WO2025031734A1

WO2025031734A1 - A method, apparatus and computer program product for management of sidelink based relaying

Info

Publication number: WO2025031734A1
Application number: PCT/EP2024/070075
Authority: WO
Inventors: Vinh Van Phan; Yu LING; György Tamás Wolfner; Faranaz SABOURI-SICHANI; Sunyoung Lee; Sayed Ali MARANDI; Jakob Lindbjerg Buthler
Original assignee: Nokia Technologies Oy
Current assignee: Nokia Technologies Oy
Priority date: 2023-08-10
Filing date: 2024-07-16
Publication date: 2025-02-13
Anticipated expiration: 2026-02-10

Abstract

There are disclosed methods and apparatuses for relaying communication between a source user equipment and a target user equipment. In accordance with an embodiment, the method comprises determining whether a transmitting user equipment of the user equipment-to-user equipment relay communication is allowed to request the relay user equipment to set up at least one relay channel over a communication link, between the relay user equipment and the transmitting user equipment, for the user equipment-to-user equipment relay communication or not; in accordance with the determining, generating at least one control message to indicate a result of the determining to the transmitting user equipment; and sending the at least one control message to the transmitting user equipment.

Description

A METHOD, APPARATUS AND COMPUTER PROGRAM PRODUCT FOR MANAGEMENT OF SIDELINK BASED RELAYING

TECHNICAL FIELD

[0001] The present invention relates to management of sidelink based relaying.

BACKGROUND

[0002] This section is intended to provide a background or context to the invention that is recited in the claims. The description herein may include concepts that could be pursued, but are not necessarily ones that have been previously conceived or pursued. Therefore, unless otherwise indicated herein, what is described in this section is not prior art to the description and claims in this application and is not admitted to be prior art by inclusion in this section.

[0003] The sidelink (SL) is a tool for direct communication between user equipment (UE to UE communication) in various use cases. In some use cases solutions including new radio (NR) sidelink are being specified mainly for vehicle-to-everything (V2X) communications while they can also be used for public safety and commercial applications when the service requirement can be met.

[0004] In new radio (NR) sidelink (SL) based layer 2 (L2) user equipment-to-user equipment (UE-to-UE, U2U) relay, a transmitting end UE (Tx End UE) may have to set up SL relay radio link control (RLC) channels, for transmissions of end-to-end (E2E) radio bearers (RB), including signaling RBs (SRB) and data RBs (DRB), to the U2U relay UE to be relayed to a receiving end UE (Rx End UE). Tx End UE may be referred to here also as Tx UE and Rx End UE as Rx UE. [0005] In NR SL based L2 UE-to-Network (U2N) relay, the serving gNB has full control over the setup and mapping of a SL relay RLC channel between a remote UE and a L2 U2N relay UE as well as a Uu relay RLC channel between a L2 U2N relay UE and a serving gNB for relaying Uu SRB(s) and DRB(s) of the remote UE via the L2 U2N relay UE. This may not work in L2 U2U relay case, as UEs involved in L2 U2U relay do not need to be in Radio Resource Control (RRC) CONNECTED state to a serving gNB.

SUMMARY

[0006] There is provided a method, apparatus and computer program product for managing sidelink based relaying i.e. utilizing a relaying device in communication between two other devices, for example between a remote user equipment (UE) and a network node or between two remote user equipment so that data is communicated via the relaying device (e.g. a relay user equipment).

[0007] The scope of protection sought for various embodiments of the invention is set out by the independent claims. The embodiments, examples and features, if any, described in this specification that do not fall under the scope of the independent claims are to be interpreted as examples useful for understanding various embodiments of the invention.

[0008] According to some aspects, there is provided the subject matter of the independent claims. Some further aspects are defined in the dependent claims. The embodiments that do not fall under the scope of the claims are to be interpreted as examples useful for understanding the disclosure.

[0009] According to a first aspect there is provided a relay user equipment for user equipment- to-user equipment relay communication comprising means for: determining whether a transmitting user equipment of the user equipment-to-user equipment relay communication is allowed to request the relay user equipment to set up at least one relay channel over a communication link, between the relay user equipment and the transmitting user equipment, for the user equipment-to-user equipment relay communication; in accordance with the determining, generating at least one control message to indicate a result of the determining to the transmitting user equipment; sending the at least one control message to the transmitting user equipment.

[0010] According to a second aspect there is provided a method for user equipment-to-user equipment relay communication, comprising: determining, by a relay user equipment, whether a transmitting user equipment of the user equipment-to-user equipment relay communication is allowed to request the relay user equipment to set up at least one relay channel over a communication link, between the relay user equipment and the transmitting user equipment, for the user equipment-to-user equipment relay communication; in accordance with the determining, generating, by the relay user equipment, at least one control message to indicate a result of the determining to the transmitting user equipment; and sending, by the relay user equipment, the at least one control message to the transmitting user equipment.

[0011 ] According to a third aspect there is provided a relay user equipment comprising at least one processor; and at least one memory including computer program code; the at least one memory and the computer program code configured to, with the at least one processor, to cause the relay user equipment to perform the following for user equipment-to-user equipment relay communication: determining whether a transmitting user equipment of the user equipment-to-user equipment relay communication is allowed to request the relay user equipment to set up at least one relay channel over a communication link, between the relay user equipment and the transmitting user equipment, for the user equipment-to-user equipment relay communication; in accordance with the determining, generating at least one control message to indicate a result of the determining to the transmitting user equipment; and sending the at least one control message to the transmitting user equipment.

[0012] According to a fourth aspect there is provided a computer program product comprising computer readable program code configured to, with at least one processor, cause a relay user equipment to perform at least the following for user equipment-to-user equipment relay communication: determining whether a transmitting user equipment of the user equipment-to-user equipment relay communication is allowed to request the relay user equipment to set up at least one relay channel over a communication link, between the relay user equipment and the transmitting user equipment, for the user equipment-to-user equipment relay communication; in accordance with the determining, generating at least one control message to indicate a result of the determining to the transmitting user equipment; and sending the at least one control message to the transmitting user equipment.

[0013] According to a fifth aspect there is provided a transmitting user equipment for user equipment-to-user equipment relay communication comprising means for: receiving at least one control message from a relay user equipment of the user equipment for user equipment-to-user equipment relay communication, the at least one control message indicating whether the transmitting user equipment is allowed to request the relay user equipment to set up at least one relay channel over a communication link, between the relay user equipment and the transmitting user equipment, for the user equipment-to-user equipment relay communication; and determining, based on the control message, whether to request the relay user equipment to set up at least one relay channel over the communication link for the user equipment-to-user equipment relay communication.

[0014] According to a sixth aspect there is provided a method for user equipment-to-user equipment relay communication comprising: receiving, by a transmitting user equipment of the user equipment for user equipment-to-user equipment relay communication, at least one control message from a relay user equipment, the control message indicating whether the transmitting user equipment is allowed to request the relay user equipment to set up at least one relay channel over a communication link, between the relay user equipment and the transmitting user equipment, for the user equipment-to-user equipment relay communication; and determining, based on the control message, whether to request the relay user equipment to set up at least one relay channel over the communication link for the user equipment-to-user equipment relay communication.

[0015] According to a seventh aspect there is provided a transmitting user equipment comprising at least one processor; and at least one memory including computer program code; the at least one memory and the computer program code configured to, with the at least one processor, to cause the transmitting user equipment to: receive at least one control message from a relay user equipment of the user equipment for user equipment-to-user equipment relay communication, the at least one control message indicating whether the transmitting user equipment is allowed to request the relay user equipment to set up at least one relay channel over a communication link, between the relay user equipment and the transmitting user equipment, for the user equipment-to-user equipment relay communication; and determine, based on the control message, whether to request the relay user equipment to set up at least one relay channel over the communication link for the user equipment-to-user equipment relay communication.

[0016] According to an eighth aspect there is provided a computer program product comprising computer readable program code configured to, with at least one processor, cause a transmitting user equipment to perform at least the following: receive at least one control message from a relay user equipment of the user equipment for user equipment-to-user equipment relay communication, the at least one control message indicating whether the transmitting user equipment is allowed to request the relay user equipment to set up at least one relay channel over a communication link, between the relay user equipment and the transmitting user equipment, for the user equipment-to-user equipment relay communication; and determine, based on the control message, whether to request the relay user equipment to set up at least one relay channel over the communication link for the user equipment-to-user equipment relay communication.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] For a more complete understanding of example embodiments of the present invention, reference is now made to the following descriptions taken in connection with the accompanying drawings in which:

[0018] Fig. 1 shows a part of an exemplifying wireless communications access network in accordance with at least some embodiments of the present invention;

[0019] Fig. 2a illustrates an example of a communication configuration in which some embodiments may be implemented;

[0020] Fig. 2b illustrates another example of a communication configuration in which some embodiments may be implemented;

[0021] Fig. 3a depicts a user plane protocol stack for layer 2 UE-to-UE Relay, in accordance with an approach;

[0022] Fig. 3b depicts a control plane protocol stack for layer 2 UE-to-UE Relay, in accordance with an approach;

[0023] Fig. 4 depicts a signaling diagram of a procedure for a U2U relay UE to configure a maximum number of SL relay RLC channels to a Tx End UE, in accordance with an approach;

[0024] Fig. 5a depicts a flow diagram of a method, in accordance with an embodiment;

[0025] Fig. 5b depicts a flow diagram of a method for a relay user equipment;

[0026] Fig. 5c depicts a flow diagram of a method for a transmitting user equipment; and [0027] Fig. 6 illustrates an apparatus in accordance with an embodiment.

DETAILED DESCRIPTON OF SOME EXAMPLE EMBODIMENTS

[0028] The following embodiments are exemplary. Although the specification may refer to "an", "one", or "some" embodiment(s) in several locations, this does not necessarily mean that each such reference is to the same embodiment(s), or that the feature only applies to a single embodiment. Single features of different embodiments may also be combined to provide other embodiments.

[0029] A radio device may be a device configured for communications on radio waves over a wireless radio link, i.e. a wireless link. The communications may comprise user traffic and/or signaling. The user traffic may comprise data, voice, video and/or audio. Examples of the wireless link comprise a point-to-point wireless link and a point-to-multipoint wireless link. The wireless link may be provided between two radio devices. It should be appreciated that the radio devices may have differences. For example, radio devices connected by a wireless link may comprise one or more of a user equipment (UE), an access node, an access point, a relay node, a user terminal and an Internet of Things (loT) device.

[0030] A radio device may be a radio access device that is configured to serve a plurality of other radio devices, user radio devices, and give radio access to a communications system for the user radio devices. A radio device may also be a radio station serving as a relay node or providing a wireless backhaul for one or more radio access nodes. Examples of the radio access devices comprise at least an access node, an access point, a base station and an (e/g)NodeB. Examples of the user radio devices comprise at least a user terminal and user equipment (UE). The radio device may be an aerial radio device and/or an extraterrestrial radio device configured to operate above the ground without a fixed installation to a specific altitude. Examples of extra- terrestrial radio devices comprise at least satellites and spacecraft that are configured for radio communications in a communications system that may comprise both terrestrial and extraterrestrial radio devices. Examples of aerial radio devices comprise at least High Altitude Platform Stations (HAPSs) and unmanned aerial vehicles (UAVs), such as drones. The radio access device may have one or more cells which the user radio devices may connect to in order to access the services of the communications system via the radio access device. The cells may comprise different sizes of cells, for example macro cells, micro cells, pico cells and femto cells. A macro cell may be a cell that is configured to provide coverage over a large coverage area in a service area of the communications system, for example in rural areas or along highways. A micro cell may be a cell that is configured to provide coverage over a smaller coverage area than the macro cell, for example in a densely populated urban area. Pico cells may be cells that are configured to provide coverage over a smaller area than the micro cells, for example in a large office, a mall or a train station. Femto cells may be cells that are configured to provide coverage over a smaller area than the pico cells, for example at homes or small offices. For example, macro cells provide coverage for user radio devices passing a city on a motorway/highway and local cells, e.g. micro cells or smaller cells, provide coverage for user radio devices within the city. In another example, macro cells provide coverage for aerial radio devices and/or extraterrestrial radio devices and local cells, e.g. micro cells or smaller cells, provide coverage for the aerial radio devices and/or extraterrestrial radio devices that are located at elevated positions with respect to one or more radio access devices of the communications system. Accordingly, an aerial radio device or extraterrestrial radio device may be connected to a micro cell of a radio access device and when the aerial radio device or extraterrestrial radio device is above a certain height from the ground, the aerial radio device or extraterrestrial radio device may be switched to a macro cell, for example by a handover procedure.

[0031] Fig. 1 depicts examples of simplified system architectures only showing some elements and functional entities, all being logical units, whose implementation may differ from what is shown. The connections shown in Fig. 1 are logical connections; the actual physical connections may be different. It is apparent to a person skilled in the art that the system typically comprises also other functions and structures than those shown in Fig. 1.

[0032] The example of Fig. 1 shows a part of an exemplifying radio access network.

[0033] Fig. 1 shows user devices 100 and 102 configured to be in a wireless connection on one or more communication channels in a cell with an access node (such as (e/g)NodeB) 104 providing the cell. The physical link from a user device to a (eZg)NodeB is called uplink or reverse link and the physical link from the (eZg)NodeB to the user device is called downlink or forward link. It should be appreciated that (eZg)NodeBs or their functionalities may be implemented by using any node, host, server or access point etc. entity suitable for such a usage. The access node provides access by way of communications of radio frequency (RF) signals and may be referred to a radio access node. It should be appreciated that the radio access network may comprise more than one access nodes, whereby a handover of a wireless connection of the user device from one cell of one access node, e.g. a source cell of a source access node, to another cell of another node, e.g. a target cell of a target access node, may be performed.

[0034] A communication system typically comprises more than one (eZg)NodeB in which case the (eZg)NodeBs may also be configured to communicate with one another over links, wired or wireless, designed for the purpose. These links may be used for signaling purposes. The (eZg)NodeB is a computing device configured to control the radio resources of communication system it is coupled to. The NodeB may also be referred to as a base station, an access point or any other type of interfacing device including a relay station capable of operating in a wireless environment. The (eZg)NodeB includes or is coupled to transceivers. From the transceivers of the (eZg)NodeB, a connection is provided to an antenna unit that establishes bi-directional radio links to user devices. The antenna unit may comprise a plurality of antennas or antenna elements. The (eZg)NodeB is further connected to core network 110 (CN or next generation core NGC). Depending on the system, the counterpart on the CN side can be a serving gateway (S-GW, routing and forwarding user data packets), packet data network gateway (P-GW), for providing connectivity of user devices (UEs) to external packet data networks, or mobile management entity (MME), etc.

[0035] The user device (also called UE, user equipment, user terminal, terminal device, wireless device, communications device, etc.) illustrates one type of an apparatus to which resources on the air interface are allocated and assigned, and thus any feature described herein with a user device may be implemented with a corresponding apparatus, such as a relay node. An example of such a relay node is a layer 3 relay (self-backhauling relay) towards the base station.

[0036] The user device typically refers to a portable computing device that includes wireless mobile communication devices operating with or without a subscriber identification module (SIM), including, but not limited to, the following types of devices: a mobile station (mobile phone), smartphone, personal digital assistant (PDA), handset, device using a wireless modem (alarm or measurement device, etc.), laptop andZor touch screen computer, tablet, game console, notebook, vehicle device, UEs mounted on vehicle, and multimedia device. It should be appreciated that a user device may also be a nearly exclusive uplink only device, of which an example is a camera or video camera loading images or video clips to a network. A user device may also be a device having capability to operate in Internet of Things (loT) network which is a scenario in which objects are provided with the ability to transfer data over a network without requiring human-to-human or human-to-computer interaction. The user device may also utilize cloud. In some applications, a user device may comprise a small portable device with radio parts (such as a watch, earphones or eyeglasses) and the computation is carried out in the cloud. The user device (or in some embodiments a layer 3 relay node) is configured to perform one or more of user equipment functionalities. The user device may also be called a subscriber unit, mobile station, remote terminal, access terminal, user terminal or user equipment (UE) just to mention but a few names or apparatuses.

[0037] Various techniques described herein may also be applied to a cyber-physical system (CPS) (a system of collaborating computational elements controlling physical entities). CPS may enable the implementation and exploitation of massive amounts of interconnected ICT devices (sensors, actuators, processors, microcontrollers, etc.) embedded in physical objects at different locations. Mobile cyber physical systems, in which the physical system in question has inherent mobility, are a subcategory of cyber-physical systems. Examples of mobile physical systems include mobile robotics and electronics transported by humans or animals.

[0038] Additionally, although the apparatuses have been depicted as single entities, different units, processors and/or memory units (not all shown in Fig. 1) may be implemented.

[0039] 5G enables using multiple input - multiple output (MIMO) antennas, many more base stations or nodes than the LTE (a so-called small cell concept), including macro sites operating in co-operation with smaller stations and employing a variety of radio technologies depending on service needs, use cases and/or spectrum available. 5G mobile communications supports a wide range of use cases and related applications including video streaming, augmented reality, different ways of data sharing and various forms of machine type applications (such as (massive) machine-type communications (mMTC)), including vehicular safety, different sensors and realtime control. 5G is expected to have multiple radio interfaces, namely below 6GHz, cmWave and mmWave, and also being capable of being integrated with existing legacy radio access technologies, such as the LTE. Integration with the LTE may be implemented, at least in the early phase, as a system, where macro coverage is provided by the LTE and 5G radio interface access comes from small cells by aggregation to the LTE. In other words, 5G is planned to support both inter-RAT operability (such as LTE-5G) and inter-RI operability (inter-radio interface operability, such as below 6GHz - cmWave, below 6GHz - cmWave - mmWave). One of the concepts considered to be used in 5G networks is network slicing in which multiple independent and dedicated virtual sub-networks (network instances) may be created within the same infrastructure to run services that have different requirements on latency, reliability, throughput and mobility.

[0040] The current architecture in LTE networks is fully distributed in the radio and fully centralized in the core network. The low latency applications and services in 5G require to bring the content close to the radio which leads to local break out and multi-access edge computing (MEC). 5G enables analytics and knowledge generation to occur at the source of the data. This approach requires leveraging resources that may not be continuously connected to a network such as laptops, smartphones, tablets and sensors. MEC provides a distributed computing environment for application and service hosting. It also has the ability to store and process content in close proximity to cellular subscribers for faster response time. Edge computing covers a wide range of technologies such as wireless sensor networks, mobile data acquisition, mobile signature analysis, cooperative distributed peer-to-peer ad hoc networking and processing also classifiable as local cloud/fog computing and grid/mesh computing, dew computing, mobile edge computing, cloudlet, distributed data storage and retrieval, autonomic self-healing networks, remote cloud services, augmented and virtual reality, data caching, Internet of Things (massive connectivity and/or latency critical), critical communications (autonomous vehicles, traffic safety, real-time analytics, time-critical control, healthcare applications).

[0041] The communication system is also able to communicate with other networks, such as a public switched telephone network or the Internet 112, or utilize services provided by them. The communication network may also be able to support the usage of cloud services, for example at least part of core network operations may be carried out as a cloud service (this is depicted in Fig. 1 by “cloud” 114). The communication system may also comprise a central control entity, an operations and maintenance manager, or a like, providing facilities for networks of different operators to cooperate for example in spectrum sharing.

[0042] Edge cloud may be brought into radio access network (RAN) by utilizing network function virtualization (NFV) and software defined networking (SDN). Using edge cloud may mean access node operations to be carried out, at least partly, in a server, host or node operationally coupled to a remote radio head or base station comprising radio parts. It is also possible that node operations will be distributed among a plurality of servers, nodes or hosts. Application of cloudRAN architecture enables RAN real time functions being carried out at the RAN side (in a distributed unit, DU 104) and non-real time functions being carried out in a centralized manner (in a centralized unit, CU 108).

[0043] It should also be understood that the distribution of labor between core network operations and base station operations may differ from that of the LTE or even be non-existent. Some other technology advancements probably to be used are Big Data and all-IP, which may change the way networks are being constructed and managed. 5G (or new radio, NR) networks are being designed to support multiple hierarchies, where MEC servers can be placed between the core and the base station or NodeB (gNB). It should be appreciated that MEC can be applied in 4G networks as well.

[0044] 5G may also utilize satellite communication to enhance or complement the coverage of 5G service, for example by providing backhauling. Possible use cases are providing service continuity for machine-to-machine (M2M) or Internet of Things (loT) devices or for passengers on board of vehicles, or ensuring service availability for critical communications, and future railway/maritime/aeronautical communications. Satellite communication may utilize geostationary earth orbit (GEO) satellite systems, but also low earth orbit (LEO) satellite systems, in particular mega-constellations (systems in which hundreds of (nano)satellites are deployed). Each satellite 106 in the mega-constellation may cover several satellite-enabled network entities that create on-ground cells. The on-ground cells may be created through an on- ground relay node 104 or by a gNB located on-ground or in a satellite.

[0045] It is obvious for a person skilled in the art that the depicted system is only an example of a part of a radio access system and in practice, the system may comprise a plurality of (eZg)NodeBs, the user device may have an access to a plurality of radio cells and the system may comprise also other apparatuses, such as physical layer relay nodes or other network elements, etc. At least one of the (eZg)NodeBs may be a Home(eZg)NodeB. Additionally, in a geographical area of a radio communication system a plurality of different kinds of radio cells as well as a plurality of radio cells may be provided. Radio cells may be macro cells (or umbrella cells) which are large cells, usually having a diameter of up to tens of kilometers, or smaller cells such as micro-, femto- or picocells. The (eZg)NodeBs of Fig. 1 may provide any kind of these cells. A cellular radio system may be implemented as a multilayer network including several kinds of cells. Typically, in multilayer networks, one access node provides one kind of a cell or cells, and thus a plurality of (eZg)NodeBs are required to provide such a network structure.

[0046] For fulfilling the need for improving the deployment and performance of communication systems, the concept of “plug-and-play” (eZg)NodeBs has been introduced. Typically, a network which is able to use “plug-and-play” (eZg)Node Bs, includes, in addition to Home (eZg)NodeBs (H(eZg)NodeBs), a home node B gateway, or HNB-GW (not shown in Fig. 1). A HNB Gateway (HNB-GW), which is typically installed within an operator’s network may aggregate traffic from a large number of HNBs back to a core network.

[0047] The embodiments are not, however, restricted to the system given as an example but a person skilled in the art may apply the solution to other communication systems provided with necessary properties.

[0048] The nature of a side link (SL) is oriented according to a transmitting user equipment (Tx UE) wherein a receiving user equipment (Rx UE) may need to keep monitoring all possible PSCCH (Physical Sidelink Control Channel) instances to receive sidelink transmission over one or more (pre-)configured resource pool(s) (RP). There are at least the following two allocation modes for sidelink transmissions. The first mode, Mode 1, is a base station (BS) scheduled mode in which the serving base station allocates resources for the user equipment for sidelink transmission, and the second mode, Mode 2, is an autonomous UE selected mode, in which the user equipment may select resources for the sidelink transmission without base station intervention. These modes make no difference to a receiving user equipment Rx UE in term of receiving sidelink, regardless of whether the sidelink is for broadcast, groupcast or unicast. The sidelink can be applied for both in-coverage and out-of-coverage situations with multi-PLMN support (Tx UE and Rx UE from different serving PLMNs).

[0049] Fig. 2a illustrates an example of a communication setup in accordance with an approach. In the example of Fig. 2a there is a base station 200 which may operate as an access point to a communication network 202 for user devices 204, 206, 208. The user devices 204, 206, 208 have wireless communication capability with other user devices and/or the base station. In the setup of Fig. 2a one user device 204 is acting as a relay between some other user devices 206, 208 and the base station 200, for example. However, some of the user devices 204, 206, 208 may also be able to have a direct, mutual communication connection without any relaying user device or the base station. In the example of Fig. 2a the second user device 206 and the third user device 208 are communicating with each other whereas the first user device 204 is communicating with the base station 200, the second user device 206 and the third user device 208.

[0050] User devices having direct connection with each other may use a sidelink connection 210, for example.

[0051 ] In the illustration of Fig. 2a, the user device 204 is communicating with the base station 200 by using both a downlink (DL) and uplink (UL) whereas the user device 206 is communicating with the base station 200 by using only the downlink (DL) i.e. is only receiving signals from the base station 200 and communicates with two other user devices 204, 208 via the sidelink. The user device 208 is communicating with the user devices 204 and 206 via the sidelink only, but the user device 204 which is able to communicate with the base station 200 may forward messages from the other user devices 206, 208 to the base station 200 and may forward messages from the base station 200 to the other user devices 206, 208. Thus, the user device 204 operates as a relay UE for the other user device(s) 206, 208 and the base station 200. [0052] In the following, an example of a layer 2 UE-to-UE Relay architecture is presented with reference to protocol stacks presented in Figs. 3a and 3b. Fig. 3a depicts a user plane (UP) protocol stack for layer 2 UE-to-UE Relay, in accordance with an approach, and Fig. 3b depicts a control plane (CP) protocol stack for layer 2 UE-to-UE Relay, in accordance with an approach. [0053] For L2 UE-to-UE Relay architecture, the protocol stacks are similar to L2 UE-to- Network Relay other than the fact that the termination points are two Remote UEs. The Sidelink Relay Adaptation Protocol (SRAP) sublayer is placed above the RLC sublayer for both CP and UP at both PC5 interfaces. The sidelink Service Data Adaptation Protocol (SDAP), the Packet Data Convergence Protocol (PDCP), and the Radio Resource Control (RRC) layer are terminated between two L2 U2U Remote UEs, while the SRAP, the Radio Link Control (RLC), the Medium Access Control (MAC), and the physical layer (PHY) are terminated in each PC5 link wherein each link is between L2 U2U Remote UE and the L2 U2U Relay UE. The U2U Remote UE is also referred to as End UE. PC5 denotes the direct radio interface over SL in 3GPP standards. [0054] For L2 UE-to-UE Relay, the SRAP sublayer existing in L2 U2U Remote UE and L2 U2U Relay UE performs bearer mapping to map end-to-end SL bearer (SRB, DRB) of L2 U2U Remote UE into PC5 U2U Relay RLC Channel. The PC5 SRAP sublayer existing in L2 U2U Relay UE and L2 U2U Remote UE supports L2 U2U Remote UE identification for the sidelink traffic from the source L2 U2U Remote UE to the destination L2 U2U Remote UE.

[0055] The identification of L2 U2U Remote UE end-to-end bearer and a Remote UE ID included in the SRAP header support is arranged to correlate the received packets with the RLC Channel of the L2 U2U Relay UE, to correlate the transmit packets for the PDCP entity associated with the end-to-end radio bearer and the destination L2 U2U Remote UE ID, and to correlate the received packets for the PDCP entity associated with the end-to-end radio bearer and the source L2 U2U Remote UE ID.

[0056] The PC5 SRAP sublayer at L2 U2U Remote UE supports identification of the destination L2 U2U Remote UE. An ID being able to be mapped to the destination L2 U2U Remote UE is included in the SRAP header of the traffic from the source L2 U2U Remote UE to the L2 U2 U Relay. The PC5 SRAP sublayer at L2 U2U Relay UE supports identification of the source L2 U2U Remote UEs. An ID being able to be mapped to the source L2 U2U Remote UE is included in the SRAP header of the traffic from L2 U2U Relay UE to the destination L2 U2U Remote UE. [0057] The SRAP sublayer at L2 U2U Relay UE can perform data multiplexing from multiple RLC channels of the different source L2 U2U Remote UE to the same RLC channel of the destination L2 U2U Remote UE for the different end-to-end bearers. The SRAP sublayer at L2 U2U Relay UE can perform data demultiplexing from the same RLC channel of the source L2 U2U Remote UE to the multiple RLC channel of the different destination L2 U2U Remote UE for the different end-to-end bearers.

[0058] It should be noted that in the above description and in the rest of this specification, the remote UE is referred to as End UE, source End UE, target End UE, Tx End UE, or Rx End UE. [0059] In direct SL communication between a source or Tx UE and a destination or Rx UE, the Tx UE when being in RRC IDLE/INACTIVE or out-of-coverage state or the serving gNB of the Tx UE when the Tx UE is in RRC CONNECTED state is responsible for initiating and configuring the setup of a SL logical channel (LC) for a SL SRB or SL DRB between the Tx UE and the Rx UE. There is 1: 1 mapping between the SL logical channel and the SL Radio Bearer (RB), which can be a SL SRB or a SL DRB.

[0060] U2U relay is used for extending SL coverage between a source End UE and a target End UE. When there is a bidirectional communication between a source End UE and a target End UE via a U2U relay UE, either the source or target End UE can act as Tx End UE. The Tx End UE is the Tx UE of the first hop between the Tx End UE and the U2U relay UE, also referred to as the ingress hop of the U2U relay UE; and the U2U relay UE is the Tx UE of the second hop between the U2U relay UE and the Rx End UE, also referred to as the egress hop of the U2U relay UE, for an end-to-end (E2E) SL RB, which is between the Tx End UE and the Rx End UE. The SL relay RLC channel was introduced to carry the E2E SL RB for SL relay connections on the first hop and the second hop. A SL relay RLC channel enables the multiplexing of E2E SL RBs into one SL relay RLC channel either by the Tx End UE or by the U2U relay UE on the respective hop. Therefore, there can be 1-to-many mapping between a SL relay RLC channel and E2E SL RB(s). It is to be noted that in multi-hop U2U relay an intermediate hop is between two neighboring U2U relay UEs and therefore Tx UE of an intermediate hop is a U2U relay UE and the egress hop of the U2U relay UE over the intermediate hop is considered as the ingress hop of its neighboring U2U relay UE.

[0061] Fig. 2b illustrates an example of a communication setup in which some embodiments may be implemented. In the setup of Fig. 2b one user device 204 is acting as a relay between one or more other user devices 206, 208, 212, for example.

[0062] In the illustration of Fig. 2b, the user device 204 is acting as the U2U relay UE providing a communication connection between two or more other UEs, such as the user devices 206, 208 and 212 of Fig. 2b. These user devices 206, 208 and 212 are labelled as End UE1, End UE2 and End UE3, respectively, in the example illustration of Fig. 2b.

[0063] According to an embodiment, the U2U relay UE 204 may configure the Tx End UE of the first hop, which can either be the source end UE or the target end UE in a bidirectional E2E communication, with a maximum number of SL relay RLC channels the Tx End UE may be allowed to set up for transmissions of E2E RBs to the U2U relay UE on the first hop. For example, the Tx End UE of the first hop may be the End UE1 206, which may also be called as the source End UE, wherein the first hop is between the End UE1 206 and the U2U Relay UE 204. The End UE2 208 and/or the end UE3 212 may be the Rx End UE, which may also be called as the target End UE. In one example, the maximum number of SL relay RLC channels may comprise a first maximum number of unacknowledged mode (UM) SL relay RLC channels and a second maximum number of acknowledged mode (AM) SL relay RLC channels in case both UM and AM are supported over SL. In another example, the maximum number of SL relay RLC channels may comprise a first maximum number of SL relay RLC channels for SRBs in control plane and a second maximum number of SL relay RLC channels for DBRs in user plane. In yet another example, the maximum number of SL relay RLC channels may be configured jointly for both control plane and user plane. The configuration may be based on using a SL RRC Reconfiguration procedure.

[0064] According to an embodiment, it is up to the Tx End UE 206 to decide how many SL relay RLC channels below the configured maximum number of SL relay RLC channels are to be established for the first hop as well as how E2E RBs are mapped on the established SL relay RLC channels. The E2E RBs from the Tx End UE 206 may be for different Rx End UEs 208, 212 as the Tx End UE 206 may have different E2E connections with different Rx End UEs 208, 212 via the same U2U relay UE 204.

[0065] According to an embodiment, the U2U relay UE 204 may reconfigure (increase or decrease) the maximum number of allowed SL relay RLC channels during the lifetime of the relay connection. For example, when the U2U relay UE 204 starts acting as a relay for additional relay connections, the maximum number of SL relay RLC channels that can be used by a single Tx End UE 206 may need to be decreased. The U2U relay UE 204 may decide to increase or decrease the maximum number of SL relay RLC channels based on load, available battery capacity, etc.

[0066] According to an embodiment, if the maximum number of allowed SL relay RLC channels is not configured to the Tx End UE 206 by the U2U relay UE 204, then if a first request from the Tx End UE 206 to the U2U relay UE 204 to set up an additional SL relay RLC channel for a new E2E RB is rejected by the U2U relay UE 204 for example, the Tx End UE 206 may perform one of the following options:

The Tx End UE 206 may receive an indication from the U2U relay UE 204 along with the rejection that the Tx End UE 206 is not allowed for requesting additional SL relay RLC channel for a specified time interval starting from the instance the indication is sent at the U2U relay UE 204 or received at the Tx End UE 206 or until further notice from the U2U relay UE 204;

The Tx End UE 206 may map the new E2E RB to one of the existing RLC channel(s) and indicate that to the U2U relay UE 204; or

The Tx End UE 206 may initiate a second request to the U2U relay UE 204 to reconfigure a selected one of the existing SL relay RLC channel(s) for accommodating or mapping the new E2E RB to the selected SL relay RLC channel. If the second request is also rejected, the new E2E RB is released by the Tx End UE 206 and, at the Tx End UE 206, the AS layer may indicate to the NAS layer that the respective QoS flow cannot be served for the time being.

[0067] In the above example, the U2U relay UE 204 rejects the request of the Tx End UE 206 for an additional SL relay RLC channel and indicates to the Tx End UE 206 along with the rejection message that the Tx End UE 206 is not allowed to request an additional SL relay RLC channel. This is to prevent the Tx End UE 206 from keeping re-initiating the request while the U2U relay UE 204 is not able to accept the request and thus wasting resources. In general, the U2U relay UE may determine and send the indication whether the Tx UE for the ingress hop of the U2U relay UE is allowed to request an additional SL relay RLC channel or not to the Tx UE during or after a setup of at least one SL relay RLC channel for the Tx UE over the ingress hop or communication link between the Tx UE and the U2U relay UE.

[0068] According to an embodiment, considering that the Tx End UE 206 or the U2U relay UE 204 may be in RRC CONNECTED state and using mode 1 resource allocation, the Tx End UE 206 or the U2U relay UE 204, when using mode 1, may indicate to the serving gNB 200 (Fig. 2a) , for example, the maximum number of allowed SL relay RLC channels and/or whether the Tx End UE 206 is allowed to request a setup of an additional SL relay RLC channel or not. The Tx End UE 206 may also indicate to the serving gNB 200 the mapping of the new E2E RB to the selected SL relay RLC channel due to the rejection of the first request or the positive outcome of the second request. The Tx End UE 206 or the U2U relay UE 204 may be configured by the serving gNB to perform SL Buffer Status Report (SL-BSR) on the E2E RB basis for one or more identified E2E RB of the Tx End UE 206 in case it is not allowed to have a separate SL relay RLC channel for the identified E2E RB. In this case, the configuration of a logical channel group (LCG) mapping for the identified E2E RB from the gNB may either be explicit configuration or implicit configuration. The latter is based on the priority of E2E RB and the priority of the SL relay RLC channel and corresponding LC carrying the E2E RB such that SL-BRS on the E2E RB basis is applied for the E2E RB whose priority is higher than the LC priority of the SL relay RLC channel carrying the E2E RB. The effect is a new UE behavior for SL BSR that the UE is allowed to report SL BSR of the same SL relay RLC channel or 1 : 1 corresponding LC using different LCGs, if multiple E2E RBs with different priorities are mapped to the same SL relay RLC channel. For example, the LC that is 1 : 1 corresponding to the existing SL relay RLC channel is configured with LCG1 for all existing E2E RBs mapped on the SL relay RLC channel. Then, upon adding the new E2E RB configured with LCG2 with priority higher than LCG1 to the same SL relay RLC channel, report of buffer size of the LC is triggered and separated by buffer size of LCG 1 and LCG2. [0069] In the following a signalling procedure for the U2U relay UE 204 to configure the maximum number of SL relay RLC channels to the Tx End UE 206 is explained with reference to Fig. 4, in accordance with an embodiment.

[0070] It may be assumed that a U2U relay connection has been established previously between a source end UE and a target end UE via the U2U relay UE 204. Therefore, the step 401 depicted in Fig. 4 may have been performed at a previous stage or just before the U2U relay UE 204 decides to determine the maximum number of SL relay RL channels for example.

[0071 ] The U2U relay UE determines 402 the maximum number of SL relay RLC channels. It can be left to the UE implementation how this happens, however the U2U relay UE 204 may consider one or more of the following options. One option is that the U2U relay UE 204 takes into consideration the number of E2E RBs and QoS requirements thereof as communicated with the Tx End UE 206. It is also possible that the U2U relay UE 204 takes into consideration the type of the service (e.g., based on the Relay Service Code) provided by the U2U relay UE 204 and/or the number of E2E connections the Tx End UE 206 has with different Rx End UEs 208, 212 via the U2U relay UE 204. One option is also that the U2U relay UE 204 takes into consideration the total number of the remaining SL relay RLC channels that can be distributed to different Tx End UEs 206 which the U2U relay UE 204 is serving. This may be considered as SL relay RLC channel capacity of the U2U relay UE 204. The U2U relay UE 204, in accordance with an implementation, may use a fixed number above a minimum constraint required for the maximum number of SL relay RLC channels to be configured to each Tx End UE 206 regardless of how many E2E RBs the Tx End UE 206 has and QoS requirements thereof and/or how many E2E connections the Tx End UE 206 has with different Rx End UEs 208, 212 via the U2U relay UE 204. One option is also that the U2U relay UE 204 takes into consideration the resource allocation mode, mode 1 or mode 2, the Tx End UE 206 is using and/or the serving PLMN ID or Cell ID of the Tx End UE 206 considering inter-operator policies or rules.

[0072] The U2U relay UE 204 may configure, e.g. by sending 403 at least one SL-RRC Reconfiguration message to the Tx End UE 206, the maximum number of SL relay RLC channels to the Tx End UE 206. SL-RRC Reconfiguration message may be one example of a control message or at least one control message as used herein. This may happen as soon as the unicast SL connection between the U2U relay UE 204 and the Tx End UE 206 is established or upon the first E2E RB between the Tx End UE 206 and the Rx End UE 208, 212 is set up for example. In case a Local ID is assigned to the Tx End UE 206 by the U2U relay UE 204 for SRAP operation, the maximum number of SL relay RLC channels may be configured along with the Local ID assignment for example.

[0073] The U2U relay UE 204 may also configure, e.g. by sending 404 a corresponding SL- RRC Reconfiguration message to the other End UE(s) 208, 212, the maximum number of SL relay RLC channels to the other End UE(s) 208, 212, as the other End UE(s) 208, 212 may also be Tx End UE in bidirectional communication while also being the Rx End UE(s) of the Tx End UE 206.

[0074] The U2U relay UE 204 may reconfigure the maximum number of SL relay RLC channels to the Tx End UE 206 if needed on the fly. In one example, the reconfiguration may be up on the addition or release of an E2E RB based on QoS requirements thereof. It is noted that the Tx End UE 206 may need to communicate with the U2U relay UE 204 for QoS handling on each E2E RB the Tx End UE 206 has, as the QoS split of at least the packet delay budget for the E2E RB for the first hop and the second hop may be controlled by the U2U relay UE 204. In another example, the reconfiguration may be up on the addition or release of an E2E connection between the same Tx End UE 206 and a Rx End UE 208, 212 via the same U2U relay UE 204. In this case, the maximum number of SL relay RLC channels may be (re)configured for each of the E2E connections or for all of the E2E connections the Tx End UE 206 has with different Rx End UE 208, 212 via the U2U relay UE 204.

[0075] An SL RRC reconfiguration procedure may be used for (re)configuring the maximum number of SL relay RLC channels to the Tx End UE 206 but not limited to.

[0076] The Tx End UE 206 determines whether an additional SL relay RLC channel needs to be set up with the U2U relay UE 204 for an additional E2E RB or not based on QoS requirements and available SL relay RLC channels. For example, the Tx End UE 206 maps the additional E2E RB to one of the existing SL relay RLC channels if the maximum number of SL relay RLC channels has been reached.

[0077] To support multi-hop U2U relay, the maximum number of SL relay RLC channels may be (re)configured hop-by-hop or, that is, by the U2U relay UE 204 acting as the Tx End UE for the egress hop from the U2U relay UE 204 to either the Tx End UE 206 or another U2U relay UE acting as the Tx End UE for the ingress hop to the U2U relay UE 204.

[0078] Fig. 5a depicts a flow diagram of a method, in accordance with an embodiment. An U2U relay connection is established 502 between the source End UE 206 and one or more target End UEs 208, 212 via the U2U Relay UE for bidirectional communication. It should be noted that the source End UE 206 may be the Tx End UE in view of communication towards the target End UE 208, 212, wherein the target End UE 208, 212 is the Rx End UE. Correspondingly, in view of communication from the target End UEs 208, 212 towards the source End UE 206, the target End UEs 208, 212 are the Tx End UEs and the source End UE 206 is the Rx End UE.

[0079] In step 504 the U2U relay UE 204 determines to (re)configure the maximum number of SL relay RLC channels that a Tx End UE is allowed to set up and use towards the U2U Relay UE on a first hop.

[0080] In step 506 the U2U relay UE 204 sends an SL-RRC Reconfiguration message to the Rx End UE(s) 208, 212. The SL-RRC Reconfiguration message indicates the maximum number of SL relay RLC channels determined by the U2U Relay UE 204 for the bidirectional, relayed sidelink communication between the source End UE 206 and target End UE(s) 208, 212. [0081 ] Fig. 5b depicts a flow diagram of a method for the relay user equipment 204, in accordance with an embodiment. The relay user equipment 204 determines 512 whether a transmitting user equipment 206 of the user equipment-to-user equipment relay communication is allowed to request the relay user equipment 204 to set up at least one relay channel over a communication link, between the relay user equipment and the transmitting user equipment, for the user equipment-to-user equipment relay communication. In accordance with the determining, the relay user equipment 204 generates 514 at least one control message to indicate a result of the determining to the transmitting user equipment 206 and sends 516 the at least one control message to the transmitting user equipment.

[0082] According to an embodiment, the relay channel is a sidelink relay radio link control channel.

[0083] The result of the determining may indicate whether the transmitting user equipment 206 is allowed to request the relay user equipment 204 to set up at least one relay channel over the communication link (e.g., the ingress hop of the relay user equipment 204). In an example, the result of the determining may be that the transmitting user equipment 206 is allowed to request the relay user equipment 204 to set up at least one relay channel over the communication link. The at least one control message may thus be generated so that it indicates that the transmitting user equipment 206 is allowed to request the relay user equipment 204 to set up at least one relay channel over the communication link. In another example, the result of the determining may be that the transmitting user equipment 206 is not allowed to request the relay user equipment 204 to set up at least one relay channel over the communication link. The at least one control message may thus be generated so that it indicates that the transmitting user equipment 206 is not allowed to request the relay user equipment 204 to set up at least one relay channel over the communication link. In yet another example, the result of the determining may be that the transmitting user equipment 206 is allowed to request the relay user equipment 204 to set up up to a maximum allowed number of relay channels over the communication link. The at least one control message may thus be generated so that it indicates the maximum allowed number of relay channels the transmitting user equipment 206 is allowed to request the relay user equipment 204 to set up over the communication link.

[0084] Fig. 5c depicts a flow diagram of a method for the transmitting user equipment 206, in accordance with an embodiment. The transmitting user equipment 206 receives 522 at least one control message from the relay user equipment 204, the control message indicating whether the transmitting user equipment 206 of the user equipment-to-user equipment relay communication is allowed to request the relay user equipment 204 to set up at least one relay channel over a communication link, between the relay user equipment 204 and the transmitting user equipment 206, for the user equipment-to-user equipment relay communication. Then the transmitting user equipment 206 determines 524, based on the control message, whether to request the relay user equipment 206 to set up at least one relay channel over the communication link for the user equipment-to-user equipment relay communication. In accordance with the determining, the transmitting user equipment 206 requests 526 the relay user equipment 204 to set up at least one relay channel over the communication link for the user equipment-to-user equipment relay communication.

[0085] For example, the transmitting user equipment 206 may determine to request the relay user equipment 204 to set up at least one relay channel over the communication link based on the at least one control message indicating that the transmitting user equipment is allowed to request the set up of the at least one relay channel. Additionally, the transmitting user equipment 206 may use further information (e.g. information on a need to establish the at least one relay channel) in determining whether it shall request the set up of the at least one relay channel if said requesting is allowed. In another example, the transmitting user equipment 206 may determine to not request the relay user equipment 204 to set up at least one relay channel over the communication link based on the at least one control message indicating that the transmitting user equipment is not allowed to request the set up of the at least one relay channel.

[0086] The at least one relay channel may be referred to as at least one additional relay channel in cases where the communication link for the user equipment-to-user equipment relay communication has already been established as in such case at least one relay channel may already exist in the communication link. Thus, the at least one control message may indicate whether additional relay channel(s) is allowed to be requested to be set up for the communication link.

[0087] As described herein, in some embodiments, the at least one control message may indicate a maximum number of relay channel(s) for the communication link (meaning total maximum for the communication link) or maximum number of additional relay channel(s) that may be requested to be set up.

[0088] In an embodiment, maximum number of relay channels or additional relay channels may be indicated separately for control plane and for user plane. Thus, for example, two maximum numbers may be indicated where one maximum number indicates maximum number of relay channels or additional relay channels for control plane and the other maximum number indicates maximum number of relay channels or additional relay channels for user plane. Such approach may further enhance flexibility of the solution.

[0089] In an embodiment, maximum number of relay channels or additional relay channels may be indicated jointly for control plane and for user plane. Thus, only one maximum number may be indicated which is the same quota for both control plane and user plane relay channel(s). Or the maximum number may indicate separate quotas of same size for control plane and user plane. [0090] In accordance with an embodiment, the at least one control message indicates the maximum allowed number of relay channels the transmitting user equipment 206 is allowed to request the relay user equipment 204 to set up over the communication link for the user equipment-to-user equipment relay communication or the maximum allowed number of relay channels for said communication link separately for user plane and for control plane.

[0091 ] In accordance with an embodiment, the at least one control message indicates the maximum allowed number of relay channels the transmitting user equipment 206 is allowed to request the relay user equipment to set up over the communication link for the user equipment-to- user equipment relay communication or the maximum allowed number of relay channels for said communication link jointly for user plane and for control plane.

[0092] Above some examples of such at least one control message were presented.

[0093] In an embodiment, the communication link for the user equipment-to-user equipment relay communication is referred to as an ingress hop of the relay user equipment 204 for the user equipment-to-user equipment relay communication.

[0094] In an embodiment, the communication link for the user equipment-to-user equipment relay communication is referred to as an ingress hop of the relay user equipment 204 for the user equipment-to-user equipment relay communication.

[0095] In an embodiment, the relay user equipment 204 is another transmitting user equipment for another communication link between the relay user equipment and a Rx End UE 206, 208 or 212 in the case of single-hop relay or another relay user equipment in the case of multi-hop relay for the user equipment-to-user equipment relay communication. The other communication link is referred to as an egress hop of the relay user equipment 204 for the user equipment-to-user equipment relay communication.

[0096] According to an embodiment, for maximizing simplicity and scalability, a layer 2 (L2) user equipment-to-user equipment (U2U) relay may be provided using one sidelink (SL) relay radio link control (RLC) channel for all the end-to-end (E2E) SL radio bearers (RBs) between the transmitting UE (Tx End UE) and the receiving UE (Rx End UE) on each of the hops from one entity to another entity communicating in the U2U relay. [0097] Alternatively, two SL relay RLC channels, one for all the E2E SL signaling radio bearers (SRB) and the other for all the E2E SL data radio bearer(s) (DRB), may be used if there is a need for a clear separation between control plane and user plane radio bearers.

[0098] A hop from the Tx End UE to a next (second) entity may be called as a first hop, a hop from the second entity to a next entity may be called as a second hop etc.

[0099] According to an embodiment, for scheduling operation in term of quality of service (QoS) support with maximized QoS differentiation among different E2E RBs, the 1: 1 (one-to- one) mapping between E2E RB and SL relay RLC channel may be preferable.

[0100] The U2U relay UE may serve multiple E2E connections for different pairs of source end UEs and target end UEs while having a certain upper limit on the total number of different SL relay RLC channels or SL non-relay RLC channels, commonly referred to as SL RLC channels, the U2U relay UE is able to handle due to, e.g., some hardware or software limitation. It is noted that for maintaining the unicast SL for a first hop and a second hop for each E2E connection when considering the case of U2U relay via a single U2E relay UE for an example, at least all mandated SL SBRs per each hop with 1 : 1 mapping with SL non-relay RLC channels may be required. Thus, a considerable portion of the total SL RLC channels of the U2U relay UE needs to be used for maintaining unicast SL connections with individual source end UEs and target end UEs. The remaining portion of the total SL RLC channels can be (re)distributed for serving E2E SL RBs for different E2E connections.

[0101] In single-hop U2U relay for example, as the U2U relay UE is serving both the Tx End UE and Rx End UE using unicast direct SL connections for the respective hops, the U2U relay UE may need to have a say on what or how it can afford to serve the source end UE and the target end UE. It is noted that the U2U relay UE may serve more than one pairs of Tx End UEs and Rx End UEs as well as have its own SL communications with other UE(s). It is further noted that the current direct SL communication is rather Tx oriented, meaning that Tx UE when operating with the autonomous resource allocation or, i.e., mode 2 in NR SL, may be in control of its own SL transmissions. The control of Tx UE includes setup of a SL non-relay RLC channel with a Rx UE for a unicast SL connection between them. If this control is applied for the first hop in U2U relay, the U2U relay UE may be forced to react to whatever initiated by the Tx End UE. This may work, as the U2U relay UE can reject the reconfiguration initiated by the Tx End UE. However, it is desirable to avoid failure operations as much as possible for not wasting resources especially in case the U2U relay UE as the reactor has full knowledge of the situation that may cause failure operations.

[0102] In case the Tx End UE or the U2U relay UE is in RRC CONNECTED state and using NR SL mode 1 resource allocation for SL transmission, the serving gNB is responsible for configuring SL relay RLC channels to the Tx End UE or the U2U relay UE.

[0103] For forward compatibility considering support for multi-hop U2U relay is desired, hop- by-hop control is preferred and thus centralized control of the SL relay RLC channel and the l:n (one-to-n, n e Z+) mapping between the SL RLC relay channel and E2E SL RBs should be avoided. Furthermore, signaling overhead and standardization impacts should be kept as low as possible.

[0104] In accordance with an embodiment, the mechanism to be presented in this specification does not require to configure and control the mapping between E2E RBs and SL relay RLC channels in L2 U2U relay but leaves it for the Tx UE of a hop to decide the mapping based on any factors that a UE implementation willing to consider such as QoS requirements, the maximum number of SL relay RLC channels, etc. It is also future proof as multi-hop U2U relays can implement this solution in hop-by-hop manner.

[0105] Thus, to avoid the situation that the Tx UE (i.e. transmitting UE) keeps initiating the request for setting up a new SL relay RLC channel and the U2U relay UE keeps rejecting the request from the Tx UE, the U2U relay UE may control whether the Tx End UE is allowed to request a setup of a new SL relay RLC channel or not. In one option, the U2U relay UE may configure the Tx End UE with a maximum number of SL relay RLC channels the Tx UE may be allowed to set up in advance. In another option, the U2U relay UE may indicate to the Tx UE on- the-fly whether the Tx End UE is allowed to request for setting up a new SL relay RLC channel or not. This indication may be sent along with the acceptance or the first rejection of the request from the Tx UE, for example. Thus, for example, the provided solution enhances communication efficiency as the Tx UE may not need request setup of one or more relay channels if it is not allowed.

[0106] Fig. 6 illustrates an example of an apparatus in accordance with at least some embodiments of the present invention. The apparatus may be a radio device, for example a user radio device. The apparatus may perform one or more functionalities according to examples described herein.

[0107] The apparatus comprises a processor 604 and a transceiver 606. The processor is operatively connected to the transceiver for controlling the transceiver. The apparatus may comprise a memory 602. The memory may be operatively connected to the processor. It should be appreciated that the memory may be a separate memory or included to the processor and/or the transceiver.

[0108] According to an embodiment, the processor is configured to control the transceiver to perform one or more functionalities described according to an embodiment.

[0109] A memory may be a computer readable medium that may be non-transitory. The memory may be of any type suitable to 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. The data processors may be of any type suitable to the local technical environment, and may include one or more of general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multi-core processor architecture, as non-limiting examples.

[01 10] Embodiments may be implemented in software, hardware, application logic or a combination of software, hardware and application logic. The software, application logic and/or hardware may reside on memory, or any computer media. In an example embodiment, the application logic, software or an instruction set is maintained on any one of various conventional computer-readable media. In the context of this document, a "memory" or "computer-readable medium" may be any media or means that can contain, store, communicate, propagate or transport the instructions for use by or in connection with an instruction execution system, apparatus, or device, such as a computer.

[01 11] Reference to, where relevant, "computer-readable storage medium", "computer program product", "tangibly embodied computer program" etc., or a "processor" or "processing circuitry" etc. should be understood to encompass not only computers having differing architectures such as single/multi-processor architectures and sequencers/parallel architectures, but also specialized circuits such as field programmable gate arrays FPGA, application specify circuits ASIC, signal processing devices and other devices. References to computer readable program code means, computer program, computer instructions, computer code etc. should be understood to express software for a programmable processor firmware such as the programmable content of a hardware device as instructions for a processor or configured or configuration settings for a fixed function device, gate array, programmable logic device, etc.

[0112] Although the above examples describe embodiments of the invention operating within a user radio device, UE, radio access device or a gNB, it would be appreciated that the invention as described above may be implemented as a part of any apparatus comprising a circuitry in which radio frequency signals are transmitted and/or received. Thus, for example, embodiments of the invention may be implemented in a mobile phone, in a base station, in a radio station, in a user radio device, in a computer such as a desktop computer or a tablet computer comprising radio frequency communication means (e.g. wireless local area network, cellular radio, etc.).

[0113] In general, the various embodiments of the invention may be implemented in hardware or special purpose circuits or any combination thereof. While various aspects of the invention may be illustrated and described as block diagrams or using some other pictorial representation, it is well understood that these blocks, apparatus, systems, techniques or methods described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

[0114] As used in this application, the term “circuitry” may refer to one or more or all of the following:

(a) hardware-only circuit implementations (such as implementations in only analogue and/or digital circuitry) and

(b) combinations of hardware circuits and software, such as (as applicable):

(i) a combination of analogue and/or digital hardware circuit(s) with software/firmware and

(ii) any portions of hardware processor(s) with software (including digital signal processors)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and

(c) hardware circuit(s) and or processor(s), such as a microprocessor(s) or a portion of a microprocessor(s), that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation.

[0115] This definition of circuitry applies to all uses of this term in this application, including in any claims. As a further example, as used in this application, the term circuitry also covers an implementation of merely a hardware circuit or processor (or multiple processors) or portion of a hardware circuit or processor and its (or their) accompanying software and/or firmware. The term circuitry also covers, for example and if applicable to the particular claim element, a baseband integrated circuit or processor integrated circuit for a mobile device or a similar integrated circuit in server, a cellular network device, or other computing or network device.

[0116] In accordance with an embodiment there is provided an apparatus for user equipment-to- user equipment relay communication comprising at least one processor; and at least one memory including computer program code; the at least one memory and the computer program code configured to, with the at least one processor, to cause the apparatus to determine whether a transmitting user equipment of the user equipment-to-user equipment relay communication is allowed to request the apparatus to set up at least one relay channel over a communication link, between the apparatus and the transmitting user equipment, for the user equipment-to-user equipment relay communication; in accordance with the determining, generating at least one control message to indicate a result of the determining to the transmitting user equipment; sending the at least one control message to the transmitting user equipment.

[0117] According to an embodiment, said at least one memory includes computer program code configured to, with the at least one processor, to cause the apparatus to send the at least one control message during or after an establishment of the user equipment-to-user equipment relay communication.

[01 18] According to an embodiment, said at least one memory includes computer program code configured to, with the at least one processor, to cause the apparatus to send the at least one control message during or after a setup of at least one relay channel over the communication link for the user equipment-to-user equipment relay communication.

[01 19] According to an embodiment, said at least one memory includes computer program code configured to, with the at least one processor, to cause the apparatus to indicate in the at least one control message a maximum allowed number of relay channels the transmitting user equipment is allowed to request the relay user equipment to set up over the communication link for the user equipment-to-user equipment relay communication or a maximum allowed number of relay channels for said communication link.

[0120] According to an embodiment, said at least one memory includes computer program code configured to, with the at least one processor, to cause the apparatus to indicate in the at least one control message the maximum allowed number of relay channels the transmitting user equipment is allowed to request the relay user equipment to set up over the communication link for the user equipment-to-user equipment relay communication or the maximum allowed number of relay channels for said communication link separately for user plane and for control plane.

[0121] According to an embodiment, said at least one memory includes computer program code configured to, with the at least one processor, to cause the apparatus to indicate in the at least one control message the maximum allowed number of relay channels the transmitting user equipment is allowed to request the relay user equipment to set up over the communication link for the user equipment-to-user equipment relay communication or the maximum allowed number of relay channels for said communication link jointly for user plane and for control plane.

[0122] According to an embodiment, said at least one memory includes computer program code configured to, with the at least one processor, to cause the apparatus to indicate in the at least one control message whether the transmitting user equipment is allowed to request the relay user equipment to set up an additional relay channel.

[0123] According to an embodiment, said at least one memory includes computer program code configured to, with the at least one processor, to cause the apparatus to send the at least one control message during or after an establishment of the user equipment-to-user equipment relay communication.

[0124] According to an embodiment, said at least one memory includes computer program code configured to, with the at least one processor, to cause the apparatus to send the at least one control message during or after a setup of at least one relay channel over the communication link for the user equipment-to-user equipment relay communication.

[0125] The foregoing description has provided by way of exemplary and non-limiting examples a full and informative description of the exemplary embodiment of this invention. However, various modifications and adaptations may become apparent to those skilled in the relevant arts in view of the foregoing description, when read in conjunction with the accompanying drawings and the appended claims. However, all such and similar modifications of the teachings of this invention will still fall within the scope of this invention.

Claims

1. A relay user equipment for user equipment-to-user equipment relay communication comprising means for: determining whether a transmitting user equipment of the user equipment-to-user equipment relay communication is allowed to request the relay user equipment to set up at least one relay channel over a communication link, between the relay user equipment and the transmitting user equipment, for the user equipment-to-user equipment relay communication; in accordance with the determining, generating at least one control message to indicate a result of the determining to the transmitting user equipment; sending the at least one control message to the transmitting user equipment.

2. The relay user equipment according to claim 1 wherein the transmitting user equipment is an end user equipment or another relay user equipment in the user equipment-to-user equipment relay communication.

3. The relay user equipment according to claim 1 or 2, wherein the at least one control message indicates a maximum allowed number of relay channels the transmitting user equipment is allowed to request the relay user equipment to set up over the communication link for the user equipment-to-user equipment relay communication or a maximum allowed number of relay channels for said communication link.

4. The relay user equipment according to claim 3, wherein the at least one control message indicates the maximum allowed number of relay channels the transmitting user equipment is allowed to request the relay user equipment to set up over the communication link for the user equipment-to-user equipment relay communication or the maximum allowed number of relay channels for said communication link separately for user plane and for control plane.

5. The relay user equipment according to claim 3, wherein the at least one control message indicates the maximum allowed number of relay channels the transmitting user equipment is allowed to request the relay user equipment to set up over the communication link for the user equipment-to-user equipment relay communication or the maximum allowed number of relay channels for said communication link jointly for user plane and for control plane.

6. The relay user equipment according to any preceding claim 1 to 5, wherein the relay user equipment comprises means for: sending the at least one control message during or after an establishment of the user equipment-to-user equipment relay communication.

7. The relay user equipment according to any preceding claim 1 to 5, wherein the relay user equipment comprises means for: sending the at least one control message during or after a setup of at least one relay channel over the communication link for the user equipment-to-user equipment relay communication.

8. The relay user equipment according to any preceding claim 1 to 7, wherein the communication link for the user equipment-to-user equipment relay communication is referred to as an ingress hop of the relay user equipment for the user equipment-to-user equipment relay communication.

9. The relay user equipment according to any preceding claim 1 to 8, wherein the at least one control message comprises an indication indicating whether the transmitting user equipment is allowed to request the relay user equipment to set up an additional relay channel.

10. The relay user equipment according to any preceding claim 1 to 9 wherein the relay channel is a side link relay radio link control channel.

11. The relay user equipment according to any preceding claims 1 to 10 wherein the at least one control message is a sidelink radio resource control message.

12. The relay user equipment according to claim 8 or any of the claims 9 to 11 when dependent on claim 8, wherein the relay user equipment is another transmitting user equipment for an egress hop of the relay user equipment to either another end user equipment or a further relay user equipment in the user equipment-to-user equipment relay communication, and the egress hop of the relay user equipment to the further relay user equipment is another ingress hop of the further relay user equipment.

13. A method for user equipment-to-user equipment relay communication, comprising: determining, by a relay user equipment, whether a transmitting user equipment of the user equipment-to-user equipment relay communication is allowed to request the relay user equipment to set up at least one relay channel over a communication link, between the relay user equipment and the transmitting user equipment, for the user equipment-to-user equipment relay communication; in accordance with the determining, generating, by the relay user equipment, at least one control message to indicate a result of the determining to the transmitting user equipment; and sending, by the relay user equipment, the at least one control message to the transmitting user equipment.

14. A transmitting user equipment for user equipment-to-user equipment relay communication comprising means for: receiving at least one control message from a relay user equipment of the user equipment for user equipment-to-user equipment relay communication, the at least one control message indicating whether the transmitting user equipment is allowed to request the relay user equipment to set up at least one relay channel over a communication link, between the relay user equipment and the transmitting user equipment, for the user equipment-to-user equipment relay communication; and determining, based on the control message, whether to request the relay user equipment to set up at least one relay channel over the communication link for the user equipment-to-user equipment relay communication.

15. The transmitting user equipment according to claim 14, wherein the transmitting user equipment is an end user equipment or another relay user equipment in the user equipment- to-user equipment relay communication.

16. The transmitting user equipment according to claim 14 or 15, wherein the at least one control message indicates a maximum allowed number of relay channels the transmitting user equipment is allowed to request the relay user equipment to set up over the communication link for the user equipment-to-user equipment relay communication or a maximum allowed number of relay channels for said communication link.

17. The transmitting user equipment according to claim 16, wherein the at least one control message indicates the maximum allowed number of relay channels the transmitting user equipment is allowed to request the relay user equipment to set up over the communication link for the user equipment-to-user equipment relay communication or the maximum allowed number of relay channels for said communication link separately for user plane and for control plane.

18. The transmitting user equipment according to claim 16, wherein the at least one control message indicates the maximum allowed number of relay channels the transmitting user equipment is allowed to request the relay user equipment to set up over the communication link for the user equipment-to-user equipment relay communication or the maximum allowed number of relay channels for said communication link jointly for user plane and for control plane.

19. The transmitting user equipment according to any preceding claim 14 to 18 comprising means for: receiving the at least one control message during or after an establishment of the user equipment-to-user equipment relay communication.

20. The transmitting user equipment according to any preceding claim 14 to 18 comprising means for: receiving the at least one control message during or after a setup of at least one relay channel over the communication link for the user equipment-to-user equipment relay communication.