CN114501414A

CN114501414A - Method for discovering relay UE, method for searching relay UE and user equipment

Info

Publication number: CN114501414A
Application number: CN202011163923.0A
Authority: CN
Inventors: 刘蕾; 刘仁茂
Original assignee: Sharp Corp
Current assignee: Sharp Corp
Priority date: 2020-10-27
Filing date: 2020-10-27
Publication date: 2022-05-13
Also published as: WO2022089318A1

Abstract

The invention provides a method for discovering a relay UE, a method for searching the relay UE and user equipment, which are executed by the user equipment UE. The method for discovering the relay UE comprises the following steps: judging whether the AS layer condition of an access layer, namely an AS layer, meets the condition; when the access stratum condition meets the condition, at least one AS layer condition message including corresponding relay type information is sent to an upper layer of the AS layer, and the AS layer condition message is used for the upper layer to determine whether to trigger a relay UE discovery process; receiving, from the upper layer, a relay UE discovery indication for triggering the relay UE discovery procedure; and performing the relay UE discovery procedure based on the relay UE discovery indication.

Description

Method for discovering relay UE, method for searching relay UE and user equipment

Technical Field

The present invention relates to the field of wireless communication technologies, and in particular, to a method for discovering a relay UE, a method for searching for a relay UE, and a corresponding user equipment, where the method is implemented by the user equipment for sidestream communication.

Background

In 6.2018, release 16 was approved based on the V2X feasibility Study Project of 5G NR networking technology (see non-patent document: RP-181480, New SID Proposal: Study on NR V2X) at the 3rd Generation Partnership Project (3 GPP) RAN #80 Congress. The NR V2X of release 16 contains the main functionality to support unicast, multicast and broadcast in both non-network overlay and network overlay scenarios.

In 12 months of 2019, RAN #86 was proposed and approved for NR Sidelink Relaying of version 17 at the same time (see non-patent document RP-193253New Study Item on NR Sidelink Relaying). The latest version of this research project is referred to non-patent literature: RP-201474reivsed SID NR sidelink relay. The research project mainly studies UE (user equipment) to network and UE to UE relay solutions for extending the coverage of sidestream based communications. One of the goals of the research project is to support discovery (discovery) models and procedures for sidestream communication relaying.

In the existing Relay architecture, a remote UE discovers a Relay UE through a discovery process, and the remote UE implements communication with a Network through the Relay UE, that is, a UE-to-Network Relay (UE-to-Network Relay). In the NR sidelink Relay research project of release 17, the discovery procedure is also used for a remote UE to discover a Relay UE and to enable communication with another remote UE through the Relay UE, i.e., UE-to-UE Relay.

The present invention discusses the problems associated with the discovery process of UE-to-UE relay and UE-to-network relay.

Disclosure of Invention

The invention aims to provide a method for rapidly and accurately determining a relay UE for sidestream communication.

According to an aspect of the present invention, there is provided a method performed by a user equipment UE for discovering a relay UE, including: judging whether the AS layer condition of an access layer, namely an AS layer, meets the condition; when the access stratum condition meets the condition, at least one AS layer condition message including the corresponding relay type information is sent to an upper layer of the AS layer, and the AS layer condition message is used for the upper layer to determine whether to trigger the relay UE discovery process; receiving, from the upper layer, a relay UE discovery indication for triggering the relay UE discovery procedure; and performing the relay UE discovery procedure based on the relay UE discovery indication.

Optionally, the relay type is UE-to-UE relay or UE-to-network relay.

Optionally, the relay UE discovery indication includes a relay type corresponding to the relay UE discovery procedure and a relay UE discovery message corresponding to the relay type, and the performing the relay UE discovery procedure based on the relay UE discovery indication includes: and when the relay UE discovery indication is received, performing discovery message transmission of the relay UE discovery message according to the relay type so as to perform the relay UE discovery process.

Optionally, the relay UE discovery indication includes a relay type corresponding to the relay UE discovery procedure, and the performing the relay UE discovery procedure based on the relay UE discovery indication includes: and when the relay UE discovery instruction is received, monitoring a relay UE discovery message according to the relay type so as to execute the relay UE discovery process.

Optionally, the method further comprises: before the discovery message transmission is executed, judging whether the current AS layer condition meets a condition, wherein the discovery message transmission is executed when the current AS layer condition meets the condition.

Optionally, the AS layer condition includes an AS layer resource configuration condition and/or an AS layer link condition, where when the AS layer condition is at least one of the following conditions, it is determined that the AS layer condition satisfies a condition: configuring resources which can be used for related data communication of a sidelink communication relay; configuring a resource capable of being used for receiving and transmitting a discovery message of a sidelink communication relay; the quality of a Uu interface wireless link meets the condition; the PC5 interface radio link quality satisfies a condition.

Optionally, when the AS layer condition satisfies a condition that includes the PC5 interface wireless link quality, obtaining a PC5 interface wireless link quality threshold configuration and a current PC5 interface wireless link quality; and determining whether the current AS layer condition satisfies a condition based on the PC5 interface radio link quality threshold and the current PC5 interface radio link quality.

Optionally, the PC5 interface radio link quality threshold comprises a first PC5 interface radio link quality threshold, and the determining whether the current AS layer condition satisfies a condition based on the PC5 interface radio link quality threshold and the current PC5 interface radio link quality comprises: when the current radio link quality is below the first PC5 interface radio link quality threshold, determining whether the current AS layer condition satisfies a condition,

optionally, the determining, by the PC5 interface radio link quality threshold including a first PC5 interface radio link quality threshold and a second PC5 interface radio link quality threshold, whether the current AS layer condition satisfies a condition includes, based on the PC5 interface radio link quality threshold and the current PC5 interface radio link quality: determining whether the current AS layer condition satisfies a condition when the current wireless link quality is below the first PC5 interface wireless link quality threshold and above a second PC5 interface wireless link quality threshold.

Optionally, the method further comprises: after discovering at least one UE capable of relaying based on the relay UE discovery indication and selecting a relay UE from the at least one UE capable of relaying, acquiring a threshold value of a sidelink communication reference signal received power between the UE and the selected relay UE; judging whether the relay UE needs to be reselected or not based on the acquired threshold value and the sidestream communication reference signal receiving power of the PC5-RRC connection between the UE and the selected relay UE; and when the judgment result is that the relay UE needs to be reselected, reselecting the relay UE from the discovered relay UE or re-executing the relay UE discovery process.

According to another aspect of the present invention, there is also provided a method performed by a user equipment UE for searching for a relay UE, including: when receiving a relay UE search indication from an upper layer of the UE, determining whether a PC5-RRC connection exists between the UE and at least one other UE with relay capability; if a PC5-RRC connection exists between the UE and the at least one other UE, determining whether the current radio link quality meets a condition; and when the current radio link quality meets a condition, performing relay UE search.

According to another aspect of the present invention, there is also provided a user equipment, including: a processor; and a memory storing instructions; wherein the instructions, when executed by the processor, perform a method according to the above.

The embodiment of the invention can enable the UE to more accurately and timely discover the relay UE, thereby achieving the purpose of expanding the sidelink communication coverage.

Drawings

Fig. 1 is a schematic diagram for explaining UE-to-UE relay according to the present invention.

Fig. 2 is a flowchart of a method of discovering a relay UE according to embodiment 1 of the present invention.

Fig. 3 is a flowchart of a method of discovering a relay UE according to embodiment 2 of the present invention.

Fig. 4 is a flowchart of an example of an AS layer situation determination procedure in the method of discovering a relay UE according to the present invention.

Fig. 5 is a schematic diagram for explaining a scenario of multihop relay related to the present invention.

Fig. 6 is a block diagram schematically illustrating a structure of a user equipment UE according to the present invention.

Detailed Description

The invention is described in detail below with reference to the figures and the detailed description. It should be noted that the present invention should not be limited to the specific embodiments described below. In addition, for the sake of brevity, detailed descriptions of well-known technologies not directly related to the present invention are omitted to prevent confusion of understanding of the present invention.

Some terms related to the present invention are described below, and specific meanings of the terms are described in the latest standard specification of 3GPP, such as TS38.300, TS38.331, TS36.300, TS36.331, and the like. Unless otherwise indicated, all terms referred to in the present invention have the following meanings.

UE: user Equipment

NR: new Radio New generation wireless technology

RRC: radio Resource Control

RRC _ CONNECTED: RRC connected state

RRC _ INACTIVE: RRC inactive state

RRC _ IDLE: RRC idle state

RAN: radio Access Network, Radio Access stratum

Sidelink communication

Sidelink Control Information, sideline communication Control Information

Reference Signal Receiving Power, Reference Signal Receiving Power

Physical Sidelink Control Channel, Physical Sidelink communication Control Channel

AS Access Stratum

PDCCH: physical downlink control channel, Physical downlink control channel

Bandwidth Part, Bandwidth fragment, BWP

DCI Downlink Control Information

DL: Downlink, Downlink

Information Element, Information Element

MIB Master Information Block, Master Information Block

New Radio, New Radio

SIB System Information Block

DCI Downlink Control Information

In the invention, a network, a base station and a RAN can be used interchangeably, and the network can be a long term evolution LET network, a New radio access technology (New RAT, NR) network, an enhanced long term evolution eLTE network or other networks defined in subsequent evolution versions of 3 GPP.

In the present invention, the UE may refer to an NR device supporting an NR Sidelink relay function described in the background art, or may refer to another type of NR device or an LTE device.

The PC5 interface is an interface for control plane and user plane Sidelink communications between UEs. For Sidelink unicast, the PC5-RRC connection is an AS layer logical connection between a pair of source layer two IDs and target layer two IDs. A PC5 unicast link establishment would correspond to a PC5-RRC connection establishment.

Fig. 1 is a diagram for illustrating UE-to-UE relay. As shown in fig. 1, the UE-to-UE relay includes remote UEs on the left and right sides (the left UE may also be referred to as a source-side remote UE, and the right UE may also be referred to as a target-side remote UE), and a relay UE in the middle. The remote UE and the relay UE are connected through a PC5 interface respectively. Because the two remote UEs are far away from each other or the communication environment is not good, the relay UE needs to relay and forward signaling and data between the two remote UEs.

The scenario of UE-to-UE relay includes:

1) in the coverage range: both the remote UEs (i.e., the source-side UE and the destination-mapping UE) and the relay UE are in coverage;

2) outside the coverage area: both the remote UEs (i.e., the source-side UE and the destination-mapping UE) and the relay UE are out of coverage;

3) partial covering: of the two remote UEs and the relay UE, at least one UE is in coverage and at least one UE is out of coverage.

The coverage refers to the coverage of the base station.

There are two modes of discovery in the Sidelink relay, mode a and mode B:

mode A is equivalent to "I am here! ".

Two roles are defined therein: notifying the UE and monitoring the UE. Informing the UE to broadcast the discovery notice periodically, and monitoring the UE to read and process the discovery notice.

Pattern B corresponds to "who is there? "or" do you there? ".

Two roles are also defined: a discovery UE and a discoveree UE. The discovering UE sends a discovery request to which the discovering UE responds.

In the UE-to-Network Relay prior art, whether a UE can initiate or process a discovery message as a remote UE or a Relay UE can be determined according to radio conditions (including radio configuration and radio interface status). The AS layer notifies the upper layer of the satisfaction of the radio conditions. The upper layer may determine to trigger the discovery procedure in combination with information such AS authentication of the UE, and configure the AS layer to send or receive the discovery message.

After the introduction of the UE-to-UE Relay, the flows and processes of the AS layer and the upper layer of the remote UE and the Relay UE may be different for the Relay from the UE to the UE and the Relay from the UE to the network.

In the following, several embodiments of the discovery procedure of the present invention for UE-to-Network Relay and UE-to-UE Relay are described in detail. The embodiment of the invention can enable the UE to more accurately and timely discover the relay UE, thereby achieving the purpose of expanding the sidelink communication coverage.

Example 1

In embodiment 1 of the present invention, the steps performed for the user equipment UE include: and (101) and (103).

In step 101, a UE with sidelink communication relay discovery capability determines whether the AS layer condition satisfies a condition.

-optionally, the sidestream Relay discovery capable UE is a Remote UE in a UE-to-UE Relay;

-optionally, the sidelink communications Relay discovery capable UE is a Remote UE of a UE-to-Network Relay;

-optionally, the sidestream Relay discovery capable UE is a Relay UE of a UE-to-UE Relay;

-optionally, the UE with sidelink communication Relay discovery capability is a Relay UE of a UE-to-Network Relay.

The AS layer case includes one or more of:

-AS layer resource configuration;

AS layer link case.

The AS layer link case may be a radio link case or a PC5-RRC connected link case.

The conditions satisfied include one or more of the following:

-configuring resources available for Sidelink relay related data communication;

-configuring resources available for Sidelink relay discovery message reception and transmission;

-the Uu interface radio link quality fulfils a condition;

the radio link quality of the PC5 interface fulfils the condition.

The resource configuration and link quality conditions may be configured by RRC-specific signaling or system messages, or pre-configured in a protocol.

In step 103, when the AS layer condition satisfies the condition, one or more of the following AS layer conditions are notified to the upper layer.

-notifying upper layer UE-to-UE Relay of AS layer conditions;

-notifying the upper layer UE of the AS layer situation of the-to-Network Relay.

Example 2

In embodiment 2 of the present invention, the steps performed for the user equipment UE include: steps 201 and 203.

In this embodiment, the UE performs discovery message transmission according to the relay type configured by the upper layer.

-optionally, the first Relay type is UE-to-UE Relay;

optionally, the first Relay type is a UE-to-Network Relay.

Wherein the discovery message transmission comprises one or more of;

-discovery message listening;

-a discovery message notification;

-a discovery message request;

-a discovery message response.

Specifically, in step 201, the UE determines that the current AS layer condition satisfies the condition.

Then, in step 203, when it is determined that the current AS layer condition satisfies the condition, the AS layer configuration bottom layer of the UE performs discovery message transmission.

The AS layer case includes one or more of:

-AS layer resource configuration;

AS layer link case.

The conditions satisfied include one or more of the following:

-configuring resources available for Sidelink relay related data communication;

-the radio link quality of the Uu interface fulfils a condition;

the radio link quality of the PC5 interface fulfils the condition.

Example 3

In embodiment 3 of the present invention, the steps of embodiment 1 and embodiment 2 may be combined together, all or part of the steps in embodiment 1 and embodiment 2 may be included, and the execution order may be arbitrarily combined. Such as but not limited to: 101, 103, 201, 203; or 101, 103, 201, etc.

Example 4

In embodiment 4 of the present invention, the steps performed for the user equipment UE include: steps 401 and 403.

For UE-to-UE Relay, the UE judges the AS layer condition in the process of discovering message transmission.

In step 401, a user equipment UE obtains a radio link quality threshold.

Optionally, the radio link quality threshold may comprise a first radio link quality threshold.

Optionally, the radio link quality thresholds may include a first radio link quality threshold and a second radio link quality threshold.

The quality of the wireless link is as follows:

optionally, the radio link quality may refer to RSRP or RSRQ measured on the PC5 interface;

optionally, the radio link quality may refer to the maximum number of retransmissions of the PC5 interface RLC layer data block;

optionally, the radio link quality may refer to RSRP measured for the PC5-RRC connection;

optionally, the radio link quality may refer to the maximum number of retransmissions of the RLC layer data block of the PC5-RRC connection;

optionally, the radio link quality may refer to the RSRP or RSRQ of sildelink.

The first threshold may be obtained by pre-configuration, or RRC dedicated signaling, or system messages.

The user equipment UE may be a remote UE or a UE-to-UE relay UE.

Optionally, in step 401, the UE obtains a second radio link quality threshold, and the pointing meaning and configuration method of the radio link quality are the same as the first radio link quality threshold.

In step 403, the UE determines whether the current AS layer condition satisfies a condition based on the radio link quality threshold.

Optionally, the UE compares the current radio link quality with the first radio link quality threshold, and determines whether a condition is satisfied, where the satisfied condition may be:

-the current radio link quality is below the first radio link quality threshold.

Here the UE may be a remote UE; or in a scenario supporting multi-hop, it may also be a relay UE for connecting to the next hop. When the UE has wireless connection with the target remote UE but the quality of a wireless link is too low, the UE and the target remote UE cannot perform high-quality communication, and a relay needs to be found to provide a relay service so as to improve the communication quality; otherwise relay service may not be required.

Optionally, in step 403, the UE simultaneously compares the current radio link quality with the first radio link quality threshold and the second quality threshold, and the condition that is satisfied may be: the current radio link quality is above the second radio link quality threshold and below the first radio link quality threshold.

Here, the UE may be a relay UE. If the quality of the wireless link is too low, the quality of the link between the relay UE and the target remote UE is poor, and good relay service quality cannot be provided, so that relay service is needed to improve the communication quality; meanwhile, if the quality of the radio link is too high, the relay UE may be too close to the target-side remote UE to establish a good-quality connection with the source-side remote UE, and at this time, even if the relay service is established, the relay service cannot provide a good quality of relay service.

Example 5

If the upper layer judges that the relay UE currently selected by the UE which has obtained the relay service is not suitable to be used AS the relay UE any more, or a new relay UE is needed to be found to provide the relay service according to the service requirement, the upper layer may trigger the AS layer to search the relay UE, so AS to instruct the AS layer of the UE to execute the search process of the relay UE. The discovery process includes two processes of receiving and monitoring the discovery message, and the search relay UE may perform a monitoring process on the discovery message based on the discovery process, and the AS layer may select or reselect the relay UE according to the radio link quality monitored by the discovery process. In embodiment 5 of the present invention, for a UE-to-UE relay, when a UE (may be a remote UE; in a scenario supporting multi-hop, it may also be a relay UE for connecting to a next hop) is configured by an upper layer and needs to search for the relay UE, if there is a PC5-RRC connection between the UE and a target remote UE, the UE determines whether the current radio link quality satisfies a condition, and if the condition is satisfied, performs a relay UE search. Wherein the radio link quality is the same as described in embodiment 4. The determination of whether the condition is satisfied may be according to the first radio quality threshold or the second radio quality threshold in embodiment 4.

Fig. 5 is a schematic diagram for explaining a scenario of multihop relay related to the present invention. As shown in fig. 5, the dashed circles C1, C2, C3, and C4 represent the coverage of the remote UE 501, the

relay UEs

502, 503, respectively, and the remote UE 504. The remote UE 501 may communicate sideways with the remote UE 504 via relay services provided by the

relay UEs

502 and 503. In this scenario, if viewed from the far-end UE 501 side, the first-level relay performed by the relay UE502 on the far-end UE 501 is the first hop, and the second-level relay performed by the relay UE 503 on the far-end UE 501 is the second hop. Fig. 5 shows a scenario of 2-hop relay, but the multi-hop scenario of the present invention may be 3-hop, 4-hop, or more hop relay. Further, fig. 5 shows a case where the far-end UE and the closest relay UE are located close to the edge of each other's coverage, but the present invention is not limited thereto as long as the far-end UE and the relay UE are within each other's coverage.

Example 6

In embodiment 6 of the present invention, if a UE (may be a remote UE; in a scenario supporting multi-hop, it may also be a relay UE for connecting to the next hop) has selected a relay UE to provide a relay service, the UE acquires a threshold of sidelink RSRP, and determines whether to reselect a relay UE by comparing a measured value of sidelink RSRP of a PC5-RRC connection between the UE and the relay UE with the threshold. The threshold value may be obtained by pre-configuration, or RRC dedicated signaling, or system messages. When the threshold comparison is performed, it may be determined that the current sidelink RSRP measurement value is higher than the threshold value, or the current sidelink RSRP measurement value is lower than the threshold value, and it is determined that the condition is satisfied.

Fig. 6 is a block diagram schematically illustrating a user equipment UE according to the present invention. As shown in fig. 6, the user equipment UE 600 includes a processor 601 and a memory 602. The processor 601 may include, for example, a microprocessor, a microcontroller, an embedded processor, or the like. The memory 602 may include, for example, volatile memory (e.g., random access memory RAM), a Hard Disk Drive (HDD), non-volatile memory (e.g., flash memory), or other memory, among others. The memory 602 has stored thereon program instructions. Which when executed by the processor 601 may perform the above-described method performed by the user equipment as described in detail herein.

The program running on the apparatus according to the present invention may be a program that causes a computer to realize the functions of the embodiments of the present invention by controlling a Central Processing Unit (CPU). The program or information processed by the program may be temporarily stored in a volatile memory (such as a random access memory RAM), a Hard Disk Drive (HDD), a nonvolatile memory (such as a flash memory), or other memory system.

A program for implementing the functions of the embodiments of the present invention may be recorded on a computer-readable recording medium. The corresponding functions can be realized by causing a computer system to read the programs recorded on the recording medium and execute the programs. The term "computer system" as used herein may be a computer system embedded in the device and may include an operating system or hardware (e.g., peripheral devices). The "computer-readable recording medium" may be a semiconductor recording medium, an optical recording medium, a magnetic recording medium, a recording medium that stores a program for short-term dynamics, or any other recording medium that is readable by a computer.

Various features or functional blocks of the devices used in the above-described embodiments may be implemented or performed by circuitry (e.g., a single or multiple chip integrated circuits). Circuitry designed to perform the functions described herein may include a general purpose processor, a Digital Signal Processor (DSP), an Application Specific Integrated Circuit (ASIC), a Field Programmable Gate Array (FPGA), or other programmable logic device, discrete gate or transistor logic, discrete hardware components, or any combination thereof. A general purpose processor may be a microprocessor, but in the alternative, the processor may be any conventional processor, controller, microcontroller, or state machine. The circuit may be a digital circuit or an analog circuit. Where new integrated circuit technologies have emerged as a replacement for existing integrated circuits due to advances in semiconductor technology, one or more embodiments of the present invention may also be implemented using these new integrated circuit technologies.

Further, the present invention is not limited to the above-described embodiments. While various examples of the embodiments have been described, the present invention is not limited thereto. Fixed or non-mobile electronic devices installed indoors or outdoors may be used as terminal devices or communication devices, such as AV devices, kitchen devices, cleaning devices, air conditioners, office devices, vending machines, and other home appliances.

As above, the embodiments of the present invention have been described in detail with reference to the accompanying drawings. However, the specific configuration is not limited to the above embodiment, and the present invention includes any design modification without departing from the gist of the present invention. In addition, the present invention can be variously modified within the scope of the claims, and embodiments obtained by appropriately combining the technical means disclosed in the different embodiments are also included in the technical scope of the present invention. Further, components having the same effects described in the above embodiments may be substituted for each other.

Claims

1. A method performed by a user equipment, UE, of discovering a relay UE, comprising:

judging whether the AS layer condition of an access layer, namely an AS layer, meets the condition;

when the access stratum condition meets the condition, at least one AS layer condition message including corresponding relay type information is sent to an upper layer of the AS layer, and the AS layer condition message is used for the upper layer to determine whether to trigger a relay UE discovery process;

receiving, from the upper layer, a relay UE discovery indication for triggering the relay UE discovery procedure; and

performing the relay UE discovery procedure based on the relay UE discovery indication.

2. The method of claim 1, wherein the relay type is a UE-to-UE relay or a UE-to-network relay.

3. The method of claim 1, wherein,

the relay UE discovery indication includes a relay type corresponding to the relay UE discovery procedure and a relay UE discovery message corresponding to the relay type, and the performing the relay UE discovery procedure based on the relay UE discovery indication includes:

upon receiving the relay UE discovery indication, performing discovery message transmission of the relay UE discovery message according to the relay type to perform the relay UE discovery procedure,

alternatively, the first and second electrodes may be,

the relay UE discovery indication includes a relay type corresponding to the relay UE discovery procedure, and the performing the relay UE discovery procedure based on the relay UE discovery indication includes:

and when the relay UE discovery instruction is received, monitoring a relay UE discovery message according to the relay type so as to execute the relay UE discovery process.

4. The method of claim 3, further comprising:

before the discovery message transmission is executed, judging whether the current AS layer condition meets a condition, wherein the discovery message transmission is executed when the current AS layer condition meets the condition.

5. The method of any one of claims 1-4,

the AS layer conditions include AS layer resource configuration conditions and/or AS layer link conditions,

wherein, when the AS layer condition is at least one of the following conditions, determining that the AS layer condition satisfies a condition:

configuring resources which can be used for related data communication of a sidelink communication relay;

configuring a resource capable of being used for receiving and transmitting a discovery message of a sidelink communication relay;

the quality of a Uu interface wireless link meets the condition;

the PC5 interface radio link quality satisfies a condition.

6. The method of claim 5, wherein,

when the AS layer condition meets the condition including the PC5 interface wireless link quality, acquiring the PC5 interface wireless link quality threshold configuration and the current PC5 interface wireless link quality; and

determining whether the current AS layer condition satisfies a condition based on the PC5 interface radio link quality threshold and the current PC5 interface radio link quality.

7. The method of claim 6, wherein,

the PC5 interface radio link quality threshold comprises a first PC5 interface radio link quality threshold, and determining whether the current AS layer condition satisfies a condition based on the PC5 interface radio link quality threshold and the current PC5 interface radio link quality comprises:

when the current radio link quality is below the first PC5 interface radio link quality threshold, determining whether the current AS layer condition satisfies a condition,

or

The PC5 interface wireless link quality threshold includes a first PC5 interface wireless link quality threshold and a second PC5 interface wireless link quality threshold, and determining whether the current AS layer condition satisfies a condition based on the PC5 interface wireless link quality threshold and the current PC5 interface wireless link quality includes:

determining whether the current AS layer condition satisfies a condition when the current radio link quality is below the first PC5 interface radio link quality threshold and above a second PC5 interface radio link quality threshold.

8. The method of any of claims 1-4, further comprising:

after discovering at least one UE capable of relaying based on the relay UE discovery indication and selecting a relay UE from the at least one UE capable of relaying, acquiring a threshold value of a sidelink communication reference signal received power between the UE and the selected relay UE;

judging whether the relay UE needs to be reselected or not based on the acquired threshold value and the sidestream communication reference signal receiving power of the PC5-RRC connection between the UE and the selected relay UE; and

and when the judgment result shows that the relay UE needs to be reselected, reselecting the relay UE from the discovered relay UE or re-executing the relay UE discovery process.

9. A method performed by a user equipment, UE, of searching for a relay UE, comprising:

when receiving a relay UE search instruction from an upper layer of the UE, judging whether PC5-RRC connection exists between the UE and at least one other UE with relay capability;

if a PC5-RRC connection exists between the UE and the at least one other UE, determining whether the current radio link quality meets a condition; and

and when the current wireless link quality meets the condition, performing relay UE search.

10. A user equipment, comprising:

a processor; and

a memory storing instructions;

wherein the instructions, when executed by the processor, perform the method of any one of claims 1 to 8 or claim 9.