Apparatus, method and computer program

Abstract

There is provided an apparatus, at a user equipment, comprising means for determining, based on a trigger, selection or reselection of another user equipment as a relay node between a first user equipment and a second user equipment, where the first user equipment and the second user equipment are in communication, determining a source of the trigger, determining, based on the determined source, selection or reselection of another user equipment as a relay node between the first user equipment and the second user equipment, in one embodiment, a request is determined to be provided from a first user equipment to a second user equipment, the request for at least one of coordinated discovery of user equipment candidates for another user equipment, selection or reselection of another user equipment in the user equipment candidates, and providing the request from the first user equipment to the second user equipment.

Description

Technical Field

[0001] Various example embodiments described herein relate to methods, apparatus, systems and computer programs, and in particular but not limited to, to sidelink (SL) user equipment to user equipment (U2U) relay (re)selection for supporting service continuity (SC). Background Art

[0002] A communication system may be viewed as a facility that enables a communication session between two or more entities (such as user terminals, base stations, and / or other nodes) by providing a carrier wave between the various entities involved in the communication path. For example, a communication system may be provided by means of a communication network and one or more compatible communication devices. A communication session may include, for example, the communication of data for carrying communications such as voice, video, electronic mail (email), text messaging, multimedia, and / or content data. Non-limiting examples of the services provided include two-way or multi-way calls, data communications or multimedia services, and access to data network systems such as the Internet.

[0003] In a wireless communication system, at least a portion of a communication session between at least two stations occurs over a wireless link. Examples of wireless systems include public land mobile networks (PLMNs), satellite-based communication systems, and different wireless local area networks, such as wireless local area networks (WLANs). Some wireless systems may be divided into cells, and are therefore often referred to as cellular systems.

[0004] A user can access the communication system with the aid of an appropriate communication device or terminal. The user's communication device may be referred to as a user equipment (UE) or user device. The communication device is provided with an appropriate signal receiving and sending device for implementing communication, such as implementing access to a communication network or communicating directly with other users. The communication device may access a carrier provided by a site (e.g., a base station of a cell) and transmit and / or receive communications on the carrier.

[0005] Communication systems and associated equipment typically operate according to a given standard or specification that specifies what the various entities associated with the system are allowed to do and how it should be achieved. Typically, communication protocols and / or parameters for the connection will also be defined. An example of a communication system is UTRAN (3G radio). Other examples of communication systems are the Long Term Evolution (LTE) of the Universal Mobile Telecommunications System (UMTS) radio access technology and the so-called 5G or New Radio (NR) networks. NR is being standardized by the Third Generation Partnership Project (3GPP). Summary of the invention

[0006] In a first example embodiment, an apparatus is provided, at a first user device, comprising components for: based on a trigger, determining to select or reselect another user device as a relay node between the first user device and a second user device, wherein the first user device and the second user are in communication; determining a source of the trigger; based on the determined source, determining to provide a request from the first user device to the second user device, the request being used for at least one of: coordinated discovery of user device candidates for another user device, selection or reselection of another user device among the user device candidates; and providing a request from the first user device to the second user device.

[0007] The source of the trigger may be the first user equipment.

[0008] The first user equipment and the second user equipment may communicate via a third user equipment acting as a relay node, and the source of the trigger may be the third user equipment acting as a relay node.

[0009] The source of the trigger may be a second user device, and the apparatus may include means for receiving information from the second user device and further determining to provide a request based on the information. The request is for at least one of: coordinating discovery, selection, or reselection.

[0010] The component for determining may include a component for determining the following items: whether the information includes a list of user equipment candidates for another user equipment, whether the number of user equipment candidates in the list is below a threshold, whether the list of user equipment candidates includes a user equipment candidate on the list of user equipment candidates at the first user equipment, or whether the information includes an indication that the second user equipment is performing a coordinated relay discovery process.

[0011] The request may include at least one of: a list of user equipment candidates for another user equipment, an indication whether coordinated discovery is requested at the second user equipment, or an indication that the first user equipment is performing a coordinated discovery procedure.

[0012] The apparatus may include a component for receiving, in response to the request, an indication from a second user device, the indication comprising at least one of: an identification of another user device, an indication that selection or reselection is currently not possible based on a list of user device candidates, an indication that the second user device is performing a coordinated discovery process, or another list of user device candidates for another user device.

[0013] The apparatus may include means for sending a discovery request from the first user equipment to a user equipment candidate in response to receiving an indication from the second user equipment that the second user equipment is performing a coordinated discovery process. The discovery request includes an indication instructing the user equipment candidate to monitor for discovery messages from the second user equipment.

[0014] In a second example embodiment, an apparatus is provided, at a second user device, comprising a component for: at the second user device, receiving a request from a first user device, the request being used for at least one of: coordinated discovery of user device candidates for another user device, selection or reselection of another user device among the user device candidates to act as a relay node between the first user device and the second user device, wherein the first user device and the second user device are in communication.

[0015] The apparatus may include means for providing a trigger from the second user equipment to the first user equipment to select or reselect another user equipment as a relay node between the first user equipment and the second user equipment.

[0016] The request may include a list of user equipment candidates for the further user equipment, an indication of whether coordinated discovery is requested at the second user equipment, or an indication that the first user equipment is performing a coordinated discovery procedure.

[0017] The apparatus may include means for determining, based on the request, to perform a coordinated discovery procedure at the second user equipment for another user equipment; performing the coordinated discovery procedure and providing an indication to the first user equipment indicating that the second user equipment is performing the coordinated discovery procedure.

[0018] The component for performing the coordinated discovery process may include: a component for providing a broadcast discovery announcement or a multicast discovery response to the user equipment candidates, the broadcast discovery announcement or the multicast discovery response including at least one of the following: a layer 2 identifier of the first user equipment, or a layer 2 identifier of the second user equipment.

[0019] The apparatus may include means for determining to perform a relay selection or reselection procedure at the second user equipment based on a request to perform a relay selection or reselection procedure at the second user equipment, and providing an indication of an identity of another user equipment from the second user equipment to the first user equipment.

[0020] The apparatus may include means for providing an indication from the second user equipment in response to the request, wherein the indication includes at least one of: an indication that selection or reselection is currently not possible based on the list of user equipment candidates, or another list of user equipment candidates for another user equipment.

[0021] The apparatus may include means for sending a discovery request from a second user equipment to a user equipment candidate in response to receiving an indication from the first user equipment that the first user equipment is performing a coordinated discovery process, the discovery request including an indication instructing the user equipment candidate to monitor discovery messages from the first user equipment.

[0022] In a third example embodiment, a method is provided, comprising: at a first user device, based on a trigger, determining to select or reselect another user device as a relay node between the first user device and a second user device, wherein the first user device and the second user are in communication; determining a source of the trigger; based on the determined source, determining to provide a request from the first user device to the second user device, the request being used for at least one of: coordinated discovery of user device candidates for another user device, selection or reselection of another user device among the user device candidates; and providing the request from the first user device to the second user device.

[0023] The source of the trigger may be the first user equipment.

[0024] The first user equipment and the second user equipment may communicate via a third user equipment acting as a relay node, and the source of the trigger may be the third user equipment acting as a relay node.

[0025] The source of the trigger may be the second user equipment, and the method may include receiving information from the second user equipment and further determining based on the information to provide a request for at least one of: coordinating discovery, selection, or reselection.

[0026] The determination may include determining whether the information includes a list of user equipment candidates for another user equipment, whether the number of user equipment candidates in the list is below a threshold, whether the list of user equipment candidates includes a user equipment candidate on the list of user equipment candidates at the first user equipment, or whether the information includes an indication that the second user equipment is performing a coordinated relay discovery process.

[0027] The request may include at least one of: a list of user equipment candidates for another user equipment, an indication of whether coordinated discovery is requested at the second user equipment, or an indication that the first user equipment is performing the coordinated discovery procedure.

[0028] The method may include: in response to the request, receiving an indication from a second user device, wherein the indication includes at least one of the following: an identification of another user device, an indication that selection or reselection is currently not possible based on a list of user device candidates, an indication that the second user device is performing a coordinated discovery process, or another list of user device candidates for another user device.

[0029] The method may include, in response to receiving an indication from the second user equipment that the second user equipment is performing a coordinated discovery process, sending a discovery request from the first user equipment to a user equipment candidate, the discovery request including an indication instructing the user equipment candidate to monitor a discovery message from the second user equipment.

[0030] In a fourth example embodiment, a method is provided, comprising: at a second user device, receiving a request from a first user device, the request being used for at least one of: coordinated discovery of user device candidates for another user device, selection or reselection of another user device among the user device candidates to act as a relay node between the first user device and the second user device, wherein the first user device and the second user device are in communication.

[0031] The method may include providing a trigger from the second user equipment to the first user equipment to select or reselect another user equipment as a relay node between the first user equipment and the second user equipment.

[0032] The request may include a list of user equipment candidates for another user equipment, an indication of whether coordinated discovery is requested at the second user equipment, or an indication that the first user equipment is performing a coordinated discovery procedure.

[0033] The method may include: determining to perform a coordinated discovery process for another user equipment at the second user equipment based on the request; performing the coordinated discovery process and providing an indication to the first user equipment indicating that the second user equipment is performing the coordinated discovery process.

[0034] Performing the coordinated discovery process may include providing a broadcast discovery announcement or a multicast discovery response to the user equipment candidates, the broadcast discovery announcement or the multicast discovery response including a layer 2 identifier of the first user equipment and a layer 2 identifier of the second user equipment.

[0035] The method may include: determining to perform a relay selection or reselection procedure at the second user equipment based on a request to perform a relay selection or relay reselection procedure at the second user equipment; and providing an indication of an identification of another user equipment from the second user equipment to the first user equipment.

[0036] The method may include providing an indication from the second user equipment in response to the request, wherein the indication includes at least one of: an indication that selection or reselection is currently not possible based on the list of user equipment candidates, or another list of user equipment candidates for another user equipment.

[0037] The method may include, in response to receiving an indication from the first user equipment that the first user equipment is performing a coordinated discovery process, sending a discovery request from the second user equipment to a user equipment candidate, the discovery request including an indication instructing the user equipment candidate to monitor a discovery message from the first user equipment.

[0038] In a fifth example embodiment, a device is provided, comprising: at least one processor and at least one memory storing instructions, which instructions, when executed by the at least one processor, cause the device to at least: at a first user device, based on a trigger, determine to select or reselect another user device as a relay node between the first user device and a second user device, wherein the first user device and the second user are in communication; determine a source of the trigger; based on the determined source, determine to provide a request from the first user device to the second user device, the request being used for at least one of: coordinated discovery of user device candidates for another user device, selection or reselection of another user device among the user device candidates.

[0039] The source of the trigger may be the first user equipment.

[0040] The first user equipment and the second user equipment may communicate via a third user equipment acting as a relay node, and the source of the trigger may be the third user equipment acting as a relay node.

[0041] The source of the trigger may be a second user equipment, and the apparatus may be caused to receive information from the second user equipment and further determine to provide the request based on the information. The request is for at least one of: coordinating discovery, selection or reselection.

[0042] The apparatus may be caused to determine whether the information includes a list of user equipment candidates for another user equipment, whether the number of user equipment candidates in the list is below a threshold, whether the list of user equipment candidates includes a user equipment candidate on a list of user equipment candidates at the first user equipment, or whether the information includes an indication that the second user equipment is performing a coordinated relay discovery procedure.

[0043] The request may include at least one of: a list of user equipment candidates for another user equipment, an indication of whether coordinated discovery is requested at the second user equipment, or an indication that the first user equipment is performing a coordinated discovery procedure.

[0044] The apparatus may be configured to: in response to the request, receive an indication from the second user equipment, wherein the indication includes at least one of the following: an identification of another user equipment, an indication that selection or reselection is currently not possible based on the list of user equipment candidates,

[0045] An indication that the second user equipment is performing a coordinated discovery procedure, or another list of user equipment candidates for another user equipment.

[0046] The apparatus may be caused to, in response to receiving an indication from the second user equipment that the second user equipment is performing a coordinated discovery process, send a discovery request from the first user equipment to a user equipment candidate, the discovery request including an indication instructing the user equipment candidate to monitor a discovery message from the second user equipment.

[0047] In a sixth example embodiment, an apparatus is provided, comprising: at least one processor and at least one memory storing instructions, which instructions, when executed by the at least one processor, cause the apparatus to at least: at a second user device, receive a request from a first user device at the second user device, the request being used for at least one of: coordinated discovery of user device candidates for another user device, selection or reselection of another user device among the user device candidates to act as a relay node between the first user device and the second user device, wherein the first user device and the second user device are in communication.

[0048] The apparatus may be caused to provide a trigger from the second user equipment to the first user equipment to select or reselect another user equipment as a relay node between the first user equipment and the second user equipment.

[0049] The request may include a list of user equipment candidates for another user equipment, an indication whether coordinated discovery is requested at the second user equipment, or an indication that the first user equipment is performing a coordinated discovery procedure.

[0050] The apparatus may be caused to: determine, based on the request, to perform a coordinated discovery procedure for another user equipment at the second user equipment; perform the coordinated discovery procedure and provide an indication to the first user equipment indicating that the second user equipment is performing the coordinated discovery procedure.

[0051] The apparatus may be caused to provide a broadcast discovery announcement or a multicast discovery response to the user equipment candidates, the broadcast discovery announcement or the multicast discovery response comprising a layer 2 identifier of the first user equipment and a layer 2 identifier of the second user equipment.

[0052] The apparatus may be caused to: determine to perform a relay selection or reselection procedure at the second user equipment based on a request to perform a relay selection or relay reselection procedure at the second user equipment; and provide an indication of an identity of another user equipment from the second user equipment to the first user equipment.

[0053] The apparatus may be caused to provide, in response to the request, an indication from the second user equipment, wherein the indication comprises at least one of: an indication that selection or reselection is currently not possible based on the list of user equipment candidates, or another list of user equipment candidates for another user equipment.

[0054] The apparatus may be caused to: in response to the first user equipment receiving an indication that the first user equipment is performing a coordinated discovery process, send a discovery request from the second user equipment to a user equipment candidate, the discovery request including an indication instructing the user equipment candidate to monitor a discovery message from the first user equipment.

[0055] In a seventh example embodiment, a computer-readable medium is provided comprising instructions, which when executed by an apparatus causes the apparatus to perform at least the following operations: at a first user device, based on a trigger, determine to select or reselect another user device as a relay node between the first user device and a second user device, wherein the first user device and the second user are in communication; determine a source of the trigger; based on the determined source, determine to provide a request from the first user device to the second user device, the request being used for at least one of: coordinated discovery of user device candidates for another user device, selection or reselection of another user device among the user device candidates; and provide a request from the first user device to the second user device.

[0056] The source of the trigger may be the first user equipment.

[0057] The first user equipment and the second user equipment may communicate via a third user equipment acting as a relay node, and the source of the trigger may be the third user equipment acting as a relay node.

[0058] The source of the trigger may be a second user equipment, and the apparatus may be caused to perform receiving information from the second user equipment and further determining based on the information to provide a request for at least one of: coordinating discovery, selection, or reselection.

[0059] The apparatus may be caused to perform a determination of whether the information includes a list of user equipment candidates for another user equipment, whether the number of user equipment candidates in the list is below a threshold, whether the list of user equipment candidates includes a user equipment candidate on a list of user equipment candidates at the first user equipment, or whether the information includes an indication that the second user equipment is performing a coordinated relay discovery procedure.

[0060] The request may include at least one of: a list of user equipment candidates for another user equipment, an indication of whether coordinated discovery is requested at the second user equipment, or an indication that the first user equipment is performing a coordinated discovery procedure.

[0061] The apparatus may be configured to perform the following operations: in response to a request, receive an indication from a second user device, wherein the indication includes at least one of: an identification of another user device, an indication that selection or reselection is currently not possible based on a list of user device candidates, an indication that the second user device is performing a coordinated discovery process, or another list of user device candidates for another user device.

[0062] The apparatus may be caused to, in response to receiving an indication from the second user equipment that the second user equipment is performing a coordinated discovery process, send a discovery request from the first user equipment to a user equipment candidate, the discovery request including an indication instructing the user equipment candidate to monitor for discovery messages from the second user equipment.

[0063] In an eighth example embodiment, a computer-readable medium comprising instructions is provided, which instructions, when executed by an apparatus, cause the apparatus to at least perform: at a second user device, receiving a request from a first user device at the second user device, the request being used for at least one of: coordinated discovery of user device candidates for another user device, selection or reselection of another user device among the user device candidates to act as a relay node between the first user device and the second user device, wherein the first user device and the second user device are in communication.

[0064] The apparatus may be caused to perform providing a trigger from the second user equipment to the first user equipment to select or reselect another user equipment as a relay node between the first user equipment and the second user equipment.

[0065] The request may include a list of user equipment candidates for another user equipment, an indication whether coordinated discovery is requested at the second user equipment, or an indication that the first user equipment is performing a coordinated discovery procedure.

[0066] The apparatus may be caused to perform: based on the request, determining to perform a coordinated discovery process for another user equipment at the second user equipment; performing the coordinated discovery process and providing an indication to the first user equipment indicating that the second user equipment is performing the coordinated discovery process.

[0067] The apparatus may be caused to perform providing a broadcast discovery advertisement or a multicast discovery response to the user equipment candidates, the broadcast discovery advertisement or the multicast discovery response comprising a layer 2 identifier of the first user equipment and a layer 2 identifier of the second user equipment.

[0068] The apparatus may be caused to perform: based on a request to perform a relay selection or relay reselection procedure at the second user equipment, determine to perform a relay selection or relay reselection procedure at the second user equipment; and provide an indication of an identification of another user equipment from the second user equipment to the first user equipment.

[0069] The apparatus may be caused to perform: in response to the request, providing an indication from the second user equipment, wherein the indication comprises at least one of: an indication that selection or reselection is currently not possible based on the list of user equipment candidates, or another list of user equipment candidates for another user equipment.

[0070] The apparatus may be caused to, in response to receiving an indication from the first user equipment that the first user equipment is performing a coordinated discovery process, send a discovery request from the second user equipment to a user equipment candidate, the discovery request including an indication instructing the user equipment candidate to monitor for discovery messages from the first user equipment.

[0071] In a ninth example embodiment, a non-transitory computer-readable medium is provided, which includes program instructions for causing an apparatus to at least perform the method according to the third or fourth example embodiment.

[0072] Many different exemplary embodiments have been described above, and it should be understood that another exemplary embodiment can be provided by combining any two or more of the above exemplary embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] Example embodiments will now be further described, by way of example only, with reference to the accompanying drawings, in which:

[0074] Figure 1 A schematic diagram of a 5GS communication system according to an example embodiment is shown;

[0075] Figure 2 A schematic diagram showing a mobile communication device according to an example embodiment is shown;

[0076] Figure 3 shows a schematic diagram of a control device according to an example embodiment;

[0077] Figure 4 A schematic diagram showing a U2U relay scenario according to an example embodiment is shown;

[0078] Figure 5 shows a signaling flow for U2U relay (re)selection according to an example embodiment;

[0079] Figure 6 shows a signaling flow for SL discovery using U2U relay according to an example embodiment;

[0080] Figure 7 A flow chart showing a method according to an example embodiment is shown;

[0081] Figure 8 A flow chart showing a method according to an example embodiment is shown;

[0082] Fig. 9 shows a signaling flow according to an example embodiment;

[0083] Fig.10 A signaling flow according to an example embodiment is shown. DETAILED DESCRIPTION

[0084] Before explaining the exemplary embodiments in detail, Figures 1 to 3 Certain principles of wireless communication systems and mobile communication devices are briefly explained to aid understanding of the technology behind the described example embodiments.

[0085] An example of a suitable communication system is the 5G or NR concept. The network architecture in NR may be similar to that of LTE Advanced. The base stations of the NR system may be referred to as next generation Node Bs (gNBs). Changes in the network architecture may depend on the need to support various radio technologies and more refined quality of service (QoS) support, as well as on-demand requirements such as quality of service (QoS) levels to support the user's quality of experience (QoE). In addition, network-aware services and applications, as well as service and application-aware networks may bring changes to the architecture. These are all related to the information-centric network (ICN) and user-centric content distribution network (UC-CDN) approaches. NR may use multiple-input-multiple-output (MIMO) antennas, with many more base stations or nodes (the so-called small cell concept) than LTE, including macro base stations operating in conjunction with smaller sites, and may also employ various radio technologies to achieve better coverage and higher data rates.

[0086] Future networks may utilize network function virtualization (NFV) technology, which is a network architecture concept that proposes virtualizing network node functions into "building blocks" or entities that can be operably connected or linked together to provide services. Virtualized network functions (VNFs) may include one or more virtual machines that use standard or general-purpose servers to run computer program code, rather than customized hardware. Cloud computing or data storage may also be utilized. In radio communications, this may mean that node operations are performed at least in part on a server, host, or node that is coupled to remote radio head operations. Node operations may also be distributed among multiple servers, nodes, or hosts. It should also be understood that the distribution of tasks between core network operations and base station operations may be different from that in LTE, or even non-existent.

[0087] Figure 1 A schematic diagram of a 5G system (5GS) 100 according to an example embodiment is shown. The 5GS may include a user equipment (UE) 102 (which may also be referred to as a communication device or terminal), a 5G radio access network (5GRAN) 104, a 5G core network (5GCN) 106, one or more application functions (AFs) 108, and one or more data networks (DNs) 110.

[0088] An example 5G core network (CN) includes functional entities. The 5GCN 106 may include one or more access and mobility management functions (AMFs) 112, one or more session management functions (SMFs) 114, an authentication server function (AUSF) 116, a unified data management (UDM) 118, one or more user plane functions (UPFs) 120, a unified data repository (UDR) 122, and / or a network exposure function (NEF) 124. The UPF is controlled by the SMF (session management function), which receives policies from the PCF (policy control function).

[0089] The CN is connected to the UE via a radio access network (RAN). The 5G RAN may include one or more gNodeB (GNB) distributed unit functions connected to one or more gNodeB (GNB) centralized unit functions. The RAN may include one or more access nodes.

[0090] A user plane function (UPF) called a PDU Session Anchor (PSA) may be responsible for forwarding frames back and forth between the DN and the tunnel established over 5G to the UE that exchanges traffic with the DN.

[0091] Now refer to Figure 2 describing in more detail possible mobile communication devices, Figure 2 A schematic partial cross-sectional view of a communication device 200 according to an example embodiment is shown. Such a communication device is generally referred to as a user equipment (UE) or a terminal. Suitable mobile communication devices can be provided by any device capable of sending and receiving radio signals. Non-limiting examples include a mobile station (MS) or a mobile device (such as a mobile phone or a so-called "smart phone"), a computer with a wireless interface card or other wireless interface facilities (e.g., a USB adapter), a personal data assistant (PDA) or a tablet computer with wireless communication capabilities, an IP voice (VoIP) phone, a portable computer, a desktop computer, an image capture terminal device such as a digital camera, a game terminal device, a music storage and playback device, a vehicle-mounted wireless terminal device, a wireless endpoint, a mobile station, a laptop embedded device (LEE), a laptop device (LME), an intelligent device, a wireless customer premises equipment (CPE) or any combination of these, etc. The mobile communication device can provide, for example, data communications for carrying communications such as voice, email (email), text messages, multimedia, etc. Therefore, users can obtain and provide many services via their communication devices. Non-limiting examples of these services include two-way or multi-way calls, data communications or multimedia services or simply access to a data communications network system such as the Internet. Users may also be provided with broadcast or multicast data. Non-limiting examples of content include downloads, television and radio programs, videos, advertisements, various alerts and other information.

[0092] The mobile device is typically provided with at least one data processing entity 201, at least one memory 202 and other possible components 203 for performing the tasks it is intended to accomplish with the assistance of software and hardware, including controlling access to and communication with access systems and other communication devices. Data processing, storage and other related control devices may be provided on appropriate circuit boards and / or in chipsets. This feature is represented by reference numeral 204. The user may control the operation of the mobile device through a suitable user interface such as a keyboard 205, voice commands, a touch screen or touchpad, a combination thereof, etc. A display 208, a speaker and a microphone may also be provided. In addition, the mobile communication device may include appropriate connectors (wired or wireless) for connecting to other devices and / or for connecting external accessories (e.g., hands-free devices).

[0093] The mobile device 200 may receive signals via the air interface or radio interface 207 by means of corresponding means for receiving, and may transmit signals via corresponding means for transmitting radio signals. Figure 2 In the mobile device, the transceiver arrangement is schematically represented by block 206. The transceiver arrangement 206 may be provided, for example, by means of a radio component and an associated antenna arrangement. The antenna arrangement may be arranged internally or externally to the mobile device.

[0094] Figure 3 A control device 300 for a communication system according to an example embodiment is shown, which is for example coupled to and / or used to control a site of an access system, such as a RAN node, such as a base station, an eNB or a gNB, a relay node or a core network node (such as an MME or an S-GW or a P-GW), or a core network function (such as an AMF / SMF), or a server or a host. The method can be implemented in a single control device or on more than one control device. The control device can be integrated with or external to a node or module of the core network or RAN. In some example embodiments, the base station includes a separate control device unit or module. In other example embodiments, the control device can be another network element, such as a radio network controller or a spectrum controller. In some example embodiments, each base station can have such a control device as well as a control device provided in a radio network controller. The control device 300 can be arranged to provide control of communications in a service area of ​​the system. The control device 300 includes at least one memory 301, at least one data processing unit 302, 303 and an input / output interface 304. Via the interface, the control device can be coupled to a receiver and a transmitter of the base station. The receiver and / or the transmitter may be implemented as a radio front end or a remote radio head.

[0095] The following relates to UE-to-UE (U2U) relay based on sidelink (SL).

[0096] Figure 4 A schematic diagram of a U2U relay scenario according to an example embodiment is shown. In this example scenario, UE-A 401 is a source UE and UE-B 402 is a destination UE. UE-A 401 and UE-B 402 can communicate directly or indirectly on a SL via a U2U relay UE 403. UE 403 is a current serving U2U relay. UE 404 is a candidate U2U relay UE.

[0097] Mode A and Mode B are two models specified in 3GPP for general sidelink discovery. Mode A: involves a UE announcing "I am here". Mode B: involves a UE asking "who is there" and / or "are you there".

[0098] Generally, improvements in speed and / or efficiency in reselecting a new U2U relay UE2 to support service continuity (SC) between a source UE (eg, UE-A 401) and a destination UE (eg, UE-B 402) may be beneficial.

[0099] How UE-A and UE-B perform U2U relay discovery (RD) and determine U2U relay (re)selection is quite open. For example, for reasons of energy saving and resource efficiency, a potential U2U relay UE using mode A may not always announce itself for U2URD. Therefore, for robust U2U RD, UE-A 401 and UE-B 402 may need to consider using both mode A and mode B. U2U relay (re)selection can be triggered by any UE (UE-A 401, UE-B 402, and serving U2U relay UE1 403). In order to ensure that the (re)selected U2U relay UE2 is suitable for both UE-A 401 and UE-B 402, U2U relay (re)selection is at least coordinated between UE-A 401 and UE-B 402. It is unclear which UE (UE-A 401 or UE-B 402) is responsible for the (re)selection decision, and it is also unclear whether and how the U2URD is coordinated between UE-A 401 and UE-B 402, since the target of the (re)selection is the SC.

[0100] Assuming that UE-A 401 and UE-B 402 have the latest information about all U2U relay UE candidates 403 in their vicinity, Figure 5 As shown, the U2U relay (re)selection between UE-A 401 and UE-B 402 to implement SC has the following steps.

[0101] In 501 , UE-A 401 sends a U2U relay reselection request to UE-B 402 , indicating a list of U2U relay UE candidates to UE-B 402 .

[0102] In 502 , UE-B 402 determines whether there is a common U2U relay UE candidate between UE-A 401 and UE-B 402 .

[0103] In 503, if there are common U2U relay UE candidates, UE-B 402 may (re)select one of them and initiate, via the selected UE, SL connection reestablishment with UE-A 401. In addition, before reestablishing the SL connection through the (re)selected relay UE, UE-B 402 may respond to UE-A 401, indicating the (re)selected U2U relay UE.

[0104] In 504 , if there is no common U2U relay UE candidate, UE-B 402 may respond to UE-A 401 indicating that U2U relay (re)selection is currently not possible.

[0105] Since whether the U2U relay UE uses mode A or mode B, or both, for U2U RD may depend on the UE and application implementation, and all UEs involved in the SL U2U relay based connection may move independently, the assumption that UE-A 401 and UE-B 402 have the latest information about all U2U relay UE candidates in their vicinity may not be taken for granted, but needs to be confirmed or verified on the fly when U2U relay (re)selection is required.

[0106] Figure 6 A signaling flow for SL discovery with U2U relay according to an example embodiment is shown, wherein UE1 is provided with access stratum (AS) assisted sidelink discovery (SD) based on SL U2U relay so that UE1 discovers UE2 and U2U relay UE candidates for reaching UE2. However, in such proposals, specific SC aspects are not considered, nor is possible coordination between UE1 and UE2 for U2U relay (re)selection in advance over an existing SL connection.

[0107] The following focuses on the coordination between UE-A 401 , UE-B 402 and the involved U2U relay UEs to achieve fast and efficient U2U relay (re)selection for SC between UE-A 401 and UE-B 402 .

[0108] Figure 7 A flow chart of a method according to an example embodiment is shown.

[0109] In S1 , the method includes determining, at a first user equipment, to select or reselect another user equipment as a relay node between the first user equipment and a second user equipment based on a trigger, wherein the first user equipment and the second user equipment are in communication.

[0110] In S2 , the method comprises determining a source of a trigger.

[0111] In S3, the method includes: based on the determined source, determining to provide a request from the first user equipment to the second user equipment, the request being used for at least one of: coordinated discovery of user equipment candidates for another user equipment, selection or reselection of another user equipment among the user equipment candidates (in other words, coordinated discovery and / or (re)selection).

[0112] In S4, the method comprises providing a request from the first user equipment to the second user equipment.

[0113] When the first UE and the second UE communicate via a third user equipment acting as a relay node, the source of the trigger may be the first user equipment, the second user equipment, or the third user equipment acting as a relay node.

[0114] Figure 8 A flow chart of a method according to an example embodiment is shown.

[0115] In T1, the method includes receiving a request at a second user equipment from a first user equipment, the request being used for at least one of: coordinated discovery of user equipment candidates for another user equipment, selection or reselection of another user equipment among the user equipment candidates to act as a relay node between the first user equipment and the second user equipment, wherein the first user equipment and the second user equipment are in communication.

[0116] The method may allow coordination of U2U relay discovery and / or (re)selection for SC at least between UE-A 401 and UE-B 402. Some example embodiments described below assume that UE-A 401 is assuming a coordination role. However, when UE-A 401 and UE-B 402 are currently communicating with each other via U2U relay UE1 403, the trigger for U2U relay discovery and / or (re)selection may be initiated by UE-A 401 or UE-B 402 or the current U2U relay UE1 403.

[0117] For example, UE-A 401 may determine that U2U relay (re)selection is required for the SC between UE-A 401 and UE-B 402 (in other words, selecting or reselecting another user equipment to act as a relay node between the first UE and the second UE).

[0118] UE-A 401 further determines whether it is necessary to initiate a SL procedure for coordinating U2U relay (re)selection (i.e., SL U2U relay (re)selection request) between UE-A 401 and UE-B 402 (e.g., whether to provide a request from the first user equipment to the second user equipment for coordinating discovery and / or (re)selection of another user equipment). The further determination is based on the trigger source for the U2U relay (re)selection, such as which of the first UE, the second UE, or the third UE acting as a relay node triggers it, such as UE-A 401, UE-B 402, or U2U relay UE1403.

[0119] In an exemplary embodiment, if the trigger comes from UE-A 401 itself or the current U2U relay UE1 403, such as SL UE information received from U2U relay UE1 403, which indicates that U2U relay UE1 403 cannot serve UE-A 401 and UE-B 402, and UE-A 401 and UE-B 402 need to reselect a new U2U relay UE2 404 within a certain period of time, then UE-A 401 will initiate a SL U2U relay (re)selection request to UE-B 402.

[0120] When the source of the trigger is a second UE (e.g., UE-B 402), the method may include receiving information from the second user equipment and further determining to provide a request based on the information, the request being used to coordinate relay discovery and / or (re)selection. The second UE may provide a list of user equipment candidates for another user equipment to the first UE in the information.

[0121] The determination may include determining whether the information includes a list of user equipment candidates for another user equipment, whether the number of user equipment candidates in the list is below a threshold, whether the list of user equipment candidates includes a user equipment candidate on the list of user equipment candidates at the first user equipment, or whether the information includes an indication that the second user equipment is performing a coordinated relay discovery process.

[0122] For example, further determination may also be based on whether UE-B provides sufficient U2U relay UE candidates, as follows.

[0123] In an example embodiment, if a trigger comes from UE-B, for example, when SL UE information is received from UE-B, which indicates that the SL between UE-B and the U2U relay UE1 has become insufficient (for example, the SL reference signal received power (RSRP) between UE-B and the U2U relay UE1 is lower than a threshold), UE-A 401 may determine whether to initiate a SL U2U relay (re)selection request based on whether UE-B 402 provides a list of U2U relay UE candidates to UE-A 401 along with the SL UE information, the number of U2U relay UE candidates in the list, whether there is a match between the list provided by UE-B 402 and the list maintained at UE-A 401 in terms of U2U relay UE candidates, or whether UE-B 402 provides an indication that UE-B 402 is taking active action to coordinate U2U RD by: Figure 6 In the scheme shown, the UE-B 402 uses the current layer 2 identifier (L2 ID) of the UE-A 401 known to it as the SRC ID to announce itself, while indicating the current L2 ID of the UE-A 401 in the announcement for coordinated U2U RD using mode A; or uses the current L2 ID of the UE-A 401 as the DST ID and the current L2 ID of the UE-B 402 as the SRC ID, and uses mode B to multicast the U2U RD response for coordinated U2U RD. The empty list of U2U relay UE candidates may mean that there is no U2U relay UE candidate that is using mode A to announce itself to UE-A 401 or UE-B 402 for possible U2U RD.

[0124] UE-A 401 may determine not to initiate a SL U2U relay (re)selection request to UE-B 402 in the following circumstances: if there is a match between the list provided by UE-B 402 and the list maintained at UE-A 401 in terms of U2U relay UE candidates, the number of U2U relay UE candidates in the list provided by UE-B 402 is higher than a threshold, there is no match between the list of UE-B 402 and the list of UE-A 401 in terms of U2U relay UE candidates (which means that UE-B 402 has provided all preferred U2U relay UE candidates and the possibility of finding a new U2U relay UE candidate that is suitable for both UE-A 401 and UE-B 402 is quite low), or the SL UE information from UE-B 402 includes an indication that UE-B 402 is taking proactive action to coordinate U2U RD.

[0125] If there is a match between the list provided by UE-B 402 and the list maintained at UE-A 401 in terms of U2U relay UE candidates, UE-A 401 may (re)select the matching U2U relay UE2 and initiate a new SL relay connection establishment with UE-B 402 via U2U relay UE2. In addition, UE-A 401 may send a SL U2U relay (re)selection indication to UE-B 402, indicating the (re)selected U2U relay UE2 404, e.g., the L2ID of the U2U relay UE2 404.

[0126] If the number of U2U relay UE candidates in the list provided by UE-B 402 is higher than a threshold and there is no match between the list of UE-B 402 and the list of UE-A 401 in terms of U2U relay UE candidates, UE-A 401 may send a SL U2U relay (re)selection indication to UE-B 402, indicating that (re)selection is currently not possible for the list provided by UE-B 402. In addition, UE-A 401 may include in the SL U2U relay (re)selection indication the list of U2U relay UE candidates maintained at UE-A 401, and cause UE-B 402 to take further action, such as to perform U2U relay UE (re)selection (including further RD) when UE-B 402 is qualified, or to update SLUE information after performing further RD as described above.

[0127] If UE-B 402 is taking active actions to coordinate U2U RD, UE-A 401 may Figure 6 Broadcast U2U RD solicitation with an indication that the U2U relay UE candidate skips relaying the U2U RD solicitation to UE-B 402, but monitors for broadcast RD announcements or multicast RD responses from UE-B 402 and necessary configuration information for monitoring, such as L2 IDs of UE-A 401 and UE-B 402.

[0128] UE-A 401 may determine to initiate a SL U2U relay (re)selection request to UE-B 402 in other ways, as follows.

[0129] Providing a request from a first user equipment to a second user equipment may include: UE-A 401 sending a SLU2U relay (re)selection request to UE-B 402. The request may include at least one of the following: a list of user equipment candidates for another user equipment, an indication of whether coordinated discovery is requested at the second user equipment, or an indication that the first user equipment is performing a coordinated discovery process. The list of user equipment candidates may be a list of U2U relay UE candidates maintained at UE-A 401 (i.e., a list of user equipment candidates for another user equipment). Depending on the number of U2U relay UE candidates in the list, the request may include an indication indicating whether coordinated U2U RD is requested. For example, if the number of U2U relay UE candidates in the list from UE-A 401 is higher than a threshold, coordinated U2U RD may not be required.

[0130] In response to receiving the request, the second user equipment may perform a discovery and / or (re)selection procedure for another user equipment to act as a relay node.

[0131] The method may include: determining to perform a coordinated discovery process for another user equipment at the second user equipment based on the request; performing the coordinated discovery process and providing an indication to the first user equipment indicating that the second user equipment is performing the coordinated discovery process.

[0132] Performing a coordinated discovery process includes means for providing a broadcast discovery announcement or a multicast discovery response to the user equipment candidates, the broadcast discovery announcement or the multicast discovery response including a layer 2 identifier of the first user equipment and a layer 2 identifier of the second user equipment.

[0133] For example, if coordinated U2U RD is requested, if no other L2 ID is configured for UE-B 402 in the request received from UE-A 401, UE-B 402 can use the existing L2 IDs of UE-A 401 and UE-B 402 to start announcing itself by broadcasting RD announcements as in mode A or multicasting RD responses as in mode B.

[0134] If coordinated U2U RD is not requested, this may implicitly mean that UE-B 402 is allowed to perform U2U relay UE (re)selection and send a SL U2U relay (re)selection indication to UE-A 401, similar to the UE-A 401 behavior described above.

[0135] The method may include: determining, based on the request, to perform a relay selection or relay reselection procedure; performing the relay selection or reselection procedure; and providing, from the second user equipment to the first user equipment, an indication of an identification of another user equipment.

[0136] The method may include providing an indication from the second user equipment in response to the request, wherein the indication includes at least one of: an indication that selection or reselection is currently not possible based on the list of user equipment candidates, or another list of user equipment candidates for another user equipment.

[0137] The indication may be provided in the SL U2U relay (re)selection indication. In response to receiving an indication from the first user equipment that the first user equipment is performing a coordinated discovery process, the method may include sending a discovery request (discovery solicitation) from the second user equipment to the user equipment candidate, the discovery request including an indication instructing the user equipment candidate to monitor for discovery messages from the first user equipment.

[0138] In an example embodiment, UE-A 401 receives a SL U2U relay (re)selection indication from UE-B 402 indicating at least one of the following: (i) the reselected U2U relay UE2 404 (i.e., another user equipment), such as the L2 ID of the U2U relay UE2 404; (ii) for the list provided by UE-A 401, (re)selection is currently not possible; or (iii) UE-B 402 is performing coordinated U2U RD (e.g., by providing the L2 IDs of UE-A 401 and UE-B 402, to actively announce that it is related to UE1403). In addition, the list of U2U relay UE candidates maintained by UE-B 402 can be included in the SL U2U relay (re)selection indication received from UE-B 402.

[0139] If the indication includes the reselected U2U relay UE2 404, UE-A 401 performs SL relay connection reestablishment via the reselected U2U relay UE.

[0140] If the indication indicates that (re)selection is currently not possible, UE-A 401 may determine to update the SL U2U relay (re)selection request to UE-B 402 and request coordinated U2U RD, or initiate coordinated U2U RD to UE-B 402 without sending a request to UE-B 402 in advance.

[0141] In response to receiving at the first user equipment an indication from the second user equipment that the second user equipment is performing a coordinated discovery process, the method may include sending a discovery request to a user equipment candidate, the discovery request including an indication instructing the user equipment candidate to monitor for discovery messages from the second user equipment.

[0142] For example, if UE-B 402 is performing coordinated U2U RD, UE-A 401 may Figure 6Broadcast U2U RD request including an indication instructing the U2U relay UE candidate to skip relaying U2U RD request to UE-B 402, but monitor broadcast RD announcement or multicast RD response from UE-B 402 and necessary configuration information for monitoring, such as L2 IDs of UE-A 401 and UE-B 402.

[0143] Fig. 9 and 10 A signaling diagram is provided for illustrating some features of the SL coordination procedure for U2U relay (re)selection of SC between UE-A 401 and UE-B 402.

[0144] Fig. 9 is an example of a case where the trigger for U2U relay (re)selection comes from the current U2U relay UE1 403. Note that if UE-A 401 recognizes by itself that U2U relay (re)selection is required, then Fig. 9 901 in it.

[0145] At 902 , UE-A 401 sends a SL U2U relay (re)selection request to UE-B 402 , the SL U2U relay (re)selection request including a list of U2U relay UE candidates and a request for coordinating U2U RD.

[0146] At 903 , UE-B 402 sends a SL U2U Relay (Re)Selection Indication including a list of U2U relay UE candidates and an indication that UE-B 402 is performing coordinated U2U RD.

[0147] At 904 , UE-B 402 broadcasts a SD announcement including the L2 IDs of UE-A 401 and UE-B 402 .

[0148] At 905 UE-A 401 broadcasts a U2U RD Request including the L2IDs of UE-A and UE-B, skips relaying the RD request but monitors for an indication of a SD announcement from UE-B.

[0149] At 906 , coordinated U2U RD is performed, and UE-B 402 (re)selects U2U relay UE2 for SC between UE-A 401 and UE-B 402 .

[0150] Fig.10is an example of a case where the trigger for U2U relay (re)selection comes from UE-B 402. In this example, UE-B 402 acts as a first user equipment and UE-A acts as a second user equipment. UE-B 402 actively performs a coordinated RD procedure and notifies UE-A 401 of it at 1001. For example, the request includes an indication that the first user equipment is performing a coordinated discovery procedure.

[0151] At 1002 , UE-B 402 broadcasts a SD announcement including the L2 IDs of UE-A 401 and UE-B 402 .

[0152] At 1003, UE-A 401 broadcasts a U2U RD request including the L2IDs of UE-A and UE-B, an indication to skip relaying the RD request but monitor for SD announcements from UE-B. In other words, in response to the request, the second user equipment sends a discovery request to the user equipment candidate, the discovery request including an indication to instruct the user equipment candidate to monitor for discovery messages from the first user equipment.

[0153] At 1004 , coordinated U2U RD is performed, and UE-B 402 (re)selects U2U relay UE2 for SC between UE-A 401 and UE-B 402 .

[0154] UE-A 401 or UE-B 402 may assume the coordination role, or in other words, may initiate a SL U2U relay (re)selection request. In this option, the initiating UE (UE-A 401 or UE-B 402) may determine to actively perform a coordinated U2URD, and indicate this to the other UE as described above with respect to UE-B 402. The other UE may then act as UE-A 401 as described above. That is, the initiating UE may determine to act as UE-A 401 or UE-B402 as described above.

[0155] The trigger for U2U relay (re)selection for SC from the current U2U relay UE1 403 may be sent to either UE-A 401 or UE-B 402 , as determined by the U2U relay UE1 403 .

[0156] The SL UE information from the currently serving U2U relay UE1 to UE-A 401 for triggering the U2U relay (re)selection of the SC between UE-A 401 and UE-B 402 may include: the reason and timing information for the U2U relay UE1 403 to commit to serve UE-A 401 and UE-B 402 to perform the U2U relay (re)selection. Based on the timing information provided by the U2U relay UE1 403, UE-A 401 may set the timing information for coordinating the U2U RD, which includes the timing information for receiving the U2U relay (re)selection indication from UE-B 402.

[0157] Fig. 9 Responsive SD announcement in step 4 of Fig.10 The active SD announcement in step 2 of the above may be implemented by using a default L2 DST ID designated for sidelink broadcasting and using a designated access stratum (AS) message (such as Figure 5 and Figure 6 In an alternative solution, UE-B can multicast a specific AS message using UE-A's L2 ID as the multicast DST ID. This is based on the assumption that: Fig. 9 Step 3 or in Fig.10 In step 1, UE-B 402 reaches an agreement with UE-A 401 or informs UE-A 401 in advance; and Fig. 9 Step 5 or Fig.10 In step 3 of , UE-A 401 configures the U2U relay UE to monitor the multicast from UE-B 402. The designated AS message may contain information such as the L2 IDs of UE-A 401 and UE-B 402, so that the U2U relay UE candidate (U2U relay UE2 404) can identify and discover UE-B 402 as requested by UE-A 401. Note that the use of the above-mentioned designated AS message can be applied to replace the two options that UE-B 402 can use Model-A to broadcast SD announcements or use Model-B to broadcast SD responses.

[0158] An apparatus, at a first user device, may include components for: based on a trigger, determining to select or reselect another user device as a relay node between the first user device and a second user device, wherein the first user device and the second user are in communication; determining a source of the trigger; based on the determined source, determining to provide a request from the first user device to the second user device, the request being used for at least one of the following: coordinated discovery of user device candidates for another user device and selection or reselection of another user device among the user device candidates, and providing a request from the first user device to the second user device.

[0159] An apparatus, at a second user device, may include a component for: at the second user device, receiving a request from a first user device, the request being used for at least one of: coordinated discovery of user device candidates for another user device, selection or reselection of another user device among the user device candidates to act as a relay node between the first user device and the second user device, wherein the first user device and the second user device are in communication.

[0160] It should be understood that the apparatus may include other units or modules in or for transmission and / or reception, such as a radio component or a radio head, etc. Although the apparatus has been described as one entity, different modules and memories may be implemented in one or more physical or logical entities.

[0161] Note that while some example embodiments have been described with respect to 5G networks, similar principles may be applied with respect to other networks and communication systems. Thus, while certain example embodiments are described above by way of example with reference to certain example architectures for wireless networks, technologies, and standards, the embodiments may be applied to any other suitable form of communication system than those shown and described herein.

[0162] It is noted herein that while the above describes example embodiments, several variations and modifications may be made to the disclosed solution without departing from the scope of the present invention.

[0163] As used herein, “at least one of: ” and “at least one of ” and similar expressions, where a list of two or more elements is connected by “and” or “or”, means at least any one of the elements, or at least any two or more of the elements, or at least all of the elements.

[0164] In general, various example embodiments may be implemented in hardware or dedicated circuits, software, logic, or any combination thereof. Some example embodiments may be implemented in hardware, while other aspects may be implemented in firmware or software that may be executed by a controller, microprocessor, or other computing device, but the disclosure is not limited thereto. Although various example embodiments may be illustrated and described as block diagrams, flow charts, or using some other graphical representation, it should be understood that the blocks, devices, systems, techniques, or methods described herein may be implemented in hardware, software, firmware, dedicated circuits or logic, general purpose hardware or controllers or other computing devices, or some combination thereof in non-limiting examples.

[0165] As used in this application, the term "circuitry" may refer to one or more or all of the following:

[0166] Hardware-only circuit implementations (such as implementations in simulation only) and / or digital circuits.

[0167] Combinations of hardware circuits and software such as (applicable):

[0168] Combination of analog and digital hardware circuits with software / firmware and

[0169] Software and memory that work together with any portion of a hardware processor (including a digital signal processor) to enable a device (such as a mobile phone or server) to perform various functions, and

[0170] A hardware circuit and / or processor, such as a microprocessor or portion of a microprocessor, that requires software (eg, firmware) for operation, but the software may not be present when not needed for operation.

[0171] This definition of circuitry applies to all uses of this term herein, including in any claims. As another example, as used herein, the term circuitry also covers implementations of only a hardware circuit or processor (or multiple processors) or portions of a hardware circuit or processor and their accompanying software and / or firmware. For example, the term circuitry also covers a baseband integrated circuit or processor integrated circuit used in a mobile device or similar integrated circuit in a server, cellular network device, or other computing or network device, if applicable to the particular claim element.

[0172] The example embodiments described herein can be implemented by computer software executable by a data processor of a mobile device, such as in a processor entity, or by hardware, or by a combination of software and hardware. Computer software or programs, also referred to as program products (including software routines, applets and / or macros), can be stored in any device-readable data storage medium, and they include program instructions for performing specific tasks. A computer program product may include one or more computer executable components that are configured to perform an embodiment when the program is running. One or more computer executable components may be at least one software code or part thereof.

[0173] In addition, in this regard, it should be noted that any box of the logic flow in the accompanying drawings can represent program steps, or interconnected logic circuits, boxes and functions, or a combination of program steps and logic circuits, boxes and functions. Software can be stored on such physical media as memory chips or memory blocks implemented in processors, magnetic media (such as hard disks or floppy disks), and optical media (such as, for example, DVDs and their data variants CDs). Physical media are non-transitory media. As used herein, the term "non-transitory" is a limitation of the medium itself (i.e., tangible rather than signals), rather than a limitation on data storage persistence (e.g., RAM vs. ROM).

[0174] The memory may be of any type suitable for the local technical environment and may be implemented using any suitable data storage technology, such as semiconductor-based memory devices, magnetic memory devices and systems, optical memory devices and systems, fixed memory, and removable memory. As non-limiting examples, the data processor may be of any type suitable for the local technical environment and may include one or more of a general-purpose computer, a special-purpose computer, a microprocessor, a digital signal processor (DSP), an application-specific integrated circuit (ASIC), an FPGA, a gate-level circuit, and a processor.

[0175] Example embodiments may be practiced in various components such as integrated circuit modules. The design of integrated circuits is a highly automated process. Complex and powerful software tools are available to convert a logic level design into a semiconductor circuit design that is ready to be etched and formed on a semiconductor substrate.

[0176] The scope of protection sought for the various exemplary embodiments of the present disclosure is set out by the independent claims. Embodiments and features described in this specification that do not belong to the scope of the independent claims are to be interpreted as examples useful for understanding the various exemplary embodiments described herein.

[0177] The above provides a complete and informative description of the example embodiments described herein by way of non-limiting examples. However, in view of the foregoing, various modifications and adaptations may become apparent to those skilled in the relevant art when read in conjunction with the accompanying drawings and claims. However, all such and similar modifications of the teachings of the present disclosure will still fall within the scope of the present disclosure. In fact, there is another example embodiment that includes a combination of one or more example embodiments with any other example embodiment described herein.

[0178]

[0179] 2. Discussion

[0180] 2.1 Scope, requirements, or working assumptions for Rel-18

[0181] NR SL Relay including SL U2U Relay targets V2X, public safety and commercial use cases as in the objectives of WID RP-221262 and reproduced above. Therefore, it is important to clarify the following aspects, with respect to the scope, requirements or working assumptions of Rel-18.

[0182] - Requirement to support indirect sidelink discovery (SD) with SL U2U relay: A source UE needs to discover a destination UE that is not in direct SL proximity of the source UE via one or more U2U relay UEs.

[0183] - The need to support service continuity of unicast between source UE and destination UE via SL U2U relay: This includes possible path switching from direct to indirect via the selected U2U relay UE, or from indirect to indirect via the reselected U2U relay UE; or mode switching between L2 and L3 relays. Note that SL U2U relay can be used to provide SL range or coverage extension and SL RLF recovery; or to enhance QoS and energy efficiency of source UE and destination UE.

[0184] - Requirement to support backward compatibility with SL U2U relay: The destination UE may have an earlier 3GPP release and therefore be unaware of the SL U2U relay, or the SL U2U relay is transparent to the destination UE.

[0185] Proposal 1: RAN2 checks and confirms with SA2 support for the above aspects, including

[0186] a) Indirect sidelink discovery,

[0187] b) Service continuity and

[0188] c) Backward compatibility in Rel-18 SL U2U trunking.

[0189] 2.2SL U2U relay discovery

[0190] In SL U2N relay, the U2N relay UE is always associated with the serving gNB. Therefore, it is sufficient for the remote UE to discover the U2N relay UE in direct SD using Mode A or Mode B. In SL U2U relay, the U2U relay UE may not have a priori knowledge or association with the source UE or the destination UE. Therefore, it may be necessary to coordinate the flight between the source UE, the destination UE and the U2U relay UE in order to ensure that the U2U relay UE candidate can reach both the source UE and the destination UE in U2U relay discovery (RD).

[0191] SA2 has so far been considered as many options related to SL U2U RD, as described in TR23.700-33. In one example, the source UE may issue an RD request to find U2U relay UE candidates that can reach the destination UE, as requested by the source UE in the RD request. This means that the source UE initiates SL U2U RD using a mode B-U2U relay UE near the source UE, and upon receiving the RD request from the source UE, may further perform SD to the destination UE by, for example, initiating an SD request using mode B. A separate U2U relay UE may in turn respond to the source UE and become a U2U relay UE candidate for the source UE. However, this example assumes that an association between the U2U relay UE candidate and the source UE or destination UE is established in advance. In another example, consider that the U2U relay UE may announce a list of destination UEs that can be reached by the announcing U2U relay UE based on using mode A. In the event that the result of the determination is positive, the announcing U2U relay UE is considered to be a U2U relay UE candidate for the source UE. However, this example assumes that the association of the Advertise U2U Relay UE with the list of destination UEs is pre-established and that the Source UE is restricted to the list of destination UEs provided by the Advertise U2U Relay UE.

[0192] Proposal 2: RAN2 studies the coordination between source UE, destination UE and U2U relay UE in U2U relay discovery for L2 and L3 SL U2U based on SA2 results.

[0193] In SL U2N relay, both the U2N remote UE and the U2N relay UE need to meet certain radio conditions on Uu, such as the DL RSRP of the remote UE is below a threshold and the DL RSRP of the relay UE is above a threshold. In SL U2U relay, if any radio conditions need to be specified for UEs acting as source UEs, destination UEs or U2U relay UEs, it will be quite open. Consider the conditions that the source UE and the destination UE are not within sufficient direct SL communication range of each other or the SL channel condition between them is below a threshold. Considering that SL U2U relay can be used to enhance the power efficiency of the source UE and the destination UE, the condition can be flexible. It can be observed from the above examples that in the first example, obvious radio conditions for or towards the U2U relay UE may not be required. In the second example, the radio conditions on the SL between the announced U2U relay UE and the individual destination UEs in the list may be considered.

[0194] Proposal 3: Considering that SL U2U relay can be used to enhance the power efficiency of source UE and destination UE, RAN2 studies the radio conditions required for source UE, destination UE and U2U relay UE in SL U2U relay.

[0195] It is further observed from the examples described above that the higher the number of U2U relay UE candidates, the higher the signaling overhead and associated delay of the overall indirect SD and SL U2U RD procedures between the source UE, the destination UE and the U2U relay UE. This is especially costly for the destination UE if it has to individually respond to SD requests from multiple U2U relay UE candidates or periodically announce itself to the U2U relay UE.

[0196] The above problems can be eliminated by allowing the destination UE to respond to the earliest SD request received from the U2U relay UE candidate using SL multicast or broadcast, or by announcing itself (e.g., by starting Mode B discovery) with the need for SL U2U RD coordinated with the source UE and therefore the U2U relay UE. This can be achieved based on, for example, configuration information provided along the SL U2U RD process. Note that the source UE and the destination UE may need to provide the U2U relay UE with the ID information of the source UE and the destination UE so that the U2U relay UE may be able to identify and verify them in the SL U2U RD. To this end, the L2 IDs of the source UE and the destination UE may be provided in the configuration information.

[0197] Proposal 4: RAN2 studies the use of sidelink discovery Mode A and Mode B for SL U2U relay discovery coordinated between source UE, destination UE and U2U relay UE, considering the support of service continuity between the source UE and the destination UE.

[0198] Proposal 5: RAN2 studies the use of L2 ID for rapid identification of source UE and destination UE at U2U relay UE in SL U2U relay discovery.

[0199] However, due to the distributed nature and usage of SL U2U relays, the SL traffic of SL U2U RDs may be high and thus generally very power and resource consuming, even in cases where UEs acting as U2U relay UEs or destination UEs do not announce themselves to the SD at all.

[0200] Proposal 6: RAN2 studies whether it is necessary to configure a dedicated resource pool for SL U2U relay discovery and indirect side-link discovery of SL U2U relay.

[0201] In many use cases, the use of SLU2U relay can be limited to members of a predefined SL group in the sense that the source UE, destination UE and U2U relay UE are members of a predefined group. For example, in a formation, a U2U relay UE member can provide SL U2U relay for other UE members of the group when moving together. The same applies to critical group communications in public safety or personal IoT networks. In these use cases, the SL U2U RD can be restricted to the group. For example, in order to prevent unnecessary communication with the outside world in the above use cases, SL multicast with the L2 group ID as the L2 DST ID can be used to send SD messages such as SD announcements or requests.

[0202] Proposal 7: RAN2 studies limiting SL U2U relay discovery to a predefined SL group using SL multicast transmission of sidelink discovery messages.

[0203] 2.3SL U2U trunk (re)selection

[0204] It is expected that SL U2U relay (re)selection is used for SL connection establishment or re-establishment between the source UE and the destination UE via the (re)selected U2U relay UE. The SL connection establishment is triggered by the source UE. The SL connection re-establishment in the context of service continuity can be triggered by the source UE, the destination UE or the currently serving U2U relay UE. However, which of the source UE and the destination UE is responsible for the SL U2U relay (re)selection decision. This may also depend on how the SL U2U RD is coordinated and executed between the source UE and the destination UE. For example, some solutions in TR23.700-33 suggest that the SL U2U RD can be integrated into the indirect unicast SL connection establishment process initiated by the source UE, and the destination UE can select the U2U relay UE. In TR23.700-33, the source UE can discover and select a U2U relay UE that announces to the source UE or indicates to the source UE that the destination UE can be reached.

[0205] Proposal 8: RAN2 considers that either the source UE or the relay UE may be responsible for SL U2U relay (re)selection.

[0206] Proposal 9: RAN2 studies the coordination between source UE, relay UE and U2U relay UE for SL U2U relay (re)selection, taking into account the support of service continuity between source UE and relay UE.

Claims

1. An apparatus, at a first user equipment, comprising: Based on the trigger, determine to select or reselect another user equipment as a relay node between the first user equipment and a second user equipment, wherein the first user equipment and the second user equipment are in communication; determining a source of the trigger; Based on the determined source, determine to provide a request from the first user equipment to the second user equipment, the request being used for at least one of: coordinated discovery of user equipment candidates for the other user equipment, selection or reselection of the other user equipment among the user equipment candidates; and The request is provided from the first user equipment to the second user equipment.

2. The apparatus of claim 1, wherein the source of the trigger is the first user equipment. 3 . The apparatus of claim 1 , wherein the first user equipment and the second user equipment communicate via a third user equipment acting as a relay node, and the source of the trigger is the third user equipment acting as the relay node.

4. The apparatus of claim 1, wherein the source of the trigger is the second user device, comprising a component for receiving information from the second user device and further determining based on the information to provide a request, the request being used for at least one of: coordinated discovery, selection, or reselection.

5. An apparatus according to claim 4, wherein the component for determining includes a component for determining the following items: whether the information includes a list of user equipment candidates for the other user equipment, whether the number of user equipment candidates in the list is lower than a threshold, whether the list of user equipment candidates includes a user equipment candidate on the list of user equipment candidates at the first user equipment, or whether the information includes an indication that the second user equipment is performing a coordinated relay discovery process.

6. An apparatus according to any one of claims 1 to 5, wherein the request comprises at least one of: a list of user equipment candidates for the other user equipment, an indication of whether coordinated discovery is requested at the second user equipment, or an indication that the first user equipment is performing the coordinated discovery process.

7. The device according to claim 6, comprising: A component for receiving an indication from the second user equipment in response to the request, wherein the indication includes at least one of the following: an identification of the other user equipment, an indication that selection or reselection is currently not possible based on the list of user equipment candidates, an indication that the second user equipment is performing the coordinated discovery process, or another list of user equipment candidates for the other user equipment.

8. The device according to claim 7, comprising: means for sending a discovery request from the first user equipment to a user equipment candidate in response to receiving the indication from the second user equipment that the second user equipment is performing the coordinated discovery process, the discovery request comprising an indication instructing the user equipment candidate to monitor for discovery messages from the second user equipment.

9. An apparatus, at a second user equipment, comprising means for: At the second user equipment, a request is received from the first user equipment, the request being used for at least one of: coordinated discovery of user equipment candidates for another user equipment, selection or reselection of the other user equipment among the user equipment candidates to act as a relay node between the first user equipment and the second user equipment, wherein the first user equipment and the second user equipment are in communication.

10. The device according to claim 9, comprising means for: A trigger is provided from the second user equipment to the first user equipment to select or reselect the other user equipment as the relay node between the first user equipment and the second user equipment.

11. The apparatus of claim 9 or claim 10, wherein the request comprises: a list of user equipment candidates for the further user equipment, an indication of whether coordinated discovery is requested at the second user equipment, or an indication that the first user equipment is performing a coordinated discovery procedure.

12. The apparatus according to claim 11 comprises a component for: determining, based on the request, to perform a coordinated discovery process for the other user equipment at the second user equipment; performing the coordinated discovery process and providing an indication to the first user equipment, indicating that the second user equipment is performing the coordinated discovery process.

13. The apparatus of claim 12, wherein the means for performing the coordinated discovery process comprises: A component for providing a broadcast discovery announcement or a multicast discovery response to a user equipment candidate, the broadcast discovery announcement or the multicast discovery response comprising at least one of the following: a layer 2 identifier of the first user equipment, or a layer 2 identifier of the second user equipment.

14. The apparatus according to claim 11 comprises a component for: determining to perform the relay selection or relay reselection process at the second user equipment based on the request to perform the relay selection or relay reselection process at the second user equipment, and providing an indication of the identification of the other user equipment from the second user equipment to the first user equipment.

15. The apparatus according to any one of claims 9 to 11, comprising a component for providing an indication from the second user equipment in response to the request, wherein the indication comprises at least one of: an indication that selection or reselection is currently not possible based on the list of user equipment candidates, or another list of user equipment candidates for the other user equipment.

16. The apparatus according to claim 11, comprising: means for sending a discovery request from the second user equipment to a user equipment candidate in response to receiving the indication from the first user equipment that the first user equipment is performing the coordinated discovery process, the discovery request comprising an indication instructing the user equipment candidate to monitor for discovery messages from the first user equipment.

17. A method comprising: At the first user device: Based on the trigger, determine to select or reselect another user equipment as a relay node between the first user equipment and a second user equipment, wherein the first user equipment and the second user equipment are in communication; determining a source of the trigger; Based on the determined source, determine to provide a request from the first user equipment to the second user equipment, the request being used for at least one of: coordinated discovery of user equipment candidates for the other user equipment, selection or reselection of the other user equipment among the user equipment candidates; and The request is provided from the first user equipment to the second user equipment.

18. A method comprising: At the second user device: At the second user equipment, a request is received from the first user equipment, the request being used for at least one of: coordinated discovery of user equipment candidates for another user equipment, selection or reselection of the other user equipment among the user equipment candidates to act as a relay node between the first user equipment and the second user equipment, wherein the first user equipment and the second user equipment are in communication.

19. An apparatus comprising: at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to at least: at a first user device: Based on the trigger, determine to select or reselect another user equipment as a relay node between the first user equipment and a second user equipment, wherein the first user equipment and the second user equipment are in communication; determining a source of the trigger; Based on the determined source, determine to provide a request from the first user equipment to the second user equipment, the request being used for at least one of: coordinated discovery of user equipment candidates for the other user equipment, selection or reselection of the other user equipment among the user equipment candidates; and The request is provided from the first user equipment to the second user equipment.

20. An apparatus comprising: at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the apparatus to at least: at a second user device: At the second user equipment, a request is received from the first user equipment, the request being used for at least one of: coordinated discovery of user equipment candidates for another user equipment, selection or reselection of the other user equipment among the user equipment candidates to act as a relay node between the first user equipment and the second user equipment, wherein the first user equipment and the second user equipment are in communication.

21. A computer-readable medium comprising instructions, which when executed by an apparatus causes the apparatus to at least perform the following operations: at a first user device: Based on the trigger, determine to select or reselect another user equipment as a relay node between the first user equipment and a second user equipment, wherein the first user equipment and the second user equipment are in communication; determining a source of the trigger; Based on the determined source, determine to provide a request from the first user equipment to the second user equipment, the request being used for at least one of: coordinated discovery of user equipment candidates for the other user equipment, selection or reselection of the other user equipment among the user equipment candidates; and The request is provided from the first user equipment to the second user equipment.

22. A computer-readable medium comprising instructions, which when executed by an apparatus causes the apparatus to at least perform the following operations: at a second user device: At the second user equipment, a request is received from the first user equipment, the request being used for at least one of: coordinated discovery of user equipment candidates for another user equipment, selection or reselection of the other user equipment among the user equipment candidates to act as a relay node between the first user equipment and the second user equipment, wherein the first user equipment and the second user equipment are in communication.

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