According to a fifth aspect of the present disclosure, a method in a second terminal device is provided. The method includes: receiving, from a first terminal device, a first message for initiating a discovery procedure over a sidelink. The first message contains one or more of following information associated with the first terminal device: first application or traffic related information, first location or mobility related information, or first connectivity related information.

In an embodiment, the first application or traffic related information may include a QoS profile of an application or traffic the first terminal device requests or is capable of providing.

In an embodiment, the QoS profile may include a type, a priority, and/or a QoS requirement of the application or traffic.

In an embodiment, the first location or mobility related information may include one or more of: location information of the first terminal device, information on an area or proximity where the first terminal device requests or is capable of providing an application or traffic, or mobility information of the first terminal device.

In an embodiment, the mobility information of the first terminal device may indicate whether the first terminal device is static or moving.

In an embodiment, the first connectivity related information may include: a serving network node of the first terminal device, an indication of whether the first terminal device requests or is capable of providing a relay path towards a network node or a terminal device, a list of identifiers of terminal devices that have been obtained in a previous discovery procedure, a radio quality indication of a PC5 or Uu link the first terminal device currently has, a load or a congestion condition of the PC5 or Uu link, an RAT of the PC5 or Uu link, an indication of a relay type the first terminal device requests or is capable of providing, or a number of hops or a maximum number of hops along a relay path the first terminal device requests or is capable of providing.

In an embodiment, the method may further include: obtaining a set of relay candidates, including the first terminal device, based at least on the first message; selecting, from the set of relay candidates, the first terminal device as a relay between the second terminal device and a network node or a third terminal device, based on the first application or traffic related information, the first location or mobility related information, and/or the first connectivity related information; and establishing a relay path from the second terminal device to the network node or the third terminal device via the first terminal device.

In an embodiment, the first message may further contain a first validity timer indicating a duration during which the information associated with the first terminal device is valid, and the operation of selecting may be based on the first validity timer.

In an embodiment, the method may further include: selecting, from the set of relay candidates, a fourth terminal device as a relay between the second terminal device and the network node or the third terminal device in response to a failure of the relay path, based on application or traffic related information, location or mobility related information, and/or connectivity related information associated with the fourth terminal device; and establishing a relay path from the second terminal device to the network node or the third terminal device via the fourth terminal device.

In an embodiment, the operation of selecting of the fourth terminal may be based on a validity timer indicating a duration during which the information associated with the fourth terminal device is valid.

In an embodiment, the method may further include: initiating another discovery procedure over the sidelink when all the relay candidates in the set have their respective validity timers expired.

In an embodiment, the method may further include: transmitting, to the first terminal device, a second message as a response to the first message. The second message may contain one or more of following information associated with the second terminal device: identifier information, second application or traffic related information, second location or mobility related information, or second connectivity related information.

In an embodiment, the second message may further contain a second validity timer indicating a duration during which the information associated with the second terminal device is valid.

In an embodiment, the identifier information may include one or more of: a global identifier of the second terminal device, a temporary identifier of the second terminal device, and/or an identifier of the second terminal device used only when the second terminal device serves as a relay for the first terminal device.

In an embodiment, the second application or traffic related information may include a QoS profile of an application or traffic the second terminal device requests or is capable of providing.

In an embodiment, the QoS profile may include a type, a priority, and/or a QoS requirement of the application or traffic the second terminal device requests or is capable of providing.

In an embodiment, the second location or mobility related information may include one or more of: location information of the second terminal device, information on an area or proximity where the second terminal device requests or is capable of providing an application or traffic, or mobility information of the second terminal device.

In an embodiment, the mobility information of the second terminal device may indicate whether the second terminal device is static or moving.

In an embodiment, the second connectivity related information may include: a serving network node of the second terminal device, an indication of whether the second terminal device requests or is capable of providing a relay path towards a network node or a terminal device, a list of identifiers of terminal devices that have been obtained in a previous discovery procedure, a radio quality indication of a PC5 or Uu link the second terminal device currently has, a load or a congestion condition of the PC5 or Uu link, an RAT of the PC5 or Uu link, an indication of a relay type the second terminal device requests or is capable of providing, or a number of hops or a maximum number of hops along a relay path the second terminal device requests or is capable of providing.

In an embodiment, the first message may further contain a measurement configuration for the second terminal device to measure a PC5 link towards the third terminal device or a fifth terminal device, or a Uu link towards the network node, and the second message further contains a measurement report for the PC5 link or the Uu link.

In an embodiment, the method may further include: receiving the measurement configuration from a network node.

In an embodiment, the method may further include: receiving an authorization to engage in the discovery procedure from a network node.

In an embodiment, the first location or mobility related information and/or the first connectivity related information may be received explicitly in one or more fields in the first message or included in a container in the first message.

In an embodiment, the second location or mobility related information and/or the second connectivity related information may be transmitted explicitly in one or more fields in the second message or included in a container in the second message.

According to a sixth aspect of the present disclosure, a second terminal device is provided. The second terminal device includes a receiving unit configured to receive, from a first terminal device, a first message for initiating a discovery procedure over a sidelink. The first message contains one or more of following information associated with the first terminal device: first application or traffic related information, first location or mobility related information, or first connectivity related information.

The respective embodiments and features described above in connection with the fifth aspect also apply to the sixth aspect.

According to a seventh aspect of the present disclosure, a second terminal device is provided. The second terminal device includes a transceiver, a processor and a memory. The memory contains instructions executable by the processor whereby the second terminal device is operative to perform the method according to the fifth aspect.

According to an eighth aspect of the present disclosure, a computer readable storage medium is provided. The computer readable storage medium has computer program instructions stored thereon. The computer program instructions, when executed by a processor in a second terminal device, cause the second terminal device to perform the method according to the fifth aspect.

According to a ninth aspect of the present disclosure, a method in a network node is provided. The method includes: transmitting, to a terminal device, an authorization to initiate or engage in a discovery procedure; and transmitting, to the terminal device, a measurement configuration for the terminal device to measure a PC5 link or a Uu link towards a network node or another terminal device.

In an embodiment, the authorization and/or the measurement configuration may be transmitted via a System Information Block (SIB) or Radio Resource Control (RRC) signaling.

According to a tenth aspect of the present disclosure, a network node is provided. The network device includes a transmitting unit configured to transmit, to a terminal device, an authorization to initiate or engage in a discovery procedure; and transmit, to the terminal device, a measurement configuration for the terminal device to measure a PC5 link or a Uu link towards a network node or another terminal device.

The respective embodiments and features described above in connection with the ninth aspect also apply to the tenth aspect.

According to an eleventh aspect of the present disclosure, a network node is provided. The network node includes a transceiver, a processor and a memory. The memory contains instructions executable by the processor whereby the network node is operative to perform the method according to the above ninth aspect.

According to a twelfth aspect of the present disclosure, a computer readable storage medium is provided. The computer readable storage medium has computer program instructions stored thereon. The computer program instructions, when executed by a processor in a network node, cause the network node to perform the method according to the above ninth aspect.

With the embodiments of the present disclosure, one or more messages in a discovery procedure can be enhanced with additional information. For example, a message for initiating a discovery procedure over a sidelink may contain application or traffic related information, location or mobility related information, and/or connectivity related information, associated with a terminal device transmitting the message. With such information, it is possible to improve the efficiency of the discovery procedure, especially for establishing a UE-to-Network or UE-to-UE relay path.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and advantages will be more apparent from the following description of embodiments with reference to the figures, in which:

FIG. 1 is a schematic diagram showing V2X scenarios with an LTE based network infrastructure;

FIG. 2 is a schematic diagram showing an example of a discovery procedure;

FIG. 3 is a flowchart illustrating a method in a first terminal device according to an embodiment of the present disclosure;

FIG. 4 is a flowchart illustrating a method in a second terminal device according to an embodiment of the present disclosure;

FIG. 5 is a flowchart illustrating a method in a network node according to an embodiment of the present disclosure;

FIG. 6 is a block diagram of a first terminal device according to an embodiment of the present disclosure;

FIG. 7 is a block diagram of a first terminal device according to another embodiment of the present disclosure;

FIG. 8 is a block diagram of a second terminal device according to an embodiment of the present disclosure;

FIG. 9 is a block diagram of a second terminal device according to another embodiment of the present disclosure;

FIG. 10 is a block diagram of a network node according to an embodiment of the present disclosure;

FIG. 11 is a block diagram of a network node according to another embodiment of the present disclosure;

FIG. 12 schematically illustrates a telecommunication network connected via an intermediate network to a host computer;

FIG. 13 is a generalized block diagram of a host computer communicating via a base station with a user equipment over a partially wireless connection; and

FIGS. 14 to 17 are flowcharts illustrating methods implemented in a communication system including a host computer, a base station and a user equipment.

DETAILED DESCRIPTION

As used herein, the term “wireless communication network” refers to a network following any suitable communication standards, such as NR, LTE-Advanced (LTE-A), LTE, Wideband Code Division Multiple Access (WCDMA), High-Speed Packet Access (HSPA), and so on. Furthermore, the communications between a terminal device and a network node in the wireless communication network may be performed according to any suitable generation communication protocols, including, but not limited to, Global System for Mobile Communications (GSM), Universal Mobile Telecommunications System (UMTS), Long Term Evolution (LTE), and/or other suitable 1G (the first generation), 2G (the second generation), 2.5G, 2.75G, 3G (the third generation), 4G (the fourth generation), 4.5G, 5G (the fifth generation) communication protocols, wireless local area network (WLAN) standards, such as the IEEE 802.11 standards; and/or any other appropriate wireless communication standard, such as the Worldwide Interoperability for Microwave Access (WiMax), Bluetooth, and/or ZigBee standards, and/or any other protocols either currently known or to be developed in the future.

The term “network node” or “network device” refers to a device in a wireless communication network via which a terminal device accesses the network and receives services therefrom. The network node or network node refers to a base station (BS), an access point (AP), or any other suitable device in the wireless communication network. The BS may be, for example, a node B (NodeB or NB), an evolved NodeB (eNodeB or eNB), or a (next) generation (gNB), a Remote Radio Unit (RRU), a radio header (RH), a remote radio head (RRH), a relay, a low power node such as a femto, a pico, and so forth. Yet further examples of the network node may include multi-standard radio (MSR) radio equipment such as MSR BSs, network controllers such as radio network controllers (RNCs) or base station controllers (BSCs), base transceiver stations (BTSs), transmission points, transmission nodes. More generally, however, the network node may represent any suitable device (or group of devices) capable, configured, arranged, and/or operable to enable and/or provide a terminal device access to the wireless communication network or to provide some service to a terminal device that has accessed the wireless communication network.

The term “terminal device” refers to any end device that can access a wireless communication network and receive services therefrom. By way of example and not limitation, the terminal device refers to a mobile terminal, user equipment (UE), or other suitable devices. The UE may be, for example, a Subscriber Station (SS), a Portable Subscriber Station, a Mobile Station (MS), or an Access Terminal (AT). The terminal device may include, but not limited to, portable computers, desktop computers, image capture terminal devices such as digital cameras, gaming terminal devices, music storage and playback appliances, a mobile phone, a cellular phone, a smart phone, voice over IP (VoIP) phones, wireless local loop phones, tablets, personal digital assistants (PDAs), wearable terminal devices, vehicle-mounted wireless terminal devices, wireless endpoints, mobile stations, laptop-embedded equipment (LEE), laptop-mounted equipment (LME), USB dongles, smart devices, wireless customer-premises equipment (CPE) and the like. In the following description, the terms “terminal device”, “terminal”, “user equipment” and “UE” may be used interchangeably. As one example, a terminal device may represent a UE configured for communication in accordance with one or more communication standards promulgated by the 3^rdGeneration Partnership Project (3GPP), such as 3GPP's GSM, UMTS, LTE, and/or 5G standards. As used herein, a “user equipment” or “UE” may not necessarily have a “user” in the sense of a human user who owns and/or operates the relevant device. In some embodiments, a terminal device may be configured to transmit and/or receive information without direct human interaction. For instance, a terminal device may be designed to transmit information to a network on a predetermined schedule, when triggered by an internal or external event, or in response to requests from the wireless communication network. Instead, a UE may represent a device that is intended for sale to, or operation by, a human user but that may not initially be associated with a specific human user.

The terminal device may support device-to-device (D2D) communication, for example by implementing a 3GPP standard for sidelink communication, and may in this case be referred to as a D2D communication device.

As yet another example, in an Internet of Things (IOT) scenario, a terminal device may represent a machine or other device that performs monitoring and/or measurements, and transmits the results of such monitoring and/or measurements to another terminal device and/or network equipment. The terminal device may in this case be a machine-to-machine (M2M) device, which may in a 3GPP context be referred to as a machine-type communication (MTC) device. As one particular example, the terminal device may be a UE implementing the 3GPP narrow band internet of things (NB-IoT) standard. Particular examples of such machines or devices are sensors, metering devices such as power meters, industrial machinery, or home or personal appliances, for example refrigerators, televisions, personal wearables such as watches etc. In other scenarios, a terminal device may represent a vehicle or other equipment that is capable of monitoring and/or reporting on its operational status or other functions associated with its operation.

As used herein, a downlink transmission refers to a transmission from the network node to a terminal device, and an uplink transmission refers to a transmission in an opposite direction.

References in the specification to “one embodiment,” “an embodiment,” “an example embodiment,” and the like indicate that the embodiment described may include a particular feature, structure, or characteristic, but it is not necessary that every embodiment includes the particular feature, structure, or characteristic. Moreover, such phrases are not necessarily referring to the same embodiment. Further, when a particular feature, structure, or characteristic is described in connection with an embodiment, it is submitted that it is within the knowledge of one skilled in the art to affect such feature, structure, or characteristic in connection with other embodiments whether or not explicitly described.

It shall be understood that although the terms “first” and “second” etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed terms. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. 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. It will be further understood that the terms “comprises”, “comprising”, “has”, “having”, “includes” and/or “including”, when used herein, specify the presence of stated features, elements, and/or components etc., but do not preclude the presence or addition of one or more other features, elements, components and/or combinations thereof.

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.

FIG. 3 is a flowchart illustrating a method 300 according to an embodiment of the present disclosure. The method 300 can be performed at a first terminal device, which may be an announcing UE in Model A, or a discoverer UE in Model B. The first terminal device may initiate a discovery procedure with a second terminal device over a sidelink (or PC5 interface), so as to establish communication between the first and second terminal devices. The sidelink or PC5 communication can serve as a segment of a relay path between a Remote UE (referred to as “RM UE” hereinafter) and another entity (which can be a network node in case of UE-to-Network relay or another UE in case of UE-to-UE relay) via a Relay UE (referred to as “RL UE” hereinafter). In this case, the first terminal device can be the RM UE and the second terminal device can be the RL UE, or alternatively the first terminal device can be the RL UE and the second terminal device can be the RM UE.

At block 310, the first terminal device transmits, to the second terminal device, a first message for initiating a discovery procedure over a sidelink. Here, the first message can be e.g., the discovery message at 2.2a in FIG. 2, or the discovery solicitation at 2.2b in FIG. 2. In an example, before the block 310, the first terminal device may receive an authorization to initiate the discovery procedure from a network node, e.g., its serving gNB.

The first message contains one or more of following information associated with the first terminal device: first application or traffic related information, first location or mobility related information, or first connectivity related information. In addition, the first message may contain: 1) ProSe UE ID, e.g., ProSe application user ID, Layer 2 ID; 2) Group ID(s) provided by the application layer; and 3) Application ID(s) or ProSe application code(s) provided by the application layer, as described above.

In an example, the first message may further contain a first validity timer indicating a duration during which the information associated with the first terminal device is valid.

In an example, the first application or traffic related information may include a QoS profile of an application or traffic the first terminal device requests or is capable of providing. Here, the QoS profile may include a type, a priority, and/or a QoS requirement of the application or traffic.

In an example, the first location or mobility related information may include one or more of: location information (e.g., Global Positioning System (GPS) coordinates) of the first terminal device, information on an area or proximity where the first terminal device requests or is capable of providing an application or traffic, or mobility information of the first terminal device. Here, the mobility information of the first terminal device may indicate whether the first terminal device is static or moving, and/or a type of mobility, e.g., pedestrian or vehicle.

In an example, the first connectivity related information may include one or more of:

- a serving network node of the first terminal device,
- an indication of whether the first terminal device requests or is capable of providing a relay path towards a network node or a peer terminal device (e.g., an ID of the network node or the peer terminal device),
- a list of IDs of terminal devices that have been obtained in a previous discovery procedure,
- a radio quality indication of a PC5 or Uu link the first terminal device currently has,
- a load or a congestion condition of the PC5 or Uu link,
- an RAT (e.g., LTE or NR) of the PC5 or Uu link,
- an indication of a relay type (e.g., UE-to-Network or UE-to-UE) the first terminal device requests or is capable of providing, or
- a number of hops or a maximum number of hops along a relay path the first terminal device requests or is capable of providing.

Here, any of the above IDs can be a temporary ID used for the discovery procedure only, which becomes invalid once the discovery procedure is completed.

In an example, the Access Stratum (AS) configuration/information in the first message, e.g., the first location or mobility related information and/or the first connectivity related information, may be transmitted explicitly in one or more fields in the first message, or may be included in a container (e.g., OCTET STRING) in the first message. The container may function as a pointer to a part of e.g., an RRC specification where the AS configuration/information is standardized.

In an example, the first terminal device can receive, from the second terminal device, a second message as a response to the first message. Here, the second message can be e.g., a response (not shown) to the discovery message at 2.2a in FIG. 2, or the discovery message at 2.2b in FIG. 2.

The second message contains one or more of following information associated with the second terminal device: identifier information, second application or traffic related information, second location or mobility related information, or second connectivity related information.

In an example, the identifier information may include one or more of: a global identifier of the second terminal device, a temporary identifier of the second terminal device (e.g., used only for the discovery procedure), and/or an identifier of the second terminal device used only when the second terminal device serves as a relay for the first terminal device.

In an example, the second application or traffic related information may include a QoS profile of an application or traffic the second terminal device requests or is capable of providing. Here, the QoS profile may include a type, a priority, and/or a QoS requirement of the application or traffic the second terminal device requests or is capable of providing.

In an example, the second location or mobility related information may include one or more of: location information (e.g., GPS coordinates) of the second terminal device, information on an area or proximity where the second terminal device requests or is capable of providing an application or traffic, or mobility information of the second terminal device. Here, the mobility information of the second terminal device may indicate whether the second terminal device is static or moving, and/or a type of mobility, e.g., pedestrian or vehicle.

In an example, the second connectivity related information may include:

- a serving network node of the second terminal device,
- an indication of whether the second terminal device requests or is capable of providing a relay path towards a network node or a peer terminal device (e.g., an ID of the network node or the peer terminal device),
- a list of IDs of terminal devices that have been obtained in a previous discovery procedure,
- a radio quality indication of a PC5 or Uu link the second terminal device currently has,
- a load or a congestion condition of the PC5 or Uu link,
- an RAT (e.g., LTE or NR) of the PC5 or Uu link,
- an indication of a relay type (e.g., UE-to-Network or UE-to-UE) the second terminal device requests or is capable of providing, or
- a number of hops or a maximum number of hops along a relay path the second terminal device requests or is capable of providing.

In an example, the AS configuration/information in the second message, e.g., the second location or mobility related information and/or the second connectivity related information, may be received explicitly in one or more fields in the second message, or may be included in a container (e.g., OCTET STRING) in the second message. The container may function as a pointer to a part of e.g., an RRC specification where the AS configuration/information is standardized.

In an example where the first terminal device operates as an RM UE, it can obtain a set of relay candidates, including the second terminal device, based at least on the second message. For example, the first terminal device may obtain the set of relay candidates by receiving a message similar to the second message from each of the relay candidates. Next, the first terminal device can select, from the set of relay candidates, the second terminal device as a relay (RL UE) between the first terminal device and a network node or a peer terminal device (e.g., referred to as a third terminal device), based on the second application or traffic related information, the second location or mobility related information, and/or the second connectivity related information. Here, the first terminal device can sort the relay candidates in the set according to certain criteria and select the “best” relay candidate as the RL UE. For example, the first terminal device may select, as the RL UE, a relay candidate that is capable of providing a particular application or traffic it is interested in with a desired QoS in a particular area (e.g., a relay candidate that is connected to a network node or a peer terminal device capable of providing the particular application or traffic with the desired QoS in the particular area). The first terminal device may prioritize a relay candidate that is capable of providing a UE-to-Network relay over a relay candidate that is capable of providing a UE-to-UE relay. The first terminal device may prioritize a relay candidate that has a PC5 or Uu link with a better radio quality and/or a lower load over a relay candidate that has a PC5 or Uu link with a worse radio quality and/or a higher load. The first terminal device may prioritize a relay candidate that has an NR PC5 or Uu link over a relay candidate that has an LTE PC5 or Uu link. Then, the first terminal device can establish a relay path from the first terminal device to the network node or the third terminal device via the (selected) second terminal device.

In an example, the second message may further contain a second validity timer indicating a duration during which the information associated with the second terminal device is valid. The second terminal device can be selected as the RL UE based on the second validity timer, e.g., only when the second validity timer has not expired.

When the above establishment of the relay path succeeds, the discover procedure ends and the first terminal device can clear the set of relay candidates from its memory. Alternatively, the first terminal device can keep the set of relay candidates and remove a relay candidate from the set only when its associated validity timer expires, or the first terminal device can keep the set of relay candidates until a new discovery procedure is triggered.

When the above establishment of the relay path fails, the first terminal device can select another (e.g., the second best) relay candidate from the set as the RL UE and establish a relay path from the first terminal device to the network node or the third terminal device via the newly selected RL UE, if its associated validity timer has not expired. The first terminal device may try yet another relay candidate when the establishment fails again. If all the relay candidates in the set have been tried and the establishment keeps failing, a new discovery procedure can be initiated.

For example, when the established relay path fails, e.g., due to deterioration of the link quality between the first terminal device (RM UE) and the RL UE, the first terminal device can select, from the set of relay candidates, another terminal device (e.g., referred to as a fourth terminal device) as a relay (RL UE) between the first terminal device and the network node or the third terminal device in response to a failure of the relay path, based on application or traffic related information, location or mobility related information, and/or connectivity related information associated with the fourth terminal device. For example, the fourth terminal device can be selected based on a validity timer indicating a duration during which the information associated with the fourth terminal device is valid, e.g., when the validity timer has not expired. Then, the first terminal device can establish a relay path from the first terminal device to the network node or the third terminal device via the fourth terminal device.

In an example, the first terminal device may initiate another discovery procedure over the sidelink when all the relay candidates in the set have their respective validity timers expired.

In an example where the first terminal device operates as an RM UE, the first message may further contain a measurement configuration for the second terminal device (which is a relay candidate) to measure a PC5 link towards a peer terminal device (e.g., the above third terminal device or another terminal device), or a Uu link towards a network node. The measurement configuration may include e.g., time-frequency resources to measure and/or quantities to measure (for example, Reference Signal Received Power (RSRP), Reference Signal Received Quality (RSRQ), or Signal to Interference plus Noise Ratio (SINR)). The first terminal device may receive the measurement configuration from a network node, e.g., its serving gNB when it is in coverage, via SIB or dedicated RRC signaling. The second message may further contain a measurement report for the PC5 link or the Uu link, containing the quantities measured by the second terminal device according to the measurement report.

FIG. 4 is a flowchart illustrating a method 400 according to an embodiment of the present disclosure. The method 400 can be performed at a second terminal device, which may be a monitoring UE in Model A, or a discoveree UE in Model B. The second terminal device may respond to a discovery procedure initiated by a first terminal device over a sidelink (or PC5 interface), so as to establish communication between the first and second terminal devices. The sidelink or PC5 communication can serve as a segment of a relay path between an RM UE and another entity (which can be a network node in case of UE-to-Network relay or another UE in case of UE-to-UE relay) via an RL UE. In this case, the first terminal device can be the RM UE and the second terminal device can be the RL UE, or alternatively the first terminal device can be the RL UE and the second terminal device can be the RM UE.

At block 410, the second terminal device receives, from the first terminal device, a first message for initiating a discovery procedure over a sidelink. Here, the first message can be e.g., the discovery message at 2.2a in FIG. 2, or the discovery solicitation at 2.2b in FIG. 2.

The first message contains one or more of following information associated with the first terminal device: first application or traffic related information, first location or mobility related information, or first connectivity related information. In addition, the first message may contain: 1) ProSe UE ID, e.g., ProSe application user ID, Layer 2 ID; 2) Group ID(s) provided by the application layer; and 3) Application ID(s) or ProSe application code(s) provided by the application layer, as described above.

In an example, the first application or traffic related information may include a QoS profile of an application or traffic the first terminal device requests or is capable of providing. Here, the QoS profile may include a type, a priority, and/or a QoS requirement of the application or traffic.

In an example, the first location or mobility related information may include one or more of: location information (e.g., GPS coordinates) of the first terminal device, information on an area or proximity where the first terminal device requests or is capable of providing an application or traffic, or mobility information of the first terminal device. Here, the mobility information of the first terminal device may indicate whether the first terminal device is static or moving, and/or a type of mobility, e.g., pedestrian or vehicle.

In an example, the first connectivity related information may include one or more of:

- a serving network node of the first terminal device,
- an indication of whether the first terminal device requests or is capable of providing a relay path towards a network node or a peer terminal device (e.g., an ID of the network node or the peer terminal device),
- a list of IDs of terminal devices that have been obtained in a previous discovery procedure,
- a radio quality indication of a PC5 or Uu link the first terminal device currently has,
- a load or a congestion condition of the PC5 or Uu link,
- an RAT (e.g., LTE or NR) of the PC5 or Uu link,
- an indication of a relay type (e.g., UE-to-Network or UE-to-UE) the first terminal device requests or is capable of providing, or
- a number of hops or a maximum number of hops along a relay path the first terminal device requests or is capable of providing.

Here, any of the above IDs can be a temporary ID used for the discovery procedure only, which becomes invalid once the discovery procedure is completed.

In an example, the AS configuration/information in the first message, e.g., the first location or mobility related information and/or the first connectivity related information, may be received explicitly in one or more fields in the first message, or may be included in a container (e.g., OCTET STRING) in the first message. The container may function as a pointer to a part of e.g., an RRC specification where the AS configuration/information is standardized.

In an example where the second terminal device operates as an RM UE, it can obtain a set of relay candidates, including the first terminal device, based at least on the first message. For example, the second terminal device may obtain the set of relay candidates by receiving a message similar to the first message from each of the relay candidates. Next, the second terminal device can select, from the set of relay candidates, the first terminal device as a relay (RL UE) between the second terminal device and a network node or a peer terminal device (e.g., referred to as a third terminal device), based on the first application or traffic related information, the first location or mobility related information, and/or the first connectivity related information. Here, the second terminal device can sort the relay candidates in the set according to certain criteria and select the “best” relay candidate as the RL UE. For example, the second terminal device may select, as the RL UE, a relay candidate that is capable of providing a particular application or traffic it is interested in with a desired QoS in a particular area (e.g., a relay candidate that is connected to a network node or a peer terminal device capable of providing the particular application or traffic with the desired QoS in the particular area). The second terminal device may prioritize a relay candidate that is capable of providing a UE-to-Network relay over a relay candidate that is capable of providing a UE-to-UE relay. The second terminal device may prioritize a relay candidate that has a PC5 or Uu link with a better radio quality and/or a lower load over a relay candidate that has a PC5 or Uu link with a worse radio quality and/or a higher load. The second terminal device may prioritize a relay candidate that has an NR PC5 or Uu link over a relay candidate that has an LTE PC5 or Uu link. Then, the second terminal device can establish a relay path from the second terminal device to the network node or the third terminal device via the (selected) first terminal device.

In an example, the first message may further contain a first validity timer indicating a duration during which the information associated with the first terminal device is valid. The first terminal device can be selected as the RL UE based on the second validity timer, e.g., only when the first validity timer has not expired.

When the above establishment of the relay path succeeds, the discover procedure ends and the second terminal device can clear the set of relay candidates from its memory. Alternatively, the second terminal device can keep the set of relay candidates and remove a relay candidate from the set only when its associated validity timer expires, or the second terminal device can keep the set of relay candidates until a new discovery procedure is triggered.

When the above establishment of the relay path fails, the second terminal device can select another (e.g., the second best) relay candidate from the set as the RL UE and establish a relay path from the second terminal device to the network node or the third terminal device via the newly selected RL UE, if its associated validity timer has not expired. The second terminal device may try yet another relay candidate when the establishment fails again. If all the relay candidates in the set have been tried and the establishment keeps failing, a new discovery procedure can be initiated.

For example, when the established relay path fails, e.g., due to deterioration of the link quality between the second terminal device (RM UE) and the RL UE, the second terminal device can select, from the set of relay candidates, another terminal device (e.g., referred to as a fourth terminal device) as a relay (RL UE) between the second terminal device and the network node or the third terminal device in response to a failure of the relay path, based on application or traffic related information, location or mobility related information, and/or connectivity related information associated with the fourth terminal device. For example, the fourth terminal device can be selected based on a validity timer indicating a duration during which the information associated with the fourth terminal device is valid, e.g., when the validity timer has not expired. Then, the second terminal device can establish a relay path from the second terminal device to the network node or the third terminal device via the fourth terminal device.

In an example, the second terminal device may initiate another discovery procedure over the sidelink when all the relay candidates in the set have their respective validity timers expired.

In an example, the second terminal device may transmit, to the first terminal device, a second message as a response to the first message. Here, the second message can be e.g., a response (not shown) to the discovery message at 2.2a in FIG. 2, or the discovery message at 2.2b in FIG. 2.

The second message contains one or more of following information associated with the second terminal device: identifier information, second application or traffic related information, second location or mobility related information, or second connectivity related information. In an example, before transmitting the second message, the second terminal device may receive an authorization to engage in the discovery procedure (e.g., by responding to the first message) from a network node, e.g., its serving gNB.

In an example, the second message may further contain a second validity timer indicating a duration during which the information associated with the second terminal device is valid.

In an example, the identifier information may include one or more of: a global identifier of the second terminal device, a temporary identifier of the second terminal device (e.g., used only for the discovery procedure), and/or an identifier of the second terminal device used only when the second terminal device serves as a relay for the first terminal device.

In an example, the second application or traffic related information may include a QoS profile of an application or traffic the second terminal device requests or is capable of providing. Here, the QoS profile may include a type, a priority, and/or a QoS requirement of the application or traffic the second terminal device requests or is capable of providing.

In an example, the second location or mobility related information may include one or more of: location information (e.g., GPS coordinates) of the second terminal device, information on an area or proximity where the second terminal device requests or is capable of providing an application or traffic, or mobility information of the second terminal device. Here, the mobility information of the second terminal device may indicate whether the second terminal device is static or moving, and/or a type of mobility, e.g., pedestrian or vehicle.

In an example, the second connectivity related information may include:

- a serving network node of the second terminal device,
- an indication of whether the second terminal device requests or is capable of providing a relay path towards a network node or a peer terminal device (e.g., an ID of the network node or the peer terminal device),
- a list of IDs of terminal devices that have been obtained in a previous discovery procedure,
- a radio quality indication of a PC5 or Uu link the second terminal device currently has,
- a load or a congestion condition of the PC5 or Uu link,
- an RAT (e.g., LTE or NR) of the PC5 or Uu link,
- an indication of a relay type (e.g., UE-to-Network or UE-to-UE) the second terminal device requests or is capable of providing, or
- a number of hops or a maximum number of hops along a relay path the second terminal device requests or is capable of providing.

In an example, the AS configuration/information in the second message, e.g., the second location or mobility related information and/or the second connectivity related information, may be transmitted explicitly in one or more fields in the second message, or may be included in a container (e.g., OCTET STRING) in the second message. The container may function as a pointer to a part of e.g., an RRC specification where the AS configuration/information is standardized.

In an example where the first terminal device operates as an RM UE, the first message may further contain a measurement configuration for the second terminal device (which is a relay candidate) to measure a PC5 link towards a peer terminal device (e.g., the above third terminal device or another terminal device), or a Uu link towards a network node. The measurement configuration may include e.g., time-frequency resources to measure and/or quantities to measure (for example, RSRP, RSRQ, or SINR). The second terminal device may also receive a measurement configuration from a network node, e.g., its serving gNB, via SIB or dedicated RRC signaling. The second terminal device can perform measurement on the PC5 link or the Uu link using the measurement configuration from the first terminal device or using the measurement configuration from the network node or using a predefined measurement configuration. The second message may further contain a measurement report for the PC5 link or the Uu link, containing the quantities measured by the second terminal device according to the measurement report.

FIG. 5 is a flowchart illustrating a method 500 according to an embodiment of the present disclosure. The method 500 can be performed at a network node, e.g., a serving network node of the above first or second terminal device.

At block 510, the network node transmits, to a terminal device (e.g., the above first or second terminal device), an authorization to initiate or engage in a discovery procedure.

At block 520, the network node transmits, to the terminal device, a measurement configuration for the terminal device to measure a PC5 link or a Uu link towards a network node or another (peer) terminal device.

In an example, the authorization and/or the measurement configuration may be transmitted via SIB or (dedicated) RRC signaling.

Correspondingly to the method 300 as described above, a first terminal device is provided. FIG. 6 is a block diagram of a first terminal device 600 according to an embodiment of the present disclosure. The first terminal device 600 can be e.g., an announcing UE in Model A, or a discoverer UE in Model B. The first terminal device 600 may function as an RM UE or an RL UE.

The first terminal device 600 can be configured to perform the method 300 as described above in connection with FIG. 3. As shown in FIG. 6, the first terminal device 600 includes a transmitting unit 610 configured to transmit, to a second terminal device, a first message for initiating a discovery procedure over a sidelink. The first message contains one or more of following information associated with the first terminal device: first application or traffic related information, first location or mobility related information, or first connectivity related information.

In an embodiment, the first message may further contain a first validity timer indicating a duration during which the information associated with the first terminal device is valid.

In an embodiment, the first application or traffic related information may include a Quality of Service (QoS) profile of an application or traffic the first terminal device requests or is capable of providing.

In an embodiment, the QoS profile may include a type, a priority, and/or a QoS requirement of the application or traffic.

In an embodiment, the first location or mobility related information may include one or more of: location information of the first terminal device, information on an area or proximity where the first terminal device requests or is capable of providing an application or traffic, or mobility information of the first terminal device.

In an embodiment, the mobility information of the first terminal device may indicate whether the first terminal device is static or moving.

In an embodiment, the first connectivity related information may include: a serving network node of the first terminal device, an indication of whether the first terminal device requests or is capable of providing a relay path towards a network node or a terminal device, a list of identifiers of terminal devices that have been obtained in a previous discovery procedure, a radio quality indication of a PC5 or Uu link the first terminal device currently has, a load or a congestion condition of the PC5 or Uu link, a Radio Access Technology (RAT) of the PC5 or Uu link, an indication of a relay type the first terminal device requests or is capable of providing, or a number of hops or a maximum number of hops along a relay path the first terminal device requests or is capable of providing.

In an embodiment, the first terminal device 600 may further include a receiving unit configured to receive, from the second terminal device, a second message as a response to the first message. The second message contains one or more of following information associated with the second terminal device: identifier information, second application or traffic related information, second location or mobility related information, or second connectivity related information.

In an embodiment, the identifier information may include one or more of: a global identifier of the second terminal device, a temporary identifier of the second terminal device, and/or an identifier of the second terminal device used only when the second terminal device serves as a relay for the first terminal device.

In an embodiment, the second application or traffic related information may include a QoS profile of an application or traffic the second terminal device requests or is capable of providing.

In an embodiment, the QoS profile may include a type, a priority, and/or a QoS requirement of the application or traffic the second terminal device requests or is capable of providing.

In an embodiment, the second location or mobility related information may include one or more of: location information of the second terminal device, information on an area or proximity where the second terminal device requests or is capable of providing an application or traffic, or mobility information of the second terminal device.

In an embodiment, the mobility information of the second terminal device may indicate whether the second terminal device is static or moving.

In an embodiment, the second connectivity related information may include: a serving network node of the second terminal device, an indication of whether the second terminal device requests or is capable of providing a relay path towards a network node or a terminal device, a list of identifiers of terminal devices that have been obtained in a previous discovery procedure, a radio quality indication of a PC5 or Uu link the second terminal device currently has, a load or a congestion condition of the PC5 or Uu link, a Radio Access Technology, RAT, of the PC5 or Uu link, an indication of a relay type the second terminal device requests or is capable of providing, or a number of hops or a maximum number of hops along a relay path the second terminal device requests or is capable of providing.

In an embodiment, the first terminal device 600 may further include: an obtaining unit configured to obtain a set of relay candidates, including the second terminal device, based at least on the second message; a selecting unit configured to select, from the set of relay candidates, the second terminal device as a relay between the first terminal device and a network node or a third terminal device, based on the second application or traffic related information, the second location or mobility related information, and/or the second connectivity related information; and an establishing unit configured to establish a relay path from the first terminal device to the network node or the third terminal device via the second terminal device.

In an embodiment, the second message may further contain a second validity timer indicating a duration during which the information associated with the second terminal device is valid, and the second terminal device may be selected based on the second validity timer.

In an embodiment, the selecting unit may be further configured to select, from the set of relay candidates, a fourth terminal device as a relay between the first terminal device and the network node or the third terminal device in response to a failure of the relay path, based on application or traffic related information, location or mobility related information, and/or connectivity related information associated with the fourth terminal device. The establishing unit may be further configured to establish a relay path from the first terminal device to the network node or the third terminal device via the fourth terminal device.

In an embodiment, the fourth terminal may be selected based on a validity timer indicating a duration during which the information associated with the fourth terminal device is valid.

In an embodiment, the first terminal device 600 may further include an initiating unit configured to initiate another discovery procedure over the sidelink when all the relay candidates in the set have their respective validity timers expired.

In an embodiment, the first message may further contain a measurement configuration for the second terminal device to measure a PC5 link towards the third terminal device or a fifth terminal device, or a Uu link towards the network node, and the second message further contains a measurement report for the PC5 link or the Uu link.

In an embodiment, the first terminal device 600 may further include a receiving unit configured to receive the measurement configuration from a network node.

In an embodiment, the first terminal device 600 may further include a receiving unit configured to receive an authorization to initiate the discovery procedure from a network node.

In an embodiment, the first location or mobility related information and/or the first connectivity related information may be transmitted explicitly in one or more fields in the first message or included in a container in the first message.

In an embodiment, the second location or mobility related information and/or the second connectivity related information may be received explicitly in one or more fields in the second message or included in a container in the second message.

The above unit 610 can be implemented as a pure hardware solution or as a combination of software and hardware, e.g., by one or more of: a processor or a micro-processor and adequate software and memory for storing of the software, a Programmable Logic Device (PLD) or other electronic component(s) or processing circuitry configured to perform the actions described above, and illustrated, e.g., in FIG. 3.

FIG. 7 is a block diagram of a first terminal device 700 according to another embodiment of the present disclosure. The first terminal device 700 can be e.g., an announcing UE in Model A, or a discoverer UE in Model B. The first terminal device 700 may function as an RM UE or an RL UE.

The first terminal device 700 includes a transceiver 710, a processor 720 and a memory 730. The memory 730 contains instructions executable by the processor 720 whereby the first terminal device 700 is operative to perform the actions, e.g., of the procedure described earlier in conjunction with FIG. 3. Particularly, the memory 730 can contain instructions executable by the processor 720 whereby the first terminal device 700 is operative to: transmit, to a second terminal device, a first message for initiating a discovery procedure over a sidelink. The first message contains one or more of following information associated with the first terminal device: first application or traffic related information, first location or mobility related information, or first connectivity related information.

In an embodiment, the first message may further contain a first validity timer indicating a duration during which the information associated with the first terminal device is valid.

In an embodiment, the first application or traffic related information may include a Quality of Service (QoS) profile of an application or traffic the first terminal device requests or is capable of providing.

In an embodiment, the QoS profile may include a type, a priority, and/or a QoS requirement of the application or traffic.

In an embodiment, the first location or mobility related information may include one or more of: location information of the first terminal device, information on an area or proximity where the first terminal device requests or is capable of providing an application or traffic, or mobility information of the first terminal device.

In an embodiment, the mobility information of the first terminal device may indicate whether the first terminal device is static or moving.

In an embodiment, the first connectivity related information may include: a serving network node of the first terminal device, an indication of whether the first terminal device requests or is capable of providing a relay path towards a network node or a terminal device, a list of identifiers of terminal devices that have been obtained in a previous discovery procedure, a radio quality indication of a PC5 or Uu link the first terminal device currently has, a load or a congestion condition of the PC5 or Uu link, a Radio Access Technology (RAT) of the PC5 or Uu link, an indication of a relay type the first terminal device requests or is capable of providing, or a number of hops or a maximum number of hops along a relay path the first terminal device requests or is capable of providing.

In an embodiment, the memory 730 may further contain instructions executable by the processor 720 whereby the first terminal device 700 is operative to: receive, from the second terminal device, a second message as a response to the first message. The second message contains one or more of following information associated with the second terminal device: identifier information, second application or traffic related information, second location or mobility related information, or second connectivity related information.

In an embodiment, the identifier information may include one or more of: a global identifier of the second terminal device, a temporary identifier of the second terminal device, and/or an identifier of the second terminal device used only when the second terminal device serves as a relay for the first terminal device.

In an embodiment, the second application or traffic related information may include a QoS profile of an application or traffic the second terminal device requests or is capable of providing.

In an embodiment, the QoS profile may include a type, a priority, and/or a QoS requirement of the application or traffic the second terminal device requests or is capable of providing.

In an embodiment, the second location or mobility related information may include one or more of: location information of the second terminal device, information on an area or proximity where the second terminal device requests or is capable of providing an application or traffic, or mobility information of the second terminal device.

In an embodiment, the mobility information of the second terminal device may indicate whether the second terminal device is static or moving.

In an embodiment, the second connectivity related information may include: a serving network node of the second terminal device, an indication of whether the second terminal device requests or is capable of providing a relay path towards a network node or a terminal device, a list of identifiers of terminal devices that have been obtained in a previous discovery procedure, a radio quality indication of a PC5 or Uu link the second terminal device currently has, a load or a congestion condition of the PC5 or Uu link, a Radio Access Technology, RAT, of the PC5 or Uu link, an indication of a relay type the second terminal device requests or is capable of providing, or a number of hops or a maximum number of hops along a relay path the second terminal device requests or is capable of providing.

In an embodiment, the memory 730 may further contain instructions executable by the processor 720 whereby the first terminal device 700 is operative to: obtain a set of relay candidates, including the second terminal device, based at least on the second message; select, from the set of relay candidates, the second terminal device as a relay between the first terminal device and a network node or a third terminal device, based on the second application or traffic related information, the second location or mobility related information, and/or the second connectivity related information; and establish a relay path from the first terminal device to the network node or the third terminal device via the second terminal device.

In an embodiment, the second message may further contain a second validity timer indicating a duration during which the information associated with the second terminal device is valid, and the operation of selecting may be based on the second validity timer.

In an embodiment, the memory 730 may further contain instructions executable by the processor 720 whereby the first terminal device 700 is operative to: select, from the set of relay candidates, a fourth terminal device as a relay between the first terminal device and the network node or the third terminal device in response to a failure of the relay path, based on application or traffic related information, location or mobility related information, and/or connectivity related information associated with the fourth terminal device; and establish a relay path from the first terminal device to the network node or the third terminal device via the fourth terminal device.

In an embodiment, the operation of selecting of the fourth terminal may be based on a validity timer indicating a duration during which the information associated with the fourth terminal device is valid.

In an embodiment, the method may further include: initiating another discovery procedure over the sidelink when all the relay candidates in the set have their respective validity timers expired.

In an embodiment, the first message may further contain a measurement configuration for the second terminal device to measure a PC5 link towards the third terminal device or a fifth terminal device, or a Uu link towards the network node, and the second message further contains a measurement report for the PC5 link or the Uu link.

In an embodiment, the memory 730 may further contain instructions executable by the processor 720 whereby the first terminal device 700 is operative to: receive the measurement configuration from a network node.

In an embodiment, the memory 730 may further contain instructions executable by the processor 720 whereby the first terminal device 700 is operative to: receive an authorization to initiate the discovery procedure from a network node.

In an embodiment, the first location or mobility related information and/or the first connectivity related information may be transmitted explicitly in one or more fields in the first message or included in a container in the first message.

In an embodiment, the second location or mobility related information and/or the second connectivity related information may be received explicitly in one or more fields in the second message or included in a container in the second message.

Correspondingly to the method 400 as described above, a second terminal device is provided. FIG. 8 is a block diagram of a second terminal device 800 according to an embodiment of the present disclosure. The second terminal device 800 can be e.g., a monitoring UE in Model A, or a discoveree UE in Model B. The second terminal device 800 may function as an RM UE or an RL UE.

The second terminal device 800 can be configured to perform the method 400 as described above in connection with FIG. 4. As shown in FIG. 8, the second terminal device 800 includes a receiving unit 810 configured to receive, from a first terminal device, a first message for initiating a discovery procedure over a sidelink. The first message contains one or more of following information associated with the first terminal device: first application or traffic related information, first location or mobility related information, or first connectivity related information.

In an embodiment, the first application or traffic related information may include a QoS profile of an application or traffic the first terminal device requests or is capable of providing.

In an embodiment, the QoS profile may include a type, a priority, and/or a QoS requirement of the application or traffic.

In an embodiment, the first location or mobility related information may include one or more of: location information of the first terminal device, information on an area or proximity where the first terminal device requests or is capable of providing an application or traffic, or mobility information of the first terminal device.

In an embodiment, the mobility information of the first terminal device may indicate whether the first terminal device is static or moving.

In an embodiment, the first connectivity related information may include: a serving network node of the first terminal device, an indication of whether the first terminal device requests or is capable of providing a relay path towards a network node or a terminal device, a list of identifiers of terminal devices that have been obtained in a previous discovery procedure, a radio quality indication of a PC5 or Uu link the first terminal device currently has, a load or a congestion condition of the PC5 or Uu link, an RAT of the PC5 or Uu link, an indication of a relay type the first terminal device requests or is capable of providing, or a number of hops or a maximum number of hops along a relay path the first terminal device requests or is capable of providing.

In an embodiment, the second terminal device 800 may further include: an obtaining unit configured to obtain a set of relay candidates, including the first terminal device, based at least on the first message; a selecting unit configured to select, from the set of relay candidates, the first terminal device as a relay between the second terminal device and a network node or a third terminal device, based on the first application or traffic related information, the first location or mobility related information, and/or the first connectivity related information; and an establishing unit configured to establish a relay path from the second terminal device to the network node or the third terminal device via the first terminal device.

In an embodiment, the first message may further contain a first validity timer indicating a duration during which the information associated with the first terminal device is valid, and the first terminal device may be selected based on the first validity timer.

In an embodiment, the selecting unit may be further configured to select, from the set of relay candidates, a fourth terminal device as a relay between the second terminal device and the network node or the third terminal device in response to a failure of the relay path, based on application or traffic related information, location or mobility related information, and/or connectivity related information associated with the fourth terminal device. The establishing unit may be further configured to establish a relay path from the second terminal device to the network node or the third terminal device via the fourth terminal device.

In an embodiment, the fourth terminal may be selected based on a validity timer indicating a duration during which the information associated with the fourth terminal device is valid.

In an embodiment, the second terminal device 800 may further include an initiating unit configured to initiate another discovery procedure over the sidelink when all the relay candidates in the set have their respective validity timers expired.

In an embodiment, the second terminal device 800 may further include a transmitting unit configured to transmit, to the first terminal device, a second message as a response to the first message. The second message may contain one or more of following information associated with the second terminal device: identifier information, second application or traffic related information, second location or mobility related information, or second connectivity related information.