Terminal, method, base station and communication system

Abstract

A terminal according to one aspect of the present disclosure comprising: a receiver configured to receive, from one or more candidate relay terminals, a sidelink discovery message including assistance information regarding a path to a base station; and a processor configured to select a relay terminal from the one or more candidate relay terminals based on the assistance information. According to one aspect of the present disclosure, improved end-to-end communication performance between a remote terminal and a base station can be achieved.

Description

TERMINAL, METHOD, BASE STATION AND COMMUNICATION SYSTEMCROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is based on and claims priority to U.S. Provisional Application No. 63 / 680,898, filed on August 8, 2024, the contents of which are incorporated herein by reference in their entirety.

[0002] Apparatuses and methods consistent with the present disclosure relate generally to communications, more specifically, methods, systems, and devices for selection and reselection of relay node in wireless communication systems.

[0003] In existing wireless communication systems, such as those based on Third Generation Partnership Project (3GPP), a UE-to-Network (U2N) relay technology is supported to extend network coverage (Non Patent Literature 1). In a conventional relay (re-)selection procedure, a remote UE selects a suitable relay UE based only on a signal quality metric, such as Sidelink Discovery Reference Signal Received Power (SD-RSRP), measured on the direct link between the remote UE and a candidate relay UE.

[0004] 3GPP TS 38.331 V18.2.0, “NR; Radio Resource Control (RRC); Protocol specification”

[0005] However, with the introduction of multi-hop relay scenarios, this conventional selection criteria is insufficient. Because the procedure only considers the quality of the first hop, it completely ignores the qualities and characteristics of the subsequent links from the candidate relay UE to the base station. Consequently, a remote UE may select a relay UE that has a strong link to itself but a poor onward connection to the network, which can lead to the selection of a relay UE with worse end-to-end link performance.

[0006] Thus, one object of the present disclosure is to provide a terminal, a method, a base station and a communication system that can enables improved end-to-end communication performance between a remote terminal and a base station.

[0007] A terminal according to one aspect of the present disclosure comprising: a receiver configured to receive, from one or more candidate relay terminals, a sidelink discovery message including assistance information regarding a path to a base station; and a processor configured to select a relay terminal from the one or more candidate relay terminals based on the assistance information.

[0008] According to one aspect of the present disclosure, improved end-to-end communication performance between a remote terminal and a base station can be achieved.

[0009] FIG. 1 is a schematic diagram illustrating a system for some embodiments of the present disclosure.

[0010] FIG. 2 is a schematic diagram illustrating an exemplary functional configuration of each device for some embodiments of the present disclosure.

[0011] FIG. 3 is a schematic diagram illustrating an exemplary hardware configuration of each device for some embodiments of the present disclosure.

[0012] FIG. 4 is a schematic diagram illustrating an example of single-hop UE-to-Network relay.

[0013] FIG. 5 is a schematic diagram illustrating a user plane protocol stack for L2 UE-to-Network Relay.

[0014] FIG. 6 is a schematic diagram illustrating a control plane protocol stack for L2 UE-to-Network Relay.

[0015] FIG. 7 is a sequence diagram illustrating an exemplary procedure for L2 U2N Remote UE connection establishment.

[0016] FIG. 8 is a sequence diagram illustrating an exemplary procedure for UE-to-Network Relay Discovery with Model A.

[0017] FIG. 9 is a sequence diagram illustrating an exemplary procedure for UE-to-Network Relay Discovery with Model B.

[0018] FIG. 10 is a schematic diagram illustrating an exemplary flow chart of a procedure used by a UE supporting NR sidelink U2N Relay UE operation to transmit sidelink discovery messages.

[0019] FIG. 11 is a schematic diagram illustrating an exemplary flow chart of a procedure used by a UE supporting NR sidelink U2N Remote UE operation to transmit sidelink discovery messages.

[0020] FIG. 12 is a schematic diagram illustrating an exemplary flow chart of a procedure of (re-)selection of NR sidelink UE-to-Network Relay UE performed by Remote UE.

[0021] FIG. 13 is a schematic diagram illustrating an example of single-hop UE-to-UE relay.

[0022] FIG. 14 is a schematic diagram illustrating a user plane protocol stack for L2 UE-to-UE Relay.

[0023] FIG. 15 is a schematic diagram illustrating a control plane protocol stack for L2 UE-to-UE Relay.

[0024] FIG. 16 is a sequence diagram illustrating an exemplary procedure for L2 U2U Remote UE connection establishment.

[0025] FIG. 17 is a sequence diagram illustrating an exemplary procedure for UE-to-UE Relay Discovery with Model A.

[0026] FIG. 18 is a sequence diagram illustrating an exemplary procedure for UE-to-UE Relay Discovery with Model B.

[0027] FIG. 19 is a schematic diagram illustrating an exemplary flow chart of a procedure used by a UE supporting NR sidelink U2U Relay UE operation to determine whether a NR sidelink UE is in proximity to NR sidelink U2U Relay UE in Model A Discovery messages.

[0028] FIG. 20 is a schematic diagram illustrating an exemplary flow chart of a procedure used by a UE supporting NR sidelink U2U Relay UE operation to transmit sidelink Model B Discovery messages.

[0029] FIG. 21 is a schematic diagram illustrating an exemplary flow chart of a procedure used by a UE supporting NR sidelink U2U Remote UE operation to transmit NR sidelink Model B discovery messages.

[0030] FIG. 22 is a schematic diagram illustrating an exemplary flow chart of a procedure used by a UE supporting NR sidelink U2U Remote UE operation to transmit NR sidelink Model B Discovery Response messages.

[0031] FIG. 23 is a schematic diagram illustrating an exemplary flow chart of a procedure of (re-)selection of U2U Relay UE by Remote UE.

[0032] FIG. 24 is a schematic diagram illustrating an example of multi-hop UE-to-Network relay.

[0033] FIG. 25 is a schematic diagram illustrating an example of limitation of Rel-17 UE-to-Network (re-)selection procedure of U2N Relay UE by Remote UE.

[0034] FIG. 26 is a schematic diagram illustrating an key idea of proposed (re-)selection of U2N Relay UE by Remote UE.

[0035] FIG. 27 is a schematic diagram illustrating an exemplary flow chart of a proposed procedure for U2N Relay UE.

[0036] FIG. 28 is a schematic diagram illustrating an exemplary flow chart of a proposed procedure for (re-)selection of U2N Relay UE by U2N Remote UE.

[0037] The present disclosure may introduce methods and apparatus for selection and reselection of relay node for multi-hop relay.

[0038] Reference will now be made in detail to exemplary embodiments, examples of which are illustrated in the accompanying drawings. The following description refers to the accompanying drawings in which the same numbers in different drawings represent the same or similar elements unless otherwise represented. The implementations set forth in the following description of exemplary embodiments do not represent all implementations consistent with the present disclosure. Instead, they are merely examples of systems, apparatuses, and methods consistent with aspects related to the present disclosure as recited in the appended claims.

[0039] In the present disclosure, "A / B," “A and / or B” and "at least one of A and B" may be used interchangeably. In the present disclosure, "A / B / C," “A and / or B and / or C” and "at least one of A, B and C" may be used interchangeably.

[0040] (System) FIG. 1 is a schematic diagram illustrating a system for some embodiments of the present disclosure. The system 1 may be a system implementing a communication using Long Term Evolution (LTE), 5th generation mobile communication system New Radio (5G NR) and so on the specifications of which have been drafted by Third Generation Partnership Project (3GPP). The system 1 may include one or more user equipment (UE) 10, one or more base stations (BS) 20, one or more core networks (CN) 30.

[0041] In the present disclosure, terms “system,” “radio system,” “radio communication system,” “radio interface,” and “network” are used as general terms which include one or both of terrestrial network systems and non-terrestrial network (NTN) systems such as satellite systems. In the present disclosure, these terms may be used interchangeably.

[0042] The UE 10 may be a terminal supporting at least one of communication schemes such as LTE, 5G NR, and so on. The UE 10 may be connected to at least one of plurality of BS 20. The UE 10 may take any form, including but not limited to, a vehicle, a component mounted in a vehicle, a road-side unit (RSU), a laptop computer, a wireless terminal including a mobile phone, a wireless handheld device, or wireless personal device.

[0043] In the present disclosure, a UE, a mobile station, a mobile node and a terminal may be used interchangeably.

[0044] Some of the UE 10 may communicate with another UE 10 via sidelink. The UE 10 may be at least one of the following: - UE-to-Network (U2N) Relay UE: a UE that provides functionality to support connectivity to the network for U2N Remote UE(s). - U2N Remote UE: a UE that communicates with the network via a U2N Relay UE. - UE-to-UE (U2U) Relay UE: a UE that provides functionality to support connectivity between two U2U Remote UEs. - U2U Remote UE: a UE that communicates with other UE(s) via a U2U Relay UE.

[0045] The plurality of base stations 10 may be connected each other by a wired connection (for example, optical fiber) or a wireless connection (for example, an NR communication). The base station 10 may be connected to a core network 30 through another base station 10 or directly.

[0046] In the present disclosure, a BS may be referred to as the terms such as a NodeB, an eNodeB (eNB), a gNodeB (gNB), a radio access network (RAN), a carrier, a component carrier, a sector, a cell, a cell group, a super cell, a macro cell, a small cell, a femto cell, a pico cell, and so on. In the present disclosure, a network may mean an apparatus (for example, a BS) included in the network.

[0047] In the present disclosure, a term “node” is used as a general term which includes user equipment (UE), a relay node, a vehicle mounted module, a station, a network infrastructure node such as a base station (BS), a roadside unit, a repeater, a transponder, a wireless router, a controller, an access point, a transmission point (TP), a reception point (RP), a transmission / reception point (TRP), a panel, and sub-systems thereof. In the present disclosure, these entities (apparatuses, devices) may be used interchangeably.

[0048] The core network 30 may include at least one of Evolved Packet Core (EPC), 5G Core Network (5GCN), and so on.

[0049] In the system 1, an orthogonal frequency division multiplexing (OFDM)-based wireless access scheme may be used. For example, in at least one of the downlink (DL) communication and the uplink (UL) communication, Cyclic Prefix OFDM (CP-OFDM), Discrete Fourier Transform Spread OFDM (DFT-s-OFDM), Orthogonal Frequency Division Multiple Access (OFDMA), Single Carrier Frequency Division Multiple Access (SC-FDMA), and the like may be used.

[0050] (Functional / Hardware Configuration of Device) FIG. 2 is a schematic diagram illustrating an exemplary functional configuration of each device for some embodiments of the present disclosure. For example, the UE 10 may have a control unit 110, a communication unit 120, an input / output unit 130, and a storage unit 140.

[0051] The BS 20 may have similar functional configurations. For this reason, in this exemplary functional configuration, the sign of the functional block corresponding to each device is also shown with the largest digit of the sign indicating each device (e.g., the largest digit "2" of "20" for BS 20) replaced with "1". In the following, the functional blocks relating to the UE 10 will be explained, but it is understood that the same explanation applies to other devices as well.

[0052] In this example, the functional blocks of the characteristic parts of the system are mainly shown, and each device may also have other functional blocks necessary for other processes. The configuration may also not include some of the functional blocks.

[0053] The control unit 110 implements control of the UE 10 and provides various functions. For example, the control unit 110 may control communication with other devices via the communication unit 120. The control unit 110 may also obtain information necessary for processing based on information received via the communication unit 120. The control unit 110 may be referred to as a processing unit.

[0054] The communication unit 120 communicates (transmits / receives) with other devices via wired / wireless communication. The communication unit 120 may obtain information from the received signal and output it to the control unit 110, or it may convert information input from the control unit 110 into a signal and transmit it. Communication unit 120 may be referred to as a transmitter, receiver, or transmitter / receiver.

[0055] The input / output unit 130 may include an input unit that accepts input from a person. The input unit may be connected to a predetermined device, storage medium, etc., and may accept data input. The input unit may output input results to, for example, the control unit 110.

[0056] The input / output unit 130 may also include an output unit that outputs data, content, etc. in a format that can be perceived by humans. The output unit may comprise a display unit that displays images, an audio output unit that outputs sound, and the like.

[0057] The storage unit 140 stores (holds) various information used by the management unit 10 for processing. The control unit 110 may instruct the storage unit 140 to read and write data.

[0058] The functional blocks (components) in FIG. 2 may be implemented in arbitrary combinations of at least one of hardware and software. Each functional block may be realized by one apparatus that is physically or logically coupled, or may be realized by directly or indirectly connecting two or more physically or logically separate apparatuses (for example, via wire, wireless, or the like) and using these apparatuses. The functional blocks may be implemented by combining softwares into the apparatus described above or the plurality of apparatuses described above.

[0059] FIG. 3 is a schematic diagram illustrating an exemplary hardware configuration of each device for some embodiments of the present disclosure. For example, the UE 10, the BS 20, and the other devices in the present disclosure may function as a computer that executes the processes of the radio communication method(s) in the present disclosure. Each device may have an antenna 910, a Radio Frequency (RF) circuit 920, a processor 930, a network interface 940, an input device / output device 950, a memory 960, and a storage 970.

[0060] For example, the above control unit X10 (e.g., X = 1, 2; same below) described above may be implemented by the processor 930. The communication unit X20 may be implemented by the antenna 910 / RF circuit 920 / network interface 940. The input / output unit X30 may be implemented by the input device / output device 950. The storage unit X40 may be implemented by the memory 960 / storage 970.

[0061] The hardware configuration of each device may be configured to include one or more of the elements shown in this exemplary hardware configuration, or may be configured without some of the elements. For example, the UE 10 may not have a network interface 940.

[0062] The antenna 910 converts signals into radio waves and radiates said radio waves into space. The antenna 910 also receives radio waves in space and converts said radio waves into signals. The antenna 910 may be mounted in plurality, may include a transmitting antenna and a receiving antenna, or may include a single antenna for transmitting and receiving. The antenna 910 may include a directional antenna or may include multiple antenna elements. The antenna 910 may include one or more antenna elements and may enable different input-output antenna configurations.

[0063] The RF circuit 920 performs analog processing of signals transmitted and received via antenna 910. The RF circuit 920 may include filters (e.g., high frequency filters, low pass filters), amplifiers, modulators, frequency synthesizers, analog-to-digital conversion circuit, digital-analog conversion circuit, Fast Fourier Transform (FFT) / Inverse Fast Fourier Transform (IFFT) processing circuit, etc.

[0064] The RF circuit 920 may perform amplification, filter processing, demodulation to a baseband signal, etc. on the received radio frequency band signal and output to processor 930 RF circuit 920 may perform modulation to a radio frequency band, filter processing, amplification and transmit the radio frequency band signals via the transmitter / receiver antenna 910. The RF circuit 920 may perform physical layer processing (e.g., processing of lower functions of the physical layer), and may perform beamforming processing such as analog beamforming and digital beamforming processing.

[0065] The processor 930 may control the entire device. The processor 930 may read programs (program code), software (software modules), data, and the like from the storage 970 to the memory 960 and perform various processes according to these. For example, the processor 930 may execute and control an operating system (OS) program that is loaded into the memory 960. The programs are used to allow computers to execute at least part of methods (operations) shown in embodiments of the present disclosure. For example, the control unit 110 (210) may be implemented by control programs that are stored in the memory 960 and that operate on the processor 930, and other functional blocks may be implemented likewise.

[0066] The processor 930 may be configured by a central processing unit (CPU), which may include interfaces to peripheral devices, control units, arithmetic units, registers, and the like. The processor 930 may also be a microprocessor, Digital Signal Processor (DSP), Application Specific Integrated Circuit (ASIC), Programmable Logic Device (PLD), Field Programmable Gate Array (FPGA), etc.

[0067] The processor 930 may perform digital processing of signals transmitted and received via the antenna 910 and the RF circuit 920. Said digital processing may include physical layer processing (e.g., processing of higher functions of the physical layer), processing of layers above the Medium Access Control (MAC) layer, modulation, demodulation, coding, decoding, scrambling, etc. The processor 930 also processes signals sent and received via network interface 940.

[0068] The processor 930 may include a plurality of processors or may be a single processor. The multiple processors may include a baseband processor that performs the digital processing described above and one or more processors that perform other processing (e.g., overall control).

[0069] The network interface 940 may be, for example, a network adapter, which may be wired to an external network to send and receive signals.

[0070] The RF circuit 920 / baseband processor / network interface 940 may be an integral part of the RF circuit 920 / baseband processor / network interface 940. The network interface 940 may be referred to as a network controller, network card, communication module, etc.

[0071] The input device / output device 950 may comprise an input device that accepts external input (e.g., keyboard, mouse, microphone, switches, buttons, sensors, etc.), an output device that performs external output (e.g., display, speaker, Light Emitting Diode (LED) lamp etc.), and a device (e.g., a touch panel) that integrates these devices.

[0072] The memory 960 is a computer-readable, non-transitory storage medium that stores a program to be executed by the processor 930, parameters related to said program, and various other information. The memory 960 is at least one of Read Only Memory (ROM), Erasable Programmable ROM (EPROM), Electrically EPROM (EEPROM), Random Access Memory (RAM), and flash memory. All or part of the memory 960 may be contained within processor 930. Memory 960 may be referred to as a register, cache, main memory (main storage), etc.

[0073] The storage 970 is a computer-readable, non-transitory storage medium that stores a variety of information. The storage 970 may include, for example, flexible disks, floppy (registered trademark) disks, magneto-optical disks (e.g., compact disc (Compact Disc ROM (CD-ROM), digital versatile disk, Blu-ray (registered trademark) disk), a removable disk, a hard disk drive (Hard Disc Drive (HDD)), a smart card, a flash memory device (e.g., Solid State Drive (SSD)), or at least one other. The storage 970 may be referred to as an auxiliary storage device.

[0074] The processor 930, memory 960, and other devices may be connected by a bus for communicating information. A single bus may be used within a device, or different buses may be used between devices.

[0075] The BS 20 may be separated into three elements: the Radio Unit (RU), the Distributed Unit (DU), and the Central Unit (CU). The RU implements RF processing and lower functions of the physical layer. The DU implements the upper functions of the physical layer, the functions of the MAC layer, and the functions of the Radio Link Control (RLC) layer. The CU realizes the functions of the Packet Data Convergence Protocol (PDCP) layer, the Service Data Adaptation Protocol (SDAP), and the Radio Resource Control (RRC) layer.

[0076] In this disclosure, BS 20 may include one device that realizes all the functions of RU, DU and CU, or may include multiple devices that each realize some of the functions of RU, DU and CU.

[0077] Other devices in the present disclosure may also be implemented by multiple devices that are physically located apart from each other. Conversely, a plurality of different devices in this disclosure may be implemented as a single device.

[0078] Some or all of the devices in this disclosure may also mean logical devices realized by virtual machines, containers, Docker, etc., or physical devices that operate such logical devices.

[0079] (NR sidelink single-hop UE-to-Network relay) For NR sidelink relay, UE-to-Network (U2N) relay was introduced in 3GPP Release 17 and enhanced in Release 18 for Uu network coverage extension and power efficiency improvement. In Release 17, Layer 2 (L2) and Layer 3 (L3) single-hop U2N sidelink relay (i.e., relaying via a single Relay UE) is supported. An example of single-hop U2N relay is shown in Figure 4.

[0080] <Protocol stacks for NR sidelink Layer 2 UE-to-Network Relay> 3GPP TS 38.300 describes the protocol stacks for the user plane and the control plane of the L2 U2N Relay architecture, which are illustrated in Figure 5 and 6, respectively. The Uu SDAP, PDCP and RRC are terminated between L2 U2N Remote UE and gNB, while SRAP, RLC, MAC and PHY are terminated in each hop (i.e., the link between L2 U2N Remote UE and the L2 U2N Relay UE and the link between L2 U2N Relay UE and the gNB).

[0081] <NR sidelink Layer 2 UE-to-Network Remote UE connection establishment> 3GPP TS 38.300 Clause 16.12.5.1 describes the procedure for L2 U2N Remote UE connection establishment, which is illustrated in Figure 7.

[0082] Below are excerpts from 3GPP TS 38.300 Clause 16.12.5.1 about the procedure for L2 U2N Remote UE connection establishment: 1. 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. 2. 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 the SidelinkUEInformationNR message 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 the SidelinkUEInformationNR message, gNB configures SRB0 relaying Uu Relay RLC channel to the U2N Relay UE. The gNB responds with an RRCSetup message to L2 U2N Remote UE. The RRCSetup message 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. NOTE 1: Void. 3. 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. 4. The RRCSetupComplete message 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. 5. 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. 6. The gNB sends an RRCReconfiguration message 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 an RRCReconfigurationComplete message 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.

[0083] <NR sidelink UE-to-Network Relay discovery> Regarding discovery in Step 1 of Figure 7, Release 17 / 18 U2N Relay supports two discovery models: Model A and Model B as shown in Figure 8 and Figure 9, respectively. Relay discovery with Model A is the case that U2N Relay UE announces its relay service to surrounding Remote UEs, while relay discovery with Model B is the case that Remote UE solicits relaying services from surrounding U2N Relay UEs. These discovery models can be applied to both L2 and L3 U2N Relay.

[0084] Below are excerpts from 3GPP TS 23.304 about the procedure for NR sidelink UE-to-Network Relay Discovery with Model A: 1. The 5G ProSe UE-to-Network Relay sends a UE-to-Network Relay Discovery Announcement message. The UE-to-Network Relay Discovery Announcement message contains the Type of Discovery Message, Announcer Info and RSC and is sent using the Source Layer-2 ID and Destination Layer-2 ID as described in clause 5.8.3. For 5G ProSe Layer-3 UE-to-Network Relay, the 5G ProSe Layer-3 UE-to-Network Relay shall only include a RSC in the UE-to-Network Relay Discovery Announcement when the S-NSSAI associated with that RSC belongs to the Allowed NSSAI of the UE-to-Network Relay. The 5G ProSe Remote UE (1 to 3) determines the Destination Layer-2 ID for signalling reception. The Destination Layer-2 ID is configured with the UE(s) as specified in clause 5.1.4.1. 5G ProSe Remote UE (1 to 3) monitors announcement messages with the 5G ProSe UE-to-Network RSC corresponding to the desired services. Optionally, the 5G ProSe UE-to-Network Relay may also send Relay Discovery Additional Information messages as defined in clause 6.5.1.3. The parameters contained in this message and the Source Layer-2 ID and Destination Layer-2 ID used for sending and receiving the message are described in clause 5.8.3. The 5G ProSe Remote UE selects the 5G ProSe UE-to-Network Relay based on the information received in step 1. NOTE: Access Stratum layer information used for 5G ProSe UE-to-Network Relay selection is specified in RAN specifications.

[0085] Below are excerpts from 3GPP TS 23.304 about the procedure for NR sidelink UE-to-Network Relay Discovery with Model B: 1. The 5G ProSe Remote UE sends a 5G ProSe UE-to-Network Relay Discovery Solicitation message. The 5G ProSe UE-to-Network Discovery Solicitation message contains the Type of Discovery Message, Discoverer Info, RSC and optionally Target Info and is send using the Source Layer-2 ID and Destination Layer-2 ID as described in clause 5.8.3. The 5G ProSe Remote UE discovering a 5G ProSe UE-to-Network Relay sends a solicitation message with the RSC which is associated to the desired connectivity service. The RSC is based on the Policy / Parameters specified in clause 5.1.4.1. How the 5G ProSe UE-to-Network Relays (1 to 3) determine the Destination Layer-2 ID for signalling reception is specified in clause 5.8.3. The Destination Layer-2 ID is configured with the UE(s) as specified in clause 5.1.4.1. 2. If the RSC contained in the solicitation message matches any of the (pre)configured RSC(s), as specified in clause 5.1.4.1, of a 5G ProSe UE-to-Network Relay, and the Target Info contained in the solicitation message, if any, matches the 5G ProSe UE-to-Network Relay, the 5G ProSe UE-to-Network Relays (e.g. 1 and 2) respond to the 5G ProSe Remote UE with a UE-to-Network Relay Discovery Response message. The 5G ProSe UE-to-Network Relay Discovery Response message contains the Type of Discovery Message, Discoveree Info and RSC and is sent using the Source Layer-2 ID and Destination Layer-2 ID as described in clause 5.8.3. For 5G ProSe Layer-3 UE-to-Network Relay, the 5G ProSe UE-to-Network Relay shall only respond to a matching RSC in the UE-to-Network Relay Discovery Solicitation message when the S-NSSAI associated with that RSC belongs to the Allowed NSSAI of the 5G ProSe UE-to-Network Relay. The 5G ProSe Remote UE selects the 5G ProSe UE-to-Network Relay based on the information received in step 2.

[0086] <Procedures used by UEs supporting NR sidelink UE-to-Network Relay to transmit sidelink discovery messages> 3GPP TS 38.331 Clauses 5.8.13.3 and 5.8.14.2 specifies a procedure used by a UE supporting NR sidelink U2N Relay UE operation configured by upper layers to transmit NR sidelink discovery messages to evaluate Access Stratum (AS) layer conditions, which is illustrated by Figure 10.

[0087] Similarly, 3GPP TS 38.331 Clauses 5.8.13.3 and 5.8.15.2 specifies a procedure used by a UE supporting NR sidelink U2N Remote UE operation configured by upper layers to transmit NR sidelink discovery messages to evaluate AS layer conditions, which is illustrated by Figure 11.

[0088] <Procedure of (re-)selection of NR sidelink UE-to-Network Relay UE performed by Remote UE> 3GPP TS 38.331 Clause 5.8.15.3 specifies the procedure of (re-)selection of NR sidelink U2N Relay UE, performed by U2N Remote UE that is configured by upper layers to search for a NR sidelink U2N Relay UE, which is illustrated by Figure 12. Based on this procedure, Remote UE identifies suitable U2N Relay UE(s) if any. If Remote UE detects multiple suitable U2N Relay UEs, it is up to Remote UE implementation to choose one U2N Relay UE.

[0089] (NR sidelink single-hop UE-to-UE relay) In Release 18 NR sidelink relay, UE-to-UE (U2U) relay was introduced for sidelink coverage extension. Similar to Release 17 / 18 U2N relay, Layer 2 and Layer 3 single-hop U2U sidelink relay (i.e., relaying via a single Relay UE) is supported. An example of single-hop U2U relay is shown in Figure 13. Source UE and / or Destination UE are U2U Remote UE.

[0090] <Protocol stacks for NR sidelink Layer 2 UE-to-UE Relay> 3GPP TS 38.300 describes the protocol stacks for the user plane and the control plane of the L2 U2U Relay, which are illustrated in Figure 14 and Figure 15, respectively. The PC5 SDAP, PDCP and RRC are terminated between two L2 U2U Remote UEs (i.e., end-to-end), while SRAP, RLC, MAC and PHY are terminated in each hop of PC5 link.

[0091] <NR sidelink Layer 2 UE-to-UE Remote UE connection establishment> 3GPP TS 38.300 Clause 16.12.7 describes the procedure for L2 U2U Remote UE connection establishment, which is illustrated in Figure 16.

[0092] Below are excerpts from 3GPP TS 38.300 about the procedure for L2 U2U Remote UE connection establishment: 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 via RRCReconfigurationSidelink message 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 obtains PDCP and SDAP configuration for the intended end-to-end SL-DRB(s) via SIB / pre-configuration or dedicated RRC signalling. The L2 U2U Remote UE provides the portion of the configuration related to reception of the end-to-end SL-DRB(s) to the peer L2 U2U Remote UE using end-to-end RRCReconfigurationSidelink message. 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. 6. The L2 U2U Remote UE sends to the L2 U2U Relay UE the QoS profiles for the end-to-end QoS flows and the mapping of the end-to-end QoS flows to SLRB via PC5-RRC message. 7. The L2 U2U Relay UE performs QoS split only for PDB, per each end-to-end QoS flow. NOTE: It is up to L2 U2U Relay UE implementation on how to split PDB. 8. The L2 U2U Relay UE sends the split QoS value (i.e., PDB) via PC5-RRC message to the L2 U2U Remote UE. 9a. The L2 U2U Remote UE obtains first hop configuration (e.g. PC5 Relay RLC Channel configuration) for each end-to-end for SL-DRB via dedicated RRC signalling or based on merged first hop QoS in RB-level via SIB / pre-configuration. 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-hop RRCReconfigurationSidelink message. 9b. The L2 U2U Relay UE obtains second hop configuration (e.g. PC5 Relay RLC Channel configuration) for each end-to-end SL-DRB via dedicated RRC signalling or based on merged second hop QoS in RB-level via SIB / pre-configuration. 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-hop RRCReconfigurationSidelink message. 10. The L2 U2U Remote UE and the peer L2 U2U Remote UE transmit or receive data via L2 U2U Relay UE.

[0093] <NR sidelink UE-to-UE Relay discovery> Regarding discovery in Step 1 of Figure 16, Release 18 U2U Relay supports two discovery models: Model A and Model B as shown in Figure 17 and Figure 18, respectively. Relay discovery with Model A is the case that U2U Relay UE announces its relay service, user info of other UEs that U2U Relay UE has discovered, etc., to surrounding other UEs, while relay discovery with Model B is the case that a discoverer End UE solicits relaying services from surrounding U2U Relay UEs to communicate with a discoveree End UE. These discovery models can be applied to both L2 and L3 U2N Relay.

[0094] Below are excerpts from 3GPP TS 23.304 about the procedure for NR sidelink UE-to-UE Relay Discovery with Model A: 1. The 5G ProSe UE-to-UE Relay has discovered other UEs in proximity and obtains the Direct discovery set from other UEs in proximity per RSC. (e.g. via a previous 5G ProSe UE-to-UE Relay Discovery or via secure PC5 connection between 5G ProSe U2U Relay and 5G ProSe End UE (refer to TS 33.503

[0029] )). 2. The 5G ProSe UE-to-UE Relay sends a UE-to-UE Relay Discovery Announcement message. The UE-to-UE Relay Discovery Announcement message contains the Type of Discovery Message, User Info ID of the 5G ProSe UE-to-UE Relay, RSC and Direct discovery set including list of protected user info (i.e. Application Layer ID) received from the 5G ProSe End UEs supporting the RSC. The UE-to-UE Relay Discovery Announcement message is sent using the Source Layer-2 ID and Destination Layer-2 ID as described in clause 5.8.4. The 5G ProSe UE-to-UE Relay shall only announce user info (i.e. Application Layer ID) of other UEs in proximity that did not include an Announce Prohibited Indication when they were previously discovered. NOTE: 5G ProSe UE-to-UE Relay announces Direct discovery set from other UEs in proximity only if their PC5 signal strength measured by the 5G ProSe UE-to-UE Relay is above configured signal strength threshold as specified in TS 38.331

[0016] . A 5G ProSe End UE monitors announcement messages from a 5G ProSe UE-to-UE Relay. The 5G ProSe End UEs determine the Destination Layer-2 ID for signalling reception as specified in clause 5.1.

[0095] Below are excerpts from 3GPP TS 23.304 about the procedure for NR sidelink UE-to-UE Relay Discovery with Model B: 1. The discoverer 5G ProSe End UE (UE-1) sends a 5G ProSe UE-to-UE Relay Discovery Solicitation message. The 5G ProSe UE-to-UE Relay Discovery Solicitation message contains the Type of Discovery Message, RSC and the Direct Discovery set which includes the protected user info (i.e. Application Layer ID) of the discoverer 5G ProSe End UE (UE-1) and the discoveree 5G ProSe End UE (UE-2). The 5G ProSe UE-to-UE Relay Discovery Solicitation message is sent using the Source Layer-2 ID and Destination Layer-2 ID as described in clause 5.8.4. A 5G ProSe UE-to-UE Relay determines the Destination Layer-2 ID for signalling reception as specified in clause 5.1. The discoverer 5G ProSe End UE may include an Announce Prohibited Indication in the UE-to-UE Relay Discovery Solicitation message. If a 5G ProSe UE-to-UE Relay receives a Relay Discovery Solicitation message with an Announce Prohibited Indication it does not consider the 5G ProSe End UE as discovered during this procedure for inclusion in 5G ProSe UE-to-UE Relay Discovery with Model A, see clause 6.3.2.4.2, step 1. 2. If the RSC contained in the solicitation message matches any of the (pre)configured RSC(s), as specified in clause 5.1.5.1, of a 5G ProSe UE-to-UE Relay, the 5G ProSe UE-to-UE Relay sends a 5G ProSe UE-to-UE Relay Discovery Solicitation message. The 5G ProSe UE-to-UE Relay Discovery Solicitation message contains the Type of Discovery Message, the Direct Discovery set which includes the list of protected user info (i.e. Application Layer ID) of the discoverer 5G ProSe End UE (UE-1) and the discoveree 5G ProSe End UE (UE-2), User Info ID of UE-to-UE Relay, RSC. 5G ProSe UE-to-UE Relay Discovery Solicitation message is sent using the Source Layer-2 ID and Destination Layer-2 ID as described in clause 5.8.4. A 5G ProSe End UE determines the Destination Layer-2 ID for signalling reception as specified in clause 5.1. The 5G ProSe UE-to-UE Relay self-selects the Source Layer-2 ID as specified in clause 5.8.4.2. 3. If the RSC contained in the solicitation message matches any of the (pre)configured RSC(s), as specified in clause 5.1.5.1, of the discoveree 5G ProSe End UE (UE-2), and the discoveree 5G ProSe End UE (UE-2) matches the user info (i.e. Application Layer ID) of the discoveree 5G ProSe End UE (UE-2) contained in the solicitation message, then the discoveree 5G ProSe End UE (UE-2) responds to the 5G ProSe UE-to-UE Relay with a 5G ProSe UE-to-UE Relay Discovery Response message. The 5G ProSe UE-to-UE Relay Discovery Response message contains the Type of Discovery Message, RSC, the Direct Discovery set which includes the protected user info (i.e. Application Layer ID) of the discoverer 5G ProSe End UE (UE-1) and the discoveree 5G ProSe End UE (UE-2). The 5G ProSe UE-to-UE Relay Discovery Response message is sent using the Source Layer-2 ID and Destination Layer-2 ID as described in clause 5.8.4. If the discoveree 5G ProSe End UE (UE-2) receives multiple UE-to-UE Relay Discovery Solicitation messages from different 5G ProSe UE-to-UE Relays with the same RSC and the user info (i.e. Application Layer ID) of the discoveree 5G ProSe End UE (UE-2), it may choose to respond or not to a 5G ProSe UE-to-UE Relay (e.g. based on the PC5 signal strength of each message received). The discoveree 5G ProSe End UE may include an Announce Prohibited Indication in the UE-to-UE Relay Discovery Response message. If a 5G ProSe UE-to-UE Relay receives a Relay Discovery Response message with an Announce Prohibited Indication it does not consider the 5G ProSe End UE as discovered during this procedure for inclusion in 5G ProSe UE-to-UE Relay Discovery with Model A, see clause 6.3.2.4.2, step 1. 4. The 5G ProSe UE-to-UE Relay sends a 5G ProSe UE-to-UE Relay Discovery Response message. The 5G ProSe UE-to-UE Relay Discovery Response message contains the Type of Discovery Message, User Info ID of UE-to-UE Relay, RSC, the Direct Discovery set which includes the list of protected user info (i.e. Application Layer ID) of the discoverer 5G ProSe End UE (UE-1) and the discoveree 5G ProSe End UE (UE-2). The 5G ProSe UE-to-UE Relay Discovery Response message is sent using the Source Layer-2 ID and Destination Layer-2 ID as described in clause 5.8.4.

[0096] <Procedures used by a UE supporting NR sidelink UE-to-UE Relay to transmit sidelink discovery messages> 3GPP TS 38.331 Clauses 5.8.13.3 and 5.8.16.3 specifies a procedure used by a UE supporting NR sidelink U2U Relay UE operation to determine whether a NR sidelink UE is in proximity to NR sidelink U2U Relay UE in Model A Discovery messages, which is illustrated by Figure 19.

[0097] 3GPP TS 38.331 Clauses 5.8.13.3 and 5.8.16.2 specifies a procedure used by a UE supporting NR sidelink U2U Relay UE operation configured by upper layers to forward NR sidelink Model B Discovery messages to evaluate AS layer conditions, which is illustrated by Figure 20.

[0098] Also, 3GPP TS 38.331 Clauses 5.8.13.3 and 5.8.17.2 specifies a procedure used by a UE supporting NR sidelink U2U Remote UE operation configured by upper layers to transmit NR sidelink Model B Discovery messages to evaluate AS layer conditions, which is illustrated by Figure 21.

[0099] Finally, 3GPP TS 38.331 Clauses 5.8.13.3 and 5.8.17.2 specifies a procedure used by a UE supporting NR sidelink U2U Remote UE operation configured by upper layers to transmit NR sidelink Model B Discovery Response messages to evaluate AS layer conditions, which is illustrated by Figure 22.

[0100] <Procedure of (re-)selection of U2U Relay UE by Remote UE> 3GPP TS 38.331 Clause 5.8.17.3 specifies the procedure of (re-)selection of U2U Relay UE by Remote UE, which is illustrated by Figure 23. Based on this procedure, Remote UE identifies suitable U2U Relay UE(s) if any. If Remote UE detects multiple suitable U2U Relay UEs, it is up to Remote UE implementation to choose one U2U Relay UE.

[0101] (Multi-hop UE-to-Network relay in NR sidelink relay) In 3GPP RAN #104 meeting (June 2024), Release 19 Work Item Description for NR sidelink multi-hop relay (RP-241609) was approved. The objective of Release 19 is as follows (excerpt from RP-241609): The objective of this work item is to specify solutions that are needed to support multi-hop Layer-2 UE-to-Network relay for a single indirect path via SL relay UEs based on Rel-17 / 18 SL relay functionalities [RAN2, RAN3] 1. Specify mechanisms to support up to two additional hops relays on top of Rel-17 U2N relay. The work starts with one additional hop relay (i.e., remote UE -> first relay UE -> last relay UE -> gNB) until RAN#107 and further check will be made in RAN#107 if it can be easily extended to two additional hops relays (i.e., remote UE -> first relay UE -> second relay UE -> last relay UE -> gNB). A necessary criterion for the specified mechanisms is easy extensibility to support two additional hop relays for the work done until RAN#107 and to be forward compatible for future extensions for additional relays. A. Relay discovery and (re)selection [RAN2] B. Signalling support for relay UEs and remote UE authorization if SA2 concludes it is needed [RAN3] C. Impact on SRAP and QoS handling for multi-hop [RAN2] D. Control plane procedures [RAN2, RAN3] 2. Specify the following intra-gNB service continuity scenarios for multi-hop U2N relay based on Rel-17 / 18 procedures (for remote UE): First Priority: A. Intra-gNB multi-hop indirect to direct path switching using existing framework B. Intra-gNB multi-hop indirect to single-hop indirect path switching using existing framework Second Priority in order of importance: C. Intra-gNB direct to multi-hop indirect path switching D. Intra-gNB single-hop indirect to multi-hop indirect path switching The scenarios C and D are limited to path switching to a target indirect path consisting of the last relay UE in “direct” RRC Connected mode and all the other intermediate relay(s) in “indirect” RRC Connected mode to the same cell. NOTE: The current existing measurement framework and existing data forwarding mechanism should be reused.

[0102] An example of multi-hop U2N relay is shown in Figure 24.

[0103] In the existing Rel-17 U2N (re-)selection procedure of U2N Relay UE by Remote UE, U2N Remote UE only uses the SD-RSRP of a candidate U2N Relay UE(s). If we reuse Rel-17 (re-)selection criteria for sidelink multi-hop relay, it does not consider the qualities / characteristics of links between the candidate U2N Relay UE and UE / gNB that the candidate U2N Relay UE is connected directly or indirectly, as illustrated in Figure 25. Therefore, it may cause selecting U2N Relay UE with worse link performance between the selected Relay UE and gNB.

[0104] The key ideas of some embodiments in the present disclosure are as follows: - U2N Relay UE may announce at least one of the following assistance information: - Type(s) / status of U2N Relay UEs that the UE is directly or indirectly connected with - Number of hops between the UE and gNB - Received signal metric(s) of links between the UE and gNB - Channel congestion metric(s) of links between the UE and gNB - Distance metric(s) of links between the candidate U2N Relay UE and gNB - Line-of-sight (LOS) / non-line-of-sight (NLOS) metric(s) of links between the UE and gNB - Round Trip Time (RTT) metric(s) of links between the UE and gNB - U2N Remote UE may use at least one of the assistance information announced by U2N Relay UE(s) to trigger (re-)selection of U2N Relay UE and to determine suitable U2N Relay UE(s). - If no candidate U2N Relay UE meets at least one of the conditions, U2N Remote UE may ignore one or more of the conditions (e.g., based on the priority order of the conditions). Then, U2N Remote UE may redo determination of candidate U2N Relay UE(s). - If U2N Remote UE detects multiple suitable U2N Relay UEs, U2N Remote UE may select one suitable U2N Relay UE among the multiple suitable U2N Relay UE(s) based on at least one of the assistance information announced by each of the multiple suitable U2N Relay UEs.

[0105] Some embodiments in the present disclosure may allow Remote UE to take into account the qualities and / or characteristics of one or multiple links for (re-)selection of U2N Relay UE, as shown in Figure 26.

[0106] The benefits of some embodiments in the present disclosure over the existing techniques may be as follows: Improve end-to-end communication performance (e.g., reliability, latency) between Remote UE and gNB by (re-)selecting U2N Relay UE with better end-to-end link performance.

[0107] (Method) The methods (wireless (or radio) communication methods, control methods) described below may be applied in the system 1 described above.

[0108] The present disclosure discloses a method and apparatus for selection and reselection of relay node in wireless communication systems.

[0109] The method can be applied to any wireless communication system that makes use of single-hop relay and / or multi-hop relay for U2N relay and / or U2U relay, but, in the rest of the disclosure, the method is exemplified with 3GPP NR sidelink multi-hop U2N relay. Therefore, “U2N” in the rest of the disclosure could be read as “U2U” or could be simply removed (e.g., U2N Relay UE could be may be considered equivalent to Relay UE). "U2N Relay UE” in the rest of the disclosure may be regarded as the first UE, the first type UE, and the like. "U2N Remote UE” in the rest of the disclosure may be regarded as the second UE, the second type UE, and the like.

[0110] <Proposed procedure of U2N Relay UE> FIG. 26 is a schematic diagram illustrating an exemplary flow chart of proposed procedure for U2N Relay UE. As shown in FIG. 26, the UE may be configured to act as a U2N Relay UE and transmit one or more sidelink discovery message(s) in Step 1.

[0111] In Step 2, the UE may transmit the sidelink discovery message(s) including at least one of the following assistance information: a. Types / status of U2N Relay UE(s) that the UE is directly or indirectly connected with, b. Number of hops between the UE and gNB, c. Received signal metric(s) (e.g., RSRP, RSSI, RSRQ, SNR, SINR) of links between the UE and gNB including relay links between the UE and gNB, d. Channel congestion metric(s) (e.g., CBR, CR) of links between the UE and gNB, e. Distance metric(s) (e.g., value in unit of meters) of links between the UE and gNB, f. LOS / NLOS metric(s) of links between the UE and gNB, g. Round Trip Time (RTT) metric(s) (e.g., value in unit of time (second, millisecond, and the like) of links between the UE and gNB.

[0112] The types / status of U2N Relay UE(s) that the UE is directly or indirectly connected with may include at least one of the following: i. Indicator of whether each of one or more U2N Relay UE(s) is static UE (e.g., RSU) or mobile UE (e.g., pedestrian UE, vehicle UE, mobile devices) ii. Indicator of whether each of one or more U2N Relay UE(s) is in-coverage or out-of-coverage iii. Location(s) or zone ID(s) of one or more U2N Relay UE(s) iv. Absolute speed(s) of one or more U2N Relay UE(s) v. Relative speed(s) of the UE and one or more U2N Relay UE(s) vi. Heading(s) of one or more U2N Relay UEs

[0113] The number of hops between the UE and gNB may include at least one of the following: i. Number of hops between the UE and gNB ii. Indicator of whether the UE is directly connected with gNB or not

[0114] The received signal metric(s) of links between the UE and gNB including relay links between the UE and gNB may include at least one of the following: i. Received signal metric(s) of U2N Relay UE or gNB measured by the UE ii. Received signal metric(s) of U2N Relay UE or gNB measured by the U2N Relay UE(s) that the UE is directly or indirectly connected with iii. The minimum value of received signal metric(s) of links between the UE and gNB iv. The maximum value of received signal metric(s) of links between the UE and gNB v. In one embodiment, received signal metric(s) may be indicated as a range index that the received signal metric(s) corresponds to. vi. In one embodiment, received signal metric(s) may be indicated as a soft value or a hard value (e.g., 0, 1), where the hard value may be calculated based on comparison of received signal measurement and received signal metric threshold (e.g., a value of 1 corresponding to received signal metric exceeding the threshold and a value of 0 corresponding to received signal metric not exceeding the threshold).

[0115] The channel congestion metric(s) (e.g., CBR) of links between the UE and gNB may include at least one of the following: i. Channel congestion metric(s) measured by the UE ii. Channel congestion metric(s) measured by the U2N Relay UE(s) that the UE is directly or indirectly connected with iii. The minimum value of channel congestion metric(s) of links between the UE and gNB iv. The maximum value of channel congestion metric(s) of links between the UE and gNB v. In one embodiment, channel congestion metric(s) may be indicated as a range index that the channel congestion metric(s) corresponds to. vi. In one embodiment, channel congestion metric(s) may be indicated as a soft value or a hard value (e.g., 0, 1), where the hard value may be calculated based on comparison of channel congestion measurement and channel congestion metric threshold (e.g., a value of 1 corresponding to channel congestion metric exceeding the threshold and a value of 0 corresponding to channel congestion metric not exceeding the threshold).

[0116] The distance metric(s) of links between the UE and gNB may include at least one of the following: i. Distance metric(s) measured by the UE ii. Distance metric(s) measured by the U2N Relay UE(s) that the UE is directly or indirectly connected with iii. The minimum value of distance metrics of links between the UE and gNB iv. The maximum value of distance metrics of links between the UE and gNB v. The total distance of links between the UE and gNB vi. In one embodiment, distance metric(s) may be indicated as a range index that the distance metric(s) corresponds to. vii. In one embodiment, distance metric(s) may be indicated as a soft value or a hard value (e.g., 0, 1), where the hard value may be calculated based on comparison of distance measurement and distance metric threshold (e.g., a value of 1 corresponding to distance metric exceeding the threshold and a value of 0 corresponding to distance metric not exceeding the threshold). viii. In one embodiment, the distance metric of each link may be estimated based on Uu positioning and / or sidelink positioning. In another embodiment, the distance metric may be derived based on zone ID of Tx UE (e.g., using SCI 2-B format) and Rx UE’s location (e.g., distance between the center of Tx UE’s zone and Rx UE’s location).

[0117] The LOS / NLOS metric(s) of links between the UE and gNB,may include at least one of the following: i. Indicator of whether each of links between the UE and gNB is LOS or NLOS ii. Indicator of whether all links between the UE and gNB are LOS iii. The number of LOS links and the number of NLOS links for links between the UE and gNB iv. In one embodiment, LOS / NLOS metric(s) may be provided by a higher layer. v. In one embodiment, LOS / NLOS metric(s) may be indicated as a soft value (e.g., 0, 0.1, …, 0.9, 1.0) or hard value (e.g., 0, 1) with the value corresponding to the likelihood of LOS or NLOS (e.g., a value of 1 corresponding to LOS and a value of 0 corresponding to NLOS).

[0118] The RTT metric(s) of links between the UE and gNB.may include at least one of the following: i. RTT metric(s) measured by the UE. ii. RTT metric(s) measured by the U2N Relay UE(s) that the UE is directly or indirectly connected with

[0119] <Proposed procedure of (re-)selection of U2N Relay UE by U2N Remote UE> FIG. 27 is a schematic diagram illustrating an exemplary flow chart of proposed procedure for (re-)selection of U2N Relay UE by U2N Remote UE. As shown in FIG. 27, an example procedure for (re-)selection of U2N Relay UE by U2N Remote UE is as follows: Step 1. A UE may be configured to act as a U2N Remote UE. Step 2. The UE may check whether it meets at least one of the following conditions based on at least one assistance information from U2N Relay UE(s) that the UE is directly or indirectly connected with for triggering (re-)selection of U2N Relay UE: a. Conditions for types / status of U2N Relay UE(s), b. Conditions for number of hops between the UE and gNB, c. Conditions for received signal metric(s) (e.g., RSRP, RSSI, RSRQ, SNR, SINR) of links between the UE and gNB, d. Conditions for channel congestion metric(s) (e.g., CBR) of links between the UE and gNB, e. Conditions for distance metric(s) of links between the UE and gNB, f. Conditions for LOS / NLOS metric(s) of links between the UE and gNB, g. Conditions for RTT metric(s) between the UE and gNB, h. The output of an AI / ML model regarding a trigger of (re-)selection. Step 3. If the UE meets at least one of the conditions in Step 2, the UE may trigger (re-)selection of U2N Relay UE and / or perform sidelink discovery procedure with potential U2N Relay UE(s) in proximity to search for candidate U2N Relay UE(s). Step 4. The UE may determine candidate U2N Relay UE(s) that meets at least one of the following conditions based on at least one assistance information from potential U2N Relay UE(s) in proximity that are discovered in Step 3: a. Conditions for types / status of potential U2N Relay UE(s), b. Conditions for number of hops between a potential U2N Relay UE and gNB, c. Conditions for received signal metric(s) (e.g., RSRP, RSSI, RSRQ, SNR, SINR) of links between a potential U2N Relay UE and gNB, d. Conditions for channel congestion metric(s) (e.g., CBR) of links between a potential U2N Relay UE and gNB, e. Conditions for distance metric(s) of links between a potential U2N Relay UE and gNB, f. Conditions for LOS / NLOS metric(s) of links between a potential U2N Relay UE and gNB, g. Conditions for RTT metric(s) between a potential U2N Relay UE and gNB, h. The output of an AI / ML model regarding a candidate U2N Relay UE. Step 5. The UE may check whether it detects any suitable U2N Relay UE(s) among the determined candidate U2N Relay UE(s). If the UE detects at least one suitable U2N Relay UE(s), the UE may consider one of the available suitable U2N Relay UE(s) can be selected. If the UE detects no suitable U2N Relay UE(s) and there may be at least one condition(s) that UE can ignore in Step 4, the UE may redo Step 4 by ignoring at least one condition(s). Otherwise, the UE may consider no U2N Relay UE to be selected. Step 6. If the UE may consider one of the available suitable U2N Relay UE(s) can be selected in Step 5, the UE may select at least one suitable U2N Relay UE(s) among the suitable U2N Relay UE(s) based on at least one of the following criteria based on at least one assistance information from the determined suitable U2N Relay UE(s): a. Criteria for types / status of U2N Relay UE(s) that the UE is directly or indirectly connected with, b. Criteria for number of hops between the UE and gNB include, c. Criteria for received signal metric(s) (e.g., RSRP, RSSI, RSRQ, SNR, SINR) of links between the UE and gNB, d. Criteria for channel congestion metric(s) (e.g., CBR) of links between the UE and gNB, e. Criteria for distance metric(s) of links between the UE and gNB, f. Criteria for LOS / NLOS metric(s) of links between the UE and gNB, g. Criteria for RTT metric(s) of links between the UE and gNB, h. Up to the UE implementation, i. The output of an AI / ML model regarding a suitable U2N Relay UE.

[0120] In Step 2, the conditions for XXX (XXX is an arbitrary string, such as types / status of U2N Relay UE(s)) may be based on at least one parameter of XXX shown above.

[0121] In Step 2, the conditions for types / status of U2N Relay UE(s) may include at least one of the followings: i. The absolute speed(s) of one or more U2N Relay UE(s) between the UE and gNB is below or above (pre-)configured threshold(s). ii. The relative speed(s) of the UE and one or more U2N Relay UE(s) between the UE and gNB is below or above (pre-)configured threshold(s).

[0122] In Step 2, the conditions for number of hops between the UE and gNB may include at least one of the followings: i. The number of hops between the UE and gNB is increased or decreased. ii. The number of hops between the UE and gNB is below or above (pre-)configured threshold(s).

[0123] In Step 2, the conditions for received signal metric(s) of links between the UE and gNB may include at least one of the followings: i. Received signal metric(s) of U2N Relay UE or gNB measured by the UE is below or above (pre-)configured threshold(s). ii. Received signal metric(s) of U2N Relay UE or gNB measured by the U2N Relay UE(s) that the UE is directly or indirectly connected with is below or above (pre-)configured threshold(s). iii. The minimum value of received signal metric(s) of links between the UE and gNB is below or above (pre-)configured threshold(s). iv. The maximum value of received signal metric(s) of links between the UE and gNB is below or above (pre-)configured threshold(s).

[0124] In Step 2, the conditions for channel congestion metric(s) (e.g., CBR) of links between the UE and gNB may include at least one of the followings: i. Channel congestion metric(s) measured by the UE is below or above (pre-)configured threshold(s). ii. Channel congestion metric(s) measured by the U2N Relay UE(s) that the UE is directly or indirectly connected with is below or above (pre-)configured threshold(s). iii. The minimum value of channel congestion metric(s) of links between the UE and gNB is below or above (pre-)configured threshold(s). iv. The maximum value of channel congestion metric(s) of links between the UE and gNB is below or above (pre-)configured threshold(s).

[0125] In Step 2, the conditions for distance metric(s) of links between the UE and gNB may include at least one of the followings: i. Distance metric(s) measured by the UE is below or above (pre-)configured threshold(s). ii. Distance metric(s) measured by the U2N Relay UE(s) that the UE is directly or indirectly connected with is below or above (pre-)configured threshold(s). iii. The minimum value of distance metrics of links between the UE and gNB is below or above (pre-)configured threshold(s). iv. The maximum value of distance metrics of links between the UE and gNB is below or above (pre-)configured threshold(s). v. The total distance of links between the UE and gNB is below or above (pre-)configured threshold(s).

[0126] In Step 2, the conditions for LOS / NLOS metric(s) of links between the UE and gNB may include at least one of the followings: i. An indicator indicates that LOS / NLOS status of one or more of links between the UE and gNB are changed from LOS to NLOS. ii. An indicator indicates that LOS / NLOS status of one or more of links between the UE and gNB are changed from NLOS to LOS. iii. An indicator indicates that not all links between the UE and gNB are LOS. iv. The number of LOS links between the UE and gNB is below a (pre-)configured threshold. v. The number of NLOS links between the UE and gNB is above a (pre-)configured threshold.

[0127] In Step 2, the conditions for RTT metric(s) between the UE and gNB may include at least one of the followings: i. RTT metric(s) measured by the UE is below or above (pre-)configured threshold(s).. ii. RTT metric(s) measured by the U2N Relay UE(s) that the UE is directly or indirectly connected with is below or above (pre-)configured threshold(s).

[0128] In one embodiment, in Step 2, triggering (re-)selection of U2N Relay UE is based on one or more AI / ML model(s) and at least one assistance information from U2N Relay UE(s). For example, the output of an AI / ML model may be a soft value (e.g., 0, 0.1, …, 0.9, 1.0) or hard value (e.g., 0, 1) with the value corresponding to the likelihood of triggering (re-)selection (e.g., a value of 1 indicating that (re-)selection is triggered, and a value of 0 indicating that (re-)selection is not triggered.).

[0129] In Step 4, the conditions for XXX (XXX is an arbitrary string, such as types / status of potential U2N Relay UE(s)) may be based on at least one parameter of XXX shown above.

[0130] In Step 4, the conditions for types / status of potential U2N Relay UE(s) may include at least one of the followings: i. For a potential U2N Relay UE and U2N Relay UE(s) that the potential U2N Relay UE is directly or indirectly connected with, one or more of the potential U2N Relay UE(s) are static UEs or mobile UEs. The number of the one or more of the UE(s) may be a (pre-)configured threshold with / without a (pre-)configured hysteresis parameter(s). ii. For a potential U2N Relay UE and U2N Relay UE(s) that the potential U2N Relay UE is directly or indirectly connected with, the number of out-of-coverage potential U2N Relay UE(s) is below a (pre-)configured threshold with / without a (pre-)configured hysteresis parameter(s). iii. For a potential U2N Relay UE and U2N Relay UE(s) that the potential U2N Relay UE is directly or indirectly connected with, absolute speed(s) of one or more of the potential U2N Relay UE(s) is below or above (pre-)configured threshold(s) with / without a (pre-)configured hysteresis parameter(s). iv. For a potential U2N Relay UE and U2N Relay UE(s) that the potential U2N Relay UE is directly or indirectly connected with, relative speed(s) of one or more of the potential U2N Relay UE(s) is below (pre-)configured threshold(s) with / without a (pre-)configured hysteresis parameter(s).

[0131] In Step 4, the conditions for number of hops between a potential U2N Relay UE and gNB may include at least one of the followings: i. The number of hops between a potential U2N Relay UE and gNB is below a (pre-)configured threshold with / without a (pre-)configured hysteresis parameter(s). ii. The number of hops between a potential U2N Relay UE and gNB is below the number of hops between the current U2N Relay UE and gNB with / without a (pre-)configured hysteresis parameter(s).

[0132] In Step 4, the conditions for received signal metric(s) of links between a potential U2N Relay UE and gNB may include at least one of the followings: i. Received signal metric(s) of a potential U2N Relay UE measured by the UE is above a (pre-)configured threshold(s) with / without a (pre-)configured hysteresis parameter(s). ii. Received signal metric(s) of a potential U2N Relay UE measured by the UE is above received signal metric(s) of the current U2N Relay UE measured by the UE with / without a (pre-)configured hysteresis parameter(s). iii. Received signal metric(s) of U2N Relay UE(s) or gNB measured by the potential U2N Relay UE(s) is above (pre-)configured threshold(s) with / without a (pre-)configured hysteresis parameter(s). iv. Received signal metric(s) of U2N Relay UE(s) or gNB measured by the potential U2N Relay UE(s) is above received signal metric(s) of U2N Relay UE(s) or gNB measured by the current U2N Relay UE(s) with / without a (pre-)configured hysteresis parameter(s). v. Received signal metric(s) of U2N Relay UE(s) or gNB measured by U2N Relay UE(s) that the potential U2N Relay UE(s) is indirectly connected with is above (pre-)configured threshold(s) with / without a (pre-)configured hysteresis parameter(s). vi. Received signal metric(s) of U2N Relay UE(s) or gNB measured by U2N Relay UE(s) that the potential U2N Relay UE(s) is indirectly connected with is above received signal metric(s) of U2N Relay UE(s) or gNB measured by U2N Relay UE(s) that the current U2N Relay UE(s) is indirectly connected with with / without a (pre-)configured hysteresis parameter(s). vii. The minimum value of received signal metric(s) of links between the UE and gNB via a potential U2N Relay UE is above (pre-)configured threshold(s) with / without a (pre-)configured hysteresis parameter(s). viii. The minimum value of received signal metric(s) of links between the UE and gNB via a potential U2N Relay UE is above the minimum value of received signal metric(s) of links between the UE and gNB via the current U2N Relay UE with / without a (pre-)configured hysteresis parameter(s). ix. The maximum value of received signal metric(s) of links between the UE and gNB via a potential U2N Relay UE is above (pre-)configured threshold(s) with / without a (pre-)configured hysteresis parameter(s). x. The maximum value of received signal metric(s) of links between the UE and gNB via a potential U2N Relay UE is above the maximum value of received signal metric(s) of links between the UE and gNB via the current U2N Relay UE with / without a (pre-)configured hysteresis parameter(s).

[0133] In Step 4, the conditions for channel congestion metric(s) (e.g., CBR) of links between a potential U2N Relay UE and gNB may include at least one of the followings: i. Channel congestion metric(s) measured by a potential U2N Relay UE is below (pre-)configured threshold(s) with / without a (pre-)configured hysteresis parameter(s). ii. Channel congestion metric(s) measured by a potential U2N Relay UE is below channel congestion metric(s) measured by the current U2N Relay UE(s) with / without a (pre-)configured hysteresis parameter(s). iii. The minimum value of channel congestion metric(s) of links between a potential U2N Relay UE and gNB is below (pre-)configured threshold(s) with / without a (pre-)configured hysteresis parameter(s). iv. The minimum value of channel congestion metric(s) of links between a potential U2N Relay UE and gNB is below the minimum value of channel congestion metric(s) of links between the current U2N Relay UE and gNB with / without a (pre-)configured hysteresis parameter(s). v. The maximum value of channel congestion metric(s) of links between a potential U2N Relay UE and gNB is below (pre-)configured threshold(s) with / without a (pre-)configured hysteresis parameter(s). vi. The maximum value of channel congestion metric(s) of links between a potential U2N Relay UE and gNB is below the maximum value of channel congestion metric(s) of links between the current U2N Relay UE and gNB with / without a (pre-)configured hysteresis parameter(s).

[0134] In Step 4, the conditions for distance metric(s) of links between a potential U2N Relay UE and gNB may include at least one of the followings: i. Distance metric(s) measured by a potential U2N Relay UE is below (pre-)configured threshold(s) with / without a (pre-)configured hysteresis parameter(s). ii. Distance metric(s) measured by a potential U2N Relay UE is below distance metric(s) measured by the current U2N Relay UE with / without a (pre-)configured hysteresis parameter(s). iii. Distance metric(s) measured by U2N Relay UE(s) that a potential U2N Relay UE is directly or indirectly connected with is below (pre-)configured threshold(s) with / without a (pre-)configured hysteresis parameter(s). iv. Distance metric(s) measured by U2N Relay UE(s) that a potential U2N Relay UE is directly or indirectly connected with is below distance metric(s) measured by U2N Relay UE(s) that the current U2N Relay UE is directly or indirectly connected with with / without a (pre-)configured hysteresis parameter(s). v. The minimum value of distance metrics of links between the UE and gNB via a potential U2N Relay UE is below (pre-)configured threshold(s) with / without a (pre-)configured hysteresis parameter(s). vi. The minimum value of distance metrics of links between the UE and gNB via a potential U2N Relay UE is below the minimum value of distance metrics of links between the UE and gNB via the current U2N Relay UE with / without a (pre-)configured hysteresis parameter(s). vii. The maximum value of distance metrics of links between the UE and gNB via a potential U2N Relay UE is below (pre-)configured threshold(s) with / without a (pre-)configured hysteresis parameter(s). viii. The maximum value of distance metrics of links between the UE and gNB via a potential U2N Relay UE is below the maximum value of distance metrics of links between the UE and gNB via the current U2N Relay UE with / without a (pre-)configured hysteresis parameter(s). ix. The total distance of links between the UE and gNB via a potential U2N Relay UE is below (pre-)configured threshold(s) with / without a (pre-)configured hysteresis parameter(s). x. The total distance of links between the UE and gNB via a potential U2N Relay UE is below the total distance of links between the UE and gNB via the current U2N Relay UE with / without a (pre-)configured hysteresis parameter(s).

[0135] In Step 4, the conditions for LOS / NLOS metric(s) of links between a potential U2N Relay UE and gNB may include at least one of the followings: i. An indicator indicates that LOS / NLOS status of links between the UE and gNB via a potential U2N Relay UE are all LOS. ii. The number of LOS links between the UE and gNB via a potential U2N Relay UE is above a (pre-)configured threshold with / without a (pre-)configured hysteresis parameter(s). iii. The number of LOS links between the UE and gNB via a potential U2N Relay UE is above the number of LOS links for links between the UE and gNB via the current U2N Relay UE with / without a (pre-)configured hysteresis parameter(s). iv. The number of NLOS links between the UE and gNB via a potential U2N Relay UE is below a (pre-)configured threshold with / without a (pre-)configured hysteresis parameter(s). v. The number of NLOS links between the UE and gNB via a potential U2N Relay UE is above the number of NLOS links for links between the UE and gNB via the current U2N Relay UE with / without a (pre-)configured hysteresis parameter(s).

[0136] In Step 4, the conditions for RTT metric(s) between a potential U2N Relay UE and gNB may include at least one of the followings: i. RTT metric(s) measured by the UE is below or above (pre-)configured threshold(s) with / without a (pre-)configured hysteresis parameter(s). ii. RTT metric(s) measured by the U2N Relay UE(s) that the UE is directly or indirectly connected with is below or above (pre-)configured threshold(s) with / without a (pre-)configured hysteresis parameter(s). iii. RTT metric(s) between a potential U2N Relay UE and gNB is below or above RTT metric(s) between a current U2N Relay UE and gNB with / without a (pre-)configured hysteresis parameter(s).

[0137] In one embodiment, in Step 4, determination of candidate U2N Relay UE(s) is based on one or more AI / ML model(s) and at least one assistance information from potential U2N Relay UE(s) in proximity. For example, the output of an AI / ML model may be one or more soft values (e.g., 0, 0.1, …, 0.9, 1.0) or one or more hard values (e.g., 0, 1) with the value corresponding to the likelihood of a candidate U2N Relay UE as a candidate U2N Relay UE (e.g., a value of 1 indicating that a potential U2N Relay UE is a candidate U2N Relay UE, and a value of 0 indicating that a potential U2N Relay UE is not a candidate U2N Relay UE.).

[0138] In one embodiment, in Step 5, one or more condition(s) may be assigned corresponding priorities. Corresponding priorities may be assigned based on (pre-)configuration, UE implementation, or a specification. The UE may ignore one or more condition(s) based on the priorities of condition(s) (i.e., condition(s) with the lowest priority is ignored first).

[0139] In another embodiment, in Step 5, the UE may iterate ignoring one or more condition(s) until the UE has at least X suitable U2N Relay UE(s). X may be an integer value, which may be set based on (pre-)configuration, UE implementation, or a specification.

[0140] In another embodiment, in Step 5, the UE may ignore one or more condition(s) if the corresponding priority is lower than a priority threshold. The priority threshold may be a function of a priority of a packet to be transmitted. Also, one or more priority threshold(s) may be set based on (pre-)configuration, UE implementation, or a specification.

[0141] In Step 6, the criteria for XXX (XXX is an arbitrary string, such as types / status of U2N Relay UE(s)) may be based on at least one parameter of XXX shown above.

[0142] In Step 6, the criteria for types / status of U2N Relay UE(s) that the UE is directly or indirectly connected with may include at least one of the followings: i. The UE may select a suitable U2N Relay UE with the lowest number of out-of-coverage U2N Relay UE(s) between the UE and gNB. ii. The UE may select a suitable U2N Relay UE with the lowest absolute speed. iii. The UE may select a suitable U2N Relay UE with the lowest relative speed of the UE and the suitable U2N Relay UE.

[0143] In Step 6, the criteria for number of hops between the UE and gNB may include at least one of the followings: i. The UE may select a suitable U2N Relay UE with the lowest number of hops between the UE and gNB.

[0144] In Step 6, the criteria for received signal metric(s) of links between the UE and gNB may include at least one of the followings: i. The UE may select a suitable U2N Relay UE with the highest received signal metric(s) measured by the UE. ii. The UE may select a suitable U2N Relay UE with the highest minimum value of received signal metric(s) for links between the UE and gNB. iii. The UE may select a suitable U2N Relay UE with the highest maximum value of received signal metric(s) for links between the UE and gNB.

[0145] In Step 6, the criteria for channel congestion metric(s) (e.g., CBR) of links between the UE and gNB may include at least one of the followings: i. The UE may select a suitable U2N Relay UE with a lowest channel congestion measured by the suitable U2N Relay UE. ii. The UE may select a suitable U2N Relay UE with the lowest minimum value of channel congestion metrics for links between the UE and gNB. iii. The UE may select a suitable U2N Relay UE with the lowest maximum value of channel congestion metrics for links between the UE and gNB.

[0146] In Step 6, the criteria for distance metric(s) of links between the UE and gNB may include at least one of the followings: i. The UE may select a suitable U2N Relay UE with a shortest distance metric between the UE and the suitable U2N Relay UE. ii. The UE may select a suitable U2N Relay UE with a shortest minimum distance metric between the UE and gNB. iii. The UE may select a suitable U2N Relay UE with a shortest maximum distance metric between the UE and gNB. iv. The UE may select a suitable U2N Relay UE with a shortest total distance metric between the UE and gNB.

[0147] In Step 6, the criteria for LOS / NLOS metric(s) of links between the UE and gNB may include at least one of the followings: i. The UE may select a suitable U2N Relay UE with the highest number of LOS links between the UE and gNB. ii. The UE may select a suitable U2N Relay UE with the lowest number of NLOS links between the UE and gNB.

[0148] In Step 6, the criteria for RTT metric(s) of links between the UE and gNB may include at least one of the followings: i. The UE may select a suitable U2N Relay UE with the lowest RTT metric between the UE and gNB.

[0149] In Step 6, it may be up to the UE implementation to select at least one suitable U2N Relay UE(s) among the suitable U2N Relay UE(s).

[0150] In one embodiment, in Step 6, selection of at least one suitable U2N Relay UE(s) among the multiple suitable U2N Relay UEs may be based on one or more AI / ML model(s) and at least one assistance information from the multiple suitable U2N Relay UEs. For example, the output of an AI / ML model may be a soft value (e.g., 0, 0.1, …, 0.9, 1.0) or hard value (e.g., 0, 1) with the value corresponding to the score of each suitable U2N Relay UE (e.g., a value of 1 indicating that a U2N Relay UE is selected, and a value of 0 indicating that a U2N Relay UE is not selected).

[0151] (U2N / U2U) Relay UE, (U2N / U2U) Remote UE, and gNB in this disclosure may be any node in any wireless communication system.

[0152] The main features and result of some embodiments in this disclosure may include radio and software installed in a node (e.g., vehicle, road-side unit, base station, smartphone, mobile device). Also, methods and apparatus in some embodiments in this disclosure may be used for future radio access technologies using similar mechanisms (e.g., 6G).

[0153] (Abbreviations) At least some of the following abbreviations may be used in this disclosure. If there is an inconsistency between abbreviations, preference should be given to how it is used in this disclosure. If listed multiple times below, the first listing may be preferred over any subsequent listing(s). UE: User Equipment U2N: UE-to-Network U2U: UE-to-UE L2: Layer 2 L3: Layer 3 SDAP: Service Data Adaptation Protocol RRC: Radio Resource Control PDCP: Packet Data Convergence Protocol SRAP: Sidelink Relay Adaptation Protocol RLC: Radio Link Control MAC: Medium Access Control PHY: Physical Layer RSC: Relay Service Code SD-RSRP: Sidelink Discovery Reference Signal Received Power SL-RSRP: Sidelink Reference Signal Received Power LOS: Line-Of-Sight NLOS: Non-Line-Of-Sight ProSe: Proximity based Services RTT: Round Trip Time RSU: Road-Side Unit RSRP: Reference Signal Received Power RSSI: Received Signal Strength Indicator RSRQ: Reference Signal Receive Quality SNR: Signal-to-Noise Ratio SINR: Signal-to-Interference-plus-Noise Ratio CBR: Channel Busy Ratio CR: Channel Occupancy Ratio SCI: Sidelink Control Information AI / ML: Artificial Intelligence / Machine Learning

[0154] (Supplementary Notes) Regarding embodiments of the present disclosure, the following supplementary notes are given. <Supplementary Note 1> A terminal comprising: a receiver configured to receive, from one or more candidate relay terminals, a sidelink discovery message including assistance information regarding a path to a base station; and a processor configured to select a relay terminal from the one or more candidate relay terminals based on the assistance information. <Supplementary Note 2> The terminal according to supplementary note 1, wherein the assistance information includes the number of hops between each candidate relay terminal and the base station. <Supplementary Note 3> The terminal according to any one of supplementary notes 1 to 2, wherein the assistance information includes a received signal metric of one or more links between each candidate relay terminal and the base station. <Supplementary Note 4> The terminal according to any one of supplementary notes 1 to 3, wherein the assistance information includes a channel congestion metric of one or more links between each candidate relay terminal and the base station. <Supplementary Note 5> The terminal according to any one of supplementary notes 1 to 4, wherein the assistance information includes a distance metric of one or more links between each candidate relay terminal and the base station. <Supplementary Note 6> The terminal according to any one of supplementary notes 1 to 5, wherein the assistance information includes a Line-Of-Sight (LOS) or Non-Line-Of-Sight (NLOS) metric of one or more links between each candidate relay terminal and the base station. <Supplementary Note 7> The terminal according to any one of supplementary notes 1 to 6, wherein the assistance information includes a Round Trip Time (RTT) metric of a path between each candidate relay terminal and the base station. <Supplementary Note 8> The terminal according to any one of supplementary notes 1 to 7, wherein the processor is further configured to trigger a reselection of a relay terminal when assistance information received from a currently connected relay terminal indicates that a quality of a current path to the base station falls below a threshold. <Supplementary Note 9> The terminal according to any one of supplementary notes 1 to 8, wherein the processor is configured to select the relay terminal that provides a path with a lowest number of hops to the base station among the one or more candidate relay terminals. <Supplementary Note 10> The terminal according to any one of supplementary notes 1 to 9, wherein the processor is further configured to, in a case that no candidate relay terminal meets a set of selection conditions, ignore at least one condition from the set based on a priority and perform the selection of the relay terminal based on remaining conditions. <Supplementary Note 11> A method performed by a terminal, the method comprising: receiving, from one or more candidate relay terminals, a sidelink discovery message including assistance information regarding a path to a base station; and selecting a relay terminal from the one or more candidate relay terminals based on the assistance information. <Supplementary Note 12> A base station comprising: a processor configured to determine a configuration for a relay terminal (the configuration may be for assistance information regarding a path to the base station or include parameters related to announcement of the assistance information); and a transmitter configured to transmit the configuration to the relay terminal. <Supplementary Note 13> A system comprising: a terminal according to any one of supplementary notes 1 to 10; and a base station according to supplementary note 12.

[0155] (Variations) Embodiments in the present disclosure may be used for any 3GPP radio access technologies, for example, 3GPP 4G technology referred to as Long Term Evolution (LTE), 3GPP 5G technology referred to as New Radio (NR) or future 3GPP radio technology generations such as 6G or 7G. While the examples in the present disclosure relate to 3GPP technologies, embodiments in the present disclosure could be used for non-3GPP technologies, for example, Bluetooth, IEEE and its 802.11 variants, Wi-Fi, WiMAX, etc.

[0156] In the present disclosure, any signals (e.g., for indication, configuration and notification of some information) from a node to another node may be transmitted using any one or combinations of Radio Resource Control (RRC) layer signaling, Medium Access Control (MAC) layer signaling, and physical (PHY) layer signaling, even if not explicitly stated.

[0157] The RRC layer signaling may be an RRC message or an RRC information element. The MAC layer signaling may be a MAC control element (MAC CE) or a MAC Protocol Data Unit (PDU). The PHY layer signaling may be downlink control information (DCI), uplink control information (UCI), or sidelink control information (SCI).

[0158] Any parameters, values and information in the present disclosure may be indicated from a node to another node, even if not explicitly stated. In the present disclosure, “X” and “information on X” may be used interchangeably.

[0159] In the present disclosure, a time unit for radio communication may be replaced with (or interchangeably used as) another time unit for radio communication. For example, a radio frame, a subframe, a slot, a sub-slot, and a symbol all express time units for radio communication.

[0160] In the present disclosure, the terms “notify,” “report,” “indicate,” “designate,” “activate,” “deactivate,” “select,” “configure,” “pre-configure,” “update,” “determine,” etc. may be read interchangeably.

[0161] As used in the present disclosure, use of the term “or” in a list of items indicates an inclusive list. The list of items may be prefaced by a phrase such as “at least one of” or “one or more of.” For example, a list of at least one of A, B, or C includes A or B or C or AB (i.e., A and B) or AC or BC or ABC (i.e., A and B and C). Also, as used in the present disclosure, prefacing a list of conditions with the phrase “based on” shall not be construed as “based only on” the set of conditions and rather shall be construed as “based at least in part on” the set of conditions. For example, an outcome described as “based on condition A” may be based on both a condition A and a condition B without departing from the scope of the present disclosure.

[0162] In the present disclosure, the terms “comprise,” “include,” or “contain” may be used interchangeably and have the same meaning and are to be construed as inclusive and open-ended. The terms “comprise,” “include,” or “contain” may be used before a list of elements and indicate that at least all of the listed elements within the list exist but other elements that are not in the list may also be present. For example, if A comprises B and C, both {B, C} and {B, C, D} are within the scope of A.

[0163] The present disclosure, in connection with the accompanied drawings, describes example configurations that are not representative of all the examples that may be implemented or all configurations that are within the scope of the present disclosure. The term “exemplary” should not be construed as “preferred” or “advantageous compared to other examples” but rather “an illustration, an instance or an example.” By reading the present disclosure, including the description of the embodiments and the drawings, it will be appreciated by a person of ordinary skills in the art that the technology disclosed herein may be implemented using alternative embodiments. The person of ordinary skill in the art would appreciate that the embodiments, or certain features of the embodiments described herein, may be combined to arrive at yet other embodiments for practicing the technology described in the present disclosure. Thus, the disclosure is not limited to the examples and designs described herein but is to be accorded the broadest scope consistent with the principles and novel features disclosed herein.

[0164] The flowcharts and block diagrams in the figures illustrate examples of the architecture, functionality, and operation of possible implementations of systems, methods, and devices according to various embodiments. It should be noted that, in some alternative implementations, the functions noted in blocks may occur out of the order noted in the figures. For example, two blocks shown in succession may, in fact, be executed substantially concurrently, or the blocks may sometimes be executed in the reverse order, depending upon the functionality involved. Likewise, additional steps may be included in such methods, and certain steps may be omitted or combined, in methods consistent with various embodiments.

[0165] It is understood that the described embodiments are not mutually exclusive, and elements, components, materials, or steps described in connection with one example embodiment may be combined with, or eliminated from, other embodiments in suitable ways to accomplish desired design objectives. Any embodiment (two or more) used in the present disclosure may be used in combination.

[0166] Reference herein to “some embodiments” or “some exemplary embodiments” means that a particular feature, structure, or characteristic described in connection with the embodiment can be included in at least one embodiment. The appearance of the phrases “one embodiment,” “some embodiments” or “another embodiment” in various places in the present disclosure do not all necessarily refer to the same embodiment, nor are separate or alternative embodiments necessarily mutually exclusive of other embodiments. In the present disclosure, “an / one embodiment,” “(some) embodiments” and “another embodiment” may be used interchangeably.

[0167] The articles “a” and “an” as used in the present disclosure and the appended claims should generally be construed to mean “one or more” unless specified otherwise or clear from context to be directed to a singular form.

[0168] Unless explicitly stated otherwise, each numerical value and range in the present disclosure may be interpreted as being approximate as if the word “about” or “approximately” preceded the value of the value or range.

[0169] The term "connected" or any variation of the terms as used in the present disclosure mean all direct or indirect connections between two or more elements, and may include the presence of one or more intermediate elements between two elements that are "connected" to each other. The connection between the elements may be physical, logical, or a combination thereof. For example, "connection" may be interpreted as "access."

[0170] Although the elements in the following method claims, if any, are recited in a particular sequence, unless the claim recitations otherwise imply a particular sequence for implementing some or all of those elements, those elements are not necessarily intended to be limited to being implemented in that particular sequence.

[0171] It is appreciated that certain features of the present disclosure, which are, for clarity, described in the context of separate embodiments, may also be provided in combination in a single embodiment. Conversely, various features of the present disclosure, which are, for brevity, described in the context of a single embodiment, may also be provided separately or in any suitable sub-combination or as suitable in any other described embodiment of the present disclosure. Certain features described in the context of various embodiments are not essential features of those embodiments, unless noted as such.

[0172] It will be further understood that various modifications, alternatives, and variations in the details, materials, and arrangements of the parts which have been described and illustrated in order to explain the nature of described embodiments may be made by those skilled in the art without departing from the scope. Accordingly, the following claims embrace all such alternatives, modifications, and variations that fall within the terms of the claims.

Claims

1. A terminal comprising: a receiver configured to receive, from one or more candidate relay terminals, a sidelink discovery message including assistance information regarding a path to a base station; and a processor configured to select a relay terminal from the one or more candidate relay terminals based on the assistance information.

2. The terminal according to claim 1, wherein the assistance information includes the number of hops between each candidate relay terminal and the base station.

3. The terminal according to claim 1, wherein the assistance information includes a received signal metric of one or more links between each candidate relay terminal and the base station.

4. The terminal according to claim 1, wherein the assistance information includes a channel congestion metric of one or more links between each candidate relay terminal and the base station.

5. The terminal according to claim 1, wherein the assistance information includes a distance metric of one or more links between each candidate relay terminal and the base station.

6. The terminal according to claim 1, wherein the assistance information includes a Line-Of-Sight (LOS) or Non-Line-Of-Sight (NLOS) metric of one or more links between each candidate relay terminal and the base station.

7. The terminal according to claim 1, wherein the assistance information includes a Round Trip Time (RTT) metric of a path between each candidate relay terminal and the base station.

8. The terminal according to claim 1, wherein the processor is further configured to trigger a reselection of a relay terminal when assistance information received from a currently connected relay terminal indicates that a quality of a current path to the base station falls below a threshold.

9. The terminal according to claim 2, wherein the processor is configured to select the relay terminal that provides a path with a lowest number of hops to the base station among the one or more candidate relay terminals.

10. The terminal according to claim 1, wherein the processor is further configured to, in a case that no candidate relay terminal meets a set of selection conditions, ignore at least one condition from the set based on a priority and perform the selection of the relay terminal based on remaining conditions.

11. A method performed by a terminal, the method comprising: receiving, from one or more candidate relay terminals, a sidelink discovery message including assistance information regarding a path to a base station; and selecting a relay terminal from the one or more candidate relay terminals based on the assistance information.

12. A base station comprising: a processor configured to determine a configuration for a relay terminal, the configuration including parameters related to announcement of assistance information regarding a path to the base station; and a transmitter configured to transmit the configuration to the relay terminal.

13. A system comprising: a terminal according to any one of claims 1 to 10; and a base station according to claim 12.

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