WO2025081358A1

WO2025081358A1 - Devices and methods for relay discovery

Info

Publication number: WO2025081358A1
Application number: PCT/CN2023/125081
Authority: WO
Inventors: Boyuan ZHANG; You Li; Gang Wang
Original assignee: NEC Corp
Current assignee: NEC Corp
Priority date: 2023-10-17
Filing date: 2023-10-17
Publication date: 2025-04-24
Anticipated expiration: 2026-04-17

Abstract

Embodiments of the present disclosure provide a solution for relay discovery. In a solution, a first terminal device obtains first information about at least one terminal device in proximity of the first terminal device, the first information comprising second information about an end terminal device provided with a relay service by a relay terminal device of the at least one terminal device; and transmits an announcement message for relay discovery, the announcement message at least comprising the first information.

Description

DEVICES AND METHODS FOR RELAY DISCOVERY

FIELDS

Example embodiments of the present disclosure generally relate to the field of communication techniques and in particular, to devices and methods for relay discovery in particular for multi-hop.

BACKGROUND

With the development of communication techniques, a variety of communication networks have been developed or studied. In some wireless communication networks, in addition to communicating with base stations via access links, user equipment (UE) can communicate with other devices using a sidelink (e.g., a communication link between a UE and another UE) as well. Such communication may relate to, for example, vehicle-based communication devices that can communicate from vehicle-to-vehicle (V2V) , vehicle-to-infrastructure (V2I) (e.g., from the vehicle-based communication device to road infrastructure nodes) , vehicle-to-network (V2N) (e.g., from the vehicle-based communication device to one or more network nodes, such as a base station) , a combination thereof and/or with other devices, which can be collectively referred to as vehicle-to-anything (V2X) communications. In some scenarios, one or more UEs may be needed to relay communication between two UEs.

SUMMARY

In a first aspect, there is provided a first terminal device comprising: a processor configured to cause the first terminal device to: obtain first information about at least one terminal device in proximity of the first terminal device, the first information comprising second information about an end terminal device provided with a relay service by a relay terminal device of the at least one terminal device; and transmit an announcement message for relay discovery, the announcement message at least comprising the first information.

In a second aspect, there is provided a second terminal device comprising: a processor configured to cause the second terminal device to: monitor an announcement message for relay discovery from a first terminal device, the announcement message comprising first information about at least one terminal device in proximity of the first terminal device, and wherein the first information comprises second information about an end terminal device provided with a relay service by a relay terminal device of the at least one terminal device.

In a third aspect, there is provided a first terminal device comprising: a processor configured to cause the first terminal device to: transmit a solicitation message for discovering relays for communication between the first terminal device and a second terminal device, the solicitation message comprising: a first identifier of the first terminal device, a second identifier of the second terminal device, and respective identifiers of a first set of relay terminal devices.

In a fourth aspect, there is provided a second terminal device comprising: a processor configured to cause the second terminal device to: receive, from a third terminal device, a solicitation message for discovering relays for communication between a first terminal device and the second terminal device, the solicitation message comprising: a first identifier of the first terminal device, a second identifier of the second terminal device, and respective identifiers of a first set of relay terminal devices.

In a fifth aspect, there is provided a third terminal device comprising: a processor configured to cause the third terminal device to: receive a solicitation message for discovering relays for communication between a first terminal device and a second terminal device, the solicitation message comprising: a first identifier of the first terminal device, a second identifier of the second terminal device, and respective identifiers of a first set of relay terminal devices; determine whether the third terminal device is comprised in the first set of relay terminal devices; and handle the solicitation message based on a result of the determining.

In a sixth aspect, there is provided a first terminal device comprising: a processor configured to cause the first terminal device to: determine a second terminal device as a candidate for replacing a relay terminal device in a relay path for communication between two end terminal devices, wherein the relay terminal device is connected to the first terminal device in the relay path; and transmit a solicitation message for candidate relay discovery, the solicitation message comprising: a first identifier of the first terminal device, a second identifier of the second terminal device, and a third identifier of a third terminal device connected to the relay terminal device in the relay path.

In a seventh aspect, there is provided a second terminal device comprising: a processor configured to cause the second terminal device to: receive, from a first terminal device, a solicitation message for candidate relay discovery, the solicitation message comprising: a first identifier of the first terminal device, a second identifier of a second terminal device determined as a candidate for replacing a relay terminal device in a relay path for communication between two end terminal devices, wherein the relay terminal device is connected to the first terminal device in the relay path, and a third identifier of a third terminal device connected to the relay terminal device in the relay path.

In an eighth aspect, there is provided a third terminal device comprising: a processor configured to cause the third terminal device to: receive, from a second terminal device, a solicitation message for candidate relay discovery, the solicitation message comprising: a first identifier of a first terminal device initiating the candidate relay discovery, a second identifier of the second terminal device, wherein the second terminal device is determined as a candidate for replacing a relay terminal device in a relay path for communication between two end terminal devices, wherein the relay terminal device is connected to the first terminal device and the third terminal device in the relay path, and a third identifier of the third terminal device.

In a ninth aspect, there is provided a terminal device comprising: a processor configured to cause the terminal device to: obtain a measurement result of a signal strength associated with a first relay terminal device; and determine a hop number of the first relay terminal device in a relay path based on the measurement result and respective ranges of the signal strength for a plurality of hop numbers, wherein the relay path is used for communication between two end terminal devices.

In a tenth aspect, there is provided a communication method performed by a first terminal device. The method comprises: obtaining first information about at least one terminal device in proximity of the first terminal device, the first information comprising second information about an end terminal device provided with a relay service by a relay terminal device of the at least one terminal device; and transmitting an announcement message for relay discovery, the announcement message at least comprising the first information.

In an eleventh aspect, there is provided a communication method performed by a second terminal device. The method comprises: monitoring an announcement message for relay discovery from a first terminal device, the announcement message comprising first information about at least one terminal device in proximity of the first terminal device, and wherein the first information comprises second information about an end terminal device provided with a relay service by a relay terminal device of the at least one terminal device.

In a twelfth aspect, there is provided a communication method performed by a first terminal device. The method comprises: transmitting a solicitation message for discovering relays for communication between the first terminal device and a second terminal device, the solicitation message comprising: a first identifier of the first terminal device, a second identifier of the second terminal device, and respective identifiers of a first set of relay terminal devices.

In a thirteenth aspect, there is provided a communication method performed by a second terminal device. The method comprises: receiving, from a third terminal device, a solicitation message for discovering relays for communication between a first terminal device and the second terminal device, the solicitation message comprising: a first identifier of the first terminal device, a second identifier of the second terminal device, and respective identifiers of a first set of relay terminal devices.

In a fourteenth aspect, there is provided a communication method performed by a third terminal device. The method comprises: receiving a solicitation message for discovering relays for communication between a first terminal device and a second terminal device, the solicitation message comprising: a first identifier of the first terminal device, a second identifier of the second terminal device, and respective identifiers of a first set of relay terminal devices; determining whether the third terminal device is comprised in the first set of relay terminal devices; and handling the solicitation message based on a result of the determining.

In a fifteenth aspect, there is provided a communication method performed by a first terminal device. The method comprises: determining a second terminal device as a candidate for replacing a relay terminal device in a relay path for communication between two end terminal devices, wherein the relay terminal device is connected to the first terminal device in the relay path; and transmitting a solicitation message for candidate relay discovery, the solicitation message comprising: a first identifier of the first terminal device, a second identifier of the second terminal device, and a third identifier of a third terminal device connected to the relay terminal device in the relay path.

In a sixteenth aspect, there is provided a communication method performed by a second terminal device. The method comprises: receiving, from a first terminal device, a solicitation message for candidate relay discovery, the solicitation message comprising: a first identifier of the first terminal device, a second identifier of a second terminal device determined as a candidate for replacing a relay terminal device in a relay path for communication between two end terminal devices, wherein the relay terminal device is connected to the first terminal device in the relay path, and a third identifier of a third terminal device connected to the relay terminal device in the relay path.

In a seventeenth aspect, there is provided a communication method performed by a third terminal device. The method comprises: receiving, from a second terminal device, a solicitation message for candidate relay discovery, the solicitation message comprising: a first identifier of a first terminal device initiating the candidate relay discovery, a second identifier of the second terminal device, wherein the second terminal device is determined as a candidate for replacing a relay terminal device in a relay path for communication between two end terminal devices, wherein the relay terminal device is connected to the first terminal device and the third terminal device in the relay path, and a third identifier of the third terminal device.

In an eighteenth aspect, there is provided a communication method performed by a terminal device. The method comprises: obtaining a measurement result of a signal strength associated with a first relay terminal device; and determining a hop number of the first relay terminal device in a relay path based on the measurement result and respective ranges of the signal strength for a plurality of hop numbers, wherein the relay path is used for communication between two end terminal devices.

In a nineteenth aspect, there is provided a computer readable medium having instructions stored thereon, the instructions, when executed on at least one processor, causing the at least one processor to carry out the method according to the tenth, eleventh, twelfth, thirteenth, fourteenth, fifteenth, sixteenth, seventeenth, or eighteenth aspect.

Other features of the present disclosure will become easily comprehensible through the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

Through the more detailed description of some example embodiments of the present disclosure in the accompanying drawings, the above and other objects, features and advantages of the present disclosure will become more apparent, wherein:

FIG. 1 illustrates an example communication environment in which example embodiments of the present disclosure can be implemented;

FIG. 2 illustrates a signaling chart of an example relay discovery procedure according to some example embodiments of the present disclosure;

FIG. 3 illustrates a signaling chart of another example relay discovery procedure according to some example embodiments of the present disclosure;

FIG. 4 illustrates a signaling chart of an example candidate relay discovery procedure according to some example embodiments of the present disclosure;

FIG. 5A illustrates a signaling chart of an example candidate relay discovery procedure initiated by an end UE according to some example embodiments of the present disclosure;

FIG. 5B illustrates a signaling chart of an example candidate relay discovery procedure initiated by a relay UE according to some example embodiments of the present disclosure;

FIG. 6 illustrates a signaling chart of handling a candidate relay according to some example embodiments of the present disclosure;

FIG. 7A illustrates a flowchart of a method implemented at a first terminal device according to some example embodiments of the present disclosure;

FIG. 7B illustrates a flowchart of a method implemented at a second terminal device according to some example embodiments of the present disclosure;

FIG. 8A illustrates a flowchart of a method implemented at a first terminal device according to some example embodiments of the present disclosure;

FIG. 8B illustrates a flowchart of a method implemented at a second terminal device according to some example embodiments of the present disclosure;

FIG. 8C illustrates a flowchart of a method implemented at a third terminal device according to some example embodiments of the present disclosure;

FIG. 9A illustrates a flowchart of a method implemented at a first terminal device according to some example embodiments of the present disclosure;

FIG. 9B illustrates a flowchart of a method implemented at a second terminal device according to some example embodiments of the present disclosure;

FIG. 9C illustrates a flowchart of a method implemented at a third terminal device according to some example embodiments of the present disclosure;

FIG. 10 illustrates a flowchart of a method implemented at a terminal device according to some example embodiments of the present disclosure;

FIG. 11 illustrates a simplified block diagram of an apparatus that is suitable for implementing example embodiments of the present disclosure.

Throughout the drawings, the same or similar reference numerals represent the same or similar element.

DETAILED DESCRIPTION

Principle of the present disclosure will now be described with reference to some example embodiments. It is to be understood that these embodiments are described only for the purpose of illustration and help those skilled in the art to understand and implement the present disclosure, without suggesting any limitation as to the scope of the disclosure. Embodiments described herein can be implemented in various manners other than the ones described below.

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

As used herein, the term ‘terminal device’ refers to any device having wireless or wired communication capabilities. Examples of the terminal device include, but not limited to, user equipment (UE) , personal computers, desktops, mobile phones, cellular phones, smart phones, personal digital assistants (PDAs) , portable computers, tablets, wearable devices, internet of things (IoT) devices, Ultra-reliable and Low Latency Communications (URLLC) devices, Internet of Everything (IoE) devices, machine type communication (MTC) devices, devices on vehicle for V2X communication where X means pedestrian, vehicle, or infrastructure/network, devices for Integrated Access and Backhaul (IAB) , Space borne vehicles or Air borne vehicles in Non-terrestrial networks (NTN) including Satellites and High Altitude Platforms (HAPs) encompassing Unmanned Aircraft Systems (UAS) , eXtended Reality (XR) devices including different types of realities such as Augmented Reality (AR) , Mixed Reality (MR) and Virtual Reality (VR) , the unmanned aerial vehicle (UAV) commonly known as a drone which is an aircraft without any human pilot, devices on high speed train (HST) , or image capture devices such as digital cameras, sensors, gaming devices, music storage and playback appliances, or Internet appliances enabling wireless or wired Internet access and browsing and the like. The ‘terminal device’ can further has ‘multicast/broadcast’ feature, to support public safety and mission critical, V2X applications, transparent IPv4/IPv6 multicast delivery, IPTV, smart TV, radio services, software delivery over wireless, group communications and IoT applications. It may also incorporate one or multiple Subscriber Identity Module (SIM) as known as Multi-SIM. The term “terminal device” can be used interchangeably with a UE, a mobile station, a subscriber station, a mobile terminal, a user terminal or a wireless device.

The term “network device” refers to a device which is capable of providing or hosting a cell or coverage where terminal devices can communicate. Examples of a network device include, but not limited to, a Node B (NodeB or NB) , an evolved NodeB (eNodeB or eNB) , a next generation NodeB (gNB) , a transmission reception point (TRP) , a remote radio unit (RRU) , a radio head (RH) , a remote radio head (RRH) , an IAB node, a low power node such as a femto node, a pico node, a reconfigurable intelligent surface (RIS) , and the like.

The terminal device or the network device may have Artificial intelligence (AI) or Machine learning capability. It generally includes a model which has been trained from numerous collected data for a specific function, and can be used to predict some information.

The terminal or the network device may work on several frequency ranges, e.g., FR1 (e.g., 450 MHz to 6000 MHz) , FR2 (e.g., 24.25GHz to 52.6GHz) , frequency band larger than 100 GHz as well as Tera Hertz (THz) . It can further work on licensed/unlicensed/shared spectrum. The terminal device may have more than one connection with the network devices under Multi-Radio Dual Connectivity (MR-DC) application scenario. The terminal device or the network device can work on full duplex, flexible duplex and cross division duplex modes.

The embodiments of the present disclosure may be performed in test equipment, e.g., signal generator, signal analyzer, spectrum analyzer, network analyzer, test terminal device, test network device, channel emulator. In some embodiments, the terminal device may be connected with a first network device and a second network device. One of the first network device and the second network device may be a master node and the other one may be a secondary node. The first network device and the second network device may use different radio access technologies (RATs) . In some embodiments, the first network device may be a first RAT device and the second network device may be a second RAT device. In some embodiments, the first RAT device is eNB and the second RAT device is gNB. Information related with different RATs may be transmitted to the terminal device from at least one of the first network device or the second network device. In some embodiments, first information may be transmitted to the terminal device from the first network device and second information may be transmitted to the terminal device from the second network device directly or via the first network device. In some embodiments, information related with configuration for the terminal device configured by the second network device may be transmitted from the second network device via the first network device. Information related with reconfiguration for the terminal device configured by the second network device may be transmitted to the terminal device from the second network device directly or via the first network device.

As used herein, the singular forms ‘a’ , ‘an’ and ‘the’ are intended to include the plural forms as well, unless the context clearly indicates otherwise. The term ‘includes’ and its variants are to be read as open terms that mean ‘includes, but is not limited to. ’ The term ‘based on’ is to be read as ‘at least in part based on. ’ The term ‘one embodiment’ and ‘an embodiment’ are to be read as ‘at least one embodiment. ’ The term ‘another embodiment’ is to be read as ‘at least one other embodiment. ’ The terms ‘first, ’ ‘second, ’ and the like may refer to different or same objects. Other definitions, explicit and implicit, may be included below.

In some examples, values, procedures, or apparatus are referred to as ‘best, ’ ‘lowest, ’ ‘highest, ’ ‘minimum, ’ ‘maximum, ’ or the like. It will be appreciated that such descriptions are intended to indicate that a selection among many used functional alternatives can be made, and such selections need not be better, smaller, higher, or otherwise preferable to other selections.

As used herein, the term “resource, ” “transmission resource, ” “uplink resource, ” or “downlink resource” may refer to any resource for performing a communication, such as a resource in time domain, a resource in frequency domain, a resource in space domain, a resource in code domain, or any other resource enabling a communication, and the like. In the following, unless explicitly stated, a resource in both frequency domain and time domain will be used as an example of a transmission resource for describing some example embodiments of the present disclosure. It is noted that example embodiments of the present disclosure are equally applicable to other resources in other domains.

As used herein, the term “end terminal device” may refer to a terminal device provided with a relay service by one or more relay device for communicating with another terminal device. The other terminal device may be also referred to as “peer terminal device” . In the following, the term “end terminal device” and “end UE” may be used interchangeably. The end UE may be also referred to as “remote UE” . One of the two remote UEs communicating with each other via at least one relay may be referred to as a source remote UE and the other one may be referred to as a target remote UE.

As used herein, the term “relay terminal device” may refer to a terminal device providing a relay service to two end terminal devices for communication. In the following, the term “relay terminal device” and “relay UE” may be used interchangeably.

Principles and implementations of the present disclosure will be described in detail below with reference to the figures.

FIG. 1 illustrates a schematic diagram of an example communication environment 100 in which example embodiments of the present disclosure can be implemented. In the communication environment 100, a plurality of communication devices, including an end terminal device 110-1 and an end terminal device 110-2, may communicate with each other. The end terminal device 110-1 and the end terminal device 110-2 may be individually referred to as “end terminal device 110” or collectively referred to as “end terminal devices 110” .

The environment 100 may further include a plurality of relay terminal devices, for example, a relay terminal device 120-1, a relay terminal device 120-2 and a relay terminal device 120-3, which may be individually referred to as “relay terminal device 120” or collectively referred to as “relay terminal devices 120” . In some scenarios, the end terminal device 110-1 may communicate with the end terminal device 110-2 via at least one relay terminal device, e.g., a relay terminal device 120-1 and a relay terminal device 120-2 as shown in FIG. 1 merely for the purpose of illustration. A relay path may be set up between the end terminal device 110-1, the relay terminal device 120-1, the relay terminal device 120-2 and the end terminal device 110-2. In some scenarios, more relay terminal devices may be discovered in proximity of the end terminal device 110-1, e.g., a relay terminal device 120-3.

In some example embodiments, the end terminal device 110-1 may be a source remote UE and the end terminal device 110-2 may be a target remote UE. In some example embodiments, the end terminal device 110 may be an end UE, such as a Proximity based Services (ProSe) End UE and the relay terminal device 120 may be a relay UE, such as a ProSe UE-to-UE relay.

In the following, the terms “end terminal device” and “end UE” may be used interchangeably. The terms “relay terminal device” and “relay UE” may be used interchangeably.

It is to be understood that the number of devices and their connections shown in FIG. 1 are only for the purpose of illustration without suggesting any limitation. The communication environment 100 may include any suitable number of devices configured to implementing example embodiments of the present disclosure. Although not shown, it would be appreciated that one or more additional devices may be located in the communication environment 100.

The communications in the communication environment 100 may conform to any suitable standards including, but not limited to, Global System for Mobile Communications (GSM) , Long Term Evolution (LTE) , LTE-Evolution, LTE-Advanced (LTE-A) , New Radio (NR) , Wideband Code Division Multiple Access (WCDMA) , Code Division Multiple Access (CDMA) , GSM EDGE Radio Access Network (GERAN) , Machine Type Communication (MTC) and the like. The embodiments of the present disclosure may be performed according to any generation communication protocols either currently known or to be developed in the future. Examples of the communication protocols include, but not limited to, the first generation (1G) , the second generation (2G) , 2.5G, 2.75G, the third generation (3G) , the fourth generation (4G) , 4.5G, the fifth generation (5G) communication protocols, 5.5G, 5G-Advanced networks, or the sixth generation (6G) networks.

Taking UE as an example of the terminal device, a UE is currently supported to connect to another UE through one hop, i.e., via a relay. However, single hop UE-to-UE (U2U) might not meet actual needs, for example, in areas with poor network signals such as basements or forests. Therefore, multi-hop U2U relay is needed.

Regarding U2U relay discovery, there are some solutions. For Model A discovery, the relay UE should only announce the neighbor UEs for which the sidelink discovery (SD) -RSRP/SL-RSRP between the relay UE and the neighbor UE is above a configured threshold in a discovery announcement message. For Model A discovery, upon discovery message reception, the remote UE considers a relay UE as a candidate relay UE if the SD-RSRP towards the relay UE is above a configured threshold.

For Model-B discovery, after receiving a discovery message from a relay UE, a target remote UE transmits the discovery response message only if the PC5 RSRP between the target remote UE and the relay UE is above a configured threshold. For Model B discovery, upon discovery response messages reception, the source remote UE considers a relay UE as a candidate relay UE if the SD-RSRP towards the relay UE is above a configured threshold.

For the integrated-discovery case, the relay UE forwards the discovery message for Direct Communication Request (DCR) message with integrated Discovery case only if the PC5 reference signal receiving power (RSRP) between the relay UE and the source remote UE is above a threshold. For integrated-discovery, when receiving DCR message from one or multiple relay UEs, the target remote UE should consider candidate relay UEs towards which the SL-RSRP is above a configured threshold to respond and that satisfy upper-layer criteria, and select a relay UE from among them.

For non-integrated U2U relay discovery model B, when relay (re) selection is triggered at the remote UE, the discovery transmission may be triggered at the same time to search for candidate relay UEs.

Despite the above solutions on U2U relay discovery, relay discovery in the case of multi-hop U2U relay discovery is to be specified. To this end, the example embodiments of the present disclosure propose some solutions on SL multi-hop U2U relay discovery.

Example embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings.

Model A discovery procedure for multi-hop U2U relay

In Model A relay discovery procedure, a relay terminal device may announce itself to other terminal devices such that an end terminal device discovers the relay terminal device. In some example embodiments, there is provided a solution on Model A discovery procedure for multi-hop U2U relay. For example, a first terminal device may obtain first information about at least one terminal device in proximity of the first terminal device. The first information may comprise second information about an end terminal device provided with a relay service by a relay terminal device of the at least one terminal device. Further, the first terminal device may transmit an announcement message for relay discovery. The announcement message may at least comprise the first information. Upon receiving the announcement message, a second terminal device which is an end terminal device may discover the first terminal device and a relay terminal device in proximity of the first terminal device as relays.

That is, the first terminal device, as a relay terminal device, may discover other terminal devices in proximity and proactively broadcast an announcement message about the relay terminal devices in proximity and their connected end terminal devices. In this way, a Mode A discovery procedure for multi-hop U2U relay is specified. Thereby, communication between the end terminal devices can be supported by multi-hop U2U relay.

Reference is made to FIG. 2, which illustrates a signaling chart 200 of an example relay discovery procedure according to some example embodiments of the present disclosure. The signaling chart 200 involves a first terminal device 201, a second terminal device 202-1, and a second terminal device 202-2. The first terminal device 201 such as a ProSe UE-to-UE Relay may be an example of the relay terminal device 120 as shown in FIG. 1. The second terminal device 202-1 may be an example of the end terminal device 110-1 and the second terminal device 202-2 may be an example of the end terminal device 110-2. In the following, the second terminal devices 202-1 and 202-2 may be individually referred to as “second terminal device 202” or collectively referred to as “second terminal devices 202” .

As shown in FIG. 2, in some example embodiments, the first terminal device 201 may determine (205) at least one terminal device in its proximity. For example, the first terminal device 201 may discover other terminal devices in proximity via any suitable procedure. The procedure may include but not limited to a previous ProSe UE-to-UE Relay Discovery procedure for single hop or multi-hop, a previous ProSe UE-to-UE Relay Communication procedure for single hop or multi-hop, a previous ProSe UE-to-Network Relay Discovery procedure for single hop or multi-hop, a previous ProSe UE-to-Network Relay Communication procedure for single hop or multi-hop, or a previous ProSe non-relay discovery procedure.

The first terminal device 201 may obtain (210) first information about the at least one terminal device in proximity. For example, the first terminal device 201 may obtain information about the terminal devices in proximity in a per relay service code (RSC) granularity, for example.

The at least one terminal device in proximity may include at least one relay terminal device which may provide a relay service to an end terminal device. As such, the first information may comprise second information about the end terminal device provided with the relay service by the relay terminal device in proximity of the first terminal device 201.

In some example embodiments, the second information may comprise an identifier of the end terminal device, for example, user information identifier (user info ID) of the end terminal device. Additionally, or alternatively, the second information may comprise a hop number from the first terminal device 201 to the end terminal device. The hop number may indicate through how many relay terminal devices the end terminal device is in proximity. Additionally, or alternatively, the second information may comprise a sequence of relay terminal devices through which the end terminal device is communicable. For example, the second information may include an ordered relay terminal device list, which may indicate through the listed relay terminal devices in the order as shown in the list, the end terminal device may be achieved.

As an example, if ProSe UE-to-UE relay discovers another ProSe UE-to-UE relay in proximity, the ProSe UE-to-UE relay may obtain the user info ID of a ProSe End UE connected to the discovered ProSe UE-to-UE relay. The ProSe UE-to-UE relay may obtain the hop number to the connected ProSe End UE, and the hop number (which may be denoted as hop number1) may indicate through how many UE-to-UE relays, the ProSe End UE is in proximity. Alternatively, or in addition, the ProSe UE-to-UE relay may obtain an ordered ProSe UE to UE Relay list, which indicates through the ProSe UE to UE Relays in an order, the End UE can be achieved.

In some example embodiments, the first information may further comprise a user information identifier of the at least one terminal device in proximity of the first terminal device 201, e.g., User Info ID of other UEs in proximity. Additionally, or alternatively, the first information may comprise a user type of the at least one terminal device. For example, the first information includes whether the terminal device in proximity is a UE-to-UE relay UE or a ProSe End UE.

Continuing with FIG. 2, the first terminal device 201 may transmit (215) an announcement message for relay discovery. The announcement message may at least comprise the first information. In an example, the ProSe UE-to-UE Relay may transmit a UE-to-UE Relay Discovery Announcement message, which may include the user info ID of the ProSe UE-to-UE Relay and may include the following information for each RSC: user info IDs of the proximity ProSe UE, a user type of the proximity ProSe UE. If the proximity ProSe UE is a UE-to-UE relay, the UE-to-UE Relay Discovery Announcement message may include a user info ID of an end UE connected to the proximity ProSe UE. The UE-to-UE Relay Discovery Announcement message may include a hop number from the ProSe UE-to-UE Relay to the proximity ProSe UE. For example, if the proximity ProSe UE is an end UE, the hop number may be 1. Otherwise, the hop number may be hop number1 plus 1. Alternatively, or in addition, the UE-to-UE Relay Discovery Announcement message may include an ordered ProSe UE to UE Relay list, which indicates through the ProSe UE to UE Relays in an order, the End UE can be achieved.

In some example embodiments, the announcement message may further comprise a type of discovery message. The type of discovery message may include a terminal device-to-terminal device relay discovery procedure, e.g., a previous ProSe single hop or multi-hop UE-to-UE Relay Discovery procedure. Additionally, or alternatively, the announcement message may comprise a terminal device-to-terminal device relay communication procedure, e.g., a previous ProSe single hop or multi-hop UE-to-UE Relay communication procedure. Additionally, or alternatively, the announcement message may comprise a terminal device-network relay discovery procedure, e.g., a previous ProSe single hop or multi-hop UE-to-Network Relay Discovery procedure. Additionally, or alternatively, the announcement message may comprise a terminal device-network relay communication procedure, e.g., a previous ProSe single hop or multi-hop UE-to-Network Relay Communication procedure. Additionally, or alternatively, the announcement message may comprise a non-relay discovery procedure, e.g., a previous ProSe non-relay discovery procedure.

As shown in FIG. 2, the second terminal devices 202-1 and 202-2 may monitor (220) the announcement message from the first terminal device 201. Then, the second terminal devices 202-1 and 202-2 may determine (225) a proximity-based service based on the announcement message. The proximity-based service is used for connecting to a peer terminal device. For example, the second terminal device 220-1 may determine the proximity-based service for connecting to the second terminal device 220-2.

In an example, a ProSe End UE may monitor announcement messages from a ProSe UE-to-UE relay. The ProSe End UE may determine the following information from the signaling reception: estimation Layer 2 ID of the ProSe peer End UE, and the ProSe Service in order to connect to the ProSe peer end UE. The ProSe Service may include at least one of the following: ProSe Direct Communication, ProSe UE to UE Relay, and ProSe multi-hop UE to UE Relay.

Model B discovery procedure for multi-hop U2U relay

In Model B relay discovery procedure, an end terminal device may proactively discover a relay in order to communicate with a peer end terminal device. In some example embodiments, there is provided a solution on Model B discovery procedure for multi-hop U2U relay. For example, a first terminal device may transmit a solicitation message for discovering relays for communication between the first terminal device and a second terminal device. The solicitation message may comprise a first identifier of the first terminal device, a second identifier of the second terminal device, and respective identifiers of a first set of relay terminal devices.

That is, the first terminal device, as a source terminal device, may proactively broadcast a related solicitation message to discover relays. In this way, a Mode A discovery procedure for multi-hop U2U relay is specified. Thereby, communication between the end terminal devices can be supported by multi-hop U2U relay.

Now the reference is made to FIG. 3, which illustrates a signaling chart 300 of a Model B discovery procedure according to some example embodiments of the present disclosure. As shown in FIG. 3, the signaling chart 300 involves a first terminal device 301, a second terminal device 302, a third terminal device 303-1 and a third terminal device 303-2. The first terminal device 301 such as a discoverer ProSe End UE may be an example of the end terminal device 110-1 as shown in FIG. 1. The second terminal device 302 such as discoveree ProSe End UE may be an example of the end terminal device 110-2. The third terminal device 303-1 and the third terminal device 303-2 such as ProSe UE-to-UE Relays may be examples of the relay terminal devices 120. In the following, the third terminal devices 303-1 and 303-2 may be individually referred to as “third terminal device 303” or collectively referred to as “third terminal devices 303” . Each of the first terminal device 301, the second terminal device 302 and the third terminal device 303 may be referred to as a node.

As shown in FIG. 3, the first terminal device 301 may transmit (305) a solicitation message for discovering relays for communication between the first terminal device 301 and a second terminal device 302. The solicitation message may comprise a first identifier of the first terminal device 301, a second identifier of the second terminal device 302, and respective identifiers of a first set of relay terminal devices. The first set of relay terminal devices may be known by the first terminal device 301 in any suitable manner, and the present disclosure is not limited in this regard. For purpose of discussion without any limitation, a relay terminal device in the first set of relay terminal devices may be also referred to as a relay terminal device-X. These identifiers of the terminal devices may be user info IDs of the terminal devices.

In some example embodiments, the solicitation message may include a solicitation indication of whether a terminal device has handled (for example, transmitted, received or forwarded) the solicitation message. This solicitation indication may be also referred to as an achievable discovery solicitation indication. In the following, if an achievable discovery solicitation indication for a terminal device is set as “yes” , it means that the terminal device has handled the solicitation message. Similarly, if an achievable discovery solicitation indication for a terminal device is set as “no” , it means that the terminal device has not handled the solicitation message yet.

To this end, the solicitation message transmitted by the first terminal device 301 may comprise at least one of: a solicitation indication that the first terminal device 301 transmits the solicitation message, a solicitation indication that the second terminal device 302 does not receives the solicitation message, or respective solicitation indications that the first set of relay terminal devices do not forward the solicitation message.

In some example embodiments, the solicitation message may further indicate respective hop numbers of the first set of relay terminal devices. In some example embodiments, the hop number of each node may be explicitly associated with the identifier of the node. Alternatively, or in addition, in some example embodiments, the respective hop numbers of the first set of relay terminal devices may be indicated by an order of the respective identifiers of the first set of relay terminal devices in the solicitation message.

For example, a discoverer ProSe End UE transmits a ProSe UE-to-UE Relay Discovery Solicitation message. The ProSe UE-to-UE Relay Discovery Solicitation solicitation message contains the User Info ID of the discoverer ProSe End UE with the achievable discovery solicitation indication set as “yes” , the User Info ID of a discoveree ProSe End UE with the achievable discovery solicitation indication set as “no” . Optionally, the solicitation message contains the User Info ID of the ProSe UE-to-UE relay UE-X (s) with the hop number (s) with the achievable discovery solicitations indication set as “no” . The relay UE-X (s) may be known by the discoverer ProSe End UE in any suitable manner. In this way, the hop number of a node can be explicitly associated with the User Info ID of the node. In addition, the User Info ID may be associated with achievable discovery solicitation indication, and the order of User Info IDs may indicate the hop order of the multi-hop UE-to-UE relays.

In some example embodiments, the solicitation message may further comprise hop number information. For example, the solicitation message may include a maximum hop number for relaying the communication between the first terminal device 301 and the second terminal device 302. Additionally, or alternatively, the solicitation message may comprise a current hop number for transferring the solicitation message. For example, the current hop of the Relay Discovery Solicitation message sent by the discoverer ProSe End UE may be set as 0 or 1.

In some example embodiments, the solicitation message may further comprise a type of discovery message. The type of discovery message may comprise at least one of: a terminal device-to-terminal device relay discovery procedure, a terminal device-to-terminal device relay communication procedure, a terminal device-network relay discovery procedure, a terminal device-network relay communication procedure, or a non-relay discovery procedure.

For example, the discoverer ProSe End UE transmits the solicitation message. The solicitation message contains the type of discovery message including a ProSe UE to Network (U2N) Relay Discovery, a ProSe U2U Relay Discovery and a ProSe non-relay Discovery. Optionally, the type of discovery message may include a ProSe multi-hop U2U Relay Discovery. Optionally, the type of discovery message may include a ProSe multi-hop U2N Relay Discovery.

Continuing to refer to FIG. 3, the third terminal device 303 may receive the solicitation message from the first terminal device 301. In some example embodiments, the third terminal device 303 may determine (310) whether it is comprised in the first set of relay terminal devices and handle the solicitation message based on a result of the determining.

In some example embodiments, as mentioned above, the solicitation message may indicate respective hop numbers for the first set of relay terminal devices. If the third terminal device 303 determines that it is comprised in the first set of relay terminal devices, it may update the current hop number for transferring the solicitation message. For example, the current hop number in the received solicitation message may be incremented by 1. Then, the third terminal device may compare the updated current hop number with a hop number indicated in the solicitation message for the third terminal device 303 and handle the solicitation message based on a result of the comparison.

Further, in some example embodiments, if the third terminal device 303 determines that the updated current hop number does not match the hop number indicated in the solicitation message, it may ignore the solicitation message. For example, as shown in FIG. 3, the third terminal device 303-2 may ignore (315) the solicitation message. Else if the third terminal device 303 determines that the updated current hop number matches the hop number indicated in the solicitation message and a difference between the updated current hop number and the maximum hop number is below a threshold difference, it may forward the solicitation message. For example, as shown in FIG. 3, the third terminal device 303-1 may forward (320) the solicitation message.

In the present disclosure, matching of two or more hop number may depend on a specific calculation approach of the hop number. For example, if the updated current hop number matches the hop number indicated in the solicitation message, it may mean that the current hop number is the same as the hop number indicated in the solicitation message. Moreover, the threshold difference for the updated current hop number and the maximum hop number may depend on a specific calculation approach of the hop number. In an example, the difference threshold may be 0 or 1.

For example, a UE-to-UE relay A may receive the solicitation message form the discoverer End UE and calculates the current hop number for transferring the solicitation message, for example by incrementing the current hop number as indicated in the received solicitation message by 1. If the UE-to-UE relay A belongs to the UE-to-UE relay X indicated in the solicitation message, but the calculated hop number is not the same as the hop number indicated in the solicitation message for the UE-to-UE relay A, then the UE-to-UE relay A may ignore the received solicitation message. Else if the UE-to-UE relay A belongs to the UE-to-UE relay X, and the calculated hop number is the same as the indicated hop number for the UE-to-UE relay A and not larger than the maximum hop number (or maximum hop number minus 1) as indicated in the solicitation message, then the UE-to-UE relay A may continue to forward the solicitation message.

In some example embodiments, the third terminal device 303-1 may update a solicitation indication corresponding to the third terminal device 303-1 in the solicitation message to indicate that the third terminal device 303-1 forwards the solicitation message. For example, the third terminal device 303-1 may update the achievable discovery solicitation indication corresponding to itself from “no” to “yes” .

In some example embodiments, if the third terminal device 303 determines that it is not comprised in the first set of relay terminal devices, it may update the current hop number. For example, the current hop number in the received solicitation message may be incremented by 1. Then, the third terminal device 303 may determine whether a difference between the updated current hop number and the maximum hop number is below a threshold difference. If the difference is below the threshold difference, the third terminal device may forward the solicitation message. For example, as shown in FIG. 3, the third terminal device 303-1 may forward (320) the solicitation message. Else if the difference is not below the threshold difference, the third terminal device 303 may ignore the solicitation message. For example, as shown in FIG. 3, the third terminal device 303-2 may ignore (315) the solicitation message.

Such forwarded solicitation message may comprise an identifier of the third terminal device 303-1. In other words, the third terminal device 303-1 may add its own identifier into the solicitation message. For example, the forwarded solicitation message may include the user info ID of the third terminal device 303-1. In some example embodiments, the forwarded solicitation message may further include a solicitation indication that the third terminal device 303-1 forwards the solicitation message. In other words, the third terminal device 303-1 may add a solicitation indication corresponding to itself into the solicitation message to indicate that it forwards the solicitation message. For example, an achievable discovery solicitation indication associated with the user info ID of the third terminal device 303-1 may be set as “yes” .

As an example, if the UE-to-UE relay A does not belong to UE-to-UE relay X, and the hop number is not larger than the received maximum hop number (or maximum hop number minus 1) , then the UE-to-UE relay A may continue to forward solicitation message. Else if the UE-to-UE relay A does not belong to UE-to-UE relay X, and the hop number is greater than the received maximum hop number or (maximum hop number minus 1) , then the UE-to-UE relay A may ignore the received discovery solicitation message without any discovery solicitation transmission. In the cases, the UE-to-UE relay A may add its User Info ID into the solicitation message. Accordingly, the achievable discovery solicitation indication associated with the User Info ID of the UE-to-UE relay A may be set as “yes” .

In some example embodiments, if the solicitation message received from the first terminal device 301 include the current hop number for transferring the solicitation message, the third terminal device 303-1 may update the current hop number. For example, the current hop number indicated in the received solicitation message may be incremented by 1.

It is to be understood that except for the above update to the solicitation message for forwarding, other information in the forwarded solicitation message may remain the same as that in the received solicitation message, for example, the type of discovery message, the identifier of the discoverer ProSe End UE and corresponding solicitation indication, the identifier of discoveree ProSe End UE and corresponding solicitation indication, the maximum hop number. Moreover, a third terminal device forwarding the solicitation message may match the RSC indicated in the solicitation message. This may mean that a relay UE receiving the solicitation message but not matching the RSC may ignore the received solicitation message.

Continuing to refer to FIG. 3, the second terminal device 302 may receive the solicitation message from the third terminal device 303-1. In some example embodiments, the second terminal device 302 may transmit (325) a response message for discovering the relays for the communication between the first terminal device 301 and the second terminal device 302.

The response message may comprise: the first identifier of the first terminal device 301, the second identifier of the second terminal device 302, and respective identifiers of a second set of relay terminal devices transferring the solicitation message. The second set of relay terminal devices may include those relay terminal devices which have forwarded the solicitation message, e.g., including the third terminal device 303-1. In some cases, the second set of relay terminal devices may be the same with the first set of relay terminal devices. In some cases, the second set of relay terminal devices may be partly different or totally different with the first set of relay terminal devices.

In some example embodiments, the response message may include the solicitation indications that the first terminal device 301, the second terminal device 302 and the second set of relay terminal devices has handled the solicitation message. Specifically, the response message may include at least one of: a solicitation indication that the first terminal device 301 transmits the solicitation message, a solicitation indication that the second terminal device 302 receives the solicitation message, or respective solicitation indications that the second set of relay terminal devices forward the solicitation message.

In some example embodiments, the response message may include a response indication of whether a terminal device has handled the response message. For example, the response message transmitted by the second terminal device 302 may comprise at least one of: a response indication that the first terminal device 301 does not receives the response message, a response indication that the second terminal device 302 transmits the response message, or respective response indications that the second set of relay terminal devices do not forward the response message. Such response indications may be referred to as achievable discovery response indications.

In an example, the discoveree ProSe End UE that matches the value of RSC and the user info ID of the discoveree ProSe End UE in the solicitation message may respond to the ProSe UE-to-UE Relay with a ProSe UE-to-UE relay discovery response message. The discovery response message may contain: the User Info ID of the discoverer ProSe End UE with the achievable discovery solicitation indication set as “yes” and the achievable discovery response indication set as “no” , the User Info ID (s) the ProSe UE-to-UE relay (s) with the achievable discovery solicitation indication (s) set as “yes” and the achievable discovery response indication (s) set as “no” , and User Info ID of the discoveree ProSe End UE with the achievable discovery solicitation indication set as “yes” and the achievable discovery response indication set as “yes” .

In some example embodiments, an order of the respective identifiers of the second set of relay terminal devices in the response message may correspond to an order of the second set of relay terminal devices for relaying the communication between the first terminal device 301 and the second terminal device 302.

For example, the order of the User Info IDs of the different ProSe UE-to-UE Relays in the response message may reflect the relay order of the complete UE-to-UE relay path. In the response message, all achievable discovery solicitation indications may be set as “yes” , which means the discovery solicitation message has been announced through all nodes within the UE-to-UE relay path. Optionally, the response message contains the discovery response indication with the User Info ID to indicate whether the discovery response message has passed through each node.

In some example embodiments, the response message may further comprise a type of discovery message. The type of discovery message may include at least one of: a terminal device-to-terminal device relay discovery procedure, a terminal device-to-terminal device relay communication procedure, a terminal device-network relay discovery procedure, a terminal device-network relay communication procedure, or a non-relay discovery procedure. For example, the ProSe UE-to-UE relay discovery response message contains the type of discovery message, including: a ProSe U2N Relay Discovery, a ProSe U2U Relay Discovery and a ProSe non-relay Discovery. Optionally, the type of discovery message may include a ProSe multi-hop U2U Relay Discovery. Optionally, the type of discovery message may include a ProSe multi-hop U2N Relay Discovery.

In some example embodiments, the second terminal device 302 may transmit the response message based on that an access-stratum (AS) layer criterion is met. For example, if the discoveree ProSe End UE receives multiple UE-to-UE Relay Discovery Solicitation messages from different ProSe UE-to-UE relays, it may choose to respond or not to a ProSe UE-to-UE relay, based on one or more AS layer criteria.

Continuing with FIG. 3, the third terminal device 303-1 may receive the response message from the second terminal device 302. In some example embodiments, the third terminal device 303-1 may forward (330) the response message.

In some example embodiments, the third terminal device 303-1 may forward the response message based on that an AS layer criterion is met. For example, the ProSe UE-to-UE relay may choose to respond or not to another ProSe UE-to-UE relay or the ProSe End UE based on one or more AS layer criteria.

The response message forwarded by the third terminal device 303-1 may include the information in the received response message. In some example embodiments, the third terminal device 303-1 may update a response indication corresponding to the third terminal device 303-1 in the response message to indicate that the third terminal device forwards the response message. For example, the ProSe UE-to-UE relay forwards a discovery response message which contains the information received from the discovery response message of discoveree ProSe end UE and sets the corresponding achievable discovery response indication as “yes” .

The first terminal device 301 may receive the response message from the third terminal device 303-1. From the response message, the first terminal device 301 can discover the second set of the relay terminal devices for communicating with the second terminal device 302. For example, the discoveree ProSe End UE can discover the ProSe UE-to-UE Relays indicated in the response message for communicating with the discoveree ProSe End UE.

It is to be understood that one or more third terminal devices may receive the response message and the first terminal device 301 may receive the response message from one or more third terminal devices.

Candidate relay discovery procedure

After a multi-hop relay path is established, a terminal device within the relay path (for example, an end terminal device or a relay terminal device) may determine to perform relay reselection. In some example embodiments, there is provided a solution on a negotiation procedure for candidate relay discovery for multi-hop U2U relay. For example, a first terminal device may determine a second terminal device as a candidate for replacing a relay terminal device in a relay path for communication between two end terminal devices. The relay terminal device to be replaced may be connected to the first terminal device in the relay path. The first terminal device may transmit a solicitation message for candidate relay discovery. The solicitation message may comprise a first identifier of the first terminal device, a second identifier of the second terminal device, and a third identifier of a third terminal device connected to the relay terminal device in the relay path.

That is, the first terminal device, as an initiating terminal device, may determine a candidate terminal device which can replace a current relay terminal device and actively broadcast related messages. In this way, the communication link quality between the two end terminal devices via the relay path can be ensured.

Now the reference is made to FIG. 4, which illustrates a signaling chart 400 of a candidate relay discovery procedure according to some example embodiments of the present disclosure. As shown in FIG. 4, the signaling chart 400 involves a first terminal device 401, a second terminal device 402, a third terminal device 403 and a relay terminal device 405. The first terminal device 401 may be an example of any one of the end terminal devices 110 or the relay terminal devices 120 as shown in FIG. 1. The second terminal device 402 may be an example of the relay terminal device 120 which may be taken as a candidate relay terminal device. The third terminal device 403 may be an example of any one of the end terminal devices 110 or the relay terminal devices 120. The first terminal device 401 and the third terminal device 403 are both connected to the relay terminal device 405 but in opposite direction in the relay path. The following will be described with reference to FIG. 1.

The existing relay path for communication between two end terminal devices involves the first terminal device 401, the relay terminal device 405, the third terminal device 403. In some cases, the existing relay path may be changed to a new relay path, e.g., due to the link quality.

As shown in FIG. 4, the first terminal device 401 may determine (410) the second terminal device 402 as a candidate for replacing the relay terminal device 405 in the existing relay path for communication between two end terminal devices. The relay terminal device 405 to be replaced is connected to the first terminal device 401 and the third terminal device 403 in the existing relay path, and the second terminal device 402 would be connected to the first terminal device 401 and the third terminal device 403 in the new relay path.

In other words, the first terminal device 401 initiates the candidate relay discovery procedure or relay reselection to replace a neighboring connected relay. Therefore, the first terminal device 401 may be referred to as an initiating terminal device, for example, an initiating UE. In some example embodiments, the first terminal device 401 may be an end terminal device, for example, a ProSe End UE. In such example embodiments, the procedure involves end terminal device-initiated candidate relay discovery, and the third terminal device 403 may be another relay terminal device.

Alternatively, in some example embodiments, the first terminal device 401 may be a relay terminal device in the existing relay path, for example, a ProSe UE-to-UE Relay. In such example embodiments, the procedure involves relay terminal device-initiated candidate relay discovery, and the third terminal device 403 may be another relay terminal device or an end terminal device.

The first terminal device 401 may transmit (415) a solicitation message for candidate relay discovery. The solicitation message may comprise a first identifier of the first terminal device 401, a second identifier of the second terminal device 402, and a third identifier of the third terminal device 403 connected to the relay terminal device 405 in the relay path. These identifiers may include respective user info IDs of these terminal devices.

In some example embodiments, the solicitation message may further include hop number information about the terminal devices. Specifically, the hop number information may comprise at least one of: a first hop number of the first terminal device 401 in the relay path, a second hop number of the second terminal device 402 in the relay path, and a third hop number of the third terminal device 403 in the relay path. It is to be understood that the second hop number of the second terminal device 402 may be the same as the hop number of the relay terminal device 405 in the existing relay path.

In some example embodiments, the solicitation message may further comprise solicitation indications of whether the terminal devices have handled the solicitation message, which may be also referred to as associated discovery solicitation indications. For example, the solicitation message may include at least one of: a solicitation indication that the first terminal device 401 transmits the solicitation message, a solicitation indication that the second terminal device 402 does not forward the solicitation message, a solicitation indication that the third terminal device 403 does not receive the solicitation message. For example, the solicitation indication associated with the first terminal device 401 may be set as “yes” , and the solicitation indications associated with the second terminal device 402 and the third terminal device 403 may be set as “no” .

In some example embodiments, the solicitation message may further comprise response indications of whether the terminal devices have handled a response message for the candidate relay discovery. For example, the solicitation message may include at least one of: a response indication that the first terminal device 401 does not receive a response message for the candidate relay discovery, a response indication that the second terminal device 402 does not forward a response message for the candidate relay discovery, or a response indication that the third terminal device 403 does not transmit a response message for the candidate relay discovery. For example, the response indications associated with the first terminal device 401, the second terminal device 402 and the third terminal device 403 may be set as “no” .

In some example embodiments, the solicitation message may further comprise an indication that the solicitation message is used for the candidate relay discovery. That is, the solicitation message may contain an indication to indicate that this is a candidate relay discovery procedure.

Continuing with FIG. 4, as the solicitation message may be broadcasted, the second terminal device 402 may receive the solicitation message from the first terminal device 401 and forward (420) the solicitation message. For example, if a relay terminal device matches the second identifier in the received solicitation message and the solicitation message includes the indication showing that this is a candidate relay discovery procedure, the relay terminal device may forward the solicitation message.

In some example embodiments, the second terminal device 402 may update a solicitation indication in the solicitation message to indicate that the second terminal device 402 forwards the solicitation message. In other words, in the forwarded solicitation message, the solicitation indication associated with the second terminal device 402 may be updated as “yes” .

It is to be understood that except for the above-mentioned update to the solicitation message, other information in the received solicitation message may remain the same in the forwarded solicitation message.

The third terminal device 403 may receive the forwarded solicitation message from the second terminal device 402. In some cases, if one or more conditions are fulfilled, the third terminal device 403 may transmit (425) a response message for the candidate relay discovery. In some example embodiments, if the third terminal device 403 determines that it matches the third identifier in the solicitation message and a terminal device in the relay path matches the first identifier, it may transmit the response message.

The response message may comprise the first identifier, the second identifier and the third identifier.

In some example embodiments, the response message may further include the solicitation indications. For example, the response message may comprise at least one of: a solicitation indication that the first terminal device 401 transmits the solicitation message, a solicitation indication that the second terminal device 402 forwards the solicitation message, or a solicitation indication that the third terminal device 403 receives the solicitation message. For example, in the response message transmitted by the third terminal device 403, the solicitation indications associated with the first terminal device 401, the second terminal device 402 and the third terminal device 403 are all set as “yes” .

In some example embodiments, the response message may further include the response indications. For example, the response message transmitted by the third terminal device 403 may include at least one of: a response indication that the first terminal device 401 does not receive the response message, a response indication that the second terminal device 402 does not forward the response message, or a response indication that the third terminal device 403 transmits the response message. For example, the response indication associated with the third terminal device 403 may be set as “yes” , and the response indications associated with the first terminal device 401 and the second terminal device 402 may be set as “no” .

In some example embodiments, the response message may further comprise an indication that the response message is used for the candidate relay discovery.

In some example embodiments, if the second terminal device 402 determines that it matches the second identifier in the received response message, it may forward the response message to the first terminal device 401. Correspondingly, the second terminal device 402 may update a response indication in the response message to indicate that it forwards the response message. For example, the response indication associated with the second terminal device 402 may be updated to “yes” in the response message forwarded by the second terminal device 402.

The first terminal device 401 may receive the forwarded response message from the second terminal device 402.

In some example embodiments, the first terminal device 401 may determine the second terminal device 402 as the candidate relay terminal device if it determines that at least one condition is fulfilled. The at least one condition may include that the first terminal device 401 matches the first identifier in the received response message. For example, the ProSe End UE matches the User Info ID of the 5G ProSe UE-to-UE relay discovery response message.

Additionally, and alternatively, the at least one condition may include that a terminal device in the relay path matches the third identifier in the received response message. For example, the third identifier in the received response message matches one of the current UE-to-UE relays within the multi-hop path.

Additionally, and alternatively, the at least one condition may include that the response message comprises a solicitation indication that the first terminal device 401 transmits the solicitation message, a solicitation indication that the second terminal device 402 forwards the solicitation message, and a solicitation indication that the third terminal device 403 receives the solicitation message. For example, all associated discovery solicitation indications are set as “yes” .

Additionally, and alternatively, the at least one condition may include that the response message comprises a response indication that the first terminal device 401 does not receive the response message, a response indication that the second terminal device 402 forwards the response message, or a response indication that the third terminal device 403 transmits the response message. For example, the response indication associated to each User Info ID are set as “yes” except the associated discovery response indication of the first terminal device 401.

Additionally, and alternatively, the at least one condition may include that the response message comprises an indication that the response message is used for the candidate relay discovery. That is, this indication of the relay discovery response message may show that it is a candidate relay discovery procedure.

In some example embodiments, the first terminal device 401 may comprise one of the two end terminal devices, the third terminal device 403 may comprise a further relay terminal device. For example, the first terminal device 401 may be a source remote terminal device or a target remote terminal device. In such example embodiments, the end terminal device initiates the candidate relay discovery.

Now the reference is made to FIG. 5A, which illustrates a signaling chart 500A of a candidate relay discovery procedure initiated by an end UE according to some example embodiments of the present disclosure. As shown in FIG. 5A, the signaling chart 500A involves an end UE 501, a relay candidate 502-1, a relay candidate 502-2, a relay UE 503, an end UE 504 and a relay UE 505. The existing relay path involves the end UE 501, the relay UE 505, the relay UE 503, and the end UE 504. The end UE 501 and end UE 504 may be ProSe End UEs, and the relay candidate 502-1, the relay candidate 502-2, the relay UE 503, and a relay UE 505 may be ProSe UE-to-UE Relays.

The end UE 501 keeps detecting whether there is more suitable relay UE (for example with AS layer and higher layer criteria) , to replace its neighboring connected relay UE, e.g., the relay UE 505.

The end UE 501 transmits a relay discovery solicitation message. In the discovery solicitation message, the RSC is not included, and the User Info IDs of candidate UE relays (as the first hop) and the existing relay UE which is previously connected to the neighboring connected relay UE 505 may be included. The user info ID of the end UE 504 may not be included in the relay discovery solicitation message. As shown in FIG. 5A, the candidate UE relays include the relay candidate 502-1 and the relay candidate 502-2, which may be collectively referred to as “relay candidates 502” or individually referred to as “relay candidate 502” .

The relay discovery solicitation message may include the user info ID of the involved UE, the hop number of the involved UE, an associated discovery solicitation indication, and an associated discovery response indication. For example, the end UE 501 may have the hop number 0/1 with the associated discovery solicitation indication set as “yes” and the associated discovery response indication set as “no” . The relay candidate 502 may have the hop number 1/2 with the associated discovery solicitation indication set as “no” and the associated discovery response indication set as “no” . The existing relay UE 503 may have the hop number 2/3 with the associated discovery solicitation indication set as “no” and the associated discovery response indication set as “no” .

Optionally, the relay discovery solicitation message may contain an indication to indicate that this is a candidate relay discovery procedure.

If a relay UE matches the User Info ID of a relay candidate received in the relay discovery solicitation message, and the indication shows that this is a candidate relay discovery procedure, the relay UE may forward the relay discovery solicitation message. In this example, the relay candidate 502 forwards the relay discovery solicitation message. In the forwarded relay discovery solicitation message, the associated discovery solicitation indication corresponding to the User Info ID of the relay UE may be updated as “yes” .

For example, in the forwarded relay discovery solicitation message, the user info ID of the relay candidate, e.g., the relay candidate 502-1, may be associated with the hop number 1/2 with the associated discovery solicitation indication updated as “yes” and the associated discovery response indication set as “no” .

If a relay UE 503 matches the User Info ID of an existing relay UE within this multi-hop path in the relay discovery solicitation message, and the end UE 501 of current multi-hop path matches the User Info ID of the relay discovery solicitation message, and optionally, if the indication of the solicitation message shows that this is a candidate relay discovery procedure, the relay UE 503 may transmit a relay discovery response message with the associated discovery solicitation and the associated discovery response corresponding to the user info ID of the relay UE 503 updated as “yes” .

The relay discovery response message may include the user info ID of the involved UE, the hop number of the involved UE, an associated discovery solicitation indication, and an associated discovery response indication. For example, the end UE 501 may have the hop number 0/1 with the associated discovery solicitation indication set as “yes” and the associated discovery response indication set as “no” . The relay candidate 502 may have the hop number 1/2 with the associated discovery solicitation indication set as “yes” and the associated discovery response indication set as “no” . The existing relay UE 503 may have the hop number 2/3 with the associated discovery solicitation indication set as “yes” and the associated discovery response indication set as “yes” .

The relay candidates 502 may perform similar handling for the relay discovery response message to the relay discovery solicitation message. The relay candidates 503 may forward the relay discovery response message, as shown in FIG. 5A.

The end UE 501 may determine a candidate based on the user info IDs of the candidate relay UEs indicated in the response message and regard the candidate as one relay candidate and trigger the candidate ProSe UE-to-UE relay up to its decision, if the following conditions are met:

the end UE 501 matches the User Info ID of the relay discovery response message;

the User Info ID of the existing relay UE matches one of the current UE relays within the multi-hop path;

the associated discovery solicitation indication and associated discovery solicitation indication for each User Info ID are set as “yes” except its own associated discovery response indication;

optionally, this indication of the response message indicates that this is a candidate relay discovery procedure.

In this way, the end UE 501 may initiate a candidate relay discovery procedure and replace the relay UE 505 as the relay candidate 502-1 or the relay candidate 502-2.

In some other example embodiments, the first terminal device 401 may comprise a further relay terminal device, and the third terminal device 403 may comprise another relay terminal device or one of the two end terminal devices depending on the location of the third terminal device 403 in the relay path. For example, the first terminal device 401 may be a neighbor relay terminal device or a relay terminal device in proximity to the relay terminal device 405. In such example embodiments, the relay terminal device initiates the candidate relay discovery.

Now the reference is made to FIG. 5B, which illustrates a signaling chart 500B of a candidate relay discovery procedure according to some example embodiments of the present disclosure. As shown in FIG. 5B, the signaling chart 500B involves the end UE 501, the relay candidate 502-1, the relay candidate 502-2, the relay UE 503, the end UE 504 and the relay UE 505. The existing relay path involves the end UE 501, the relay UE 505, the relay UE 503, and the end UE 504. The end UE 501 and end UE 504 may be ProSe End UEs, and the relay candidate 502-1, the relay candidate 502-2, the relay UE 503, and a relay UE 505 may be ProSe UE-to-UE Relays.

The difference between the example of FIG. 5A and the example of FIG. 5B is that: the end UE 501 initiates the candidate relay discovery procedure in the example of FIG. 5A, and the relay UE 503 initiates the candidate relay discovery procedure in the example of FIG. 5B.

The relay UE 503, which has already been selected by the end UE 501, keeps detecting whether there is more suitable relay UEs (for example with AS layer and higher layer criteria) , to replace its neighboring connected relay UE, e.g., the relay UE 505.

The relay UE 503 transmits a relay discovery solicitation message. In the relay discovery solicitation message, the RSC is not included, and the User Info IDs of candidate UE relays and the existing relay UE which is previously connected to the neighboring connected relay UE 505 may be included. As shown in FIG. 5B, the candidate UE relays include the relay candidate 502-1 and the relay candidate 502-2, which may be collectively referred to as “relay candidates 502” or individually referred to as “relay candidate 502” .

The relay discovery solicitation message may include the user info ID of the involved UE, the hop number of the involved UE, an associated discovery solicitation indication, and an associated discovery response indication. For example, the relay UE 503 may have the hop number 0/1 with the associated discovery solicitation indication set as “yes” and the associated discovery response indication set as “no” . The relay candidate, relay candidate 502 may have the hop number 1/2 with the associated discovery solicitation indication set as “no” and the associated discovery response indication set as “no” . The existing relay UE or the end UE connected to the relay UE 505 to be replaced (which is the end UE 501 in this example) may have the hop number 2/3 with the associated discovery solicitation indication set as “no” and the associated discovery response indication set as “no” .

If a UE matches the User Info ID of an existing relay UE or the end UE within this multi-hop path in the relay discovery solicitation message, and another UE in the current multi-hop path matches the User Info ID of the relay discovery solicitation message, the UE may transmit a relay discovery response message with the associated discovery solicitation and the associated discovery response corresponding to the user info ID of the UE updated as “yes” . In this example, the end UE 501 transmits the relay discovery response message.

The relay discovery response message may include the user info ID of the involved UE, the hop number of the involved UE, an associated discovery solicitation indication, and an associated discovery response indication. For example, the initiating relay UE 503 may have the hop number 0/1 with the associated discovery solicitation indication set as “yes” and the associated discovery response indication set as “no” . The relay candidate 502 may have the hop number 1/2 with the associated discovery solicitation indication set as “yes” and the associated discovery response indication set as “no” . The end UE 501 may have the hop number 2/3 with the associated discovery solicitation indication set as “yes” and the associated discovery response indication set as “yes” .

The relay candidates 502 may perform similar handling for the relay discovery response message to the relay discovery solicitation message. The relay candidates 502 may forward the relay discovery response message, as shown in FIG. 5A.

The relay UE 503 may determine a candidate based on the user info IDs of the candidate relay UEs indicated in the response message and regard the candidate as one relay candidate and trigger the candidate ProSe UE-to-UE relay up to its decision, if the following conditions are met:

the relay UE 503 matches the User Info ID of the discovery response message;

the User Info ID of the existing relay UE matches one of the current UE relay within the multi-hop path or the User Info ID of the end UE in the response message matches an end UE of the multi-hop path;

all associated discovery solicitation indication and associated discovery indication associated to each User Info ID are set as “yes” except its own associated discovery response indication;

optionally, this indication of the relay discovery response message may indicate that this is a candidate relay discovery procedure.

In this way, the relay UE 503 may initiate a candidate relay discovery procedure and replace the relay UE 505 as the relay candidate 502-1 or the relay candidate 502-2.

In the above examples as described with reference to FIG. 5A and FIG. 5Bm once one or more PC5 RSRP criteria is satisfied, the initiating UE, which is the end UE 501 in the example of FIG. 5A or the relay UE 503 in the example of FIG. 5B, may indicate to upper layer.

AS layer criteria for candidate relay

The above describes some new solutions about discovery procedures, and the following will describe an AS criterion to support 5G ProSe Discovery for multi-hop U2U relay. In this solution, a terminal device may obtain a measurement result of a signal strength associated with a first relay terminal device. Then the terminal device may determine a hop number of the first relay terminal device in a relay path based on the measurement result and respective ranges of the signal strength for a plurality of hop numbers. The relay path may be used for communication between two end terminal devices.

In this way, whether a candidate relay is a suitable relay terminal device and the position of the candidate relay in the multi-hop relay path can be determined. This can facilitate a multi-hop relay path with a high link quality.

Now the reference is made to FIG. 6, which illustrates a signaling chart 600 of handling a candidate relay according to some example embodiments of the present disclosure. As shown in FIG. 6, the signaling chart 600 involves a device 602 and a terminal device 601. The terminal device 601 may be an example of any one of the end terminal devices 110 and the relay terminal devices 120. In some example embodiments, the terminal device 601 may be an end terminal device, such as a ProSe End UE, and the device 602 may be a network device. In some example embodiments, the terminal device 601 may be a relay terminal device, such as a ProSe relay, and the device 602 may be the network device or an end terminal device.

The terminal device 601 may receive (605) a threshold configuration from the device 602. The threshold configuration may indicate one or more thresholds for a signal strength. For example, if the terminal device 601 is an end terminal device, the network device may configure the thresholds to the end terminal device. If the terminal device is a relay terminal device, the network device may configure the thresholds or the end terminal device may indicate the thresholds to the relay terminal device.

In some example embodiments, the threshold may be configured per hop number. For example, each hop number may be configured with an upper threshold for the signal strength and a lower threshold for the signal strength.

The signal strength may be any suitable link quality metric. In some example embodiments, the signal strength may be RSRP. Further, in some example embodiment, the RSRP may comprise at least one of: a sidelink (SL) -RSRP, or a sidelink discovery (SD) -RSRP. For example, a PC5-RSRP may include SL-RSRP or SD-RSRP.

The terminal device 601 may obtain (610) a measurement result of a signal strength associated with a first relay terminal device. The first relay terminal device may be one of relay candidates. That is, the terminal device 601 may obtain the measurement result of the signal strength of all relay candidates.

In some example embodiments, the measurement result may be obtained by measuring at least one of: a relay discovery announcement message from the first relay terminal device, a relay discovery solicitation message from the first relay terminal device, a relay discovery response message from the first relay terminal device, or sidelink data transmission from the first relay terminal device. For example, the terminal device 601 may be a 5G ProSe End UE and take sidelink RSRP measurement on at least one of the following messages: Relay Discovery announcement message, Relay Discovery solicitation message, Relay Discovery response message, or other sidelink data transmission.

The terminal device 601 may determine (615) a hop number of the first relay terminal device in a relay path based on the measurement result and respective ranges of the signal strength for a plurality of hop numbers. The relay path is used for communication between two end terminal devices. The plurality of hop numbers may be configured with different requirements for the signal strength, for example, RSRP. As used herein, the term “range” may include a single value, multiple values or a continuous range of values.

For example, the terminal device 601 may decide whether a relay UE is suitable to be as a candidate relay UE. Furthermore, based on the configured upper and lower thresholds (such as PC5 RSRP thresholds) , the terminal device 601 may further decide which hop shall this candidate relay UE be.

In some example embodiments, respective ranges of the signal strength may be associated with at least one of: a relay discovery announcement message, a relay discovery solicitation message, a relay discovery response message, or sidelink data transmission. For example, a configured PC5 RSRP threshold may be associated with the following messages: SL data transmission, Relay Discovery announcement message, Relay Discovery solicitation message, or Relay Discovery response message.

Continuing with FIG. 6, in some example embodiments, the terminal device 601 may comprise one of the two end terminal devices, and a rang of the signal strength for a hop number of the plurality of hop numbers may be defined by an upper threshold and a lower threshold configured by a network device.

In some example embodiments, the end terminal device may perform the measurement of the signal strength, and thus obtain the measurement result.

Alternatively, or in addition, in some example embodiments, a second relay terminal device may perform the measurement of the signal strength associated with the first terminal device. In this case, the terminal device 601 may receive the measurement result from the second relay terminal device in a message. The message may include in at least one of: a relay discovery announcement message, a relay discovery solicitation message, or a relay discovery response message.

In some example embodiments, the terminal device 601 may comprise a second relay terminal device, and a rang of the signal strength for a hop number of the plurality of hop numbers is defined by: an upper threshold and a lower threshold configured by a network device, or an upper threshold and a lower threshold indicated by one of the two end terminal devices. For example, the PC5-RSRP threshold configuration may come from the network device, or a 5G ProSe End UE via PC5-radio resource control (RRC) signalling. In this way, the relay UE may measure the signal strength and determine the hop number.

In this case, the terminal device 601 may transmit, to at least one of the two end terminal devices, an indication of the determined hop number of the first relay terminal device. That is, if the relay UE measures the signal strength and determines the hop number, it may inform the end UE of the related information. In some example embodiments, the indication may be comprised in at least one of: a relay discovery announcement message, a relay discovery solicitation message, or a relay discovery response message.

In some example embodiments, the measurement result may be transmitted from a terminal device to another terminal device within a RRC container into a message. The message may include at least one of: a relay discovery announcement message, a relay discovery solicitation message, or a relay discovery response message. For example, the measurement of the PC5-RSRP to other candidate relay UEs from a relay UE or an end UE may be carried within a RRC container into one of the following messages: Relay Discovery announcement message, Relay Discovery solicitation message, or Relay Discovery response message.

Example methods, and devices

FIG. 7A illustrates a flowchart of a communication method 700A implemented at a first terminal device (e.g., the first terminal device 201 in FIG. 2) in accordance with some embodiments of the present disclosure.

At block 710, the first terminal device obtains first information about at least one terminal device in proximity of the first terminal device, the first information comprising second information about an end terminal device provided with a relay service by a relay terminal device of the at least one terminal device.

At block 720, the first terminal device transmits an announcement message for relay discovery, the announcement message at least comprising the first information.

In some example embodiments, the second information comprises at least one of: an identifier of the end terminal device, a hop number from the first terminal device to the end terminal device, or a sequence of relay terminal devices through which the end terminal device is communicable.

In some example embodiments, the first information further comprises at least one of: an identifier of the at least one terminal device, a user type of the at least one terminal device.

In some example embodiments, the announcement message further comprises a type of discovery message comprising at least one of: a terminal device-to-terminal device relay discovery procedure, a terminal device-to-terminal device relay communication procedure, a terminal device-network relay discovery procedure, a terminal device-network relay communication procedure, or a non-relay discovery procedure.

FIG. 7B illustrates a flowchart of a communication method 700B implemented at a second terminal device (e.g., the second terminal device 202-1 or the second terminal device 202-2 in FIG. 2) in accordance with some embodiments of the present disclosure.

At block 730, the second terminal device monitors an announcement message for relay discovery from a first terminal device, the announcement message comprising first information about at least one terminal device in proximity of the first terminal device, and wherein the first information comprises second information about an end terminal device provided with a relay service by a relay terminal device of the at least one terminal device.

In some example embodiments, the second terminal device determines, based on the announcement message, a proximity-based service for connecting to a peer terminal device associated with the second terminal device.

In some example embodiments, the second information comprises at least one of: an identifier of the end terminal device, a hop number from the first terminal device to the end terminal device, or a sequence of relay terminal devices through which to achieve the end terminal device.

FIG. 8A illustrates a flowchart of a communication method 800A implemented at a first terminal device (e.g., the first terminal device 301 in FIG. 3) in accordance with some embodiments of the present disclosure.

At block 810, the first terminal device transmits a solicitation message for discovering relays for communication between the first terminal device and a second terminal device, the solicitation message comprising: a first identifier of the first terminal device, a second identifier of the second terminal device, and respective identifiers of a first set of relay terminal devices.

In some example embodiments, the solicitation message further comprises at least one of: a solicitation indication that the first terminal device transmits the solicitation message, a solicitation indication that the second terminal device does not receive the solicitation message, or respective solicitation indications that the first set of relay terminal devices do not forward the solicitation message.

In some example embodiments, the solicitation message further indicates respective hop numbers of the first set of relay terminal devices.

In some example embodiments, the respective hop numbers are indicated by an order of the respective identifiers of the first set of relay terminal devices in the solicitation message.

In some example embodiments, the solicitation message further comprises at least one of: a maximum hop number for relaying the communication between the first and second terminal devices, or a current hop number for transferring the solicitation message.

In some example embodiments, the solicitation message further comprises a type of discovery message comprising at least one of: a terminal device-to-terminal device relay discovery procedure, a terminal device-to-terminal device relay communication procedure, a terminal device-network relay discovery procedure, a terminal device-network relay communication procedure, or a non-relay discovery procedure.

In some example embodiments, the first terminal device receives, from a third terminal device, a response message for discovering the relays for the communication between the first and second terminal devices, the response message comprising: the first identifier of the first terminal device, the second identifier of the second terminal device, and respective identifiers of a second set of relay terminal devices transferring the solicitation message.

FIG. 8B illustrates a flowchart of a communication method 800 B implemented at a second terminal device (e.g., the second terminal device 302 in FIG. 3) in accordance with some embodiments of the present disclosure.

At block 820, the second terminal device receives, from a third terminal device, a solicitation message for discovering relays for communication between a first terminal device and the second terminal device, the solicitation message comprising: a first identifier of the first terminal device, a second identifier of the second terminal device, and respective identifiers of a first set of relay terminal devices.

In some example embodiments, the second terminal device transmits a response message for discovering the relays for the communication between the first and second terminal devices, the response message comprising: the first identifier of the first terminal device, the second identifier of the second terminal device, and respective identifiers of a second set of relay terminal devices transferring the solicitation message.

In some example embodiments, the response message is transmitted based on that an access-stratum layer criterion is met.

In some example embodiments, an order of the respective identifiers of the second set of relay terminal devices corresponds to an order of the second set of relay terminal devices for relaying the communication between the first and second terminal devices.

In some example embodiments, the response message comprises at least one of: a solicitation indication that the first terminal device transmits the solicitation message, a solicitation indication that the second terminal device receives the solicitation message, or respective solicitation indications that the second set of relay terminal devices forward the solicitation message.

In some example embodiments, the response message comprises at least one of: a response indication that the first terminal device does not receives the response message, a response indication that the second terminal device transmits the response message, or respective response indications that the second set of relay terminal devices do not forward the response message.

In some example embodiments, the response message further comprises a type of discovery message comprising at least one of: a terminal device-to-terminal device relay discovery procedure, a terminal device-to-terminal device relay communication procedure, a terminal device-network relay discovery procedure, a terminal device-network relay communication procedure, or a non-relay discovery procedure.

FIG. 8C illustrates a flowchart of a communication method 800C implemented at a third terminal device (e.g., the third terminal device 303-1 or the third terminal device 303-2 in FIG. 3) in accordance with some embodiments of the present disclosure.

At block 830, the third terminal device receives a solicitation message for discovering relays for communication between a first terminal device and a second terminal device, the solicitation message comprising: a first identifier of the first terminal device, a second identifier of the second terminal device, and respective identifiers of a first set of relay terminal devices.

At block 840, the third terminal device determines whether the third terminal device is comprised in the first set of relay terminal devices.

At block 850, the third terminal device handles the solicitation message based on a result of the determining.

In some example embodiments, the solicitation message further indicates respective hop numbers for the first set of relay terminal devices, and the third terminal device is further caused to: in accordance with a determination that the third terminal device is comprised in the first set of relay terminal devices, update the current hop number; compare the updated current hop number with a hop number indicated in the solicitation message for the third terminal device; and handle the solicitation message based on a result of the comparison.

In some example embodiments, the third terminal device, in accordance with a determination that the updated current hop number does not match the hop number indicated in the solicitation message, ignores the solicitation message; and in accordance with a determination that the updated current hop number matches the hop number indicated in the solicitation message and a difference between the updated current hop number and the maximum hop number is below a threshold difference, forward the solicitation message.

In some example embodiments, the third terminal device updates a solicitation indication corresponding to the third terminal device in the solicitation message to indicate that the third terminal device forwards the solicitation message.

In some example embodiments, the respective hop numbers are indicated by an order of the respective identifiers of the one or more relay terminal devices in the solicitation message.

In some example embodiments, the third terminal device, in accordance with a determination that the third terminal device is not comprised in the first set of relay terminal devices, updates the current hop number; determines whether a difference between the updated current hop number and the maximum hop number is below a threshold difference; in accordance with a determination that the difference is below the threshold difference, forwards the solicitation message, the forwarded solicitation message comprising an identifier of the third terminal device; and in accordance with a determination that the difference is not below the threshold difference, ignores the solicitation message.

In some example embodiments, the third terminal device adds a solicitation indication corresponding to the third terminal device into the solicitation message to indicate that the third terminal device forwards the solicitation message.

In some example embodiments, the third terminal device receives a response message for discovering the relays for the communication between the first and second terminal devices, the response message comprising: the first identifier of the first terminal device, the second identifier of the second terminal device, and respective identifiers of a second set of relay terminal devices transferring the solicitation message; and transmit the response message.

In some example embodiments, the third terminal device updates a response indication corresponding to the third terminal device in the response message to indicate that the third terminal device forwards the response message.

FIG. 9A illustrates a flowchart of a communication method 900A implemented at a first terminal device (e.g., the first terminal device 401 in FIG. 4) in accordance with some embodiments of the present disclosure.

At block 910, the first terminal device determines a second terminal device as a candidate for replacing a relay terminal device in a relay path for communication between two end terminal devices, wherein the relay terminal device is connected to the first terminal device in the relay path.

At block 920, the first terminal device transmits a solicitation message for candidate relay discovery, the solicitation message comprising: a first identifier of the first terminal device, a second identifier of the second terminal device, and a third identifier of a third terminal device connected to the relay terminal device in the relay path.

In some example embodiments, the solicitation message further comprises at least one of: a first hop number of the first terminal device in the relay path, a second hop number of the second terminal device in the relay path, and a third hop number of the third terminal device in the relay path.

In some example embodiments, the solicitation message further comprises at least one of: a solicitation indication that the first terminal device transmits the solicitation message, a solicitation indication that the second terminal device does not forward the solicitation message, a solicitation indication that the third terminal device does not receive the solicitation message, a response indication that the first terminal device does not receive a response message for the candidate relay discovery, a response indication that the second terminal device does not forward a response message for the candidate relay discovery, or a response indication that the third terminal device does not transmit a response message for the candidate relay discovery.

In some example embodiments, the solicitation message further comprises an indication that the solicitation message is used for the candidate relay discovery.

In some example embodiments, the first terminal device receives, from the second terminal device, a response message for the candidate relay discovery, wherein the response message comprises the first identifier, the second identifier and the third identifier.

In some example embodiments, the first terminal device determines the second terminal device as a candidate relay terminal device in accordance with a determination of at least one of: that the first terminal device matches the first identifier, that a terminal device in the relay path matches the third identifier, that the response message comprises a solicitation indication that the first terminal device transmits the solicitation message, a solicitation indication that the second terminal device forwards the solicitation message, and a solicitation indication that the third terminal device receives the solicitation message, that the response message comprises a response indication that the first terminal device does not receive the response message, a response indication that the second terminal device forwards the response message, or a response indication that the third terminal device transmits the response message, or that the response message comprises an indication that the response message is used for the candidate relay discovery.

In some example embodiments, the first terminal device comprises one of the two end terminal devices, the third terminal device comprises a further relay terminal device.

In some example embodiments, the first terminal device comprises a further relay terminal device, and the third terminal device comprises another relay terminal device or one of the two end terminal devices.

FIG. 9B illustrates a flowchart of a communication method 900B implemented at a second terminal device (e.g., the second terminal device 402 in FIG. 4) in accordance with some embodiments of the present disclosure.

At block 930, the second terminal device receives, from a first terminal device, a solicitation message for candidate relay discovery, the solicitation message comprising: a first identifier of the first terminal device, a second identifier of a second terminal device determined as a candidate for replacing a relay terminal device in a relay path for communication between two end terminal devices, wherein the relay terminal device is connected to the first terminal device in the relay path, and a third identifier of a third terminal device connected to the relay terminal device in the relay path.

In some example embodiments, the second terminal device, in accordance with a determination that the second terminal device matches the second identifier in the solicitation message, forwards the solicitation message to the third terminal device.

In some example embodiments, the second terminal device updates a solicitation indication in the solicitation message to indicate that the second terminal device forwards the solicitation message.

In some example embodiments, the second terminal device receives, from a third terminal device, a response message for the candidate relay discovery, wherein the response message comprises the first identifier, the second identifier and the third identifier.

In some example embodiments, the second terminal device, in accordance with a determination that the second terminal device matches the second identifier, forwards the response message to the first terminal device.

In some example embodiments, the second terminal device updates a response indication in the response message to indicate that the second terminal device forwards the response message.

FIG. 9C illustrates a flowchart of a communication method 900C implemented at a third terminal device (e.g., the third terminal device 403 in FIG. 4) in accordance with some embodiments of the present disclosure.

At block 940, the third terminal device receives, from a second terminal device, a solicitation message for candidate relay discovery, the solicitation message comprising: a first identifier of a first terminal device initiating the candidate relay discovery, a second identifier of the second terminal device, wherein the second terminal device is determined as a candidate for replacing a relay terminal device in a relay path for communication between two end terminal devices, wherein the relay terminal device is connected to the first terminal device and the third terminal device in the relay path, and a third identifier of the third terminal device.

In some example embodiments, the third terminal device, in accordance with a determination that the third terminal device matches the third identifier in the solicitation message and a terminal device in the relay path matches the first identifier, transmits a response message for the candidate relay discovery, and wherein the response message comprises the first identifier, the second identifier and the third identifier.

In some example embodiments, the response message further comprises at least one of: a solicitation indication that the first terminal device transmits the solicitation message, a solicitation indication that the second terminal device forwards the solicitation message, a solicitation indication that the third terminal device receives the solicitation message, a response indication that the first terminal device does not receive the response message, a response indication that the second terminal device does not forward the response message, or a response indication that the third terminal device transmits the response message.

In some example embodiments, the response message further comprises an indication that the response message is used for the candidate relay discovery.

In some example embodiments, the first terminal device comprises one of the two end terminal devices, and the third terminal device comprises a further relay terminal device.

FIG. 10 illustrates a flowchart of a communication method 1000 implemented at a terminal device (e.g., the terminal device 601 in FIG. 6) in accordance with some embodiments of the present disclosure.

At block 1010, the terminal device obtains a measurement result of a signal strength associated with a first relay terminal device.

At block 1020, the terminal device determines a hop number of the first relay terminal device in a relay path based on the measurement result and respective ranges of the signal strength for a plurality of hop numbers, wherein the relay path is used for communication between two end terminal devices.

In some example embodiments, the measurement result is obtained by measuring at least one of: a relay discovery announcement message from the first relay terminal device, a relay discovery solicitation message from the first relay terminal device, a relay discovery response message from the first relay terminal device, or sidelink data transmission from the first relay terminal device.

In some example embodiments, respective ranges of the signal strength are associated with at least one of: a relay discovery announcement message, a relay discovery solicitation message, a relay discovery response message, or sidelink data transmission.

In some example embodiments, the signal strength comprises a Reference Singal Receiving Power (RSRP) .

In some example embodiments, the RSRP comprises at least one of: a sidelink RSRP, or a sidelink discovery RSRP.

In some example embodiments, the terminal device comprises one of the two end terminal devices, and a rang of the signal strength for a hop number of the plurality of hop numbers is defined by an upper threshold and a lower threshold configured by a network device.

In some example embodiments, the terminal device receives the measurement result from a second relay terminal device in at least one of: a relay discovery announcement message, a relay discovery solicitation message, or a relay discovery response message.

In some example embodiments, the terminal device comprises a second relay terminal device, and a rang of the signal strength for a hop number of the plurality of hop numbers is defined by: an upper threshold and a lower threshold configured by a network device, or an upper threshold and a lower threshold indicated by one of the two end terminal devices.

In some example embodiments, the terminal device transmits, to at least one of the two end terminal devices, an indication of the determined hop number of the first relay terminal device.

In some example embodiments, the indication is comprised in at least one of: a relay discovery announcement message, a relay discovery solicitation message, or a relay discovery response message.

FIG. 11 is a simplified block diagram of a device 1100 that is suitable for implementing embodiments of the present disclosure. The device 1100 can be considered as a further example implementation of any of the devices as shown in FIG. 1. Accordingly, the device 1100 can be implemented at or as at least a part of the end terminal device 110 or the relay terminal device 120.

As shown, the device 1100 includes a processor 1110, a memory 1120 coupled to the processor 1110, a suitable transceiver 1140 coupled to the processor 1110, and a communication interface coupled to the transceiver 1140. The memory 1120 stores at least a part of a program 1130. The transceiver 1140 may be for bidirectional communications or a unidirectional communication based on requirements. The transceiver 1140 may include at least one of a transmitter 1142 and a receiver 1144. The transmitter 1142 and the receiver 1144 may be functional modules or physical entities. The transceiver 1140 has at least one antenna to facilitate communication, though in practice an Access Node mentioned in this application may have several ones. The communication interface may represent any interface that is necessary for communication with other network elements, such as X2/Xn interface for bidirectional communications between eNBs/gNBs, S1/NG interface for communication between a Mobility Management Entity (MME) /Access and Mobility Management Function (AMF) /SGW/UPF and the eNB/gNB, Un interface for communication between the eNB/gNB and a relay node (RN) , or Uu interface for communication between the eNB/gNB and a terminal device.

The program 1130 is assumed to include program instructions that, when executed by the associated processor 1110, enable the device 1100 to operate in accordance with the embodiments of the present disclosure, as discussed herein with reference to FIGS. 1 to 10. The embodiments herein may be implemented by computer software executable by the processor 1110 of the device 1100, or by hardware, or by a combination of software and hardware. The processor 1110 may be configured to implement various embodiments of the present disclosure. Furthermore, a combination of the processor 1110 and memory 1120 may form processing means 1150 adapted to implement various embodiments of the present disclosure.

The memory 1120 may be of any type suitable to the local technical network and may be implemented using any suitable data storage technology, such as a non-transitory computer readable storage medium, semiconductor based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory and removable memory, as non-limiting examples. While only one memory 1120 is shown in the device 1100, there may be several physically distinct memory modules in the device 1100. The processor 1110 may be of any type suitable to the local technical network, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multicore processor architecture, as non-limiting examples. The device 1100 may have multiple processors, such as an application specific integrated circuit chip that is slaved in time to a clock which synchronizes the main processor.

According to embodiments of the present disclosure, a first terminal device comprising a circuitry is provided. The circuitry is configured to: obtain first information about at least one terminal device in proximity of the first terminal device, the first information comprising second information about an end terminal device provided with a relay service by a relay terminal device of the at least one terminal device; and transmit an announcement message for relay discovery, the announcement message at least comprising the first information. According to embodiments of the present disclosure, the circuitry may be configured to perform any method implemented by the first terminal device as discussed above.

According to embodiments of the present disclosure, a second terminal device comprising a circuitry is provided. The circuitry is configured to: monitor an announcement message for relay discovery from a first terminal device, the announcement message comprising first information about at least one terminal device in proximity of the first terminal device, and wherein the first information comprises second information about an end terminal device provided with a relay service by a relay terminal device of the at least one terminal device. According to embodiments of the present disclosure, the circuitry may be configured to perform any method implemented by the second terminal device as discussed above.

According to embodiments of the present disclosure, a first terminal device comprising a circuitry is provided. The circuitry is configured to: transmit a solicitation message for discovering relays for communication between the first terminal device and a second terminal device, the solicitation message comprising: a first identifier of the first terminal device, a second identifier of the second terminal device, and respective identifiers of a first set of relay terminal devices. According to embodiments of the present disclosure, the circuitry may be configured to perform any method implemented by the first terminal device as discussed above.

According to embodiments of the present disclosure, a second terminal device comprising a circuitry is provided. The circuitry is configured to: receive, from a third terminal device, a solicitation message for discovering relays for communication between a first terminal device and the second terminal device, the solicitation message comprising: a first identifier of the first terminal device, a second identifier of the second terminal device, and respective identifiers of a first set of relay terminal devices. According to embodiments of the present disclosure, the circuitry may be configured to perform any method implemented by the second terminal device as discussed above.

According to embodiments of the present disclosure, a third terminal device comprising a circuitry is provided. The circuitry is configured to: receive a solicitation message for discovering relays for communication between a first terminal device and a second terminal device, the solicitation message comprising: a first identifier of the first terminal device, a second identifier of the second terminal device, and respective identifiers of a first set of relay terminal devices; determine whether the third terminal device is comprised in the first set of relay terminal devices; and handle the solicitation message based on a result of the determining. According to embodiments of the present disclosure, the circuitry may be configured to perform any method implemented by the third terminal device as discussed above.

According to embodiments of the present disclosure, a first terminal device comprising a circuitry is provided. The circuitry is configured to: determine a second terminal device as a candidate for replacing a relay terminal device in a relay path for communication between two end terminal devices, wherein the relay terminal device is connected to the first terminal device in the relay path; and transmit a solicitation message for candidate relay discovery, the solicitation message comprising: a first identifier of the first terminal device, a second identifier of the second terminal device, and a third identifier of a third terminal device connected to the relay terminal device in the relay path. According to embodiments of the present disclosure, the circuitry may be configured to perform any method implemented by the first terminal device as discussed above.

According to embodiments of the present disclosure, a second terminal device comprising a circuitry is provided. The circuitry is configured to: receive, from a first terminal device, a solicitation message for candidate relay discovery, the solicitation message comprising: a first identifier of the first terminal device, a second identifier of a second terminal device determined as a candidate for replacing a relay terminal device in a relay path for communication between two end terminal devices, wherein the relay terminal device is connected to the first terminal device in the relay path, and a third identifier of a third terminal device connected to the relay terminal device in the relay path. According to embodiments of the present disclosure, the circuitry may be configured to perform any method implemented by the second terminal device as discussed above.

According to embodiments of the present disclosure, a third terminal device comprising a circuitry is provided. The circuitry is configured to: receive, from a second terminal device, a solicitation message for candidate relay discovery, the solicitation message comprising: a first identifier of a first terminal device initiating the candidate relay discovery, a second identifier of the second terminal device, wherein the second terminal device is determined as a candidate for replacing a relay terminal device in a relay path for communication between two end terminal devices, wherein the relay terminal device is connected to the first terminal device and the third terminal device in the relay path, and a third identifier of the third terminal device. According to embodiments of the present disclosure, the circuitry may be configured to perform any method implemented by the third terminal device as discussed above.

According to embodiments of the present disclosure, a terminal device comprising a circuitry is provided. The circuitry is configured to: obtain a measurement result of a signal strength associated with a first relay terminal device; and determine a hop number of the first relay terminal device in a relay path based on the measurement result and respective ranges of the signal strength for a plurality of hop numbers, wherein the relay path is used for communication between two end terminal devices. According to embodiments of the present disclosure, the circuitry may be configured to perform any method implemented by the terminal device as discussed above.

The term “circuitry” used herein may refer to hardware circuits and/or combinations of hardware circuits and software. For example, the circuitry may be a combination of analog and/or digital hardware circuits with software/firmware. As a further example, the circuitry may be any portions of hardware processors with software including digital signal processor (s) , software, and memory (ies) that work together to cause an apparatus, such as a terminal device or a network device, to perform various functions. In a still further example, the circuitry may be hardware circuits and or processors, such as a microprocessor or a portion of a microprocessor, that requires software/firmware for operation, but the software may not be present when it is not needed for operation. As used herein, the term circuitry also covers an implementation of merely a hardware circuit or processor (s) or a portion of a hardware circuit or processor (s) and its (or their) accompanying software and/or firmware.

According to embodiments of the present disclosure, a first terminal apparatus is provided. The first terminal apparatus comprises means for obtaining first information about at least one terminal device in proximity of the first terminal device, the first information comprising second information about an end terminal device provided with a relay service by a relay terminal device of the at least one terminal device; and means for transmitting an announcement message for relay discovery, the announcement message at least comprising the first information. In some embodiments, the first apparatus may comprise means for performing the respective operations of the method 700A. In some example embodiments, the first apparatus may further comprise means for performing other operations in some example embodiments of the method 700A. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

According to embodiments of the present disclosure, a second terminal apparatus is provided. The second terminal apparatus comprises means for monitoring an announcement message for relay discovery from a first terminal device, the announcement message comprising first information about at least one terminal device in proximity of the first terminal device, and means for wherein the first information comprises second information about an end terminal device provided with a relay service by a relay terminal device of the at least one terminal device. In some embodiments, the second apparatus may comprise means for performing the respective operations of the method 700B. In some example embodiments, the second apparatus may further comprise means for performing other operations in some example embodiments of the method 700B. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

According to embodiments of the present disclosure, a first terminal apparatus is provided. The first terminal apparatus comprises means for transmitting a solicitation message for discovering relays for communication between the first terminal device and a second terminal device, the solicitation message comprising: means for a first identifier of the first terminal device, means for a second identifier of the second terminal device, and means for respective identifiers of a first set of relay terminal devices. In some embodiments, the third apparatus may comprise means for performing the respective operations of the method 800A. In some example embodiments, the third apparatus may further comprise means for performing other operations in some example embodiments of the method 800A. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

According to embodiments of the present disclosure, a second terminal apparatus is provided. The second terminal apparatus comprises means for receiving, from a third terminal device, a solicitation message for discovering relays for communication between a first terminal device and the second terminal device, the solicitation message comprising: means for a first identifier of the first terminal device, means for a second identifier of the second terminal device, and means for respective identifiers of a first set of relay terminal devices. In some embodiments, the fourth apparatus may comprise means for performing the respective operations of the method 800B. In some example embodiments, the fourth apparatus may further comprise means for performing other operations in some example embodiments of the method 800B. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

According to embodiments of the present disclosure, a third terminal apparatus is provided. The third terminal apparatus comprises means for receiving a solicitation message for discovering relays for communication between a first terminal device and a second terminal device, the solicitation message comprising: means for a first identifier of the first terminal device, means for a second identifier of the second terminal device, and means for respective identifiers of a first set of relay terminal devices; means for determining whether the third terminal device is comprised in the first set of relay terminal devices; and means for handling the solicitation message based on a result of the determining. In some embodiments, the fifth apparatus may comprise means for performing the respective operations of the method 800C. In some example embodiments, the fifth apparatus may further comprise means for performing other operations in some example embodiments of the method 800C. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

According to embodiments of the present disclosure, a first terminal apparatus is provided. The first terminal apparatus comprises means for determining a second terminal device as a candidate for replacing a relay terminal device in a relay path for communication between two end terminal devices, wherein the relay terminal device is connected to the first terminal device in the relay path; and means for transmitting a solicitation message for candidate relay discovery, the solicitation message comprising: means for a first identifier of the first terminal device, means for a second identifier of the second terminal device, and means for a third identifier of a third terminal device connected to the relay terminal device in the relay path. In some embodiments, the sixth apparatus may comprise means for performing the respective operations of the method 900A. In some example embodiments, the sixth apparatus may further comprise means for performing other operations in some example embodiments of the method 900A. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

According to embodiments of the present disclosure, a second terminal apparatus is provided. The second terminal apparatus comprises means for receiving, from a first terminal device, a solicitation message for candidate relay discovery, the solicitation message comprising: means for a first identifier of the first terminal device, means for a second identifier of a second terminal device determined as a candidate for replacing a relay terminal device in a relay path for communication between two end terminal devices, wherein the relay terminal device is connected to the first terminal device in the relay path, and means for a third identifier of a third terminal device connected to the relay terminal device in the relay path. In some embodiments, the seventh apparatus may comprise means for performing the respective operations of the method 900B. In some example embodiments, the seventh apparatus may further comprise means for performing other operations in some example embodiments of the method 900B. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

According to embodiments of the present disclosure, a third terminal apparatus is provided. The third terminal apparatus comprises means for receiving, from a second terminal device, a solicitation message for candidate relay discovery, the solicitation message comprising: means for a first identifier of a first terminal device initiating the candidate relay discovery, means for a second identifier of the second terminal device, wherein the second terminal device is determined as a candidate for replacing a relay terminal device in a relay path for communication between two end terminal devices, wherein the relay terminal device is connected to the first terminal device and the third terminal device in the relay path, and means for a third identifier of the third terminal device. In some embodiments, the eighth apparatus may comprise means for performing the respective operations of the method 900C. In some example embodiments, the eighth apparatus may further comprise means for performing other operations in some example embodiments of the method 900C. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

According to embodiments of the present disclosure, a terminal apparatus is provided. The terminal apparatus comprises means for obtaining a measurement result of a signal strength associated with a first relay terminal device; and means for determining a hop number of the first relay terminal device in a relay path based on the measurement result and respective ranges of the signal strength for a plurality of hop numbers, wherein the relay path is used for communication between two end terminal devices. In some embodiments, the ninth apparatus may comprise means for performing the respective operations of the method 1000. In some example embodiments, the ninth apparatus may further comprise means for performing other operations in some example embodiments of the method 1000. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

In summary, embodiments of the present disclosure provide the following aspects.

In an aspect, it is proposed a first terminal device comprising: a processor configured to cause the first terminal device to: obtain first information about at least one terminal device in proximity of the first terminal device, the first information comprising second information about an end terminal device provided with a relay service by a relay terminal device of the at least one terminal device; and transmit an announcement message for relay discovery, the announcement message at least comprising the first information.

In some embodiments, the second information comprises at least one of: an identifier of the end terminal device, a hop number from the first terminal device to the end terminal device, or a sequence of relay terminal devices through which the end terminal device is communicable.

In some embodiments, the first information further comprises at least one of: an identifier of the at least one terminal device, a user type of the at least one terminal device.

In some embodiments, the announcement message further comprises a type of discovery message comprising at least one of: a terminal device-to-terminal device relay discovery procedure, a terminal device-to-terminal device relay communication procedure, a terminal device-network relay discovery procedure, a terminal device-network relay communication procedure, or a non-relay discovery procedure.

In an aspect, it is proposed a second terminal device comprising: a processor configured to cause the second terminal device to: monitor an announcement message for relay discovery from a first terminal device, the announcement message comprising first information about at least one terminal device in proximity of the first terminal device, and wherein the first information comprises second information about an end terminal device provided with a relay service by a relay terminal device of the at least one terminal device.

In some embodiments, the second terminal device is further caused to: determine, based on the announcement message, a proximity-based service for connecting to a peer terminal device associated with the second terminal device.

In some embodiments, the second information comprises at least one of: an identifier of the end terminal device, a hop number from the first terminal device to the end terminal device, or a sequence of relay terminal devices through which to achieve the end terminal device.

In an aspect, it is proposed a first terminal device comprising: a processor configured to cause the first terminal device to: transmit a solicitation message for discovering relays for communication between the first terminal device and a second terminal device, the solicitation message comprising: a first identifier of the first terminal device, a second identifier of the second terminal device, and respective identifiers of a first set of relay terminal devices.

In some embodiments, the solicitation message further comprises at least one of: a solicitation indication that the first terminal device transmits the solicitation message, a solicitation indication that the second terminal device does not receive the solicitation message, or respective solicitation indications that the first set of relay terminal devices do not forward the solicitation message.

In some embodiments, the solicitation message further indicates respective hop numbers of the first set of relay terminal devices.

In some embodiments, the respective hop numbers are indicated by an order of the respective identifiers of the first set of relay terminal devices in the solicitation message.

In some embodiments, the solicitation message further comprises at least one of: a maximum hop number for relaying the communication between the first and second terminal devices, or a current hop number for transferring the solicitation message.

In some embodiments, the solicitation message further comprises a type of discovery message comprising at least one of: a terminal device-to-terminal device relay discovery procedure, a terminal device-to-terminal device relay communication procedure, a terminal device-network relay discovery procedure, a terminal device-network relay communication procedure, or a non-relay discovery procedure.

In some embodiments, the first terminal device is further caused to: receives, from a third terminal device, a response message for discovering the relays for the communication between the first and second terminal devices, the response message comprising: the first identifier of the first terminal device, the second identifier of the second terminal device, and respective identifiers of a second set of relay terminal devices transferring the solicitation message.

In an aspect, it is proposed a second terminal device comprising: a processor configured to cause the second terminal device to: receive, from a third terminal device, a solicitation message for discovering relays for communication between a first terminal device and the second terminal device, the solicitation message comprising: a first identifier of the first terminal device, a second identifier of the second terminal device, and respective identifiers of a first set of relay terminal devices.

In some embodiments, the second terminal device is further caused to: transmit a response message for discovering the relays for the communication between the first and second terminal devices, the response message comprising: the first identifier of the first terminal device, the second identifier of the second terminal device, and respective identifiers of a second set of relay terminal devices transferring the solicitation message.

In some embodiments, the response message is transmitted based on that an access-stratum layer criterion is met.

In some embodiments, an order of the respective identifiers of the second set of relay terminal devices corresponds to an order of the second set of relay terminal devices for relaying the communication between the first and second terminal devices.

In some embodiments, the response message comprises at least one of: a solicitation indication that the first terminal device transmits the solicitation message, a solicitation indication that the second terminal device receives the solicitation message, or respective solicitation indications that the second set of relay terminal devices forward the solicitation message.

In some embodiments, the response message comprises at least one of: a response indication that the first terminal device does not receives the response message, a response indication that the second terminal device transmits the response message, or respective response indications that the second set of relay terminal devices do not forward the response message.

In some embodiments, the response message further comprises a type of discovery message comprising at least one of: a terminal device-to-terminal device relay discovery procedure, a terminal device-to-terminal device relay communication procedure, a terminal device-network relay discovery procedure, a terminal device-network relay communication procedure, or a non-relay discovery procedure.

In an aspect, it is proposed a third terminal device comprising: a processor configured to cause the third terminal device to: receive a solicitation message for discovering relays for communication between a first terminal device and a second terminal device, the solicitation message comprising: a first identifier of the first terminal device, a second identifier of the second terminal device, and respective identifiers of a first set of relay terminal devices; determine whether the third terminal device is comprised in the first set of relay terminal devices; and handle the solicitation message based on a result of the determining.

In some embodiments, the solicitation message further indicates respective hop numbers for the first set of relay terminal devices, and the third terminal device is further caused to: in accordance with a determination that the third terminal device is comprised in the first set of relay terminal devices, update the current hop number; compare the updated current hop number with a hop number indicated in the solicitation message for the third terminal device; and handle the solicitation message based on a result of the comparison.

In some embodiments, the third terminal device is further caused to: in accordance with a determination that the updated current hop number does not match the hop number indicated in the solicitation message, ignore the solicitation message; and in accordance with a determination that the updated current hop number matches the hop number indicated in the solicitation message and a difference between the updated current hop number and the maximum hop number is below a threshold difference, forward the solicitation message.

In some embodiments, the third terminal device is further caused to: update a solicitation indication corresponding to the third terminal device in the solicitation message to indicate that the third terminal device forwards the solicitation message.

In some embodiments, the respective hop numbers are indicated by an order of the respective identifiers of the one or more relay terminal devices in the solicitation message.

In some embodiments, the third terminal device is further caused to: in accordance with a determination that the third terminal device is not comprised in the first set of relay terminal devices, update the current hop number; determine whether a difference between the updated current hop number and the maximum hop number is below a threshold difference; in accordance with a determination that the difference is below the threshold difference, forward the solicitation message, the forwarded solicitation message comprising an identifier of the third terminal device; and in accordance with a determination that the difference is not below the threshold difference, ignore the solicitation message.

In some embodiments, the third terminal device is further caused to: add a solicitation indication corresponding to the third terminal device into the solicitation message to indicate that the third terminal device forwards the solicitation message.

In some embodiments, the third terminal device is further caused to: receive a response message for discovering the relays for the communication between the first and second terminal devices, the response message comprising: the first identifier of the first terminal device, the second identifier of the second terminal device, and respective identifiers of a second set of relay terminal devices transferring the solicitation message; and transmit the response message.

In some embodiments, the third terminal device is further caused to: update a response indication corresponding to the third terminal device in the response message to indicate that the third terminal device forwards the response message.

In an aspect, it is proposed a first terminal device comprising: a processor configured to cause the first terminal device to: determine a second terminal device as a candidate for replacing a relay terminal device in a relay path for communication between two end terminal devices, wherein the relay terminal device is connected to the first terminal device in the relay path; and transmit a solicitation message for candidate relay discovery, the solicitation message comprising: a first identifier of the first terminal device, a second identifier of the second terminal device, and a third identifier of a third terminal device connected to the relay terminal device in the relay path.

In some embodiments, the solicitation message further comprises at least one of: a first hop number of the first terminal device in the relay path, a second hop number of the second terminal device in the relay path, and a third hop number of the third terminal device in the relay path.

In some embodiments, the solicitation message further comprises at least one of: a solicitation indication that the first terminal device transmits the solicitation message, a solicitation indication that the second terminal device does not forward the solicitation message, a solicitation indication that the third terminal device does not receive the solicitation message, a response indication that the first terminal device does not receive a response message for the candidate relay discovery, a response indication that the second terminal device does not forward a response message for the candidate relay discovery, or a response indication that the third terminal device does not transmit a response message for the candidate relay discovery.

In some embodiments, the solicitation message further comprises an indication that the solicitation message is used for the candidate relay discovery.

In some embodiments, the first terminal device is further caused to: receive, from the second terminal device, a response message for the candidate relay discovery, wherein the response message comprises the first identifier, the second identifier and the third identifier.

In some embodiments, the first terminal device is further caused to: determine the second terminal device as a candidate relay terminal device in accordance with a determination of at least one of: that the first terminal device matches the first identifier, that a terminal device in the relay path matches the third identifier, that the response message comprises a solicitation indication that the first terminal device transmits the solicitation message, a solicitation indication that the second terminal device forwards the solicitation message, and a solicitation indication that the third terminal device receives the solicitation message, that the response message comprises a response indication that the first terminal device does not receive the response message, a response indication that the second terminal device forwards the response message, or a response indication that the third terminal device transmits the response message, or that the response message comprises an indication that the response message is used for the candidate relay discovery.

In some embodiments, the first terminal device comprises one of the two end terminal devices, the third terminal device comprises a further relay terminal device.

In some embodiments, the first terminal device comprises a further relay terminal device, and the third terminal device comprises another relay terminal device or one of the two end terminal devices.

In an aspect, it is proposed a second terminal device comprising: a processor configured to cause the second terminal device to: receive, from a first terminal device, a solicitation message for candidate relay discovery, the solicitation message comprising: a first identifier of the first terminal device, a second identifier of a second terminal device determined as a candidate for replacing a relay terminal device in a relay path for communication between two end terminal devices, wherein the relay terminal device is connected to the first terminal device in the relay path, and a third identifier of a third terminal device connected to the relay terminal device in the relay path.

In some embodiments, the second terminal device is further caused to: in accordance with a determination that the second terminal device matches the second identifier in the solicitation message, forward the solicitation message to the third terminal device.

In some embodiments, the second terminal device is further caused to: update a solicitation indication in the solicitation message to indicate that the second terminal device forwards the solicitation message.

In some embodiments, the second terminal device is further caused to: receive, from a third terminal device, a response message for the candidate relay discovery, wherein the response message comprises the first identifier, the second identifier and the third identifier.

In some embodiments, the second terminal device is further caused to: in accordance with a determination that the second terminal device matches the second identifier, forward the response message to the first terminal device.

In some embodiments, the second terminal device is further caused to: update a response indication in the response message to indicate that the second terminal device forwards the response message.

In an aspect, it is proposed a third terminal device comprising: a processor configured to cause the third terminal device to: receive, from a second terminal device, a solicitation message for candidate relay discovery, the solicitation message comprising: a first identifier of a first terminal device initiating the candidate relay discovery, a second identifier of the second terminal device, wherein the second terminal device is determined as a candidate for replacing a relay terminal device in a relay path for communication between two end terminal devices, wherein the relay terminal device is connected to the first terminal device and the third terminal device in the relay path, and a third identifier of the third terminal device.

In some embodiments, the third terminal device is further caused to: in accordance with a determination that the third terminal device matches the third identifier in the solicitation message and a terminal device in the relay path matches the first identifier, transmit a response message for the candidate relay discovery, and wherein the response message comprises the first identifier, the second identifier and the third identifier.

In some embodiments, the response message further comprises at least one of: a solicitation indication that the first terminal device transmits the solicitation message, a solicitation indication that the second terminal device forwards the solicitation message, a solicitation indication that the third terminal device receives the solicitation message, a response indication that the first terminal device does not receive the response message, a response indication that the second terminal device does not forward the response message, or a response indication that the third terminal device transmits the response message.

In some embodiments, the response message further comprises an indication that the response message is used for the candidate relay discovery.

In some embodiments, the first terminal device comprises one of the two end terminal devices, and the third terminal device comprises a further relay terminal device.

In an aspect, it is proposed a terminal device comprising: a processor configured to cause the terminal device to: obtain a measurement result of a signal strength associated with a first relay terminal device; and determine a hop number of the first relay terminal device in a relay path based on the measurement result and respective ranges of the signal strength for a plurality of hop numbers, wherein the relay path is used for communication between two end terminal devices.

In some embodiments, the measurement result is obtained by measuring at least one of: a relay discovery announcement message from the first relay terminal device, a relay discovery solicitation message from the first relay terminal device, a relay discovery response message from the first relay terminal device, or sidelink data transmission from the first relay terminal device.

In some embodiments, respective ranges of the signal strength are associated with at least one of: a relay discovery announcement message, a relay discovery solicitation message, a relay discovery response message, or sidelink data transmission.

In some embodiments, the signal strength comprises a Reference Singal Receiving Power (RSRP) .

In some embodiments, the RSRP comprises at least one of: a sidelink RSRP, or a sidelink discovery RSRP.

In some embodiments, the terminal device comprises one of the two end terminal devices, and a rang of the signal strength for a hop number of the plurality of hop numbers is defined by an upper threshold and a lower threshold configured by a network device.

In some embodiments, the terminal device is further caused to: receive the measurement result from a second relay terminal device in at least one of: a relay discovery announcement message, a relay discovery solicitation message, or a relay discovery response message.

In some embodiments, the terminal device comprises a second relay terminal device, and a rang of the signal strength for a hop number of the plurality of hop numbers is defined by: an upper threshold and a lower threshold configured by a network device, or an upper threshold and a lower threshold indicated by one of the two end terminal devices.

In some embodiments, the terminal device is further caused to: transmit, to at least one of the two end terminal devices, an indication of the determined hop number of the first relay terminal device.

In some embodiments, the indication is comprised in at least one of: a relay discovery announcement message, a relay discovery solicitation message, or a relay discovery response message.

In an aspect, a first terminal device comprises: at least one processor; and at least one memory coupled to the at least one processor and storing instructions thereon, the instructions, when executed by the at least one processor, causing the device to perform the method implemented by the first terminal device discussed above.

In an aspect, a second terminal device comprises: at least one processor; and at least one memory coupled to the at least one processor and storing instructions thereon, the instructions, when executed by the at least one processor, causing the device to perform the method implemented by the second terminal device discussed above.

In an aspect, a third terminal device comprises: at least one processor; and at least one memory coupled to the at least one processor and storing instructions thereon, the instructions, when executed by the at least one processor, causing the device to perform the method implemented by the third terminal device discussed above.

In an aspect, a terminal device comprises: at least one processor; and at least one memory coupled to the at least one processor and storing instructions thereon, the instructions, when executed by the at least one processor, causing the device to perform the method implemented by the terminal device discussed above.

In an aspect, a computer readable medium having instructions stored thereon, the instructions, when executed on at least one processor, causing the at least one processor to perform the method implemented by the first terminal device discussed above.

In an aspect, a computer readable medium having instructions stored thereon, the instructions, when executed on at least one processor, causing the at least one processor to perform the method implemented by the second terminal device discussed above.

In an aspect, a computer readable medium having instructions stored thereon, the instructions, when executed on at least one processor, causing the at least one processor to perform the method implemented by the third terminal device discussed above.

In an aspect, a computer readable medium having instructions stored thereon, the instructions, when executed on at least one processor, causing the at least one processor to perform the method implemented by the terminal device discussed above.

In an aspect, a computer program comprising instructions, the instructions, when executed on at least one processor, causing the at least one processor to perform the method implemented by the first terminal device discussed above.

In an aspect, a computer program comprising instructions, the instructions, when executed on at least one processor, causing the at least one processor to perform the method implemented by the second terminal device discussed above.

In an aspect, a computer program comprising instructions, the instructions, when executed on at least one processor, causing the at least one processor to perform the method implemented by the third terminal device discussed above.

In an aspect, a computer program comprising instructions, the instructions, when executed on at least one processor, causing the at least one processor to perform the method implemented by the terminal device discussed above.

Generally, various embodiments of the present disclosure may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device. While various aspects of embodiments of the present disclosure are illustrated and described as block diagrams, flowcharts, or using some other pictorial representation, it will be appreciated that the blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

The present disclosure also provides at least one computer program product tangibly stored on a non-transitory computer readable storage medium. The computer program product includes computer-executable instructions, such as those included in program modules, being executed in a device on a target real or virtual processor, to carry out the process or method as described above with reference to FIGS. 1 to 11. Generally, program modules include routines, programs, libraries, objects, classes, components, data structures, or the like that perform particular tasks or implement particular abstract data types. The functionality of the program modules may be combined or split between program modules as desired in various embodiments. Machine-executable instructions for program modules may be executed within a local or distributed device. In a distributed device, program modules may be located in both local and remote storage media.

Program code for carrying out methods of the present disclosure may be written in any combination of one or more programming languages. These program codes may be provided to a processor or controller of a general purpose computer, special purpose computer, or other programmable data processing apparatus, such that the program codes, when executed by the processor or controller, cause the functions/operations specified in the flowcharts and/or block diagrams to be implemented. The program code may execute entirely on a machine, partly on the machine, as a stand-alone software package, partly on the machine and partly on a remote machine or entirely on the remote machine or server.

The above program code may be embodied on a machine readable medium, which may be any tangible medium that may contain, or store a program for use by or in connection with an instruction execution system, apparatus, or device. The machine readable medium may be a machine readable signal medium or a machine readable storage medium. A machine readable medium may include but not limited to an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of the machine readable storage medium would include an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM) , a read-only memory (ROM) , an erasable programmable read-only memory (EPROM or Flash memory) , an optical fiber, a portable compact disc read-only memory (CD-ROM) , an optical storage device, a magnetic storage device, or any suitable combination of the foregoing.

Further, while operations are depicted in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Likewise, while several specific implementation details are contained in the above discussions, these should not be construed as limitations on the scope of the present disclosure, but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable sub-combination.

Although the present disclosure has been described in language specific to structural features and/or methodological acts, it is to be understood that the present disclosure defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

Claims

A first terminal device comprising:

a processor configured to cause the first terminal device to:

obtain first information about at least one terminal device in proximity of the first terminal device, the first information comprising second information about an end terminal device provided with a relay service by a relay terminal device of the at least one terminal device; and

transmit an announcement message for relay discovery, the announcement message at least comprising the first information.
The first terminal device of claim 1, wherein the second information comprises at least one of:

an identifier of the end terminal device,

a hop number from the first terminal device to the end terminal device, or

a sequence of relay terminal devices through which the end terminal device is communicable.
The first terminal device of claim 1, wherein the announcement message further comprises a type of discovery message comprising at least one of:

a terminal device-to-terminal device relay discovery procedure,

a terminal device-to-terminal device relay communication procedure,

a terminal device-network relay discovery procedure,

a terminal device-network relay communication procedure, or

a non-relay discovery procedure.
A first terminal device comprising:

a processor configured to cause the first terminal device to:

transmit a solicitation message for discovering relays for communication between the first terminal device and a second terminal device, the solicitation message comprising:

a first identifier of the first terminal device,

a second identifier of the second terminal device, and

respective identifiers of a first set of relay terminal devices.
The first terminal device of claim 4, wherein the solicitation message further comprises at least one of:

a solicitation indication that the first terminal device transmits the solicitation message,

a solicitation indication that the second terminal device does not receive the solicitation message, or

respective solicitation indications that the first set of relay terminal devices do not forward the solicitation message.
The first terminal device of claim 4, wherein the solicitation message further indicates respective hop numbers of the first set of relay terminal devices.
The first terminal device of claim 6, wherein the respective hop numbers are indicated by an order of the respective identifiers of the first set of relay terminal devices in the solicitation message.
The first terminal device of claim 4, wherein the solicitation message further comprises at least one of:

a maximum hop number for relaying the communication between the first and second terminal devices, or

a current hop number for transferring the solicitation message.
The first terminal device of claim 4, wherein the solicitation message further comprises a type of discovery message comprising at least one of:

a terminal device-to-terminal device relay discovery procedure,

a terminal device-to-terminal device relay communication procedure,

a terminal device-network relay discovery procedure,

a terminal device-network relay communication procedure, or

a non-relay discovery procedure.
A first terminal device comprising:

a processor configured to cause the first terminal device to:

determine a second terminal device as a candidate for replacing a relay terminal device in a relay path for communication between two end terminal devices, wherein the relay terminal device is connected to the first terminal device in the relay path; and

transmit a solicitation message for candidate relay discovery, the solicitation message comprising:

a first identifier of the first terminal device,

a second identifier of the second terminal device, and

a third identifier of a third terminal device connected to the relay terminal device in the relay path.
The first terminal device of claim 10, wherein the solicitation message further comprises at least one of:

a first hop number of the first terminal device in the relay path,

a second hop number of the second terminal device in the relay path, and

a third hop number of the third terminal device in the relay path.
The first terminal device of claim 10, wherein the solicitation message further comprises at least one of:

a solicitation indication that the first terminal device transmits the solicitation message,

a solicitation indication that the second terminal device does not forward the solicitation message,

a solicitation indication that the third terminal device does not receive the solicitation message,

a response indication that the first terminal device does not receive a response message for the candidate relay discovery,

a response indication that the second terminal device does not forward a response message for the candidate relay discovery, or

a response indication that the third terminal device does not transmit a response message for the candidate relay discovery.
The first terminal device of claim 10, wherein the first terminal device is further caused to:

receive, from the second terminal device, a response message for the candidate relay discovery, wherein the response message comprises the first identifier, the second identifier and the third identifier.
The first terminal device of claim 13, wherein the first terminal device is further caused to:

determine the second terminal device as a candidate relay terminal device in accordance with a determination of at least one of:

that the first terminal device matches the first identifier,

that a terminal device in the relay path matches the third identifier,

that the response message comprises a solicitation indication that the first terminal device transmits the solicitation message, a solicitation indication that the second terminal device forwards the solicitation message, and a solicitation indication that the third terminal device receives the solicitation message,

that the response message comprises a response indication that the first terminal device does not receive the response message, a response indication that the second terminal device forwards the response message, or a response indication that the third terminal device transmits the response message, or

that the response message comprises an indication that the response message is used for the candidate relay discovery.
A terminal device comprising:

a processor configured to cause the terminal device to:

obtain a measurement result of a signal strength associated with a first relay terminal device; and

determine a hop number of the first relay terminal device in a relay path based on the measurement result and respective ranges of the signal strength for a plurality of hop numbers, wherein the relay path is used for communication between two end terminal devices.
The terminal device of claim 15, wherein the measurement result is obtained by measuring at least one of:

a relay discovery announcement message from the first relay terminal device,

a relay discovery solicitation message from the first relay terminal device,

a relay discovery response message from the first relay terminal device, or

sidelink data transmission from the first relay terminal device.
The terminal device of claim 15, wherein the terminal device comprises one of the two end terminal devices, and

a rang of the signal strength for a hop number of the plurality of hop numbers is defined by an upper threshold and a lower threshold configured by a network device.
The terminal device of claim 17, wherein the terminal device is further caused to:

receive the measurement result from a second relay terminal device in at least one of:

a relay discovery announcement message,

a relay discovery solicitation message, or

a relay discovery response message.
The terminal device of claim 15, wherein the terminal device comprises a second relay terminal device, and

a rang of the signal strength for a hop number of the plurality of hop numbers is defined by:

an upper threshold and a lower threshold configured by a network device, or

an upper threshold and a lower threshold indicated by one of the two end terminal devices.
The terminal device of claim 19, wherein the terminal device is further caused to:

transmit, to at least one of the two end terminal devices, an indication of the determined hop number of the first relay terminal device.