WO2024256040A1

WO2024256040A1 - Relay (re)selection in multi-hop ue-to-network relaying

Info

Publication number: WO2024256040A1
Application number: PCT/EP2024/053401
Authority: WO
Inventors: Vinh Van Phan; Ling Yu; Faranaz SABOURI-SICHANI; Apostolos KOUSARIDAS; Sayed Ali MARANDI; Ravi Krishna PRASAD; Jakob Lindbjerg Buthler
Original assignee: Nokia Technologies Oy
Current assignee: Nokia Technologies Oy
Priority date: 2023-06-14
Filing date: 2024-02-12
Publication date: 2024-12-19
Anticipated expiration: 2025-12-14

Abstract

Embodiments of the present disclosure relate to relay (re)selection in MH U2N relaying. In an aspect, a terminal device discovers one or more tier structures corresponding to one or more cells, and a tier structure characterizes MH U2N relaying in the one or more cells. The terminal device associates itself with a tier structure set among the one or more tier structures such that itself acts as a U2U relay UE in the tier structure set. The terminal device announces information on the tier structure set associated with itself, and for each tier structure in the tier structure set, the information comprises a cell ID of a cell corresponding to the tier structure, a tier level of the terminal device in the tier structure. In this way, the embodiments can enable the remote UE in a RRC connected state to perform a U2N relay (re)selection.

Description

RELAY (RE)SELECTION IN MULTI-HOP UE-TO-NETWORK RELAYING

FIELD

Various example embodiments generally relate to the field of communication, and in particular, to terminal devices, a network device, methods, apparatuses and a computer readable storage medium for relay (re)selection in multi-hop (MH) UE-to-Network (U2N) relaying.

BACKGROUND

In 3 GPP Release- 17 and Release- 18, sidelink (SL) based U2N relaying is single-hop (SH) U2N relaying. A remote UE is connected to the single U2N relay UE directly over SL. The remote UE uses the U2N relay UE to connect to a serving network. A UE-to-UE (U2U) relay is currently specified in Release-18. It is limited to a single relayed hop or, that is, a 2-hop End- to-End (E2E) connection between a source End UE and a target End UE via a U2U relay UE.

SUMMARY

In general, example embodiments of the present disclosure provide terminal devices, a network device, methods, apparatuses and a computer readable storage medium for relay (re)selection in MH U2N relaying. For example, the solution provided by the example embodiments of the present disclosure can enable the remote UE in a radio resource control (RRC) connected state to perform U2N relay (re)selection.

In a first aspect, there is provided a terminal device. The terminal device may comprise at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the terminal device at least to: discover one or more tier structures corresponding to one or more cells, wherein a tier structure characterizes MH U2N relaying in the one or more cells; associate the terminal device with a tier structure set among the one or more tier structures such that the terminal device acts as a U2U relay UE in the tier structure set; and announce information on the tier structure set associated with the terminal device, wherein for each tier structure in the tier structure set, the information comprises a cell identifier (ID) of a cell corresponding to the tier structure, a tier level of the terminal device in the tier structure.

In a second aspect, there is provided a terminal device. The terminal device may comprise at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the terminal device at least to: receive, from at least one U2U relay UE discovered by the terminal device acting as a remote UE in MH U2N relaying, at least one first information on at least one first tier structure set associated with the at least one U2U relay UE, wherein the at least one first tier structure set corresponds to at least one first cell set and characterizes MH U2N relaying in the at least one first cell set; determine, based on the at least one first information, second information on a second tier structure set associated with the terminal device, wherein the second tier structure set corresponds to a second cell set which is a subset of the at least one first cell set; transmit the second information to a network device; and receive, from the network device, a configuration for a conditional path switch in the MH U2N relaying for the terminal device, wherein the configuration is indicative of at least one target cell for the conditional path switch from the second cell set.

In a third aspect, there is provided a network device. The network device may comprise at least one processor and at least one memory storing instructions that, when executed by the at least one processor, cause the network node at least to: receive, from a remote UE, information on a tier structure set associated with the remote UE, wherein the tier structure set corresponds to a cell set and characterizes MH U2N relaying in the cell set; determine, based on the received information, a configuration for a conditional path switch in the MH U2N relaying for the remote UE, wherein the configuration is indicative of at least one target cell for the conditional path switch selected from the cell set; and transmit the configuration to the remote UE.

In a fourth aspect, there is provided a method. The method may comprise: discovering, at a terminal device, one or more tier structures corresponding to one or more cells, wherein a tier structure characterizes MH U2N relaying in the one or more cells; associating the terminal device with a tier structure set among the one or more tier structures such that the terminal device acts as a U2U relay UE in the tier structure set; and announcing information on the tier structure set associated with the terminal device, wherein for each tier structure in the tier structure set, the information comprises a cell ID of a cell corresponding to the tier structure, a tier level of the terminal device in the tier structure.

In a fifth aspect, there is provided a method. The method may comprise: receiving, at a terminal device, from at least one U2U relay UE discovered by the terminal device acting as a remote UE in MH U2N relaying, at least one first information on at least one first tier structure set associated with the at least one U2U relay UE, wherein the at least one first tier structure set corresponds to at least one first cell set and characterizes MH U2N relaying in the at least one first cell set; determining, based on the at least one first information, second information on a second tier structure set associated with the terminal device, wherein the second tier structure set corresponds to a second cell set which is a subset of the at least one first cell set; transmitting the second information to a network device; and receiving, from the network device, a configuration for a conditional path switch in the MH U2N relaying for the terminal device, wherein the configuration is indicative of at least one target cell for the conditional path switch from the second cell set.

In a sixth aspect, there is provided a method. The method may comprise: receiving, at a network device, from a remote UE, information on a tier structure set associated with the remote UE, wherein the tier structure set corresponds to a cell set and characterizes MH U2N relaying in the cell set; determining, based on the received information, a configuration for a conditional path switch in the MH U2N relaying for the remote UE, wherein the configuration is indicative of at least one target cell for the conditional path switch selected from the cell set; and transmitting the configuration to the remote UE.

In a seventh aspect, there is provided an apparatus. The apparatus may comprise: means for discovering, at a terminal device, one or more tier structures corresponding to one or more cells, wherein a tier structure characterizes MH U2N relaying in the one or more cells; means for associating the terminal device with a tier structure set among the one or more tier structures such that the terminal device acts as a U2U relay UE in the tier structure set; and means for announcing information on the tier structure set associated with the terminal device, wherein for each tier structure in the tier structure set, the information comprises a cell ID of a cell corresponding to the tier structure, a tier level of the terminal device in the tier structure.

In an eighth aspect, there is provided an apparatus. The apparatus may comprise: means for receiving, at a terminal device, from at least one U2U relay UE discovered by the terminal device acting as a remote UE in MH U2N relaying, at least one first information on at least one first tier structure set associated with the at least one U2U relay UE, wherein the at least one first tier structure set corresponds to at least one first cell set and characterizes MH U2N relaying in the at least one first cell set; means for determining, based on the at least one first information, second information on a second tier structure set associated with the terminal device, wherein the second tier structure set corresponds to a second cell set which is a subset of the at least one first cell set; means for transmitting the second information to a network device; and means for receiving, from the network device, a configuration for a conditional path switch in the MH U2N relaying for the terminal device, wherein the configuration is indicative of at least one target cell for the conditional path switch from the second cell set.

In a ninth aspect, there is provided an apparatus. The apparatus may comprise: means for receiving, at a network device, from a remote UE, information on a tier structure set associated with the remote UE, wherein the tier structure set corresponds to a cell set and characterizes MH U2N relaying in the cell set; means for determining, based on the received information, a configuration for a conditional path switch in the MH U2N relaying for the remote UE, wherein the configuration is indicative of at least one target cell for the conditional path switch selected from the cell set; and means for transmitting the configuration to the remote UE.

In a tenth aspect, there is provided a non-transitory computer readable medium comprising program instructions for causing an apparatus to perform at least the method according to any of the fourth to the sixth aspect.

In an eleventh aspect, there is provided a computer program comprising instructions, which, when executed by an apparatus, cause the apparatus at least to: discover one or more tier structures corresponding to one or more cells, wherein a tier structure characterizes MH U2N relaying in the one or more cells; associate the terminal device with a tier structure set among the one or more tier structures such that the terminal device acts as a U2U relay UE in the tier structure set; and announce information on the tier structure set associated with the terminal device, wherein for each tier structure in the tier structure set, the information comprises a cell identifier ID of a cell corresponding to the tier structure, a tier level of the terminal device in the tier structure.

In a twelfth aspect, there is provided a computer program comprising instructions, which, when executed by an apparatus, cause the apparatus at least to: receive, from at least one U2U relay UE discovered by the terminal device acting as a remote UE in MH U2N relaying, at least one first information on at least one first tier structure set associated with the at least one U2U relay UE, wherein the at least one first tier structure set corresponds to at least one first cell set and characterizes MH U2N relaying in the at least one first cell set; determine, based on the at least one first information, second information on a second tier structure set associated with the terminal device, wherein the second tier structure set corresponds to a second cell set which is a subset of the at least one first cell set; transmit the second information to a network device; and receive, from the network device, a configuration for a conditional path switch in the MH U2N relaying for the terminal device, wherein the configuration is indicative of at least one target cell for the conditional path switch from the second cell set.

In a thirteenth aspect, there is provided a computer program comprising instructions, which, when executed by an apparatus, cause the apparatus at least to: receive, from a remote UE, information on a tier structure set associated with the remote UE, wherein the tier structure set corresponds to a cell set and characterizes MH U2N relaying in the cell set; determine, based on the received information, a configuration for a conditional path switch in the MH U2N relaying for the remote UE, wherein the configuration is indicative of at least one target cell for the conditional path switch selected from the cell set; and transmit the configuration to the remote UE.

In an fourteenth aspect, there is provided a terminal device. The terminal device may comprise a discovering circuitry configured to discover one or more tier structures corresponding to one or more cells, wherein a tier structure characterizes MH U2N relaying in the one or more cells; an associating circuitry configured to associate the terminal device with a tier structure set among the one or more tier structures such that the terminal device acts as a U2U relay UE in the tier structure set; an announcing receiving circuitry configured to announce information on the tier structure set associated with the terminal device, wherein for each tier structure in the tier structure set, the information comprises a cell identifier (ID) of a cell corresponding to the tier structure, a tier level of the terminal device in the tier structure.

In a fifteenth aspect, there is provided a terminal device. The terminal device may comprise a first receiving circuitry configured to receive, from at least one U2U relay UE discovered by the terminal device acting as a remote UE in MH U2N relaying, at least one first information on at least one first tier structure set associated with the at least one U2U relay UE, wherein the at least one first tier structure set corresponds to at least one first cell set and characterizes MH U2N relaying in the at least one first cell set; a determining circuitry configured to determine, based on the at least one first information, second information on a second tier structure set associated with the terminal device, wherein the second tier structure set corresponds to a second cell set which is a subset of the at least one first cell set; a transmitting circuitry configured to transmit the second information to a network device; and a second receiving circuitry configured to receive, from the network device, a configuration for a conditional path switch in the MH U2N relaying for the terminal device, wherein the configuration is indicative of at least one target cell for the conditional path switch from the second cell set.

In a sixteenth aspect, there is provided a network device. The network device may comprise a receiving circuitry configured to receive, from a remote UE, information on a tier structure set associated with the remote UE, wherein the tier structure set corresponds to a cell set and characterizes MH U2N relaying in the cell set; a determining circuitry configured to determine, based on the received information, a configuration for a conditional path switch in the MH U2N relaying for the remote UE, wherein the configuration is indicative of at least one target cell for the conditional path switch selected from the cell set; and a transmitting circuitry configured to transmit the configuration to the remote UE.

It is to be understood that the summary section is not intended to identify key or essential features of embodiments of the present disclosure, nor is it intended to be used to limit the scope of the present disclosure. Other features of the present disclosure will become easily comprehensible through the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

Some example embodiments will now be described with reference to the accompanying drawings, in which:

FIG. 1 A illustrates an example network environment in which example embodiments of the present disclosure may be implemented;

FIG. IB illustrates an example tier model for support of MH U2N relay related to some example embodiments of the present disclosure;

FIG. 2 illustrates an example signaling process for U2N relay (re)selection in MH U2N relaying with conditional path switch configuration in accordance with some example embodiments of the present disclosure;

FIGS. 3 A-3B illustrate an example signaling process for facilitating a remote UE initiated U2N relay reselection in MH U2N relaying using a tier model in which an inter-cell conditional path switch is selected in accordance with some example embodiments of the present disclosure; FIGS. 4A-4B illustrate an example signaling process for facilitating a remote UE initiated U2N relay reselection in MH U2N relaying using a tier model in which an intra-cell conditional path switch is selected in accordance with some example embodiments of the present disclosure;

FIG. 5 illustrates an example flowchart of a method of U2N relay (re)selection in MH U2N relaying at a U2U terminal device in accordance with some example embodiments of the present disclosure;

FIG. 6 illustrates an example flowchart of a method of U2N relay (re)selection in MH U2N relaying at a remote terminal device in accordance with some example embodiments of the present disclosure;

FIG. 7 illustrates an example flowchart of a method of U2N relay (re)selection in MH U2N relaying at a network device in accordance with some example embodiments of the present disclosure;

FIG. 8 illustrates an example simplified block diagram of a device that is suitable for implementing embodiments of the present disclosure; and

FIG. 9 illustrates an example block diagram of an example computer readable medium in accordance with some example embodiments of the present disclosure.

Throughout the drawings, the same or similar reference numerals represent the same or similar element.

DETAILED DESCRIPTION

Principles of the present disclosure will now be described with reference to some example embodiments. It is to be understood that these embodiments are described only for the purpose of illustration and help those skilled in the art to understand and implement the present disclosure, without suggesting any limitation as to the scope of the disclosure. The disclosure described herein may be implemented in various manners other than the ones described below.

In the following description and claims, unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skills in the art to which the present disclosure belongs.

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

It may be understood that although the terms “first” and “second” etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another. For example, a first element could be termed a second element, and similarly, a second element could be termed a first element, without departing from the scope of example embodiments. As used herein, the term “and/or” includes any and all combinations of one or more of the listed terms.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of example embodiments. As used herein, the singular forms “a”, “an” and “the” are intended to include the plural forms as well, unless the context clearly indicates otherwise. It will be further understood that the terms “comprises”, “comprising”, “has”, “having”, “includes” and/or “including”, when used herein, specify the presence of stated features, elements, and/or components etc., but do not preclude the presence or addition of one or more other features, elements, components and/ or combinations thereof. As used herein, “at least one of the following: <a list of two or more elements>” and “at least one of <a list of two or more elements>” and similar wording, where the list of two or more elements are joined by “and” or “or”, mean at least any one of the elements, or at least any two or more of the elements, or at least all the elements.

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

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

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

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

(ii) any portions of hardware processor(s) with software (including digital signal processor(s)), software, and memory(ies) that work together to cause an apparatus, such as a mobile phone or server, to perform various functions) and (c) hardware circuit(s) and or processor(s), such as a microprocessor s) or a portion of a microprocessor s) that requires software (e.g., firmware) for operation, but the software may not be present when it is not needed for operation.

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

As used herein, the term “communication network” refers to a network following any suitable communication standards, such as long term evolution (LTE), LTE-advanced (LTE-A), wideband code division multiple access (WCDMA), high-speed packet access (HSPA), narrow band Internet of things (NB-IoT) and so on. Furthermore, the communications between a terminal device and a network node in the communication network may be performed according to any suitable generation communication protocols, including, but not limited to, the third generation (3G), the fourth generation (4G), 4.5G, the fifth generation (5G) communication protocols, and/or beyond. Embodiments of the present disclosure may be applied in various communication systems. Given the rapid development in communications, there will of course also be future type communication technologies and systems with which the present disclosure may be embodied. It should not be seen as limiting the scope of the present disclosure to only the aforementioned system.

As used herein, the term “network node” refers to a node in a communication network via which a terminal device accesses the network and receives services therefrom. The network node may refer to a base station (BS) or an access point (AP), for example, a node B (NodeB or NB), an evolved NodeB (eNodeB or eNB), a NR. NB (also referred to as a gNB), a remote radio unit (RRU), a radio header (RH), a remote radio head (RRH), a relay, a low power node such as a femto, a pico, and so forth, depending on the applied terminology and technology.

The term “terminal device” refers to any end device that may be capable of wireless communication. By way of example rather than limitation, a terminal device may also be referred to as a communication device, user equipment (UE), a subscriber station (SS), a portable subscriber station, a mobile station (MS), or an access terminal (AT). The terminal device may include, but not limited to, a mobile phone, a cellular phone, a smart phone, voice over IP (VoIP) phones, wireless local loop phones, a tablet, a wearable terminal device, a personal digital assistant (PDA), portable computers, desktop computer, image capture terminal devices such as digital cameras, gaming terminal devices, music storage and playback appliances, vehicle-mounted wireless terminal devices, wireless endpoints, mobile stations, laptop-embedded equipment (LEE), laptop-mounted equipment (LME), USB dongles, smart devices, wireless customer-premises equipment (CPE), an Internet of things (loT) device, a watch or other wearable, a head-mounted display (HMD), a vehicle, a drone, a medical device and applications (e.g., remote surgery), an industrial device and applications (e.g., a robot and/or other wireless devices operating in an industrial and/or an automated processing chain contexts), a consumer electronics device, a device operating on commercial, a relay node, an integrated access and backhaul (IAB) node, and/or industrial wireless networks, and the like. In the following description, the terms “terminal device”, “communication device”, “terminal”, “user equipment” and “UE” may be used interchangeably.

As used herein, the term “resource”, “transmission resource”, “resource block”, “physical resource block” (PRB), “uplink (UL) resource” or “downlink (DL) resource” may refer to any resource for performing a communication, for example, a communication between a terminal device and a network node, such as a resource in time domain, a resource in frequency domain, a resource in space domain, a resource in code domain, a resource in a combination of more than one domain or any other resource enabling a communication, and the like. In the following, a resource in time domain (such as, a subframe) will be used as an example of a transmission resource for describing some example embodiments of the present disclosure. It is noted that example embodiments of the present disclosure are equally applicable to other resources in other domains.

In future 3GPP releases, Release- 19 and beyond, MH U2U relaying and U2N relaying may be supported. In the MH U2N relaying, the remote UE may be connected to the U2N relay UE indirectly using U2U relay via one or more U2U relay UEs. Thus, it is important to enable enhancements of SL based U2N relay in Release- 19 and beyond. In the MH U2N relaying, a remote UE needs to discover and select a U2N relay UE via one or more U2U relay UE. The U2N relay discovery (RD) may be initiated by the remote UE broadcasting a solicitation message to find a suitable U2N relay UE within a preconfigured maximum allowed number of hops for example. This may cause a flooding of the solicitation message of the remote UE by suitable U2U relay UE candidates forwarding it in all possible directions until reaching either one or more suitable U2N relay UE candidates or the maximum allowed number of hops.

The suitable U2N relay UE candidates may individually respond to the solicitation message of the remote UE via selected U2U relay UEs, triggering subsequent U2U relay UE selections by selected U2U relay UEs individually for forwarding the responses of the suitable U2N relay UE candidates to the remote UE. The remote UE may then select one of the suitable U2N relay UE candidates to establish the MH U2N relay connection. Thus, in addition to the message flooding problem, considerable latency may be expected for U2N relay UE (re)selection for the remote UE in MH U2N relaying. The term ‘(re) sei ection’ means at least one of selection or reselection. The term ‘relay UE selection’ refers to a process to select a relay UE among one or more suitable relay UE candidates to provide a service for a remote UE when the remote UE is currently not served by another relay UE for providing the service for the remote UE. The term relay UE reselection refers to a process to select a relay UE among one or more suitable relay UE candidates to replace an existing relay UE that is currently serving the remote UE. The one or more suitable relay UE candidates may need to be discovered that may also need to fulfil predefined or configured criteria to be selectable for the remote UE. Therefore, there is a need to resolve U2N relay (re)selection issues in MH U2N relaying for a remote UE.

Example embodiments of the present disclosure provide a solution for U2N relay (re)selection in MH U2N relaying. According to some embodiments of the present disclosure, a terminal device discovers one or more tier structures corresponding to one or more cells. A tier structure characterizes MH U2N relaying in the one or more cells. For example, the tier structure may tell how many hops there are in the relaying chain from remote UE to the network. The terminal device further associates the terminal device with a tier structure set among the one or more tier structures such that the terminal device acts as a U2U relay UE in the tier structure set. The terminal device further announces information on the tier structure set associated with the terminal device. For each tier structure in the tier structure set, the information comprises a cell ID of a cell corresponding to the tier structure (e.g. the cell ID of the cell provided by the network node to which the relaying chain corresponding to the tier structure provides a connection), a tier level of the terminal device in the tier structure (e.g. is the terminal device on a tier 0, 1, 2, or 3, etc. of the tier structure). The example embodiments of U2N relay (re)selection in MH U2N relaying as provided in the present disclosure can enable the remote UE to perform a U2N relay (re)selection and, in particular, a U2N relay reselection for a path switch when being in a radio resource control (RRC) connected state.

For illustrative purposes, principles and example embodiments of the present disclosure for U2N relay (re)selection in MH U2N relaying will be described below with reference to FIG.

1 A- FIG. 9. However, it is to be noted that these embodiments are given to enable the skilled in the art to understand inventive concepts of the present disclosure and implement the solution as proposed herein, and not intended to limit scope of the present application in any way.

Reference is made to FIG. 1A, which illustrates an example network environment 100A in which example embodiments of the present disclosure may be implemented. The network environment 100 A, which may be a part of a communication network, includes a terminal device 102, a terminal device 104, a terminal device 106 and a network device 108.

As illustrated in FIG. 1A, the network environment lOOA may comprise terminal devices 102, 104 and 106. The terminal device 102 may also be referred as a user equipment 102 or a UE 102. The terminal device 104 may also be referred as a user equipment 104 or a UE 104. The terminal device 106 may also be referred as a user equipment 106 or a UE 106.

The terminal device 102 may communicate with the terminal device 104 via sidelink channels. The terminal device 104 may communicate with the terminal device 106 via sidelink channels. The network environment 100 may comprise a network device 108. The network device 108 may also be referred as a gNB 108. The network device 108 may communicate with the terminal device 106 directly via uplink or downlink channels, also referred to as Uu interface. The terminal device 102 and the terminal device 104 are not able to communicate with the network device 108 directly via uplink or downlink channels.

It is to be understood that the number of terminal devices is given only for the purpose of illustration without suggesting any limitations. The communication environment 100 may include any suitable number of network devices and/or terminal devices adapted for implementing embodiments of the present disclosure.

Communications in the network environment 100 A may be implemented according to any proper communication protocol(s), comprising, but not limited to, the third generation (3G), the fourth generation (4G), the fifth generation (5G), 5G-Advanced or beyond (6G), wireless local network communication protocols such as institute for electrical and electronics engineers (IEEE) 802.11 and the like, and/or any other protocols currently known or to be developed in the future. Moreover, the communication may utilize any proper wireless communication technology, comprising but not limited to: orthogonal frequency division multiplexing (OFDM), time division multiplexing (TDM), frequency division multiplexing (FDM), code division multiplexing (CDM), spatial division multiplexing (SDM) by means of beam-forming or multiple-input multiple-output (MIMO) transmission, carrier aggregation (CA), dual connectivity (DC), new radio unlicensed (NR-U) communication, Bluetooth, ZigBee, etc. The communication may be of any type, comprising but not limited to: machine type communication (MTC), enhanced mobile broadband (eMBB), massive machine type communication (mMTC), ultra-reliable low latency communication (URLLC), etc.

Reference is made to FIG. IB, which illustrates an example tier model for support of MH U2N relay related to some example embodiments of the present disclosure. As shown in FIG. IB, the tier model resolves the extended coverage of a cell supporting MH U2N relay. The tier model also provides a tier structure associated with the cell. The tier structure consisting of a preconfigured maximum allowed number of tiers, which are indexed from 0 to M and denoted as tier O, tier l, ..., tier M. M is equal to the maximum allowed number of hops for the supported MH U2N relay, which may be defined as a cell specific parameter or a network specific parameter common to all cells of the network that support MH U2N relay. In the latter option, the parameter M may be preconfigured to all gNBs and UEs capable of supporting MH U2N relay so that no explicit configuration or indication of the parameter M is needed. In an embodiment, the information for each tier structure in the tier structure set may comprise the parameter M for the tier structure.

It is to be noted that there can be similar parameters defined for individual services or service classes, for example, based on quality of service (QoS) requirements supported by the cell via MH U2N relaying. These are not larger than M. Thus, each cell supporting the MH U2N relay is associated with a tier structure for its extended coverage in supporting MH U2N relay. The serving cell may indicate in a system information block (SIB) that it supports MH U2N relay with the tier structure of the maximum allowed number of hops M.

The tier structure is a logical structure and fully self-organized. For example, U2N relay UEs that are in coverage of a serving cell 112 and meeting conditions to serve MH U2N relay form tier_0 of the tier structure associated with the serving cell 112. These U2N relay UEs are also referred to as tier_0 UEs. Tier_0 UEs may individually announce themselves as U2N relay UEs with their serving Cell ID, tier ID=0, and M.

U2U relay UEs that are able to serve MH U2N relay, meaning acting as U2U relay UEs to provide an E2E MH U2N relay connection between a remote UE and a U2N relay UE for the remote UE, may determine their associated tier structures and belonging tier indexes, also referred to as tier levels, and may form the respective tiers (fier i , . . . , tier M) of the associated tier structures such that at least one of the following (1) - (4) will be provided.

(1) AU2U relay UE may determine to associate with a tier structure and belong to tier k thereof, where k represents a tier level. This U2U relay UE may be referred to as tier k UE. The determination of the tier level k by the tier k UE is based on the condition that the tier k UE discovers at least one tier_(k-l) UE and no tier_(k-2) UE of the same associated tier structure for 2<=k<=M. (2) For k=l, the condition is that the tier_(k=l) UE discovers at least one tier O UE or, that is, U2N relay UE, of the same associated tier structure and the tier_(k=l) UE is in partial coverage or out of coverage of the serving cell of the at least one tier O UE and the associated tier structure. The discovery in (1) and (2) may need to fulfill certain predefined or configured relay selection criteria such that a reference signal received power (RSRP) related to a SL message the tier k UE needs to receive from a UE in tier level lower than k in order to discover the UE is above a predefined or configured threshold. The SL message may be a relay discovery (RD) announcement message and the RSRP measured on a received RD announcement message is referred to as RD-RSRP. The SL message may be a unicast SL message in case the tier k UE is communicating with the UE in tier level lower than k over an established unicast SL connection. In this case, the RSRP measured on the received unicast SL message is referred to as SL-RSRP.

(3) The tier_k UE may announce itself as a U2U relay UE supporting MH U2N relay with its tier structure association information including Cell ID, tier ID=k, and M. (4) The Cell ID and M may be inherited from the tier structure association information received from the at least one tier_(k-l) UE, according to the condition described above in (1) and (2).

The remote UE which may or may not be a U2U relay UE may discover and select one of U2U relay UEs with best possible SL condition (based on RD-RSRP or SL-RSRP), and lowest tier index associated with a suitable tier structure (based on Cell ID of the serving cell thereof) to request MH U2N relay (to access the serving cell of the associated tier structure of the selected U2U relay UE) right away without a need to discover and select a specific U2N relay UE for the requested MH U2N relay.

Thus, the tier model enables fast relay discovery and selection for the remote UE for setting up MH U2N relay with the shortest path. This is because the tier model implements a proactive tier-to-tier relay discovery and association (corresponding to hop-to-hop in MH relay) that allows the remote UE to skip performing E2E discovery and selection of a specific U2N relay UE but to discover and select a U2U relay UE for its immediate hop (the first hop from the remote UE) right away to request for an E2E connection with a U2N relay UE for MH U2N relay.

In current layer 2 (L2) U2N relay, the remote UE from RRC idle/inactive state is responsible for U2N relay selection for connecting to the serving gNB 110. Thus, the tier model, as described above, may be applied right away for the remote UE in RRC idle/inactive state. However, for the remote UE in RRC connected state using either direct path or indirect path via L2 U2N relay to the serving gNB, the serving gNB 110 is responsible for U2N relay selection or reselection for the remote UE for a path switch based on a report of U2N relay UE candidates from the remote UE. The remote UE in RRC connected state thus needs to discover and report U2N relay UE candidates to the gNB 110. If this principle is applied for MH U2N relay, the remote UE needs to perform conventional E2E U2N relay discovery for MH U2N relay and therefore diminishes all the advantages of using the tier model described above. In other words, use of the tier model is not effective for the remote UE in RRC connected state if the conventional U2N relay (re)selection by the gNB 110 based on the report of U2N relay UE candidates from the remote UE is applied.

As discussed above, these problems can be resolved proactively using the tier model. In some example embodiments of the present disclosure, the remote UE in RRC connected state is enabled to perform U2N relay (re)selection for an inter-cell path switch to a MH U2N relaying path using a target tier structure associated with a target cell that has been proactively prepared for a conditional path switch (that may also be considered as conditional handover (HO)) for the remote UE. The remote UE in RRC connected state is also enabled to perform U2N relay reselection for a conditional intra-cell path switch with MH U2N relay. The remote UE in RRC connected state therefore can still take advantage of the tier model, bypassing the need to discover and report U2N relay UE candidates to the gNB 110.

Reference is made to FIG. 2, which illustrates an example signaling process for U2N relay (re)selection in MH U2N relaying in accordance with some example embodiments of the present disclosure. FIG. 2 will be described with reference to FIG. 1A. It is to be noted that there may be the terminal device 106 in between the terminal device 104 and the network device 108 acting as U2N relay UE, as depicted in FIG. lAbut not depicted in FIG. 2.

As shown in FIG. 2, the terminal device 104 discovers (202) one or more tier structures corresponding to one or more cells. A tier structure characterizes MH U2N relaying in the one or more cells, which is discussed as in FIG. IB. The terminal device 104 associates (204) itself with a tier structure set among the one or more tier structures such that it acts as a U2U relay UE in the tier structure set. The terminal device 104 announces (206) first information 210 on the tier structure set associated with itself. For each tier structure in the tier structure set, the first information 210 comprises a cell ID of a cell corresponding to the tier structure, a tier level of the terminal device 104 in the tier structure.

As an example, to enable a remote UE in RRC connected state to perform U2N relay (re)selection for a conditional inter-cell path switch with MH U2N relay, the U2U relay UE may be configured to discover and associate itself with up to N (where N may be an integer) different tier structures of N different cells among the tier structures of the cells associated with other relay UEs in lower tiers with respect to the up to N different tier structures. The association may mean that the U2U relay UE may be able to serve as a U2U relay UE or as U2N relay for a remote UE to get access to any one of the up to N different cells using the tier structure thereof. For example, the U2U relay UE may determine, based on the tier model as discussed in FIG. IB, that it is a fier i UE of tier structure#! of Cell#l and a tier_4 UE of tier structure#2 of Cell#2. The U2U relay UE may be configured to announce the tier structure association information comprising up to N different tier structures. The tier structure association information thus may be a table 1 consisting of

Table 1

In table 1, M may indicate that the highest allowed tier level for a U2U relay UE to associate with the tier structure. For example, if this is set to 10 and a U2U relay UE discovers only other U2U relay UE of the tier level 10 of the given tier structure then it will not be allowed to associate itself with the tier structure as a U2U relay UE of the tier level 11.

As another example, to enable a remote UE in RRC connected state to perform U2N relay reselection for a conditional intra-cell path switch with MH U2N relay, the tier structure association information above may be extended to include a list of U2N relay UE candidates per an associated tier structure. For this, starting from fier i U2U relay UE, fier i UE of a tier structure 1 may be configured to announce up to N1 tier O UE candidates of tier structure 1 that the fier i UE has discovered. Then tier_2 UE of tier structure 1 may be configured to announce up to N2 tier_0 UE candidates of tier structure 1 based on the respective U2N relay candidate lists announced by the fier i UE candidates of tier structurel that the tier_2 UE has discovered.

For example, the tier_2 UE has discovered fier i UE1 with a list of three U2N relay UE candidates: tier_0 UE1, UE2 and UE3, and fier i UE2 with a list of two 2 U2N relay UE candidates: tier O UE1 and UE4. The tier_2 UE, after associating itself with tier structure 1 via fier i UE1 and fier i UE2, may determine and announce a list of four U2N relay UE candidates: tier_0 UE1, UE2, UE3 and UE4 (in case that N2 is larger than 4). The tier_2 UE may not announce fier i UE1 and UE2 but store their contexts including their announced tier structure association information. Thus, the tier structure association information may be extended as table 2.

Table2

The terminal device 102 receives (208), from the terminal device 104, among at least one U2U relay UE discovered by the terminal device 102 acting as a remote UE in MH U2N relaying, the first information 210 on the first tier structure set associated with the U2U relay UE 104. The first tier structure set corresponds to the first cell set and characterizes MH U2N relaying in the first cell set.

The terminal device 102 determines (212), based on the first information 210, second information 218 on a second tier structure set associated with the terminal device 102. The second tier structure set corresponds to a second cell set which is a subset of the first cell set, or which corresponds to the first cell set.

As an example, to enable a remote UE in RRC connected state to perform L2 U2N relay (re)selection for a conditional inter-cell path switch with MH L2 U2N relay, the remote UE in RRC connected state may be configured to determine and report to the serving gNB, based on the tier structure association information of U2U relay UEs the remote UE has discovered in its proximity (including the one that is serving the remote UE in case the remote UE is currently using a MH L2 U2N relay), candidate tier structure association information. The candidate tier structure association information may consist of up to P (where P may be an integer) different tier structures of up to P respective cells among the tier structures of the cells associated with the discovered U2U relay UEs, as shown in table 3. It is to be noted that the list of tier O UE candidates per associated tier structure may also be included in table 3 if it is available based on the tier structure association information of the discovered U2U relay UEs. The up to P cells may be selectable for the remote UE.

Table3 The terminal device 102 transmits (214) the second information 218 to the network device 108. The network device 108 receives (216) the second information 218 from the terminal device 102. The network device 108 determines (220), based on the second information 218, a configuration 226 for a conditional path switch in the MH U2N relaying for the terminal device 102. The configuration is indicative of at least one target cell for the conditional path switch selected from the second cell set.

As an example, to enable the remote UE in RRC connected state to perform U2N relay (re)selection for a conditional inter-cell path switch with MH U2N relay, the gNB may receive from the remote UE in RRC connected state a report of the candidate tier structure association information consisting of up to P different tier structures of up to P respective cells. The gNB may perform, based on the report from the remote UE, proactive preparation for conditional path switch to MH U2N relay for the remote UE to one or more target cell(s) selected from those reported in the candidate tier structure association information from the remote UE without identifying target U2N relay UE(s).

The network device 108 transmits (224) the configuration 226 to the terminal device 102. The terminal device 102 receives (222) the configuration 226 from network device 108.

As an example, the remote UE may receive from the serving gNB a proactive conditional path switch configuration for MH U2N relay to one or more target cells among the up to P cells without identifying target U2N relay UEs. The remote UE may determine that it is going to perform U2N relay (re)selection for a path switch to a selected one of the target cells configured for conditional path switch to a MH U2N path when at least one configured condition is met.. The remote UE may perform U2N relay (re)selection for the path switch to the selected one of the target cells configured for conditional path switch to the MH U2N path.

As another example, to enable the remote UE in RRC connected state to perform U2N relay (re)selection for a conditional intra-cell path switch with MH U2N relay, the gNB may configure the remote UE with conditions or triggers such that the remote UE prioritizes U2N relay reselection for intra-cell path switch over inter-cell path switch, e.g., in case Uu RLF or HO happens to the current serving U2N relay UE. This may be further conditioned to that the list of tier O UE candidates associated with the current serving cell and tier structure thereof is not empty. In this example, the remote UE may determine the list of tier O UE candidates associated with the current serving cell and tier structure thereof. The remote UE may determine that it is going to perform U2N relay reselection for an intra-cell path switch when one or more conditions are met. The remote UE may perform U2N relay reselection for the intra-cell path switch, indicating a particular U2N relay UE from the list of the tier O UE candidates to be reselected or the current serving U2N relay UE to be excluded or deselected for the reselection.

By implementing the example embodiments shown in FIG.2, the remote UE in RRC connected state is enabled to perform U2N relay (re)selection for an inter-cell path switch to a MH U2N relaying path using a target tier structure associated with a target cell that has been proactively prepared for a conditional path switch (conditional HO) for the remote UE. It also enables the remote UE in RRC connected state to perform U2N relay reselection for a conditional intra- cell path switch with MH U2N relay. The remote UE in RRC connected state therefore can take advantage of the tier model, bypassing the need to discover and report U2N relay UE candidates to the gNB for using MH U2N relay.

Reference is made to FIGS. 3A-3B, which illustrate an example signaling process (300A and 300B) for facilitating a remote UE initiated U2N relay reselection in MH U2N relaying using a tier model in which an inter-cell conditional path switch is performed in accordance with some example embodiments of the present disclosure. As shown in FIGS. 3 A and 3B, a remote UE 302 may correspond to the terminal device 102 in FIG. 1 A. U2U relay UEs 304-1 and 304- 2 may respectively correspond to the terminal device 104 in FIG. 1A. U2N relay UEs 308-1 and 308-2 may respectively correspond to the terminal device 106 in FIG. 1 A. gNBs 310-1 and 310-2 may respectively correspond to the network device 108 in FIG. 1 A. It is to be understood that there may be more U2U relay UEs, U2N relay UEs or gNBs. The numbers of remote UEs, U2U relay UEs, U2N relay UEs or gNBs are given only for the purpose of illustration without suggesting any limitations.

FIGS. 3A-3B illustrate some signalling interactions between the remote UE, U2U relay UE(s), U2N relay UE(s) and gNB(s) in MH U2N relay for inter-cell conditional path switch. It is to be noted that during this process, it maintains a remote UE’s connection to the network utilizing a multi-hop U2N relay. Herein, the U2N relay UE’s (tier_0) behaviour is considered to be inherited from single-hop U2N relay while there is a need to specify the behaviour of the U2U relay UE(s) (tier_l+), i.e., for the added hops between the remote UE and the U2N relay UE, the remote UE, and the corresponding network configurations.

As shown in FIG. 3 A, at 312, the remote UE 302 may be in RRC connected state towards the serving gNB 310-1 using L2 MH U2N relay or, that is, the remote UE 302 is connected to the serving gNB via the U2N relay UE 308-1 and a number of serving U2U relay UEs forming a MH relay chain for serving the remote UE. The U2N relay UE 308-1 may transmit (314) tier structure association information 315 to the U2U relay UE 306-1. The U2U relay UE 306-1 may receive (313) the tier structure association information 315. The U2N relay UE 308-1 may transmit (317) tier structure association information 318 to the U2U relay UE 306-2. The U2U relay UE 306-2 may receive (316) the tier structure association information 318. The transmitting (314) and (317) and the tier structure association information 315 and 318 may be of the same broadcast transmission from the U2N relay UE 308-1.

Similarly, the U2N relay UE 308-2 may transmit (320) tier structure association information 321 to the U2U relay UE 306-2. The U2U relay UE 306-2 may receive (319) the tier structure association information 321. The U2N relay UE 308-2 may transmit (323) tier structure association information 324 to the U2U relay UE 306-1. The U2U relay UE 306-2 may receive (322) the tier structure association information 324. The transmitting (320) and (323) and the tier structure association information 321 and 324 may be of the same broadcast transmission from the U2N relay UE 308-2.

The U2U relay UE 306-1 may transmit (326) tier structure association information 327 to the U2U relay UE 304-1 (which is in a higher adjacent tier level). The U2U relay UE 304-1 may receive (325) the tier structure association information 327. The U2N relay UEs 306-1 may transmit (329) tier structure association information 330 to the U2U relay UE 304-2 (which is in a higher adjacent tier level). The U2U relay UE 304-2 may receive (328) the tier structure association information 330. The transmitting (326) and (329) and the tier structure association information 327 and 330 may be of the same broadcast transmission from the U2U relay UE 306-1.

Similarly, the U2U relay UE 306-2 may transmit (332) tier structure association information 333 to the U2U relay UE 304-2 (which is in a higher adjacent tier level). The U2U relay UE 304-2 may receive (331) the tier structure association information 333. The U2N relay UE 306- 2 may transmit (335) tier structure association information 336 to the U2U relay UE 304-1 (which is in a higher adjacent tier level). The U2U relay UE 304-1 may receive (334) the tier structure association information 336. The transmitting (332) and (335) and the tier structure association information 333 and 336 may be of the same broadcast transmission from the U2N relay UE 308-2.

The U2U relay UE 304-1 may transmit (338) the tier structure association information 339 to the remote UE 302. The remote UE 302 may receive (337) the tier structure association information 339. The U2U relay UE 304-2 may transmit (341) the tier structure association information 342 to the remote UE 302. The remote UE 302 may receive (340) the tier structure association information 342. Any one or more of the tier structure association information 315, 318, 321, 324, 327, 330, 333, 336, 339 and 342 may be in form of table 1 or table 2.

The remote UE 302 may determine (343) tier structure association information 346 based on the tier structure association information 339 and 342. The remote UE 302 may report (344) the tier structure association information 346 to the gNB 310-1. The gNB 310-1 may receive (345) the tier structure association information 346.

The gNB 310-1 may perform (347) conditional path switch preparation with one or more gNBs of one or more target cells (directly or via a network entity) for the remote UE 302 based on the received tier structure association information 346 of the remote UE 302. The gNB 310-1 may transmit (349) a reconfiguration 350 comprising a conditional path switch configuration to the remote UE 302. The remote UE 302 may receive (348) the reconfiguration 350. The conditional path switch configuration may comprise one or more reconfigurations from the one or more target cells for the remote UE.

The remote UE 302 may transmit (351) a reconfiguration complete message 353 to the gNB 310-1. The gNB 310-1 may receive (352) the reconfiguration complete message 353. The U2U relay UE 304-1 may transmit (355) a notification 356 to the remote UE 302. The notification 356 may indicate a break or failure in the MH relay chain serving the MH relay connection of the remote UE 302.

The remote UE 302 may determine (357) to perform U2N relay reselection for an inter-cell path switch to one of the one or more target cells based on the conditional path switch configuration in the reconfiguration 350 received from gNB 310-1 and the latest tier structure association information the remote UE 302 has, as determined in 343 based on the latest tier structure association information received from discovered U2U relay UEs.

FIG. 3A is continued with FIG. 3B, as shown in FIG. 3B, the remote UE 302 may transmit (360) a direct communication request (DCR) 362, or other type of communication request to the U2U relay UE 304-2. The U2U relay UE 304-2 may receive (361) the DCR 362. The DCR 362 may comprise the remote UE ID, the target cell ID of the one of the one or more target cells, as determined (357) by the remote UE 302. The U2U relay UE 304-2 is selected by the remote UE 302 among discovered U2U relay UE candidates in the lower adjacent tier of the tier structure associated with the target cell ID. The transmission may use a SL unicast.

The U2U relay UE 304-2 may transmit (363) a DCR 365 to the U2U relay UE 306-2 that is selected by the U2U relay UE 304-2 among discovered U2U relay UE candidates in the lower adjacent tier of the tier structure associated with the target cell ID for forwarding the DCR of the remote UE 302. The U2U relay UE 306-2 may receive (364) the DCR 365. The U2U relay 306-2 may transmit (366) a DCR 368 to the U2N relay UE 308-2 that is selected by the U2U relay UE 304-2 among discovered U2N relay UE candidates in tier_0 of the tier structure associated with the target cell ID for forwarding the DCR of the remote UE 302. The U2N relay UE 308-2 may receive (367) the DCR 368. The U2N relay UE 308-2 may transmit (370) a direct communication accept (DC A) 370 to the U2U relay 306-2, upon accepting the DCR of the remote UE 302. The U2U relay 306-2 may receive (369) the DCA 371. The U2U relay UE 306-2 may transmit (373) a DCA 374 to the U2U relay UE 304-2 for forwarding the DCA of the U2N relay UE 308-2 towards the remote UE 302. The U2U relay UE 304-2 may receive (372) the DCA 374. The U2U relay UE 304-2 may transmit (376) a DCA 377 to the remote UE 302 for forwarding the DCA of the U2N relay UE 308-2 to the remote UE 302. The remote UE 302 may receive (375) the DCA 377, thus completing a MH relay E2E connection setup between the remote UE 302 and the U2N relay UE 302-2 for the MH relay reselection.

The remote UE 302 may transmit (378) a reconfiguration complete message 380 to the gNB 310-2 of the target cell ID via the U2N relay UE 308-2 in a SL message. The reconfiguration complete message is corresponding to the reconfiguration of the target cell ID included the conditional path switch configuration. The U2N relay UE 308-2 may receive (379) the SL message carrying the reconfiguration complete message 380. The U2N relay UE 308-2 may transmit (381) remote UE information 383 to the gNB 310-2, as triggered by the reception (379) of the SL message carrying the reconfiguration complete message 380 from the remote UE 302. The gNB 310-2 may receive (382) the remote UE information 383. The gNB 310-2 may transmit (385) a reconfiguration 386 to the U2N relay UE 308-2 to configure the U2N relay UE 308-2 to relay for the remote UE 302. The U2N relay UE 308-2 may receive (384) the reconfiguration 386.

The U2N relay UE 308-2 transmit (387) a reconfiguration complete message 389 to the gNB 310-2. The gNB 310-2 may receive (382) the reconfiguration complete message 389. The U2N relay UE 308-2 transmit or, that is, relay (390) a reconfiguration complete of the remote UE 302 corresponding to the reconfiguration of the target cell ID included the conditional path switch configuration, referred to as message 392, to the gNB 310-2. The gNB 310-2 may receive (391) the message 392. At 393, the new path via the reselected U2N relay UE may be ready.

Reference is made to FIGS. 4A-4B, which illustrate an example signaling process (400A and 400B) for facilitating a remote UE initiated U2N relay reselection in MH U2N relaying using a tier model in which an intra-cell conditional path switch is performed in accordance with some example embodiments of the present disclosure. As shown in FIGS. 4Aand 4B, a remote UE 402 may correspond to the terminal device 102 in FIG. 1A, and may correspond to the remote UE 302 in FIGS. 3A-3B. U2U relay UEs 404-1 and 404-2 may respectively correspond to the terminal device 104 in FIG. 1 A, and may respectively correspond to the U2U relay UEs 304-1 and 304-2 in FIGS. 3A-3B. U2N relay UEs 408-1 and 408-2 may respectively correspond to the terminal device 106 in FIG. 1A, and may respectively correspond to U2N relay UEs 308-1 and 308-2 in FIGS. 3A-3B. gNBs 410-1 and 410-2 may respectively correspond to the network device 108 in FIG. 1 A, and may respectively correspond to the gNBs 310-1 and 310-2 in FIGS. 3 A-3B. It is to be understand that there may more U2U relay UEs, U2N relay UEs or gNBs. The numbers of remote UEs, U2U relay UEs, U2N relay UEs or gNBs are given only for the purpose of illustration without suggesting any limitations.

FIGS. 4A-4B illustrate some signalling interactions between the remote UE, U2U relay UE(s), U2N relay UE(s) and gNB(s) in MH U2N relay for intra-cell conditional path switch. For brevity, some signalling interactions similar to FIGS. 3 A-3B will not be described in detail. For example, the signalling (413, 414 and 415) may correspond to the signalling (313, 314 and 315). The signalling (451, 452 and 453) may correspond to the signalling (351, 352 and 353). The different signalling interactions will be described in detail.

The U2N relay UE 408-1 may transmit (455) a notification 456 of a handover of U2N relay UE to the remote UE 402. The remote UE 402 may receive (454) the notification 456. The remote UE 402 may determine (457) to perform intra-cell U2N relay reselection based on received configuration from gNB 310-1 and the tier structure association information.

FIG. 4A is continued with FIG. 4B, as shown in FIG. 4B, the remote UE 402 may transmit (460) a direct communication request (DCR) 462 to the U2U relay UE 404-2. The U2U relay UE 404-2 may receive (462) the DCR 462. The DCR 462 may comprise the remote UE ID, the target cell ID set to the cell ID of the current serving cell for the intra-cell path switch, the excluded U2N relay UE ID set to UE ID of the current serving U2N relay UE to be deselected. This also indicates that a suitable U2N relay UE other than the excluded U2N relay UE ID in the same tier structure associated with the current serving cell may be reselected. The transmission may use a SL unicast.

The U2U relay UE 404-2 may transmit (463) a DCR 465 to the U2U relay 406-1. The U2U relay 406-1 may transmit (466) a DCR 468 to the U2N relay UE 408-2. The U2N relay UE 408-2 may receive (467) the DCR 468. The U2N relay UE 408-2 may transmit (470) a direct communication accept (DC A) 471 to the U2U relay 406-1. The U2U relay 406-1 may receive (469) the DCA 471. The U2U relay 406-2 may transmit (473) the DCA 474 to the U2U relay UE 404-2. The U2U relay UE 404-2 may receive (472) the DCA 474. The U2U relay UE 404- 1 may transmit (476) a DCA 477 to the remote UE 402. The remote UE 402 may receive (475) the DCA 477. The transmitting and forwarding of the DCR and DCA may follow the same analogy described above for FIG. 3B. The (re)selection of relay UE(s), such as the U2U relay UE 404-2 by the remote UE 402 and the U2N relay UE 408-2 by the U2U relay UE 406-1 in the example of FIG. 4B, may be based on the target cell ID and the excluded U2N relay UE ID indicated in the DCR initiated by the remote UE 402. That is, the relay (re)selection in the example of FIG. 4B may be determined at individual UEs involved in the U2N relay reselection such that a new path via a U2N relay UE having UE ID different from the excluded U2N relay UE in the same tier structure can be found and established for the remote UE. The remote UE 402 may transmit (478) a connection reestablishment request 480 to the gNB 410-1 of the current serving cell via the U2N relay UE 408-2 in a SL message. The U2N relay UE 408-2 may receive (479) the SL message carrying the request 480. The U2N relay UE 408- 2 may transmit (481) remote UE information 483 to the gNB 410-1. The gNB 410-1 may receive (482) the remote UE information 483. The gNB 410-1 may transmit (485) a reconfiguration 486 to the U2N relay UE 408-2 to configure the U2N relay UE 408-2 to relay for the remote UE 402. The U2N relay UE 408-2 may receive (484) the reconfiguration 486.

The U2N relay UE 408-2 transmit (487) a reconfiguration complete message 489 to the gNB 410-1. The gNB 410-1 may receive (482) the reconfiguration complete message 489. The U2N relay UE 408-2 transmit or, that is, relay (490) the connection reestablishment request 492 to the gNB 410-1. The gNB 410-1 may receive (491) the request 492. At 493, the remote UE 402 may be reconfigured for the new path via the reselected U2N relay UE 408-2.

In some example embodiments, the U2U relay UE may be configured to prioritize association with up to N discovered tier structures of corresponding cells (to be a tier k UE of an associated tier structure), also referred to as a tier structure set of a corresponding cell set, using one or more options or criteria. For example, the association may be based on the shortest paths. That is, the association may prioritize tier structures in which it has the lowest tier level (k). If the U2U relay UE sees it as of tier level 2 with a first tier structure, tier level 3 with a second tier structure and tier 5 with a third tier structure then it may associate itself with the first and second tier structures, assuming that it can associate with a maximum 2 tier structures. In other words, tier level of the U2U relay UE in each tier structure of the tier structure set is as low as possible.

For another example, there may be configured a maximum number of tier structures the U2U relay UE is allowed to associate with.

For yet another example, the association may prioritize tier structures according to a given list of cells, tracking areas, or public land mobile networks (PLMNs). For a further example, the association may prioritize tier structures with the highest number of neighbouring U2U relay UEs in the lower tier_(k-l) as discovered tier_(k-l) UE candidates for increased robustness in relay (re) sei ection. That is, the association is such that a number of discovered relay UE candidates in a tier level lower than the tier level of the U2U relay UE in each tier structure of the tier structure set is as high as possible. In some example embodiments, the U2U relay UE, as tier kfi] UE of the tier structure [i], may be configured to announce the number of discovered tier_(k[i]-l) relay UE candidates in its tier structure association information.

In some example embodiments, the U2U relay UE located in tier kfi] may inform the UEs located at its higher adjacent tier about whether it is serving a multi-hop relay connection as a U2U relay UE or is a remote UE of a multi-hop connection. The U2U relay UE may include additional information in the announcement, e.g., about QoS (especially if it is acting as a remote UE for another established multi-hop connection). In some example embodiments, the information for each tier structure in the tier structure set may comprise an indication indicating whether the U2U relay UE is participating in at least one MH relay connection as either a relay UE or a remote UE.

In some example embodiments, the U2U relay UE may announce the tier structure association information or, that is, the information about the tier structure set, using configured resources (such as a transmission pattern) independent from or common to the tier structure set or dependent on at least one tier structure in the tier structure set.

In some example embodiments, the U2U relay UE may be configured to announce the tier structure association information depending on its belonging tier index k[i] of a selected tier structure [i] (as being a tier kfi] UE thereof), among the up to N tier structures or, that is, the tier structure set, listed in the tier structure association information using at least one of the following options (a)-(d).

Option (a) may be that it is up to the U2U relay UE to determine the selected tier structure [i] on per announcement basis. Option (b) may be that the U2U relay UE is configured to select different tier structures for successive announcements in round-robin fashion, i.e., as a tier kfi] UE of the selected tier structure [i] with different [i] per announcement.

Option (c) may be that the U2U relay UE is configured to select the tier structure in which it has the lowest number of neighbouring U2U relay UE and/or has the highest number of remote UEs in the higher tier (k[i]+ 1 ) or, that is, discovered tier_(k[i]+ 1 ) UEs. This is because the U2U relay UE may be configured to adapt the frequency of sending announcements depending on the number of discovered tier_(k[i]+l) UEs. For example, the higher number of discovered tier_(k[i]+ 1 ) UEs the more frequent the announcement is.

Option (d) may be that the U2U relay UE as tier kfi] UE of the selected tier structure [i] is configured to select a time interval among multiple time intervals for announcing the information based on whether the tier level of the U2U relay UE is odd or even in the tier structure corresponding to the announcement and announce the information in the selected time interval. For example, there is a period reserved for announcing the information and the period can be divided into the intervals and then one interval is used based on odd/even criterion.

The U2U relay UE as tier kfi] UE of the selected tier structure [i] may be configured to send the announcement in a first or a second time interval in an announcing periodicity depending on whether k[i] is odd or even, as U2U relay UEs need to monitor announcements of only neighbouring tiers within a tier structure.

In some example embodiments, the U2U relay UE, as tier kfi] UE of the tier structure [i], may be configured to adapt the frequency or transmit range (power level) for sending the announcement of the tier structure association information depending on at least one of option (e) or (f). Option (e) may be based on the number of discovered tier_(k[i]+ 1 ) UEs, as mentioned above. Option (f) may be based on channel busy ratio (CBR) measured on the resource pool used for broadcasting the announcement for congestion control (the higher the CBR the lower the frequency prolonging the periodicity and/or the lower the transmit power shortening the range of the hop).

In some example embodiments, the U2U relay UE may be configured to discover and monitor the tier structure association information of other U2U and U2N relay UEs in proximity to determine and update its own tier association information.

In some example embodiments, the U2U relay UE, as a tier kfi] UE of a tier structure [i], is configured to forward, e.g., a DCR of the remote UE received from the remote UE or a tier_(k[i]+ 1 ) UE that selects the U2U relay UE to a tier_(k[i]-l) UE selected by the U2U relay UE using SL unicast. The DCR includes at least the remote UE ID Cell ID of the respective tier structure [i] and tier level of the remote UE in the respective tier structure [i]. The selection of the tier_(k[i]-l) UE is based on whether the information of the (re)selected U2N relay UE and/or the excluded or deselected U2N relay UE is provided in the DCR message or not. For the latter, the tier kfi] UE may have full freedom to select the tier_(k[i]-l) UE. In other words, the remote UE may indicate the ID of the current serving U2N relay UE to be excluded or deselected in case it does not indicate the ID of the U2N relay UE to be (re)selected, as this is needed for intra-cell path switch described above.

In some example embodiments, the U2U relay UE that is serving the remote UE as the tier kfi] UE may be configured to detect and notify the remote UE or the tier_(k[i]+ 1) UE of the MH relay chain serving the remote UE of a break or failure in the MH relay chain serving the remote UE. The break or failure may be due to, e.g., a locally unrecoverable SL radio link failure (RLF) or failure of U2U relay reselection at some hop in upstream towards the tier O UE or, that is, the U2N relay UE serving the remote UE in the tier structure [i] . The detection may be based on such the notification received from the tier_(k[i]-l) UE of the MH relay chain serving the remote UE.

In some example embodiments, the U2U relay may update its tier structure association information with SL radio information (e.g., RSRP from received messages with tier structure association information, CBR/CR of local measurements) and/or SL QoS information. This information can help the remote UE’s and/or gNB’s relay (re-)selection procedure. This extra information, which characterises the MH relay path towards each Cell ID#, may be estimated at each hop via the received announcements.

In some example embodiments, the remote UE may be configured to report the candidate tier structure association information to the gNB periodically when using MH U2N relay if the number of hops in the MH relay chain serving the remote UE or, that is, the tier level of the remote UE in the serving tier structure, is above a threshold. The reporting periodicity may depend on the number of hops, e.g., the higher the number of hops the more frequent or shorter the reporting periodicity. The candidate tier structure association information comprises a second tier structure set.

In some example embodiments, the remote UE may be configured to report the candidate tier structure association information upon a change to the current candidate tier structure association information. In some example embodiments, pre-configurations at the UE or Policy and Charging Function (PCF) of the serving network or gNB may provide thresholds and criteria to control the reporting process of the candidate tier structure association information from the remote UE to the gNB. Those thresholds and criteria may refer to any feature of the tier structure association information.

In some example embodiments, the remote UE may be configured to report the candidate tier structure association information depending on the proactive conditional path switch configuration received from the gNB. In one example, considering the proactive conditional path switch configuration received from the gNB includes a configuration for Cell#3 with a validity time until T end, the remote UE may not need to report on changes of the tier structure association information related to Cell#3 until T end. In another example, the remote UE may be configured by the gNB not to report the candidate tier structure association information as long as the remote UE has a preconfigured minimum number of the tier structure associations that are included in the valid proactive conditional path switch configuration received from the gNB.

In some example embodiments, the remote UE may be configured to prioritize candidate tier structures of corresponding cells with at least one of the following criteria (a)-(c) to report to the gNB. Criteria (a) may be based on the shortest paths. For example, a number of hops in MH U2N relaying for the remote UE corresponding to a tier level of the remote UE in each tier structure of the second tier structure set (the candidate tier structures) is as low as possible.

Criteria (b) may be based on a given list of cells, tracking areas, or PLMNs. Criteria (c) may be based on the highest number of neighbouring U2U relay UEs in the lower tier (k-1). That is, the remote UE prioritize candidate tier structures in which the number of discovered tier_(k-l) UEs is as high as possible for increased robustness in relay (re)selection. For example, a number of discovered relay UEs candidates in a tier level lower than the tier level of the remote UE in each tier structure of the second tier structure set is as high as possible.

In some example embodiments, the remote UE may be configured to announce itself and its candidate tier structures in form of the tier structure association information similar to a U2U relay UE described above. In case the remote UE is also a U2U relay UE, it may announce the tier structure association information as a U2U relay UE. In some example embodiments, the remote UE may determine that a configured condition for a U2N relay reselection for a path switch is met based on a notification received from at least one of the U2U relay UE(s) or the U2N relay UE in the MH relay chain serving the remote UE. The notification from the U2U relay UE may comprise an indication of a break or failure of the MH relay chain serving the remote UE at some hop in upstream, as described above for the U2U relay UE. The notification from the U2N relay UE may be similar to that specified in the current U2N relay in Rel-17 including a notification of Uu RLF or HO of the U2N relay UE.

In some example embodiments, the remote UE may send a notification to the U2U relay UE(s) and U2N relay UE in the MH relay chain serving the remote UE that it is going to perform a U2N relay reselection for a path switch to a selected one of the target cells configured for conditional path switch to MH U2N path. The notification as well as the determined U2N relay reselection for the path switch may be due to the following reasons for examples. In one example, the reason is that the remote UE may need to reselect the neighbouring U2U relay UE in the MH relay chain serving the remote UE, as SL-RSRP between them drops below a threshold and there is no U2U relay UE associated with the current serving cell and the tier structure thereof is discovered for a local U2U relay reselection but the discovered U2U relay UE(s) are associated with other cell(s) and tier structures thereof. In another example, the reason is that the remote UE may need to perform the U2N relay reselection for the path switch for a shorter path by at least a predefined minimum number of hops.

In some example embodiments, the remote UE in RRC connected state is configured to select a tier k UE of a respective tier structure and send, for example, a DCR message to the tier k UE for initiating MH U2N relay (re)selection for a conditional path switch. The DCR message includes at least the remote UE ID, Cell ID of the respective tier structure and tier level of the remote UE in the respective tier structure. The respective tier structure may be a selected one among those included in the proactive conditional path switch configuration received from the gNB. It is to be noted that when the remote UE is in RRC idle/inactive state the remote UE may be configured to select a tier k UE of a respective tier structure and send, for example, a DCR message to the tier k UE for initiating MH U2N relay selection. The respective tier structure is a selected one among those included in the candidate tier structure association information, as determined by the remote UE. In some example embodiments, the gNB may configure U2U relay UEs and remote UEs under its control (those in idle/inactive or connected state towards the gNB) using common or dedicated signalling for the above operations (via tier O UEs), including N and P parameters, rules and/or triggers for associating, announcing, determining, reporting, or notifying.

In some example embodiments, to avoid repetition, further embodiments for the gNB may be derived from those embodiments for the U2U relay UE and the remote UE above that involve interactions with the gNB. The gNB that can request the other cells or gNBs to determine their availability to support/participate in the MH U2N relay for the remote UE with proactive conditional path switch configuration, may also optionally provide configuration information/requirements of the MH U2N relay. The other gNBs may be of the cell IDs included in the report of the candidate tier structure association information received from the remote UE.

By implementing the example embodiments of FIGS. 3 A-4B, the remote UE in RRC connected state is enabled to perform U2N relay (re)selection for an inter-cell path switch to a MH U2N relaying path using a target tier structure associated with a target cell that has been proactively prepared for a conditional path switch (also considered as conditional HO at least to some extents) for the remote UE. It also enables the remote UE in RRC connected state to perform U2N relay reselection for a conditional intra-cell path switch with MH U2N relay. The remote UE in RRC connected state therefore can take advantage of the tier model, bypassing the need to discover and report U2N relay UE candidates to the gNB.

Reference is made to FIG. 5, which illustrates an example flowchart of a method 500 of U2N relay (re)selection in MH U2N relaying at a U2U terminal device in accordance with some example embodiments of the present disclosure. FIG. 5 will be described with reference to FIG.1A.

At 502, the terminal device 104 discovers one or more tier structures corresponding to one or more cells. A tier structure characterizes MH U2N relaying in the one or more cells. At 504, the terminal device 104 associates the terminal device 104 with a tier structure set among the one or more tier structures such that the terminal device 104 acts as a U2U relay UE in the tier structure set. At 506, the terminal device 104 announces information on the tier structure set associated with the terminal device 104. For each tier structure in the tier structure set, the information comprises a cell ID of a cell corresponding to the tier structure, a tier level of the terminal device 104 in the tier structure.

In some example embodiments, the terminal device 104 may associate the terminal device 104 with the tier structure set among the one or more tier structures based on at least one of the following: (i) a maximum number of tier structures the terminal device is allowed to associate with; (ii) the tier level of the terminal device in each tier structure of the tier structure set is as low as possible; (iii) a given list of cells; (iv) a given list of tracking areas; (v) a given list of PLMNs; and (vi) a number of discovered relay UE candidates in a tier level lower than the tier level of the terminal device in each tier structure of the tier structure set is as high as possible.

In some example embodiments, the information for each tier structure in the tier structure set further may comprise a number of discovered relay UE candidates in a tier level lower than the tier level of the terminal device 104 in the tier structure.

In some example embodiments, the information for each tier structure in the tier structure set further may comprise an indication indicating whether the terminal device 104 is participating in at least one MH relay connection as either a relay UE or a remote UE.

In some example embodiments, the terminal device 104 may announce the information using configured resources independent from or common to the tier structure set or dependent on at least one tier structure in the tier structure set.

In some example embodiments, the terminal device 104 may select at least one tier structure in the tier structure set of which the configured resources are used by the terminal device 104 to announce the information. The selecting may comprise at least one of the following: (i) selecting the at least one tier structure on per announcement basis; (ii) selecting different tier structures for successive announcements in a round-robin manner; (iii) selecting a tier structure with a lowest number of discovered relay UEs in a tier level higher than the tier level of the terminal device 104; or (iv) selecting a tier structure with a highest number of discovered remote UEs in a tier level higher than the tier level of terminal device 104.

In some example embodiments, the terminal device 104 may select a time interval among multiple time intervals for announcing the information based on whether the tier level of the terminal device 104 is odd or even in the tier structure corresponding to the announcement. The terminal device 104 may announce the information in the selected time interval.

In some example embodiments, the terminal device 104 may adjust at least one of a frequency, a transmit range or a power level for transmitting the announcement based on a number of discovered relay UEs and/or remote UEs in a tier level higher than the tier level of the terminal device 104.

In some example embodiments, the terminal device 104 may discover at least one relay UE. The discovery may comprise receiving from the at least one relay UE information on associated tier structures of the at least one relay. The terminal device 104 may discover the one or more tier structures based on the information on associated tier structures of the at least one relay UE.

In some example embodiments, the information for each tier structure in the tier structure set may further comprise a list of U2N relay UE candidates. In some example embodiments, the terminal device 104 may select a discovered relay UE candidate in a tier level lower than the tier level of the the terminal device 104 in a tier structure of the tier structure set. The terminal device 104 may forward a communication request to the discovered relay UE candidate. The communication request may be received from either a remote UE or a relay UE in a tier level higher than the tier level of the terminal device 104.

In some example embodiments, the selection of the discovered relay UE candidate may be based on at least one of a cell ID, a first relay UE ID, or a second relay UE ID indicated in the communication request. The cell ID may be selected by the remote UE, the first relay UE ID may be selected by the remote UE, and the second relay UE ID may be deselected by the remote UE.

In some example embodiments, the terminal device 104 may detect a failure in a MH relay connection between a remote UE and a U2N relay UE being served by the terminal device 104. The terminal device 104 may notify, at least one of the remote UE or the U2N relay UE of the failure. Reference is made to FIG. 6, which illustrates an example flowchart of a method 600 of U2N (re)relay selection in MH U2N relaying at a remote terminal device in accordance with some example embodiments of the present disclosure. FIG. 6 will be described with reference to FIG.1A.

At 602, the terminal device 102 receives, from at least one U2U relay UE discovered by the terminal device 102 acting as a remote UE in MH U2N relaying, at least one first information on at least one first tier structure set associated with the at least one U2U relay UE. The at least one first tier structure set corresponds to at least one first cell set and characterizes MH U2N relaying in the at least one first cell set. At 604, the terminal device 102 determines, based on the at least one first information, second information on a second tier structure set associated with the terminal device 102. The second tier structure set corresponds to a second cell set which is a subset of the at least one first cell set. At 606, the terminal device 102 transmits the second information to a network device 108. At 608, the terminal device 102 receives, from the network device 108, a configuration for a conditional path switch in the MH U2N relaying for the terminal device 102. The configuration is indicative of at least one target cell for the conditional path switch from the second cell set.

In some example embodiments, the terminal device 102 may determine to perform a U2N relay (re)selection for a path switch to a target cell of the at least one target cell configured for the conditional path switch based on a satisfaction of at least one condition. The terminal device 102 may perform the U2N relay (re)selection for the path switch to the target cell.

In some example embodiments, the terminal device 102 may transmit the second information by transmitting the second information to the network device 108 based on determining that a number of hops in the MH U2N relaying for the terminal device 102 is above a threshold.

In some example embodiments, the terminal device 102 may transmit the second information periodically. The periodicity may be based on the number of hops in the MH U2N relaying for the terminal device 102.

In some example embodiments, the terminal device 102 may transmit the second information by transmitting the second information in response to a change to the second information. In some example embodiments, the terminal device 102 may determine the second tier structure set with at least one of the following criteria: (i) a number of hops in MH U2N relaying for the terminal device 102 corresponding to a tier level of the terminal device 102 in each tier structure of the second tier structure set is as low as possible; (ii) a given list of cells; (iii) a given list of PLMNs; (iv) a number of discovered relay UEs candidates in a tier level lower than the tier level of the terminal device 102 in each tier structure of the second tier structure set is as high as possible.

In some example embodiments, the terminal device 102 may determine that a condition for a U2N relay reselection for a path switch is met based on a notification received from at least one of relay UE in the MH U2N relaying for the terminal device 102.

In some example embodiments, the terminal device 102 may transmit a notification to at least one of relay UE in the MH U2N relaying for the terminal device 102. The notification may indicate that the terminal device 102 is going to perform a U2N relay reselection for a path switch to a target cell of the at least one target cell configured for the conditional path switch.

In some example embodiments, the terminal device 102 may generate a communication request message comprising at least one of the following: (i) a cell ID selected, by the terminal device 102, among the second cell set or among the at least one target cell for a relay UE (re)selection; (ii) a tier level of the terminal device 102 in a tier structure corresponding to the cell ID; (iii) a first relay UE ID selected for the relay UE (re)selection; or (iv) a second relay UE ID excluded from the relay UE (re) sei ection. The terminal device 102 may transmit the communication request message to a relay UE in a tier level lower than the tier level of the terminal device 102.

Reference is made to FIG. 7, which illustrates an example flowchart of a method 700 of U2N relay (re)selection in MH U2N relaying at a network device in accordance with some example embodiments of the present disclosure. FIG. 7 will be described with reference to FIG.1A.

At 702, the network device 108 receives, from a remote UE, information on a tier structure set associated with the remote UE. The tier structure set corresponds to a cell set and characterizes MH U2N relaying in the cell set. At 704, the network device 108 determines, based on the received information, a configuration for a conditional path switch in the MH U2N relaying for the remote UE. The configuration is indicative of at least one target cell for the conditional path switch selected from the cell set. At 706, the network device 108 transmits the configuration to the remote UE.

By implementing the example embodiments of methods 500-700, the remote UE in RRC connected state can be enabled to perform U2N relay (re)selection for an inter-cell path switch to a MH U2N relaying path using a target tier structure associated with a target cell that has been proactively prepared for a conditional path switch (conditional HO) for the remote UE. It also enables the remote UE in RRC connected state to perform U2N relay reselection for a conditional intra-cell path switch with MH U2N relay. The remote UE in RRC connected state therefore can take advantage of the tier model, bypassing the need to discover and report U2N relay UE candidates to the gNB.

In some example embodiments, an apparatus capable of performing the method 500 (for example, the terminal device 104) may comprise means for performing the respective steps of the method 500. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

In some example embodiments, the apparatus may comprise means for discovering, at a terminal device, one or more tier structures corresponding to one or more cells, wherein a tier structure characterizes MH U2N relaying in the one or more cells; means for associating the terminal device with a tier structure set among the one or more tier structures such that the terminal device acts as a U2U relay UE in the tier structure set; and means for announcing information on the tier structure set associated with the terminal device, wherein for each tier structure in the tier structure set, the information comprises a cell ID of a cell corresponding to the tier structure, a tier level of the terminal device in the tier structure.

In some example embodiments, the means for associating the terminal device with a tier structure set among the one or more tier structures may associate the terminal device with the tier structure set among the one or more tier structures based on at least one of the following: (i) a maximum number of tier structures the terminal device is allowed to associate with; (ii) the tier level of the terminal device in each tier structure of the tier structure set is as low as possible; (iii) a given list of cells; (iv) a given list of tracking areas; (v) a given list of PLMNs; and (vi) a number of discovered relay UE candidates in a tier level lower than the tier level of the terminal device in each tier structure of the tier structure set is as high as possible. In some example embodiments, the information for each tier structure in the tier structure set further may comprise a number of discovered relay UE candidates in a tier level lower than the tier level of the terminal device in the tier structure.

In some example embodiments, the apparatus may comprise means for announce the information using configured resources independent from or common to the tier structure set or dependent on at least one tier structure in the tier structure set.

In some example embodiments, the apparatus may comprise means for selecting at least one tier structure in the tier structure set of which the configured resources are used by the terminal device to announce the information. The means for selecting the at least one tier structure may comprise at least one of the following: (i) means for selecting the at least one tier structure on per announcement basis; (ii) means for selecting different tier structures for successive announcements in a round-robin manner; (iii) means for selecting a tier structure with a lowest number of discovered relay UEs in a tier level higher than the tier level of the terminal device; or (iv) means for selecting a tier structure with a highest number of discovered remote UEs in a tier level higher than the tier level of terminal device.

In some example embodiments, the apparatus may comprise means for selecting a time interval among multiple time intervals for announcing the information based on whether the tier level of the terminal device is odd or even in the tier structure corresponding to the announcement; and means for announce the information in the selected time interval.

In some example embodiments, the apparatus may comprise means for adjusting at least one of a frequency, a transmit range or a power level for transmitting the announcement based on a number of discovered relay UEs and/or remote UEs in a tier level higher than the tier level of the terminal device. In some example embodiments, the apparatus may comprise means for discovering at least one relay UE. The means for discovering at least one relay UE may comprises means for receiving from the at least one relay UE information on associated tier structures of the at least one relay; and means for discovering the one or more tier structures based on the information on associated tier structures of the at least one relay UE.

In some example embodiments, the information for each tier structure in the tier structure set may further comprise a list of U2N relay UE candidates.

In some example embodiments, the apparatus may comprise means for selecting a discovered relay UE candidate in a tier level lower than the tier level of the the terminal device in a tier structure of the tier structure set; and means for forwarding a communication request to the discovered relay UE candidate. The communication request may be received from either a remote UE or a relay UE in a tier level higher than the tier level of the terminal device.

In some example embodiments, the apparatus may comprise means for detecting a failure in a MH relay connection between a remote UE and a U2N relay UE being served by the terminal device; and means for notifying, at least one of the remote UE or the U2N relay UE of the failure.

In some example embodiments, the apparatus may further comprise means for performing other steps in some example embodiments of the method 500. In some example embodiments, the means comprises at least one processor and at least one memory including computer program code, the at least one memory and computer program code configured to, with the at least one processor, cause the performance of the apparatus.

In some example embodiments, an apparatus capable of performing the method 600 (for example, the terminal device 102) may comprise means for performing the respective steps of the method 600. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

In some example embodiments, the apparatus may comprise means for receiving, at a terminal device, from at least one U2U relay UE discovered by the terminal device acting as a remote UE in MH U2N relaying, at least one first information on at least one first tier structure set associated with the at least one U2U relay UE, wherein the at least one first tier structure set corresponds to at least one first cell set and characterizes MH U2N relaying in the at least one first cell set; means for determining, based on the at least one first information, second information on a second tier structure set associated with the terminal device, wherein the second tier structure set corresponds to a second cell set which is a subset of the at least one first cell set; means for transmitting the second information to a network device; and means for receiving, from the network device, a configuration for a conditional path switch in the MH U2N relaying for the terminal device, wherein the configuration is indicative of at least one target cell for the conditional path switch from the second cell set.

In some example embodiments, the apparatus may comprise means for determining to perform a U2N relay (re)selection for a path switch to a target cell of the at least one target cell configured for the conditional path switch based on a satisfaction of at least one condition; and means for performing the U2N relay (re)selection for the path switch to the target cell.

In some example embodiments, the means for transmitting the second information may comprise means for transmitting the second information to the network device based on determining that a number of hops in the MH U2N relaying for the terminal device is above a threshold.

In some example embodiments, the means for transmitting the second information may transmit the second information periodically. The periodicity may be based on the number of hops in the MH U2N relaying for the terminal device.

In some example embodiments, the means for transmitting the second information may comprise means for transmitting the second information in response to a change to the second information. In some example embodiments, the apparatus may comprise means for determining the second tier structure set with at least one of the following criteria: (i) a number of hops in MH U2N relaying for the terminal device 102 corresponding to a tier level of the terminal device 102 in each tier structure of the second tier structure set is as low as possible; (ii) a given list of cells; (iii) a given list of PLMNs; (iv) a number of discovered relay UEs candidates in a tier level lower than the tier level of the terminal device 102 in each tier structure of the second tier structure set is as high as possible.

In some example embodiments, the apparatus may comprise means for determining that a condition for a U2N relay reselection for a path switch is met based on a notification received from at least one of relay UE in the MH U2N relaying for the terminal device.

In some example embodiments, the apparatus may comprise means for transmitting a notification to at least one of relay UE in the MH U2N relaying for the terminal device. The notification may indicate that the terminal device is going to perform a U2N relay reselection for a path switch to a target cell of the at least one target cell configured for the conditional path switch.

In some example embodiments, the apparatus may comprise means for generating a communication request message comprising at least one of the following: (i) a cell ID selected, by the terminal device, among the second cell set or among the at least one target cell for a relay UE (re)selection; (ii) a tier level of the terminal device in a tier structure corresponding to the cell ID; (iii) a first relay UE ID selected for the relay UE (re)selection; or (iv) a second relay UE ID excluded from the relay UE (re) sei ection. The terminal device may transmit the communication request message to a relay UE in a tier level lower than the tier level of the terminal device, the apparatus may comprise means for transmitting the communication request message to a relay UE in a tier level lower than the tier level of the terminal device.

In some example embodiments, the apparatus may further comprise means for performing other steps in some example embodiments of the method 600. In some example embodiments, the means comprises at least one processor and at least one memory including computer program code, the at least one memory and computer program code configured to, with the at least one processor, cause the performance of the apparatus. In some example embodiments, an apparatus capable of performing the method 700 (for example, the network device 108) may comprise means for performing the respective steps of the method 700. The means may be implemented in any suitable form. For example, the means may be implemented in a circuitry or software module.

In some example embodiments, the apparatus may comprise means for receiving, at a network device, from a remote UE, information on a tier structure set associated with the remote UE, wherein the tier structure set corresponds to a cell set and characterizes MH U2N relaying in the cell set; means for determining, based on the received information, a configuration for a conditional path switch in the MH U2N relaying for the remote UE, wherein the configuration is indicative of at least one target cell for the conditional path switch selected from the cell set; and means for transmitting the configuration to the remote UE.

In some example embodiments, the apparatus may further comprise means for performing other steps in some example embodiments of the method 700. In some example embodiments, the means comprises at least one processor and at least one memory including computer program code, the at least one memory and computer program code configured to, with the at least one processor, cause the performance of the apparatus.

Reference is made to FIG. 8, which illustrates an example simplified block diagram of a device that is suitable for implementing embodiments of the present disclosure. The device 800 may be provided to implement the communication device, for example the terminal device 102 or 104 as shown in FIG. 1A. As shown, the device 800 includes one or more processors 810, one or more memories 820 may couple to the processor 810, and one or more communication modules 840 may couple to the processor 810.

The communication module 840 is for bidirectional communications. The communication module 840 has at least one antenna to facilitate communication. The communication interface may represent any interface that is necessary for communication with other network elements, for example the communication interface may be wireless or wireline to other network elements, or software based interface for communication.

The processor 810 may be of any type suitable to the local technical network and may include one or more of the following: general purpose computers, special purpose computers, microprocessors, digital signal processors (DSPs) and processors based on multicore processor architecture, as non-limiting examples. The device 800 may have multiple processors, such as an application specific integrated circuit chip that is slaved in time to a clock which synchronizes the main processor.

The memory 820 may include one or more non-volatile memories and one or more volatile memories. Examples of the non-volatile memories include, but are not limited to, a read only memory (ROM) 824, an electrically programmable read only memory (EPROM), a flash memory, a hard disk, a compact disc (CD), a digital video disk (DVD), and other magnetic storage and/or optical storage. Examples of the volatile memories include, but are not limited to, a random access memory (RAM) 822 and other volatile memories that will not last in the power-down duration.

A computer program 830 includes computer executable instructions that are executed by the associated processor 810. The program 830 may be stored in the ROM 824. The processor 810 may perform any suitable actions and processing by loading the program 830 into the RAM 822.

The embodiments of the present disclosure may be implemented by means of the program so that the device 800 may perform any process of the disclosure as discussed with reference to FIG. 2 to FIG. 7. The embodiments of the present disclosure may also be implemented by hardware or by a combination of software and hardware.

In some example embodiments, the program 830 may be tangibly contained in a computer readable medium which may be included in the device 800 (such as in the memory 820) or other storage devices that are accessible by the device 800. The device 800 may load the program 830 from the computer readable medium to the RAM 822 for execution. The computer readable medium may include any types of tangible non-volatile storage, such as ROM, EPROM, a flash memory, a hard disk, CD, DVD, and the like. FIG. 9 shows an example of the computer readable medium 900 in form of CD or DVD. The computer readable medium has the program 830 stored thereon.

Generally, various embodiments of the present disclosure may be implemented in hardware or special purpose circuits, software, logic or any combination thereof. Some aspects may be implemented in hardware, while other aspects may be implemented in firmware or software which may be executed by a controller, microprocessor or other computing device. While various aspects of embodiments of the present disclosure are illustrated and described as block diagrams, flowcharts, or using some other pictorial representations, it is to be understood that the block, apparatus, system, technique or method described herein may be implemented in, as non-limiting examples, hardware, software, firmware, special purpose circuits or logic, general purpose hardware or controller or other computing devices, or some combination thereof.

The present disclosure also provides at least one computer program product tangibly stored on a non-transitory computer readable storage medium. The computer program product includes computer-executable instructions, such as those included in program modules, being executed in a device on a target real or virtual processor, to carry out any of the methods 500 to 700 as described above with reference to FIG. 5 or FIG. 7. Generally, program modules include routines, programs, libraries, objects, classes, components, data structures, or the like that perform particular tasks or implement particular abstract data types. The functionality of the program modules may be combined or split between program modules as desired in various embodiments. Machine-executable instructions for program modules may be executed within a local or distributed device. In a distributed device, program modules may be located in both local and remote storage media.

Program code for carrying out methods of the present disclosure may be written in any combination of one or more programming languages. These program codes may be provided to a processor or controller of a general purpose computer, special purpose computer, or other programmable data processing apparatus, such that the program codes, when executed by the processor or controller, cause the functions/operations specified in the flowcharts and/or block diagrams to be implemented. The program code may execute entirely on a machine, partly on the machine, as a stand-alone software package, partly on the machine and partly on a remote machine or entirely on the remote machine or server.

In the context of the present disclosure, the computer program codes or related data may be carried by any suitable carrier to enable the device, apparatus or processor to perform various processes and operations as described above. Examples of the carrier include a signal, computer readable medium, and the like. The computer readable medium may be a computer readable signal medium or a computer readable storage medium. A computer readable medium may include but not limited to an electronic, magnetic, optical, electromagnetic, infrared, or semiconductor system, apparatus, or device, or any suitable combination of the foregoing. More specific examples of the computer readable storage medium would include an electrical connection having one or more wires, a portable computer diskette, a hard disk, a random access memory (RAM), a read-only memory (ROM), an erasable programmable read-only memory (EPROM or Flash memory), an optical fiber, a portable compact disc read-only memory (CD-ROM), an optical storage device, a magnetic storage device, or any suitable combination of the foregoing. The term “non- transitory,” as used herein, is a limitation of the medium itself (i.e., tangible, not a signal) as opposed to a limitation on data storage persistency (e.g., RAM vs. ROM).

Further, while operations are depicted in a particular order, this should not be understood as requiring that such operations be performed in the particular order shown or in sequential order, or that all illustrated operations be performed, to achieve desirable results. In certain circumstances, multitasking and parallel processing may be advantageous. Likewise, while several specific implementation details are contained in the above discussions, these should not be construed as limitations on the scope of the present disclosure, but rather as descriptions of features that may be specific to particular embodiments. Certain features that are described in the context of separate embodiments may also be implemented in combination in a single embodiment. Conversely, various features that are described in the context of a single embodiment may also be implemented in multiple embodiments separately or in any suitable sub-combination.

Although the present disclosure has been described in languages specific to structural features and/or methodological acts, it is to be understood that the present disclosure defined in the appended claims is not necessarily limited to the specific features or acts described above. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.

Claims

CLAIMS:

1. A terminal device comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the terminal device at least to: discover one or more tier structures corresponding to one or more cells, wherein a tier structure characterizes multi-hop (MH) UE-to-Network (U2N) relaying in the one or more cells; associate the terminal device with a tier structure set among the one or more tier structures such that the terminal device acts as a UE-to-UE (U2U) relay UE in the tier structure set; and announce information on the tier structure set associated with the terminal device, wherein for each tier structure in the tier structure set, the information comprises a cell identifier (ID) of a cell corresponding to the tier structure, a tier level of the terminal device in the tier structure.

2. The terminal device of claim 1, wherein the terminal device is further caused to associate the terminal device with the tier structure set among the one or more tier structures based on at least one of the following: a maximum number of tier structures the terminal device is allowed to associate with; the tier level of the terminal device in each tier structure of the tier structure set; a given list of cells; a given list of tracking areas; a given list of public land mobile networks (PLMNs); or a number of discovered relay UE candidates in a tier level lower than the tier level of the terminal device in each tier structure of the tier structure set.

3. The terminal device of claim 1 or 2, wherein the information for each tier structure in the tier structure set further comprises a number of discovered relay UE candidates in a tier level lower than the tier level of the terminal device in the tier structure.

4. The terminal device of any of claims 1-3, wherein the information for each tier structure in the tier structure set further comprises an indication indicating whether the terminal device is participating in at least one MH relay connection as either a relay UE or a remote UE.

5. The terminal device of any of claims 1-4, wherein the terminal device is further caused to: announce the information using configured resources independent from or common to the tier structure set or dependent on at least one tier structure in the tier structure set.

6. The terminal device of any of claims 1-5, wherein the terminal device is further caused to: select at least one tier structure in the tier structure set of which the configured resources are used by the terminal device to announce the information, wherein the selecting comprises at least one of the following: selecting the at least one tier structure on per announcement basis; selecting different tier structures for successive announcements in a round-robin manner; selecting a tier structure with a lowest number of discovered relay UEs in a tier level higher than the tier level of the terminal device; or selecting a tier structure with a highest number of discovered remote UEs in a tier level higher than the tier level of terminal device.

7. The terminal device of any of claims 1-6, wherein the terminal device is further caused to: select a time interval among multiple time intervals for announcing the information based on whether the tier level of the terminal device is odd or even in the tier structure corresponding to the announcement; and announce the information in the selected time interval.

8. The terminal device of any of claims 1-7, wherein the terminal device is further caused to: adjust at least one of a frequency, a transmit range or a power level for transmitting the announcement based on a number of discovered relay UEs and/or remote UEs in a tier level higher than the tier level of the terminal device.

9. The terminal device of any of claims 1-8, wherein the terminal device is further caused to: discover at least one relay UE, wherein the discovery comprises receiving from the at least one relay UE information on associated tier structures of the at least one relay; and discover the one or more tier structures based on the information on associated tier structures of the at least one relay UE.

10. The terminal device of any of claims 1-9, wherein the information for each tier structure in the tier structure set further comprises a list of U2N relay UE candidates.

11. The terminal device of claims 1-10, wherein the terminal device is further caused to: select a discovered relay UE candidate in a tier level lower than the tier level of the the terminal device in a tier structure of the tier structure set; and forward a communication request to the discovered relay UE candidate, the communication request being received from either a remote UE or a relay UE in a tier level higher than the tier level of the terminal device.

12. The terminal device of claim 11, wherein the selection of the discovered relay UE candidate is based on at least one of a cell ID, a first relay UE ID, or a second relay UE ID indicated in the communication request, wherein the cell ID is selected by the remote UE, the first relay UE ID is selected by the remote UE, and the second relay UE ID is deselected by the remote UE.

13. The terminal device of any of claims 1-12, wherein the terminal device is further caused to: detect a failure in a MH relay connection between a remote UE and a U2N relay UE being served by the terminal device; and notify, at least one of the remote UE or the U2N relay UE of the failure.

14. A terminal device comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the terminal device at least to: receive, from at least one UE-to-UE (U2U) relay UE discovered by the terminal device acting as a remote UE in multi-hop (MH) UE-to-Network (U2N) relaying, at least one first information on at least one first tier structure set associated with the at least one U2U relay UE, wherein the at least one first tier structure set corresponds to at least one first cell set and characterizes the MH U2N relaying in the at least one first cell set; determine, based on the at least one first information, second information on a second tier structure set associated with the terminal device, wherein the second tier structure set corresponds to a second cell set which is a subset of the at least one first cell set; transmit the second information to a network device; and receive, from the network device, a configuration for a conditional path switch in the MH U2N relaying for the terminal device, wherein the configuration is indicative of at least one target cell for the conditional path switch from the second cell set.

15. The terminal device of claim 14, wherein the terminal device is further caused to: determine to perform a U2N relay (re)selection for a path switch to a target cell of the at least one target cell configured for the conditional path switch based on a satisfaction of at least one condition; and perform the U2N relay (re)selection for the path switch to the target cell.

16. The terminal device of claim 14 or 15, wherein the terminal device is caused to transmit the second information by: transmitting the second information to the network device based on determining that a number of hops in the MH U2N relaying for the terminal device is above a threshold.

17. The terminal device of claim 16, wherein the terminal device is caused to transmit the second information periodically, wherein the periodicity is based on the number of hops in the MH U2N relaying for the terminal device.

18. The terminal device of claim 14 or 16, wherein the terminal device is caused to transmit the second information by: transmitting the second information in response to a change to the second information.

19. The terminal device of any of claims 14-18, wherein the terminal device is further caused to: determine the second tier structure set with at least one of the following criteria: a number of hops in the MH U2N relaying for the terminal device corresponding to a tier level of the terminal device in each tier structure of the second tier structure set; a given list of cells; a given list of tracking areas; a given list of public land mobile networks (PLMNs); or a number of discovered relay UEs candidates in a tier level lower than the tier level of the terminal device in each tier structure of the second tier structure set.

20. The terminal device of any of claims 14-19, wherein the terminal device is further caused to: determine that a condition for a U2N relay reselection for a path switch is met based on a notification received from at least one of relay UE in the MH U2N relaying for the terminal device.

21. The terminal device of any of claims 14-20, wherein the terminal device is further caused to: transmit a notification to at least one of relay UE in the MH U2N relaying for the terminal device, the notification indicating that the terminal device is going to perform a U2N relay reselection for a path switch to a target cell of the at least one target cell configured for the conditional path switch.

22. The terminal device of any of claims 14-21, wherein the terminal device is further caused to: generate a communication request message comprising at least one of the following: a cell ID selected, by the terminal device, among the second cell set or among the at least one target cell for a relay UE (re)selection; a tier level of the terminal device in a tier structure corresponding to the cell ID; a first relay UE ID selected for the relay UE (re)selection; or a second relay UE ID excluded from the relay UE (re)selection; transmit the communication request message to a relay UE in a tier level lower than the tier level of the terminal device.

23. A network device comprising: at least one processor; and at least one memory storing instructions that, when executed by the at least one processor, cause the network device at least to: receive, from a remote UE, information on a tier structure set associated with the remote UE, wherein the tier structure set corresponds to a cell set and characterizes multihop (MH) UE-to-Network (U2N) relaying in the cell set; determine, based on the received information, a configuration for a conditional path switch in the MH U2N relaying for the remote UE, wherein the configuration is indicative of at least one target cell for the conditional path switch selected from the cell set; and transmit the configuration to the remote UE.

24. A method comprising: discovering, at a terminal device, one or more tier structures corresponding to one or more cells, wherein a tier structure characterizes multi-hop (MH) UE-to-Network (U2N) relaying in the one or more cells; associating the terminal device with a tier structure set among the one or more tier structures such that the terminal device acts as a UE-to-UE (U2U) relay UE in the tier structure set; and announcing information on the tier structure set associated with the terminal device, wherein for each tier structure in the tier structure set, the information comprises a cell identifier (ID) of a cell corresponding to the tier structure, a tier level of the terminal device in the tier structure.

25. A method comprising: receiving, at a terminal device, from at least one UE-to-UE (U2U) relay UE discovered by the terminal device acting as a remote UE in multi-hop (MH) UE-to-Network (U2N) relaying, at least one first information on at least one first tier structure set associated with the at least one U2U relay UE, wherein the at least one first tier structure set corresponds to at least one first cell set and characterizes MH U2N relaying in the at least one first cell set; determining, based on the at least one first information, second information on a second tier structure set associated with the terminal device, wherein the second tier structure set corresponds to a second cell set which is a subset of the at least one first cell set; transmitting the second information to a network device; and receiving, from the network device, a configuration for a conditional path switch in the MH U2N relaying for the terminal device, wherein the configuration is indicative of at least one target cell for the conditional path switch from the second cell set.

26. A method comprising: receiving, at a network device, from a remote UE, information on a tier structure set associated with the remote UE, wherein the tier structure set corresponds to a cell set and characterizes multi-hop (MH) UE-to-Network (U2N) relaying in the cell set; determining, based on the received information, a configuration for a conditional path switch in the MH U2N relaying for the remote UE, wherein the configuration is indicative of at least one target cell for the conditional path switch selected from the cell set; and transmitting the configuration to the remote UE.

27. An apparatus comprising: means for discovering, at a terminal device, one or more tier structures corresponding to one or more cells, wherein a tier structure characterizes multi-hop (MH) UE-to-Network (U2N) relaying in the one or more cells; means for associating the terminal device with a tier structure set among the one or more tier structures such that the terminal device acts as a UE-to-UE (U2U) relay UE in the tier structure set; and means for announcing information on the tier structure set associated with the terminal device, wherein for each tier structure in the tier structure set, the information comprises a cell identifier (ID) of a cell corresponding to the tier structure, a tier level of the terminal device in the tier structure.

28. An apparatus comprising: means for receiving, at a terminal device, from at least one UE-to-UE (U2U) relay UE discovered by the terminal device acting as a remote UE in multi-hop (MH) UE-to-Network (U2N) relaying, at least one first information on at least one first tier structure set associated with the at least one U2U relay UE, wherein the at least one first tier structure set corresponds to at least one first cell set and characterizes MH U2N relaying in the at least one first cell set; means for determining, based on the at least one first information, second information on a second tier structure set associated with the terminal device, wherein the second tier structure set corresponds to a second cell set which is a subset of the at least one first cell set; means for transmitting the second information to a network device; and means for receiving, from the network device, a configuration for a conditional path switch in the MH U2N relaying for the terminal device, wherein the configuration is indicative of at least one target cell for the conditional path switch from the second cell set.

29. An apparatus comprising: means for receiving, at a network device, from a remote UE, information on a tier structure set associated with the remote UE, wherein the tier structure set corresponds to a cell set and characterizes multi-hop (MH) UE-to-Network (U2N) relaying in the cell set; means for determining, based on the received information, a configuration for a conditional path switch in the MH U2N relaying for the remote UE, wherein the configuration is indicative of at least one target cell for the conditional path switch selected from the cell set; and means for transmitting the configuration to the remote UE.

30. A non-transitory computer readable medium comprising program instructions for causing an apparatus to perform at least a method of any of claims 24-26.