipment, On-Board Unit (OBU), etc.

[0062] Simultaneously, communication between UE 235 and 236 can be performed based on sidelink communication technology. Sidelink communication can be performed using a one-to-one or one-to-many scheme. When performing V2V communication using sidelink communication technology, UE 235 can be located at... Figure 1 The communication node in the first vehicle 100, while UE 236 may be located in Figure 1 The communication node in the second vehicle 110. When performing V2I communication using sidelink communication technology, UE 235 can be located in Figure 1 The communication node in the first vehicle 100, while UE 236 may be located in Figure 1 The communication node in infrastructure 120. When performing V2P communication using sidelink communication technology, UE 235 can be located in Figure 1 The communication node in the first vehicle 100, while UE 236 can be... Figure 1 The communication node carried by person 130.

[0063] Scenarios for applying sidelink communication can be categorized based on the location of the UEs participating in the sidelink communication (e.g., UEs 235 and 236), as shown in Table 1 below. For example, Figure 2 The sidelink communication scenario between UEs 235 and 236 shown in the figure can be sidelink communication scenario C.

[0064] [Table 1] Meanwhile, the user plane protocol stack of the UE performing sidelink communication (e.g., UE 235 and 236) can be configured as follows.

[0065] Figure 4 This is a block diagram illustrating an exemplary implementation of the user plane protocol stack of a UE performing sidelink communication. Figure 4 As shown, the UE on the left can be Figure 2 The UE 235 shown in the diagram, the UE on the right can be... Figure 2 The UE 236 shown is an example. The sidelink communication scenario between UE 235 and 236 can be one of the sidelink communication scenarios A to D in Table 1. The user plane protocol stack of each of UE 235 and 236 can include: Physical (PHY) layer, Media Access Control (MAC) layer, Radio Link Control (RLC) layer, and Packet Data Convergence Protocol (PDCP) layer.

[0066] Sidelink communication between UEs 235 and 236 can be performed using a PC5 interface (e.g., a PC5-U interface). Layer 2 identifiers (IDs) (e.g., source Layer 2 ID, destination Layer 2 ID) can be used for sidelink communication, and these IDs can be IDs configured for V2X communication (e.g., V2X services). Furthermore, hybrid Automatic Repeat Request (HARQ) feedback operations can be supported in sidelink communication, and RLC acknowledge mode (RLC AM) or RLC unacknowledged mode (RLC UM) can be supported. The control plane protocol stack of the UEs performing sidelink communication (e.g., UEs 235 and 236) can be configured as follows.

[0067] Figure 5 This is a block diagram illustrating a first exemplary implementation of the control plane protocol stack of a UE performing sidelink communication, and Figure 6 This is a block diagram illustrating a second exemplary implementation of the control plane protocol stack of a UE performing sidelink communication. (See diagram for example.) Figure 5 and 6 As shown, the UE on the left can be Figure 2 The UE 235 shown in the diagram, the UE on the right can be... Figure 2 The sidelink communication scenario between UE 235 and 236 can be one of the sidelink communication scenarios A to D in Table 1. Figure 5 The control plane protocol stack shown may be a control plane protocol stack used for sending and receiving broadcast information (e.g., Physical Side Link Broadcast Channel (PSBCH)).

[0068] Figure 5The control plane protocol stack shown may include a PHY layer, a MAC layer, an RLC layer, and a Radio Resource Control (RRC) layer. Sidelink communication between UEs 235 and 236 can be performed using a PC5 interface (e.g., a PC5-C interface). Figure 6 The control plane protocol stack shown can be a control plane protocol stack used for one-to-one side link communication. Figure 6 The control plane protocol stack shown may include: PHY layer, MAC layer, RLC layer, PDCP layer and PC5 signaling protocol layer.

[0069] Meanwhile, the channels used in sidelink communication between UEs 235 and 236 may include: Physical Sidelink Shared Channel (PSSCH), Physical Sidelink Control Channel (PSCCH), Physical Sidelink Discovery Channel (PSDCH), and Physical Sidelink Broadcast Channel (PSBCH). The PSSCH can be used to send and receive sidelink data and can be configured in the UE (e.g., UE 235 or 236) via upper-layer signaling. The PSCCH can be used to send and receive Sidelink Control Information (SCI) and can also be configured in the UE (e.g., UE 235 or 236) via upper-layer signaling.

[0070] PSDCH can be used in the discovery process. For example, a discovery signal can be sent via PSDCH. PSBCH can be used to send and receive broadcast information (e.g., system information). Furthermore, demodulation reference signals (DM-RS), synchronization signals, etc., can be used in sidelink communication between UEs 235 and 236. Meanwhile, sidelink transmission modes (TM) can be classified into sidelink TM 1 to 4, as shown in Table 2 below.

[0071] [Table 2] When sidelink TM 3 or 4 is supported, each of UEs 235 and 236 can be configured to perform sidelink communication using a resource pool configured by base station 210. A resource pool can be configured for each of the sidelink control information and sidelink data.

[0072] The resource pool for receiving sidelink control information can be configured based on RRC signaling procedures (e.g., dedicated RRC signaling procedures, broadcast RRC signaling procedures, etc.). The resource pool for receiving sidelink control information can be configured by the broadcast RRC signaling procedure. When sidelink TM 3 is supported, the resource pool for sending sidelink control information can be configured through a dedicated RRC signaling procedure. Specifically, sidelink control information can be sent through resources scheduled by base station 210 within the resource pool configured by the dedicated RRC signaling procedure. When sidelink TM 4 is supported, the resource pool for sending sidelink control information can be configured through either a dedicated RRC signaling procedure or a broadcast RRC signaling procedure. Specifically, sidelink control information can be sent through resources autonomously selected by the UE (e.g., UE 235 or 236) within the resource pool configured by the dedicated RRC signaling procedure or the broadcast RRC signaling procedure.

[0073] When sidelink TM 3 is supported, a resource pool for transmitting and receiving sidelink data does not need to be configured. In this case, sidelink data can be transmitted and received using resources scheduled by base station 210. When sidelink TM 4 is supported, a resource pool for transmitting and receiving sidelink data can be configured using a dedicated RRC signaling procedure or a broadcast RRC signaling procedure. Specifically, sidelink data can be transmitted and received using resources autonomously selected by the UE (e.g., UE 235 or 236) within the resource pool configured by the dedicated RRC signaling procedure or the broadcast RRC signaling procedure.

[0074] The following describes methods for detecting radio link failures (RLF) and restoring radio links in sidelink communication. Even when a method (e.g., transmitting or receiving a signal) to be performed by a first communication node is described, a corresponding second communication node can be configured to perform a method (e.g., receiving or transmitting a signal) corresponding to the method performed by the first communication node. In other words, when the operation of a first vehicle is described, a corresponding second vehicle can be configured to perform an operation corresponding to the operation of the first vehicle. Conversely, when the operation of a second vehicle is described, a corresponding first vehicle can be configured to perform an operation corresponding to the operation of the second vehicle. In the exemplary embodiments described below, the operation of the vehicle can be the operation of a communication node located within the vehicle.

[0075] In exemplary embodiments, the HARQ response can be ACK, NACK, and / or Discontinuous Transmission (DTX). Exemplary embodiments applicable when the HARQ response is ACK can also be applied, even when the HARQ response is NACK or DTX. Exemplary embodiments applicable when the HARQ response is DTX can also be applied, even when the HARQ response is NACK or DTX.

[0076] Sidelink signals can be synchronization signals and reference signals used for sidelink communication. For example, synchronization signals can be Synchronization Signal / Physical Broadcast Channel (SS / PBCH) blocks, Sidelink Synchronization Signals (SLSS), Primary Sidelink Synchronization Signals (PSSS), Secondary Sidelink Synchronization Signals (SSSS), etc. Reference signals can be Channel State Information Reference Signals (CSI-RS), DM-RS, Phase Tracking Reference Signals (PT-RS), Cell-Specific Reference Signals (CRS), Sound Reference Signals (SRS), Discovery Reference Signals (DRS), etc.

[0077] Sidelink channels can be PSSCH, PSCCH, PSDCH, PSBCH, Physical Sidelink Feedback Channel (PSFCH), etc. Furthermore, a sidelink channel can refer to a sidelink channel that includes sidelink signals mapped to specific resources within the sidelink channel. Sidelink communication can support broadcast, multicast, and unicast services.

[0078] In a cellular communication system, a terminal can perform Radio Link Detection (RLM) operations to check the status of the radio link (e.g., Uu interface) between the terminal and the base station. The terminal can detect (e.g., declare) an RLF based on the result of the RLM operation. For example, a lower layer of the terminal (e.g., an entity performing lower-layer functions) can send an out-of-synchronization (OSS) indicator to an upper layer of the terminal (e.g., an entity performing upper-layer functions) based on the result of the RLM operation. Here, the lower layer can be the Physical (PHY) layer, and the upper layer can be the RRC layer.

[0079] When the number of OSS indicators received from the lower layer of the terminal is greater than or equal to a preset number (e.g., N310 as defined in the technical specification), the upper layer of the terminal can start a T310 timer. When the state of the radio link does not improve until the T310 timer expires (e.g., when less than a preset number of Continuous Synchronization (IS) indicators are received until the T310 timer expires (e.g., N311 as defined in the technical specification), the terminal (e.g., the upper layer of the terminal) can declare an RLF.

[0080] When an RLF (Recurrent Leakage Failure) is declared (i.e., when an RLF occurs), an RRC (Recurrent Route Control) re-establishment procedure can be executed. The terminal can search for a new cell and attempt to establish an RRC connection to the new cell by executing the RRC re-establishment procedure. When the RRC re-establishment procedure completes successfully, the radio link between the terminal and the base station can be restored. On the other hand, when the RRC re-establishment procedure fails, the terminal's operating state can change from RRC connected state to RRC idle state. That is, the RRC connection between the terminal and the base station can be released. To restore communication in this state, a new RRC connection should be established between the terminal and the base station.

[0081] Meanwhile, in communication systems that support sidelink communication (e.g., V2X communication), the transmitting terminal and / or receiving terminal can perform RLM operations (e.g., operations for RLF detection) to detect (e.g., declare) an RLF. The RLF detection method (e.g., RLF declaration method) and the radio link recovery method for sidelink communication can be performed as follows.

[0082] Figure 7 This is a sequence diagram illustrating a first exemplary embodiment of a method for RLF detection and radio link recovery in a communication system supporting sidelink communication. (See diagram for example.) Figure 7 As shown, the communication system may include a base station, a first terminal, and a second terminal. The base station can be... Figure 2 The base station 210 shown. The first terminal can be... Figure 2 The second terminal of the UE 235 shown can be... Figure 2 The UE shown is 236. Alternatively, the first terminal could be... Figure 2 The second terminal of the UE 236 shown can be... Figure 2 The UE235 shown. Each of the first and second terminals can be located in the vehicle. It can be connected to... Figure 3 The communication nodes 300 shown are configured with the same or similar base station, first terminal, and second terminal. The first terminal and second terminal can support... Figures 4 to 6 The protocol stack is shown. The first and second terminals can connect to the base station and perform sidelink communication based on the base station's scheduling. Alternatively, the first and second terminals can be located outside the base station's coverage area and can perform sidelink communication without base station scheduling.

[0083] The first terminal can send sidelink UE information to the base station to initiate sidelink communication (e.g., V2X communication) (S701). The sidelink UE information may include performance information of the first terminal. For example, the sidelink UE information may include information indicating the initiation of sidelink communication. The base station can receive the sidelink UE information from the first terminal and can identify the information elements included in the sidelink UE information. Furthermore, when the base station receives the sidelink UE information from the first terminal, it can determine that the first terminal has initiated sidelink communication. The base station can generate configuration information for sidelink communication (hereinafter referred to as "sidelink configuration information") and can send the sidelink configuration information (S702). When the sidelink UE information (e.g., sidelink UE information including information indicating the initiation of sidelink communication) is received from the first terminal, the sidelink configuration information can be sent. Alternatively, the sidelink configuration information can be sent regardless of the receipt of the sidelink UE information. In this case, step S701 can be omitted.

[0084] Sidelink configuration information can be transmitted through one or more of the following: system information (e.g., Master Information Block (MIB), System Information Block (SIB)), RRC messages (e.g., cell-specific RRC messages, UE-specific RRC messages, RRC reconfiguration messages, etc.), MAC messages (e.g., MAC control element (CE)), and PHY messages (e.g., downlink control information (DCI)). For example, sidelink configuration information can be transmitted solely through RRC messages. Alternatively, some information elements included in the sidelink configuration information can be transmitted through RRC messages, and other information elements included in the sidelink configuration information can be transmitted through MAC messages and / or PHY messages. Sidelink configuration information may include one or more information elements described in Table 3 below.

[0085] [Table 3] Sidelink configuration information may include parameters related to RLF. Furthermore, sidelink configuration information may further include information elements required for sidelink communication and parameters related to RLF. For example, information elements required for sidelink communication may include: configuration information for the bandwidth portion of the sidelink, configuration information for the resource pool, configuration information for the semi-static scheduling of the sidelink, and / or configuration information for the configuration authorization (CG) of the sidelink.

[0086] Terminals (e.g., a first terminal and / or a second terminal) can receive sidelink configuration information from the base station and identify the information elements included in the sidelink configuration information. When the first terminal is within the coverage area of ​​the base station and the second terminal is outside the coverage area of ​​the base station, the first terminal can receive the sidelink configuration information from the base station, but the second terminal cannot. In this case, the first terminal can send a MAC message and / or PHY message (e.g., SCI, first-stage SCI, second-stage SCI) including the sidelink configuration information to the second terminal. The second terminal can receive the MAC message and / or PHY message from the first terminal and identify the sidelink configuration information included in the MAC message and / or PHY message. Alternatively, the sidelink configuration information can be predefined in the technical specifications. In this case, since the communication nodes (e.g., the base station, the first terminal, and the second terminal) already know the sidelink configuration information, step S702 can be omitted.

[0087] Simultaneously, the first terminal can send sidelink data to the second terminal via the PSSCH (S703). The resource (e.g., PSSCH) through which the sidelink data is sent can be an SPS resource, a CG resource, or a resource scheduled by the SCI. Each of the SPS and CG resources can be pre-configured by the base station, and the configuration information for each of the SPS and CG resources can be included in the sidelink configuration information in step S702. When sending sidelink data via a resource scheduled by the SCI, the first terminal can send an SCI including scheduling information to the second terminal before step S703. Step S703 can be performed based on the scheduling information included in the SCI.

[0088] The second terminal can perform a monitoring operation to receive sidelink data. When sidelink data is successfully received, the second terminal can send a HARQ ACK to the first terminal in response to the sidelink data (S704). When the decoding operation of the sidelink data fails, the second terminal can send a HARQ NACK to the first terminal in response to the sidelink data (S704). When sidelink data is not detected in SPS resources, CG resources, or resources scheduled by SCI, the second terminal may not send a HARQ ACK or HACK NACK to the first terminal, or may send a discontinuous transmission (DTX) (e.g., HARQ DTX) to the first terminal. In this case, the second terminal can determine that a DTX situation has occurred (e.g., the situation where sidelink data is not detected in SPS resources, CG resources, or resources scheduled by SCI).

[0089] When the sidelink configuration information includes an RLF time period, or when an RLF time period is defined in the technical specification, the first terminal can perform a monitoring operation to receive a HARQ response (e.g., HARQ feedback) within the RLF time period. The RLF time period may begin from the transmission time (e.g., transmission start time or transmission end time) of the SCI for scheduling sidelink data in step S703. Alternatively, the RLF time period may begin from the transmission time (e.g., transmission start time or transmission end time) of the sidelink data in step S703.

[0090] When the first terminal receives a HARQ response (e.g., ACK or NACK) for sidelink data from the second terminal during the RLF period, the first terminal can determine that no RLF has occurred. Even if the second terminal sends a HARQ response, if the channel condition between the first and second terminals is poor, or if the distance between the first and second terminals increases, the first terminal may not receive a HARQ response from the second terminal. Alternatively, in the event of a DTX (Distributed Transaction) situation, the second terminal may not send a HARQ response, in which case the first terminal may not receive a HARQ response from the second terminal.

[0091] When no HARQ response (e.g., ACK or NACK) for sidelink data is received from the second terminal during the RLF period (e.g., when no HARQ response is received), the first terminal can determine that an RLF has occurred (S705). Alternatively, when DTX for sidelink data is received from the second terminal during the RLF period, the first terminal can determine that an RLF has occurred (S705). In this case, the first terminal can declare an RLF. For example, when no HARQ response (e.g., ACK or NACK) for sidelink data is received from the second terminal during the RLF period, or when DTX for sidelink data is received from the second terminal during the RLF period, the lower layer of the first terminal (e.g., the entity performing PHY layer functions) can send an RLF indicator (or an OSS indicator) to the upper layer of the first terminal (e.g., the entity performing RRC layer functions). When the RLF indicator is received from the lower layer of the first terminal, the upper layer of the first terminal can declare an RLF. When an RLF is declared, the first terminal can release the sidelink resources between the first terminal and the second terminal. For example, the first terminal (e.g., the upper layer of the first terminal) can release the PC5 interface (e.g., PC5 connection).

[0092] When an RLF is declared (e.g., when an RLF is detected), the first terminal can send information indicating that an RLF has been declared (hereinafter referred to as an "RLF declaration indicator") to the base station (S706). The RLF declaration indicator can be sent to the base station via an RRC message, a MAC message, or a PHY message (e.g., uplink control information (UCI)). For example, the RLF declaration indicator can be included in sidelink UE information or UE assistance information, and the sidelink UE information or UE assistance information can be sent from the first terminal to the base station. The RLF declaration indicator can be information requesting the release of sidelink resources configured in the first terminal and information indicating that the first terminal has declared an RLF. Alternatively, in step S706, information requesting the release of sidelink resources configured in the first terminal (hereinafter referred to as a "resource release indicator") can be sent together with the RLF declaration indicator. Step S706 can be performed when using sidelink TM 1 or sidelink TM 3 as shown in Table 2 (e.g., when sidelink resources are allocated by the base station). When using the side link TM 2 or side link TM 4 described in Table 2 (e.g., when the first terminal autonomously selects the side link resource), step S706 may be omitted.

[0093] The base station can receive an RLF declaration indicator from the first terminal, or it can receive both an RLF declaration indicator and a resource release indicator from the first terminal. In this case, the base station can determine that the first terminal has declared an RLF. Furthermore, the base station can release sidelink resources configured in the terminals (e.g., the first terminal and / or the second terminal). The base station can allocate the released sidelink resources to another terminal (e.g., a third terminal). In this case, the released sidelink resources can be used for sidelink communication of the other terminal (e.g., the third terminal) until the radio link between the first terminal and the second terminal is restored.

[0094] Furthermore, the base station can reconfigure sidelink resources (e.g., bandwidth portion, resource pool, SPS resources, CG resources) for the first terminal (S707). Sidelink reconfiguration information, including reconfiguration information of sidelink resources, can be sent to the terminal (e.g., the first terminal and / or the second terminal) (S708). Sidelink reconfiguration information can be sent to the terminal (e.g., the first terminal and / or the second terminal) through one or more combinations of system information, RRC messages, MAC messages, and PHY messages.

[0095] On the other hand, when an RLF has been declared, the first terminal can perform a wireless link recovery process between the first terminal and the second terminal. For example, the first terminal can transmit a sidelink signal using a sidelink resource different from the sidelink resource used in step S703 (e.g., a sidelink resource belonging to a different bandwidth portion, a sidelink resource belonging to a different resource pool, another SPS resource, another CG resource, a candidate sidelink resource). Here, the sidelink signal can be a discovery signal, an SCI (e.g., an SCI including scheduling information for initial transmission or retransmission of sidelink data) and / or sidelink data (e.g., initial transmission or retransmission of sidelink data). When a response to the sidelink signal (e.g., a discovery response signal, a HARQ response) is received from the second terminal, the first terminal can determine that the wireless link between the first terminal and the second terminal has been restored. Alternatively, when no response to the sidelink signal (e.g., a discovery response signal, a HARQ response) is received from the second terminal, the first terminal can determine that the wireless link recovery process between the first terminal and the second terminal has failed. In an exemplary implementation, the first terminal may declare an RLF if no HARQ response is received from the second terminal during the RLF period and the wireless link recovery process fails. Alternatively, the first terminal may declare an RLF if a DTX is received from the second terminal during the RLF period and the wireless link recovery process fails. That is, step S705 can be performed after the wireless link recovery process has been executed.

[0096] Figure 8 This is a sequence diagram illustrating a second exemplary embodiment of a method for RLF detection and radio link recovery in a communication system supporting sidelink communication. (See diagram for example.) Figure 8 As shown, the communication system may include a base station, a first terminal, and a second terminal. The base station can be... Figure 2 The base station 210 shown. The first terminal can be... Figure 2 The second terminal of the UE 235 shown can be... Figure 2 The UE shown is 236. Alternatively, the first terminal could be... Figure 2 The second terminal of the UE 236 shown can be... Figure 2 The UE235 shown. Each of the first and second terminals can be located in the vehicle. It can be connected to... Figure 3 The communication nodes 300 shown are configured with the same or similar base station, first terminal, and second terminal. The first terminal and second terminal can support... Figures 4 to 6 The protocol stack is shown. The first and second terminals can connect to the base station and perform sidelink communication based on the base station's scheduling. Alternatively, the first and second terminals can be located outside the base station's coverage area and can perform sidelink communication without base station scheduling.

[0097] The first terminal can send sidelink UE information to the base station to initiate sidelink communication (e.g., V2X communication) (S801). The sidelink UE information may include performance information of the first terminal. For example, the sidelink UE information may include information indicating the initiation of sidelink communication. The base station can receive the sidelink UE information from the first terminal and can identify the information elements included in the sidelink UE information. Furthermore, when the base station receives the sidelink UE information from the first terminal, it can determine that the first terminal has initiated sidelink communication. The base station can generate sidelink configuration information and can send the sidelink configuration information (S802). When the sidelink UE information (e.g., sidelink UE information including information indicating the initiation of sidelink communication) is received from the first terminal, the sidelink configuration information can be sent. Alternatively, the sidelink configuration information can be sent regardless of the receipt of the sidelink UE information. In this case, step S801 can be omitted.

[0098] Sidelink configuration information can be sent via one or more of the following: system information, RRC messages (e.g., RRC reconfiguration messages), MAC messages, and PHY messages. For example, sidelink configuration information can be sent solely via RRC messages. Alternatively, some information elements included in the sidelink configuration information can be sent via RRC messages, and other information elements included in the sidelink configuration information can be sent via MAC messages and / or PHY messages. Sidelink configuration information may include one or more information elements described in Table 3 below.

[0099] That is, the sidelink configuration information may include parameters related to RLF. Furthermore, the sidelink configuration information may further include information elements required for sidelink communication and parameters related to RLF. For example, information elements required for sidelink communication may include: configuration information for the bandwidth portion of the sidelink, configuration information for the resource pool, configuration information for the semi-static scheduling of the sidelink, and / or configuration information for the configuration authorization (CG) of the sidelink.

[0100] Terminals (e.g., a first terminal and / or a second terminal) can receive sidelink configuration information from the base station and identify the information elements included in the sidelink configuration information. When the first terminal is within the coverage area of ​​the base station and the second terminal is outside the coverage area of ​​the base station, the first terminal can receive the sidelink configuration information from the base station, but the second terminal cannot. In this case, the first terminal can send a MAC message and / or a PHY message including the sidelink configuration information to the second terminal. The second terminal can receive the MAC message and / or the PHY message from the first terminal and identify the sidelink configuration information included in the MAC message and / or the PHY message. Alternatively, the sidelink configuration information can be predefined in the technical specifications. In this case, since the communication nodes (e.g., the base station, the first terminal, and the second terminal) already know the sidelink configuration information, step S802 can be omitted.

[0101] Simultaneously, the first terminal can send sidelink data to the second terminal via the PSSCH (S803). The resource (e.g., PSSCH) through which the sidelink data is sent can be an SPS resource, a CG resource, or a resource scheduled by the SCI. Each of the SPS and CG resources can be pre-configured by the base station, and the configuration information for each of the SPS and CG resources can be included in the sidelink configuration information in step S802. When sending sidelink data via a resource scheduled by the SCI, the first terminal can send an SCI including scheduling information to the second terminal before step S803. Step S803 can be performed based on the scheduling information included in the SCI.

[0102] The second terminal can perform a monitoring operation to receive sidelink data. When the decoding operation of the sidelink data fails, the second terminal can send a HARQ NACK to the first terminal in response to the sidelink data (S804). When no sidelink data is detected in the SPS resource, CG resource, or resource scheduled by the SCI, the second terminal may not send a HARQ ACK or HACK NACK to the first terminal. In this case, the first terminal cannot receive a HARQ response (e.g., HARQ ACK or HARQ NACK) from the second terminal within a predetermined time period. Therefore, the first terminal can determine that a DTX situation has occurred in the second terminal, or that a HARQ DTX has been received from the second terminal. In an exemplary embodiment, the occurrence of a DTX situation or the reception of a HARQ DTX may indicate the absence of a HARQ response. Alternatively, when no sidelink data is detected in the SPS resource, CG resource, or resource scheduled by the SCI, the second terminal may send a DTX to the first terminal (S804).

[0103] After step S803 or S804, the first terminal may send one or more sidelink data (e.g., initial transmission or retransmission of sidelink data) to the second terminal. For example, in step S805, the first terminal may send sidelink data to the second terminal via PSSCH. The resource (e.g., PSSCH) through which the sidelink data is sent may be an SPS resource, a CG resource, or a resource scheduled by SCI. Each of the SPS and CG resources may be pre-configured by the base station. When sending sidelink data via a resource scheduled by SCI, the first terminal may send an SCI including scheduling information to the second terminal before step S805. Step S805 may be performed based on the scheduling information included in the SCI.

[0104] The second terminal can perform a monitoring operation to receive sidelink data. When the decoding operation of the sidelink data fails, the second terminal can send a HARQ NACK to the first terminal in response to the sidelink data (S806). When no sidelink data is detected in the SPS resource, CG resource, or resource scheduled by SCI, the second terminal may not send a HARQ ACK or HACK NACK to the first terminal. In this case, the first terminal cannot receive a HARQ response (e.g., HARQ ACK or HARQ NACK) from the second terminal within a predetermined time period. Therefore, the first terminal can determine that a DTX situation has occurred in the second terminal, a HARQ DTX has been received from the second terminal, or no HARQ response has been received. Alternatively, when no sidelink data is detected in the SPS resource, CG resource, or resource scheduled by SCI, the second terminal can send a DTX to the first terminal (S806).

[0105] Simultaneously, the first terminal can receive HARQ NACK and / or DTX from the second terminal, and can determine whether an RLF has occurred based on the number of HARQ NACK or DTX received from the second terminal (e.g., consecutive HARQ NACK and / or DTX). The first terminal can compare the number of HARQ NACK or DTX received from the second terminal (e.g., consecutive HARQ NACK and / or DTX) with the number of RLF-HARQ responses included in the sidelink configuration information or the number of RLF-HARQ responses defined in the technical specification. If the number of HARQ NACK and / or DTX received from the second terminal (e.g., consecutive HARQ NACK and / or DTX) is less than the number of RLF-HARQ responses, the first terminal can determine that no RLF has occurred. On the other hand, if the number of HARQ NACK and / or DTX received from the second terminal (e.g., consecutive HARQ NACK and / or DTX) is greater than or equal to the number of RLF-HARQ responses, the first terminal can declare an RLF (S807).

[0106] As another method for detecting RLF, the number of RLF-HARQ responses and the RLF time period can be considered together. In this case, the first terminal can compare the number of HARQ NACKs and / or DTXs (e.g., consecutive HARQ NACKs and / or DTXs) ​​received from the second terminal within the RLF time period included in the sidelink configuration information or the RLF time period defined in the technical specification with the number of RLF-HARQ responses. If the number of HARQ NACKs and / or DTXs (e.g., consecutive HARQ NACKs and / or DTXs) ​​received from the second terminal within the RLF time period is less than the number of RLF-HARQ responses, the first terminal can determine that no RLF has occurred. On the other hand, when the number of HARQ NACKs and / or DTXs (e.g., consecutive HARQ NACKs and / or DTXs) ​​received from the second terminal within the RLF time period is greater than or equal to the number of RLF-HARQ responses, the first terminal can declare an RLF (S807).

[0107] Step S807 can be performed as follows. For example, when the number of HARQ NACKs and / or DTXs (e.g., consecutive HARQ NACKs and / or DTXs) ​​received from the second terminal is greater than or equal to the number of RLF-HARQ responses, or when the number of HARQ NACKs and / or DTXs (e.g., consecutive HARQ NACKs and / or DTXs) ​​received from the second terminal within the RLF time period is greater than or equal to the number of RLF-HARQ responses, the lower layer of the first terminal (e.g., the entity performing PHY layer functions) can send an RLF indicator (or OSS indicator) to the upper layer of the first terminal (e.g., the entity performing RRC layer functions). When the RLF indicator is received from the lower layer of the first terminal, the upper layer of the first terminal can declare an RLF. When an RLF is declared, the first terminal can release the sidelink resources between the first terminal and the second terminal. For example, the first terminal (e.g., the upper layer of the first terminal) can release the PC5 interface (e.g., the PC5 connection).

[0108] When an RLF is declared (e.g., when an RLF is detected), the first terminal can send an RLF declaration indicator to the base station (S808). The RLF declaration indicator can be sent to the base station via an RRC message, a MAC message, or a PHY message. For example, the RLF declaration indicator can be included in sidelink UE information or UE assistance information, and the sidelink UE information or UE assistance information can be sent from the first terminal to the base station. The RLF declaration indicator can be information requesting the release of sidelink resources configured in the first terminal and information indicating that the first terminal has declared an RLF. Alternatively, in step S808, a resource release indicator can be sent together with the RLF declaration indicator. Step S808 can be performed when using sidelink TM 1 or sidelink TM 3 as shown in Table 2 (e.g., when sidelink resources are allocated by the base station). Step S808 can be omitted when using sidelink TM 2 or sidelink TM 4 described in Table 2 (e.g., when the first terminal autonomously selects sidelink resources).

[0109] The base station can receive an RLF declaration indicator from the first terminal, or it can receive both an RLF declaration indicator and a resource release indicator from the first terminal. In this case, the base station can determine that the first terminal has declared an RLF. Furthermore, the base station can release sidelink resources configured in the terminals (e.g., the first terminal and / or the second terminal). The base station can allocate the released sidelink resources to another terminal (e.g., a third terminal). In this case, the released sidelink resources can be used for sidelink communication of the other terminal (e.g., the third terminal) until the radio link between the first terminal and the second terminal is restored.

[0110] Furthermore, the base station can reconfigure sidelink resources (e.g., bandwidth portion, resource pool, SPS resources, CG resources) for the first terminal (S809). Sidelink reconfiguration information, including reconfiguration information of sidelink resources, can be sent to the terminal (e.g., the first terminal and / or the second terminal) (S810). Sidelink reconfiguration information can be sent to the terminal (e.g., the first terminal and / or the second terminal) through one or more combinations of system information, RRC messages, MAC messages, and PHY messages.

[0111] On the other hand, when an RLF is declared, the first terminal can perform a process to restore the wireless link between the first terminal and the second terminal. For example, the first terminal can transmit a sidelink signal using a sidelink resource different from the sidelink resource used in step S803 and / or step S805 (e.g., a sidelink resource belonging to a different bandwidth portion, a sidelink resource belonging to a different resource pool, another SPS resource, another CG resource, a candidate sidelink resource). Here, the sidelink signal can be a discovery signal, an SCI (e.g., an SCI including scheduling information for initial transmission or retransmission of sidelink data), and / or sidelink data (e.g., initial transmission or retransmission of sidelink data). When a response to the sidelink signal is received from the second terminal (e.g., a discovery response signal, a HARQ response), the first terminal can determine that the wireless link between the first terminal and the second terminal has been restored. Alternatively, when no response to the sidelink signal is received from the second terminal (e.g., a discovery response signal, a HARQ response), the first terminal can determine that the process to restore the wireless link between the first terminal and the second terminal has failed.

[0112] In an exemplary implementation, if the number of HARQ NACKs and / or DTXs (e.g., consecutive HARQ NACKs and / or DTXs) ​​received from the second terminal is greater than or equal to the number of RLF-HARQ responses, and the radio link recovery process fails, the first terminal may declare an RLF. Alternatively, if the number of HARQ NACKs and / or DTXs (e.g., consecutive HARQ NACKs and / or DTXs) ​​received from the second terminal during the RLF period is greater than or equal to the number of RLF-HARQ responses, and the radio link recovery process fails, the first terminal may declare an RLF. That is, step S807 can be performed after the radio link recovery process has been executed.

[0113] Figure 9 This is a sequence diagram illustrating a third exemplary embodiment of a method for RLF detection and radio link recovery in a communication system supporting sidelink communication. (See diagram for example.) Figure 9 As shown, the communication system may include a base station, a first terminal, and a second terminal. The base station can be... Figure 2The base station 210 shown. The first terminal can be... Figure 2 The second terminal of the UE 235 shown can be... Figure 2 The UE shown is 236. Alternatively, the first terminal could be... Figure 2 The second terminal of the UE 236 shown can be... Figure 2 The UE235 shown. Each of the first and second terminals can be located in the vehicle. It can be connected to... Figure 3 The communication nodes 300 shown are configured with the same or similar base station, first terminal, and second terminal. The first terminal and second terminal can support... Figures 4 to 6 The protocol stack is shown. The first and second terminals can connect to the base station and perform sidelink communication based on the base station's scheduling. Alternatively, the first and second terminals can be located outside the base station's coverage area and can perform sidelink communication without base station scheduling.

[0114] The first terminal can send sidelink UE information to the base station to initiate sidelink communication (e.g., V2X communication) (S901). The sidelink UE information may include performance information of the first terminal. For example, the sidelink UE information may include information indicating the initiation of sidelink communication. The base station can receive the sidelink UE information from the first terminal and can identify the information elements included in the sidelink UE information. Furthermore, when the base station receives the sidelink UE information from the first terminal, it can determine that the first terminal has initiated sidelink communication. The base station can generate sidelink configuration information and can send the sidelink configuration information (S902). When the sidelink UE information (e.g., sidelink UE information including information indicating the initiation of sidelink communication) is received from the first terminal, the sidelink configuration information can be sent. Alternatively, the sidelink configuration information can be sent regardless of the receipt of the sidelink UE information. In this case, step S901 can be omitted.

[0115] Sidelink configuration information can be sent via one or more of the following: system information, RRC messages (e.g., RRC reconfiguration messages), MAC messages, and PHY messages. For example, sidelink configuration information can be sent solely via RRC messages. Alternatively, some information elements included in the sidelink configuration information can be sent via RRC messages, and other information elements included in the sidelink configuration information can be sent via MAC messages and / or PHY messages. Sidelink configuration information may include one or more information elements described in Table 3 below.

[0116] That is, the sidelink configuration information may include parameters related to RLF. Furthermore, the sidelink configuration information may further include information elements required for sidelink communication and parameters related to RLF. For example, information elements required for sidelink communication may include configuration information for the bandwidth portion of the sidelink, configuration information for the resource pool, configuration information for the semi-static scheduling of the sidelink, and / or configuration information for the authorization (CG) of the sidelink configuration.

[0117] Terminals (e.g., a first terminal and / or a second terminal) can receive sidelink configuration information from the base station and identify the information elements included in the sidelink configuration information. When the first terminal is within the coverage area of ​​the base station and the second terminal is outside the coverage area of ​​the base station, the first terminal can receive the sidelink configuration information from the base station, but the second terminal cannot. In this case, the first terminal can send a MAC message and / or a PHY message including the sidelink configuration information to the second terminal. The second terminal can receive the MAC message and / or the PHY message from the first terminal and identify the sidelink configuration information included in the MAC message and / or the PHY message. Alternatively, the sidelink configuration information can be predefined in the technical specifications. In this case, since the communication nodes (e.g., the base station, the first terminal, and the second terminal) already know the sidelink configuration information, step S902 can be omitted.

[0118] Simultaneously, the first terminal can perform a Channel Busy Rate (CBR) measurement operation (S903). For example, the first terminal can perform the CBR measurement operation on the wireless link (e.g., a PC5 interface) between the first terminal and the second terminal, and the CBR measurement operation can be performed within a predetermined time period. The predetermined time period can be an RLF time period included in the sidelink configuration information, or an RLF time period defined in the technical specification. The first terminal can determine whether an RLF has occurred based on the CBR measurement result. That is, the first terminal can compare the CBR measurement result with the RLF-CBR threshold included in the sidelink configuration information or the RLF-CBR threshold defined in the technical specification. When the CBR measurement result in step S903 is less than the RLF-CBR threshold, the first terminal can determine that an RLF has not occurred. On the other hand, when the CBR measurement result in step S903 is equal to or greater than the RLF-CBR threshold, the first terminal can determine that an RLF has occurred. In this case, the first terminal can declare an RLF (S904).

[0119] For example, when the CBR measurement result in the wireless link between the first terminal and the second terminal is greater than or equal to the RLF-CBR threshold, the lower layer of the first terminal (e.g., an entity performing PHY layer functions) can send an RLF indicator (or OSS indicator) to the upper layer of the first terminal (e.g., an entity performing RRC layer functions). Upon receiving the RLF indicator from the lower layer of the first terminal, the upper layer of the first terminal can declare an RLF. When an RLF is declared, the first terminal can release the sidelink resources between the first terminal and the second terminal. For example, the first terminal (e.g., the upper layer of the first terminal) can release the PC5 interface (e.g., the PC5 connection).

[0120] When an RLF is declared (e.g., when an RLF is detected), the first terminal can send an RLF declaration indicator to the base station (S905). The RLF declaration indicator can be sent to the base station via an RRC message, a MAC message, or a PHY message. For example, the RLF declaration indicator can be included in sidelink UE information or UE assistance information, and the sidelink UE information or UE assistance information can be sent from the first terminal to the base station. The RLF declaration indicator can be information requesting the release of sidelink resources configured in the first terminal and information indicating that the first terminal has declared an RLF. Alternatively, in step S905, a resource release indicator can be sent together with the RLF declaration indicator. Step S905 can be performed when using sidelink TM 1 or sidelink TM 3 shown in Table 2 (e.g., when sidelink resources are allocated by the base station). Step S905 can be omitted when using sidelink TM 2 or sidelink TM 4 described in Table 2 (e.g., when the first terminal autonomously selects sidelink resources).

[0121] The base station can receive an RLF declaration indicator from the first terminal, or it can receive both an RLF declaration indicator and a resource release indicator from the first terminal. In this case, the base station can determine that the first terminal has declared an RLF. Furthermore, the base station can release sidelink resources configured in the terminals (e.g., the first terminal and / or the second terminal). The base station can allocate the released sidelink resources to another terminal (e.g., a third terminal). In this case, the released sidelink resources can be used for sidelink communication of the other terminal (e.g., the third terminal) until the radio link between the first terminal and the second terminal is restored.

[0122] Furthermore, the base station can reconfigure sidelink resources (e.g., bandwidth portion, resource pool, SPS resources, CG resources) for the first terminal (S906). Sidelink reconfiguration information, including reconfiguration information of sidelink resources, can be sent to the terminal (e.g., the first terminal and / or the second terminal) (S907). Sidelink reconfiguration information can be sent to the terminal (e.g., the first terminal and / or the second terminal) through one or more combinations of system information, RRC messages, MAC messages, and PHY messages.

[0123] On the other hand, when an RLF has been declared, the first terminal can perform the wireless link restoration process between the first terminal and the second terminal. For example, the first terminal can transmit a sidelink signal by utilizing a sidelink resource different from the sidelink resource used in step S803 and / or step S805 (e.g., a sidelink resource belonging to a different bandwidth portion, a sidelink resource belonging to a different resource pool, another SPS resource, another CG resource, a candidate sidelink resource). Here, the sidelink signal is a discovery signal, an SCI (e.g., an SCI that includes scheduling information for initial transmission or retransmission of sidelink data), and / or sidelink data (e.g., initial transmission or retransmission of sidelink data).

[0124] When the first terminal receives a response from the second terminal regarding the peer link signal (e.g., a discovery response signal, a HARQ response), it can determine that the wireless link between the first and second terminals has been restored. Alternatively, if no response from the second terminal is received (e.g., a discovery response signal, a HARQ response), the first terminal can determine that the wireless link restoration process between the first and second terminals has failed. In an exemplary embodiment, the first terminal can declare an RLF when the CBR measurement result in the wireless link between the first and second terminals is greater than or equal to the RLF-CBR threshold. That is, step S904 can be performed after the wireless link restoration process has been completed.

[0125] Figure 10 This is a sequence diagram illustrating a fourth exemplary embodiment of a method for RLF detection and radio link recovery in a communication system supporting sidelink communication. (See diagram for example.) Figure 10 As shown, the communication system may include a base station, a first terminal, and a second terminal. The base station can be... Figure 2 The base station 210 shown. The first terminal can be... Figure 2 The second terminal of the UE 235 shown can be... Figure 2 The UE shown is 236. Alternatively, the first terminal could be... Figure 2 The second terminal of the UE 236 shown can be... Figure 2 The UE235 shown. Each of the first and second terminals can be located in the vehicle. It can be connected to... Figure 3 The communication nodes 300 shown are configured with the same or similar base station, first terminal, and second terminal. The first terminal and second terminal can support... Figures 4 to 6 The protocol stack is shown. The first and second terminals can connect to the base station and perform sidelink communication based on the base station's scheduling. Alternatively, the first and second terminals can be located outside the base station's coverage area and can perform sidelink communication without base station scheduling.

[0126] The first terminal can send sidelink UE information to the base station to initiate sidelink communication (e.g., V2X communication) (S1001). The sidelink UE information may include performance information of the first terminal. For example, the sidelink UE information may include information indicating the initiation of sidelink communication. The base station can receive the sidelink UE information from the first terminal and can identify the information elements included in the sidelink UE information. Furthermore, when the base station receives the sidelink UE information from the first terminal, it can determine that the first terminal has initiated sidelink communication. The base station can generate sidelink configuration information and can send the sidelink configuration information (S1002). When the sidelink UE information (e.g., sidelink UE information including information indicating the initiation of sidelink communication) is received from the first terminal, the sidelink configuration information can be sent. Alternatively, the sidelink configuration information can be sent regardless of the receipt of the sidelink UE information. In this case, step S1001 can be omitted.

[0127] Sidelink configuration information can be sent via one or more of the following: system information, RRC messages (e.g., RRC reconfiguration messages), MAC messages, and PHY messages. For example, sidelink configuration information can be sent solely via RRC messages. Alternatively, some information elements included in the sidelink configuration information can be sent via RRC messages, and other information elements included in the sidelink configuration information can be sent via MAC messages and / or PHY messages. Sidelink configuration information may include one or more information elements described in Table 3 below.

[0128] That is, the sidelink configuration information may include parameters related to RLF. Furthermore, the sidelink configuration information may further include information elements required for sidelink communication and parameters related to RLF. For example, information elements required for sidelink communication may include configuration information for the bandwidth portion of the sidelink, configuration information for the resource pool, configuration information for the semi-static scheduling of the sidelink, and / or configuration information for the authorization (CG) of the sidelink configuration.

[0129] Terminals (e.g., a first terminal and / or a second terminal) can receive sidelink configuration information from the base station and identify the information elements included in the sidelink configuration information. When the first terminal is within the coverage area of ​​the base station and the second terminal is outside the coverage area of ​​the base station, the first terminal can receive the sidelink configuration information from the base station, but the second terminal cannot. In this case, the first terminal can send a MAC message and / or a PHY message including the sidelink configuration information to the second terminal. The second terminal can receive the MAC message and / or the PHY message from the first terminal and identify the sidelink configuration information included in the MAC message and / or the PHY message. Alternatively, the sidelink configuration information can be predefined in the technical specifications. In this case, since the communication nodes (e.g., the base station, the first terminal, and the second terminal) already know the sidelink configuration information, step S1002 can be omitted.

[0130] Simultaneously, the first terminal can generate a SCI (Schedule Instruction) including sidelink data scheduling information (e.g., a first-stage SCI and / or a second-stage SCI), and can send the SCI to the second terminal (S1003). Sidelink data can be sent according to transmission periodicity. The SCI sent in step S1003 may include information indicating the transmission periodicity of the sidelink data. Alternatively, the transmission periodicity of the sidelink data can be configured by the base station. In this case, the sidelink configuration information sent in step S1002 may include information indicating the transmission periodicity of the sidelink data, and the SCI sent in step S1003 may include information indicating the activation of the sidelink data transmission periodicity.

[0131] The second terminal can perform monitoring operations on the sidelink to receive SCI. When no SCI is received (e.g., when the SCI decoding operation fails), the second terminal can send a HARQ NACK to the first terminal (e.g., a HARQ NACK in response to the SCI). This operation can be performed when the DTX-NACK indicator included in the sidelink configuration information or the DTX-NACK indicator defined in the technical specification is enabled (e.g., when the DTX-NACK indicator is set to 1). That is, when no SCI is received, the second terminal can determine that a DTX situation has occurred and can send a HARQ NACK indicating that a DTX situation has occurred to the first terminal. When the DTX-NACK indicator is set to 1 and a HARQ NACK is received from the second terminal, the first terminal can determine that a DTX situation has occurred in the second terminal. In this case, the first terminal can interpret the HARQ NACK received from the second terminal as a HARQ DTX.

[0132] After executing step S1003, the first terminal can send sidelink data to the second terminal through the resource indicated by the SCI (S1004). Step S1004 can be executed if no HARQ NACK is received from the second terminal for the SCI. Alternatively, step S1004 can be executed regardless of whether a HARQ NACK is received from the second terminal for the SCI. The second terminal, having successfully received the SCI, can perform a monitoring operation on the resource indicated by the corresponding SCI to receive sidelink data. When sidelink data is successfully received, the second terminal can send a HARQ ACK to the first terminal in response to the sidelink data. On the other hand, when no sidelink data is detected in the resource indicated by the SCI, the second terminal can determine that a DTX situation has occurred. When it is determined that a DTX situation has occurred and the DTX-NACK indicator is set to 1, the second terminal can send a HARQ NACK to the first terminal (S1005). The first terminal can receive a HARQ NACK from the second terminal in response to the sidelink data sent in step S1004. When the DTX-NACK indicator is set to 1, the first terminal can interpret the HARQNACK received from the second terminal as HARQ DTX. That is, the first terminal can determine that a DTX situation has occurred in the second terminal.

[0133] After step S1004 or S1005, the first terminal may send one or more sidelink data to the second terminal (e.g., initial transmission or retransmission of sidelink data). For example, in step S1006, the first terminal may send sidelink data to the second terminal. In step S1006, the sidelink data may be sent using the resources indicated by the SCI in step S1003. Alternatively, separate from step S1003, the first terminal may send an SCI including scheduling information for each sidelink data to the second terminal before sending the corresponding sidelink data.

[0134] When the sidelink data of step S1006 is sent through the resource indicated by the SCI in step S1003, the second terminal can perform a monitoring operation on the resource indicated by the SCI received in step S1003 to receive the sidelink data. When the sidelink data is successfully received, the second terminal can send a HARQ ACK to the first terminal in response to the sidelink data. On the other hand, when no sidelink data is detected in the resource indicated by the SCI, the second terminal can determine that a DTX situation has occurred. When it is determined that a DTX situation has occurred and the DTX-NACK indicator is set to 1, the second terminal can send a HARQ NACK to the first terminal (S1007). The first terminal can receive a HARQ NACK from the second terminal in response to the sidelink data sent in step S1006. When the DTX-NACK indicator is set to 1, the first terminal can interpret the HARQ NACK received from the second terminal as a HARQ DTX. That is, the first terminal can determine that a DTX situation has occurred in the second terminal.

[0135] Alternatively, when the sidelink data of step S1006 is sent via a resource indicated by another SCI (e.g., an SCI that includes scheduling information for the sidelink data sent in step S1006) instead of the SCI of step S1003, the second terminal can perform a monitoring operation on the sidelink to receive the corresponding SCI. If no SCI is received (e.g., when the SCI decoding operation fails), the second terminal can send a HARQ NACK (e.g., a HARQ NACK in response to the SCI) to the first terminal. The second terminal can determine that a DTX situation has occurred and can send a HARQ NACK indicating that a DTX situation has occurred to the first terminal. When the DTX-NACK indicator is set to 1 and a HARQ NACK is received from the second terminal, the first terminal can determine that a DTX situation has occurred in the second terminal. In this case, the first terminal can interpret the HARQ NACK received from the second terminal as a HARQ DTX.

[0136] When a Sidelink Message Confirmation (SCI) is successfully received (i.e., an SCI different from the SCI in step S1003), the second terminal can perform a monitoring operation on the resource indicated by the SCI to receive sidelink data. Upon successful reception of sidelink data, the second terminal can send a HARQ ACK to the first terminal in response to the sidelink data. Conversely, if no sidelink data is detected in the resource indicated by the SCI, the second terminal can determine that a DTX situation has occurred. When it is determined that a DTX situation has occurred and the DTX-NACK indicator is set to 1, the second terminal can send a HARQ NACK to the first terminal (S1007). The first terminal can receive a HARQ NACK from the second terminal in response to the sidelink data sent in step S1006. When the DTX-NACK indicator is set to 1, the first terminal can interpret the HARQ NACK received from the second terminal as a HARQ DTX. That is, the first terminal can determine that a DTX situation has occurred in the second terminal.

[0137] Simultaneously, the first terminal can determine whether an RLF has occurred based on the number of HARQ NACKs received from the second terminal (e.g., information indicating that a DTX situation has occurred in the second terminal). Here, the first terminal can interpret the HARQ NACKs received from the second terminal as HARQ DTX or the absence of a HARQ response. That is, a HARQ NACK can indicate HARQ DTX. The first terminal can compare the number of HARQ NACKs received from the second terminal (e.g., consecutive HARQ NACKs) with the number of RLF-HARQ responses included in the sidelink configuration information or defined in the technical specification. If the number of HARQ NACKs received from the second terminal (e.g., consecutive HARQ NACKs) is less than the number of RLF-HARQ responses, the first terminal can determine that no RLF has occurred. On the other hand, when the number of HARQ NACKs received from the second terminal (e.g., consecutive HARQ NACKs) is greater than or equal to the number of RLF-HARQ responses, the first terminal can declare an RLF (S1008).

[0138] As another method for detecting RLF, the number of RLF-HARQ responses and the RLF time period can be considered together. In this case, the first terminal can compare the number of HARQ NACKs (e.g., consecutive HARQ NACKs) received from the second terminal within the RLF time period included in the sidelink configuration information or the RLF time period defined in the technical specification with the number of RLF-HARQ responses. If the number of HARQ NACKs (e.g., consecutive HARQ NACKs) received from the second terminal within the RLF time period is less than the number of RLF-HARQ responses, the first terminal can determine that no RLF has occurred. On the other hand, when the number of HARQ NACKs (e.g., consecutive HARQ NACKs) received from the second terminal within the RLF time period is greater than or equal to the number of RLF-HARQ responses, the first terminal can declare an RLF (S1008).

[0139] Step S1008 can be performed as follows. For example, when the number of HARQ NACKs (e.g., consecutive HARQ NACKs) received from the second terminal is greater than or equal to the number of RLF-HARQ responses, or when the number of HARQ NACKs (e.g., consecutive HARQ NACKs) received from the second terminal within the RLF time period is equal to or greater than the number of RLF-HARQ responses, the lower layer of the first terminal (e.g., the entity performing PHY layer functions) can send an RLF indicator (or OSS indicator) to the upper layer of the first terminal (e.g., the entity performing RRC layer functions). When the RLF indicator is received from the lower layer of the first terminal, the upper layer of the first terminal can declare an RLF. When an RLF is declared, the first terminal can release the sidelink resources between the first terminal and the second terminal. For example, the first terminal (e.g., the upper layer of the first terminal) can release the PC5 interface (e.g., the PC5 connection).

[0140] When an RLF is declared (e.g., when an RLF is detected), the first terminal can send an RLF declaration indicator to the base station (S1009). The RLF declaration indicator can be sent to the base station via an RRC message, a MAC message, or a PHY message. For example, the RLF declaration indicator can be included in sidelink UE information or UE assistance information, and the sidelink UE information or UE assistance information can be sent from the first terminal to the base station. The RLF declaration indicator can be information requesting the release of sidelink resources configured in the first terminal and information indicating that the first terminal has declared an RLF. Alternatively, in step S1009, a resource release indicator can be sent together with the RLF declaration indicator. Step S1009 can be performed when using sidelink TM 1 or sidelink TM 3 as shown in Table 2 (e.g., when sidelink resources are allocated by the base station). Step S1009 can be omitted when using sidelink TM 2 or sidelink TM 4 described in Table 2 (e.g., when the first terminal autonomously selects sidelink resources).

[0141] The base station can receive an RLF declaration indicator from the first terminal, or it can receive both an RLF declaration indicator and a resource release indicator from the first terminal. In this case, the base station can determine that the first terminal has declared an RLF. Furthermore, the base station can release sidelink resources configured in the terminals (e.g., the first terminal and / or the second terminal). The base station can allocate the released sidelink resources to another terminal (e.g., a third terminal). In this case, the released sidelink resources can be used for sidelink communication of the other terminal (e.g., the third terminal) until the radio link between the first terminal and the second terminal is restored.

[0142] Furthermore, the base station can reconfigure sidelink resources (e.g., bandwidth portion, resource pool, SPS resources, CG resources) for the first terminal (S1010). Sidelink reconfiguration information, including reconfiguration information of sidelink resources, can be sent to the terminal (e.g., the first terminal and / or the second terminal) (S1011). Sidelink reconfiguration information can be sent to the terminal (e.g., the first terminal and / or the second terminal) through one or more combinations of system information, RRC messages, MAC messages, and PHY messages.

[0143] On the other hand, once an RLF has been declared, the first terminal can perform the wireless link restoration process between the first terminal and the second terminal. For example, the first terminal can transmit a sidelink signal by utilizing a sidelink resource different from the sidelink resource used in step S1004 and / or step S1006 (e.g., a sidelink resource belonging to a different bandwidth portion, a sidelink resource belonging to a different resource pool, another SPS resource, another CG resource, a candidate sidelink resource). Here, the sidelink signal is a discovery signal, an SCI (e.g., an SCI including scheduling information for initial transmission or retransmission of sidelink data), and / or sidelink data (e.g., initial transmission or retransmission of sidelink data).

[0144] When the first terminal receives a response from the second terminal regarding the peer link signal (e.g., a discovery response signal, a HARQ response), it can determine that the wireless link between the first and second terminals has been restored. Alternatively, if no response from the second terminal is received regarding the peer link signal (e.g., a discovery response signal, a HARQ response), the first terminal can determine that the wireless link restoration process between the first and second terminals has failed.

[0145] In an exemplary implementation, if the number of HARQ NACKs (e.g., consecutive HARQ NACKs) received from the second terminal is greater than or equal to the number of RLF-HARQ responses, and the radio link recovery process fails, the first terminal may declare an RLF. Alternatively, if the number of HARQ NACKs (e.g., consecutive HARQ NACKs) received from the second terminal during the RLF period is greater than or equal to the number of RLF-HARQ responses, and the radio link recovery process fails, the first terminal may declare an RLF. That is, step S1008 can be performed after the radio link recovery process has been executed.

[0146] Exemplary embodiments of the present invention can be implemented as program instructions executed by various computers and recorded in a non-volatile computer-readable medium. The non-volatile computer-readable medium may include program instructions, data files, data structures, or combinations thereof. The program instructions recorded in the non-volatile computer-readable medium may be specifically designed and configured for the present invention, or may be those known and available to those skilled in the art of computer software.

[0147] Examples of non-volatile computer-readable media may include hardware devices specifically configured to store and execute program instructions, such as ROM, RAM, and flash memory. Examples of program instructions include, for example, machine code generated by a compiler, and high-level language code executed by a computer using an interpreter. The aforementioned exemplary hardware devices may be configured to operate as at least one software module to perform exemplary embodiments of the present invention, and vice versa.

[0148] While exemplary embodiments of the invention and their advantages have been described in detail, it should be understood that various changes, substitutions and modifications may be made herein without departing from the scope of the invention.

Claims

1. A method for detecting a sidelink wireless link fault by a first user equipment in a wireless communication system, the method comprising: Information is received from the base station via the radio resource control layer, the information including a threshold for detecting sidelink radio link failures in the sidelink radio link between the first user equipment and the second user equipment; Send at least one sidelink data to the second user equipment; Monitoring to receive at least one hybrid automatic repeat request message in response to at least one sidelink data, wherein each of the at least one hybrid automatic repeat request message includes an acknowledgment or a negative acknowledgment; During the period when no at least one Hybrid Automatic Repeat Request message is received consecutively, a counter value related to the threshold is counted. Sidelink radio link failure is detected based on the fact that no at least one hybrid automatic repeat request message has been received continuously until the count value reaches a threshold. The threshold-related count is initialized based on receiving at least one hybrid automatic repeat request message before the count value reaches the threshold.

2. The method according to claim 1, further comprising: Based on the detection of a sidelink radio link failure, the radio resource control layer sends a notification to the base station that a sidelink radio link failure has been detected.

3. The method according to claim 1, wherein, A sidelink radio link is maintained between the first user equipment and the second user equipment based on receiving at least one hybrid automatic repeat request message before the count value reaches a threshold.

4. The method according to claim 1, further comprising: Based on the detection of a sidelink radio link failure, the sidelink radio link between the first user equipment and the second user equipment is released.

5. The method of claim 4, further comprising: Based on the release of the sidelink radio link, the sidelink radio link is rebuilt between the first user equipment and the second user equipment.

6. A first user equipment configured to detect a sidelink radio link failure in a wireless communication system, the first user equipment comprising: At least one transceiver; At least one processor; as well as At least one computer memory operatively connected to at least one processor and storing instructions, which, when executed, cause the at least one processor to perform operations including: Information is received from the base station via the radio resource control layer and at least one transceiver, the information including a threshold for detecting a sidelink radio link failure in the sidelink radio link between the first user equipment and the second user equipment. Send at least one sidelink data to the second user equipment through at least one transceiver; Monitoring to receive at least one hybrid automatic repeat request message in response to at least one sidelink data, wherein each of the at least one hybrid automatic repeat request message includes an acknowledgment or a negative acknowledgment; During the period when no at least one Hybrid Automatic Repeat Request message is received consecutively, a counter value related to the threshold is counted. Sidelink radio link failure is detected based on the fact that no at least one hybrid automatic repeat request message has been received continuously until the count value reaches a threshold. The threshold-related count is initialized based on receiving at least one hybrid automatic repeat request message before the count value reaches the threshold.

7. The first user equipment according to claim 6, wherein the operation further comprises: Based on the detection of a sidelink radio link failure, a notification of the detected sidelink radio link failure is sent to the base station through the radio resource control layer and at least one transceiver.

8. The first user equipment according to claim 6, wherein, A sidelink radio link is maintained between the first user equipment and the second user equipment based on receiving at least one hybrid automatic repeat request message before the count value reaches a threshold.

9. The first user equipment according to claim 6, further comprising: Based on the detection of a sidelink radio link failure, the sidelink radio link between the first user equipment and the second user equipment is released.

10. The first user equipment according to claim 9, further comprising: Based on the release of the sidelink radio link, the sidelink radio link is rebuilt between the first user equipment and the second user equipment.

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