Terminal, method, base station and communication system

Abstract

A terminal according to one aspect of the present disclosure comprising: a receiver configured to receive one or more sidelink discovery messages from one or more terminals; a processor configured to determine to forward at least one sidelink discovery message of the one or more sidelink discovery messages based on at least one criterion; and a transmitter configured to forward the at least one sidelink discovery message. According to one aspect of the present disclosure, more efficient use of radio resources and / or reduced channel congestion 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 / 716,843, filed on November 6, 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 selective forwarding of relay discovery messages in multi-hop relay.

[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. For example, discovery procedure for multi-hop U2N relay is presented (Non Patent Literature 1). In multi-hop relay communication systems, an intermediate relay terminal may receive multiple discovery messages originating from a single source, such as a base station or a remote terminal, via several different paths.

[0004] 3GPP TS 23.304 V19.1.0, “Proximity based Services (ProSe) in the 5G System (5GS)”

[0005] A problem arises in how the intermediate relay terminal should handle these multiple received messages. One simple approach is to forward all received discovery messages, but this leads to inefficiency and consumes excessive radio resources, especially as the number of potential paths increases. Another approach is to forward only the message from the path with the fewest hops; however, this method ignores the radio quality of the links and may result in the selection of a path with poor end-to-end performance. Both approaches can cause unnecessary forwarding of discovery messages, leading to inefficient use of radio resources and increased channel congestion.

[0006] Thus, one object of the present disclosure is to provide a terminal, a method, a base station and a communication system that can solve the problem of unnecessary forwarding and enable more efficient relay discovery in a multi-hop relay system, thereby improving the overall efficiency of radio resource usage.

[0007] A terminal according to one aspect of the present disclosure comprising: a receiver configured to receive one or more sidelink discovery messages from one or more terminals; a processor configured to determine to forward at least one sidelink discovery message of the one or more sidelink discovery messages based on at least one criterion; and a transmitter configured to forward the at least one sidelink discovery message.

[0008] According to one aspect of the present disclosure, more efficient use of radio resources and / or reduced channel congestion 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 sequence diagram illustrating an exemplary procedure for Model A discovery for multi-hop UE-to-Network relay.

[0034] FIG. 26 is a sequence diagram illustrating an exemplary procedure for Model B discovery for multi-hop UE-to-Network relay.

[0035] FIGs. 27A and 27B are schematic diagrams illustrating an example of forwarding problem in relay discovery for multi-hop UE-to-Network relay.

[0036] FIGs. 28A and 28B are schematic diagrams illustrating an example of selective forwarding based on the hop count in relay discovery for multi-hop UE-to-Network relay.

[0037] FIGs. 29A and 29B are schematic diagrams illustrating an example of selective forwarding based on radio metric(s) in relay discovery for multi-hop UE-to-Network relay.

[0038] FIGs. 30A and 30B are schematic diagrams illustrating an example of selective forwarding based on radio metric(s) in relay discovery for multi-hop UE-to-Network relay.

[0039] FIGs. 31A and 31B are schematic diagrams illustrating an example of selective forwarding based on the hop count and radio metric(s) in relay discovery for multi-hop UE-to-Network relay.

[0040] FIG. 32 is a schematic diagram illustrating an exemplary flow chart for selective forwarding of discovery messages by an Intermediate Relay UE.

[0041] The present disclosure may introduce methods and apparatus for selection and reselection of relay node for multi-hop relay.

[0042] 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.

[0043] 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.

[0044] <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 at least one of Evolved Packet System (EPS), 5G system (5GS), and so on. 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.

[0045] 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.

[0046] 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.

[0047] In the present disclosure, a UE, a mobile station, a mobile node and a terminal may be used interchangeably.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] 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.

[0052] The core network 30 may include at least one of Evolved Packet Core (EPC), 5G Core Network (5GCN), and so on.

[0053] 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.

[0054] <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.

[0055] 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.

[0056] 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.

[0057] Note that in the present disclosure, the words such as an apparatus, a circuit, a device, a section, a unit, and so on may be used interchangeably.

[0058] 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.

[0059] 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. The communication unit 120 may perform measurement on the received signal and output the measurement result to the control unit 110. The communication unit 120 may be referred to as a transmitter, receiver, or transmitter / receiver. The communication unit 120 may be referred to as a measurement unit.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] 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.

[0071] 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), Graphics Processing Unit (GPU), Neural Processing Unit (NPU), etc.

[0072] 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.

[0073] 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).

[0074] The network interface 940 may be, for example, a network adapter, which may be wired to an external network to send and receive signals.

[0075] 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.

[0076] 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. The sensors may include a locator (e.g., a receiver corresponding to Global Navigation Satellite System (GNSS)) to obtain position information.

[0077] 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.

[0078] 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.

[0079] 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.

[0080] 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.

[0081] 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.

[0082] 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.

[0083] 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.

[0084] <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 FIG. 4.

[0085] <<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 FIGs. 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).

[0086] <<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 FIG. 7.

[0087] 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.

[0088] <<NR sidelink UE-to-Network Relay discovery>> Regarding discovery in Step 1 of FIG. 7, Release 17 / 18 U2N Relay supports two discovery models: Model A and Model B as shown in FIG. 8 and FIG. 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.

[0089] 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.

[0090] 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.

[0091] <<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 FIG. 10.

[0092] 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 FIG. 11.

[0093] <<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 FIG. 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.

[0094] <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 FIG. 13. Source UE and / or Destination UE are U2U Remote UE.

[0095] <<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 FIG. 14 and FIG. 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.

[0096] <<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 FIG. 16.

[0097] 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.

[0098] <<NR sidelink UE-to-UE Relay discovery>> Regarding discovery in Step 1 of FIG. 16, Release 18 U2U Relay supports two discovery models: Model A and Model B as shown in FIG. 17 and FIG. 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.

[0099] 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.

[0100] 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.

[0101] <<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 FIG. 19.

[0102] 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 FIG. 20.

[0103] 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 FIG. 21.

[0104] 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 FIG. 22.

[0105] <<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 FIG. 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.

[0106] <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.

[0107] An example of multi-hop U2N relay is shown in FIG. 24.

[0108] 3GPP TS 23.304 presents the procedure for the Model A discovery and Model B discovery for multi-hop U2N relay as shown in FIG. 25 and FIG. 26.

[0109] Regarding FIG. 25, below are excerpts from 3GPP TS 23.304 about the procedure for 5G ProSe multi-hop UE-to-Network Relay Discovery with Model A: 0. The 5G ProSe Remote UE, the 5G ProSe Intermedidate UE-to-Network Relay and the 5G ProSe UE-to-Network Relay are (pre-)configured or provisioned with the related information to support multi-hop UE-to-Network Relay discovery, as specified in clause 5.1.4. If the 5G ProSe Remote UE, 5G ProSe Intermedidate UE-to-Network Relay and 5G ProSe UE-to-Network Relay belong to different PLMNs, their HPLMNs ensure that consistent configuraitons are provided. 1. If a 5G ProSe UE-to-Network Relay is successfully registered and authorized by the 5GS and has the configurations to operate multi-hop UE-to-Network Relay in the current region, it can start the discovery procedure. Otherwise, it shall not perfrom the 5G ProSe multi-hop UE-to-Network Relay discovery, i.e. not sending any announcement message. 2. The 5G ProSe UE-to-Network Relay sends a 5G ProSe UE-to-Network Relay Discovery Announcement message. To support multi-hop UE-to-Network Relay discovery, the 5G ProSe UE-to-Network Relay sets the Hop-Count to 1, sets the Announcer Info to its own User Info ID, and sets the RSC according to the configuration as in clause 5.1.4. 3. The 5G ProSe Intermedidate UE-to-Network Relay creates a corresponding discovery entry based on the received 5G ProSe UE-to-Network Relay Discovery Announcement message, if the discovery message meets the AS layer criteria, and the Hop-Count is less than the (pre-)configured maximum number of hops for the associated RSC and the optional Hop-Limit in the message. The discovery entry includes the following information: RSC, (optional) Root Relay Info, Announcer Info, Hop-Count, (optional) Accumlated QoS for PC5 link, (optional) NCGI, (optional) RRC Container. The Announcer Info is set to the Announcer Info of the received message. The Root Relay Info is set to the Root Relay Info of the reived message. The Hop-count is set to the value of the received message. The Accumlated QoS for PC5 link, if present in the received discovery message, will be updated based on the QoS of the PC5 link between the 5G ProSe Intermedidate UE-to-Network Relay and the sender of the message. If an discovery entry already exist, i.e. with the same RSC and (optional) Root Relay Info, and if the Hop-Count of the received message is less than the Hop-Count stored in the discovery entry, the 5G ProSe Intermedidate UE-to-Network Relay updates the discovery entry accordingly. The Announcer Info and Hop-Count are set to the Annoncer Info and Hop-Count of the newly received discovery message. NOTE: Based on implementation, a 5G ProSe Intermedidate UE-to-Network Relay may decide to update the discovery entry based on the Accumlated QoS for PC5 link instead of the Hop-Count, or a combination of the two information elements. 4a. 5G ProSe Intermedidate UE-to-Network Relay sends a 5G ProSe UE-to-Network Relay Discovery Announcement message, using the information from the stored discovery entry. The Hop-Count value will be incremented by 1, and the Announcer Info is set to the User Info of the 5G ProSe Intermedidate UE-to-Network Relay. When received by the 5G ProSe Remote UE, the information in the 5G ProSe UE-to-Network Relay Discovery Announcement message will be used for relay (re)selection, if the Hop-Count is less or equal to the (pre-)configured maximum number of hops for the associated RSC and the optional Hop-Limit in the message. The 5G ProSe Remote UE can also take the Accomulated QoS for PC5 link into account. For relay reselection, the Root Relay Info may be used to prioritize a relay offering the connection to the same 5G ProSe UE-to-Network Relay. 4b. 5G ProSe Intermedidate UE-to-Network Relay sends a 5G ProSe UE-to-Network Relay Discovery Announcement message, using the information from the stored discovery entry. This message may reach another 5G ProSe Intermedidate UE-to-Network Relay. 5. The 5G ProSe Intermedidate UE-to-Network Relay drops the received message if the Hop-Count is not less than the (pre-)configured maximum number of hops for the associated RSC and the optional Hop-Limit in the message. 6. The 5G ProSe Intermedidate UE-to-Network Relay sets a locally configured timer for each of the discovery entry based on implementation. If the 5G ProSe Intermedidate UE-to-Network Relay does not have an active PC5 link with the relay identfied by the Announcer Info, and it does not receive any new announcement message from that relay, the 5G ProSe Intermedidate UE-to-Network Relay removes the corresponding discovery entry and stops sending related 5G ProSe UE-to-Network Relay Discovery Announcement message. Based on configuration, the 5G ProSe Intermedidate UE-to-Network Relay may need to establish a Layer-2 link with the relay identified by the Announcer Info in the discovery entry before sending the 5G ProSe UE-to-Network Relay Discovery Announcement message.

[0110] Regarding FIG. 26, below are excerpts from 3GPP TS 23.304 about the procedure for 5G ProSe multi-hop UE-to-Network Relay Discovery with Model B: 1. The 5G ProSe Remote UE determines the Hop-Limit for discovery based on policy configuration (i.e. a mapping between maximum number of hops and RSC) or QoS requirements. If the Hop-Limit is determined based on configuration associated with the RSC, the 5G ProSe Remote UE does not include the Hop-Limit in the Solicitation message. Otherwise, the 5G ProSe Remote UE includes the Hop-Limit in the Solicitation message. 2a. The 5G ProSe Remote UE sends a 5G ProSe UE-to-Network Relay Discovery Solicitation message. The 5G ProSe UE-to-Network Relay Discovery Solicitation message additionally contains following IEs compared with that in clause 6.3.2.3.3: an indication that multi-hop relay is supported, hop count and Hop-Limit. The Target Info may contain the User Info ID of the UE-to-Network Relay and Intermediate Relay(s). 3a. If an indication that multi-hop relay is supported is contained in the received Solicitation message, the RSC contained in the Solicitation message matches any of the (pre)configured RSC(s), as specified in clause 5.1.4.1a, of a 5G ProSe Intermediate Relay, and the Target Info matches the User Info ID of the 5G ProSe Intermediate Relay (if any), the 5G ProSe Intermediate Relay may decide to send a 5G ProSe UE-to-Network Relay Discovery Solicitation message. The 5G ProSe Intermediate Relay shall drop the received Solicitation message if the hop count (corresponding to the number of Relays included in the message) has reached the Hop-Limit of the received Solicitation message or the (pre)configured maximum number of hops associated with the RSC. The 5G ProSe Intermediate Relay may send a Response message when it has already found or established PC5 link with 5G ProSe UE-to-Network Relay(s), without sending Solicitation message. i.e., steps 4a-8a are skipped and step 9a is performed directly. The response message additionally contains the User Info ID of UE-to-Network Relay, path information to the UE-to-Network Relay which is an (ordered) list of User Info ID of intermediate Relay(s). If the same information on User Info IDs of Remote UE and UE-to-Network Relay is received from different ProSe UEs, the 5G ProSe Intermediate UE-to- Network Relay may select a Solicitation message to be sent to the next hop based on various criteria (e.g., hop count, delay, channel quality of received messages, etc.). NOTE: If the 5G ProSe Remote UE does not receive any response after a pre-configured time, based on application requirement, it may increase the Hop-Limit and send the discovery message again. 4a. A 5G ProSe Intermediate Relay sends a Solicitation message, it additionally includes its own User Info ID in the message. i.e., the message contains the path information which is an (ordered) list of User Info ID of Relays in the path that has relayed the Solicitation message. The hop count is increased by 1. 2b.-5b. The Solicitation message from the same Remote UE goes through a different ordered list of 5G ProSe Intermediate Relays. 6-7. 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 the 5G ProSe UE-to-Network Relay, and the Target Info matches the User Info ID of the 5G ProSe UE-to-Network Relay (if any), then the 5G ProSe UE-to-Network Relay responds to the 5G ProSe Intermediate Relay with a 5G ProSe UE-to-Network Relay Discovery Response message. The 5G ProSe UE-to- Network Relay Discovery Response message additionally contains the path information compared with that in clause 6.3.2.3.3. The 5G ProSe UE-to-Network Relay may choose the path based on e.g., the PC5 signal strength of each message received, hops to the Remote UE, the path information, etc. Editor's note: It is FFS how the 5G ProSe UE-to-Network Relay decides when to send the Relay Discovery Response message. 8-10. A 5G ProSe Intermediate Relay forwards the a 5G ProSe UE-to-Network Relay Discovery Response message. The Response message additionally contains the path information. Editor's note: It is FFS if and how the Relay Discovery Response message is forwarded along the path indicated in the path information. 11. The Remote UE may perform relay path selection based on e.g., the PC5 signal strength and the number of hops to the 5G ProSe UE-to-Network Relay.

[0111] FIGs. 27A and 27B shows examples of relay discovery in multi-hop U2N relay: Model A discovery and Model B discovery. In an example of Model A discovery as shown in FIG. 27A, Intermediate Relay UE #3 receives discovery messages from three paths: one directly from Last Relay UE with 1 hop (referred to as Path A), another indirectly via Intermediate Relay UE #1 with 2 hops (referred to as Path B1), and the other indirectly via Intermediate Relay UE #2 with 2 hops (referred to as Path B2). Similarly, in an example of Model B discovery as shown in FIG. 27B, Intermediate Relay UE #3 receives discovery messages from three paths: one directly from Remote UE with 1 hop (referred to as Path A), another indirectly via Intermediate Relay UE #1 with 2 hops (referred to as Path B1), and the other indirectly via Intermediate Relay UE #2 with 2 hops (referred to as Path B2). These examples can be generalized to more than 2 hops and / or more than 3 relay paths.

[0112] The problem to be addressed in the present disclosure is which discovery message(s) each Intermediate Relay UE should forward.

[0113] One approach is to forward all discovery messages regardless of the number of hops and radio metrics in each path. However, it consumes more radio resources for discovery. Also, in more generalized cases with greater numbers of paths, this problem becomes more pronounced. Hence, this approach may not be efficient. In addition, the existing Rel-17 U2N Relay discovery procedure cannot be applied because it assumed single-hop relay, and thus there are no multiple paths from Last Relay UE.

[0114] Another approach is to determine whether to forward discovery messages based on the hop count as mentioned in 3GPP TS 23.304

[0012] and as shown in FIG. 25 and FIG. 26. However, this approach does not consider radio metric(s) of each relay path. It allows an Intermediate Relay UE to forward discovery messages with worse radio metric(s), which should not be forwarded. Hence, this approach may not be efficient.

[0115] In summary, the existing solutions may cause unnecessary forwarding of discovery messages. Therefore, a new mechanism is needed to efficiently forward discovery messages by an Intermediate Relay UE.

[0116] The key ideas of some embodiments in the present disclosure are as follows: - When Intermediate Relay UE receives discovery messages from multiple paths, it selectively forwards the discovery message(s) based on at least one of: a hop count, radio metric(s), resource metric(s), channel metric(s), hop count threshold, radio metric threshold(s), threshold(s) for the number of discovery messages to be forwarded by the UE, type of each relay path, and priority of each relay path.

[0117] For example, in FIGs. 28A and 28B where the hop count of Path A is smaller than that of Paths B1 and B2, Intermediate Relay UE #3 only forwards the discovery message of Path A based on the hop count because the hop count of Path A is smaller than that of Paths B1 and B2.

[0118] In another example, in FIGs. 29A and 29B where the radio metric(s) of Path B1 is better than that of Paths A and B2, Intermediate Relay UE #3 only forwards the discovery message of Path B1 based on radio metric(s) because the radio metric(s) of Path B1 is better than that of Paths A and B2.

[0119] In another example, in FIGs. 30A and 30B where the radio metric(s) of Path B1 and B2 is better than that of Paths A, Intermediate Relay UE #3 only forwards the discovery messages of Path B1 and B2 based on radio metric(s) because the radio metric(s) of Path B1 and B2 are better than that of Paths A.

[0120] In another example, in FIGs. 31A and 31B where the hop count of Path A is smaller than that of Paths B1 and B2, and also the radio metric(s) of Path B1 is better than that of Paths A and B2, Intermediate Relay UE #3 only forwards the discovery messages of Paths A and B1 based on the hop count and radio metric(s) because the hop count of Path A is smaller than that of Paths B1 and B2, while the radio metric(s) of Path B1 is better than that of Paths A and B2.

[0121] These examples can be generalized to more than 2 hops and / or more than 3 relay paths.

[0122] Some embodiments in the present disclosure may allow Intermediate Relay UEs to take into account based on at least one of a hop count, radio metric(s), hop count threshold, radio metric threshold(s), threshold(s) for the number of discovery messages to be forwarded by the UE, type of each relay path, and priority of each relay path, for forwarding received discovery messages. The benefits of some embodiments in the present disclosure over the existing solutions may be as follows: - Enables more efficient use of radio resources; - Reduces channel congestion.

[0123] <Method> The methods (wireless (or radio) communication methods, control methods) described below may be applied in the system 1 described above.

[0124] The present disclosure discloses a method and apparatus for selective forwarding of discovery messages in multi-hop wireless communication systems. The method may be applied to any wireless communication system that makes use of multi-hop relay for U2N relay and / or U2U relay, but, in the rest of the present disclosure, the method is exemplified with 3GPP NR sidelink multi-hop relay. Therefore, Relay UE in the rest of the present disclosure may be considered equivalent to U2N Relay UE and / or U2U Relay UE.

[0125] "Intermediate Relay UE" in the rest of the present disclosure may be regarded as the first UE, the first type UE, the UE between Remote UE and Last Relay UE, the U2U Relay UE, and the like. "Remote UE" in the rest of the present disclosure may be regarded as the second UE, the second type UE, and the like. "Last Relay UE" in the rest of the present disclosure may be regarded as the third UE, the third type UE, the UE nearest to the base station, the U2N Relay UE, and the like.

[0126] In the rest of the present disclosure, the term “discovery message” may be used interchangeably with any message or information.

[0127] In the rest of the present disclosure, the words regarding “forward,” “select,” “drop,” “ignore,” “not forward,” “not drop,” and the like may be used interchangeably.

[0128] <<Proposed procedure for selective forwarding of discovery messages by an Intermediate Relay UE>> FIG. 32 is a schematic diagram illustrating an exemplary flow chart for selective forwarding of discovery messages by an Intermediate Relay UE. As shown in FIG. 32, a UE may be configured to act as an Intermediate Relay UE in Step 1.

[0129] In Step 2, the UE receives one or more sidelink discovery message(s) from one or more UEs.

[0130] In Step 3, the UE forwards one or more of the received sidelink discovery message(s) based on at least one of the following criterion / criteria: a hop count, radio metric(s), resource metric(s), channel metric(s), hop count threshold, radio metric threshold(s), threshold(s) for the number of discovery messages to be forwarded by the UE, type of each relay path, or priority of each relay path.

[0131] In the present disclosure, the threshold(s) for the number of discovery messages to be forwarded may be expressed as N. In the present disclosure, the threshold(s) for the number of discovery messages to be forwarded for hop count i (e.g., i = 1, 2, 3, …) may be expressed as Ni.

[0132] In one embodiment, a radio metric may include at least one of: RSRP, SD-RSRP, SL-RSRP, RSSI, RSRQ, SNR, and SINR. The radio metric(s) may be referred to as radio quality metric(s), quality metric(s), and the like.

[0133] In another embodiment, a resource metric may include at least one of a CBR, a CR, and throughput. This may involve knowledge using already established relay links. The resource metric(s) may be referred to as channel congestion metric(s).

[0134] In another embodiment, a channel metric may be at least one of: frequency, frequency band, frequency band combination, frequency range, bandwidth part (BWP), resource block, subcarrier, cell, component carrier, and Radio Access Technology (RAT) such as Universal Terrestrial Radio Access (UTRA), Evolved Universal Terrestrial Radio Access (E-UTRA) (or LTE), and NR. The channel metric may be related to one or more of the relay path(s). The channel metric(s) may be referred to as frequency metric(s), frequency domain metric(s), and the like.

[0135] In another embodiment, a radio metric may be associated with at least one of: the radio metric between the UE and another UE that the UE directly receives discovery message(s), and the radio metric between the UE and another UE that the UE indirectly receives discovery message(s) via another Intermediate Relay UE.

[0136] In another embodiment, the UE may consider received discovery messages within time duration T to determine which discovery message(s) the UE will forward. The UE may forward the received discovery messages at a specific timing, the received discovery messages being received within time duration T before the specific timing.

[0137] In another embodiment, the type of each relay path may be at least one of: a relay path with a static Relay UE (e.g., RSU), a relay path with mobile Relay UE (e.g., pedestrian UE, vehicle UE, mobile devices), a relay path with LOS, and a relay path with NLOS.

[0138] In another embodiment, at least one of the hop count threshold, the radio metric threshold(s), the threshold(s) for the number of discovery messages to be forwarded, the time duration T, type of each relay path, and priority of each relay path may be (pre-)configured or provided to the UE by another UE or the network.

[0139] In another embodiment, at least one of the radio metric threshold(s), and the threshold(s) for the number of discovery messages to be forwarded by the UE may be associated with at least one of: a hop count, type of each relay path, and priority of each relay path.

[0140] In another embodiment, the UE may forward up to N discovery message(s) with smallest hop count(s) (or N discovery message(s) with N smallest hop count(s)), among the received discovery message(s). N may be a positive integer value.

[0141] In another embodiment, the UE may forward up to N discovery message(s) with highest radio metric(s) and / or lowest resource metric(s), among the received discovery message(s). N may be a positive integer value.

[0142] In another embodiment, the UE may forward up to N discovery message(s) with smallest hop count(s) with the radio metric(s) above the corresponding radio metric threshold(s). N may be a positive integer value.

[0143] In another embodiment, the UE may forward up to N discovery message(s) with highest radio metric(s) with hop count(s) that is equal to or less than the hop count threshold, among the received discovery message(s). N may be a positive integer value.

[0144] In another embodiment, the UE may forward up to N discovery message(s) if the hop count(s) is less than the minimum hop count of the previously forwarded discovery message(s) and the radio metric(s) is above the radio metric threshold. N may be a positive integer value.

[0145] In another embodiment, the UE may forward up to N discovery message(s) if the hop count(s) is the same as the minimum hop count of the previously forwarded discovery message(s), the radio metric(s) is above the radio metric threshold, and the radio metric(s) is higher than the highest radio metric of the previously forwarded discovery message(s). N may be a positive integer value.

[0146] In another embodiment, the UE may forward up to N discovery message(s) if the UE previously received and forwarded discovery message(s) from the same UE(s). N may be a positive integer value.

[0147] In another embodiment, the UE may not forward discovery message(s) if the UE previously received and forwarded discovery message(s) from the same UE(s).

[0148] In another embodiment, the UE may forward up to Ni discovery message(s) for each hop count i (e.g., i = 1, 2, 3, …), among the received discovery message(s). Ni is a non-negative integer value.

[0149] In another embodiment, the UE may forward up to Ni discovery message(s) for each hop count i (e.g., i = 1, 2, 3, …) with the radio metric(s) above the radio metric threshold(s), among the received discovery message(s). Ni is a non-negative integer value.

[0150] In a further embodiment for one or more of the above embodiments, if there are more than N discovery message(s) that meet the condition(s), the UE may select up to N of them for forwarding, based on a selection mechanism. For example, the selection mechanism may be random selection, or weighted random selection, e.g., the weight may be associated with at least one of: the hop count and the radio metric. In another example, one or more relay paths with one or more types of relay path may be prioritized over the others for selection. In another example, one or more relay paths with higher priorities may be prioritized over the others for selection.

[0151] In a further embodiment for one or more of the above embodiments, if there are more than Ni discovery message(s) for each hop count i that meet the condition(s), the UE may select up to Ni of them for forwarding, based on a selection mechanism. For example, the selection mechanism may be random selection, or weighted random selection, e.g., the weight may be associated with at least one of: the hop count, the resource metric(s), and the radio metric(s). In another example, one or more relay paths with one or more types of relay path may be prioritized over the others for selection. In another example, one or more relay paths with higher priorities may be prioritized over the others for selection.

[0152] In the decision for selecting the forwarded sidelink discovery message(s), it is possible to combine at least two criteria / metrics from the present disclosure by using a function (e.g., weighted average). For example, the decision process may involve calculating a weighted average where inputs are provided based on at least one of radio metric(s), resource metric(s), and number of paths. The weighted average may make use of the inverse, (1-x), or any other formula where those criteria are provided. Each weight can be a positive or negative value. More generally, any formula combining inputs from one or more of the criterium described in the present disclosure may be used.

[0153] (U2N / U2U) Relay UE, (U2N / U2U) Remote UE, and gNB in the present disclosure may be any node in any wireless communication system.

[0154] The main features and result of some embodiments in the present 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 the present disclosure may be used for future radio access technologies using similar mechanisms (e.g., 6G).

[0155] <Abbreviations> At least some of the following abbreviations may be used in the present disclosure. If there is an inconsistency between abbreviations, preference should be given to how it is used in the present disclosure. If listed multiple times below, the first listing may be preferred over any subsequent listing(s). AI / ML: Artificial Intelligence / Machine Learning AS: Access Stratum CBR: Channel Busy Ratio CR: Channel Occupancy Ratio L2: Layer 2 L3: Layer 3 LOS: Line-Of-Sight MAC: Medium Access Control NLOS: Non-Line-Of-Sight PDCP: Packet Data Convergence Protocol PHY: Physical Layer RLC: Radio Link Control RRC: Radio Resource Control ProSe: Proximity based Services RSC: Relay Service Code RSRP: Reference Signal Received Power RSRQ: Reference Signal Receive Quality RSSI: Received Signal Strength Indicator RSU: Road-Side Unit RTT: Round Trip Time SCI: Sidelink Control Information SD-RSRP: Sidelink Discovery Reference Signal Received Power SDAP: Service Data Adaptation Protocol SINR: Signal-to-Interference-plus-Noise Ratio SL-RSRP: Sidelink Reference Signal Received Power SNR: Signal-to-Noise Ratio SRAP: Sidelink Relay Adaptation Protocol U2N: UE-to-Network U2U: UE-to-UE UE: User Equipment

[0156] <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 one or more sidelink discovery messages from one or more terminals; a processor configured to determine to forward at least one sidelink discovery message of the one or more sidelink discovery messages based on at least one criterion; and a transmitter configured to forward the at least one sidelink discovery message. <Supplementary Note 2> The terminal according to supplementary note 1, wherein the at least one criterion includes a hop count associated with each of the one or more sidelink discovery messages. <Supplementary Note 3> The terminal according to any one of supplementary notes 1 to 2, wherein the processor is configured to determine to forward the at least one sidelink discovery message if its associated hop count is less than a hop count threshold. <Supplementary Note 4> The terminal according to any one of supplementary notes 1 to 3, wherein the at least one criterion includes a radio metric associated with a path of each of the one or more sidelink discovery messages. <Supplementary Note 5> The terminal according to any one of supplementary notes 1 to 4, wherein the processor is configured to determine to forward the at least one sidelink discovery message if its associated radio metric is greater than a radio metric threshold. <Supplementary Note 6> The terminal according to any one of supplementary notes 1 to 5, wherein the at least one criterion relates to a threshold for a number of the one or more sidelink discovery messages to be forwarded. <Supplementary Note 7> The terminal according to supplementary note 6, wherein the processor is configured to determine to forward a quantity of the one or more sidelink discovery messages that does not exceed a maximum quantity defined by the threshold. <Supplementary Note 8> The terminal according to supplementary note 6, wherein the threshold defines a respective maximum quantity of the one or more sidelink discovery messages to be forwarded for each of one or more distinct hop count values associated with the one or more sidelink discovery messages, and wherein the processor is configured to determine to forward messages in accordance with the respective maximum quantity for each distinct hop count value. <Supplementary Note 9> The terminal according to any one of supplementary notes 1 to 8, wherein the at least one criterion includes a resource metric associated with a path of each of the one or more sidelink discovery messages, the resource metric including at least one of: a Channel Busy Ratio (CBR), a Channel Occupancy Ratio (CR), or throughput. <Supplementary Note 10> The terminal according to any one of supplementary notes 1 to 9, wherein the at least one criterion includes a type of a relay path associated with each of the one or more sidelink discovery messages. <Supplementary Note 11> The terminal according to any one of supplementary notes 1 to 10, wherein the at least one criterion includes a priority of a relay path associated with each of the one or more sidelink discovery messages. <Supplementary Note 12> A method performed by a terminal, the method comprising: receiving one or more sidelink discovery messages from one or more terminals; determining to forward at least one sidelink discovery message of the one or more sidelink discovery messages based on at least one criterion; and forwarding the at least one sidelink discovery message. <Supplementary Note 13> A base station comprising: a processor configured to determine a configuration for a relay terminal, the configuration including at least one criterion for selective forwarding of a sidelink discovery message by the relay terminal; and a transmitter configured to transmit the configuration to the relay terminal. <Supplementary Note 14> A terminal comprising: a receiver configured to receive at least one sidelink discovery message, the at least one sidelink discovery message having been forwarded by another terminal, wherein the other terminal selected the at least one sidelink discovery message for forwarding from a plurality of sidelink discovery messages based on at least one criterion applied by the other terminal; and a processor configured to perform communication based on the at least one sidelink discovery message. <Supplementary Note 15> A system comprising: a first terminal according to any one of supplementary notes 1 to 11; and a second terminal according to supplementary note 14.

[0157] <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, Institute of Electrical and Electronics Engineers (IEEE) and its 802.11 variants, Wi-Fi, Worldwide Interoperability for Microwave Access (WiMAX), etc.

[0158] 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.

[0159] 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).

[0160] Furthermore, a BS in the present disclosure may be interpreted as a UE. For example, each embodiment of the present disclosure may be applied to the case where a communication between a BS and a UE is replaced with a communication between a plurality of UEs. In the case, the UE may have the functions of the BS described above. In the case, "uplink" and "downlink" may be interpreted as a UE-to-UE link (for example, "sidelink"). For example, an uplink channel, a downlink channel and so on may be interpreted as a sidelink channel.

[0161] 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.

[0162] 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 (frame), a hyper frame, a subframe, a slot, a sub-slot, and a symbol all express time units for radio communication.

[0163] In the present disclosure, the terms “notify,” “report,” “indicate,” “designate,” “activate,” “deactivate,” “select,” “configure,” “pre-configure,” “update,” “determine,” and any variation of the terms may be read interchangeably.

[0164] In the present disclosure, "equal to or smaller than," "smaller than," "equal to or larger than," "larger than," "equal to," and the like may be interchangeably used. In the present disclosure, words such as "good," "bad," "much," "little," "large," "small," "high," "low," "early," "late," "wide," "narrow," and the like may be interchangeably used irrespective of positive degree, comparative degree, and superlative degree. In the present disclosure, the words (such as "good," "bad," ...) and expressions obtained by adding "i-th" (i is any integer) to the words may be interchangeably used irrespective of positive degree, comparative degree, and superlative degree (for example, "best" may be interpreted as "i-th best," and vice versa).

[0165] In the present disclosure, "of," "for," "regarding," "related to," "associated with," and the like may be used interchangeably.

[0166] 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.

[0167] 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.

[0168] 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.

[0169] 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.

[0170] 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. The combination could make use of logical function(s) “or”, “and", and / or "exclusive or”.

[0171] 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.

[0172] 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.

[0173] 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.

[0174] 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."

[0175] 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.

[0176] 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.

[0177] 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 one or more sidelink discovery messages from one or more terminals; a processor configured to determine to forward at least one sidelink discovery message of the one or more sidelink discovery messages based on at least one criterion; and a transmitter configured to forward the at least one sidelink discovery message.

2. The terminal according to claim 1, wherein the at least one criterion includes a hop count associated with each of the one or more sidelink discovery messages.

3. The terminal according to claim 2, wherein the processor is configured to determine to forward the at least one sidelink discovery message if its associated hop count is less than a hop count threshold.

4. The terminal according to claim 1, wherein the at least one criterion includes a radio metric associated with a path of each of the one or more sidelink discovery messages.

5. The terminal according to claim 4, wherein the processor is configured to determine to forward the at least one sidelink discovery message if its associated radio metric is greater than a radio metric threshold.

6. The terminal according to claim 1, wherein the at least one criterion relates to a threshold for a number of the one or more sidelink discovery messages to be forwarded.

7. The terminal according to claim 6, wherein the processor is configured to determine to forward a quantity of the one or more sidelink discovery messages that does not exceed a maximum quantity defined by the threshold.

8. The terminal according to claim 6, wherein the threshold defines a respective maximum quantity of the one or more sidelink discovery messages to be forwarded for each of one or more distinct hop count values associated with the one or more sidelink discovery messages, and wherein the processor is configured to determine to forward messages in accordance with the respective maximum quantity for each distinct hop count value.

9. The terminal according to claim 1, wherein the at least one criterion includes a resource metric associated with a path of each of the one or more sidelink discovery messages, the resource metric including at least one of: a Channel Busy Ratio (CBR), a Channel Occupancy Ratio (CR), or throughput.

10. The terminal according to claim 1, wherein the at least one criterion includes a type of a relay path associated with each of the one or more sidelink discovery messages.

11. The terminal according to claim 1, wherein the at least one criterion includes a priority of a relay path associated with each of the one or more sidelink discovery messages.

12. A method performed by a terminal, the method comprising: receiving one or more sidelink discovery messages from one or more terminals; determining to forward at least one sidelink discovery message of the one or more sidelink discovery messages based on at least one criterion; and forwarding the at least one sidelink discovery message.

13. A base station comprising: a processor configured to determine a configuration for a relay terminal, the configuration including at least one criterion for selective forwarding of a sidelink discovery message by the relay terminal; and a transmitter configured to transmit the configuration to the relay terminal.

14. A terminal comprising: a receiver configured to receive at least one sidelink discovery message, the at least one sidelink discovery message having been forwarded by another terminal, wherein the other terminal selected the at least one sidelink discovery message for forwarding from a plurality of sidelink discovery messages based on at least one criterion applied by the other terminal; and a processor configured to perform communication based on the at least one sidelink discovery message.

15. A system comprising: a first terminal according to any one of claims 1 to 11; and a second terminal according to claim 14.

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