Method for performing relay communication and device therefor in wireless communication system

Abstract

Disclosed are a method for a first relay terminal to perform multi-hop-based relay and a device therefor in a wireless communication system according to various embodiments. The method comprises the steps of: forming a first hop connection and a second hop connection for the multi-hop-based relay; monitoring whether a radio link failure (RLF) occurs in the first hop connection or the second hop connection; and, on the basis that an RLF occurred in one of the first hop connection or the second hop connection, triggering a reselection procedure of the relay terminal for the one hop connection.

Description

Method for performing relay communication in a wireless communication system and device therefor

[0001] The present invention relates to a method for a relay terminal to perform multi-hop-based relay communication in a wireless communication system and a device therefor.

[0002] Wireless communication systems are multiple access systems that support communication with multiple users by sharing available system resources (e.g., bandwidth, transmission power, etc.). Examples of multiple access systems include code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), single carrier frequency division multiple access (SC-FDMA), and multi-carrier frequency division multiple access (MC-FDMA).

[0003] Sidelink (SL) refers to a communication method that establishes a direct link between user equipment (UE), allowing voice or data to be exchanged directly between terminals without going through a base station (BS). SL is being considered as a solution to address the burden on base stations due to rapidly increasing data traffic.

[0004] V2X (vehicle-to-everything) refers to a communication technology that exchanges information with other vehicles, pedestrians, and infrastructure-based objects through wired / wireless communication. V2X can be divided into four types: V2V (vehicle-to-vehicle), V2I (vehicle-to-infrastructure), V2N (vehicle-to-network), and V2P (vehicle-to-pedestrian). V2X communication can be provided through the PC5 interface and / or Uu interface.

[0005] Meanwhile, as more and more communication devices demand greater communication capacity, the need for improved mobile broadband communication compared to existing radio access technology (RAT) is emerging. Accordingly, communication systems that consider services or terminals sensitive to reliability and latency are being discussed. Next-generation wireless access technologies that consider improved mobile broadband communication, massive machine type communication (MTC), and ultra-reliable and low latency communication (URLLC) can be called new radio access technology (RAT) or new radio (NR). NR can also support vehicle-to-everything (V2X) communication.

[0006] Figure 1 is a diagram for comparing and explaining V2X communication based on RAT before NR and V2X communication based on NR.

[0007] In relation to V2X communication, in RATs prior to NR, methods for providing safety services based on V2X messages such as Basic Safety Message (BSM), Cooperative Awareness Message (CAM), and Decentralized Environmental Notification Message (DENM) were mainly discussed. V2X messages may include location information, dynamic information, attribute information, etc. For example, a terminal may transmit a CAM of a periodic message type and / or a DENM of an event triggered message type to another terminal.

[0008] For example, a CAM may include basic vehicle information such as dynamic vehicle status information, such as direction and speed, static vehicle data, such as dimensions, external lighting conditions, and route history. For example, a terminal may broadcast a CAM, and the latency of the CAM may be less than 100 ms. For example, in the event of an emergency, such as a vehicle breakdown or accident, a terminal may generate a DENM and transmit it to other terminals. For example, all vehicles within the transmission range of the terminal may receive the CAM and / or DENM. In this case, the DENM may have a higher priority than the CAM.

[0009] Since then, various V2X scenarios have been proposed in NR in relation to V2X communications. For example, various V2X scenarios may include vehicle platooning, advanced driving, extended sensors, and remote driving.

[0010] For example, based on vehicle platooning, vehicles can dynamically form groups and move together. For example, to perform platoon operations based on vehicle platooning, vehicles in the group can receive periodic data from the lead vehicle. For example, vehicles in the group can use this periodic data to narrow or widen the gap between vehicles.

[0011] For example, based on improved driving, vehicles can become semi-autonomous or fully automated. For example, each vehicle can adjust its trajectories or maneuvers based on data acquired from local sensors of nearby vehicles and / or nearby logical entities. Furthermore, for example, each vehicle can share driving intentions with nearby vehicles.

[0012] For example, based on extended sensors, raw data, processed data, or live video data acquired through local sensors can be exchanged between vehicles, logical entities, pedestrian terminals, and / or V2X application servers. Thus, for example, a vehicle can perceive its environment better than it can perceive using its own sensors.

[0013] For example, based on remote driving, a remote driver or V2X application can operate or control the remote vehicle for people who cannot drive or for remote vehicles located in hazardous environments. For example, in cases where the route is predictable, such as public transportation, cloud computing-based driving can be utilized to operate or control the remote vehicle. Additionally, access to a cloud-based back-end service platform, for example, can be considered for remote driving.

[0014] Meanwhile, a method to specify service requirements for various V2X scenarios, such as vehicle platooning, enhanced driving, expanded sensors, and remote driving, is being discussed in NR-based V2X communication.

[0015] The technical problem to be solved by the present invention is to provide a method for performing relay communication more accurately and efficiently.

[0016] The technical challenges are not limited to the technical challenges mentioned above, and other technical challenges not mentioned will be clearly understood by those skilled in the art to which the present invention pertains from the description below.

[0017] A method for a first relay terminal to perform multi-hop based relaying in a wireless communication system according to one aspect may include: forming a first hop connection and a second hop connection for the multi-hop based relaying; monitoring whether an RLF (Radio Link Failure) has occurred for the first hop connection or the second hop connection; and triggering a reselection procedure of a relay terminal for one of the first hop connection and the second hop connection based on the occurrence of an RLF for the one hop connection.

[0018] Alternatively, based on the fact that a new relay terminal is not discovered through the reselection procedure of the relay terminal within a preset time, the first relay terminal is characterized in that it reports RLF detection information for RLF detection of the one hop connection through the hop connection in which the RLF is not detected among the first hop connection and the second hop connection.

[0019] Alternatively, the RLF detection information is characterized in that it includes a value of a hop number corresponding to the one hop connection.

[0020] Alternatively, the RLF detection information is reported via a release message for releasing a hop connection in which the RLF is not detected, and the release message is characterized in that the detection of the RLF is set as a cause value.

[0021] Alternatively, the reselection procedure of the relay terminal is not triggered based on the fact that a hop connection in which the RLF is not detected among the first hop connection and the second hop connection is formed with the source remote terminal or the network.

[0022] Alternatively, the first relay terminal is characterized in that it reports information about the occurrence of RLF of the one-hop connection to the source remote terminal or the network.

[0023] Alternatively, the method further comprises a step of re-establishing the one-hop connection with a new relay terminal through a re-selection procedure of the relay terminal; and a step of reporting information on the re-establishment of the one-hop connection through a hop connection in which the RLF is not detected among the first hop connection and the second hop connection.

[0024] Alternatively, information on the re-establishment of the one-hop connection is characterized in that it is reported only when the total number of hops for the multi-hop based relay increases due to the re-establishment of the one-hop connection.

[0025] Alternatively, the multi-hop based relay is characterized as a U2N (User equipment to Network) relay for transmitting and receiving data between a remote terminal and a network.

[0026] Alternatively, the multi-hop based relay is characterized as a U2U (User equipment to User equipment) relay for transmitting and receiving data between a source remote terminal and a target remote terminal.

[0027] According to another aspect, a non-transitory computer-readable storage medium having recorded thereon instructions for performing the method for performing the multi-hop based relay described above may be provided.

[0028] According to another aspect, a first relay terminal may be provided that performs the method for performing the multi-hop based relay described above.

[0029] According to another aspect, a processing device may be provided for controlling a first relay terminal performing the multi-hop based relay described above.

[0030] According to one embodiment of the present invention, relay communication can be performed more accurately and efficiently in a wireless communication system.

[0031] The effects that can be obtained in various embodiments are not limited to the effects mentioned above, and other effects not mentioned will be clearly understood by those skilled in the art to which the present invention pertains from the description below.

[0032] The drawings attached to this specification are intended to provide an understanding of the present invention, illustrate various embodiments of the present invention, and together with the description of the specification serve to explain the principles of the present invention.

[0033] Figure 1 is a diagram for comparing and explaining V2X communication based on RAT before NR and V2X communication based on NR.

[0034] Figure 2 shows the structure of the LTE system.

[0035] Figure 3 shows the structure of the NR system.

[0036] Figure 4 shows the structure of a radio frame of NR.

[0037] Figure 5 shows the slot structure of an NR frame.

[0038] FIG. 6 illustrates a communication structure that can be provided in a 6G system according to one embodiment of the present disclosure.

[0039] FIG. 7 illustrates an electromagnetic spectrum according to one embodiment of the present disclosure.

[0040] Figure 8 shows a radio protocol architecture for SL communication.

[0041] Figure 9 shows a terminal performing V2X or SL communication.

[0042] Figure 10 shows resource units for V2X or SL communication.

[0043] FIG. 11 illustrates an example of a BWP according to one embodiment of the present disclosure.

[0044] FIG. 12 illustrates a procedure for a terminal to perform V2X or SL communication according to a resource allocation mode, according to one embodiment of the present disclosure.

[0045] Figure 13 is a diagram for explaining the control plane procedure of L2 U2N relay (UE-to-Network Relay).

[0046] Figure 14 is a diagram for explaining the control plane procedure of L2 U2U relay (UE-to-UE Relay).

[0047] FIG. 15 and FIG. 16 are diagrams for explaining a procedure for U2U relay selection (UE-to-UE Relay Selection) without relay discovery.

[0048] Figure 17 schematically illustrates a flat protocol stack for L2 U2U relay.

[0049] Figure 18 is a diagram for explaining how a first relay terminal performs multi-hop based relay.

[0050] Figure 19 illustrates a communication system applied to the present invention.

[0051] Figure 20 illustrates a wireless device applicable to the present invention.

[0052] Figure 21 illustrates another example of a wireless device applicable to the present invention. The wireless device may be implemented in various forms depending on the use case / service.

[0053] Figure 22 illustrates a vehicle or autonomous vehicle to which the present invention is applied.

[0054] A wireless communication system is a multiple access system that supports communication with multiple users by sharing available system resources (e.g., bandwidth, transmission power, etc.). Examples of multiple access systems include code division multiple access (CDMA), frequency division multiple access (FDMA), time division multiple access (TDMA), orthogonal frequency division multiple access (OFDMA), single carrier frequency division multiple access (SC-FDMA), and multi-carrier frequency division multiple access (MC-FDMA).

[0055] Sidelink refers to a communication method that establishes a direct link between user equipment (UE), allowing voice or data to be exchanged directly between terminals without going through a base station (BS). Sidelink is being considered as a solution to address the burden on base stations due to rapidly increasing data traffic.

[0056] V2X (vehicle-to-everything) refers to a communication technology that exchanges information with other vehicles, pedestrians, and infrastructure-based objects through wired / wireless communication. V2X can be divided into four types: V2V (vehicle-to-vehicle), V2I (vehicle-to-infrastructure), V2N (vehicle-to-network), and V2P (vehicle-to-pedestrian). V2X communication can be provided through the PC5 interface and / or Uu interface.

[0057] Meanwhile, as more and more communication devices demand greater communication capacity, the need for improved mobile broadband communication compared to existing radio access technology (RAT) is emerging. Accordingly, communication systems that consider services or terminals sensitive to reliability and latency are being discussed. Next-generation wireless access technologies that consider improved mobile broadband communication, massive MTC, and URLLC (Ultra-Reliable and Low Latency Communication) can be called new radio access technology (RAT) or new radio (NR). NR can also support V2X (vehicle-to-everything) communication.

[0058] The following technologies can be used in various wireless communication systems, such as CDMA (code division multiple access), FDMA (frequency division multiple access), TDMA (time division multiple access), OFDMA (orthogonal frequency division multiple access), and SC-FDMA (single carrier frequency division multiple access). CDMA can be implemented with wireless technologies such as UTRA (universal terrestrial radio access) or CDMA2000. TDMA can be implemented with wireless technologies such as GSM (global system for mobile communications) / GPRS (general packet radio service) / EDGE (enhanced data rates for GSM evolution). OFDMA can be implemented with wireless technologies such as IEEE (Institute of Electrical and Electronics Engineers) 802.11 (Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802-20, and E-UTRA (evolved UTRA). IEEE 802.16m is an evolution of IEEE 802.16e, providing backward compatibility with systems based on IEEE 802.16e. UTRA is part of UMTS (universal mobile telecommunications system). 3GPP (3rd generation partnership project) LTE (long term evolution) is a part of E-UMTS (evolved UMTS) that uses E-UTRA (evolved-UMTS terrestrial radio access), employing OFDMA in the downlink and SC-FDMA in the uplink.LTE-A (advanced) is an evolution of 3GPP LTE.

[0059] 5G NR, the successor to LTE-A, is a new clean-slate mobile communications system featuring high performance, low latency, and high availability. 5G NR can utilize all available spectrum resources, from low-frequency bands below 1 GHz, mid-frequency bands between 1 GHz and 10 GHz, and high-frequency (millimeter wave) bands above 24 GHz.

[0060] For clarity, the description will focus on LTE-A or 5G NR, but the technical ideas of the embodiment(s) are not limited thereto.

[0061] Figure 2 illustrates the architecture of an applicable LTE system. This may be referred to as an Evolved-UMTS Terrestrial Radio Access Network (E-UTRAN) or a Long Term Evolution (LTE) / LTE-A system.

[0062] Referring to FIG. 2, the E-UTRAN includes a base station (20; BS) that provides a control plane and a user plane to a terminal (10). The terminal (10) may be fixed or mobile, and may be referred to by other terms such as a mobile station (MS), a user terminal (UT), a subscriber station (SS), a mobile terminal (MT), a wireless device, etc. The base station (20) refers to a fixed station that communicates with the terminal (10), and may be referred to by other terms such as an evolved-NodeB (eNB), a base transceiver system (BTS), an access point, etc.

[0063] Base stations (20) can be connected to each other via the X2 interface. The base station (20) is connected to an EPC (Evolved Packet Core, 30) via the S1 interface, more specifically, to an MME (Mobility Management Entity) via the S1-MME, and to an S-GW (Serving Gateway) via the S1-U.

[0064] The EPC (30) consists of an MME, an S-GW, and a P-GW (Packet Data Network-Gateway). The MME holds information about terminal access and capabilities, and this information is primarily used for terminal mobility management. The S-GW is a gateway with the E-UTRAN as its endpoint, and the P-GW is a gateway with the PDN as its endpoint.

[0065] The layers of the radio interface protocol between the terminal and the network can be divided into L1 (Layer 1), L2 (Layer 2), and L3 (Layer 3) based on the three lower layers of the Open System Interconnection (OSI) standard model, which is widely known in communication systems. Among these, the physical layer belonging to Layer 1 provides an information transfer service using a physical channel, and the RRC (Radio Resource Control) layer located in Layer 3 controls radio resources between the terminal and the network. To this end, the RRC layer exchanges RRC messages between the terminal and the base station.

[0066] Figure 3 shows the structure of the NR system.

[0067] Referring to FIG. 3, the NG-RAN may include a gNB and / or an eNB that provides user plane and control plane protocol termination to the UE. FIG. 7 illustrates a case where only a gNB is included. The gNB and eNB are connected to each other via an Xn interface. The gNB and eNB are connected to the 5th generation core network (5G Core Network: 5GC) via the NG interface. More specifically, the gNB is connected to the access and mobility management function (AMF) via the NG-C interface, and the gNB is connected to the user plane function (UPF) via the NG-U interface.

[0068] Figure 4 shows the structure of a radio frame of NR.

[0069] Referring to FIG. 4, radio frames can be used for uplink and downlink transmission in NR. A radio frame has a length of 10 ms and can be defined as two 5 ms half-frames (Half-Frames, HF). A half-frame can include five 1 ms sub-frames (Subframes, SF). A sub-frame can be divided into one or more slots, and the number of slots within a sub-frame can be determined by the Subcarrier Spacing (SCS). Each slot can include 12 or 14 OFDM (A) symbols depending on the cyclic prefix (CP).

[0070] When normal CP is used, each slot can contain 14 symbols. When extended CP is used, each slot can contain 12 symbols. Here, the symbols can include OFDM symbols (or CP-OFDM symbols), SC-FDMA (Single Carrier - FDMA) symbols (or DFT-s-OFDM (Discrete Fourier Transform-spread-OFDM) symbols).

[0071] Table 1 below shows the number of symbols per slot ((N)) depending on the SCS setting (u) when normal CP is used. slot symb ), number of slots per frame ((N frame,u slot ) and the number of slots per subframe ((N subframe,u slot ) is an example.

[0072] SCS (15*2 u )N slot symb N frame,u slot N subframe,u slot 15KHz (u=0)1410130KHz (u=1)1420260KHz (u=2)14404120KHz (u=3)14808240KHz (u=4)1416016

[0073] Table 2 illustrates the number of symbols per slot, the number of slots per frame, and the number of slots per subframe according to SCS when extended CP is used.

[0074] SCS (15*2 u )N slot symb N frame,u slot N subframe,u slot 60KHz (u=2)12404

[0075] In an NR system, OFDM(A) numerology (e.g., SCS, CP length, etc.) may be set differently between multiple cells that are merged into a single terminal. Accordingly, the (absolute time) interval of a time resource (e.g., subframe, slot, or TTI) (conveniently referred to as TU (Time Unit)) consisting of the same number of symbols may be set differently between the merged cells.

[0076] In NR, multiple numerologies, or SCSs, can be supported to support various 5G services. For example, a 15 kHz SCS can support wide areas in traditional cellular bands, while a 30 kHz / 60 kHz SCS can support dense urban areas, lower latency, and wider carrier bandwidth. A 60 kHz or higher SCS can support bandwidths greater than 24.25 GHz to overcome phase noise.

[0077] The NR frequency band can be defined by two types of frequency ranges. The two types of frequency ranges can be FR1 and FR2. The numerical values ​​of the frequency ranges can be changed, and for example, the two types of frequency ranges can be as shown in Table 3 below. Among the frequency ranges used in the NR system, FR1 can mean the "sub 6 GHz range", and FR2 can mean the "above 6 GHz range" and can be called millimeter wave (mmW).

[0078] Frequency Range designationCorresponding frequency rangeSubcarrier Spacing (SCS)FR1450MHz - 6000MHz15, 30, 60kHzFR224250MHz - 52600MHz60, 120, 240kHz

[0079] As described above, the numerical value of the frequency range of the NR system can be changed. For example, FR1 may include a band from 410 MHz to 7125 MHz, as shown in Table 4 below. That is, FR1 may include a frequency band above 6 GHz (or 5850, 5900, 5925 MHz, etc.). For example, the frequency band above 6 GHz (or 5850, 5900, 5925 MHz, etc.) included within FR1 may include an unlicensed band. The unlicensed band may be used for various purposes, such as for vehicular communications (e.g., autonomous driving).

[0080] Frequency Range designationCorresponding frequency rangeSubcarrier Spacing (SCS)FR1410MHz - 7125MHz15, 30, 60kHzFR224250MHz - 52600MHz60, 120, 240kHz

[0081] Figure 5 shows the slot structure of an NR frame.

[0082] Referring to Figure 5, a slot includes multiple symbols in the time domain. For example, in the case of a normal CP, one slot may include 14 symbols, but in the case of an extended CP, one slot may include 12 symbols. Alternatively, in the case of a normal CP, one slot may include 7 symbols, but in the case of an extended CP, one slot may include 6 symbols.

[0083] A carrier includes multiple subcarriers in the frequency domain. An RB (Resource Block) can be defined as multiple (e.g., 12) consecutive subcarriers in the frequency domain. A BWP (Bandwidth Part) can be defined as multiple consecutive (P)RBs ((Physical) Resource Blocks) in the frequency domain, and can correspond to one numerology (e.g., SCS, CP length, etc.). A carrier can include up to N (e.g., 5) BWPs. Data communication can be performed through activated BWPs. Each element can be referred to as a Resource Element (RE) in the resource grid, and one complex symbol can be mapped to it.

[0084] Meanwhile, the wireless interface between terminals or between terminals and a network may be composed of an L1 layer, an L2 layer, and an L3 layer. In various embodiments of the present disclosure, the L1 layer may refer to a physical layer. Furthermore, for example, the L2 layer may refer to at least one of a MAC layer, an RLC layer, a PDCP layer, and an SDAP layer. Furthermore, for example, the L3 layer may refer to an RRC layer.

[0085] FIG. 6 illustrates a communication structure that can be provided in a 6G system according to an embodiment of the present disclosure. The embodiment of FIG. 6 can be combined with various embodiments of the present disclosure.

[0086] New network characteristics in 6G may include:

[0087] - Satellite integrated network

[0088] - Connected Intelligence: Unlike previous generations of wireless communication systems, 6G is revolutionary, upgrading the wireless evolution from "connected objects" to "connected intelligence." AI can be applied at every stage of the communication process (or at every signal processing step, as described below).

[0089] - Seamless integration of wireless information and energy transfer

[0090] - Ubiquitous super 3D connectivity: Access to networks and core network functions of drones and very low Earth orbit satellites will create super 3D connectivity in 6G ubiquitous.

[0091] Some general requirements for the new network characteristics of 6G, such as the above, may be as follows:

[0092] - small cell networks

[0093] - Ultra-dense heterogeneous network

[0094] - High-capacity backhaul

[0095] - Radar technology integrated with mobile technology: High-precision localization (or location-based services) through communications is a key feature of 6G wireless communication systems. Therefore, radar systems will be integrated with 6G networks.

[0096] - Softwarization and virtualization

[0097] Below, the core implementation technologies of the 6G system are described.

[0098] - Artificial Intelligence: Incorporating AI into communications can streamline and improve real-time data transmission. AI can use numerous analytics to determine how complex target tasks should be performed. This means AI can increase efficiency and reduce processing delays. Time-consuming tasks such as handovers, network selection, and resource scheduling can be performed instantly using AI. AI can also play a crucial role in machine-to-machine (M2M), machine-to-human, and human-to-machine communications. Furthermore, AI can facilitate rapid communication in brain-computer interfaces (BCIs). AI-based communication systems can be supported by metamaterials, intelligent structures, intelligent networks, intelligent devices, intelligent cognitive radios, self-sustaining wireless networks, and machine learning.

[0099] - THz communication (terahertz communication): Data rates can be increased by increasing the bandwidth. This can be achieved by using sub-THz communication with wide bandwidths and applying advanced massive MIMO technology. THz waves, also known as sub-millimeter waves, typically refer to the frequency range between 0.1 THz and 10 THz, with corresponding wavelengths ranging from 0.03 mm to 3 mm. The 100 GHz to 300 GHz band (sub-THz band) is considered a key part of the THz spectrum for cellular communications. Adding the sub-THz band to the mmWave band will increase the capacity of 6G cellular communications. Among the defined THz bands, 300 GHz to 3 THz lies in the far infrared (IR) frequency band. While part of the optical band, the 300 GHz to 3 THz band lies at the boundary of the optical band, immediately following the RF band. Therefore, this 300 GHz to 3 THz band exhibits similarities to RF.

[0100] Figure 7 illustrates the electromagnetic spectrum according to one embodiment of the present disclosure. The embodiment of Figure 7 can be combined with various embodiments of the present disclosure. Key characteristics of THz communications include (i) a widely available bandwidth to support very high data rates, and (ii) high path loss at high frequencies (highly directional antennas are essential). The narrow beamwidth generated by the highly directional antenna reduces interference. The small wavelength of THz signals allows for a much larger number of antenna elements to be integrated into devices and base stations operating in this band. This enables the use of advanced adaptive array techniques to overcome range limitations.

[0101] - Large-scale MIMO technology

[0102] - Hologram beamforming (HBF)

[0103] - Optical wireless technology

[0104] - Free-space optical transmission backhaul network (FSO backhaul network)

[0105] - Quantum communication

[0106] - Cell-free communication

[0107] - Integration of wireless information and power transmission

[0108] - Integration of wireless communication and sensing

[0109] - Integrated access and backhaul network

[0110] - Big data analysis

[0111] - Reconfigurable intelligent surface

[0112] - metaverse

[0113] - Blockchain

[0114] Unmanned aerial vehicles (UAVs): UAVs, or drones, will be a key element in 6G wireless communications. In most cases, high-speed data wireless connectivity can be provided using UAV technology. Base stations (BSs) can be installed on UAVs to provide cellular connectivity. UAVs may offer specific capabilities not found in fixed BS infrastructure, such as easy deployment, robust line-of-sight links, and controlled mobility. During emergencies such as natural disasters, deploying terrestrial communications infrastructure is not economically feasible and sometimes cannot provide services in volatile environments. UAVs can easily handle these situations. UAVs will become a new paradigm in wireless communications. This technology facilitates three fundamental requirements for wireless networks: enhanced mobile broadband (eMBB), URLLC, and mMTC. UAVs can also support various purposes, such as enhancing network connectivity, fire detection, disaster emergency services, security and surveillance, pollution monitoring, parking monitoring, and accident monitoring. Therefore, UAV technology is recognized as one of the most important technologies for 6G communications.

[0115] - Autonomous driving (self-driving): V2X (vehicle to everything), a key element in building autonomous driving infrastructure, can be a technology that allows cars to communicate and share with various elements on the road for autonomous driving, such as vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) wireless communication. Fast transmission speeds and low-latency technologies are essential to maximize autonomous driving performance and ensure high safety. Furthermore, in the future, autonomous driving will go beyond simply providing warnings or guidance messages to drivers and may require active intervention in vehicle operation and direct control of the vehicle in dangerous situations. To this end, the amount of information that needs to be transmitted and received may become enormous, so 6G is expected to maximize autonomous driving with faster transmission speeds and lower latency than 5G.

[0116] Figure 8 illustrates a radio protocol architecture for SL communication. Specifically, Figure 8 (a) illustrates the user plane protocol stack of NR, and Figure 8 (b) illustrates the control plane protocol stack of NR.

[0117] Below, the SL synchronization signal (Sidelink Synchronization Signal, SLSS) and synchronization information are described.

[0118] SLSS is an SL-specific sequence and may include a Primary Sidelink Synchronization Signal (PSSS) and a Secondary Sidelink Synchronization Signal (SSSS). The PSSS may be referred to as a Sidelink Primary Synchronization Signal (S-PSS), and the SSSS may be referred to as a Sidelink Secondary Synchronization Signal (S-SSS). For example, length-127 M-sequences may be used for the S-PSS, and length-127 Gold sequences may be used for the S-SSS. For example, a terminal may detect an initial signal and acquire synchronization using the S-PSS. For example, a terminal may acquire detailed synchronization and detect a synchronization signal ID using the S-PSS and the S-SSS.

[0119] PSBCH (Physical Sidelink Broadcast Channel) may be a (broadcast) channel that transmits basic (system) information that a terminal must know first before transmitting or receiving an SL signal. For example, the basic information may be information related to SLSS, duplex mode (DM), TDD UL / DL (Time Division Duplex Uplink / Downlink) configuration, resource pool-related information, type of application related to SLSS, subframe offset, broadcast information, etc. For example, in NR V2X, for evaluating PSBCH performance, the payload size of PSBCH may be 56 bits, including a 24-bit CRC.

[0120] S-PSS, S-SSS and PSBCH may be included in a block format supporting periodic transmission (e.g., SL SS (Synchronization Signal) / PSBCH block, hereinafter referred to as S-SSB (Sidelink-Synchronization Signal Block)). The S-SSB may have the same numerology (i.e., SCS and CP length) as the PSCCH (Physical Sidelink Control Channel) / PSSCH (Physical Sidelink Shared Channel) in the carrier, and the transmission bandwidth may be within a (pre-)configured SL BWP (Sidelink BWP). For example, the bandwidth of the S-SSB may be 11 RBs (Resource Blocks). For example, the PSBCH may span 11 RBs. And, the frequency location of the S-SSB may be (pre-)configured. Therefore, the terminal does not need to perform hypothesis detection in the frequency to discover the S-SSB in the carrier.

[0121] Meanwhile, in the NR SL system, multiple numerologies having different SCS and / or CP lengths may be supported. In this case, as the SCS increases, the length of the time resource for a transmitting terminal to transmit an S-SSB may become shorter. Accordingly, the coverage of the S-SSB may decrease. Therefore, in order to ensure the coverage of the S-SSB, the transmitting terminal may transmit one or more S-SSBs to a receiving terminal within one S-SSB transmission period according to the SCS. For example, the number of S-SSBs that the transmitting terminal transmits to the receiving terminal within one S-SSB transmission period may be pre-configured or configured for the transmitting terminal. For example, the S-SSB transmission period may be 160 ms. For example, an S-SSB transmission period of 160 ms may be supported for all SCSs.

[0122] For example, when the SCS is 15 kHz at FR1, the transmitting terminal can transmit one or two S-SSBs to the receiving terminal within one S-SSB transmission period. For example, when the SCS is 30 kHz at FR1, the transmitting terminal can transmit one or two S-SSBs to the receiving terminal within one S-SSB transmission period. For example, when the SCS is 60 kHz at FR1, the transmitting terminal can transmit one, two, or four S-SSBs to the receiving terminal within one S-SSB transmission period.

[0123] For example, when the SCS is 60 kHz at FR2, the transmitting terminal can transmit 1, 2, 4, 8, 16, or 32 S-SSBs to the receiving terminal within one S-SSB transmission period. For example, when the SCS is 120 kHz at FR2, the transmitting terminal can transmit 1, 2, 4, 8, 16, 32, or 64 S-SSBs to the receiving terminal within one S-SSB transmission period.

[0124] Meanwhile, when the SCS is 60 kHz, two types of CP may be supported. In addition, the structure of the S-SSB transmitted by the transmitting terminal to the receiving terminal may be different depending on the CP type. For example, the CP type may be Normal CP (NCP) or Extended CP (ECP). Specifically, for example, when the CP type is NCP, the number of symbols to which the PSBCH is mapped within the S-SSB transmitted by the transmitting terminal may be 9 or 8. On the other hand, for example, when the CP type is ECP, the number of symbols to which the PSBCH is mapped within the S-SSB transmitted by the transmitting terminal may be 7 or 6. For example, the PSBCH may be mapped to the first symbol within the S-SSB transmitted by the transmitting terminal. For example, the receiving terminal receiving the S-SSB may perform an Automatic Gain Control (AGC) operation in the first symbol section of the S-SSB.

[0125] Figure 9 shows a terminal performing V2X or SL communication.

[0126] Referring to FIG. 9, the term "terminal" in V2X or SL communication may primarily refer to a user's terminal. However, if a network device such as a base station transmits and receives signals according to a communication method between terminals, the base station may also be considered a type of terminal. For example, terminal 1 may be a first device (100), and terminal 2 may be a second device (200).

[0127] For example, terminal 1 can select a resource unit corresponding to a specific resource within a resource pool, which represents a set of resources. Then, terminal 1 can transmit an SL signal using the resource unit. For example, terminal 2, which is a receiving terminal, can be configured with a resource pool in which terminal 1 can transmit a signal, and can detect a signal from terminal 1 within the resource pool.

[0128] Here, if terminal 1 is within the connection range of the base station, the base station can inform terminal 1 of the resource pool. On the other hand, if terminal 1 is outside the connection range of the base station, another terminal can inform terminal 1 of the resource pool, or terminal 1 can use a pre-configured resource pool.

[0129] In general, a resource pool can be composed of multiple resource units, and each terminal can select one or multiple resource units to use for its SL signal transmission.

[0130] Figure 10 shows resource units for V2X or SL communication.

[0131] Referring to Figure 10, the entire frequency resources of the resource pool can be divided into NF units, and the entire time resources of the resource pool can be divided into NT units. Therefore, a total of NF * NT resource units can be defined within the resource pool. Figure 13 illustrates an example where the resource pool repeats with a cycle of NT subframes.

[0132] As shown in Figure 10, a single resource unit (e.g., Unit #0) may appear periodically and repeatedly. Alternatively, to achieve diversity effects in the time or frequency dimensions, the index of the physical resource unit to which a single logical resource unit is mapped may change in a predetermined pattern over time. In this resource unit structure, a resource pool may refer to a set of resource units that a terminal wishing to transmit an SL signal can use for transmission.

[0133] Resource pools can be subdivided into several categories. For example, based on the content of the SL signal transmitted from each resource pool, resource pools can be categorized as follows:

[0134] (1) Scheduling Assignment (SA) may be a signal that includes information such as the location of resources used by a transmitting terminal for transmission of an SL data channel, MCS (Modulation and Coding Scheme) or MIMO (Multiple Input Multiple Output) transmission method required for demodulation of other data channels, and TA (Timing Advance). SA may also be transmitted multiplexed with SL data on the same resource unit, in which case the SA resource pool may mean a resource pool in which SA is multiplexed with SL data and transmitted. SA may also be called an SL control channel.

[0135] (2) The SL data channel (Physical Sidelink Shared Channel, PSSCH) may be a resource pool used by a transmitting terminal to transmit user data. If SA is multiplexed and transmitted together with SL data on the same resource unit, only the SL data channel excluding SA information may be transmitted from the resource pool for the SL data channel. In other words, the REs (Resource Elements) that were used to transmit SA information on individual resource units within the SA resource pool may still be used to transmit SL data in the resource pool of the SL data channel. For example, the transmitting terminal may transmit the PSSCH by mapping it to consecutive PRBs.

[0136] (3) A discovery channel may be a resource pool for transmitting terminals to transmit information such as their IDs. Through this, transmitting terminals can enable neighboring terminals to discover them.

[0137] Even if the content of the SL signal described above is the same, different resource pools may be used depending on the transmission and reception properties of the SL signal. For example, even if it is the same SL data channel or discovery message, it may be again divided into different resource pools depending on the transmission timing determination method of the SL signal (for example, whether it is transmitted at the time of reception of a synchronization reference signal or whether it is transmitted by applying a certain timing advance at the time of reception), the resource allocation method (for example, whether the base station designates transmission resources for individual signals to individual transmitting terminals or whether individual transmitting terminals independently select individual signal transmission resources within the resource pool), the signal format (for example, the number of symbols each SL signal occupies in one subframe or the number of subframes used for transmission of one SL signal), the signal strength from the base station, the transmission power strength of the SL terminal, etc.

[0138] FIG. 11 illustrates an example of a BWP according to an embodiment of the present disclosure. The embodiment of FIG. 11 can be combined with various embodiments of the present disclosure. In the embodiment of FIG. 11, it is assumed that there are three BWPs.

[0139] Referring to Figure 11, a common resource block (CRB) may be a carrier resource block numbered from one end of a carrier band to the other. Furthermore, a PRB may be a numbered resource block within each BWP. Point A may indicate a common reference point for the resource block grid.

[0140] The BWP can be set by Point A, an offset from Point A (NstartBWP), and a bandwidth (NsizeBWP). For example, Point A can be an outer reference point of a PRB of a carrier where subcarrier 0 of all numerologies (e.g., all numerologies supported by the network on that carrier) are aligned. For example, the offset can be the PRB spacing between the lowest subcarrier in a given numerology and Point A. For example, the bandwidth can be the number of PRBs in a given numerology.

[0141] SLSS (Sidelink Synchronization Signal) is a SL (sidelink) specific sequence and may include PSSS (Primary Sidelink Synchronization Signal) and SSSS (Secondary Sidelink Synchronization Signal). The PSSS may be referred to as S-PSS (Sidelink Primary Synchronization Signal) and the SSSS may be referred to as S-SSS (Sidelink Secondary Synchronization Signal). For example, length-127 M-sequences may be used for S-PSS and length-127 Gold sequences may be used for S-SSS. For example, a terminal may detect an initial signal (signal detection) and obtain synchronization using S-PSS. For example, the terminal can obtain detailed synchronization using S-PSS and S-SSS and detect a synchronization signal ID.

[0142] PSBCH (Physical Sidelink Broadcast Channel) may be a (broadcast) channel that transmits basic (system) information that a terminal must know first before transmitting or receiving an SL signal. For example, the basic information may be information related to SLSS, duplex mode (DM), TDD UL / DL (Time Division Duplex Uplink / Downlink) configuration, resource pool-related information, type of application related to SLSS, subframe offset, broadcast information, etc. For example, in order to evaluate PSBCH performance, in NR V2X, the payload size of PSBCH may be 56 bits, including a 24-bit CRC (Cyclic Redundancy Check).

[0143] S-PSS, S-SSS and PSBCH may be included in a block format supporting periodic transmission (e.g., SL SS (Synchronization Signal) / PSBCH block, hereinafter referred to as S-SSB (Sidelink-Synchronization Signal Block)). The S-SSB may have the same numerology (i.e., SCS and CP length) as the PSCCH (Physical Sidelink Control Channel) / PSSCH (Physical Sidelink Shared Channel) in the carrier, and the transmission bandwidth may be within a (pre-)configured SL BWP (Sidelink BWP). For example, the bandwidth of the S-SSB may be 11 RBs (Resource Blocks). For example, the PSBCH may span 11 RBs. And, the frequency location of the S-SSB may be (pre-)configured. Therefore, the terminal does not need to perform hypothesis detection in the frequency to discover the S-SSB in the carrier.

[0144] FIG. 12 illustrates a procedure for a terminal to perform V2X or SL communication according to a resource allocation mode, according to an embodiment of the present disclosure. The embodiment of FIG. 12 may be combined with various embodiments of the present disclosure.

[0145] Referring to (a) of FIG. 12, in resource allocation mode 1, the base station may schedule SL resources to be used by the terminal for SL transmission. For example, in step S1200, the base station may transmit information related to SL resources and / or information related to UL resources to the first terminal. For example, the UL resources may include PUCCH resources and / or PUSCH resources. For example, the UL resources may be resources for reporting SL HARQ feedback to the base station.

[0146] For example, a first terminal may receive information related to a dynamic grant (DG) resource and / or information related to a configured grant (CG) resource from a base station. For example, a CG resource may include a CG type 1 resource or a CG type 2 resource. In this specification, a DG resource may be a resource that a base station configures / allocates to the first terminal via downlink control information (DCI). In this specification, a CG resource may be a (periodic) resource that a base station configures / allocates to the first terminal via DCI and / or an RRC message. For example, in the case of a CG type 1 resource, the base station may transmit an RRC message including information related to the CG resource to the first terminal. For example, in the case of a CG type 2 resource, the base station may transmit an RRC message including information related to the CG resource to the first terminal, and the base station may transmit a DCI related to activation or release of the CG resource to the first terminal.

[0147] In step S1510, the first terminal may transmit a PSCCH (e.g., Sidelink Control Information (SCI) or 1st-stage SCI) to the second terminal based on the resource scheduling. In step S1220, the first terminal may transmit a PSSCH (e.g., 2nd-stage SCI, MAC PDU, data, etc.) related to the PSCCH to the second terminal. In step S1230, the first terminal may receive a PSFCH related to the PSCCH / PSSCH from the second terminal. For example, HARQ feedback information (e.g., NACK information or ACK information) may be received from the second terminal via the PSFCH. In step S1240, the first terminal may transmit / report HARQ feedback information to the base station via a PUCCH or a PUSCH. For example, the HARQ feedback information reported to the base station may be information generated by the first terminal based on the HARQ feedback information received from the second terminal. For example, the HARQ feedback information reported to the base station may be information generated by the first terminal based on a rule set in advance. For example, the DCI may be DCI for scheduling SL.

[0148] Referring to (b) of FIG. 12, in resource allocation mode 2, a terminal can determine an SL transmission resource within the SL resources set by the base station / network or within the preset SL resources. For example, the set SL resources or the preset SL resources may be a resource pool. For example, the terminal can autonomously select or schedule resources for SL transmission. For example, the terminal can perform SL communication by selecting a resource by itself within the set resource pool. For example, the terminal can select a resource by itself within a selection window by performing sensing and resource (re)selection procedures. For example, the sensing can be performed on a subchannel basis. For example, in step S1210, a first terminal that has selected a resource by itself within the resource pool can transmit a PSCCH (e.g., Sidelink Control Information (SCI) or 1st-stage SCI) to a second terminal using the resource. In step S1220, the first terminal may transmit a PSSCH (e.g., 2nd-stage SCI, MAC PDU, data, etc.) related to the PSCCH to the second terminal. In step S1230, the first terminal may receive a PSFCH related to the PSCCH / PSSCH from the second terminal.

[0149] Referring to (a) or (b) of FIG. 12, for example, a first terminal may transmit an SCI to a second terminal on a PSCCH. Or, for example, the first terminal may transmit two consecutive SCIs (e.g., 2-stage SCIs) to the second terminal on the PSCCH and / or the PSSCH. In this case, the second terminal may decode the two consecutive SCIs (e.g., 2-stage SCIs) to receive the PSSCH from the first terminal. In this specification, an SCI transmitted on a PSCCH may be referred to as a 1st SCI, a 1st SCI, a 1st-stage SCI, or a 1st-stage SCI format, and an SCI transmitted on a PSSCH may be referred to as a 2nd SCI, a 2nd SCI, a 2nd-stage SCI, or a 2nd-stage SCI format.

[0150] Referring to (a) or (b) of FIG. 12, in step S1530, the first terminal may receive a PSFCH. For example, the first terminal and the second terminal may determine PSFCH resources, and the second terminal may use the PSFCH resources to transmit HARQ feedback to the first terminal.

[0151] Referring to (a) of FIG. 12, in step S1540, the first terminal may transmit SL HARQ feedback to the base station via PUCCH and / or PUSCH.

[0152] Meanwhile, the aforementioned sidelink can be defined as terminal-to-terminal communication or direct terminal-to-terminal communication. In this case, the PSCCH can be defined as a physical control channel for direct terminal-to-terminal communication, the PSSCH as a physical data channel or physical shared channel for direct terminal-to-terminal communication, and the PSFCH as a physical feedback transmission channel for direct terminal-to-terminal communication.

[0153] Figure 13 is a diagram for explaining the control plane procedure of L2 U2N relay (UE-to-Network Relay).

[0154] The PC5-RRC aspect PC5 unicast link establishment procedure of Rel-16 NR V2X can be reused to establish a secure unicast link for L2 U2N relay (layer 2 UE-to-Network relaying) between the remote UE and the relay UE before the remote UE establishes a Uu RRC connection with the network via the relay UE.

[0155] For both in-coverage and out-of-coverage scenarios, when a remote UE initiates the first RRC message to establish a connection with a gNB, the PC5 L2 configuration for transmissions between the remote UE and the U2N relay UE can be based on the RLC / MAC configuration defined in the standard. The establishment of Uu SRB1 / SRB2 and DRB of the remote UE follows the legacy Uu configuration procedure for the L2 U2N relay.

[0156] The given scenario (TS 38.300) describes the control plane procedures of L2 U2N relay as shown in Table 5 below.

[0157] The L2 U2N Remote UE needs to establish its own PDU sessions / DRBs with the network before user plane data transmission.The NR sidelink PC5 unicast link establishment procedures can be used to setup a secure unicast link between L2 U2N Remote UE and L2 U2N Relay UE before L2 U2N Remote UE establishes a Uu RRC connection with the network via L2 U2N Relay UE.The establishment of Uu SRB1 / SRB2 and DRB of the L2 U2N Remote UE is subject to Uu configuration procedures for L2 UE-to-Network Relay.The following high level connection establishment procedure in Figure 13 applies to a L2 U2N Relay and L2 U2N Remote UE:-S1300, S1301: The L2 U2N Remote and L2 U2N Relay UE perform discovery procedure, and establish a PC5-RRC connection using the NR sidelink PC5 unicast link establishment procedure.-S1302, S1303: The L2 U2N Remote UE sends the first RRC message (i.e.,RRCSetupRequest) for its connection establishment with gNB via the L2 U2N Relay UE, using a specified PC5 Relay RLC channel configuration.The L2 U2N Relay UE sends theSidelinkUEInformationNRmessage to request for the dedicated configurations required to support the relay operation for the L2 U2N Remote UE. If the L2 U2N Relay UE is not in RRC_CONNECTED, it needs to do its own Uu RRC connection establishment upon reception of a message on the specified PC5 Relay RLC channel. After L2 U2N Relay UE's RRC connection establishment procedure and sending theSidelinkUEInformationNRmessage, gNB configures SRB0 relaying Uu Relay RLC channel to the U2N Relay UE. The gNB responds with anRRCSetupmessage to L2 U2N Remote UE. TheRRCSetupmessage is sent to the L2 U2N Remote UE using SRB0 relaying Uu Relay RLC channel over Uu and a specified PC5 Relay RLC channel over PC5.-S1304: The gNB and L2 U2N Relay UE perform relaying channel setup procedure over Uu. According to the configuration from gNB, the L2 U2N Relay / Remote UE establishes a PC5 Relay RLC channel for relaying of SRB1 towards the L2 U2N Remote / Relay UE over PC5.-S1305: TheRRCSetupCompletemessage is sent by the L2 U2N Remote UE to the gNB via the L2 U2N Relay UE using SRB1 relaying channel over PC5 and SRB1 relaying channel configured to the L2 U2N Relay UE over Uu. Then the L2 U2N Remote UE is as in RRC_CONNECTED with the gNB.- S1306, S1307: The L2 U2N Remote UE and gNB establish security following the Uu security mode procedure and the security messages are forwarded through the L2 U2N Relay UE.- S1308, S1309 and S1310: The gNB sends anRRCReconfigurationmessage to the L2 U2N Remote UE via the L2 U2N Relay UE, to setup the end-to-end SRB2 / DRBs of the L2 U2N Remote UE. The L2 U2N Remote UE sends anRRCReconfigurationCompletemessage to the gNB via the L2 U2N Relay UE as a response. In addition, the gNB may configure additional Uu Relay RLC channels between the gNB and L2 U2N Relay UE, and PC5 Relay RLC channels between L2 U2N Relay UE and L2 U2N Remote UE for the relaying traffic.

[0158] In the above scenario, in addition to the connection setup procedure, for L2 UE-to-Network relay:

[0159] - RRC reconfiguration and RRC disconnection procedures can reuse legacy RRC procedures with message content / configuration design left in the WI phase.

[0160] - The RRC connection re-establishment and RRC connection resumption procedures can be reused as a baseline by considering the connection establishment procedure of the L2 U2N relay above to handle relay-specific parts along with the message content / structure design. The message content / structure can be defined later.

[0161] Figure 14 is a diagram for explaining the control plane procedure of L2 U2U relay (UE-to-UE Relay).

[0162] The control plane procedure of L2 U2U relay (UE-to-UE Relay) can be defined as shown in Table 6 below.

[0163] 1. The L2 U2U Remote UE, L2 U2U Relay UE, and peer L2 U2U Remote UE perform discovery procedure or integrated discovery procedure.2a. The L2 U2U Remote UE establishes / modifies a PC5-RRC connection with the selected L2 U2U Relay UE (i.e., as specified in TS 23.304

[0048] ).2b. The L2 U2U Relay UE establishes / modifies a PC5-RRC connection with the peer L2 U2U Remote UE (i.e., as specified in TS 23.304

[0048] ).3. The L2 U2U Relay UE allocates two local IDs and the two local IDs are delivered viaRRCReconfigurationSidelinkmessage to each of the L2 U2U Remote UEs: one local ID to identify the L2 U2U Remote UE, the other local ID to identify the peer L2 U2U Remote UE. When the local IDs are delivered, an L2 ID of the peer L2 U2U Remote UE is also delivered to the U2U Remote UE for making the association between the local ID and the L2 ID of the peer U2U Remote UE.4. The L2 U2U Remote UE establishes end-to-end PC5-RRC connection with the peer L2 U2U Remote UE via the L2 U2U Relay UE.For the end-to-end connection establishment, fixed indexes (i.e., 0 / 1 / 2 / 3) are defined for end-to-end SL-SRB 0 / 1 / 2 / 3 respectively, and specified PC5 Relay RLC Channel configuration is used on each hop. The sidelink UE capability is exchanged between the L2 U2U Remote UEs via PC5-RRC (e.g., SL-SRB3) message.5. The L2 U2U Remote UE sends to the L2 U2U Relay UE all the QoS profiles for the end-to-end QoS flows via PC5-RRC message.6. The L2 U2U Relay UE performs QoS split only for PDB.NOTE: It is up to L2 U2U Relay UE implementation on how to split PDB.7. The L2 U2U Relay UE sends the split QoS value (i.e., PDB) via PC5-RRC message to the L2 U2U Remote UE.8. The L2 U2U Remote UE or the serving gNB of the L2 U2U Remote UE derives the PDCP and SDAP configuration for end-to-end SL-DRB. The L2 U2U Remote UE provides the portion of the configuration related to reception to the peer L2 U2U Remote UE using end-to-endRRCReconfigurationSidelinkmessages.The end-to-end bearer IDs for SL-SRB and SL-DRB are used as input for the L2 U2U Relay ciphering and integrity protection at SL PDCP.9a. The L2 U2U Remote UE or the serving gNB of the L2 U2U Remote UE derives the first hop configuration (e.g. PC5 Relay RLC Channel configuration) for SL-DRB, The L2 U2U Remote UE provides the L2 U2U Relay UE with the configuration related to receiving on the first hop (i.e., Rx by the relay UE), using per-hopRRCReconfigurationSidelinkmessage.9b. The L2 U2U Relay UE or the serving gNB of the L2 U2U Relay UE derives the second hop configuration (e.g. PC5 Relay RLC Channel configuration) for each SL-DRB. The Relay UE provides the peer L2 U2U Remote UE with the configuration related to receiving on the second hop (i.e., RX by the peer remote UE), using per-hopRRCReconfigurationSidelinkmessage.10. The L2 U2U Remote UE and the peer L2 U2U Remote UE transmit or receive data via L2 U2U Relay UE.

[0164] Here, the PC5 connection or direct connection between the U2U remote UE and the U2U relay UE can be defined as a 1st-hop connection, and the PC5 connection or direct connection between the U2U relay UE and the peer U2U remote UE (or target remote UE) can be defined as a 2nd-hop connection.

[0165] Below, we describe a method for performing U2U relay selection without a discovery procedure.

[0166] FIG. 15 and FIG. 16 are diagrams for explaining a procedure for U2U relay selection (UE-to-UE Relay Selection) without relay discovery.

[0167] Referring to a given scenario (TR 23.752 section 6.8), when a source UE wants to communicate with a target UE, the source UE may first try to find the target UE by transmitting a Direct Communication Request or Solicitation message containing target UE information. If the source UE cannot reach the target UE directly, the source UE may try to discover a UE-to-UE relay to reach the target UE, and may also trigger the relay to discover the target UE. The source UE may integrate the discovery of the target UE and / or the discovery / selection of a U2U relay based on the following two alternatives:

[0168] - Alternative 1: U2U relay discovery / selection can be integrated into the unicast link setup procedure (see clause 6.3.3 of TS 23.287).

[0169] - Alternative 2: U2U relay discovery / selection can be integrated into the Model B direct discovery procedure.

[0170] A new field may be added to the Direct Communication Request or Solicitation message to indicate whether a relay is available for communication. This new field may be defined as Relay_indication. When a (source) UE broadcasts a Direct Communication Request or Solicitation message, the request message may include Relay_indication indicating whether a U2U relay is available. Meanwhile, for Release 17, the value of Relay_indication may be assumed to be limited to a single hop.

[0171] When the U2U relay receives the request message with the Relay_indication set, the U2U relay can decide whether to forward the request message (i.e., modify the message and broadcast it nearby). For example, the U2U relay can decide whether to forward the request message by considering the Application ID, authorization policy (e.g., Relay for a specific ProSe service), current traffic load of the Relay, and radio conditions between the Source UE and the Relay UE if there is a Relay Service Code.

[0172] Alternatively, multiple U2U relays may be used to reach the target UE (case 1), or the target UE may directly receive the request message from the source UE (case 2). In this case, the target UE may choose whether to respond to either the first or the second case. For example, the target UE may choose whether to respond to either the first or the second case based on signal strength, local policy (e.g., traffic load of the UE-UE relay), relay service code (if any), and / or operator policy (e.g., always preferring direct communication or only using some specific UE-UE relays).

[0173] Alternatively, the source UE may receive responses to the request message from multiple U2U relays, or may receive responses to the request message directly from the target UE. In this case, the source UE may select a communication path (direct path or indirect path) based on signal strength or operator policy (e.g., always preferring direct communication or using only certain UE-UE relays).

[0174] Specifically, the above-described alternative 1 can be performed as described in Table 7 and FIG. 15.

[0175] 6.8.2 Procedures6.8.2.1 UE-to-UE relay discovery and selection is integrated into the unicast link establishment procedure (Alternative 1)Fig 14 illustrates the procedure of the proposed method.0. UEs are authorized to use the service provided by the UE-to-UE relays. UE-to-UE relays are authorized to provide service of relaying traffic among UEs. The authorization and the parameter provisioning can use solutions for KI#8, e.g. Sol#36. The authorization can be done when UEs / relays are registered to the network. Security related parameters may be provisioned so that a UE and a relay can verify the authorization with each other if needed.1. UE-1 wants to establish unicast communication with UE-2 and the communication can be either through direct link with UE-2 or via a UE-to-UE relay. Then UE-1 broadcasts Direct Communication Request with relay_indication enabled. The message will be received by relay-1, relay-2. The message may also be received by UE-2 if it is in the proximity of UE-1.UE-1 includes source UE info, target UE info, Application ID, as well as Relay Service Code if there is any. If UE-1 does not want relay to be involved in the communication, then it will made relay_indication disabled.NOTE 1: The data type of relay_indication can be determined in Stage 3. Details of Direct Communication Request / Accept messages will be determined in stage 3.2. Relay-1 and relay-2 decide to participate in the procedure. They broadcast a new Direct Communication Request message in their proximity without relay_indication enabled. If a relay receives this message, it will just drop it. When a relay broadcasts the Direct Communication Request message, it includes source UE info, target UE info and Relay UE info (e.g. Relay UE ID) in the message and use Relay's L2 address as the source Layer-2 ID. The Relay maintains association between the source UE information (e.g. source UE L2 ID) and the new Direct Communication Request.3.UE-2 receives the Direct Communication Requests from relay-1 and relay-2. UE-2 may also receive Direct Communication Request message directly from the UE-1 if the UE-2 is in the communication range of UE-1.4. UE-2 chooses relay-1 and replies with Direct Communication Accept message. If UE-2 directly receives the Direct Communication Request from UE-1, it may choose to setup a direct communication link by sending the Direct Communication Accept message directly to UE-1. After receiving Direct Communication Accept, a UE-to-UE relay retrieves the source UE information stored in step 2 and sends the Direct Communication Accept message to the source UE with its Relay UE info added in the message.After step 4, UE-1 and UE-2 have respectively setup the PC5 links with the chosen UE-to-UE relay.NOTE 2: The security establishment between the UE1 and Relay-1, and between Relay-1 and UE-2 are performed before the Relay-1 and UE-2 send Direct Communication Accept message.Details of the authentication / security establishment procedure are determined by SA WG3. The security establishment procedure can be skipped if there already exists a PC5 link between the source (or target) UE and the relay which can be used for relaying the traffic.5. UE-1 receives the Direct Communication Accept message from relay-1. UE-1 chooses path according to e.g. policies (e.g. always choose direct path if it is possible), signal strength, etc. If UE-1 receives Direct Communication Accept / Response message request accept directly from UE-2, it may choose to setup a direct PC5 L2 link with UE-2 as described in clause 6.3.3 of TS 23.287 [5], then step 6 is skipped.6a. For the L3 UE-to-UE Relay case, UE-1 and UE-2 finish setting up the communication link via the chosen UE-to-UE relay. The link setup information may vary depending on the type of relay, e.g. L2 or L3 relaying. Then UE-1 and UE-2 can communicate via the relay.Regarding IP address allocation for the source / remote UE, the addresses can be either assigned by the relay or by the UE itself (e.g. link-local IP address) as defined in clause 6.3.3 of TS 23.287 [5].6b. For the Layer 2 UE-to-UE Relay case, the source and target UE can setup an end-to-end PC5 link via the relay. UE-1 sends a unicast E2E Direct Communication Request message to UE-2 via the Relay-1, and UE-2 responds with a unicast E2E Direct Communication Accept message to UE-1 via the Relay-1. Relay-1 transfers the messages based on the identity information of UE-1 / UE-2 in the Adaptation Layer.NOTE 3: How Relay-1 can transfer the messages based on the identity information of UE-1 / UE-2 in the Adaptation Layer requires cooperation with RAN2 during the normative phase.NOTE 4: In order to make a relay or path selection, the source UE can setup a timer after sending out the Direct Communication Request for collecting the corresponding response messages before making a decision.Similarly, the target UE can also setup a timer after receiving the first copy of the Direct Communication Request / message for collecting multiple copies of the message from different paths before making a decision.NOTE 5: In the first time when a UE receives a message from a UE-to-UE relay, the UE needs to verify if the relay is authorized be a UE-to-UE relay. Similarly, the UE-to-UE relay may also need to verify if the UE is authorized to use the relay service. The verification details and the how to secure the communication between two UEs through a UE-to-UE relay is to be defined by SA WG3.

[0176] 상술한 대안 2은 표 8 및 도 16에 기술된 바와 같이 수행될 수 있다.

[0177] 6.8.2.2 UE-to-UE relay discovery and selection is integrated into Model B direct discovery procedure (Alternative 2)Depicted in Fig 15 is the procedure for UE-UE Relay discovery Model B, and the discovery / selection procedure is separated from hop by hop and end-to-end link establishment.1. UE-1 broadcasts discovery solicitation message carrying UE-1 info, target UE info (UE-2), Application ID, Relay Service Code if any, the UE-1 can also indicate relay_indication enabled.2. On reception of discovery solicitation, the candidate Relay UE-R broadcasts discovery solicitation carrying UE-1 info, UE-R info, Target UE info. The Relay UE-R uses Relay's L2 address as the source Layer-2 ID.3. The target UE-2 responds the discovery message. If the UE-2 receives discovery solicitation message in step 1, then UE-2 responds discovery response in step 3b with UE-1 info, UE-2 info.If not and UE-2 receives discovery solicitation in step 2, then UE-2 responds discovery response message in step 3a with UE-1 info, UE-R info, UE-2 info.4. On reception of discovery response in step 3a, UE-R sends discovery response with UE-1 info, UE-R info, UE-2 info. If more than one candidate Relay UEs responding discovery response message, UE-1 can select one Relay UE based on e.g. implementation or link qualification.5. The source and target UE may need to setup PC5 links with the relay before communicating with each other. Step 5a can be skipped if there already exists a PC5 link between the UE-1 and UE-R which can be used for relaying. Step 5b can be skipped if there already exists a PC5 link between the UE-2 and UE-R which can be used for relaying.6a. Same as step 6a described in clause 6.8.2.1.6b.For the Layer-2 UE-to-UE Relay, the E2E unicast Direct Communication Request message is sent from UE1 to the selected Relay via the per-hop link (established in steps 5a) and the Adaptation layer info identifying the peer UE (UE3) as the destination. The UE-to-UE Relay transfers the E2E messages based on the identity information of peer UE in the Adaptation Layer. The initiator (UE1) knows the Adaptation layer info identifying the peer UE (UE3) after a discovery procedure. UE3 responds with E2E unicast Direct Communication Accept message in the same way.NOTE 1: For the Layer 2 UE-to-UE Relay case, whether step5b is performed before step 6b or triggered during step 6b will be decided at normative phase.NOTE 2: How Relay-1 can transfer the messages based on the identity information of UE-1 / UE-2 in the Adaptation Layer requires cooperation with RAN2 during the normative phase.6.8.3 Impacts on services, entities and interfacesUE impacts to support new Relay related functions.

[0178] Figure 17 schematically illustrates a flat protocol stack for L2 U2U relay.

[0179] Figure 17(a) illustrates a user plane protocol stack for an L2 U2U relay, and Figure 17(b) illustrates a control plane protocol stack for an L2 U2U relay. Table 9 below provides a description related to Figure 17 regarding the architecture and protocol stack of a Layer-2 relay.

[0180] 5.5 Layer-2 Relay5.5.1 Architecture and Protocol StackFor L2 UE-to-UE Relay architecture, the protocol stacks are similar to L2 UE-to-Network Relay other than the fact that the termination points are two Remote UEs. The protocol stacks for the user plane and control plane of L2 UE-to-UE Relay architecture are described in Figure 5.5.1-1 and Figure 5.5.1-2.An adaptation layer is supported over the second PC5 link (i.e. the PC5 link between Relay UE and Destination UE) for L2 UE-to-UE Relay. For L2 UE-to-UE Relay, the adaptation layer is put over RLC sublayer for both CP and UP over the second PC5 link. The sidelink SDAP / PDCP and RRC are terminated between two Remote UEs, while RLC, MAC and PHY are terminated in each PC5 link.For the first hop of L2 UE-to-UE Relay,- The N:1 mapping is supported by first hop PC5 adaptation layer between Remote UE SL Radio Bearers and first hop PC5 RLC channels for relaying.- The adaptation layer over first PC5 hop between Source Remote UE and Relay UE supports to identify traffic destined to different Destination Remote UEs.For the second hop of L2 UE-to-UE Relay,- The second hop PC5 adaptation layer can be used to support bearer mapping between the ingress RLC channels over first PC5 hop and egress RLC channels over second PC5 hop at Relay UE.- PC5 Adaptation layer supports the N:1 bearer mapping between multiple ingress PC5 RLC channels over first PC5 hop and one egress PC5 RLC channel over second PC5 hop and supports the Remote UE identification function.For L2 UE-to-UE Relay,- The identity information of Remote UE end-to-end Radio Bearer is included in the adaptation layer in first and second PC5 hop.- In addition, the identity information of Source Remote UE and / or the identity information of Destination Remote UE are candidate information to be included in the adaptation layer, which are to be decided in WI phase.

[0181] Although the above describes U2U relay and U2N relay operations based on a single hop (i.e., one relay UE), U2U relay and U2N relay operations may also be performed based on a multi-hop using multiple relay UEs rather than a single relay UE. Therefore, the following describes in detail a method for performing U2U relay and U2N relay operations based on a multi-hop using multiple relay UEs rather than a single relay UE.

[0182] Meanwhile, the multi-hop relay operation described below can be applied not only to U2U relay operation but also to U2N relay operation. For example, the proposed method described below can be applied to U2N relay operation by replacing the source relay UE or target relay UE described below with a base station (or network). For convenience of explanation, the following description focuses on U2U relay operation.

[0183] Relay (re)selection method for multi-hop relay operation

[0184] 1. In multi-hop relay operation, a source remote UE can select a relay UE. The relay UE selected by the source remote UE can then select a relay UE for the next hop. The method by which the relay UE selects the relay UE for the next hop may be as follows.

[0185] - If the RSRP (Reference Signals Received Power; e.g., SL (sidelink)-RSRP / SD (sidelink discovery)-RSRP) value between other relay UEs that the relay UE is to select is greater than or equal to a pre-configured threshold strength,

[0186] - and / or, a candidate relay UE having the smallest number of hops that can reach the target remote UE among other candidate relay UEs to be selected. In this case, the number of hops that can reach the target remote UE may be information included in a PC5-S message (e.g., discovery, discovery response, DCR / DCA, etc.) and / or a PC5-RRC message (e.g., RRCReconfigurationSidelink, RRCReconfigurationCompleteSidelink).

[0187] - and / or, among other candidate relay UEs to be selected, the candidate relay UE with the largest remaining PDB (Packet Delay Budget), etc.

[0188] 2. In a multi-hop U2U relay operation, if an RLF (Radio Link Failure) occurs for a direct connection (or hop connection) between terminals for relay operation, the relay UE may perform at least one of the following operations.

[0189] (1) Case 1

[0190] When an RLF is detected for a hop connection (or a hop connection with another relay UE) for a far-hop-based relay operation, the relay UE can report the detection of the RLF to the source remote UE. The relay UE can notify the source remote UE that an RLF has occurred in a hop (or hop connection) associated with it in the following manner.

[0191] The relay UE may generate a PC5-RRC message (e.g., a notification message) to report an RLF for a hop connection connected to it. The generated message may have an SRC (Source or Source UE) / DST (Destination or Destination UE) address of an adaptation layer set to a value that identifies the target remote UE and the source remote UE used in the existing relay operation (e.g., so that the generated message can be treated as a message that the target / source remote UE delivers to the source / target remote UE). This is because the source remote UE may not be able to clearly identify the presence of the relay UE (the source remote UE may not control all of the relay UEs that formed the multi-hop connections and may therefore not be aware of all of the relay UEs). When the relay UE reports an RLF for a hop connection to the source remote UE, the relay UE may further include in the message for reporting the RLF information indicating the hop number of the hop / hop connection in which the RLF was detected. That is, the message for reporting a multi-hop RLF may further include a value for the hop number or hop count in which the RLF occurred.

[0192] (2) Case 2

[0193] When relay UE A detects an RLF for a hop connection (or a first-hop connection) connected to itself, relay UE A may notify information about the RLF (e.g., via an RLF notification message) only to relay UE B that has formed another hop connection (or a second-hop connection). In this case, relay UE B or relay UE A may release the second-hop connection and transmit an RLF notification message including RLF detection information for the first-hop connection to relay UE C that has formed another hop connection (or a third-hop connection) connected to itself. At this time, relay UE B may release the third-hop connection with relay UE C while transmitting the RLF notification message. If relay UE B provides the RLF notification message to relay UE C, relay UE C may release the third-hop connection with relay UE B.

[0194] Such a process (e.g., transmitting sequential RLF notification messages and releasing hop connections) may continue until the source remote UE is notified of an RLF for the first-hop connection (or until a relay UE, with which the source remote UE has a first-hop connection, releases the first-hop connection due to an RLF for the first-hop connection). In this case, the RLF notification message may further include information about at which hop the RLF occurred.

[0195] Alternatively, relay UE A, which detects an RLF for a hop connection, may send a release message to relay UE B, indicating that the cause value of the release of the hop connection is RLF, while also releasing the hop connection with relay UE B, which formed another hop connection with itself. Relay UE B, which receives the release message, may send a release message indicating that the cause value of the release of the hop connection is RLF while releasing the hop connection with another relay UE (C) connected to itself. In this case, the release message may further include indication information on which hop the RLF occurred.

[0196] (3) Case 3

[0197] When a source remote UE controls / manages all hop connections and an RLF occurs in a hop connection between relay UEs, the relay UE that detects the RLF may inform the source remote UE of its ID (e.g., L2 ID (and / or) local ID) and / or the relay UE ID (e.g., L2 ID and / or local ID) that formed the hop connection (or link) where the RLF occurred.

[0198] Alternatively, a source remote UE that receives an RLF notification message and / or a release message with RLF as a cause value in case 1 and / or case 2 described above may trigger relay re-selection. Alternatively, if there are multiple other relay UEs and / or source remote UEs that have formed different hop connections with the relay UE that detected the RLF, the relay UE may transmit the RLF notification message and / or the release message with RLF as a cause value to all of the multiple other relay UEs and / or source remote UEs.

[0199] Meanwhile, the above-described proposed method can be applied by replacing the source remote UE with a target remote UE or base station, or by replacing the target remote UE with a source remote UE or base station.

[0200] 3. Triggering relay reselection based on RLF detection

[0201] Relay reselection based on RLF detection and / or reporting may also be triggered directly by the relay UE (rather than the source / target remote UE). That is, a relay UE performing multi-hop U2U relay operation may trigger relay reselection based on detection of an RLF for its established hop connection. In this case, the relay UE may perform the following relay reselection operation.

[0202] (1) Case 1

[0203] As described above, when a relay UE detects an RLF for a hop connection, the relay UE may broadcast a discovery message. At this time, the source address of the discovery message may be set to an address (i.e., an L2 address, a local / temporal address) for identifying a source remote UE (e.g., a remote UE transmitting data through the hop connection) rather than its own address. The destination address of the discovery message may be set to an address for identifying a target remote UE. Alternatively, the relay UE may transmit a discovery message for relay reselection using a discovery message (pre-stored) of a source remote UE that was used to select another relay UE that formed a hop connection in which an RLF was detected.

[0204] In a multi-hop U2U relay operation, if a relay UE forms a hop connection (or SL connection) with a new relay UE as a trigger for relay reselection, the relay UE may report the hop connection with the new relay UE to the source remote UE. Alternatively, if (or only if) the total number of hops increased by the relay UE due to the hop connection resulting from the reselection of the new relay UE compared to the previous RLF occurrence, the relay UE may need to report information about the reselection of the new relay UE to the source remote UE.

[0205] When a relay UE triggers relay reselection by detecting an RLF for a hop connection, the relay UE may start / start a newly defined timer. The relay UE may stop / suspend the timer when the connection to the target remote UE is restored / reestablished if a new relay UE is discovered. If a new relay UE is not discovered by the time the timer expires, the relay UE may report information about the detection of an RLF (or information about relay reselection failure) to the source remote UE and / or other relay UEs connected to it. The other relay UEs and / or the source remote UE, upon receiving such information, may release their own hop connection or trigger relay reselection.

[0206] Alternatively, the manner in which the relay UE triggers relay reselection in the above multi-hop relay operation may not be applicable to a relay UE that has formed a direct hop connection with the source remote UE (or target remote UE). For example, it may be more appropriate for the source remote UE (or target remote UE) to directly perform relay reselection instead of the relay UE that has formed a direct hop connection with the source remote UE (or target remote UE).

[0207] In this way, the proposed invention can quickly recover an intermediate hop connection in which an RLF has occurred by having a relay UE detect an RLF occurrence directly perform relay reselection when an RLF has occurred for a hop connection.

[0208] Meanwhile, as described above, the above-described proposal can be applied not only to multi-hop-based U2U relays but also to U2N relays. In this case, it is obvious that the above-described proposal can also be applied to the operation of multi-hop U2N relays when the source remote UE or target remote UE is replaced with a base station (gNB).

[0209] Figure 18 is a diagram for explaining how a first relay terminal performs multi-hop based relay.

[0210] Referring to FIG. 18, a first relay terminal can form or establish a first hop connection and a second hop connection for a multi-hop based relay (S181). Here, the multi-hop based relay is a relay communication that connects a first device and a second device through at least two relays, wherein the first device may be a remote terminal (or a source remote terminal) or a network, and the second device may be a remote terminal (or a target remote terminal, or a network). For example, the multi-hop based relay may be a multi-hop based U2N relay for transmitting and receiving data between a remote terminal and a network, or a multi-hop based U2U relay for transmitting and receiving data between a source remote terminal and a target remote terminal.

[0211] Specifically, the first relay terminal can form the first hop connection and the second hop connection for the multi-hop based relay through a discovery procedure. Here, the first hop connection can be a connection with the first device (PC5 connection or Uu connection) or a connection with another relay terminal (PC5 connection), and the second hop connection can be a connection with the second device (PC5 connection or Uu connection) or a connection with another relay terminal (PC5 connection). Alternatively, as described in FIG. 13 or FIG. 14, the first relay terminal can perform configuration for each hop connection and configuration for a connection (or end-to-end connection) between the first device and the second device through an RRC message (or PC5 RRC message) with the first device, the second device, and / or the other relay terminal.

[0212] Next, the first relay terminal can monitor whether a Radio Link Failure (RLF) is detected for the first-hop connection or the second-hop connection (S183). The first relay terminal can measure the signal quality (Reference Signal Received Power (RSRP) or Reference Signal Received Quality (RSRP)) for the first-hop connection and / or the second-hop connection, and determine or declare that an RLF has occurred or been detected if the signal quality is below a specific threshold for a preset threshold time.

[0213] Next, the first relay terminal may perform a procedure for reselecting a relay terminal for one of the first hop connection and the second hop connection when an RLF is detected for the one hop connection (S185). For example, when an RLF is detected for the second hop connection, the first relay terminal may perform a relay reselection procedure for selecting a new relay terminal for the second hop connection without reporting the RLF detection through the first hop connection. Meanwhile, when the relay communication is performed through one relay terminal, the relay terminal only reports information about the RLF detection to the source device (or target device) and does not directly perform the relay reselection procedure.

[0214] The relay reselection procedure for the one-hop connection in which the RLF is detected may be performed through a discovery procedure. Specifically, the first relay terminal may perform a procedure for re-establishing the one-hop connection with the new relay terminal when a new relay terminal for the one-hop connection is discovered / searched through the discovery procedure within a preset time. At this time, the first relay terminal may report information about the re-establishment of the one-hop connection with the new relay terminal to the first device or the second device. Alternatively, the first relay terminal may report information about the re-establishment of the one-hop connection to the first device or the second device only when the total number of hops for the multi-hop-based relay increases due to the re-establishment of the one-hop connection with the new relay terminal.

[0215] Alternatively, if a new relay terminal is not discovered / searched for the one-hop connection through the discovery procedure within a preset time, the first relay terminal may report RLF detection information (or information about failure of relay reselection) for the one-hop connection. For example, if an RLF for the second-hop connection is detected and a discovery procedure for the second-hop connection is performed but a new relay terminal is not discovered, the first relay terminal may report RLF detection information for the second-hop connection to the first device (and / or another relay terminal connected to the first device through the first-hop connection) via the first-hop connection. In this case, the RLF detection information may further include a value of a hop number for the second-hop connection. Alternatively, the RLF detection information may be reported via a release message defined to release the hop connection, and the release message may be configured to set a cause value of RLF detection even if an RLF is not detected for the first-hop connection. At this time, the other relay terminals that formed the first hop connection with the first relay UE may perform a release procedure for the first hop connection and / or the remaining hop connections while reporting the RLF detection information to the first device. Meanwhile, the preset time described above may be the operation time of a newly defined timer for a relay terminal reselection procedure directly performed by the relay terminal. The timer may operate when an RLF for the second hop connection is detected or the relay reselection procedure is triggered, and may expire when the preset time elapses without a new relay terminal being searched for. The timer may be stopped / suspended when a new relay terminal is searched / discovered through the relay reselection procedure.

[0216] Alternatively, if an RLF for the second hop connection is detected and the first hop connection is connected to a first device (source remote terminal or network) other than the relay terminal, the first relay terminal may not perform a relay reselection procedure for the second hop connection. In this case, the first relay terminal may report RLF detection information for the second hop connection to the first device without performing the relay reselection procedure. Here, the RLF detection information may be transmitted via a release message as described above. In this case, hop connections connected for the multi-hop relay may be sequentially released along with sequential reporting / forwarding of the release messages.

[0217] In this way, the proposed invention can quickly restore a hop connection in which an RLF is detected even in relay communication based on multiple hop connections by having the relay terminal directly perform a reselection procedure for the hop connection in which an RLF is detected. Alternatively, the proposed invention can quickly release the remaining hop connections related to the hop connection in which an RLF is detected by sequentially reporting RLF detection information through multiple hop connections and sequentially releasing the hop connections.

[0218] Examples of communication systems to which the invention applies

[0219] Although not limited thereto, the various descriptions, functions, procedures, proposals, methods and / or operational flowcharts of the present invention disclosed in this document may be applied to various fields requiring wireless communication / connection (e.g., 5G) between devices.

[0220] Hereinafter, more specific examples will be provided with reference to the drawings. In the drawings / descriptions below, the same drawing reference numerals may represent identical or corresponding hardware blocks, software blocks, or functional blocks, unless otherwise described.

[0221] Figure 19 illustrates a communication system applied to the present invention.

[0222] Referring to FIG. 19, a communication system (1) applied to the present invention includes a wireless device, a base station, and a network. Here, the wireless device refers to a device that performs communication using a wireless access technology (e.g., 5G NR (New RAT), LTE (Long Term Evolution)) and may be referred to as a communication / wireless / 5G device. Although not limited thereto, the wireless device may include a robot (100a), a vehicle (100b-1, 100b-2), an XR (eXtended Reality) device (100c), a hand-held device (100d), a home appliance (100e), an IoT (Internet of Things) device (100f), and an AI device / server (400). For example, the vehicle may include a vehicle equipped with a wireless communication function, an autonomous vehicle, a vehicle capable of performing vehicle-to-vehicle communication, etc. Here, the vehicle may include an Unmanned Aerial Vehicle (UAV) (e.g., a drone). XR devices include AR (Augmented Reality) / VR (Virtual Reality) / MR (Mixed Reality) devices, and can be implemented in the form of HMD (Head-Mounted Device), HUD (Head-Up Display) installed in a vehicle, television, smartphone, computer, wearable device, home appliance, digital signage, vehicle, robot, etc. Mobile devices can include smartphone, smart pad, wearable device (e.g., smart watch, smart glass), computer (e.g., laptop, etc.), etc. Home appliances can include TV, refrigerator, washing machine, etc. IoT devices can include sensors, smart meters, etc. For example, base stations and networks can also be implemented as wireless devices, and a specific wireless device (200a) can act as a base station / network node to other wireless devices.

[0223] Wireless devices (100a to 100f) can be connected to a network (300) via a base station (200). Artificial Intelligence (AI) technology can be applied to the wireless devices (100a to 100f), and the wireless devices (100a to 100f) can be connected to an AI server (400) via the network (300). The network (300) can be configured using a 3G network, a 4G (e.g., LTE) network, a 5G (e.g., NR) network, etc. The wireless devices (100a to 100f) can communicate with each other via the base station (200) / network (300), but can also communicate directly (e.g., sidelink communication) without going through the base station / network. For example, vehicles (100b-1, 100b-2) can communicate directly (e.g., V2V (Vehicle to Vehicle) / V2X (Vehicle to Everything) communication). In addition, IoT devices (e.g., sensors) can communicate directly with other IoT devices (e.g., sensors) or other wireless devices (100a to 100f).

[0224] Wireless communication / connection (150a, 150b, 150c) can be established between wireless devices (100a~100f) / base stations (200), and base stations (200) / base stations (200). Here, wireless communication / connection can be achieved through various wireless access technologies (e.g., 5G NR) such as uplink / downlink communication (150a), sidelink communication (150b) (or D2D communication), and communication between base stations (150c) (e.g., relay, IAB (Integrated Access Backhaul). Through wireless communication / connection (150a, 150b, 150c), wireless devices and base stations / wireless devices, and base stations and base stations can transmit / receive wireless signals to each other. For example, wireless communication / connection (150a, 150b, 150c) can transmit / receive signals through various physical channels. To this end, at least some of various configuration information setting processes for transmitting / receiving wireless signals, various signal processing processes (e.g., channel encoding / decoding, modulation / demodulation, resource mapping / demapping, etc.), and resource allocation processes can be performed based on various proposals of the present invention.

[0225] Examples of wireless devices to which the present invention is applied

[0226] Figure 20 illustrates a wireless device applicable to the present invention.

[0227] Referring to FIG. 20, the first wireless device (100) and the second wireless device (200) can transmit and receive wireless signals through various wireless access technologies (e.g., LTE, NR). Here, {the first wireless device (100), the second wireless device (200)} can correspond to {the wireless device (100x), the base station (200)} and / or {the wireless device (100x), the wireless device (100x)} of FIG. 19.

[0228] A first wireless device (100) includes one or more processors (102) and one or more memories (104), and may further include one or more transceivers (106) and / or one or more antennas (108). The processor (102) controls the memories (104) and / or the transceivers (106), and may be configured to implement the descriptions, functions, procedures, proposals, methods, and / or operational flowcharts disclosed in this document. For example, the processor (102) may process information in the memory (104) to generate first information / signal, and then transmit a wireless signal including the first information / signal via the transceiver (106). In addition, the processor (102) may receive a wireless signal including second information / signal via the transceiver (106), and then store information obtained from signal processing of the second information / signal in the memory (104). The memory (104) may be connected to the processor (102) and may store various information related to the operation of the processor (102). For example, the memory (104) may perform some or all of the processes controlled by the processor (102), or may store software code including commands for performing the descriptions, functions, procedures, proposals, methods, and / or operation flowcharts disclosed in this document. Here, the processor (102) and the memory (104) may be part of a communication modem / circuit / chipset designed to implement wireless communication technology (e.g., LTE, NR). The transceiver (106) may be connected to the processor (102) and may transmit and / or receive wireless signals via one or more antennas (108). The transceiver (106) may include a transmitter and / or a receiver. The transceiver (106) may be used interchangeably with an RF (Radio Frequency) unit. In the present invention, a wireless device may also mean a communication modem / circuit / chipset.

[0229] Specifically, the first wireless device or terminal (100) may include a processor (102) and a memory (104) connected to a transceiver (106). The memory (104) may include at least one program capable of performing operations related to the “Method for (re)selection of relays for multi-hop relay operation” and the embodiments described in FIG. 18.

[0230] The processor (102) controls the transceiver (106) to form a first hop connection and a second hop connection for the multi-hop based relay, monitors whether an RLF (Radio Link Failure) occurs for the first hop connection or the second hop connection, and triggers a reselection procedure of a relay terminal for one of the first hop connection and the second hop connection based on the occurrence of an RLF for the one hop connection.

[0231] Alternatively, a processing device including a processor (102) and a memory (104) may be configured. In this case, at least one processor; and at least one memory connected to the at least one processor and storing instructions, wherein the instructions, based on being executed by the at least one processor, cause the first relay terminal to: form a first hop connection and a second hop connection for the multi-hop-based relay, monitor whether an RLF (Radio Link Failure) occurs for the first hop connection or the second hop connection, and trigger a reselection procedure of the relay terminal for the one hop connection based on the occurrence of an RLF for one of the first hop connection and the second hop connection.

[0232] The second wireless device (200) includes one or more processors (202), one or more memories (204), and may further include one or more transceivers (206) and / or one or more antennas (208). The processor (202) controls the memories (204) and / or the transceivers (206), and may be configured to implement the descriptions, functions, procedures, proposals, methods, and / or operational flowcharts disclosed in this document. For example, the processor (202) may process information in the memory (204) to generate third information / signals, and then transmit a wireless signal including the third information / signals via the transceivers (206). Furthermore, the processor (202) may receive a wireless signal including fourth information / signals via the transceivers (206), and then store information obtained from signal processing of the fourth information / signals in the memory (204). The memory (204) may be connected to the processor (202) and may store various information related to the operation of the processor (202). For example, the memory (204) may perform some or all of the processes controlled by the processor (202), or may store software code including commands for performing the descriptions, functions, procedures, proposals, methods, and / or operation flowcharts disclosed in this document. Here, the processor (202) and the memory (204) may be part of a communication modem / circuit / chip designed to implement wireless communication technology (e.g., LTE, NR). The transceiver (206) may be connected to the processor (202) and may transmit and / or receive wireless signals via one or more antennas (208). The transceiver (206) may include a transmitter and / or a receiver. The transceiver (206) may be used interchangeably with an RF unit. In the present invention, a wireless device may also mean a communication modem / circuit / chip.

[0233] Hereinafter, the hardware elements of the wireless device (100, 200) will be described in more detail. Although not limited thereto, one or more protocol layers may be implemented by one or more processors (102, 202). For example, one or more processors (102, 202) may implement one or more layers (e.g., functional layers such as PHY, MAC, RLC, PDCP, RRC, SDAP). One or more processors (102, 202) may generate one or more Protocol Data Units (PDUs) and / or one or more Service Data Units (SDUs) according to the descriptions, functions, procedures, proposals, methods, and / or operation flowcharts disclosed in this document. One or more processors (102, 202) may generate messages, control information, data, or information according to the descriptions, functions, procedures, proposals, methods, and / or operation flowcharts disclosed in this document. One or more processors (102, 202) can generate signals (e.g., baseband signals) including PDUs, SDUs, messages, control information, data or information according to the functions, procedures, proposals and / or methods disclosed herein, and provide the signals to one or more transceivers (106, 206). One or more processors (102, 202) can receive signals (e.g., baseband signals) from one or more transceivers (106, 206) and obtain PDUs, SDUs, messages, control information, data or information according to the descriptions, functions, procedures, proposals, methods and / or operational flowcharts disclosed herein.

[0234] One or more processors (102, 202) may be referred to as a controller, a microcontroller, a microprocessor, or a microcomputer. One or more processors (102, 202) may be implemented by hardware, firmware, software, or a combination thereof. For example, one or more Application Specific Integrated Circuits (ASICs), one or more Digital Signal Processors (DSPs), one or more Digital Signal Processing Devices (DSPDs), one or more Programmable Logic Devices (PLDs), or one or more Field Programmable Gate Arrays (FPGAs) may be included in one or more processors (102, 202). The descriptions, functions, procedures, proposals, methods, and / or operational flowcharts disclosed in this document may be implemented using firmware or software, and the firmware or software may be implemented to include modules, procedures, functions, etc. The descriptions, functions, procedures, suggestions, methods and / or operation flowcharts disclosed in this document may be implemented using firmware or software configured to perform one or more processors (102, 202) or stored in one or more memories (104, 204) and executed by one or more processors (102, 202). The descriptions, functions, procedures, suggestions, methods and / or operation flowcharts disclosed in this document may be implemented using firmware or software in the form of codes, instructions and / or sets of instructions.

[0235] One or more memories (104, 204) may be coupled to one or more processors (102, 202) and may store various forms of data, signals, messages, information, programs, codes, instructions, and / or commands. The one or more memories (104, 204) may be configured as ROM, RAM, EPROM, flash memory, hard drives, registers, cache memory, computer-readable storage media, and / or combinations thereof. The one or more memories (104, 204) may be located internally and / or externally to the one or more processors (102, 202). Additionally, the one or more memories (104, 204) may be coupled to the one or more processors (102, 202) via various technologies, such as wired or wireless connections.

[0236] One or more transceivers (106, 206) can transmit user data, control information, wireless signals / channels, etc., as mentioned in the methods and / or flowcharts of this document, to one or more other devices. One or more transceivers (106, 206) can receive user data, control information, wireless signals / channels, etc., as mentioned in the descriptions, functions, procedures, proposals, methods and / or flowcharts of this document, from one or more other devices. For example, one or more transceivers (106, 206) can be connected to one or more processors (102, 202) and can transmit and receive wireless signals. For example, one or more processors (102, 202) can control one or more transceivers (106, 206) to transmit user data, control information, or wireless signals to one or more other devices. Additionally, one or more processors (102, 202) may control one or more transceivers (106, 206) to receive user data, control information, or wireless signals from one or more other devices. Additionally, one or more transceivers (106, 206) may be coupled to one or more antennas (108, 208), and one or more transceivers (106, 206) may be configured to transmit and receive user data, control information, wireless signals / channels, or the like, as referred to in the descriptions, functions, procedures, proposals, methods, and / or operational flowcharts disclosed herein, via one or more antennas (108, 208). In this document, one or more antennas may be multiple physical antennas or multiple logical antennas (e.g., antenna ports). One or more transceivers (106, 206) can convert received user data, control information, wireless signals / channels, etc. from RF band signals to baseband signals in order to process the received user data, control information, wireless signals / channels, etc. using one or more processors (102, 202).One or more transceivers (106, 206) may convert user data, control information, wireless signals / channels, etc. processed by one or more processors (102, 202) from baseband signals to RF band signals. For this purpose, one or more transceivers (106, 206) may include an (analog) oscillator and / or filter.

[0237] Examples of wireless devices to which the present invention is applied

[0238] Figure 21 illustrates another example of a wireless device applicable to the present invention. The wireless device may be implemented in various forms depending on the use case / service (see Figure 19).

[0239] Referring to FIG. 21, the wireless device (100, 200) corresponds to the wireless device (100, 200) of FIG. 20 and may be composed of various elements, components, units / units, and / or modules. For example, the wireless device (100, 200) may include a communication unit (110), a control unit (120), a memory unit (130), and additional elements (140). The communication unit may include a communication circuit (112) and a transceiver(s) (114). For example, the communication circuit (112) may include one or more processors (102, 202) and / or one or more memories (104, 204) of FIG. 21. For example, the transceiver(s) (114) may include one or more transceivers (106, 206) and / or one or more antennas (108, 208) of FIG. 20. The control unit (120) is electrically connected to the communication unit (110), the memory unit (130), and the additional elements (140) and controls the overall operation of the wireless device. For example, the control unit (120) may control the electrical / mechanical operation of the wireless device based on the program / code / command / information stored in the memory unit (130). In addition, the control unit (120) may transmit information stored in the memory unit (130) to an external device (e.g., another communication device) via a wireless / wired interface through the communication unit (110), or store information received from an external device (e.g., another communication device) via a wireless / wired interface in the memory unit (130).

[0240] The additional element (140) may be configured in various ways depending on the type of the wireless device. For example, the additional element (140) may include at least one of a power unit / battery, an input / output unit (I / O unit), a driving unit, and a computing unit. Although not limited thereto, the wireless device may be implemented in the form of a robot (Fig. 19, 100a), a vehicle (Fig. 19, 100b-1, 100b-2), an XR device (Fig. 19, 100c), a portable device (Fig. 19, 100d), a home appliance (Fig. 19, 100e), an IoT device (Fig. 19, 100f), a digital broadcasting terminal, a hologram device, a public safety device, an MTC device, a medical device, a fintech device (or a financial device), a security device, a climate / environmental device, an AI server / device (Fig. 19, 400), a base station (Fig. 19, 200), a network node, etc. Wireless devices may be mobile or stationary depending on the use / service.

[0241] In FIG. 21, various elements, components, units / parts, and / or modules within the wireless device (100, 200) may be entirely interconnected via a wired interface, or at least some may be wirelessly connected via a communication unit (110). For example, within the wireless device (100, 200), the control unit (120) and the communication unit (110) may be wired, and the control unit (120) and a first unit (e.g., 130, 140) may be wirelessly connected via the communication unit (110). In addition, each element, component, unit / part, and / or module within the wireless device (100, 200) may further include one or more elements. For example, the control unit (120) may be composed of a set of one or more processors. For example, the control unit (120) may be composed of a set of a communication control processor, an application processor, an electronic control unit (ECU), a graphics processing processor, a memory control processor, etc. As another example, the memory unit (130) may be composed of RAM (Random Access Memory), DRAM (Dynamic RAM), ROM (Read Only Memory), flash memory, volatile memory, non-volatile memory, and / or a combination thereof.

[0242] Examples of vehicles or autonomous vehicles to which the present invention is applied

[0243] Figure 22 illustrates a vehicle or autonomous vehicle applicable to the present invention. The vehicle or autonomous vehicle may be implemented as a mobile robot, car, train, manned / unmanned aerial vehicle (AV), ship, etc.

[0244] Referring to FIG. 22, a vehicle or autonomous vehicle (100) may include an antenna unit (108), a communication unit (110), a control unit (120), a driving unit (140a), a power supply unit (140b), a sensor unit (140c), and an autonomous driving unit (140d). The antenna unit (108) may be configured as a part of the communication unit (110). Blocks 110 / 130 / 140a to 140d correspond to blocks 110 / 130 / 140 of FIG. 21, respectively.

[0245] The communication unit (110) can transmit and receive signals (e.g., data, control signals, etc.) with external devices such as other vehicles, base stations (e.g., base stations, road side units, etc.), and servers. The control unit (120) can control elements of the vehicle or autonomous vehicle (100) to perform various operations. The control unit (120) can include an ECU (Electronic Control Unit). The drive unit (140a) can drive the vehicle or autonomous vehicle (100) on the ground. The drive unit (140a) can include an engine, a motor, a power train, wheels, brakes, a steering device, etc. The power supply unit (140b) supplies power to the vehicle or autonomous vehicle (100) and can include a wired / wireless charging circuit, a battery, etc. The sensor unit (140c) can obtain vehicle status, surrounding environment information, user information, etc. The sensor unit (140c) may include an IMU (inertial measurement unit) sensor, a collision sensor, a wheel sensor, a speed sensor, an incline sensor, a weight detection sensor, a heading sensor, a position module, a vehicle forward / backward sensor, a battery sensor, a fuel sensor, a tire sensor, a steering sensor, a temperature sensor, a humidity sensor, an ultrasonic sensor, an illuminance sensor, a pedal position sensor, etc. The autonomous driving unit (140d) may implement a technology for maintaining a driving lane, a technology for automatically controlling speed such as adaptive cruise control, a technology for automatically driving along a set path, a technology for automatically setting a path and driving when a destination is set, etc.

[0246] For example, the communication unit (110) can receive map data, traffic information data, etc. from an external server. The autonomous driving unit (140d) can generate an autonomous driving route and driving plan based on the acquired data. The control unit (120) can control the drive unit (140a) so that the vehicle or autonomous vehicle (100) moves along the autonomous driving route according to the driving plan (e.g., speed / direction control). During autonomous driving, the communication unit (110) can irregularly / periodically acquire the latest traffic information data from an external server and can acquire surrounding traffic information data from surrounding vehicles. In addition, during autonomous driving, the sensor unit (140c) can acquire vehicle status and surrounding environment information. The autonomous driving unit (140d) can update the autonomous driving route and driving plan based on newly acquired data / information. The communication unit (110) can transmit information regarding the vehicle location, autonomous driving route, driving plan, etc. to the external server. External servers can predict traffic information data in advance using AI technology or other technologies based on information collected from vehicles or autonomous vehicles, and provide the predicted traffic information data to the vehicles or autonomous vehicles.

[0247] Here, the wireless communication technology implemented in the wireless device (XXX, YYY) of the present specification may include not only LTE, NR, and 6G, but also Narrowband Internet of Things for low-power communication. At this time, for example, NB-IoT technology may be an example of LPWAN (Low Power Wide Area Network) technology, and may be implemented with standards such as LTE Cat NB1 and / or LTE Cat NB2, and is not limited to the above-described names. Additionally or alternatively, the wireless communication technology implemented in the wireless device (XXX, YYY) of the present specification may perform communication based on LTE-M technology. At this time, for example, LTE-M technology may be an example of LPWAN technology, and may be called by various names such as eMTC (enhanced Machine Type Communication). For example, LTE-M technology can be implemented by at least one of various standards such as 1) LTE CAT 0, 2) LTE Cat M1, 3) LTE Cat M2, 4) LTE non-BL (non-Bandwidth Limited), 5) LTE-MTC, 6) LTE Machine Type Communication, and / or 7) LTE M, and is not limited to the above-described names. Additionally or alternatively, the wireless communication technology implemented in the wireless device (XXX, YYY) of the present specification can include at least one of ZigBee, Bluetooth, and Low Power Wide Area Network (LPWAN) considering low-power communication, and is not limited to the above-described names. For example, ZigBee technology can create PAN (personal area networks) related to small / low-power digital communication based on various standards such as IEEE 802.15.4, and can be called by various names.

[0248] The embodiments described above are combinations of components and features of the present invention in a predetermined form. Each component or feature should be considered optional unless explicitly stated otherwise. Each component or feature may be implemented without being combined with other components or features. Furthermore, it is also possible to form an embodiment of the present invention by combining some components and / or features. The order of operations described in the embodiments of the present invention may be changed. Some components or features of one embodiment may be included in another embodiment or may be replaced with corresponding components or features of another embodiment. It is self-evident that claims that do not have an explicit citation relationship in the patent claims may be combined to form an embodiment or may be incorporated as a new claim through a post-application amendment.

[0249] In this document, embodiments of the present invention have been described primarily focusing on the signal transmission and reception relationship between a terminal and a base station. This transmission and reception relationship is equally / similarly extended to signal transmission and reception between a terminal and a relay or a base station and a relay. Certain operations described as being performed by a base station in this document may, in some cases, be performed by its upper node. That is, it is obvious that various operations performed for communication with a terminal in a network composed of multiple network nodes including a base station may be performed by the base station or other network nodes other than the base station. The base station may be replaced by terms such as fixed station, Node B, eNode B (eNB), and access point. In addition, the terminal may be replaced by terms such as UE (User Equipment), MS (Mobile Station), MSS (Mobile Subscriber Station).

[0250] Embodiments of the present invention may be implemented by various means, for example, hardware, firmware, software, or a combination thereof. In the case of hardware implementation, an embodiment of the present invention may be implemented by one or more application specific integrated circuits (ASICs), digital signal processors (DSPs), digital signal processing devices (DSPDs), programmable logic devices (PLDs), field programmable gate arrays (FPGAs), processors, controllers, microcontrollers, microprocessors, etc.

[0251] When implemented via firmware or software, an embodiment of the present invention may be implemented in the form of modules, procedures, functions, etc. that perform the functions or operations described above. The software code may be stored in a memory unit and executed by a processor. The memory unit may be located within or outside the processor and may exchange data with the processor via various known means.

[0252] It will be apparent to those skilled in the art that the present invention can be embodied in other specific forms without departing from the scope of the invention. Therefore, the above detailed description should not be construed as limiting in any respect, but rather as illustrative. The scope of the present invention should be determined by a reasonable interpretation of the appended claims, and all modifications within the scope of equivalents of the present invention are intended to be included within the scope of the present invention.

[0253] The embodiments of the present invention as described above can be applied to various mobile communication systems.

Claims

1. In a method for a first relay terminal to perform multi-hop based relaying in a wireless communication system, A step of forming a first hop connection and a second hop connection for the multi-hop based relay; A step of monitoring whether RLF (Radio Link Failure) occurs for the first hop connection or the second hop connection; and A method comprising the step of triggering a reselection procedure of a relay terminal for one of the first hop connection and the second hop connection based on the occurrence of an RLF for the one hop connection.

2. In paragraph 1, A method characterized in that, based on the fact that a new relay terminal is not discovered through a reselection procedure of the relay terminal within a preset time, the first relay terminal reports RLF detection information for RLF detection of the one hop connection through a hop connection in which the RLF is not detected among the first hop connection and the second hop connection.

3. In paragraph 2, A method, characterized in that the RLF detection information includes a value of a hop number corresponding to the one hop connection.

4. In paragraph 2, The above RLF detection information is reported through a release message to release the hop connection where the RLF is not detected, A method characterized in that the above release message is set to a cause value for detection of the RLF.

5. In paragraph 1, A method characterized in that the reselection procedure of the relay terminal is not triggered based on the fact that a hop connection in which the RLF is not detected among the first hop connection and the second hop connection is formed with the source remote terminal or the network.

6. In paragraph 5, A method characterized in that the first relay terminal reports RLF detection information for RLF detection of the one-hop connection to the source remote terminal or the network.

7. In paragraph 1, A step of re-establishing the one-hop connection with a new relay terminal through a reselection procedure of the relay terminal; and A method characterized in that it further comprises a step of reporting information on the re-establishment of the one hop connection through a hop connection in which the RLF is not detected among the first hop connection and the second hop connection.

8. In paragraph 7, A method characterized in that information about the re-establishment of the one-hop connection is reported only when the total number of hops for the multi-hop based relay increases due to the re-establishment of the one-hop connection.

9. In paragraph 1, A method characterized in that the above multi-hop based relay is a U2N (User equipment to Network) relay for transmitting and receiving data between a remote terminal and a network.

10. In paragraph 1, A method characterized in that the above multi-hop based relay is a U2U (User equipment to User equipment) relay for transmitting and receiving data between a source remote terminal and a target remote terminal.

11. A computer-readable recording medium recording a program for performing the method described in paragraph 1.

12. In a first relay terminal performing multi-hop based relay in a wireless communication system, RF (Radio Frequency) transmitter and receiver; and A processor connected to the RF transceiver, A first relay terminal, wherein the processor controls the RF transceiver to form a first hop connection and a second hop connection for the multi-hop based relay, monitors whether an RLF (Radio Link Failure) occurs for the first hop connection or the second hop connection, and triggers a reselection procedure of a relay terminal for one of the first hop connection and the second hop connection based on the occurrence of an RLF for the one hop connection.

13. In paragraph 12, A first relay terminal, characterized in that, based on the fact that a new relay terminal is not discovered through a reselection procedure of the relay terminal within a preset time, the processor controls the RF transceiver to report RLF detection information for RLF detection of the one hop connection through a hop connection in which the RLF is not detected among the first hop connection and the second hop connection.

14. In paragraph 13, A first relay terminal, characterized in that the RLF detection information includes a value of a hop number corresponding to the one hop connection.

15. In a processing device for controlling a first relay terminal performing multi-hop based relay in a wireless communication system, at least one processor; and At least one memory connected to said at least one processor and storing instructions, said instructions being executed by said at least one processor, wherein said first relay terminal: A processing device that forms a first hop connection and a second hop connection for the multi-hop-based relay, monitors whether an RLF (Radio Link Failure) occurs for the first hop connection or the second hop connection, and triggers a reselection procedure of a relay terminal for one of the first hop connection and the second hop connection based on the occurrence of an RLF for the one hop connection.

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