Apparatus, method, and computer program

Abstract

An apparatus in a user equipment, the apparatus comprising: means for determining, based on a trigger, to select or reselect a further user equipment to function as a relay node between a first user equipment and a second user equipment in communication; means for determining a source of the trigger; means for determining, based on the determined source, to provide a request from the first user equipment to the second user equipment for at least one of cooperative detection of user equipment candidates for the further user equipment and selection or reselection of the further user equipment from among the user equipment candidates; and means for providing the request from the first user equipment to the second user equipment.

Description

[Technical Field]

[0001] Various exemplary embodiments described herein relate to methods, apparatus, systems, and computer programs, particularly, but not exclusively, to sidelink (SL) user equipment to user equipment (U2U) relay (re)selection for service continuity (SC) support. [Background technology]

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

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

[0004] A user may access a communication system by means of a suitable communication device or terminal. A user's communication device may be referred to as user equipment (UE) or user device. A communication device is equipped with suitable signal receiving and transmitting equipment to enable communication, e.g., accessing a communication network or directly communicating with other users. A communication device may access a carrier provided by a station, e.g., a cell base station, and transmit and / or receive communications on the carrier.

[0005] Communication systems and associated devices typically operate according to a given standard or specification that defines what the various entities associated with the system are allowed to do and how to achieve this. The communication protocols and / or parameters used for connectivity are also typically defined. One 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 standardized by the 3rd Generation Partnership Project (3GPP). Summary of the Invention [Means for solving the problem]

[0006] In a first exemplary embodiment, an apparatus is provided in a first user equipment, the apparatus comprising: means for determining, based on a trigger, to select or reselect a further user equipment to function as a relay node between the first user equipment and a second user equipment in communication; means for determining a source of the trigger; means for determining, based on the determined source, to provide a request from the first user equipment to the second user equipment for at least one of the following: cooperative detection of user equipment candidates for the further user equipment; and selection or reselection of the further user equipment from among the user equipment candidates; and means for providing the request from the first user equipment to the second user equipment.

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

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

[0009] The source of the trigger may be a second user equipment, and the apparatus may comprise means for receiving information from the second user equipment and means for determining, based on the information, to provide a request for at least one of the following: cooperative detection, selection, or reselection.

[0010] The means for determining may comprise means for determining whether the information includes a list of user equipment candidates for the further user equipment, whether a number of user equipment candidates in the list is below a threshold, whether the list of user equipment candidates includes a user equipment candidate in a list of user equipment candidates at the first user equipment, or whether the list of user equipment candidates includes an indication that the second user equipment is performing a cooperative relay detection procedure.

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

[0012] The apparatus may comprise means for receiving an indication from the second user equipment in response to the request, the indication may include at least one of the following: an identification of the further 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 a cooperative detection procedure, or a further list of user equipment candidates for the further user equipment.

[0013] The apparatus may comprise means for transmitting, in response to receiving an indication from the second user equipment that the second user equipment is performing a cooperative detection procedure, a detection request from the first user equipment to the candidate user equipment including an indication instructing the candidate user equipment to monitor for detection messages from the second user equipment.

[0014] In a second exemplary embodiment, an apparatus is provided in a second user equipment, the apparatus comprising means for the second user equipment to receive from a first user equipment a request for at least one of the following: collaborative detection of user equipment candidates for the further user equipment; and selection or reselection from among the user equipment candidates of the further user equipment to function as a relay node between the first user equipment and the second user equipment in communication.

[0015] The apparatus may comprise means for providing a trigger from the second user equipment to the first user equipment for selecting or reselecting a further user equipment to act 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 cooperative detection is requested at the second user equipment, or an indication that the first user equipment is performing a cooperative detection procedure.

[0017] The apparatus may comprise means for determining, at the second user equipment, based on the request, to perform a cooperative detection procedure for the further user equipment, means for performing the cooperative detection procedure, and means for providing an indication to the first user equipment that the second user equipment is performing the cooperative detection procedure.

[0018] The means for performing a cooperative discovery procedure comprises means for providing a broadcast discovery announcement or a groupcast discovery response to the candidate user equipment, the broadcast discovery announcement or groupcast discovery response including Layer 2 identifiers of the first user equipment and the second user equipment.

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

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

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

[0022] In a third exemplary embodiment, a method, in a first user equipment, the method includes: determining, based on a trigger, to select or reselect a further user equipment to function as a relay node between the first user equipment and a second user equipment in communication; determining a source of the trigger; determining, based on the determined source, to provide a request from the first user equipment to the second user equipment for at least one of the following: cooperative detection of user equipment candidates for the further user equipment; and selection or reselection of the further user equipment from among the user equipment candidates; and providing the request from the first user equipment to the second user equipment.

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

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

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

[0026] Determining may include determining whether the information includes a list of user equipment candidates for the further 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 in a list of user equipment candidates in the first user equipment, or whether the information includes an indication that the second user equipment is performing a cooperative relay detection procedure.

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

[0028] The method may include receiving an indication from the second user equipment in response to the request, the indication including at least one of the following: an identification of the further 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 a cooperative detection procedure, or a further list of user equipment candidates for the further user equipment.

[0029] The method may include, in response to receiving an indication from the second user equipment that the second user equipment is performing a cooperative detection procedure, transmitting a detection request from the first user equipment to the candidate user equipment including an indication instructing the candidate user equipment to monitor for detection messages from the second user equipment.

[0030] In a fourth exemplary embodiment, a method, wherein at a second user equipment, the method includes the second user equipment receiving from a first user equipment a request for at least one of the following: cooperative detection of user equipment candidates for the further user equipment; and selection or reselection of the further user equipment from among the user equipment candidates to function as a relay node between the first user equipment and the second user equipment in communication.

[0031] The method may include providing a trigger from the second user equipment to the first user equipment for selecting or reselecting a further user equipment to act 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 the further user equipment, an indication of whether cooperative detection is requested in the second user equipment, or an indication that the first user equipment is performing a cooperative detection procedure.

[0033] The method may include determining, at the second user equipment, based on the request, to perform a cooperative detection procedure for the further user equipment; performing the cooperative detection procedure; and providing an indication to the first user equipment that the second user equipment is performing the cooperative detection procedure.

[0034] Performing the cooperative discovery procedure may include providing a broadcast discovery announcement or a groupcast discovery response to the user equipment candidate that includes Layer 2 identifiers of the first user equipment and the second user equipment.

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

[0036] The method may include providing an indication from the second user equipment in response to the request, the indication including at least one of the following: an indication that selection or reselection is currently not possible based on the list of user equipment candidates, or a further list of user equipment candidates for the further 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 cooperative detection procedure, transmitting a detection request from the second user equipment to the candidate user equipment including an indication instructing the candidate user equipment to monitor for detection messages from the first user equipment.

[0038] In a fifth exemplary embodiment, there is provided an apparatus comprising at least one processor and at least one memory storing instructions, the instructions, when executed by the at least one processor, causing the apparatus to at least: determine, in a first user equipment, based on a trigger, to select or reselect a further user equipment to function as a relay node between the first user equipment and a second user equipment that are in communication; determine a source of the trigger; and, based on the determined source, determine to provide from the first user equipment to the second user equipment a request for at least one of: cooperative detection of user equipment candidates for the further user equipment; and selection or reselection of the further user equipment from among the user equipment candidates; and cause the apparatus to provide the request from the first user equipment to the second user equipment.

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

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

[0041] The source of the trigger may be a second user equipment, and the device may be caused to receive information from the second user equipment and, based on the information, to decide to provide a request for at least one of the following: cooperative detection, selection, or reselection.

[0042] The apparatus may be caused to determine whether the information includes a list of user equipment candidates for the further 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 in the list of user equipment candidates in the first user equipment, or whether the information includes an indication that the second user equipment is performing a cooperative relay detection procedure.

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

[0044] The apparatus may be caused to receive an indication from the second user equipment in response to the request, the indication including at least one of the following: identification information of the further 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 a cooperative detection procedure, or a further list of user equipment candidates for the further user equipment.

[0045] In response to receiving an indication from the second user equipment that the second user equipment is performing a cooperative detection procedure, the apparatus may cause the first user equipment to transmit a detection request to the candidate user equipment including an indication instructing the candidate user equipment to monitor for detection messages from the second user equipment.

[0046] In a sixth exemplary embodiment, an apparatus is provided 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 receive, at the second user equipment, from a first user equipment, a request for at least one of the following: cooperative detection of user equipment candidates for the further user equipment; and selection or reselection of a further user equipment from among the user equipment candidates to function as a relay node between the first user equipment and the second user equipment in communication.

[0047] The apparatus may be caused to cause a trigger to be provided from the second user equipment to the first user equipment for selecting or reselecting a further user equipment to act as a relay node between the first user equipment and the second user equipment.

[0048] The request may include a list of user equipment candidates for the further user equipment, an indication of whether cooperative detection is requested in the second user equipment, or an indication that the first user equipment is performing a cooperative detection procedure.

[0049] The apparatus may be configured to determine, based on the request, to perform, at the second user equipment, a cooperative detection procedure for the further user equipment, cause the cooperative detection procedure to be performed, and cause an indication to be provided to the first user equipment that the second user equipment is performing the cooperative detection procedure.

[0050] The apparatus may be caused to provide a broadcast discovery announcement or a groupcast discovery response to a candidate user equipment that includes Layer 2 identifiers of the first user equipment and the second user equipment.

[0051] The apparatus may determine, based on the request, to perform a relay selection procedure or a relay reselection procedure in the second user equipment, perform the relay selection procedure or the reselection procedure in the second user equipment, and cause the second user equipment to provide an indication to the first user equipment indicating identification information of the further user equipment.

[0052] The device may be caused to provide an indication from the second user equipment in response to the request, the indication including at least one of the following: an indication that selection or reselection is currently not possible based on the list of user equipment candidates, or a further list of user equipment candidates for the further user equipment.

[0053] In response to receiving an indication from the first user equipment that the first user equipment is performing a cooperative detection procedure, the apparatus may cause the second user equipment to transmit a detection request to the candidate user equipment including an indication instructing the candidate user equipment to monitor for detection messages from the first user equipment.

[0054] In a seventh exemplary embodiment, a computer-readable medium is provided comprising instructions that, when executed by the apparatus, cause the apparatus to perform at least the following at a first user equipment: determining, based on a trigger, to select or reselect a further user equipment to function as a relay node between the first user equipment and a second user equipment that are in communication; determining a source of the trigger; and, based on the determined source, determining to provide, from the first user equipment to the second user equipment, a request for at least one of cooperative detection of user equipment candidates for the further user equipment and selection or reselection of the further user equipment from among the user equipment candidates; and providing the request from the first user equipment to the second user equipment.

[0055] The source of the trigger may be the first user equipment.

[0056] The first user equipment and the second user equipment may be in communication via a third user equipment acting as a relay node, and the source of the trigger may be the third user equipment acting as the relay node.

[0057] The source of the trigger may be a second user equipment, and the device may be configured to receive information from the second user equipment and, based on the information, determine to provide a request for at least one of the following: cooperative detection, selection, or reselection.

[0058] The apparatus may be configured to determine whether the information includes a list of user equipment candidates for the further 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 in a list of user equipment candidates in the first user equipment, or whether the information comprises an indication that the second user equipment is performing a cooperative relay detection procedure.

[0059] The request may include at least one of the following: a list of user equipment candidates for the further user equipment, an indication of whether cooperative detection is requested in the second user equipment, or an indication that the first user equipment is performing a cooperative detection procedure.

[0060] The apparatus may be caused to receive an indication from the second user equipment in response to the request, the indication including at least one of the following: identification information of the further 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 a cooperative detection procedure, a further list of user equipment candidates for the further user equipment.

[0061] 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 cooperative detection procedure, transmit a detection request from the first user equipment to the candidate user equipment including an indication instructing the candidate user equipment to monitor for detection messages from the second user equipment.

[0062] In an eighth exemplary embodiment, a computer-readable medium is provided that includes instructions that, when executed by an apparatus, cause the apparatus to perform at least one of the following at the second user equipment: receiving, from a first user equipment, a request for at least one of cooperative detection of user equipment candidates for the further user equipment; and selection or reselection of a further user equipment from among the user equipment candidates to function as a relay node between the first user equipment and the second user equipment in communication.

[0063] The apparatus may be caused to provide, from the second user equipment to the first user equipment, a trigger for selecting or reselecting a further user equipment to act as a relay node between the first user equipment and the second user equipment.

[0064] The request may include a list of user equipment candidates for the further user equipment, an indication of whether cooperative detection is requested at the second user equipment, or an indication that the first user equipment is performing a cooperative detection procedure.

[0065] The apparatus may be caused to determine, based on the request, at the second user equipment, to perform a cooperative detection procedure for the further user equipment; and perform the cooperative detection procedure and provide an indication to the first user equipment that the second user equipment is performing the cooperative detection procedure.

[0066] The apparatus may be caused to provide a broadcast discovery announcement or a groupcast discovery response to a candidate user equipment that includes Layer 2 identifiers of the first user equipment and the second user equipment.

[0067] The apparatus may be caused to determine, based on the request, to perform a relay selection procedure or a relay reselection procedure at the second user equipment, perform the relay selection procedure or the reselection procedure at the second user equipment, and provide, from the second user equipment to the first user equipment, an indication of an identity of the further user equipment.

[0068] The apparatus may be executed to provide an indication from the second user equipment in response to the request, the indication including at least one of the following: an indication that selection or reselection is currently not possible based on the list of user equipment candidates, or a further list of user equipment candidates for the further user equipment.

[0069] 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 cooperative detection procedure, transmit, from the second user equipment, to the candidate user equipment, a detection request including an indication instructing the candidate user equipment to monitor for detection messages from the first user equipment.

[0070] In a ninth exemplary embodiment, a non-transitory computer-readable medium is provided that includes program instructions for causing an apparatus to perform a method according to at least the third exemplary embodiment or the fourth exemplary embodiment.

[0071] A number of different exemplary embodiments have been described above. It should be appreciated that further exemplary embodiments may be provided by combining any two or more of the exemplary embodiments described above.

[0072] Exemplary embodiments will now be further described, by way of example only, with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0073] [Figure 1] 1 is a schematic diagram of a 5GS communication system according to an exemplary embodiment. [Figure 2] 1 is a schematic diagram of a mobile communication device according to an exemplary embodiment. [Figure 3] FIG. 1 is a schematic diagram of a control device in accordance with an exemplary embodiment. [Figure 4] FIG. 1 is a schematic diagram of a U2U relay scenario according to an example embodiment. [Figure 5] 1 is a signaling flow for U2U relay (re)selection according to an example embodiment; [Figure 6] 1 is a signaling flow for SL detection using U2U relay according to an example embodiment. [Figure 7] 1 is a flowchart of a method according to an exemplary embodiment. [Figure 8] 1 is a flowchart of a method according to an exemplary embodiment. [Figure 9] 1 is a signaling flow according to an example embodiment; [Figure 10] 1 is a signaling flow according to an example embodiment; DETAILED DESCRIPTION OF THE INVENTION

[0074] Before describing the exemplary embodiments in detail, some principles of wireless communication systems and mobile communication devices will be briefly described with reference to Figures 1 to 3 to aid in understanding the technology underlying the exemplary embodiments described.

[0075] Examples of suitable communication systems include the 5G or NR concept. The network architecture in NR may be similar to that of LTE-Advanced. Base stations in NR systems may be known as next-generation Node Bs (gNBs). Changes to the network architecture may depend on the need to accommodate various radio technologies, more granular QoS support, and some on-demand requirements for Quality of Service (QoS) levels, for example, to support user Quality of Experience (QoE). Network-enabled services and applications and service- and application-enabled networks may also bring about changes to the architecture. These are related to Information Centric Network (ICN) and User-Centric Content Delivery Network (UC-CDN) approaches. NR may use multiple-input, multiple-output (MIMO) antennas, more base stations or nodes than LTE (the so-called small cell concept), including macro sites operating in cooperation with smaller base stations, and possibly employing various radio technologies for wider coverage and faster data rates.

[0076] Future networks may utilize network function virtualization (NFV), a network architecture concept that proposes virtualizing network node functions into "building blocks" or entities and operationally connecting or linking them to provide services. A virtualized network function (VNF) may comprise one or more virtual machines running computer program code using standard or generic types of servers rather than customized hardware. Cloud computing or data storage may also be utilized. In wireless communications, this may mean node operations being performed at least in part on a server, host, or node operatively coupled to a remote radio head. It is also possible for node operations to be distributed among multiple servers, nodes, or hosts. It should also be understood that load distribution between core network operations and base station operations may differ from that in LTE and may even be nonexistent.

[0077] 1 is a schematic diagram of a 5G system (5GS) 100 according to an example embodiment. 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.

[0078] An exemplary 5G Core Network (CN) comprises functional entities. The 5GCN 106 may comprise 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 Publication Function (NEF) 124. The UPF is controlled by a Session Management Function (SMF) that receives policies from a Policy Control Function (PCF).

[0079] The CN is connected to the UE via a Radio Access Network (RAN). The RAN may comprise one or more gNodeB (GNB) distributed unit functions connected to one or more gNodeB (GNB) centralized unit functions. The RAN may comprise one or more access nodes.

[0080] The User Plane Function (UPF), referred to as the PDU Session Anchor (PSA), may be responsible for forwarding frames to and from the tunnel established via 5G towards the DN and the UE(s) exchanging traffic.

[0081] A possible mobile communication device is described in further detail with reference to FIG. 2 , which illustrates a schematic, partial cross-sectional view of a communication device 200 according to an exemplary embodiment. Such communication devices are often referred to as user equipment (UE) or terminals. A suitable mobile communication device may be provided by any device capable of transmitting and receiving wireless signals. Non-limiting examples include mobile stations (MS) or mobile devices, also known as mobile phones or so-called “smartphones,” computers equipped with wireless interface cards or other wireless interface facilities (e.g., USB dongles), personal digital assistants (PDAs) or tablets equipped with wireless communication capabilities, voice-over-IP (VoIP) phones, portable computers, desktop computers, image capture terminal devices such as digital cameras, gaming terminal devices, music storage and playback equipment, in-vehicle wireless terminal devices, wireless endpoints, mobile stations, laptop embedded equipment (LEE), laptop mounted equipment (LME), smart devices, wireless customer premises equipment (CPE), or any combination thereof. A mobile communication device may provide communication of data, for example, to transmit communications such as voice, electronic mail (email), text messages, multimedia, etc. Thus, a user may be offered and provided with numerous services via the communication device. Non-limiting examples of these services include two-way or multi-way calls, data communication or multimedia services, or simply access to a data communication network system such as the Internet. A user may also be provided with broadcast or multicast data. Non-limiting examples of content include downloads, television or radio programs, videos, advertisements, various alerts, and other information.

[0082] A mobile device typically includes at least one data processing entity 201, at least one memory 202, and possible other components 203 for use by the software and hardware in executing the tasks it is designed to perform, including controlling access to and communication with an access system or other communication devices. Data processing, storage, and other related controls may be provided on a suitable circuit board and / or within a chipset. This feature is indicated by reference numeral 204. A user may control the operation of the mobile device using a suitable user interface, such as a keypad 205, voice commands, a touch-sensitive screen or pad, or a combination thereof. A display 208, a speaker, and a microphone may also be included. Additionally, the mobile communication device may include suitable connectors (wired or wireless) for connecting to other devices and / or external accessories, such as, for example, hands-free equipment.

[0083] The mobile device 200 may receive signals over the air or wireless interface 207 via a suitable receiving device and may transmit signals via a suitable device for transmitting wireless signals. In Figure 2, a transceiver device is indicated schematically by block 206. The transceiver device 206 may be equipped, for example, with a radio section and an associated antenna arrangement. The antenna arrangement may be located internal or external to the mobile device.

[0084] FIG. 3 illustrates a controller 300 for a communication system according to an exemplary embodiment, which may be coupled to and / or for controlling stations of an access system, such as base stations, RAN nodes, eNBs, or gNBs, relay nodes or core network nodes, such as MMEs, S-GWs, or P-GWs, core network functions, such as AMFs / SMFs, or servers or hosts. The method may be implemented in a single controller or across multiple controllers. The controller may be integrated with a core network or RAN node or module, or may be external. In some exemplary embodiments, a base station comprises a separate controller unit or module. In other exemplary embodiments, the controller may be another network element, such as a radio network controller or spectrum controller. In some exemplary embodiments, each base station may have such a controller, or the controller may be provided in a radio network controller. The controller 300 may be arranged to control communications within a service area of ​​the system. The controller 300 comprises at least one memory 301, at least one data processing unit 302, 303, and an input / output interface 304. Via an interface, the control device can be coupled to a receiver and a transmitter of the base station, which can be implemented as a radio front end or a remote radio head.

[0085] The following relates to Sidelink (SL) based UE to UE (U2U) relay.

[0086] 4 shows a schematic diagram of a U2U relay scenario according to an example embodiment. 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 may communicate with each other directly or indirectly via SL via U2U relay UE 403. UE 403 is the currently serving U2U relay. UE 404 is a candidate for U2U relay UE.

[0087] Model A and Model B are two models specified by 3GPP for general sidelink discovery. Model A: One UE announces "I'm here." Model B: One UE asks "Is anyone there?" and / or "Are you there?"

[0088] In general, improving the speed and / or efficiency of the (re)selection of a new U2U Relay UE2 is beneficial to support service continuity (SC) between a source UE (e.g.: UE-A401) and a destination UE (e.g.: UE-B402).

[0089] It is unclear how UE-A and UE-B perform U2U relay discovery (RD) and decide on U2U relay (re)selection. For example, a potential U2U relay UE using Model A may not always announce for U2U RD for power-saving and resource-efficiency reasons. Therefore, to achieve robust U2U RD, UE-A 401 and UE-B 402 may need to be considered using both Model A and Model B. U2U relay (re)selection can be triggered by any of the UEs (UE-A 401, UE-B 402, and serving U2U Relay UE1 403). U2U relay (re)selection is coordinated between at least UE-A 401 and UE-B 402 to ensure that the (re)selected U2U Relay UE2 is suitable for both UE-A 401 and UE-B 402. It is unclear which UE (UE-A401 or UE-B402) is responsible for the (re)selection decision, and whether and how U2U RD will be coordinated between UE-A401 and UE-B402, since the (re)selection is targeted at the SC.

[0090] Assuming that UE-A401 and UE-B402 have up-to-date information about all U2U Relay UE candidates 403 in their vicinity, U2U relay (re)selection for SC between UE-A401 and UE-B402 involves the following steps, as shown in Figure 5:

[0091] In 501, UE-A401 transmits a U2U Relay Reselection Request to UE-B402, and notifies UE-B402 of a list of U2U Relay UE candidates.

[0092] In 502, UE-B402 determines whether there is a common U2U Relay UE candidate between UE-A401 and UE-B402.

[0093] In 503, if there are common U2U Relay UE candidates, UE-B402 may (re)select one of them and initiate re-establishment of the SL connection with UE-A401 via the selected U2U Relay UE candidate. In addition, UE-B402 may send a response to UE-A401 indicating the (re)selected U2U Relay UE before the SL connection is re-established via the (re)selected Relay UE.

[0094] At 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.

[0095] Whether a U2U Relay UE uses Model A and / or Model B for U2U RD is up to the UE and application implementation, and since all UEs involved in a connection based on SL U2U Relay may be moving independently, the assumption that UE-A401 and UE-B402 have up-to-date information about all U2U Relay UE candidates in their vicinity cannot be taken for granted and must be checked or verified each time the need for U2U Relay (re)selection arises.

[0096] 6 illustrates a signaling flow for SL discovery with U2U Relay according to an example embodiment, in which Access Stratum (AS) assisted Sidelink Discovery (SD) with SL-based U2U Relay is provided for UE1 to discover UE2 and U2U Relay UE candidates to reach UE2. However, such proposal does not take into account certain SC aspects and possible prior coordination between UE1 and UE2 over an existing SL connection for U2U Relay (re)selection.

[0097] In the following, we focus on the cooperation between UE-A401, UE-B402 and the involved U2U Relay UEs, enabling fast and efficient U2U Relay (re)selection of the SC between UE-A401 and UE-B402.

[0098] FIG. 7 illustrates a flowchart of a method according to an exemplary embodiment.

[0099] In S1, the method includes the first user equipment determining, based on a trigger, to select or reselect a further user equipment to act as a relay node between the first user equipment and a second user equipment that are in communication.

[0100] At S2, the method includes determining a source of the trigger.

[0101] At S3, the method includes determining, based on the determined source, to provide from the first user equipment to the second user equipment a request for at least one of cooperative detection of user equipment candidates for the further user equipment and selection or reselection of the further user equipment from among the user equipment candidates (in other words, cooperative detection and / or (re)selection).

[0102] At S4, the method includes providing the request from the first user equipment to the second user equipment.

[0103] 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, if the first UE and the second UE are communicating via a third user equipment acting as a relay node.

[0104] FIG. 8 illustrates a flowchart of a method according to an exemplary embodiment.

[0105] At T1, the method includes the second user equipment receiving from the first user equipment a request for at least one of cooperative detection of user equipment candidates for the further user equipment and selection or reselection from among the user equipment candidates of the further user equipment to act as a relay node between the first user equipment and the second user equipment in communication.

[0106] The method may enable coordination between at least UE-A401 and UE-B402 for U2U relay detection and / or SC (re)selection. In some of the example embodiments described below, it is assumed that UE-A401 plays the role of coordination. However, if UE-A401 and UE-B402 currently communicate with each other via U2U Relay UE1 403, the trigger for U2U relay detection and / or (re)selection may be initiated by either UE-A401 or UE-B402, or the current U2U Relay UE1 403.

[0107] For example, UE-A401 may determine that a U2U relay (re)selection is required for the SC between UE-A401 and UE-B402 (in other words, to select or reselect a further user equipment to act as a relay node between the first UE and the second UE).

[0108] UE-A401 further determines whether an SL procedure for coordinating U2U relay (re)selection between UE-A401 and UE-B402, i.e., an SL U2U Relay (re)selection request, needs to be initiated (e.g., whether a request for cooperative detection and / or (re)selection of additional user equipment is provided from the first user equipment to the second user equipment). The further decision is based on where the trigger for U2U relay (re)selection comes from, e.g., whether it is the first UE, the second UE, or a third UE acting as a relay node, e.g., UE-A401, UE-B402, or U2U Relay UE1 403.

[0109] In an exemplary embodiment, for example, if the SL UE information received from U2U Relay UE1 403 indicates that U2U Relay UE1 403 cannot serve UE-A401 and UE-B402 and UE-A401 and UE-B402 need to reselect a new U2U Relay UE2 404 within a time limit, then UE-A401 will initiate a SL U2URelay (re)selection request to UE-B402 when a trigger comes from UE-A401 itself or the current U2U Relay UE1 403.

[0110] If the trigger originates from a second UE, e.g., UE-B 402, the method may include receiving information from the second user equipment and, based on the information, determining to provide a cooperative relay discovery and / or (re)selection request. The second UE may provide the information to the first UE including a list of user equipment candidates for the further user equipment.

[0111] The determining may include determining whether the information includes a list of user equipment candidates for the further user equipment, whether a number of user equipment candidates in the list is below a threshold, whether the list of user equipment candidates includes a user equipment candidate in the list of user equipment candidates in the first user equipment, or whether the information includes an indication that the second user equipment is performing a cooperative relay detection procedure.

[0112] For example, a further decision may also be based on whether there are enough U2U Relay UE candidates provided by UE-B, as follows:

[0113] In an exemplary embodiment, if the trigger comes from UE-B, for example, if the SL UE information received from UE-B indicates that the SL between UE-B and U2U Relay UE1 has become inappropriate (e.g., the SL RSRP between UE-B and U2U Relay UE1 is below a threshold), UE-A401 may decide whether to initiate an SL U2U Relay (re)selection request based on the following factors: specifically, whether UE-B402 provides UE-A401 with a list of U2U Relay UE candidates along with the SL UE information; the number of U2U Relay UE candidates in the list; whether the U2U Relay UE candidates match between the list provided by UE-B402 and the list maintained in UE-A401; or whether UE-B402 has selected a cooperative U2U Relay UE. The active action is whether to provide an indication that active action for RD is being taken, which is performed based on the scheme shown in Figure 6, by: using Model A, UE-B402 announcing itself using UE-B402's current L2 ID known to UE-A401 as the SRC ID and performing cooperative U2U RD by including UE-A401's current L2 ID in the announcement, or using Model B, UE-B402 groupcasting a U2U RD response for cooperative U2U RD using UE-A401's current L2 ID as the DST ID and UE-B402's current L2 ID as the SRC ID. An empty list of U2U Relay UE candidates may indicate that there are no U2U Relay UE candidates announcing themselves to UE-A401 or UE-B402 using Model A for possible U2U RD.

[0114] UE-A401 may decide not to initiate an SL U2U Relay (re)selection request to UE-B402 in cases where there is a match between the U2U Relay UE candidates in the list provided by UE-B402 and the list maintained by UE-A401, where the number of U2U Relay UE candidates in the list provided by UE-B402 exceeds a threshold, where there is no match between the U2U Relay UE candidates in the list of UE-B402 and the list of UE-A401 (which means that UE-B402 has already provided all preferred U2U Relay UE candidates and it is unlikely that a new U2U Relay UE candidate that is compatible with both UE-A401 and UE-B402 will be found), or where the SL UE information from UE-B402 includes an indication that UE-B402 is taking active action for cooperative U2U RD.

[0115] If there is a match between the U2U Relay UE candidates in the list provided by UE-B402 and the list maintained in UE-A401, UE-A401 may (re)select the matching U2U Relay UE2 and initiate establishment of a new SL relay connection with UE-B402 via U2U Relay UE2. In addition, UE-A401 may send an SL U2U Relay (re)selection notification to UE-B402 indicating the (re)selected U2U Relay UE2 404, such as the L2 ID of U2U Relay UE2 404.

[0116] If the number of U2U Relay UE candidates in the list provided by UE-B402 exceeds a threshold and there is a mismatch in U2U Relay UE candidates between the list of UE-B402 and the list of UE-A401, UE-A401 may send an SL U2U Relay (re)selection indication to UE-B402, which includes information indicating that (re)selection is not currently possible using the list provided by UE-B 402. In addition, UE-A401 may include the list of U2U Relay UE candidates maintained by UE-A401 in the SL U2U Relay (re)selection indication, which may cause UE-B402 to perform U2U Relay UE (re)selection when further RD becomes possible at UE-B402, or to take further action, such as updating SL UE information after performing further RD, as described above.

[0117] If UE-B402 is taking active action for cooperative U2U RD, UE-A401 may broadcast a U2U RD request based on FIG. 6, and this broadcast includes an indication to U2U Relay UE candidates to skip relaying the U2U RD request to UE-B402 but to monitor for a broadcast RD announcement or groupcast RD response from UE-B402, along with configuration information required for monitoring, such as the L2 IDs of UE-A401 and UE-B402.

[0118] Otherwise, UE-A401 may decide to initiate a SL U2U Relay (re)selection request to UE-B402 as follows:

[0119] Providing a request from the first user equipment to the second user equipment may include UE-A401 sending an SL U2U Relay (re)selection request to UE-B402. The request may include at least one of the following: a list of user equipment candidates for the additional user equipment, an indication indicating whether cooperative detection is requested in the second user equipment, or an indication that the first user equipment is performing a cooperative detection procedure. The list of user equipment candidates may be a list of U2U Relay UE candidates maintained in UE-A401 (i.e., a list of user equipment candidates for the additional user equipment). The request may include an indication indicating whether cooperative U2U RD is requested depending on the number of U2U Relay UE candidates in the list. For example, if the number of U2U Relay UE candidates in the list from UE-A401 exceeds a threshold, cooperative U2U RD may not be required.

[0120] Upon receiving the request, the second user equipment may perform a discovery and / or (re)selection procedure for further user equipment to act as a relay node.

[0121] The method may include determining, based on the request, to perform a cooperative detection procedure at the second user equipment for the further user equipment, performing the cooperative detection procedure, and providing an indication to the first user equipment that the second user equipment is performing the cooperative detection procedure.

[0122] Performing the cooperative discovery procedure comprises means for providing a broadcast discovery announcement or a groupcast discovery response to the candidate user equipment, the broadcast discovery announcement or groupcast discovery response including Layer 2 identifiers of the first user equipment and the second user equipment.

[0123] For example, when a cooperative U2U RD is requested, UE-B402 may initiate its own announcement using the existing L2 IDs of UE-A401 and UE-B402 by broadcasting an RD announcement as in Model A, or by groupcasting an RD response as in Model B, if no other L2 ID is configured for UE-B402 in the request received from UE-A401.

[0124] If cooperative U2U RD is not required, this may implicitly mean that UE-B402 is permitted to perform U2U Relay UE (re)selection and send a SL U2U Relay (re)selection indication to UE-A401, similar to the behavior of UE-A401 described above.

[0125] The method may include determining, based on the request, to perform a relay selection procedure or a relay reselection procedure; performing the relay selection procedure or the reselection procedure; and providing an indication from the second user equipment to the first user equipment indicating an identity of the further user equipment.

[0126] The method may include providing an indication from the second user equipment in response to the request, the indication including at least one of the following: an indication that selection or reselection is currently not possible based on the list of user equipment candidates, or a further list of user equipment candidates for the further user equipment.

[0127] The indication may be included in an SL U2U Relay (re)selection indication. The method may include, in response to receiving an indication from the first user equipment that the first user equipment is performing a cooperative detection procedure, transmitting a detection request from the second user equipment to the candidate user equipment including an indication instructing the candidate user equipment to monitor for detection messages from the first user equipment.

[0128] In an example embodiment, UE-A401 receives an SL U2U Relay (re)selection indication from UE-B402 indicating at least one of the following: (i) a reselected U2U Relay UE2 404 (i.e., additional user equipment), such as the L2 ID of U2U Relay UE2 404, (ii) (re)selection is currently not possible for the list provided by UE-A401, or (iii) UE-B402 is performing cooperative U2U RD (e.g., by actively announcing itself via the provision of L2 IDs of both UE-A401 and UE-B402 in relation to UE1 403). In addition, a list of U2U Relay UE candidates maintained by UE-B402 may be included in the SL U2U Relay (re)selection indication received from UE-B402.

[0129] If the indication includes the reselected U2U Relay UE2 404, the UE-A 401 performs re-establishment of the SL Relay connection via the reselected U2U Relay UE.

[0130] If the indication indicates that (re)selection is not currently possible, UE-A401 may decide to update the SL U2U Relay (re)selection request to UE-B402 with a request for cooperative U2U RD, or to initiate cooperative U2U RD towards UE-B402 without sending a request to UE-B402 in advance.

[0131] The method may include, in response to the first user equipment receiving an indication from the second user equipment that the second user equipment is performing a cooperative detection procedure, sending a detection request to the candidate user equipment including an indication instructing the candidate user equipment to monitor for detection messages from the second user equipment.

[0132] For example, when UE-B402 is performing cooperative U2U RD, UE-A401 may broadcast a U2U RD request based on FIG. 6, and may include an indication to instruct U2U Relay UE candidates to skip relaying the U2U RD request to UE-B402 and to monitor for a broadcast RD announcement or groupcast RD response from UE-B402, and may further provide configuration information necessary for monitoring, such as the L2 IDs of UE-A401 and UE-B402.

[0133] 9 and 10 provide signaling diagrams to illustrate some features of the SL coordination procedure for U2U Relay (re)selection of the SC between UE-A 401 and UE-B 402.

[0134] Figure 9 shows an example in which the trigger for U2U Relay (re)selection comes from the current U2U Relay UE1 403. Note that 901 in Figure 9 is not necessary if UE-A 401 itself identifies the need for U2U Relay (re)selection.

[0135] At 902, UE-A401 sends a SL U2U relay (re)selection request to UE-B402, which includes a list of U2U relay UE candidates and a request for cooperative U2U RD.

[0136] 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 cooperative U2U RD.

[0137] At 904, UE-B 402 broadcasts an SD announcement including the L2 IDs of UE-A 401 and UE-B 402.

[0138] At 905, UE-A 401 broadcasts a U2U RD request including the L2 IDs of UE-A and UE-B and an indication to skip relaying the RD request and listen for an SD announcement from UE-B.

[0139] At 906, a cooperative U2U RD is performed, and UE-B402 (re)selects a U2U relay UE2 for the SC between UE-A401 and UE-B402.

[0140] 10 shows an example in which 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 is actively performing a cooperative RD procedure and notifies UE-A 401 of this in 1001. For example, the request includes an indication that the first user equipment is performing a cooperative detection procedure.

[0141] At 1002, UE-B 402 broadcasts an SD announcement including the L2 IDs of UE-A 401 and UE-B 402.

[0142] At 1003, UE-A 401 broadcasts a U2U RD request including the L2 IDs of UE-A and UE-B and an indication to skip relaying the RD request but to monitor for an SD announcement from UE-B. In other words, the second user equipment, in response to the request, sends to the candidate user equipment a detection request including an indication to the candidate user equipment to monitor for a detection message from the first user equipment.

[0143] At 1004, a cooperative U2U RD is performed, and UE-B402 (re)selects a U2U relay UE2 for the SC between UE-A401 and UE-B402.

[0144] Either UE-A401 or UE-B402 may take the coordinating role, in other words, may initiate the SL U2U Relay (re)selection request. In this option, the initiating UE (either UE-A401 or UE-B402) may decide to actively perform cooperative U2U RD as described above for UE-B402 and notify the other UE. The other UE may then operate as UE-A401 as described above. That is, the initiating UE may decide to operate as either UE-A401 or UE-B402 as described above.

[0145] A trigger from the current U2U Relay UE1 403 for U2U Relay (re)selection for the SC can be sent to either UE-A 401 or UE-B 402 as determined by the U2U Relay UE1 403.

[0146] The SL UE information from the current serving U2U Relay UE1 to the UE-A401 is for triggering U2U Relay (re)selection for SC between UE-A401 and UE-B402, and U2U Relay UE1 403 may include serving reason and timing information to perform U2U Relay (re)selection for UE-A401 and UE-B402. Based on the timing information provided by U2U Relay UE1 403, UE-A401 may configure timing information for cooperative U2U RD, including timing information for receiving a U2U Relay (re)selection indication from UE-B402.

[0147] The reactive SD announcement in step 4 of FIG. 9 or the active SD announcement in step 2 of FIG. 10 can be achieved by using a designated access stratum (AS) message broadcast by UE-B 402 over SL (similar to the examples in FIGS. 5 and 6) using the default L2 DST ID designated for sidelink broadcasting instead of an actual SD announcement from higher layers. Alternatively, the designated AS message can be groupcast by UE-B over SL using UE-A's L2 ID as the DST ID for the groupcast. This assumes that UE-B 402 has previously agreed or made aware of UE-A 401 in step 3 of FIG. 9 or step 1 of FIG. 10, and that UE-A 401 then configures its U2U Relay UE to monitor the groupcast from UE-B 402 in step 5 of FIG. 9 or step 3 of FIG. 10. The designated AS message may include information such as the L2 IDs of UE-A 401 and UE-B 402, allowing the U2U Relay UE candidate (U2U Relay UE2 404) to identify and detect UE-B 402 in response to a request by UE-A 401. Note that the use of the above designated AS message may apply to replace both the options when UE-B 402 broadcasts an SD Announcement using Model-A or groupcasts an SD Response using Model-B.

[0148] The apparatus in the first user equipment may comprise means for determining, based on a trigger, to select or reselect a further user equipment to function as a relay node between the first user equipment and a second user equipment in communication; means for determining a source of the trigger; means for determining, based on the determined source, to provide a request from the first user equipment to the second user equipment for at least one of the following: cooperative detection of user equipment candidates for the further user equipment; and selection or reselection of a further user equipment from among the user equipment candidates; and means for providing the request from the first user equipment to the second user equipment.

[0149] The apparatus in the second user equipment may comprise means for the second user equipment to receive from the first user equipment a request for at least one of the following: cooperative detection of user equipment candidates for the further user equipment; and selection or reselection from among the user equipment candidates of the further user equipment to act as a relay node between the first user equipment and the second user equipment in communication.

[0150] It is to be understood that the apparatus may comprise or be coupled to other units or modules, such as radio components or radio heads, used in or for transmitting and / or receiving. Although the apparatus is described as one entity, the different modules and memories may be implemented in one or more physical or logical entities.

[0151] It should be noted that while some exemplary embodiments are described in the context of 5G networks, similar principles may be applied in the context of other networks and communication systems. Thus, although certain exemplary embodiments are described above by way of example with reference to particular exemplary architectures for wireless networks, technologies, and standards, the embodiments may be applied to any other suitable type of communication system other than those illustrated and described herein.

[0152] It should also be noted that although the above describes exemplary embodiments, several variations and modifications may be made to the disclosed solutions without departing from the scope of the present disclosure.

[0153] As used herein, "at least one of: ," "at least one of ," and similar phrases, when a list of two or more elements is joined by "and" or "or," mean at least any one of the elements, or at least any two or more of the elements, or at least all of the elements.

[0154] In general, various exemplary embodiments may be implemented in hardware or special purpose circuitry, software, logic, or any combination thereof. While some exemplary embodiments may be implemented in hardware, other aspects may be implemented in firmware or software that may be executed by a controller, microprocessor, or other computing device, although the present disclosure is not limited in this regard. Although various exemplary embodiments may be illustrated and described as block diagrams, flowcharts, or using some other graphical representations, it will be understood that these blocks, apparatus, systems, techniques, or methods described herein may be implemented in, by way of non-limiting example, hardware, software, firmware, special purpose circuitry or logic, general purpose hardware or controller, other computing device, or combinations thereof.

[0155] The term "circuitry" as used herein may refer to one or more or all of the following: (a) a hardware-only circuit implementation (e.g., an implementation with only analog and / or digital circuitry); (b) (where applicable) the following: (i) a combination of analog and / or digital hardware circuitry and software / firmware; (ii) a combination of hardware circuitry and software (including digital signal processors), software, and any portion of a hardware processor with memory that cooperate to cause a device such as a mobile phone or server to perform various functions; and (c) hardware circuitry and / or processors, such as microprocessors or portions of microprocessors, that require software (e.g., firmware) to operate, although software may be absent if not necessary for operation.

[0156] This definition of circuitry applies to all uses of the term in this specification, including any claims. As a further example, as used herein, the term circuitry covers implementations of only a hardware circuit or processor (or processors), or of portions of a hardware circuit or processor along with accompanying software and / or firmware. The term circuitry also covers, for example, baseband or processor integrated circuits for mobile devices, or similar integrated circuits on servers, cellular network devices, or other computing or network devices, if applicable to certain claim elements.

[0157] The exemplary embodiments described herein may be implemented by computer software executable by a data processor of a mobile device, such as in a processor entity, or by hardware, or a combination of software and hardware. Computer software, or a program, also called a program product, includes software routines, applets, and / or macros, and may be stored on any device-readable data storage medium and includes program instructions for performing specific tasks. A computer program product may comprise one or more computer-executable components configured to perform an embodiment when the program is executed. The one or more computer-executable components may be at least one software code or portion thereof.

[0158] Further, in this regard, it should be noted that any block of logic flow as in the figures may represent a program step, or interconnected logic circuits, blocks, and functions, or a combination of program steps and logic circuits, blocks, and functions. Software may be stored on physical media such as memory chips or memory blocks implemented within a processor, magnetic media such as hard disks or floppy disks, and optical media such as DVDs and their data variants, CDs, etc. The physical media is non-transitory. As used herein, the term "non-transitory" refers not to a limitation on the permanence of the data storage (e.g., RAM vs. ROM), but to a limitation of the media itself (i.e., tangible rather than signal).

[0159] The memory may be of any type suitable for the local technology 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. The data processor may be of any type suitable for the local technology environment and may comprise, by way of non-limiting examples, 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, a processor based on a multi-core processor architecture, and the like.

[0160] Exemplary embodiments may be implemented in a variety of components, such as integrated circuit modules. Integrated circuit design is generally a highly automated process. Complex and powerful software tools are available for converting logic-level designs into semiconductor circuit designs that can be etched onto semiconductor substrates.

[0161] The scope of protection sought for various exemplary embodiments of the present disclosure is defined by the independent claims. Embodiments and features described herein that do not fall within the scope of the independent claims, if any, should be interpreted as examples that serve to understand the various exemplary embodiments described herein.

[0162] The foregoing has provided, by way of non-limiting example, a complete and informative description of the exemplary embodiments described herein. However, various changes and modifications will become apparent to those skilled in the art in light of the foregoing, when read in conjunction with the accompanying drawings and claims. However, all such and similar variations upon the teachings of the present disclosure will still fall within the scope of the present disclosure. Indeed, there may be further exemplary embodiments that consist of a combination of one or more exemplary embodiments with any of the other exemplary embodiments described herein.

[0163] 1. Prologue The revised WID, RP-221262, on NR Sidelink Relay Enhancements includes the following objectives: 1. Specify mechanisms to support single-hop Layer 2 and Layer 3 UE-to-UE relay (i.e., source UE -> relay UE -> destination UE) for unicast [RAN2, RAN3, RAN4]. A. Intersection for Layer 2 and Layer 3 relays to be prioritized up to RAN#98 i. Relay discovery and (re)selection [RAN2, RAN4] ii. Signaling support for relay and remote UE authentication when deemed necessary by SA2 [RAN3] In this post, we will discuss the RAN2 aspects of SL U2U relays that are common to both L2 and L3 SL U2U relays.

[0164] 2 Discussion 2.1 Rel-18 Scope, Requirements, or Operating Assumptions NR SL relays, including SL U2U relays, are targeted at V2X, public safety, and commercial use cases as described in the objectives of WID RP-221262 and reproduced above. Therefore, it is important to clarify the following aspects related to the scope, requirements, or operational assumptions of Rel-18:

[0165] - The need to support indirect sidelink discovery (SD) using SL U2U relays: A source UE needs to discover destination UEs that are not in the source UE's direct SL neighborhood via one or more U2U Relay UEs.

[0166] - The need to support unicast service continuity between source and destination UEs via SL U2U relays: this includes direct to indirect path switching via a selected U2U Relay UE, or indirect to indirect path switching via a reselected U2U Relay UE, or mode switching between L2 and L3 relays. Note that SL U2U relays can be used to provide SL range or coverage extension and SL RLF recovery, or to improve QoS and energy efficiency for source and destination UEs.

[0167] - The need to support backward compatibility with SL U2U relays: the destination UE may be from an earlier 3GPP release and therefore is unaware of the SL U2U relay, i.e. the SL U2U relay is transparent to the destination UE.

[0168] Proposal 1: RAN2 is a) Indirect sidelink detection; b) Service continuity, and c) Check and confirm with SA2 support for above aspects including backward compatibility in Rel-18 SL U2U relays.

[0169] 2.2 SL U2U Relay Detection In SL U2N relaying, the U2N Relay UE is always pre-associated with the serving gNB. Therefore, it is sufficient for the Remote UE to discover the U2N Relay UE using either Model A or Model B, similar to direct SD. In SL U2U relaying, the U2U Relay UE may not have prior knowledge or association with either the source or destination UE. Therefore, on-the-fly coordination may be required between the source UE, destination UE, and U2U Relay UE to reconfirm that the U2U Relay UE candidate can reach both the source and destination UEs in U2U Relay Discovery (RD).

[0170] SA2 has previously considered several options related to SL U2U RD, as documented in TR23.700-33. In one example, a source UE may issue an RD request to search for U2U Relay UE candidates that can reach the destination UE in response to a request by the source UE in an RD request. This suggests that SL U2U RD is initiated by the source UE using Model B. Upon receiving an RD request from the source UE, a U2U Relay UE in the vicinity of the source UE may further perform SD toward the destination UE, for example, by initiating an SD request using Model B. Upon receiving an SD request from each U2U Relay UE, the destination UE may respond to each U2U Relay UE. Each U2U Relay UE may then respond to the source UE and become a U2U Relay UE candidate for the source UE. However, this example assumes that no association between a U2U Relay UE candidate and the source UE or destination UE has been pre-established. In another example, a U2U Relay UE may announce a list of destination UEs that the U2U Relay UE can reach based on the use of Model A. The source UE may then detect the announcing U2U Relay UE and determine whether the intended destination UE is included in the list of destination UEs provided by the announcing U2U Relay UE. If the determination result is positive, the announcing U2U Relay UE is considered a U2U Relay UE candidate for the source UE. However, this example assumes that the association between the announcing U2U Relay UE and the list of destination UEs has been pre-established, and the source UE is limited to the list of destination UEs provided by the announcing U2U Relay UE.

[0171] Proposal 2: RAN2 considers the cooperation between source UE, destination UE, and U2U relay UE in U2URelay detection for SL U2U in L2 and L3 based on the results of SA2.

[0172] In SL U2N relaying, both the U2N Remote UE and the U2N Relay UE must meet certain radio conditions on the Uu in advance, such as the Remote UE's DL RSRP being below a threshold and the Relay UE's DL RSRP being above a threshold. For SL U2U relaying, it is not clear yet whether any radio conditions need to be specified for the UEs acting as source UE, destination UE, or U2U Relay UE. A condition may be considered in which the source UE and destination UE are not in sufficient direct SL communication range with each other, or the SL channel conditions between them are below a threshold. This condition may be flexible, considering that SL U2U relaying may be used to improve the power efficiency of the source UE and destination UE. From the examples described above, it can be observed that in the first example, explicit radio conditions may not be required for or from the U2U Relay UE. In a second example, the radio conditions on the SL between the announcing U2U relay UE and each destination UE in the list may be considered.

[0173] Proposal 3: RAN2 considers that SL U2U relays can be used to improve the power efficiency of source UEs and destination UEs, and considers the radio conditions required for source UEs, destination UEs, and U2U Relay UEs in SL U2U relays.

[0174] Furthermore, from the examples described above, it can be observed that the larger the number of U2U Relay UE candidates, the larger the signaling overhead and associated latency for the overall indirect SD and SL U2U RD procedure between the source UE, destination UE, and U2U Relay UE. This is particularly costly for the destination UE if it needs to respond individually to SD requests from a large number of U2U Relay UE candidates or if it needs to constantly announce itself to the U2U Relay UE periodically.

[0175] The above problem can be solved by enabling the destination UE to respond to the earliest SD request received from a U2U Relay UE candidate using SL groupcast or broadcast, or to announce itself (e.g., by initiating Model B discovery) in cooperation with the source UE and, consequently, the U2U Relay UE, as needed for SL U2U RD. This can be achieved, for example, based on configuration information provided along with the SL U2U RD procedure. Note that the source UE and destination UE may need to provide their identity information to the U2U Relay UE so that the U2U Relay UE can identify and verify them in the SL U2U RD. In this regard, the L2 identities of the source UE and destination UE may be provided in the configuration information.

[0176] Proposal 4: RAN2 considers the use of sidelink detection Model A and Model B during cooperation between source UE, destination UE, and U2U Relay UE for SL U2U relay detection, taking into account the support of service continuity between source UE and destination UE.

[0177] Proposal 5: RAN2 considers using the L2 IDs of source UE and destination UE to enable U2U Relay UE to quickly identify source UE and destination UE in SL U2U relay detection.

[0178] Therefore, due to the distributed nature of SL U2U Relay and its applications, even if UEs acting as U2U Relay UEs or destination UEs do not always announce themselves for SD periodically, SL traffic in SL U2U RD can be high and generally consume significant power and resources.

[0179] Proposal 6: RAN2 should consider whether a dedicated resource pool configured for SL U2U relay discovery and SL U2U relay-based indirect sidelink discovery is required.

[0180] In many use cases, the use of SL U2U relaying may be restricted to members of a predefined SL group, in the sense that the source UE, destination UE, and U2U Relay UE are members of the predefined group. For example, in a platoon, U2U Relay UE members may travel together and provide SL U2U relaying for other UE members of the group. The same applies to critical group communications in public safety and personal IoT networks. In these use cases, SL U2U RD may be restricted within the group. For example, in the above use cases, SD messages such as SD announcements or requests may be sent using SL groupcast with the L2 group ID as the L2 DST ID to prevent unwanted communication with outsiders.

[0181] Proposal 7: RAN2 considers SL U2U relay discovery restricted within a predefined SL group, using SL groupcast to transmit sidelink discovery messages.

[0182] 2.3 SL U2U Relay (Re)Selection SL U2U Relay (re)selection is performed to establish or re-establish an SL connection between a source UE and a destination UE via a (re)selected U2U Relay UE. The SL connection establishment is triggered by the source UE. The SL connection re-establishment in terms of service continuity can be triggered by either the source UE, the destination UE, or the currently serving U2U Relay UE. However, it is not clear whether the source UE or 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 performed between the source UE and the destination UE. For example, some solutions in TR 23.700-33 suggest that the SL U2U RD can be integrated into an indirect unicast SL connection establishment procedure initiated by the source UE and the destination UE, and the destination UE can select the U2U Relay UE. In another solution in TR23.700-33, the source UE may detect and select a U2U Relay UE that announces or indicates to the source UE that it can reach the destination UE.

[0183] Proposal 8: RAN2 considers that either the source UE or the relay UE may be responsible for the SL U2U relay (re)selection.

[0184] Proposal 9: RAN2 considers supporting service continuity between source UE and relay UE and considers coordination between source UE, relay UE and U2U Relay UE for SL U2U relay (re)selection.

Claims

1. 1. An apparatus in a first user equipment, comprising: means for determining, based on a trigger, to select or reselect a further user equipment to act as a relay node between a first user equipment and a second user equipment in communication; means for determining the source of the trigger; means for determining, based on the determined source, to provide, from the first user equipment to the second user equipment, a request for at least one of cooperative detection of user equipment candidates for the further user equipment and selection or reselection of the further user equipment from among the user equipment candidates; and means for providing the request 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. 10. The apparatus of claim 1, wherein the first user equipment and the second user equipment communicate through 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. 10. The apparatus of claim 1, wherein a source of the trigger is a second user equipment, the apparatus comprising: means for receiving information from the second user equipment; and means for determining, based on the information, to provide a request for at least one of cooperative detection, selection, or reselection.

5. 5. The apparatus of claim 4, wherein the means for determining comprises means for determining whether the information includes a list of user equipment candidates for the further user equipment, whether a number of user equipment candidates in the list is below a threshold, whether the list of user equipment candidates includes a user equipment candidate in the list of user equipment candidates for the first user equipment, or whether the information includes an indication that the second user equipment is performing a cooperative relay discovery procedure.

6. 6. The apparatus of claim 1, wherein the request includes at least one of a list of user equipment candidates for the further user equipment, an indication of whether cooperative detection is requested in the second user equipment, or an indication that the first user equipment is performing a cooperative detection procedure.

7. 7. The apparatus of claim 6, comprising: means for receiving an indication from the second user equipment in response to the request, the indication including at least one of an identity of the further 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 a cooperative detection procedure, or a further list of user equipment candidates for the further user equipment.

8. 10. The apparatus of claim 7, comprising: means for transmitting, in response to receiving an indication from a second user equipment that the second user equipment is performing a cooperative detection procedure, a detection request from the first user equipment to the candidate user equipment, the detection request including an indication instructing the candidate user equipment to monitor for detection messages from the second user equipment.

9. 1. An apparatus in a second user equipment, comprising: means for the second user equipment to receive from a first user equipment a request for at least one of cooperative detection of user equipment candidates for a further user equipment and selection or reselection from among the user equipment candidates of a further user equipment to function as a relay node between the first user equipment and the second user equipment in communication.

10. 10. The apparatus of claim 9, comprising means for providing a trigger from the second user equipment to the first user equipment for selecting or reselecting a further user equipment to act as a relay node between the first and second user equipment.

11. 11. The apparatus of claim 9 or 10, wherein the request includes a list of user equipment candidates for the further user equipment, an indication of whether cooperative detection is requested in the second user equipment, or an indication that the first user equipment is performing a cooperative detection procedure.

12. 12. The apparatus of claim 11, comprising: means for determining, at the second user equipment based on the request, to perform a cooperative detection procedure for the further user equipment; means for performing the cooperative detection procedure; and means for providing an indication to the first user equipment that the second user equipment is performing the cooperative detection procedure.

13. 13. The apparatus of claim 12, wherein the means for performing a cooperative discovery procedure comprises means for providing a broadcast discovery announcement or a groupcast discovery response to the candidate user equipment, the broadcast discovery announcement or groupcast discovery response including at least one of a Layer 2 identifier of the first user equipment or the second user equipment.

14. 12. The apparatus of claim 11, comprising: means for determining, based on the request, to perform a relay selection procedure or a relay reselection procedure in the second user equipment; means for performing, in the second user equipment, the relay selection procedure or the relay reselection procedure; and means for providing, from the second user equipment to the first user equipment, an indication of an identity of the further user equipment.

15. 12. The apparatus of claim 9, further comprising means for providing an indication from the second user equipment in response to the request, the indication including at least one of an indication that selection or reselection is currently not possible based on the list of user equipment candidates, or a further list of user equipment candidates for the further user equipment.

16. 12. The apparatus of claim 11, comprising: means for transmitting, from a second user equipment to a candidate user equipment, a detection request including an indication instructing the candidate user equipment to monitor for detection messages from the first user equipment, in response to receiving an indication from the first user equipment that the first user equipment is performing a cooperative detection procedure.

17. 1. A method, comprising: determining, based on the trigger, to select or reselect a further user equipment to act as a relay node between the first user equipment and the second user equipment in communication; determining a source of the trigger; determining, based on the determined source, to provide, from the first user equipment to the second user equipment, a request for at least one of cooperative detection of user equipment candidates for the further user equipment and selection or reselection of the further user equipment from among the user equipment candidates; providing a request from a first user equipment to a second user equipment.

18. 1. A method, comprising:

1. The method of claim 1, wherein a second user equipment receives a request from a first user equipment for at least one of cooperative detection of user equipment candidates for a further user equipment and selection or reselection from among the user equipment candidates of a further user equipment to act as a relay node between the first user equipment and the second user equipment in communication.

19. 1. An apparatus comprising at least one processor and at least one memory storing instructions, the instructions, when executed by the at least one processor, causing the apparatus to perform at least: determining, based on the trigger, to select or reselect a further user equipment to act as a relay node between the first user equipment and the second user equipment in communication; Determine the source of the trigger, determining, based on the determined source, to provide, from the first user equipment to the second user equipment, a request for at least one of cooperative detection of user equipment candidates for the further user equipment and selection or reselection of the further user equipment from among the user equipment candidates; An apparatus for causing a request to be provided from a first user equipment to a second user equipment.

20. 1. An apparatus comprising at least one processor and at least one memory storing instructions, the instructions, when executed by the at least one processor, causing the apparatus to perform at least:

1. An apparatus for causing a second user equipment to receive, from a first user equipment, a request for at least one of cooperative detection of user equipment candidates for a further user equipment and selection or reselection from among the user equipment candidates of a further user equipment to function as a relay node between the first user equipment and the second user equipment in communication.

21. 1. A computer-readable medium comprising instructions that, when executed by an apparatus, cause the apparatus to perform at least: determining, based on the trigger, to select or reselect a further user equipment to act as a relay node between the first user equipment and the second user equipment in communication; determining a source of the trigger; determining, based on the determined source, to provide, from the first user equipment to the second user equipment, a request for at least one of cooperative detection of user equipment candidates for the further user equipment and selection or reselection of the further user equipment from among the user equipment candidates; and providing a request from the first user equipment to the second user equipment.

22. 1. A computer-readable medium comprising instructions that, when executed by an apparatus, cause the apparatus to perform at least one of the following operations on a second user device:

1. A computer-readable medium that causes a second user equipment to receive, from a first user equipment, a request for at least one of cooperative detection of user equipment candidates for a further user equipment and selection or reselection from among the user equipment candidates of a further user equipment to function as a relay node between the first user equipment and the second user equipment in communication.

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