WO2022194853A1

WO2022194853A1 - Technique for switching a relayed radio communication

Info

Publication number: WO2022194853A1
Application number: PCT/EP2022/056672
Authority: WO
Inventors: Antonio ORSINO; Min Wang; Zhang Zhang; Zhang FU
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2021-03-15
Filing date: 2022-03-15
Publication date: 2022-09-22

Abstract

A technique for switching a radio communication between a remote radio device (100-RM) and a radio access network, RAN (700) is provided. The radio communication is switched from a relayed radio communication being relayed through a relay radio device (100-RL) served by a network node (200) of the RAN (700) to a direct radio communication between the remote radio device (100-RM) and the RAN (700). As to a method aspect of the technique, a degradation of a radio link quality of a radio link between the remote radio device (100-RM) and the relay radio device (100-RL) for the relayed radio communication relayed through the relay radio device (100-RL) is determined. Responsive to the determined degradation of the radio link quality, a random access, RA, to the RAN (700) is performed for switching to the direct radio communication between the remote radio device (100-RM) and the RAN (700).

Description

Technique for switching a relayed radio communication

Technical Field

The present disclosure relates to a technique for switching a relayed radio communication. More specifically, and without limitation, methods and devices are provided for switching a radio device relayed through a relay radio device to a direct radio communication between a remote radio device and a radio access network.

Background

The Third Generation Partnership Project (3GPP) defined sidelinks (SLs) in Release 12 as an adaptation of the Long Term Evolution (LTE) radio access technology for direct communication between two radio devices, also referred to as user equipment (UE), without going through a network node of a radio access network (RAN). Such device-to-device (D2D) communications through SLs are also referred to as proximity service (ProSe). 3GPP has extended SLs in Release 13 for public safety, which allows interworking of different public safety groups across geographical regions and countries. 3GPP Release 14 extended SLs for vehicle-to-everything (V2X) communication.

A radio communication between a remote radio device and the RAN can be relayed through a relay radio device using a SL between the remote radio device and the relay radio device. When channel conditions of the remote radio device become bad, the SL can get lost. This is especially problematic when the network node serving the relay radio device does not provided with measurements reports from the remote radio or does not even know that the relay radio device is SL-connected to the remote radio device, which is the case when the radio communication is relayed on Layer 3. The network node cannot decide a target node such as a target cell or a target relay radio device similar to a normal handover.

When the SL as the serving relay connection is released, the remote radio device has to establish a new path towards a target cell. During this procedure, the remote radio device has to find a target cell and initiate a random access procedure to connect to the target cell. This conventional procedure causes a connectivity interruption due to the random access procedure, which may last for several second.

Summary

Accordingly, there is a need for a technique for switching a relayed radio communication, which reduces or eliminates a connectivity loss during the switch.

As to a first method aspect, a method of switching a radio communication between a remote radio device and a radio access network (RAN) from a relayed radio communication being relayed through a relay radio device to a direct radio communication between the remote radio device and the RAN is provided. The relay radio device may be served by a network node of the RAN. The method comprises or initiates a step of determining a degradation of a radio link quality of a radio link between the remote radio device and the relay radio device for the relayed radio communication relayed through the relay radio device. The method further comprises or initiates a step of performing a random access to the RAN for switching to the direct radio communication between the remote radio device and the RAN, responsive to the determined degradation of the radio link quality.

Alternatively or in addition, the first method aspect may relate to a method of path switching in a radio communication between a remote radio device and a radio access network (RAN). The radio communication is relayed through a relay radio device served by a network node of the RAN. The method comprises or initiates a step of determining a degradation of a radio link quality of a radio link between the remote radio device and the relay radio device for the radio communication relayed through the relay radio device. The method further comprises or initiates a step of performing a random access to the RAN, responsive to the determined degradation of the radio link quality, for the path switching to a direct radio communication between the remote radio device and the RAN.

The radio link between the remote radio device and the relay radio device for the relayed radio communication relayed through the relay radio device may be, or may be referred to as, a sidelink (SL). The first method aspect may be implemented alone or in combination with any one of the claims in the claim set, particularly the first method aspect or the first chain of claims.

The first method aspect may be performed by the remote radio device.

As to a second method aspect, a method of triggering a switching of a radio communication between a remote radio device and a radio access network (RAN) from a relayed radio communication being relayed through a relay radio device served by a network node of the RAN to a direct radio communication between the remote radio device and the RAN is provided.

The second method aspect may be implemented alone or in combination with any one of the claims in the claim set, particularly the second method aspect or the second chain of claims.

The second method aspect may be performed by the relay radio device.

The second method aspect may further comprise any feature and/or any step disclosed in the context of the first method aspect, or a feature and/or step corresponding thereto, e.g., a receiver counterpart to a transmitter feature or step.

As to a third method aspect, a method of triggering a switching of a radio communication between a remote radio device and a radio access network (RAN) from a relayed radio communication being relayed through a relay radio device served by a network node of the RAN to a direct radio communication between the remote radio device and the RAN is provided.

The third method aspect may be implemented alone or in combination with any one of the claims in the claim set, particularly the third method aspect or the third chain of claims.

The third method aspect may be performed by the network node.

The third method aspect may further comprise any feature and/or any step disclosed in the context of the first and/or second method aspect, or a feature and/or step corresponding thereto, e.g., a network counterpart to a radio device feature or step.

The technique may be applied in the context of 3GPP New Radio (NR). Unlike a SL according to 3GPP LTE, a SL according to 3GPP NR can provide a wide range of QoS levels. Therefore, at least some embodiments of the technique can ensure that the switching causes no interruption in the radio communication or an interruption short enough to comply with the QoS of the traffic (e.g., data or data packet or QoS flow) transmitted and/or received at the remote radio device in the radio communication.

The technique may be implemented in accordance with a 3GPP specification, e.g., for 3GPP release 16, 17 or 18. The technique may be implemented for 3GPP LTE or 3GPP NR according to (e.g., a modification of) at least one of 3GPP document TR 23.752, version 1.0.0; 3GPP document TR 38.836, version 1.1.0; 3GPP document TS 22.261, version 18.1.1; 3GPP document TS 23.237, version 16.4.0; 3GPP document TS 23.280, version 17.5.0; 3GPP document TS 23.287, version 16.5.0; 3GPP document TS 23.303, version 16.0.0; 3GPP document TS 23.401, version 16.9.0; 3GPP document TS 23.501, version 16.7.0; and 3GPP document TS 23.502, version 16.7.1. For example, the SL may be implemented using proximity services (ProSe), e.g. according to at least one of the above-identified 3GPP documents.

In any radio access technology (RAT), the technique may be implemented for reducing a connection interruption during path switch, e.g., in case of the relay radio device functioning as a Layer (L3) SL relay. The SL may be any device-to- device (D2D) radio link, e.g., for vehicular communication (V2X).

Alternatively or in addition, the technique may be implemented as a technique for performing a handover, a path switch, and/or a random access.

Any radio device may be a user equipment (UE), e.g., according to a 3GPP specification. The relay radio device may also be referred to as a relay UE (or briefly: relay). Alternatively or in addition, the remote radio device may also be referred to as a remote UE.

The relay radio device and the RAN may be wirelessly connected in an uplink (UL) and/or a downlink (DL) through a Uu interface. Alternatively or in addition, the SL may enable a direct radio communication between proximal radio devices, e.g., the remote radio device and the relay radio device, optionally using a PC5 interface. Services provided using the SL or the PC5 interface may be referred to as proximity services (ProSe). Any radio device (e.g., the remote radio device and/or the relay radio device and/or the further radio device) supporting a SL may be referred to as ProSe-enabled radio device.

The relay radio device may also be referred to as ProSe UE-to-Network Relay or briefly UE-to-Network Relay.

The remote radio device and/or the relay radio device and/or the RAN and/or the further remote radio device may form, or may be part of, a radio network, e.g., according to the Third Generation Partnership Project (3GPP) or according to the standard family IEEE 802.11 (Wi-Fi). The first method aspect, the second method aspect and third method aspect may be performed by one or more embodiments of the remote radio device, the relay radio device, and the RAN (e.g., the network node, optionally a base station), respectively.

The RAN may comprise one or more network nodes (e.g., base stations), e.g., performing the third method aspect. Alternatively or in addition, the radio network may be a vehicular, ad hoc and/or mesh network comprising two or more radio devices, e.g., acting as the remote radio device and/or the relay radio device and/or the further remote radio device.

Any of the radio devices may be a 3GPP user equipment (UE) or a Wi-Fi station (STA). The radio device may be a mobile or portable station, a device for machine- type communication (MTC), a device for narrowband Internet of Things (NB-loT) or a combination thereof. Examples for the UE and the mobile station include a mobile phone, a tablet computer and a self-driving vehicle. Examples for the portable station include a laptop computer and a television set. Examples for the MTC device or the NB-loT device include robots, sensors and/or actuators, e.g., in manufacturing, automotive communication and home automation. The MTC device or the NB-loT device may be implemented in a manufacturing plant, household appliances and consumer electronics.

Whenever referring to the RAN, the RAN may be implemented by one or more network nodes (e.g., base stations). The remote radio device may be wirelessly connected or connectable (e.g., according to a radio resource control, RRC, state or active mode) with the relay radio device and, optionally, at least one network node (e.g., base station) of the RAN. The relay radio device may be wirelessly connected or connectable (e.g., according to a radio resource control, RRC, state or active mode) with at least one network node of the RAN, comprising the network node serving the relay radio device. Furthermore, the relay radio device may be wirelessly connected or connectable (e.g., according to 3GPP ProSe) with the remote radio device.

The network node may encompass any station that is configured to provide radio access to any of the radio devices. The network node may be referred to, may function as, and/or may comprise at least one of a base station, a cell, a transmission and reception point (TRP), a radio access node, and an access point (AP). The network node and/or the relay radio device may provide a data link to a host computer providing user data to the remote radio device or gathering user data from the remote radio device in the radio communication.

Examples for the network node may include a 3G base station or Node B, 4G base station or eNodeB, a 5G base station or gNodeB, a Wi-Fi AP and a network controller (e.g., according to Bluetooth, ZigBee or Z-Wave).

The RAN may be implemented according to the Global System for Mobile Communications (GSM), the Universal Mobile Telecommunications System (UMTS), 3GPP Long Term Evolution (LTE) and/or 3GPP New Radio (NR).

Any aspect of the technique may be implemented on a Physical Layer (PHY), a Medium Access Control (MAC) layer, a Radio Link Control (RLC) layer, a packet data convergence protocol (PDCP) layer, and/or a Radio Resource Control (RRC) layer of a protocol stack for the radio communication.

Herein, referring to a protocol of a layer may also refer to the corresponding layer in the protocol stack. Vice versa, referring to a layer of the protocol stack may also refer to the corresponding protocol of the layer. Any protocol may be implemented by a corresponding method. As to another aspect, a computer program product is provided. The computer program product comprises program code portions for performing any one of the steps of the first, second and/or third method aspect disclosed herein when the computer program product is executed by one or more computing devices. The computer program product may be stored on a computer-readable recording medium. The computer program product may also be provided for download, e.g., via the radio network, the RAN, the Internet and/or the host computer. Alternatively, or in addition, the method may be encoded in a Field-Programmable Gate Array (FPGA) and/or an Application-Specific Integrated Circuit (ASIC), or the functionality may be provided for download by means of a hardware description language.

As to a first device aspect, a device for switching a radio communication between a remote radio device and a radio access network (RAN) from a relayed radio communication, which is relayed through a relay radio device served by a network node of the RAN, to a direct radio communication between the remote radio device and the RAN is provided. The device, e.g., the remote radio device, comprising memory operable to store instructions and processing circuitry operable to execute the instructions, such that the (e.g., remote radio) device is operable to perform the first method aspect.

As to a further first device aspect, a device for switching a radio communication between a remote radio device and a radio access network (RAN) from a relayed radio communication, which is relayed through a relay radio device served by a network node of the RAN, to a direct radio communication between the remote radio device and the RAN is provided. The device, e.g., the remote radio device, is configured to perform the first method aspect.

As to a second device aspect, a device for triggering a switching of a radio communication between a remote radio device and a radio access network (RAN) from a relayed radio communication, which is relayed through a relay radio device served by a network node of the RAN, to a direct radio communication between the remote radio device and the RAN is provided. The device, e.g., the relay radio device, comprising memory operable to store instructions and processing circuitry operable to execute the instructions, such that the (e.g., relay radio) device is operable to perform the second method aspect. As to a further second device aspect, a device for triggering a switching of a radio communication between a remote radio device and a radio access network (RAN) from a relayed radio communication, which is relayed through a relay radio device served by a network node of the RAN, to a direct radio communication between the remote radio device and the RAN is provided. The device, e.g., the relay radio device, is configured to perform the second method aspect.

As to a third device aspect, a device for triggering a switching of a radio communication between a remote radio device and a radio access network (RAN) from a relayed radio communication, which is relayed through a relay radio device served by a network node of the RAN, to a direct radio communication between the remote radio device and the RAN is provided. The device, e.g., network node, comprising memory operable to store instructions and processing circuitry operable to execute the instructions, such that the device (e.g., network node) is operable to perform the third method aspect.

As to a further third device aspect, a device for triggering a switching of a radio communication between a remote radio device and a radio access network (RAN) from a relayed radio communication, which is relayed through a relay radio device served by a network node of the RAN, to a direct radio communication between the remote radio device and the RAN is provided. The device, e.g., network node, is configured to perform the third method aspect.

As to a still further aspect a communication system including a host computer is provided. The host computer comprises a processing circuitry configured to provide user data, e.g., included in the first and/or second data of the multi-layer transmission. The host computer further comprises a communication interface configured to forward the first and/or second data to a cellular network (e.g., the RAN and/or the base station) for transmission to a UE. A processing circuitry of the cellular network is configured to execute any one of the steps of the first and/or second method aspects. The UE comprises a radio interface and processing circuitry, which is configured to execute any one of the steps of the first and/or second method aspects.

The communication system may further include the UE. Alternatively, or in addition, the cellular network may further include one or more base stations configured for radio communication with the UE and/or to provide a data link between the UE and the host computer using the first and/or second method aspects.

The processing circuitry of the host computer may be configured to execute a host application, thereby providing the first and/or second data and/or any host computer functionality described herein. Alternatively, or in addition, the processing circuitry of the UE may be configured to execute a client application associated with the host application.

Any one of the devices, the UE, the base station, the communication system or any node or station for embodying the technique may further include any feature disclosed in the context of the method aspect, and vice versa. Particularly, any one of the units and modules disclosed herein may be configured to perform or initiate one or more of the steps of the method aspect.

Brief Description of the Drawings

Further details of embodiments of the technique are described with reference to the enclosed drawings, wherein:

Fig. 1-RM shows a schematic block diagram of an embodiment of a device for switching a radio communication from a relayed radio communication to a direct radio communication;

Fig. 1-RL shows a schematic block diagram of an embodiment of a device for triggering a switching of a radio communication from a relayed radio communication to a direct radio communication;

Fig. 2 shows a schematic block diagram of an embodiment of a device for triggering a switching of a radio communication from a relayed radio communication to a direct radio communication;

Fig. 3-RM shows a flowchart for a method of switching a radio communication from a relayed radio communication to a direct radio communication, which method may be implementable by the device of Fig. 1-RM; Fig. 3-RL shows a flowchart for a method of triggering a switching of a radio communication from a relayed radio communication to a direct radio communication, which method may be implementable by the device of Fig. 1-RL;

Fig. 4 shows a flowchart for a method of triggering a switching of a radio communication from a relayed radio communication to a direct radio communication, which method may be implementable by the device of Fig. 2;

Fig. 5 schematically illustrates an example of a radio network comprising embodiments of the devices of Figs. 1-RM, 1-RL, and 2 for performing the methods of Figs. 3-RM, 3-RL, and 4, respectively;

Fig. 6 schematically illustrates a user plane stacks for a remote radio device, a Layer-2 relay radio device, and a network node embodying the devices of Figs. 1-RM, Fig. 1-RL, and Fig. 2, respectively;

Fig. 7 schematically illustrates a control plane stacks for a remote radio device, a Layer-2 relay radio device, and a network node embodying the devices of Figs. 1-RM, Fig. 1-RL, and Fig. 2, respectively;

Fig. 8 schematically illustrates a signaling diagram for establishing a relayed radio communication through the relay radio device, which may be used for performing the methods of Figs. 3-RM, 3-RL, and 4;

Fig. 9A schematically illustrates a signaling diagram of a reference example for switching from a relayed radio communication to a direct radio communication;

Fig. 9B schematically illustrates a signaling diagram of an embodiment for switching from a relayed radio communication to a direct radio communication, which may be used for performing the methods of Figs. 3-RM, 3-RL, and 4;

Fig. 10 schematically illustrates an architecture of a relayed radio communication using a remote radio device, a relay radio device, and a network node embodying the devices of Figs. 1-RM, Fig. 1-RL, and Fig. 2, respectively;

Fig. 11 schematically illustrates examples of protocol stacks for a Layer-3 remote radio device-to-network relay;

Fig. 12 schematically illustrates a signaling diagram for establishing a relayed radio communication through the relay radio device, which may be used for performing the methods of Figs. 3-RM, 3-RL, and 4;

Fig. 13 shows a schematic block diagram of a remote radio device embodying the device of Fig. 1-RM;

Fig. 14 shows a schematic block diagram of a relay radio device embodying the device of Fig. 1-RL;

Fig. 15 shows a schematic block diagram of a radio access network embodying the device of Fig. 2;

Fig. 16 schematically illustrates an example telecommunication network connected via an intermediate network to a host computer;

Fig. 17 shows a generalized block diagram of a host computer communicating via a base station or radio device functioning as a gateway with a user equipment over a partially wireless connection; and

Figs. 18 and 19 show flowcharts for methods implemented in a communication system including a host computer, a base station or radio device functioning as a gateway and a user equipment.

Detailed Description

In the following description, for purposes of explanation and not limitation, specific details are set forth, such as a specific network environment in order to provide a thorough understanding of the technique disclosed herein. It will be apparent to one skilled in the art that the technique may be practiced in other embodiments that depart from these specific details. Moreover, while the following embodiments are primarily described for a New Radio (NR) or 5G implementation, it is readily apparent that the technique described herein may also be implemented for any other radio communication technique, including a Wireless Local Area Network (WLAN) implementation according to the standard family IEEE 802.11, 3GPP LTE (e.g., LTE-Advanced or a related radio access technique such as MulteFire), for Bluetooth according to the Bluetooth Special Interest Group (SIG), particularly Bluetooth Low Energy, Bluetooth Mesh Networking and Bluetooth broadcasting, for Z-Wave according to the Z-Wave Alliance or for ZigBee based on IEEE 802.15.4.

Moreover, those skilled in the art will appreciate that the functions, steps, units and modules explained herein may be implemented using software functioning in conjunction with a programmed microprocessor, an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA), a Digital Signal Processor (DSP) or a general purpose computer, e.g., including an Advanced RISC Machine (ARM). It will also be appreciated that, while the following embodiments are primarily described in context with methods and devices, the invention may also be embodied in a computer program product as well as in a system comprising at least one computer processor and memory coupled to the at least one processor, wherein the memory is encoded with one or more programs that may perform the functions and steps or implement the units and modules disclosed herein.

Fig. 1-RM schematically illustrates a block diagram of an embodiment of a device for switching a radio communication between a remote radio device and a radio access network (RAN) from a relayed radio communication to a direct radio communication between the remote radio device and the RAN. The relayed radio communication is an indirect radio communication in that the relayed radio communication is relayed through a relay radio device served by a network node of the RAN. The device is generically referred to by reference sign 100-RM.

The device 100-RM comprises a Link Quality Determining Module 102-RM that determines a degradation of a radio link quality of a radio link between the remote radio device and the relay radio device for the relayed radio communication relayed through the relay radio device. The device 100-RM further comprises a Random Access Performing Module 104-RM that performs, responsive to the determined degradation of the radio link quality, a random access to the RAN for switching to the direct radio communication between the remote radio device and the RAN.

Any of the modules of the device 100-RM may be implemented by units configured to provide the corresponding functionality.

The device 100-RM may also be referred to as, or may be embodied by, the remote radio device (or briefly: remote UE). The remote radio device 100-RM and the relay radio device may be in direct radio communication, e.g., at least up until completion of the switching to the direct radio communication. The relay radio device may be embodied by the device 100-RL defined below. The network node may be embodied by the device 200 defined below.

Fig. 1-RL schematically illustrates a block diagram of an embodiment of a device for triggering a switching of a radio communication between a remote radio device and a radio access network (RAN) from a relayed radio communication to a direct radio communication between the remote radio device and the RAN. The relayed radio communication is an indirect radio communication in that the relayed radio communication is relayed through a relay radio device served by a network node of the RAN. The device is generically referred to by reference sign 100-RL.

The device 100-RL comprises a Link Quality Determining Module 102-RL that determines a degradation of a radio link quality of a radio link between the remote radio device and the relay radio device for the relayed radio communication relayed through the relay radio device. The device 100-RL further comprises a Random Access Triggering Module 104-RL that triggers, responsive to the determined degradation of the radio link quality, the remote radio device to perform a random access to the RAN for the switching to the direct radio communication between the remote radio device and the RAN.

Any of the modules of the device 100-RL may be implemented by units configured to provide the corresponding functionality.

The device 100-RL may also be referred to as, or may be embodied by, the relay radio device (or briefly: relay UE). The relay radio device 100-RL and the remote radio device may be in direct radio communication, e.g., at least up until completion of the switching to the direct radio communication. The remote radio device may be embodied by the device 100-RM defined herein. The network node may be embodied by the device 200 defined below.

Fig. 2 schematically illustrates a block diagram of an embodiment of a device for triggering a switching of a radio communication between a remote radio device and a radio access network (RAN) from a relayed radio communication to a direct radio communication between the remote radio device and the RAN. The relayed radio communication is an indirect radio communication in that the relayed radio communication is relayed through a relay radio device served by a network node of the RAN. The device is generically referred to by reference sign 200.

The device 200 comprises a Link Quality Determining Module 202 that determines a degradation of a radio link quality of a radio link between the remote radio device and the relay radio device for the relayed radio communication relayed through the relay radio device. The device 200 further comprises a Random Access Triggering Module 204 that triggers, responsive to the determined degradation of the radio link quality, the remote radio device to perform a random access to the RAN for the switching to the direct radio communication between the remote radio device and the RAN.

Any of the modules of the device 200 may be implemented by units configured to provide the corresponding functionality.

The device 200 may also be referred to as, or may be embodied by, the network node (e.g., an eNB or gNB). The network node 200 and the remote radio device may be in at least one of relayed and direct radio communication before, during and after switching from the relayed radio communication to the direct radio communication. The remote radio device may be embodied by the device 100-RM defined herein. The relay radio device 100-RL may be embodied by the device 100- RL defined herein.

Fig. 3-RM shows an example flowchart for a method 300-RM of switching a radio communication between a remote radio device and a RAN from a relayed radio communication being relayed through a relay radio device served by a network node of the RAN to a direct radio communication between the remote radio device and the RAN. In a step 302-RM, a degradation of a radio link quality of a radio link between the remote radio device and the relay radio device for the relayed radio communication relayed through the relay radio device is determined (e.g., measured). Responsive to the determined degradation of the radio link quality, a random access (RA) to the RAN is performed for switching to the direct radio communication between the remote radio device and the RAN (e.g., the network node) in a step 304-RM.

The method 300-RM may be performed by the device 100-RM. For example, the modules 102-RM and 104-RM may perform the steps 302-RM and 304-RM, respectively.

Fig. 3-RL shows an example flowchart for a method 300-RL of triggering a switching of a radio communication between a remote radio device and a RAN from a relayed radio communication being relayed through a relay radio device served by a network node of the RAN to a direct radio communication between the remote radio device and the RAN.

In a step 302-RL, a degradation of a radio link quality of a radio link between the remote radio device and the relay radio device for the relayed radio communication relayed through the relay radio device is determined (e.g., measured). Responsive to the determined degradation of the radio link quality, the remote radio device is triggered to perform a RA to the RAN for switching to the direct radio communication between the remote radio device and the RAN (e.g., the network node) in a step 304-RL.

The method 300-RL may be performed by the device 100-RL. For example, the modules 102-RL and 104-RL may perform the steps 302-RL and 304-RL, respectively.

Fig. 4 shows an example flowchart for a method 400 of triggering a switching of a radio communication between a remote radio device and a RAN from a relayed radio communication being relayed through a relay radio device served by a network node of the RAN to a direct radio communication between the remote radio device and the RAN. In a step 402, a degradation of a radio link quality of a radio link between the remote radio device and the relay radio device for the relayed radio communication relayed through the relay radio device is determined (e.g., reported by the relay radio device). Responsive to the determined degradation of the radio link quality, the remote radio device is triggered (e.g., by means of NAS signaling) to perform a RA to the RAN for switching to the direct radio communication between the remote radio device and the RAN (e.g., the network node) in a step 404.

The method 400 may be performed by the device 200. For example, the modules 202 and 204 may perform the steps 402 and 404, respectively.

In any aspect, the remote radio device may perform the random access in a pro active way. In other words, the remote radio device may perform the random access to the RAN when the radio link between the remote radio device and the relay radio device (e.g., the sidelink) and/or the relayed radio communication (i.e., an indirect path or relay path of the relayed radio communication through the relay radio device) is not failed yet and/or is going to fails soon. Thus, the remote radio device has still a way to communicate using the relayed radio communication (i.e., through the indirect path) when and/or while and/or after performing the random access.

The radio link between the remote radio device and the relay radio device may be a sidelink (SL) or may comprise one or more SLs. The radio link between the remote radio device and the relay radio device may be referred to as the radio link for the relayed radio communication.

The random access (RA) may also be referred to as a random access procedure or a random access channel (RACH) procedure.

Herein, a radio device, which is initially in the relayed radio communication with the RAN, may be referred to as the remote radio device also during the switching or after the switching, e.g., for a consistent and persistent designation.

Furthermore, the radio communication between the remote radio device and the RAN does not have to be terminated at the RAN. For example, the radio communication may extend to a user plane of a core network (CN) associated with the RAN and/or to an application server (AS), at least on one or more layers of a protocol stack used by the radio communication.

The switching may be referred to as path switching or a path switch, e.g., because the relayed radio communication and the direct radio communication may be associated with first and second (e.g., physical or logical) paths, respectively, for bearing the radio communication. The first and second paths may include and exclude the relay radio device, respectively. Alternatively or in addition, the switching may be referred to as a handover.

The relayed radio communication may also be referred to as an indirect radio communication (or briefly: indirect communication). The radio link between the remote radio device and the relay radio device may be a first segment of the relayed radio communication. A radio link between the relay radio device and network node may be a second segment of the relayed radio communication.

Alternatively or in addition, the relayed radio communication may comprise at least two segments that are (e.g., linearly) connected (i.e., relayed, e.g., forwarded) through the relay radio device. Any one of the segments may also be referred to and/or may function as a portion, a radio link, a hop, a leg, or a branch of the radio communication.

The path switching may comprise reducing the number of segments (i.e., portions or links) of the radio communication, for example a reduction by at least one segment and/or a reduction to one segment. Alternatively or in addition, the path switching may be referred to as a handover of the remote radio device (e.g., initiated by the remote radio device) or as a relay selection or relay reselection (e.g., performed by the remote radio device).

As a result of the random access, the radio communication between the remote radio device and the RAN may comprise the direct radio communication. The direct radio communication between the remote radio device and the RAN may comprise a direct or single radio link between the remote radio device and the RAN resulting from the random access. The direct radio communication may be without any relay radio device, e.g., without any radio node actively processing traffic of the radio communication. The direct radio communication may comprise a passive and/or coherent effect in a radio propagation for the direct radio communication, e.g., a reflection of electromagnetic waves of the radio link between the remote radio device and the RAN.

The relayed radio communication and/or the direct radio communication may be bidirectional between the remote radio device and the RAN.

The RAN may be implemented by the network node. For example, whenever referring to the RAN, the functionality of the RAN may be embodied by the network node of the RAN. Alternatively or in addition, the RAN may comprise one or more network nodes including the network node serving the relay radio device.

The degradation of the radio link quality may be determined per at least one of traffic using the relayed radio communication; service using the relayed radio communication; quality of service (QoS) type; and QoS flow.

The technique may be applied to a radio communication from remote radio device (e.g., initially relayed through the relay radio device) involving the RAN (e.g., the network node). Embodiments of the technique can reduce a delay caused by the random access, which occurs when switching to direct radio communication with the RAN (e.g., a direct UE-to-RAN link). Alternatively or in addition, the technique may be applied whenever the RAN (e.g., the network node) does not or cannot decide how to handle the switching (i.e., the mobility) of the remote radio device.

The random access may be performed (in the step 304-RM) to the network node 200 serving the relay radio device 100-RL or to another network node of the RAN.

The radio link quality may depend on, and/or may be indicative of, a channel condition of the radio link between the remote radio device and the relay radio device.

The random access to a network node may also be referred to as the random access towards the respective network node. The random access to a network node may encompass the random access towards a Uu interface of the respective network node.

The random access may be performed to a cell of the RAN. The step 304-RM of performing the random access may comprise selecting the cell of the RAN. Optionally, the cell serving the relay radio device 100-RL may be preferred over other cells of the RAN.

Alternatively or in addition, the random access may be performed to a network node of the RAN. The step of performing the random access may comprise selecting the network node of the RAN. The network node serving the relay radio device may be preferred (e.g., selected if available) over other network nodes of the RAN.

The radio link quality may comprise at least one of a reference signal received power (RSRP), a reference signal received quality (RSRQ), a signal to noise ratio (SNR), a signal to interference-and-noise ratio (SNIR), a block error rate (BLER), and a bit error rate (BER).

The radio link quality of the radio link may be measured at the remote radio device and/or at the relay radio device.

The degradation of the radio link quality may be determined if the radio link quality is less than a predefined threshold value for the radio link quality.

The step 304-RM of performing the random access to the RAN may be triggered if the radio link quality is less than the threshold value.

Different predefined threshold values for the radio link quality may be associated with at least one of different traffic, different services, different quality of service (QoS) types, and different QoS flows.

The random access may be performed if the radio link quality is less than the threshold value for at least one of the different traffic using the relayed radio communication, for at least one service using the relayed radio communication, for at least one QoS type, and/or for at least one QoS flow.

The predefined threshold value for the radio link quality may be greater or less than a threshold value of a link failure of the radio link between the remote radio device and the relay radio device. The threshold value may ensure that the random access is performed (e.g., completed) before the radio link between the remote radio device and the relay radio device fails. The random access may be performed 304-RM before the radio link between the remote radio device 100-RM and the relay radio device 100-RL is (e.g., has) failed.

The direct radio communication and the relayed radio communication may coexist after the random access.

The direct radio communication and the relayed radio communications may at least temporarily coexist.

The relayed radio communication may comprise measurement gaps for determining a radio link quality of a radio link of the direct radio communication during the coexistence of the direct radio communication and the relayed radio communication. Alternatively or in addition, the direct radio communication comprises measurement gaps for determining the radio link quality of the radio link between the remote radio device 100-RM and the relay radio device 100-RL during the coexistence of the direct radio communication and the relayed radio communication.

Herein, determining a radio link quality may comprise measuring a radio link quality. Alternatively or in addition, the remote radio device may determine the radio link quality. The measurement gaps may enable the remote radio device to determine the radio link quality.

The method 300-RM may further comprise or initiate a step of releasing the radio link between the relay radio device 100-RL and the network node 200 for the relayed radio communication after establishing the direct radio communication between the remote radio device 100-RM and the RAN.

The radio link between the relay radio device and the network node and/or the relayed radio communication may be released after (e.g., responsive to) completion of a radio resource control (RRC) connection setup.

The radio link for the relayed radio communication may be released by the remote radio device 100-RM. The release of the radio link for the relayed radio communication may depend on a comparison of the radio link quality of the radio link of the relayed radio communication and the radio link quality of the radio link of the direct radio communication.

The radio link between the relay radio device and the network node and/or the relayed radio communication may be released if the radio link quality of the radio link of the direct radio communication between the remote radio device and the RAN is greater than the radio link of the relayed radio communication between the remote radio device and the RAN through the relay radio device.

The method 300-RM may further comprise or initiate a step of starting a timer at the remote radio device 100-RM responsive to the determined degradation of the radio link quality or when starting the random access. The radio link for the relayed radio communication may be released upon expiry of the timer.

A duration of the timer (i.e., the time of expiry of the timer after starting the timer) may be equal to or greater than (e.g., equal to or greater than twice) an average time period for establishing the direct radio communication between the remote radio device and the RAN.

The method 300-RM may be performed by the remote radio device 100-RM.

The radio link between the remote radio device 100-RM and the relay radio device (100-RL) for the relayed radio communication may comprise a PC5 interface.

The random access to the RAN for the direct radio communication may use a Uu interface.

The random access performed responsive to the determined degradation of the radio link quality may use a configuration that is specific or dedicated for the switching from a relayed radio communication. The random access performed responsive to the determined degradation may be different from a random access (RA) performed by the remote radio device in other states of radio connectivity, e.g., during initial access. At least one of a random access procedure and a configuration parameter of the random access (RA) to the RAN performed 304-RM for the switching to the direct radio communication may be different from a random access (RA) performed by the remote radio device (100-RM) in the absence of the relayed radio communication and/or during initial access and/or when the remote radio device 100-RM operates as a radio device in direct radio communication with the RAN.

Herein, referring to alternatives A; B; and/or C as well as referring to at least one of A; B; and C encompasses the alternatives A; and/or B; and/or C, or combinations (i.e., subsets) thereof.

The random access may be trigger by a physical downlink control channel (PDCCH) order from the RAN or by a medium access control (MAC) layer of the remote radio device.

The random access to the RAN performed 304-RM for the switching to the direct radio communication may be a 2-step random access.

As opposed to the random access performed for the path switching in a relayed radio communication, a random access performed by the remote radio device in the absence of the relayed radio communication and/or during initial access and/or when the remote radio device operates as a radio device in direct radio communication with the RAN may be a 4-step random access.

At least one of the random access procedure and the configuration parameter of the random access to the RAN performed 304-RM for the switching to the direct radio communication may depend on the determined degradation of the radio link quality.

For example, if the radio link quality is rapidly decreasing, the random access procedure and/or the configuration parameter of the random access to the RAN may shorten the random access compared to a random access performed by the remote radio device in the absence of the relayed radio communication and/or during initial access and/or when the remote radio device operates as a radio device in direct radio communication with the RAN. For example, the remote radio device may indicate in the random access (e.g., in a RA preamble) that the random access is related to a relayed radio communication or a determined degradation of a SL for the relayed radio communication (e.g., a SL to a relay radio device serving the remote radio device) or that a cause of the random access is the relayed radio communication using layer 3 for the relaying (which may also be referred to as SL L3 relay mobility).

The radio link between the remote radio device 100-RM and the relay radio device 100-RL may be a sidelink (SL).

Herein, the SL may be a direct device-to-device (D2D) radio connection, e.g., using 3GPP ProSe.

The relayed radio connection may be relayed through the relay radio device 100- RL on a layer 3 and/or using Internet Protocol (IP) encapsulation or IP decapsulation towards a core network of the RAN.

The relaying on layer 3 (L3) may be implemented based on, or in extension of, clause 6.6 of the 3GPP document TR 23.752, version 1.0.0.

The step 302-RM of determining the degradation of a radio link quality comprises receiving a control message from the relay radio device 100-RL and/or from the network node 200 of the RAN, the control message being indicative of the degradation of a radio link quality of the radio link between the remote radio device 100-RM and the relay radio device 100-RL.

The method 300-RM may further comprise or initiate a step of receiving a configuration message from the relay radio device 100-RL and/or from the network node 200 of the RAN. The configuration message may be indicative of at least one of the random access procedure and the configuration parameter of the random access to the RAN performed 304-RM for the switching to the direct radio communication if the degradation of the radio link quality is determined 302-RM.

The configuration message may be indicative of using the 2-step RA as the RA procedure. Alternatively or in addition, the configuration message may be indicative of the predefined threshold value for the radio link quality. The degradation of the radio link quality may be determined if at least one of the following criteria is met.

As to a first criterion, the radio link between the remote radio device 100-RM and the relay radio device 100-RL may comprises a PC5 interface, and a radio link quality of the PC5 interface is less than the predefined threshold value of the radio link for the relayed radio communication.

As to a second criterion, the relayed radio communication may comprises a Uu interface between the relay radio device 100-RL and the RAN, and a radio link quality of the Uu interface is less than a predefined first threshold value of the radio link for the direct radio communication.

As to a third criterion, the direct radio communication may comprise a Uu interface between the remote radio device 100-RM and the RAN, and a radio link quality of the Uu interface is greater than a predefined second threshold value of the radio link for the direct radio communication. For example, the predefined second threshold value may be greater than the predefined first threshold value.

As to a fourth criterion, a radio link failure (RLF) is detected on the radio link between the remote radio device 100-RM and the relay radio device 100-RL and/or on the radio link between the relay radio device 100-RL and the RAN.

As to a fifth criterion, the radio communication serves a predefined type of service and/or bearers and/or QoS flows associated with a predefined QoS requirements.

As to a sixth criterion, a control message received from the relay radio device 100- RL is indicative of the switching.

As to a seventh criterion, a control message received from the RAN, optionally from the network node 200, is indicative of the switching.

As to an eighth criterion, a configuration message received from the relay radio device 100-RL is indicative of the RA configuration to be used when performing the switching or whether a RA configuration for switching from the relayed radio communication is to be used when performing the switching. As to a ninth criterion, a configuration message received from the RAN, optionally from the network node 200, is indicative of the RA configuration to be used when performing the switching or whether a RA configuration for switching from the relayed radio communication is to be used when performing the switching.

As to a tenth criterion, a predefined estimator evaluated for a time sequence of the radio link quality is indicative of a radio link failure within a predefined future time.

Alternatively or in addition, at least one of the criteria may be pre-configured (e.g., hard coded and/or defined in the technical specification).

A RA configuration used for the RA when switching from the relayed radio communication may be indicative of at least one of:

- whether the RA is a 2-step RA procedure or a 4-step RA procedure;

- whether the RA is contention-based or contention-free;

- a type of service to be delivered by the radio communication;

- a type of traffic to be delivered by the radio communication; and

- a QoS of the radio communication;

For contention-free RA, the RAN (e.g., the network node) may indicate dedicated RA preambles and/or RA occasions (ROs).

A RA preamble and/or a cause of the RA may be indicative of the switching from the relayed radio communication and/or the degradation of the radio link quality.

For example, the remote UE in the RACFI preamble may indicate that this RACH procedure is related to SL relay link degradation or that the cause if the RACH is SL L3 relay mobility.

The method 300-RM may further comprise or initiate a step of receiving, at the remote radio device 100-RM, from the RAN (optionally from the network node 200), at least one of a contention-free RA configuration, one or more RA preambles, and one or more RA occasions (ROs) that are to be used only for the RA for switching from the relayed radio communication. The radio link for the relayed radio communication may be released responsive to at least one of the following criteria.

According to a first criterion, a first uplink data packet is received by the RAN, optionally by the network node over the direct radio communication. Further optionally, the RAN or the network node 200 may transmit a release signaling to the remote radio device 100-RM.

According to a second criterion, a first downlink data packet is received at the remote radio device 100-RM over the direct radio communication.

According to a third criterion, a control message is received via the relayed radio communication. The control message may be indicative of releasing the radio link between the remote radio device 100-RM and the relay radio device 100-RL. Optionally, the remote radio device 100-RM may be identified by its layer 2 identifier.

A fourth criterion comprises reception of a control message indicative of completion of a radio resource control (RRC) setup and/or a RRC resume.

The method 300-RM may further comprise or initiate a step of receiving a control message that is indicative of at least one of:

- the at least one criteria for determining the degradation of the radio link quality;

- the at least one criteria for releasing the radio link for the relayed radio communication; and

- whether to use the timer.

In the second aspect, or accordingly in any other aspect, the method 300-RL may be performed by the relay radio device 100-RL.

The step 304-RL of triggering the remote radio device 100-RM may comprise transmitting a control message to the remote radio device 100-RL. The control message may be indicative of the degradation of a radio link quality of the radio link between the remote radio device 100-RM and the relay radio device 100-RL. The method 300-RL may further comprise or initiate a step of relaying, at the relay radio device 100-RL, the relayed radio connection between the remote radio device 100-RM and the RAN on a layer 3 and/or using Internet Protocol (IP) encapsulation or IP decapsulation towards a core network of the RAN.

The method 300-RL may further comprise the features or the steps of any one of the embodiments of the first aspect, or any feature or step corresponding thereto.

In the third aspect, or accordingly in any other aspect, the method may be performed by the RAN, optionally by the network node 200 serving the relay radio device 100-RL.

The step 404 of triggering the remote radio device 100-RM may comprise transmitting a control message to the remote radio device 100-RL. The control message may be indicative of the degradation of a radio link quality of the radio link between the remote radio device 100-RM and the relay radio device 100-RL.

The method 400 may further comprise or initiate a step of scheduling radio resources for the radio link between the remote radio device 100-RM and the relay radio device 100-RL for the relayed radio communication relayed through the relay radio device 100-RL.

The method 400 may further comprising the features or the steps of any one of the embodiments of the first or second aspect, or any feature or step corresponding thereto.

In any aspect, the relayed and the direct radio communication may comprise an uplink (UL) and/or a downlink (DL). The relayed radio communication may further comprise a SL as the radio link between remote and relay radio devices. The SL may comprise one or more direct communications between radio devices, i.e., device-to-device (D2D) communications.

Each of the relay radio device 100-RL, the remote radio device 100-RM, and the network node 200 may be a radio device and/or a network node (e.g., a base station). Herein, any radio device may be a mobile or portable station and/or any radio device wirelessly connectable to the network node (e.g., a base station) and/or the RAN, or to another radio device. A radio device may be a user equipment (UE), a device for machine-type communication (MTC) or a device for (e.g., narrowband) Internet of Things (loT). Two or more radio devices may be configured to wirelessly connect to each other, e.g., in an ad hoc radio network or via a 3GPP sidelink connection. Furthermore, any base station may be a station providing radio access, may be part of a radio access network (RAN) and/or may be a node connected to the RAN for controlling radio access. Further a base station may be an access point, for example a Wi-Fi access point.

The relay radio connection may comprise at least one sidelink (SL) between the relay radio device and the remote radio device. Embodiments of the technique are applicable to at least one of Public Safety, vehicular communication (i.e., vehicle to anything or V2X), 3GPP Long Term Evolution (LTE) or 4G, 3GPP New Radio (NR), device-to-device (D2D) communication and/or discovery for establishing the SL, a relayed radio communication on the relay radio connection, which may include one hop or multiple hops.

Any embodiment of the technique may use a SL (e.g., SL transmissions) for the relaying.

Herein, whenever referring to noise or a signal-to-noise ratio (SNR), a corresponding step, feature or effect is also disclosed for noise and/or interference or a signal-to-interference-and-noise ratio (SINR).

Fig. 5 shows an example deployment scenario for a relay radio connection in a radio network 700 comprising the RAN 720 and a core network (CN) 710. The RAN 720 comprises at least one embodiment of the network node 200. The network node serves at least the relay radio device 100-RL in one or more cells 201 of the network node 200. The CN 710 comprises a Core User Plane 712, e.g., a user plane function (UPF) in an NR employment or a serving gateway in an LTE employment.

The deployment scenario comprises a network node 200 of the RAN 720 with the cell 201. A relay radio device 100-RL is in the coverage area 201 of the network node 200. A remote radio device 100-RM is inside or outside of the coverage area 201 of the network node 200, and in proximity to the relay radio device 100-RL. By being in the proximity, the remote radio device 100-RM and the relay radio device 100-RL may be in a D2D communication using a SL as the radio link between the remote radio device 100-RM and the relay radio device 100-RL for the relayed radio communication.

The Third Generation Partnership Project (3GPP) has specified the SL (or SL transmissions) for the radio access technology (RAT) of Fifth Generation New Radio (5G NR, or briefly: NR) in Release 16. 3GPP Release 16 comprises enhancements of PROximity-based SErvices (ProSe, including device-to-device services) previously specified for the RAT of Fourth Generation Long Term Evolution (4G LTE, or briefly: LTE). Four new enhancements are particularly introduced to NR sidelink transmissions as follows:

• Support for unicast and groupcast transmissions are added in NR SL. For unicast and groupcast, the physical sidelink feedback channel (PSFCH) is introduced for a receiver radio device (e.g., a receiver UE) to reply the decoding status to a transmitter radio device (e.g., a transmitter UE).

• Grant-free transmissions (i.e., transmission by a UE using resources of a grant-free scheduling), which are adopted in NR uplink transmissions, are also provided in NR sidelink transmissions, to improve the latency performance. Grant-free scheduling is also referred to as Configured Grant (CG).

• To alleviate resource collisions among different SL transmissions launched by different radio devices (e.g., different UEs), it enhances channel sensing and resource selection procedures, which also lead to a new design of PSCCH.

• To achieve a high connection density, congestion control and thus the quality of service (QoS) management is supported in NR SL transmissions.

To enable the above enhancements, physical channels and reference signals are introduced in NR, at least some of which are also available in LTE:

PSSCH (Physical Sidelink Shared Channel, SL version of PDSCH): The PSSCH is transmitted by a SL transmitter radio device (e.g., SL transmitter UE), which conveys SL transmission data, system information blocks (SIBs) for radio resource control (RRC) configuration, and a part of the sidelink control information (SCI).

• PSFCH (Physical Sidelink, SL version of PUCCH): The PSFCH is transmitted by a SL receiver radio device (e.g., a SL receiver UE) for unicast and groupcast, which conveys 1 bit information over 1 RB for the HARQ acknowledgement (ACK) and the negative ACK (NACK). In addition, channel state information (CSI) is carried in the medium access control (MAC) control element (CE) over the PSSCH instead of the PSFCH.

• PSCCH (Physical Sidelink Common Control Channel, SL version of PDCCH): When the traffic to be sent to a receiver radio device (e.g., a receiver UE) arrives at a transmitter radio device (e.g., a transmitter UE), a transmitter radio device (e.g., transmitter UE) should first send the PSCCH, which conveys a part of SCI (Sidelink Control information, SL version of DCI) to be decoded by any radio device (e.g., UE) for the channel sensing purpose, including the reserved time-frequency resources for transmissions, demodulation reference signal (DMRS) pattern and antenna port, etc.

• Sidelink Primary/Secondary Synchronization Signal (S-PSS/S-SSS): Similar DL transmissions in NR, in SL transmissions, primary and secondary synchronization signals (called S-PSS and S-SSS, respectively) are supported. Through detecting the S-PSS and S-SSS, a radio device (e.g., a UE) is able to identify the SL synchronization identity (SSID) from the radio device (e.g.,

UE) sending the S-PSS/S-SSS. Through detecting the S-PSS/S-SSS, a radio device (e.g., UE) is therefore able to know the characteristics of the radio device (e.g., UE) transmitting the S-PSS/S-SSS. A series of processes of acquiring timing and frequency synchronization together with SSIDs of radio devices (e.g., UEs) is called initial cell search. Note that the radio device (e.g., UE) sending the S-PSS/S-SSS may not be necessarily involved in SL transmissions, and a node (e.g., a UE and/or eNB and/or gNB) sending the S- PSS/S-SSS is called a synchronization source. There are 2 S-PSS sequences and 336 S-SSS sequences forming a total of 672 SSIDs in a cell.

• Physical Sidelink Broadcast Channel (PSBCH): The PSBCH is transmitted along with the S-PSS/S-SSS as a synchronization signal/PSBCH block (SSB). The SSB has the same numerology as PSCCH/PSSCH on that carrier, and an SSB should be transmitted within the bandwidth of the configured BWP. The PSBCH conveys information related to synchronization, such as the direct frame number (DFN), indication of the slot and symbol level time resources for sidelink transmissions, in-coverage indicator, etc. The SSB is transmitted periodically at every 160 ms.

• DMRS, phase tracking reference signal (PT-RS), channel state information reference signal (CSI-RS): These physical reference signals supported by NR DL/UL transmissions are also adopted by SL transmissions. Similarly, the PT- RS is only applicable for FR2 transmission.

Another feature introduced in 3GPP Release 16 is the two-stage SL control information (SCI). This a version of the DCI for SL. Unlike the DCI, only part (first stage) of the SCI is sent on the PSCCH. This part is used for channel sensing purposes (including the reserved time-frequency resources for transmissions, demodulation reference signal (DMRS) pattern and antenna port, etc.) and can be read by all radio devices (e.g., UEs) while the remaining (second stage) scheduling and control information such as a 8-bits source identity (ID) and a 16-bits destination ID, NDI, RV and HARQ. process ID is sent on the PSSCH to be decoded by the receiver radio device (e.g., UE).

Similar as for PRoSE in LTE, NR SL transmissions have the following two modes of resource allocations:

• Mode 1: SL resources are scheduled by a network node (e.g., gNB).

• Mode 2: The radio device (e.g., UE) autonomously selects SL resources from a configured or preconfigured SL resource pool(s) based on the channel sensing mechanism.

For the in-coverage radio device (e.g., UE), a network node (e.g., gNB) can be configured to adopt Mode 1 or Mode 2. For the out-of-coverage radio device (e.g., UE), only Mode 2 can be adopted.

As in LTE, scheduling over the SL in NR is done in different ways for Mode 1 and Mode 2. In Mode 1, the network node 200 may use at least one of the following two scheduling mechanisms (also referred to as grants) for granting radio resources to the remote radio device 100-RM and/or the relay radio device 100-RL.

A first scheduling mechanism is dynamic scheduling (also referred to as dynamic grant). When the traffic to be sent over SL arrives at a transmitter LIE, this UE should perform or initiate a four-message exchange procedure to request SL resources from a gNB (SR on UL, grant, BSR on UL, grant for data on SL sent to UE). During the resource request procedure, a gNB may allocate a SL radio network temporary identifier (SL-RNTI) to the transmitter UE. If this SL resource request is granted by a gNB, then a gNB indicates the resource allocation for the PSCCH and the PSSCH in the downlink control information (DCI) conveyed by PDCCH with a cyclic redundancy check (CRC) scrambled with the SL-RNTI. When a transmitter UE receives such a DCI, a transmitter UE can obtain the grant only if the scrambled CRC of DCI can be successfully solved by the assigned SL-RNTI. A transmitter UE then indicates the time-frequency resources and the transmission scheme of the allocated PSSCH in the PSCCH, and initiates (e.g., transmits on) the PSCCH and the PSSCH on the allocated resources for SL transmissions. When a grant is obtained from a gNB, a transmitter UE can only transmit a single TB. As a result, this kind of grant is suitable for traffic with a loose latency requirement.

A second scheduling mechanism is configured grant. For the traffic with a strict latency requirement, performing the four-message exchange procedure to request SL resources may induce unacceptable latency. In this case, prior to the traffic arrival, a transmitter UE may perform the four-message exchange procedure and request a set of resources. If a grant can be obtained from a gNB, then the requested resources are reserved in a periodic manner. Upon traffic arriving at a transmitter UE, this UE can initiate (e.g., transmit on) the PSCCH and the PSSCH on the upcoming resource occasion. This kind of grant may be referred to as grant-free, or a transmission using this kind of grant may be referred to as a grant-free transmission.

In both dynamic grant and configured grant, a SL receiver UE cannot receive the DCI (since it is addressed to the transmitter UE), and therefore a receiver UE should perform blind decoding to identify the presence of PSCCH and find the resources for the PSSCH through the SCI. When a transmitter UE initiates (e.g., transmits on) the PSCCH, a CRC is also inserted in the SCI without any scrambling.

In the Mode 2 resource allocation, when traffic arrives at a transmitter UE, this transmitter UE should autonomously select resources for the PSCCH and the PSSCH. To further minimize the latency of the feedback HARQ ACK/NACK transmissions and subsequently retransmissions, a transmitter UE may also reserve resources for PSCCH/PSSCH for retransmissions. To further enhance the probability of successful transport block (TB) decoding at one shot and thus suppress the probability to perform retransmissions, a transmitter UE may repeat the TB transmission along with the initial TB transmission. This mechanism is also known as blind retransmission. As a result, when traffic arrives at a transmitter UE, then this transmitter UE should select resources for the following transmissions: (1) The PSSCH associated with the PSCCH for initial transmission and blind retransmissions. (2) The PSSCH associated with the PSCCH for retransmissions.

Since each transmitter UE in SL transmissions should autonomously select resources for above transmissions, how to prevent different transmitter UEs from selecting the same resources turns out to be a critical issue in Mode 2. A particular resource selection procedure is therefore imposed to Mode 2 based on channel sensing. The channel sensing algorithm involves measuring RSRP on different subchannels and requires knowledge of the different UEs power levels of DMRS on the PSSCH or the DMRS on the PSCCH depending on the configuration. This information is known only after receiver SCI transmitted by (e.g., all) other UEs. The sensing and selection algorithm may be rather complex.

The relayed radio communication may be established by a D2D discovery procedure (i.e., SL discovery procedure) between the remote radio device 100- RM and the relay radio device 100-RL.

There are D2D discovery procedures for detection of services and applications offered by other UEs in close proximity. This is part of LTE Release 12 and Release 13. The discovery procedure has two modes, mode A based on open announcements (broadcasts) and mode B, which is request/response. The discovery mechanism is controlled by the application layer (ProSe). The discovery message is sent on the Physical Sidelink Discovery Channel (PSDCH) which is not available in NR. Also, there is a specific resource pool for announcement and monitoring of discovery messages. The discovery procedure can be used to detect UEs supporting certain services or applications before initiating direct communication.

Any embodiment of any aspect may use Layer 2-based (i.e., L2-based) UE-to- Network relaying (briefly referred to as L2 relaying) for the relayed radio communication. The 3GPP document TR 23.752, version 1.0.0, clause 6.7, describes an example for implementing the L2 relaying, which may relate to a study on system enhancement for Proximity based Services (ProSe) in the 5G System (5GS), e.g., for 3GPP release 17.

The relay UE 100-RL may comprise a protocol stack (e.g., a protocol architecture) supporting a L2 UE-to-Network Relay UE, which may be referred to as L2 UE-to- Network Relay UE or L2 relay radio device (or briefly: L2 relay). The L2 relay 100- RL may comprise forwarding (i.e., relaying) functionality that is configured to relay (e.g., any type of) traffic over the SL 150 (e.g., the PC5 link) to the remote UE 100-RM.

The L2 relay UE 100-RL provides the functionality to support connectivity to a Fifth Generation System (5GS) for Remote UEs. A UE is considered to be a remote UE 100-RM if it has successfully established the SL 150 (e.g., the PC5 link) to the L2 relay UE 100-RL. A remote UE 100-RM can be located within NG-RAN coverage 201 or outside of NG-RAN coverage 201.

Fig. 6 schematically illustrates the protocol stack for the user plane (UP) transport (e.g., for the relay data), related to a PDU Session, including a Layer 2 UE-to- Network Relay UE 100-RL. The PDU layer in the protocol stack 110-RM of the remote UE 100-RM and in the protocol stack 714 of the UPF 712 corresponds to the PDU carried between the remote UE 100-RM and a Data Network (e.g., connected through the interface 850 to the UPF 712) over the PDU session. It is important to note that the two endpoints of the PDCP link are the remote UE 100-RM and the gNB 200. The relay function is performed below the PDCP. This means that data security is ensured between the Remote UE and the gNB without exposing raw data at the UE-to-Network Relay UE 100-RL. Alternatively or in addition, the User Plane Stack for L2 UE-to-Network Relay UE 100 may be implemented according to the 3GPP document TR 23.752, version 1.0.0, e.g., as illustrated in Figure A.2.1-1 therein.

The adaptation relay layer within the UE-to-Network Relay UE 100-RL can differentiate between signaling radio bearers (SRBs) and data radio bearers (DRBs) for a particular remote UE 100-RL. The adaption relay layer is also responsible for mapping the relay data in the PC5 link 150 to one or more DRBs of the Uu link 250.

Fig. 7 schematically illustrates the protocol stacks 110-RM at the remote UE 100- RM and the Access and Mobility Management Function (AMF) 716 for a non- access stratum (NAS) connection for the remote UE 100-RM to the NAS-MM and NAS-SM components. The NAS messages are transparently transferred between the remote UE 100-RM and 5G Access Network (5G-AN) 720 over the Layer 2 UE- to-Network Relay UE 100-RL using:

- PDCP end-to-end connection, wherein a role of the UE-to-Network Relay UE 100-RL is to relay the PDUs over the signaling radio bear without any modifications; and/or

- an N2 connection between the 5G-AN 720 and AMF 726 over the interface N2; and/or

- an N3 connection AMF 716 and SMF over an interface Nil.

The role of the UE-to-Network Relay UE 100-RL is to relay the PDUs from the signaling radio bearer without any modifications.

Alternatively or in addition, the control plane (CP) for the L2 UE-to-Network Relay UE 100-RL may be implemented according to the 3GPP document TR 23.752, version 1.0.0, e.g., as illustrated in Figure A.2.2-1 therein.

Any embodiment of any aspect may implement at least one step of the following procedure for establishing the relayed radio communication, which is also referred to as an indirect radio communication. At least one of the following steps may be implemented as schematically illustrated in Fig. 8. Fig. 8 schematically illustrates a Connection Establishment for Indirect Communication via UE-to-Network Relay UE. Alternatively, the steps may be implemented in accordance with Figure 6.7.3-1 of the 3GPP document TR 23.752, version 1.0.0. 0. If in coverage, the Remote UE 100-RM and UE-to-Network Relay UE 100-RL may independently perform the initial registration to the network 700 according to registration procedures in the 3GPP document TS 23.502, version 16.7.1. The allocated 5G Global Unique Temporary Identifier (GUTI) of the Remote UE 100-RM is maintained when later non-access stratum (NAS) signaling between the Remote UE 100-RM and the Network 700 (e.g., the CN 710) is exchanged via the UE-to-Network Relay UE 100-RL.

The procedure illustrated in Fig. 8 assumes a single hop relay for clarity and not limitation of the technique.

1. If in coverage 201, the Remote UE 100-RM and the UE-to-Network Relay UE 100-RL independently get the service authorization for indirect communication from the network 700.

2-3. The Remote UE 100-RM and the UE-to-Network Relay UE 100-RL perform UE-to-Network Relay UE discovery and selection.

4. The Remote UE 100-RM initiates a one-to-one communication connection with the selected UE-to-Network Relay UE 100-RL over PC5 150, by transmitting an indirect communication request message to the UE-to- Network Relay 100-RL.

5. If the UE-to-Network Relay UE 100-RL is in CMJDLE state, triggered by the communication request received from the Remote UE 100-RM, the UE-to- Network Relay UE 100-RL transmits a Service Request message over PC5 to its serving AMF.

The Relay's AMF may perform authentication of the UE-to-Network Relay UE based on NAS message validation and if needed the AMF will check the subscription data.

If the UE-to-Network Relay UE is already in CM_CONNECTED state and is authorized to perform Relay service then step 5 is omitted. 6. The UE-to-Network Relay UE 100-RL transmits the indirect communication response message to the Remote UE 100-RM.

7. Remote UE 100-RM sends a NAS message to the serving AMF. The NAS message is encapsulated in an RRC message that is sent over PC5 to the UE- to-Network Relay UE, and the UE-to-Network Relay UE 100-RL forwards the message to the NG-RAN 200. The NG-RAN 200 derives Remote UE's serving AMF and forwards the NAS message to this AMF.

For clarity and not limitation, it may be assumed that the Remote UE's PLMN is accessible by the UE-to-Network Relay's PLMN and that UE-to-Network Relay UE's AMF supports all S-NSSAIs the Remote UE may want to connect to.

If the Remote UE 100-RM has not performed the initial registration to the network in step 0, the NAS message is initial registration message. Otherwise, the NAS message is service request message.

If the Remote UE 100-RM performs initial registration via the UE-to-Network relay, the Remote UE's serving AMF may perform authentication of the Remote UE based on NAS message validation and if needed the Remote UE's AMF checks the subscription data.

For service request case, User Plane connection for PDU Sessions can also be activated. The other steps may follow the clause 4.2.3.2 in the 3GPP document TS 23.502, version 16.7.1, which may relate to procedures for the 5G System (5GS).

8. The Remote UE 100-RM may trigger the PDU Session Establishment procedure as defined in clause 4.3.2.2 of the 3GPP document TS 23.502, version 16.7.1.

9. The data is transmitted between the Remote UE 100-RM and the UPF 712 via UE-to-Network Relay UE 100-RL and NG-RAN 200. The UE-to-Network Relay UE 100-RL forwards all the data messages between the Remote UE 100-RM and NG-RAN 200 using a RAN-specified L2 relay method. The technique may be implemented for service continuity as the radio communication used by a service is switched from the relayed radio communication to the direct radio communication.

As described in clause 4.5.4 of the 3GPP document TR 38.836, version 1.1.0, which may relate to a study on NR sidelink relay for 3GPP release 17, a UE-to-Network Relay 100-RL performing L2 relaying (also referred to as an L2 relay UE 100-RL or L2 relay 100-RL) uses the RAN2 principle of the handover procedure (e.g., according to 3GPP release 15) as a baseline for an Application Server (AS) layer to guarantee service continuity.

Conventionally, the gNB hands over the remote UE to a target cell or target relay UE, including (1) performing procedure between the gNB and the relay UE (if needed) of the type of a handover preparation, (2) transmitting a message "RRCReconfiguration" to remote UE, remote UE switching to the target, and (3) Handover complete message, similar to the legacy procedure.

Fig. 9A schematically illustrates a reference example for a procedure of switching a remote UE to a direct radio communication (i.e., a direct Uu cell). The common parts of intra-gNB cases and inter-gNB cases are captured. For the inter-gNB cases, compared to the intra-gNB cases, potential different parts on RAN2 Uu interface in details are studied by 3GPP in a study item phase or in a work item phase.

Alternatively, Figure 4.5.4-1 of the 3GPP document TR 38.836, version 1.1.0, provides a reference example for the switching.

In contrast, Fig. 9B schematically illustrates the switching from the relayed radio communication (i.e., an indirect path) to the direct radio communication (i.e., a direct path) according to an embodiment of the method 300-RM.

For service continuity of the radio communication relayed through an L2 UE-to- Network relay 100-RL, conventional procedure of Fig. 9A may serve as a baseline procedure, in case of the remote UE 100-RM switches to the direct radio communication (e.g., a direct Uu cell).

In step 0, the relayed radio communication between the remote UE 100-RM and the network node 200 through the relay UE 100-RL is used for UL and/or DL data. In the conventional procedure, step 1 comprises a measurement configuration and reporting of the measurement. Step 2 comprises a decision of switching to a direct cell by the gNB. Step 3 comprises transmitting an RRC Reconfiguration message to the remote UE.

In contrast, in an embodiment of the method 300-RL, the degradation of the radio link quality is determined by the remote UE 100-RM according to the step 302-RM. The network node 200 does not have to be involved.

In step 4 of Fig. 9B, the Remote UE 100-RM performs Random Access to the gNB 200 according to the step 304-RM.

In step 5, the Remote UE 100 may transmit a message

"RRCReconfigurationComplete" to the gNB 100 via the target path, i.e. using the direct radio communication and/or using the target configuration provided in the RRC Reconfiguration message.

In step 6, an RRC Reconfiguration is transmitted from the gNB 200 to the relay UE 100-RL. In step 7, the SL (e.g., the PC5 link) is released between the remote UE 100-RM and the relay UE 100-RL, if needed.

In step 8, the data path is switched. The order of step 6, 7, and 8 is not restricted. For example, the Remote UE may suspend data transmission via relay link after step 3, or step 6 can be before or after step 3 (or may be omitted), or step 7 can be after step 3 or step 5 (or may be omitted or replaced by a PC5 reconfiguration), or step 8 can be after step 5.

Alternatively or in addition, any embodiments of any aspect may use Layer 3 (L3)- based UE-to-Network relaying (briefly referred to as L3 relaying). The 3GPP document TR 23.752, version 1.0.0, clause 6.6, describes an example for implementing the L3 relaying.

For example, a ProSe 5G UE-to-Network Relay entity may provide the functionality to support connectivity to the network node 200 for the remote UEs 100-RM, which is schematically illustrated in Fig. 10. It can be used for both public safety services and commercial services (e.g. interactive service). The relay UE 100-RL may also be referred to as a ProSe UE-to-Network relay. A UE is considered to be a remote UE 100-RM for a certain ProSe UE-to-Network relay 100-RL if it has successfully established a SL 150 (e.g., a PC5 link) to this ProSe 5G UE-to-Network Relay 100-RL. A remote UE 100-RM can be located within NG-RAN coverage 201 or outside of NG-RAN coverage 201.

The Remote UE 100-RM may perform communication path selection between the direct radio communication (e.g., a direct Uu path) and the relayed radio communication (e.g., an indirect Uu path) based on the link quality and/or the configured threshold (pre-configured or provided by NG-RAN 200). For example, if Uu link quality exceeds configured threshold, the direct Uu path is selected. Otherwise, the indirect Uu path is selected by performing the UE-to-Network Relay discovery and selection.

Fig. 10, or alternatively Figure 6.6.1-1 in the 3GPP document TR 23.752, version 1.0.0, schematically illustrates an architecture model using a ProSe 5G UE- to-Network Relay for the relaying at the relay UE 100-RL.

The DL data may be provided by the CN 710 through an interface between the CN 710 and the RAN 720. An Application Server (AS) 800, e.g., the host computer, may be a data source for the relay data provided to the CN (e.g., to the UPF 712) though an interface 850.

The ProSe 5G UE-to-Network Relay 100-RL relays unicast traffic (e.g., UL and DL data) between the Remote UE 100-RM and the network 700 (e.g., the gNB 200). The ProSe UE-to-Network Relay 100-RL may provide a generic function that can relay any IP, Ethernet or Unstructured traffic. For IP traffic over PC5 reference point 150, the ProSe UE-to-Network Relay 100-RL may use IP type PDU Session towards 5GC. For Ethernet traffic over PC5 reference point 150, the ProSe UE-to- Network Relay 100-RL may use Ethernet type PDU Session or IP type PDU Session towards 5GC. For Unstructured traffic over PC5 reference point 150, the ProSe UE-to-Network Relay 100-RL may use Unstructured type PDU Session or IP type PDU Session (i.e. IP encapsulation/de-capsulation by UE-to-Network Relay) towards 5GC 710. The type of traffic supported over PC5 reference point is indicated by the ProSe UE-to-Network Relay e.g. using the corresponding Relay Service Code. The UE-to- Network Relay determines the PDU Session Type based on, e.g. ProSe policy/parameters, URSP rule, Relay Service Code, etc.

How the UE-to-NW relay 100-RL determines PDU session type may be implemented independently from the subject technique, e.g., considering other PDU session parameters, e.g. DNN, SSC mode.

IP type PDU Session and Ethernet type PDU Session can be used to support more than one Remote UEs 100-RM, while Unstructured type PDU Session can be used to support only one Remote UE 100-RM.

A maximum number of PDU Sessions can affect the maximum number of Remote UEs 100-RM that the UE-to-Network Relay 100-RL can support.

One-to-one Direct Communication is used between Remote UEs and ProSe 5G UE-to-Network Relays for unicast traffic as specified in solutions for Key Issue #2 in the 3GPP document TR 23.752, version 1.0.0.

An example for a protocol stack 110-RL for the Layer-3 UE-to-Network Relay at the relay UE 100-RL is shown in Fig. 11. The remote UE 100-RM and the network node 200 comprise associated protocol stacks 110-RM and 210, respectively. Alternatively or in addition, protocol stacks for Layer-3 UE-to-Network Relays may be implemented according to 3GPP document TR 23.752, version 1.0.0, e.g., as illustrated in Figure 6.6.1-2 therein.

Hop-by-hop security is supported in the SL 150 (e.g., the PC5 link) and radio link 250 between relay UE 100-RL and network node 200 (e.g., the Uu link). If there are requirements beyond hop-by-hop security for protection of the relay data, security over IP layer may be applied. Further security details (e.g., as to integrity and privacy protection for the relay radio connection, which may also be referred to as a remote UE-NW communication) may be specified by SA WG3 at 3GPP.

According to the definition of service continuity in the 3GPP document TS 22.261, version 18.1.1 (which may relate to service requirements for the 5GS), and the 3GPP document TS 23.501, version 16.7.0 (which may relate to a system architecture for the 5GS), it can be seen that "service continuity" is different from "session continuity" by definition, and service continuity can be achieved at application layer regardless of IP address preservation: For Mission Critical Service in Public Safety, service continuity can be achieved by the application layer mechanism, e.g. as described in Annex B in the 3GPP document TS 23.280, version 17.5.0. For commercial IMS use cases, service continuity can be achieved using mechanisms described in the 3GPP document TS 23.237, version 16.4.0. For commercial use cases with application layer out of 3GPP scope (e.g. non IMS), service continuity can be achieved using similar way, e.g. QUIC.

It is noted that all of the above application layer mechanisms can be reused for Layer-3 UE-to-Network Relay, optionally without enhancements.

Any embodiment of any aspect may implement at least one of the following steps, e.g., for establishing the relayed radio communication.

The relay radio UE 100-RL may be capable to function as a ProSe 5G UE-to- Network Relay. The relay radio UE 100-RL may register to the network 700 (if not already registered) and establish a PDU session enabling the necessary relay traffic, or it may need to connect to one or more additional PDU sessions or modify the existing PDU session in order to provide relay traffic towards the one or more Remote UEs 100-RM. Preferably, the PDU session supporting the UE-to- Network Relay 100-RL is only be used for relaying traffic of the Remote UE 100- RM.

Fig. 12 schematically illustrates a signaling diagram for establishing a relayed radio communication through the relay radio UE 100-RL, which may be used by embodiments of any of the methods 300-RM, 300-RL, and/or 400. Alternatively or in addition, the relayed radio communication may be established according to Figure 6.6.2-1 on ProSe 5G UE-to-Network Relay in the 3GPP document TR 23.752, version 1.0.0.

0. During the Registration procedure, Authorization and provisioning is performed for the ProSe UE-to-NW relay (0a) and Remote UE (0b).

1. The ProSe 5G UE-to-Network Relay may establish a PDU session for relaying with default PDU session parameters received in step 0 or pre-configured in the UE-to-NW relay, e.g. S-NSSAI, DNN, SSC mode or PDU Session Type. In case of IP PDU Session Type and IPv6, the ProSe UE-to- Network Relay obtains the IPv6 prefix via prefix delegation function from the network as defined in the 3GPP document TS 23.501, version 16.7.0. Based on the Authorization and provisioning in step 0, the Remote UE performs discovery of a ProSe 5G UE-to-Network Relay. As part of the discovery procedure the Remote UE learns about the connectivity service the ProSe UE-to-Network Relay provides. The Remote UE selects a ProSe 5G UE-to-Network Relay and establishes a connection for One-to-one ProSe Direct Communication as described in the 3GPP document TS 23.287, version 16.5.0, which may relate to architecture enhancements for 5G System (5GS) to support Vehicle-to-Everything (V2X) services.

If there is no PDU session satisfying the requirements of the PC5 connection with the remote UE, e.g. S-NSSAI, DNN, QoS, the ProSe 5G UE-to-Network Relay initiates a new PDU session establishment or modification procedure for relaying.

According to the PDU Session Type for relaying, the ProSe 5G UE-to-Network Relay performs relaying function at the corresponding layer, e.g. acts as an IP router when the traffic type is IP, acts as an Ethernet switch when the traffic type is Ethernet, and performs generic forwarding for Unstructured traffic.

When the ProSe 5G UE-to-Network Relay uses Unstructured PDU session type for Unstructured traffic over PC5 reference point, it creates a mapping between the PC5 Link Identifier and the PDU Session ID, and a mapping between PFI for PC5 L2 link and the QFI for the PDU Session.

When the ProSe 5G UE-to-Network Relay uses IP PDU session type for Ethernet or Unstructured traffic over PC5 reference point, it locally assigns an IP address/prefix for the Remote UE and use that to encapsulate the data from the Remote UE. For downlink traffic, the ProSe 5G UE-to-Network Relay decapsulates the traffic from the IP headers and forwards to the corresponding Remote UE via PC5 reference point. The ProSe 5G UE-to-Network Relay's subscription, and if applicable the Remote UE's subscription, can be considered for QoS decision. If the ProSe 5G UE-to-Network Relay reports Remote UE's SUCI to the network, as described in sol#47 step 3, 5, 7, Relay UE's AMF gets Remote UE's SUPI from Remote UE's AUSF. Then Relay UE's AMF retrieves Remote UE's subscribed UE-AMBR from Remote UE's UDM using Remote UE's SUPI. Relay UE's AMF could also provide Remote UE's SUPI together with N1 SM container (PDU Session Establishment Request) to Relay UE's SMF, then Relay UE's SMF retrieves Remote UE's subscribed QoS profile and Subscribed Session-AMBR from Remote UE's UDM. Relay UE's AMF and SMF then provides Remote UE's subscription to PCF for QoS decision.

The UE-to-Network Relay distinguishes and performs the rate limitation for the traffic of a specific Remote UE, if the configuration from PCF supports to do that.

4. For IP PDU Session Type and IP traffic over PC5 reference point, IPv6 prefix or IPv4 address is allocated for the remote UE as it is defined in the

3GPP document TS 23.303, version 16.0.0, clauses 5.4.4.2 and 5.4.4.3. From this point the uplink and downlink relaying can start. For downlink traffic forwarding, the PC5 QoS Rule is used to map the downlink IP packet to the PC5 QoS Flow. For uplink traffic forwarding, the 5G QoS Rule is used to map the uplink IP packet to the Uu QoS Flow.

General functionality for IPv6 prefix delegation as defined in the 3GPP document TS 23.401, version 16.9.0, clause 5.3.1.2.6 needs to be added in 5GS and reference to the 3GPP document TS 23.501, version 16.7.0, can be added above.

5. The ProSe 5G UE-to-Network Relay sends a Remote UE Report (Remote User ID, Remote UE info) message to the SMF for the PDU session associated with the relay. The Remote User ID is an identity of the Remote UE user (provided via User Info) that was successfully connected in step 3. The Remote UE info is used to assist identifying the Remote UE in the 5GC. For IP PDU Session Type, the Remote UE info is Remote UE IP info. For Ethernet PDU Session Type, the Remote UE info is Remote UE MAC address which is detected by the UE-to-Network Relay. For Unstructured PDU Session Type, the Remote UE info contains the PDU session ID. The SMF stores the Remote User IDs and the related Remote UE info (if available) in the ProSe 5G UE-to-Network Relay's SM context for this PDU session associated with the relay.

For IP info the following principles apply:

- for IPv4, the UE-to-network Relay shall report TCP/UDP port ranges assigned to individual Remote UE(s) (along with the Remote User ID);

- for IPv6, the UE-to-network Relay shall report IPv6 prefix(es) assigned to individual Remote UE(s) (along with the Remote User ID).

The Remote UE Report message shall be sent when the Remote UE disconnects from the ProSe 5G UE-to-Network Relay (e.g. upon explicit layer-2 link release or based on the absence of keep alive messages over PC5) to inform the SMF that the Remote UE(s) have left.

In the case of Registration Update procedure involving SMF change the Remote User IDs and related Remote UE info corresponding to the connected Remote UEs are transferred to the new SMF as part of SM context transfer for the ProSe 5G UE-to-Network Relay.

In order for the SMF to have the Remote UE(s) information, a Home Public Land Mobile Network (HPLMN) and the Visited Public Land Mobile Network (VPLMN), in which the ProSe 5G UE-to-Network Relay 100-RL is authorized to operate, may support the transfer of the Remote UE related parameters in case the SMF is in the HPLMN.

When the Remote UE 100-RM disconnects from the ProSe UE-to-Network Relay 100-RL, it is up to implementation how relaying PDU sessions are cleared and/or disconnected by the ProSe 5G UE-to-Network Relay 100-RL.

After being connected to the ProSe 5G UE-to-Network Relay, the Remote UE keeps performing the measurement of the signal strength of PC5 unicast link with the ProSe 5G UE-to-Network Relay for relay reselection.

The technique may be implemented when the ProSe 5G UE-to-Network Relay UE 100-RL connects in EPS 700 using LTE. In this case, for the Remote UE 100-RM report, the procedures defined in the 3GPP document TS 23.303, version 16.0.0, which may relate to proximity-based services (ProSe), can be used.

At least some embodiments of any aspect may use an L3 relay 100-RL, e.g., according to what has been studied in the SL relay study item at 3GPP and/or what has been included in the 3GPP document TR 23.752, version 1.0.0, and the 3GPP document TR 38.836, version 1.1.0, in case a remote UE 100-RM connects to a gNB 200 via a L3 relay UE 100-RL.

For example, the remote UE 100-RM may be invisible to the gNB 200. In other words, the gNB 200 is not aware of the presence of the remote UE 100-RM and does not store any UE context referred to the remote UE 100-RM.

When the channel conditions of the remote UE 100-RM become bad (i.e., the radio link quality is determined to degrade so that the serving PC5 link quality drops below a configured threshold, the remote UE 100-RM may initiate a relay selection and/or reselection, which eventually leads to a path switch. In this case, since the gNB does not get measurements reports from the remote UE and does not even know that the relay UE is connected to a remote UE, the gNB 200 cannot decide the target node (i.e., a target cell or a target relay UE) as in a normal handover case. The remote UE 100-RM will follow a UE triggered procedure to perform the path switch, i.e., the serving relay connection is released and a new path should be established towards a target cell or a target relay UE. During the procedure, the remote UE 100-RM performs a RACH procedure if the remote UE selects a target cell to connect preemptively, so that a connectivity interruption is shortened or does not occur due to the RACH procedure, which may last for several second.

Therefore, the technique may be advantageously implemented to avoid or reduce as much as possible the connectivity loss during a path switch or handover in case of L3 relay.

Any embodiment of any aspect may implement at least one of the following options.

According to a first option, the Remote UE 100-RM may apply a special configuration of the random access (RA, e.g., using RACH) in the step 304-RM. The RA (e.g., the RA procedure and/or RA parameters of the RA) may be linked (or not) to the SL (e.g., PC5 link) targeting service continuity. In a first variant, the step 304-RM may be triggered according to a configured threshold for the radio link quality. For example, the Remote UE 100-RM triggers the RA (e.g., using the RACH) towards a cell (e.g., a Uu target cell) before the SL (e.g., the PC5 link) goes too bad (e.g., before the SL fails). In a second variant, which may be combined with the first variant, the Remote UE 100-RM keeps the old connection while connecting to the new connection. This may imply that measurement gaps and/or transmission gap are needed when keeping both connections (i.e., the relayed and the direct radio communication) active at the same time.

According to a second option, the Remote UE 100-RM may apply a 2-step RA towards the RAN (e.g., the network node 200, the cell and/or the Uu interface 250). In a first variant, a trigger event and/or trigger condition (e.g., PC5 link quality degradation as the determined degradation of the radio link quality) is defined for the 2-step RA. In a second variant (combinable with the first variant), this trigger and/or event could be set per traffic, service, or QoS type. In a third variant (combinable with the first and second variants), an indication to use the 2-step RA may be indicated into the relay configuration or by the gNB 200.

The embodiments are described in the context of NR, i.e., the remote UE 100-RM and the relay UE 100-RL are deployed in a same or different NR cell 201. The embodiments are also applicable to other relay scenarios including UE to network relay or UE to UE relay where the remote UE and the relay UE may be based on LTE sidelink or NR sidelink, the Uu connection between the relay UE and the base station may be LTE Uu or NR Uu.

In the below embodiments, it is assumed that a remote UE 100-RM is connected to a gNB 200 via a relay UE 100-RL based on L3 relay mechanism (i.e., using L3 relaying).

The description of embodiments uses terms "direct radio communication",

"direct radio link", "direct connection", "direct path", or "Uu connection" to stand for a connection between a (e.g., formerly remote) radio device (e.g., UE) and a network node (e.g., a gNB), while we use terms "relayed radio communication", "indirect radio communication", "indirect connection", or "indirect path" to stand for a connection between a remote radio device (e.g., a UE) and the network node (e.g., a gNB) via a relay radio device (e.g., a relay UE). In addition, the term "path switch" may be used when the remote radio device changes between a direct path (i.e., Uu connection) and an indirect path (i.e., relay connection via a SL relay UE). Other terms such as "relay selection/reselection" are equally applicable for the path switch without loss of meaning.

For conciseness and not limitation, below embodiments focus on a scenario, in which the remote UE 100-RM switches from the relayed radio communication (i.e., an indirect path) to the direct radio communication (i.e., a direct path, e.g., a cell of the RAN 720). In a variant of any of the embodiments, the remote UE 100-RM switches from an indirect path to another indirect path (e.g., another relay UE).

Features of the following ten detailed embodiments may be combinable with embodiments described above and/or any of the claims in the claim set.

In a first detailed embodiment, a remote UE 100-RM connects to a gNB 200 via an active L3 relay path, i.e., using a relay UE 100-RL function as L3 relay. According to types of services, traffic or applications which are being relayed from the remote UE to the gNB via the relay UE, the remote UE 100-RM selects a (e.g., pre-) configured threshold (e.g., in terms of RSRP) for radio channel quality measurement on the serving PC5 link, wherein the threshold may be service type/QoS requirement dependent. When the measured radio channel quality is below the threshold, the remote UE decides to perform a path switch (e.g., a target cell or a target relay UE). In order to select a target node (e.g., a target cell or a target relay UE), the remote UE may also perform measurements on neighbor PC5 links and/or Uu links. The measurements on neighbor PC5 and/or Uu links may be performed ahead or after the path switch has been triggered. While connecting to a selected target cell, the remote UE may maintain the current serving PC5 path.

In a second detailed embodiment, while connecting to a selected target cell, the remote UE maintains the current serving path (i.e., current indirect path), meaning that the remote UE still keeps transmissions and/or receptions from the relay UE while connecting to the target cell. In a third detailed embodiment, when the remote UE selects a target cell, the remote UE may prioritize the serving cell of the relay UE over other neighbor cells. In case the remote UE has select the serving cell of the relay UE as the target cell.

In a fourth detailed embodiment, when deciding to perform a path switch to a direct path, the remote UE uses a special RACH configuration to establish a new connection towards the gNB. This new RACH configuration can be a separate RACH configuration for the case of path switch from a SL relay path (e.g., an L3 relayed radio communication) or can be an existing RACH configuration with parameters specific for the case of path switch from the SL relay path (e.g., the L3 relayed radio communication). The special RACH configuration may be adapted to achieve a fast random access (e.g., a fast RACH access) to the target cell for the remote UE 100-RM during the path switch from the relayed radio communication (e.g., from the L3 relay path).

In a fifth detailed embodiment, when the remote UE 100-RM triggers the path switch from the relayed radio communication (e.g., an indirect path) to the direct radio communication (e.g., a direct path), the new or existing sidelink (e.g., L3) relay specific RACH configuration may be used when one, or more, of the following criteria are met:

- The (e.g., serving) PC5 link quality goes below a threshold.

- The (e.g., neighbor) Uu link quality goes below a threshold (while the quality is not bad and the UE could connect over the Uu link).

- In case RLF is detected on the PC5 and/or Uu hop of the relay path.

- Specific types of service are running, or bearers/flows associated with specific QoS requirements are active.

- Upon indication from the Relay UE indicating a path switch.

- Upon indication from the gNB indicating a path switch.

- Upon indication from the Relay UE explicitly indicating which RACH configuration to use or whether L3 relay specific RACH configuration should be used when performing path switch.

- Upon indication from the gNB explicitly indicating which RACH configuration to use or whether L3 relay specific RACH configuration should be used when performing path switch.

Is pre-configured (hard coded in the specification) when to use the new or existing sidelink relay specific RACH configuration. According to any one of the above criteria, the remote UE 100-RM triggers a path switch from the current serving indirect path to a direct path. In typical cases, the remote UE 100-RM uses this specific RA configuration (e.g., a RACH configuration) to connect to the same serving cell as the relay UE 100-RL In other cases, the remote UE 100-RM uses this specific RACH configuration to connect to a different cell from the serving cell of the relay UE. For the former case, the remote UE may obtain the specific RACH configuration and/or the criteria for using the specific RACH configuration from SIBs relayed by the relay UE. For the latter case, the remote UE obtains the specific RACH configuration and/or the criteria for using the specific RACH configuration via reading SIBs from the other cell.

The remote UE 100-RM may prioritize switching to the one or more cells which provide L3 relay specific RACH configuration and/or the configuration may be used according to the (e.g., pre-) configured criteria.

In the sixth embodiment, the sidelink L3 relay specific RACH configuration may comprise one or more of the following fields:

* A field indicating the RA is 2-step or 4-step.

* A field indicating the RA is contention-based or contention-free. For the latter case, dedicated PRACH preambles and/or RACH occasions (ROs) may be also configured.

* A field indicating specific RACH configuration parameters comprising at least one of the following (e.g., as specified in clause 5.1.1 of 3GPP document TS 38.321, version 16.3.0): prach-Configurationlndex;

- msgA-PRACH-Configurationlndex;

- preambleReceivedTargetPower;

- msgA-PreambleReceivedTargetPower;

- rsrp-ThresholdSSB ;

- rsrp-ThresholdCSI-RS;

- msgA-RSRP-ThresholdSSB;

- rsrp-ThresholdSSB-SUL;

- msgA-RSRP-Threshold;

- msgA-TransMax;

- candidateBeamRSList; recoverySearchSpoceld;

- powerRompingStep;

- msgA-PreamblePowerRampingStep;

- powerRompingStepHighPriority;

- scalingFactorBI;

- ra-Preamblelndex;

- ra-ssb-OccasionMasklndex;

- msgA-SSB-SharedRO-Masklndex;

- ra-OccasionList;

- ra-PreambleStart!ndex;

- preambleTransMax;

- ssb-perRACH-OccasionAndCB-PreamblesPerSSB;

- msgA-CB-PreamblesPerSSB-PerSharedRO;

- msgA-SSB-PerRACH-OccasionAndCB-PreamblesPerSSB;

- msgA-PUSCH-ResourceGroupA;

- msgA-PUSCH-ResourceGroupB;

- msgA-PUSCH-Resource-lndex;

- ra-Msg3SizeGroupA;

- msg3-DeltaPreamble;

- messogePowerOffsetGroupB ;

- numberOfRA-PreamblesGroupA.

- msgA-DeltaPreamble;

- messogePowerOffsetGroupB;

- numberOfRA-PreamblesGroupA;

- ra-MsgA-SizeGroupA.

- ra-ResponseWindow;

- ra-ContentionResolutionTimer;

- msgB-ResponseWindow A field indicating a type of service to be delivered.

* A field indicating a type of traffic to be delivered.

* A field indicating a QoS.

In a seventh detailed embodiment, the new (or existing) sidelink L3 relay specific RACH configuration can be a 4-step RACH configuration or a 2-step RACH configuration. Further, the 4-step RACH configuration can be for contention- based RACH or contention-free RACH. Whether the remote UE should use the 4- step or 2-step RACH when performing the RACH procedure can be decided according to the one (or more) or the following criteria:

- PC5 link goes below threshold A (where threshold A is for using 4-step RACH) or PC5 link goes below threshold B (where threshold B is for 2-step RACH). Obviously, threshold A and threshold B are different.

Uu link goes below threshold A^' (where threshold A^' is for using 4-step RACH) or PC5 link goes below threshold B^' (where threshold B^' is for 2-step RACH). Obviously, threshold A^’ and threshold B^' are different.

- A certain service/traffic type is served

- A certain QoS needs to be guaranteed.

- Based on the buffer status of the remote UE (if the UE has also data to transmit in the queue, the 2-step RACH can be used since the data can be multiplexed with the msgA).

In an eighth detailed embodiment, the remote UE triggers the path switch, and thus use the sidelink relay specific RACH configuration in a pro-active way. This basically means that the remote UE will start to send the RACH preamble because the sidelink relay connection gets bad (thus will soon not possible to receive or transmit data). In this case, the remote UE may be (pre)configured with a threshold in order to quantify how early (with respect to the possible RLF) the RACH procedure should be started.

In a ninth detailed embodiment, if the remote UE triggers the RACH in a pro active way (e.g., before the sidelink relay connection is failed), the remote UE keep the sidelink relay path active until the RACH procedure towards the gNB is completed and a new direct connection has been established. The sidelink relay path can be released when one of the following criteria are fulfilled:

- The first data downlink or uplink packet is received by the gNB over the direct path, in which case the gNB sends an indirect path release signaling to the remote UE.

- The first data downlink packet is received by the remote UE over the direct path

- An indication via the indirect path is received to release the sidelink relay path, wherein the remote UE is identified by its L2 ID. The indication may be sent by the serving gNB of the relay and then relayed by the relay UE or sent by the relay UE. - An indication via the new direct path is received to release the sidelink relay path. During path switching the remote UE may inform the new serving gNB that it is switched from a (L3) relay path and the old relay path is still active.

- An indication (e.g. end marker) via the old path from the Core Network (e.g. from SMF or UPF). This can be achieved if the remote UE informs the Core Network that it is switching from the relay UE PDU session to its own PDU session, then the SMF or UPF can send an end marker via the old path. When the remote UE receives the end marker from the old path, it indicates that there will be no packets from the old path anymore, so that the old path can be released.

- Upon the reception of the RRCSetupComplete or RRCResumeComplete message or any other RRC message that indicates that the direct RRC connection has been correctly established.

- The link quality of the new direct path becomes better than a (pre)configured threshold.

- Upon the expiry of a timer that is started when the RACH procedure is started.

In a tenth detailed embodiment, which option described in the previous embodiments the remote UE should use is decided by the gNB and communicated to the UE via dedicated RRC signaling (via the Relay UE) of via system information. As an alternative, which option the remote UE should use is pre-configured or decided by the relay UE.

Fig. 13 shows a schematic block diagram for an embodiment of the device 100-RM. The device 100-RM comprises processing circuitry, e.g., one or more processors 1304 for performing the method 300-RM and memory 1306 coupled to the processors 1304. For example, the memory 1306 may be encoded with instructions that implement at least one of the modules 102-RM and 104-RM.

The one or more processors 1304 may be a combination of one or more of a microprocessor, controller, microcontroller, central processing unit, digital signal processor, application specific integrated circuit, field programmable gate array, or any other suitable computing device, resource, or combination of hardware, microcode and/or encoded logic operable to provide, either alone or in conjunction with other components of the device 100-RM, such as the memory 1306, remote radio device functionality. For example, the one or more processors 1304 may execute instructions stored in the memory 1306. Such functionality may include providing various features and steps discussed herein, including any of the benefits disclosed herein. The expression "the device being operative to perform an action" may denote the device 100 being configured to perform the action.

As schematically illustrated in Fig. 13, the device 100-RM may be embodied by a remote radio device 1300, e.g., functioning as a remote UE. The remote radio device 1300 comprises a radio interface 1302 coupled to the device 100-RM for radio communication with one or more relay radio devices, e.g., functioning as a relay UE.

Fig. 14 shows a schematic block diagram for an embodiment of the device 100-RL. The device 100-RL comprises processing circuitry, e.g., one or more processors 1404 for performing the method 300-RL and memory 1406 coupled to the processors 1404. For example, the memory 1406 may be encoded with instructions that implement at least one of the modules 102-RL and 104-RL.

The one or more processors 1404 may be a combination of one or more of a microprocessor, controller, microcontroller, central processing unit, digital signal processor, application specific integrated circuit, field programmable gate array, or any other suitable computing device, resource, or combination of hardware, microcode and/or encoded logic operable to provide, either alone or in conjunction with other components of the device 100-RL, such as the memory 1406, relay radio device functionality. For example, the one or more processors 1404 may execute instructions stored in the memory 1406. Such functionality may include providing various features and steps discussed herein, including any of the benefits disclosed herein. The expression "the device being operative to perform an action" may denote the device 100-RL being configured to perform the action.

As schematically illustrated in Fig. 14, the device 100-RL may be embodied by a relay radio device 1400, e.g., functioning as a relay UE. The relay radio device 1400 comprises a radio interface 1402 coupled to the device 100-RL for radio communication with one or more remote radio devices and network nodes, e.g., functioning as a remote UE and base station. Fig. 15 shows a schematic block diagram for an embodiment of the device 200. The device 200 comprises processing circuitry, e.g., one or more processors 1504 for performing the method 400 and memory 1506 coupled to the processors 1504.

For example, the memory 1506 may be encoded with instructions that implement at least one of the modules 202 and 204.

The one or more processors 1504 may be a combination of one or more of a microprocessor, controller, microcontroller, central processing unit, digital signal processor, application specific integrated circuit, field programmable gate array, or any other suitable computing device, resource, or combination of hardware, microcode and/or encoded logic operable to provide, either alone or in conjunction with other components of the device 200, such as the memory 1506, network node functionality. For example, the one or more processors 1504 may execute instructions stored in the memory 1506. Such functionality may include providing various features and steps discussed herein, including any of the benefits disclosed herein. The expression "the device being operative to perform an action" may denote the device 200 being configured to perform the action.

As schematically illustrated in Fig. 15, the device 200 may be embodied by a network node 1500, e.g., functioning as a base station of the RAN. The network node 1500 comprises a radio interface 1502 coupled to the device 200 for radio communication with one or more relay radio devices and remote radio device, e.g., functioning as a relay UE and remote UE.

With reference to Fig. 16, in accordance with an embodiment, a communication system 1600 includes a telecommunication network 1610, such as a 3GPP-type cellular network, which comprises an access network 1611, such as a radio access network, and a core network 1614. The access network 1611 comprises a plurality of base stations 1612a, 1612b, 1612c, such as NBs, eNBs, gNBs or other types of wireless access points, each defining a corresponding coverage area 1613a, 1613b, 1613c. Each base station 1612a, 1612b, 1612c is connectable to the core network 1614 over a wired or wireless connection 1615. A first user equipment (UE) 1691 located in coverage area 1613c is configured to wirelessly connect to, or be paged by, the corresponding base station 1612c. A second UE 1692 in coverage area 1613a is wirelessly connectable to the corresponding base station 1612a. While a plurality of UEs 1691, 1692 are illustrated in this example, the disclosed embodiments are equally applicable to a situation where a sole UE is in the coverage area or where a sole UE is connecting to the corresponding base station 1612.

Any of the base stations 1612 and the UEs 1691, 1692 may embody the device 100.

The telecommunication network 1610 is itself connected to a host computer 1630, which may be embodied in the hardware and/or software of a standalone server, a cloud-implemented server, a distributed server or as processing resources in a server farm. The host computer 1630 may be under the ownership or control of a service provider, or may be operated by the service provider or on behalf of the service provider. The connections 1621, 1622 between the telecommunication network 1610 and the host computer 1630 may extend directly from the core network 1614 to the host computer 1630 or may go via an optional intermediate network 1620. The intermediate network 1620 may be one of, or a combination of more than one of, a public, private or hosted network; the intermediate network 1620, if any, may be a backbone network or the Internet; in particular, the intermediate network 1620 may comprise two or more sub-networks (not shown).

The communication system 1600 of Fig. 16 as a whole enables connectivity between one of the connected UEs 1691, 1692 and the host computer 1630. The connectivity may be described as an over-the-top (OTT) connection 1650. The host computer 1630 and the connected UEs 1691, 1692 are configured to communicate data and/or signaling via the OTT connection 1650, using the access network 1611, the core network 1614, any intermediate network 1620 and possible further infrastructure (not shown) as intermediaries. The OTT connection 1650 may be transparent in the sense that the participating communication devices through which the OTT connection 1650 passes are unaware of routing of uplink and downlink communications. For example, a base station 1612 need not be informed about the past routing of an incoming downlink communication with data originating from a host computer 1630 to be forwarded (e.g., handed over) to a connected UE 1691. Similarly, the base station 1612 need not be aware of the future routing of an outgoing uplink communication originating from the UE 1691 towards the host computer 1630.

By virtue of the method 300-RM and 300-RL being performed by any one of the UEs 1691 or 1692 and/or the method 400 being performed by any one of the base stations 1612, the performance or range of the OTT connection 1650 can be improved, e.g., in terms of increased throughput and/or reduced latency. More specifically, the host computer 1630 may indicate to the RAN 720 or the relay radio device 100-RL or the remote radio device 100-RM (e.g., on an application layer) the QoS of the traffic, which may trigger or configure the switching.

Example implementations, in accordance with an embodiment of the UE, base station and host computer discussed in the preceding paragraphs, will now be described with reference to Fig. 17. In a communication system 1700, a host computer 1710 comprises hardware 1715 including a communication interface 1716 configured to set up and maintain a wired or wireless connection with an interface of a different communication device of the communication system 1700. The host computer 1710 further comprises processing circuitry 1718, which may have storage and/or processing capabilities. In particular, the processing circuitry 1718 may comprise one or more programmable processors, application-specific integrated circuits, field programmable gate arrays or combinations of these (not shown) adapted to execute instructions. The host computer 1710 further comprises software 1711, which is stored in or accessible by the host computer 1710 and executable by the processing circuitry 1718. The software 1711 includes a host application 1712. The host application 1712 may be operable to provide a service to a remote user, such as a UE 1730 connecting via an OTT connection 1750 terminating at the UE 1730 and the host computer 1710. In providing the service to the remote user, the host application 1712 may provide user data, which is transmitted using the OTT connection 1750. The user data may depend on the location of the UE 1730. The user data may comprise auxiliary information or precision advertisements (also: ads) delivered to the UE 1730. The location may be reported by the UE 1730 to the host computer, e.g., using the OTT connection 1750, and/or by the base station 1720, e.g., using a connection 1760.

The communication system 1700 further includes a base station 1720 provided in a telecommunication system and comprising hardware 1725 enabling it to communicate with the host computer 1710 and with the UE 1730. The hardware 1725 may include a communication interface 1726 for setting up and maintaining a wired or wireless connection with an interface of a different communication device of the communication system 1700, as well as a radio interface 1727 for setting up and maintaining at least a wireless connection 1770 with a UE 1730 located in a coverage area (not shown in Fig. 17) served by the base station 1720. The communication interface 1726 may be configured to facilitate a connection 1760 to the host computer 1710. The connection 1760 may be direct, or it may pass through a core network (not shown in Fig. 17) of the telecommunication system and/or through one or more intermediate networks outside the telecommunication system. In the embodiment shown, the hardware 1725 of the base station 1720 further includes processing circuitry 1728, which may comprise one or more programmable processors, application-specific integrated circuits, field programmable gate arrays or combinations of these (not shown) adapted to execute instructions. The base station 1720 further has software 1721 stored internally or accessible via an external connection.

The communication system 1700 further includes the UE 1730 already referred to. Its hardware 1735 may include a radio interface 1737 configured to set up and maintain a wireless connection 1770 with a base station serving a coverage area in which the UE 1730 is currently located. The hardware 1735 of the UE 1730 further includes processing circuitry 1738, which may comprise one or more programmable processors, application-specific integrated circuits, field programmable gate arrays or combinations of these (not shown) adapted to execute instructions. The UE 1730 further comprises software 1731, which is stored in or accessible by the UE 1730 and executable by the processing circuitry 1738. The software 1731 includes a client application 1732. The client application 1732 may be operable to provide a service to a human or non-human user via the UE 1730, with the support of the host computer 1710. In the host computer 1710, an executing host application 1712 may communicate with the executing client application 1732 via the OTT connection 1750 terminating at the UE 1730 and the host computer 1710. In providing the service to the user, the client application 1732 may receive request data from the host application 1712 and provide user data in response to the request data. The OTT connection 1750 may transfer both the request data and the user data. The client application 1732 may interact with the user to generate the user data that it provides.

It is noted that the host computer 1710, base station 1720 and UE 1730 illustrated in Fig. 17 may be identical to the host computer 1630, one of the base stations 1612a, 1612b, 1612c and one of the UEs 1691, 1692 of Fig. 16, respectively. This is to say, the inner workings of these entities may be as shown in Fig. 17, and, independently, the surrounding network topology may be that of Fig. 16. In Fig. 17, the OTT connection 1750 has been drawn abstractly to illustrate the communication between the host computer 1710 and the UE 1730 via the base station 1720, without explicit reference to any intermediary devices and the precise routing of messages via these devices. Network infrastructure may determine the routing, which it may be configured to hide from the UE 1730 or from the service provider operating the host computer 1710, or both. While the OTT connection 1750 is active, the network infrastructure may further take decisions by which it dynamically changes the routing (e.g., on the basis of load balancing consideration or reconfiguration of the network).

The wireless connection 1770 between the UE 1730 and the base station 1720 is in accordance with the teachings of the embodiments described throughout this disclosure. One or more of the various embodiments improve the performance of OTT services provided to the UE 1730 using the OTT connection 1750, in which the wireless connection 1770 forms the last segment. More precisely, the teachings of these embodiments may reduce the latency and improve the data rate and thereby provide benefits such as better responsiveness and improved QoS.

A measurement procedure may be provided for the purpose of monitoring data rate, latency, QoS and other factors on which the one or more embodiments improve. There may further be an optional network functionality for reconfiguring the OTT connection 1750 between the host computer 1710 and UE 1730, in response to variations in the measurement results. The measurement procedure and/or the network functionality for reconfiguring the OTT connection 1750 may be implemented in the software 1711 of the host computer 1710 or in the software 1731 of the UE 1730, or both. In embodiments, sensors (not shown) may be deployed in or in association with communication devices through which the OTT connection 1750 passes; the sensors may participate in the measurement procedure by supplying values of the monitored quantities exemplified above, or supplying values of other physical quantities from which software 1711, 1731 may compute or estimate the monitored quantities. The reconfiguring of the OTT connection 1750 may include message format, retransmission settings, preferred routing etc.; the reconfiguring need not affect the base station 1720, and it may be unknown or imperceptible to the base station 1720. Such procedures and functionalities may be known and practiced in the art. In certain embodiments, measurements may involve proprietary UE signaling facilitating the host computer's 1710 measurements of throughput, propagation times, latency and the like. The measurements may be implemented in that the software 1711, 1731 causes messages to be transmitted, in particular empty or "dummy" messages, using the OTT connection 1750 while it monitors propagation times, errors etc.

Fig. 18 is a flowchart illustrating a method implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station and a UE which may be those described with reference to Figs. 16 and 17. For simplicity of the present disclosure, only drawing references to Fig. 18 will be included in this paragraph. In a first step 1810 of the method, the host computer provides user data. In an optional substep 1811 of the first step 1810, the host computer provides the user data by executing a host application. In a second step 1820, the host computer initiates a transmission carrying the user data to the UE. In an optional third step 1830, the base station transmits to the UE the user data which was carried in the transmission that the host computer initiated, in accordance with the teachings of the embodiments described throughout this disclosure. In an optional fourth step 1840, the UE executes a client application associated with the host application executed by the host computer.

Fig. 19 is a flowchart illustrating a method implemented in a communication system, in accordance with one embodiment. The communication system includes a host computer, a base station and a UE which may be those described with reference to Figs. 16 and 17. For simplicity of the present disclosure, only drawing references to Fig. 19 will be included in this paragraph. In a first step 1910 of the method, the host computer provides user data. In an optional substep (not shown) the host computer provides the user data by executing a host application. In a second step 1920, the host computer initiates a transmission carrying the user data to the UE. The transmission may pass via the base station, in accordance with the teachings of the embodiments described throughout this disclosure. In an optional third step 1930, the UE receives the user data carried in the transmission.

As has become apparent from above description, at least some embodiments of the technique can reduce or avoid a connectivity interruption, particularly for L3 relay, during path switch and/or handover procedures.

This can avoid losses in the radio communication, which is particularly relevant for reliability-sensible applications such as V2X or public safety. Many advantages of the present invention will be fully understood from the foregoing description, and it will be apparent that various changes may be made in the form, construction and arrangement of the units and devices without departing from the scope of the invention and/or without sacrificing all of its advantages. Since the invention can be varied in many ways, it will be recognized that the invention should be limited only by the scope of the following claims.

Claims

1. A method (300-RM) of switching a radio communication between a remote radio device (100-RM) and a radio access network, RAN (700), from a relayed radio communication being relayed through a relay radio device (100-RL) served by a network node (200) of the RAN (700) to a direct radio communication between the remote radio device (100-RM) and the RAN (700), the method (300-RM) comprising or initiating the steps of: determining (302-RM) a degradation of a radio link quality of a radio link between the remote radio device (100-RM) and the relay radio device (100-RL) for the relayed radio communication relayed through the relay radio device (100-RL); and responsive to the determined degradation of the radio link quality, performing (304-RM) a random access, RA, to the RAN (700) for switching to the direct radio communication between the remote radio device (100-RM) and the RAN (700).

2. The method (300-RM) of embodiment 1, wherein the random access is performed (304-RM) to the network node (200) serving the relay radio device (100-RL) or to another network node of the RAN (700).

3. The method (300-RM) of embodiment 1 or 2, wherein the random access is performed to a cell of the RAN (700), and wherein the step of performing the random access comprises selecting the cell of the RAN (700), optionally wherein the cell serving the relay radio device (100-RL) is preferred over other cells of the RAN (700).

4. The method (300-RM) of any one of embodiments 1 to 3, wherein the radio link quality comprises at least one of a reference signal received power, RSRP; a reference signal received quality, RSRQ; a signal to noise ratio, SNR; a signal to interference-and-noise ratio, SNIR; a block error rate, BLER; and a bit error rate, BER.

5. The method (300-RM) of any one of embodiments 1 to 4, wherein the degradation of the radio link quality is determined (302-RM) if the radio link quality is less than a predefined threshold value for the radio link quality.

6. The method (300-RM) of embodiment 5, wherein different predefined threshold values for the radio link quality are associated with at least one of: different traffic; different services; different quality of service, QoS, types; and different QoS flows.

7. The method (300-RM) of embodiment 5 or 6, wherein the predefined threshold value for the radio link quality is greater or less than a threshold value of a link failure of the radio link between the remote radio device and the relay radio device.

8. The method (300-RM) of any one of embodiments 1 to 7, wherein the random access is performed (304-RM) before the radio link between the remote radio device (100-RM) and the relay radio device (100-RL) is failed.

9. The method (300-RM) of any one of embodiments 1 to 8, wherein the direct radio communication and the relayed radio communication coexist after the random access.

10. The method (300-RM) of any one of embodiments 1 to 9, further comprising or initiating the step of: releasing the radio link between the relay radio device (100-RL) and the network node (200) for the relayed radio communication after establishing the direct radio communication between the remote radio device (100-RM) and the RAN (700).

11. The method (300-RM) of any one of embodiments 1 to 10, wherein the release of the radio link for the relayed radio communication depends on a comparison of the radio link quality of the radio link of the relayed radio communication and the radio link quality of the radio link of the direct radio communication.

12. The method (300-RM) of any one of embodiments 1 to 11, further comprising or initiating the step of: starting a timer at the remote radio device (100-RM) responsive to the determined degradation of the radio link quality or when starting the random access, wherein the radio link for the relayed radio communication is released upon expiry of the timer.

13. The method (300-RM) of any one of embodiments 1 to 12, wherein the method (300-RM) is performed by the remote radio device (100-RM).

14. The method (300-RM) of any one of embodiments 1 to 13, wherein the radio link between the remote radio device (100-RM) and the relay radio device (100-RL) for the relayed radio communication comprises a PC5 interface.

15. The method (300-RM) of any one of embodiments 1 to 14, wherein the random access to the RAN for the direct radio communication uses a Uu interface.

16. The method (300-RM) of any one of embodiments 1 to 15, wherein the random access to the RAN (700) performed (304-RM) for the switching to the direct radio communication is a 2-step random access.

17. The method (300-RM) of any one of embodiments 1 to 16, wherein at least one of the random access procedure and the configuration parameter of the random access to the RAN (700) performed (304-RM) for the switching to the direct radio communication depends on the determined degradation of the radio link quality.

18. The method (300-RM) of any one of embodiments 1 to 17, wherein the radio link between the remote radio device (100-RM) and the relay radio device (100-RL) is a sidelink, SL.

19. The method (300-RM) of any one of embodiments 1 to 18, wherein the relayed radio connection is relayed through the relay radio device (100-RL) on a layer 3 and/or using Internet Protocol, IP, encapsulation or IP decapsulation towards a core network of the RAN.

20. The method (300-RM) of any one of embodiments 1 to 19, wherein the step of determining (302-RM) the degradation of a radio link quality comprises receiving a control message from the relay radio device (100-RL) and/or from the network node (200) of the RAN (700), the control message being indicative of the degradation of a radio link quality of the radio link between the remote radio device (100-RM) and the relay radio device (100-RL).

21. The method (300-RM) of any one of embodiments 1 to 20, further comprising or initiating the step of: receiving a configuration message from the relay radio device (100-RL) and/or from the network node (200) of the RAN (700), the configuration message being indicative of at least one of the random access procedure and the configuration parameter of the random access to the RAN (700) performed (304- RM) for the switching to the direct radio communication if the degradation of the radio link quality is determined (302-RM).

22. The method (300-RM) of any one of embodiments 1 to 21, wherein the degradation of the radio link quality is determined if at least one of the following criteria is met: the radio link between the remote radio device (100-RM) and the relay radio device (100-RL) comprises a PC5 interface (150), and a radio link quality of the PC5 interface (150) is less than the predefined threshold value of the radio link for the relayed radio communication; the relayed radio communication comprises a Uu interface (250) between the relay radio device (100-RL) and the RAN (720), and a radio link quality of the Uu interface is less than a predefined first threshold value of the radio link for the direct radio communication; the direct radio communication comprises a Uu interface (250) between the remote radio device (100-RM) and the RAN (720), and a radio link quality of the Uu interface is greater than a predefined second threshold value of the radio link for the direct radio communication, optionally the predefined second threshold value being greater than the predefined first threshold value; a radio link failure, RLF, is detected on the radio link (150) between the remote radio device (100-RM) and the relay radio device (100-RL) and/or on the radio link (250) between the relay radio device (100-RL) and the RAN (720); the radio communication serves a predefined type of service and/or bearers and/or QoS flows associated with a predefined QoS requirements; a control message received from the relay radio device (100-RL) is indicative of the switching; a control message received from the RAN (720), optionally from the network node (200), is indicative of the switching; a configuration message received from the relay radio device (100-RL) is indicative of the RA configuration to be used when performing the switching or whether a RA configuration for switching from the relayed radio communication is to be used when performing the switching; a configuration message received from the RAN (720), optionally from the network node (200), is indicative of the RA configuration to be used when performing the switching or whether a RA configuration for switching from the relayed radio communication is to be used when performing the switching; and a predefined estimator evaluated for a time sequence of the radio link quality is indicative of a radio link failure within a predefined future time.

23. The method (300-RM) of any one of embodiments 1 to 22, wherein the radio link for the relayed radio communication is released responsive to at least one of the following criteria: a first uplink data packet is received by the RAN (720), optionally by the network node (200) over the direct radio communication, optionally wherein the RAN (720) or the network node (200) transmits a release signaling to the remote radio device (100-RM); a first downlink data packet is received at the remote radio device (100-RM) over the direct radio communication; a control message is received via the relayed radio communication, the control message being indicative of releasing the radio link between the remote radio device (100-RM) and the relay radio device (100-RL), optionally wherein the remote radio device (100-RM) is identified by its layer 2 identifier; reception of a control message indicative of completion of a radio resource control, RRC, setup and/or a RRC resume.

24. The method (300-RM) of any one of embodiments 1 to 23, further comprising or initiating the step of receiving a control message that is indicative of at least one of: the at least one criteria for determining the degradation of the radio link quality; the at least one criteria for releasing the radio link for the relayed radio communication; and whether to use the timer.

25. A method (300-RL) of triggering a switching of a radio communication between a remote radio device (100-RM) and a radio access network, RAN (700), from a relayed radio communication being relayed through a relay radio device (100-RL) served by a network node (200) of the RAN (700) to a direct radio communication between the remote radio device (100-RM) and the RAN (700), the method (300-RL) comprising or initiating the steps of: determining (302-RL) a degradation of a radio link quality of a radio link between the remote radio device (100-RM) and the relay radio device (100-RL) for the relayed radio communication relayed through the relay radio device (100-RL); and responsive to the determined degradation of the radio link quality, triggering (304-RL) the remote radio device (100-RM) to perform a random access to the RAN (700) for switching to the direct radio communication between the remote radio device (100-RM) and the RAN (700).

26. The method (300-RL) of embodiment 25, wherein the method (300-RL) is performed by the relay radio device (100-RL).

27. The method (300-RL) of embodiment 24 or 25, wherein the step of triggering (304-RL) the remote radio device (100-RM) comprises transmitting a control message to the remote radio device (100-RL), the control message being indicative of the degradation of a radio link quality of the radio link between the remote radio device (100-RM) and the relay radio device (100-RL).

28. The method (300-RL) of any one of embodiments 25 to 27, further comprising or initiating the step of: relaying, at the relay radio device (100-RL), the relayed radio connection between the remote radio device (100-RM) and the RAN (700) on a layer 3 and/or using Internet Protocol, IP, encapsulation or IP decapsulation towards a core network of the RAN (700).

29. The method (300-RL) of any one of embodiments 25 to 28, further comprising the features or the steps of any one of embodiments 2 to 24 or any feature or step corresponding thereto.

30. A method (400) of triggering a switching of a radio communication between a remote radio device (100-RM) and a radio access network, RAN (700), from a relayed radio communication being relayed through a relay radio device (100-RL) served by a network node (200) of the RAN (700) to a direct radio communication between the remote radio device (100-RM) and the RAN (700), the method (400) comprising or initiating the steps of: determining (402) a degradation of a radio link quality of a radio link between the remote radio device (100-RM) and the relay radio device (100-RL) for the relayed radio communication relayed through the relay radio device (100-RL); and responsive to the determined degradation of the radio link quality, triggering (404) the remote radio device (100-RM) to perform a random access to the RAN (700) for switching to the direct radio communication between the remote radio device (100-RM) and the RAN (700).

31. The method (400) of embodiment 30, wherein the method (400) is performed by the RAN (700), optionally by the network node (200) serving the relay radio device (100-RL).

32. The method (400) of embodiment 30 or 31, wherein the step of triggering (404) the remote radio device (100-RM) comprises transmitting a control message to the remote radio device (100-RL), the control message being indicative of the degradation of a radio link quality of the radio link between the remote radio device (100-RM) and the relay radio device (100-RL).

33. The method (400) of any one of embodiments 30 to 32, further comprising or initiating the step of: scheduling radio resources for the radio link between the remote radio device (100-RM) and the relay radio device (100-RL) for the relayed radio communication relayed through the relay radio device (100-RL).

34. The method (400) of any one of embodiments 30 to 33, further comprising the features or the steps of any one of embodiments 2 to 24 or 25 to 29 or any feature or step corresponding thereto.

35. A computer program product comprising program code portions for performing the steps of any one of the embodiments 2 to 24 or 25 to 29 or 30 to 34 when the computer program product is executed on one or more computing devices (1304; 1404; 1504), optionally stored on a computer-readable recording medium (1306; 1306; 1506).

36. A remote radio device (100-RM; 1300; 1691; 1692; 1730) for switching a radio communication between the remote radio device (100-RM; 1300; 1691;

1692; 1730) and a radio access network, RAN (700), from a relayed radio communication being relayed through a relay radio device (100-RL) served by a network node (200) of the RAN (700) to a direct radio communication between the remote radio device (100-RM; 1300; 1691; 1692; 1730) and the RAN (700), the remote radio device (100-RM; 1300; 1691; 1692; 1730) comprising memory operable to store instructions and processing circuitry operable to execute the instructions, such that the remote radio device (100-RM; 1300; 1691; 1692; 1730) is operable to: determine (302-RM) a degradation of a radio link quality of a radio link between the remote radio device (100-RM; 1300; 1691; 1692; 1730) and the relay radio device (100-RL) for the relayed radio communication relayed through the relay radio device (100-RL); and responsive to the determined degradation of the radio link quality, perform (304-RM) a random access, RA, to the RAN (700) for switching to the direct radio communication between the remote radio device (100-RM) and the RAN (700).

37. The remote radio device (100-RM; 1300; 1691; 1692; 1730) of embodiment 36, further operable to perform the steps of any one of embodiments 2 to 24.

38. A relay radio device (100-RL; 1400; 1691; 1692; 1730) for triggering a switching of a radio communication between the remote radio device (100-RM) and a radio access network, RAN (700), from a relayed radio communication being relayed through a relay radio device (100-RL; 1400; 1691; 1692; 1730) served by a network node (200) of the RAN (700) to a direct radio communication between the remote radio device (100-RM) and the RAN (700), the relay radio device (100-RL; 1400; 1691; 1692; 1730) comprising memory operable to store instructions and processing circuitry operable to execute the instructions, such that the relay radio device (100-RL; 1400; 1691; 1692; 1730) is operable to: determine (302-RL) a degradation of a radio link quality of a radio link between the remote radio device (100-RM) and the relay radio device (100-RL) for the relayed radio communication relayed through the relay radio device (100-RL); and responsive to the determined degradation of the radio link quality, trigger (304-RL) the remote radio device (100-RM) to perform a random access to the RAN (700) for switching to the direct radio communication between the remote radio device (100-RM) and the RAN (700).

39. The relay radio device (100-RL; 1400; 1691; 1692; 1730) of embodiment 38, further operable to perform the steps of any one of embodiments 25 to 29.

40. A network node (200; 1500; 1612; 1720) for triggering a switching of a radio communication between a remote radio device (100-RM) and a radio access network, RAN (700), from a relayed radio communication being relayed through a relay radio device (100-RL) served by the network node (200; 1500; 1612; 1720) of the RAN (700) to a direct radio communication between the remote radio device (100-RM) and the RAN (700), the network node (200; 1500; 1612; 1720) comprising memory operable to store instructions and processing circuitry operable to execute the instructions, such that the network node (200; 1500;

1612; 1720) is operable to: determine (402) a degradation of a radio link quality of a radio link between the remote radio device (100-RM) and the relay radio device (100-RL) for the relayed radio communication relayed through the relay radio device (100-RL); and responsive to the determined degradation of the radio link quality, trigger (404) the remote radio device (100-RM) to perform a random access to the RAN (700) for switching to the direct radio communication between the remote radio device (100-RM) and the RAN (700).

41. The network node (200; 1500; 1612; 1720) of embodiment 40, further operable to perform the steps of any one of embodiments 30 to 34.

42. A remote radio device (100-RM; 1300; 1691; 1692; 1730) for switching a radio communication between the remote radio device (100-RM; 1300; 1691;

1692; 1730) and a radio access network, RAN (700), from a relayed radio communication being relayed through a relay radio device (100-RL) served by a network node (200) of the RAN (700) to a direct radio communication between the remote radio device (100-RM; 1300; 1691; 1692; 1730) and the RAN (700), the remote radio device (100-RM; 1300; 1691; 1692; 1730) being configured to: determine (302-RM) a degradation of a radio link quality of a radio link between the remote radio device (100-RM; 1300; 1691; 1692; 1730) and the relay radio device (100-RL) for the relayed radio communication relayed through the relay radio device (100-RL); and responsive to the determined degradation of the radio link quality, perform (304-RM) a random access, RA, to the RAN (700) for switching to the direct radio communication between the remote radio device (100-RM; 1300; 1691; 1692; 1730) and the RAN (700).

43. The remote radio device (100-RM; 1300; 1691; 1692; 1730) of embodiment 42, further configured to perform the steps of any one of embodiments 2 to 24.

44. A relay radio device (100-RL; 1400; 1691; 1692; 1730) for triggering a switching of a radio communication between the remote radio device (100-RM) and a radio access network, RAN (700), from a relayed radio communication being relayed through a relay radio device (100-RL; 1400; 1691; 1692; 1730) served by a network node (200) of the RAN (700) to a direct radio communication between the remote radio device (100-RM) and the RAN (700), the relay radio device (100-RL; 1400; 1691; 1692; 1730) being configured to: determine (302-RL) a degradation of a radio link quality of a radio link between the remote radio device (100-RM) and the relay radio device (100-RL; 1400; 1691; 1692; 1730) for the relayed radio communication relayed through the relay radio device (100-RL; 1400; 1691; 1692; 1730); and responsive to the determined degradation of the radio link quality, trigger (304-RL) the remote radio device (100-RM) to perform a random access to the RAN (700) for switching to the direct radio communication between the remote radio device (100-RM) and the RAN (700).

45. The relay radio device (100-RL; 1400; 1691; 1692; 1730) of embodiment 44, further configured to perform the steps of any one of embodiments 25 to 29.

46. A network node (200; 1500; 1612; 1720) for triggering a switching of a radio communication between a remote radio device (100-RM) and a radio access network, RAN (700), from a relayed radio communication being relayed through a relay radio device (100-RL) served by the network node (200) of the RAN (700) to a direct radio communication between the remote radio device (100-RM) and the RAN (700), the network node (200; 1500; 1612; 1720) being configured to: determine (402) a degradation of a radio link quality of a radio link between the remote radio device (100-RM) and the relay radio device (100-RL) for the relayed radio communication relayed through the relay radio device (100-RL); and responsive to the determined degradation of the radio link quality, trigger (404) the remote radio device (100-RM) to perform a random access to the RAN (700) for switching to the direct radio communication between the remote radio device (100-RM) and the RAN (700).

47. The network node (200; 1500; 1612; 1720) of embodiment 46, further configured to perform the steps of any one of embodiments 30 to 34.

48. A user equipment, UE, (100; 1300; 1400; 1691; 1692; 1730) configured to communicate with a base station (200; 1500; 1612; 1720) or with a radio device functioning as a gateway, the UE (100; 1300; 1400; 1691; 1692; 1730) comprising a radio interface (1302; 1402; 1737) and processing circuitry (1304; 1404; 1738) configured to perform the method according to any one of embodiments 1 to 29.

49. A base station (200; 1500; 1612; 1720) configured to communicate with a user equipment, UE, the base station (200; 1500; 1612; 1720) comprising a radio interface (1502; 1727) and processing circuitry (1504; 1728) configured to perform the method according to any one of embodiments 30 to 34.

50. A communication system (700; 1600; 1700) including a host computer (1330; 1410) comprising: processing circuitry (1718) configured to provide user data; and a communication interface (1716) configured to forward user data to a cellular or ad hoc radio network (700; 1610) for transmission to a user equipment, UE, (100; 1300; 1400; 1691; 1692; 1730) wherein the UE (100; 1300; 1400; 1691; 1692; 1730) comprises a radio interface (1302; 1402; 1737) and processing circuitry (1304; 1404; 1738), the processing circuitry (1304; 1404; 1738) of the UE (100; 1300; 1400; 1691; 1692; 1730) being configured to execute the steps of any one of embodiments 1 to 24 or embodiments 25 to 29.

51. The communication system (700; 1600; 1700) of embodiment 50, further including the UE (100; 1300; 1400; 1691; 1692; 1730).

52. The communication system (700; 1600; 1700) of embodiment 50 or 51, wherein the radio network (700; 1610) further comprises a base station (200; 1500; 1612; 1720), or a radio device functioning as a gateway, which is configured to communicate with the UE (100; 1300; 1400; 1691; 1692; 1730).

53. The communication system (700; 1600; 1700) of embodiment 52, wherein the base station (200; 1500; 1612; 1720), or the radio device functioning as a gateway, comprises processing circuitry (1504; 1728), which is configured to execute the steps of any one of embodiments 30 to 34.

54. The communication system (700; 1600; 1700) of any one of embodiments 50 to 53, wherein: the processing circuitry (1718) of the host computer (1630; 1710) is configured to execute a host application (1712), thereby providing the user data; and the processing circuitry (1304; 1404; 1738) of the UE (10100; 1300; 1400; 1691; 1692; 1730) is configured to execute a client application (1732) associated with the host application (1712).