Method and apparatus for relay UE selection and reselection in terminal (UE)-to-UE scenario

Abstract

An embodiment of the present disclosure discloses a method and apparatus for relay UE selection and reselection in a terminal (UE)-to-UE scenario, the method including: determining a candidate relay UE based on a first selection condition for a first UE; and determining a target relay UE to be selected or reselected based on the first UE-to-candidate relay UE, the first selection condition including any one of: selecting, as the candidate relay UE, a relay UE whose sidelink communication reference signal received power (SL-RSRP) or sidelink discovery reference signal received power (SD-RSRP) satisfies a threshold condition; and selecting, as the candidate relay UE, a relay UE whose notification message or neighbor list includes the terminal identifier of the second UE and whose SL-RSRP or SD-RSRP satisfies a threshold condition. By implementing the embodiment of the present disclosure, it is possible to solve the problem of how to select and reselect a relay UE in a UE-to-UE scenario and ensure normal communication between terminal devices.

Description

[Technical Field]

[0001] The present disclosure relates to the field of communication technologies, and more particularly to a method and apparatus for relay UE selection and reselection in a terminal (UE)-to-UE scenario. [Background technology]

[0002] To support direct communication between terminal devices (also known as user equipment, or UEs), the direct connection communication (also known as sidelink, or SL) communication method has been introduced, and the interface between UEs is PC-5. Sidelink supports three transmission methods: unicast, multicast, and broadcast, depending on the correspondence between the transmitting and receiving UEs. The transmitting UE transmits sidelink control information (SCI) on the physical sidelink control channel (PSCCH) and the second-stage SCI on the physical sidelink shared channel (PSSCH). This SCI includes the resource location for data transmission and source and target identifiers. After receiving the SCI, the receiving UE determines whether to receive the corresponding data and which process to use based on the source UE and destination UE identifiers contained therein. In a unicast connection, each UE corresponds to one destination identifier; in a multicast connection, each UE may belong to one or more groups, each group corresponding to one destination identifier; and in a broadcast connection, all UEs correspond to at least one destination identifier.

[0003] A UE can communicate with a base station through the relay of another UE without directly connecting to the base station. Here, a UE not connected to a base station is called a remote UE, and a UE providing relay functionality is called a relay UE. One scenario is when UE A does not directly connect to UE B, but instead can connect to UE B through the relay of UE C. Here, UE A and UE B are remote UEs, and UE C providing relay functionality is a relay UE, and all UEs communicate via sidelink unicast. This architecture is called U2U (UE to UE, terminal to terminal) relay.

[0004] However, the related art currently lacks an effective means for relay UE selection and reselection in U2U scenarios. Summary of the Invention

[0005] An embodiment of the present disclosure provides a method and apparatus for selecting and reselecting a relay UE in a terminal (UE)-to-UE scenario, which can be used in fields such as telematics such as vehicle-to-everything (V2X) communication, long term evolution-vehicle (LTE-V), and vehicle-to-vehicle (V2V) communication, or fields such as smart driving and smart interconnected vehicles. By selecting or reselecting a target relay UE according to a relay selection condition, the problem of how to select and reselect a relay UE in a UE-to-UE (U2U) scenario can be solved, and normal communication between terminal devices can be ensured.

[0006] According to a first aspect, an embodiment of the present disclosure provides a relay UE selection and reselection method in a terminal (UE)-to-UE scenario, the method being executed by a first UE and including: determining a candidate relay UE based on a first selection condition; and determining a target relay UE to be selected or reselected based on the candidate relay UE, wherein the first selection condition includes any one of: selecting a relay UE including a terminal identifier of a second UE in a notification message or a neighbor list as the candidate relay UE, where the second UE is a target communication UE of the first UE and the first UE communicates with the second UE via the relay UE; selecting a relay UE whose sidelink communication reference signal received power (SL-RSRP) or sidelink discovery reference signal received power (SD-RSRP) satisfies a threshold condition as the candidate relay UE; and selecting a relay UE whose terminal identifier of the second UE in the notification message or the neighbor list and whose SL-RSRP or SD-RSRP satisfies a threshold condition as the candidate relay UE.

[0007] In this technical solution, the first UE selects or reselects a target relay UE based on the relay selection conditions, thereby solving the problem of how to select and reselect a relay UE in a UE-to-UE (U2U) scenario and ensuring normal communication of the terminal device.

[0008] In one implementation, the relay UEs whose SL-RSRP or SD-RSRP satisfies the threshold condition include any one of the following: a relay UE whose SL-RSRP or SD-RSRP with the first UE satisfies a first threshold condition; a relay UE whose SL-RSRP or SD-RSRP with the second UE satisfies a second threshold condition; and a relay UE whose SL-RSRP or SD-RSRP with the first UE satisfies a first threshold condition and whose SL-RSRP or SD-RSRP with the second UE satisfies a second threshold condition.

[0009] In one alternative implementation, the SL-RSRP or SD-RSRP satisfying a threshold condition includes the SL-RSRP or SD-RSRP being greater than or equal to a predefined threshold, or the SL-RSRP or SD-RSRP being greater than the predefined threshold by at least one hysteresis parameter value (hysteresis).

[0010] In one alternative implementation, the predefined thresholds include a first predefined threshold and a second predefined threshold, wherein the first predefined threshold is a lowest threshold and the second predefined threshold is a highest threshold, wherein the SL-RSRP or SD-RSRP being greater than or equal to the predefined thresholds includes the SL-RSRP or SD-RSRP being greater than or equal to the first predefined threshold and less than or equal to the second predefined threshold, and wherein the SL-RSRP or SD-RSRP being greater than the predefined thresholds by at least one hysteresis parameter value includes the SL-RSRP or SD-RSRP being greater than the first predefined threshold by at least one hysteresis parameter value and less than the second predefined threshold by at least one hysteresis parameter value.

[0011] In one implementation, the step of determining a target relay UE to be selected or reselected based on the candidate relay UEs includes, based on implementation, selecting one candidate relay UE from the candidate relay UEs as the target relay UE, or, based on implementation, selecting multiple relay UEs from the candidate relay UEs as the target relay UE.

[0012] According to a second aspect, an embodiment of the present disclosure provides another relay UE selection and reselection method in a terminal (UE)-to-UE scenario, the method being executed by a first UE, the method including: determining a candidate relay UE based on a second selection condition; and determining a target relay UE to be selected or reselected based on the candidate relay UE, wherein the second selection condition includes any one of: selecting a relay UE whose SL-RSRP or SD-RSRP between the first UE and the relay UE satisfies a first threshold condition as the candidate relay UE; and selecting a relay UE whose SL-RSRP or SD-RSRP between the first UE and the relay UE satisfies a first threshold condition and whose SL-RSRP or SD-RSRP between a second UE and the relay UE satisfies a second threshold condition as the candidate relay UE, wherein the first UE is a source remote UE in the terminal (UE)-to-UE scenario, and the second UE is a target remote UE in the terminal (UE)-to-UE scenario.

[0013] In this technical solution, the source remote UE selects or reselects a target relay UE based on the relay selection conditions of the source remote UE, thereby solving the problem of how to select and reselect a relay UE in a UE-to-UE (U2U) scenario and ensuring normal communication of the terminal device.

[0014] In one implementation, the step of determining candidate relay UEs based on the second selection condition includes the steps of: sending a discovery request message to the second UE via at least one first relay UE; receiving a discovery response message sent from at least one second relay UE, where the at least one second relay UE is a relay UE selected by the second UE from among the at least one first relay UE, the SL-RSRP or SD-RSRP between the second UE satisfying a second threshold condition; and selecting, from the at least one second relay UE, all second relay UEs whose SL-RSRP or SD-RSRP between the first UE and the second UE satisfy the first threshold condition as the candidate relay UEs.

[0015] In one alternative implementation, the step of determining candidate relay UEs based on the second selection condition includes the steps of obtaining an SL-RSRP or SD-RSRP between the second UE and a relay UE, and selecting as the candidate relay UEs all relay UEs whose SL-RSRP or SD-RSRP with the first UE satisfies a first threshold condition and whose SL-RSRP or SD-RSRP with the second UE satisfies a second threshold condition.

[0016] In one alternative implementation, the step of determining a target relay UE to be selected or reselected based on the candidate relay UEs includes, based on implementation, selecting one candidate relay UE from the candidate relay UEs as the target relay UE, or, based on implementation, selecting multiple relay UEs from the candidate relay UEs as the target relay UE.

[0017] According to a third aspect, an embodiment of the present disclosure provides another relay UE selection and reselection method in a terminal (UE)-to-UE scenario, the method being executed by a second UE, the method including: receiving a discovery request message transmitted from at least one first relay UE; selecting, from the at least one first relay UE, a relay UE whose SL-RSRP or SD-RSRP between the first relay UE and the second UE satisfies a second threshold condition as a second relay UE; and transmitting a discovery response message to the first UE based on the second relay UE, the second relay UE being used by the first UE to select and reselect a relay UE, wherein the first UE is a source remote UE in the terminal (UE)-to-UE scenario and the second UE is a target remote UE in the terminal (UE)-to-UE scenario.

[0018] In this technical solution, the target remote UE selects or reselects a relay UE based on the relay selection conditions of the target remote UE to transmit a discovery response message; and the source remote UE selects relay UEs that meet the relay selection conditions of the source remote UE based on the relay UEs selected or reselected by the target remote UE, and sets them as candidate relay UEs. This solves the problem of how to select and reselect relay UEs in UE-to-UE (U2U) scenarios, and ensures normal communication between terminal devices.

[0019] According to a fourth aspect, an embodiment of the present disclosure provides another relay UE selection and reselection method in a terminal (UE)-to-UE scenario, the method being executed by a second UE, the method including: determining a candidate relay UE based on a third selection condition; and determining a target relay UE to be selected or reselected based on the candidate relay UE, wherein the third selection condition includes any one of: selecting a relay UE for which SL-RSRP or SD-RSRP between the second UE and the relay UE satisfies a second threshold condition as the candidate relay UE; and selecting a relay UE for which SL-RSRP or SD-RSRP between a first UE and the relay UE satisfies a first threshold condition and the SL-RSRP or SD-RSRP between the second UE and the relay UE satisfies a second threshold condition as the candidate relay UE, wherein the first UE is a source remote UE in the terminal (UE)-to-UE scenario and the second UE is a target remote UE in the terminal (UE)-to-UE scenario.

[0020] In this technical solution, the target remote UE selects or reselects a target relay UE based on the relay selection conditions of the target remote UE, thereby solving the problem of how to select and reselect a relay UE in a UE-to-UE (U2U) scenario and ensuring normal communication of the terminal device.

[0021] In one implementation, the step of determining candidate relay UEs based on the third selection condition includes the steps of receiving a discovery request message transmitted from at least one third relay UE, where the at least one third relay UE is a relay UE selected by the first UE and whose SL-RSRP or SD-RSRP between the first UE satisfies a first threshold condition; and selecting, from the at least one third relay UE, all third relay UEs whose SL-RSRP or SD-RSRP between the second UE satisfies a second threshold condition as the candidate relay UEs.

[0022] In one implementation, the step of determining candidate relay UEs based on the third selection condition includes the steps of obtaining an SL-RSRP or SD-RSRP between the first UE and a relay UE, and selecting as the candidate relay UEs all relay UEs whose SL-RSRP or SD-RSRP with the first UE satisfies a first threshold condition and whose SL-RSRP or SD-RSRP with the second UE satisfies a second threshold condition.

[0023] In one possible implementation, the step of determining a target relay UE to be selected or reselected based on the candidate relay UEs includes, based on implementation, selecting one candidate relay UE from the candidate relay UEs as the target relay UE, or, based on implementation, selecting multiple relay UEs from the candidate relay UEs as the target relay UE.

[0024] According to a fifth aspect, an embodiment of the present disclosure provides another relay UE selection and reselection method in a terminal (UE)-to-UE scenario, the method being executed by a first UE, the method including: selecting a relay UE whose SL-RSRP or SD-RSRP between the first UE and the first UE satisfies a first threshold condition as a third relay UE; and transmitting a discovery request message to a second UE based on the third relay UE, the third relay UE being used by the second UE to select and reselect a relay UE, wherein the first UE is a source remote UE in the terminal (UE)-to-UE scenario, and the second UE is a target remote UE in the terminal (UE)-to-UE scenario.

[0025] In this technical solution, the source remote UE selects or reselects a relay UE based on the relay selection conditions of the source remote UE to transmit a discovery response message; the target remote UE selects relay UEs that meet the relay selection conditions of the target remote UE based on the relay UEs selected or reselected by the source remote UE, and sets them as candidate relay UEs. This solves the problem of how to select and reselect relay UEs in UE-to-UE (U2U) scenarios, and ensures normal communication between terminal devices.

[0026] According to a sixth aspect, an embodiment of the present disclosure provides a method for triggering selection and reselection of a relay terminal in a terminal (UE)-to-UE scenario, the method being executed by a terminal device, the method including: triggering selection or reselection of a relay terminal in response to a sidelink communication reference signal received power (SL-RSRP) or a sidelink discovery reference signal received power (SD-RSRP) between the terminal device and another terminal device satisfying a trigger condition for selection and reselection of a relay terminal.

[0027] In this technical solution, if a terminal device determines that the SL-RSRP or SD-RSRP between it and another terminal device meets the trigger conditions for relay terminal selection and reselection, it triggers relay terminal selection or reselection, thereby solving the problem of relay UE selection and reselection in UE-to-UE (U2U) scenarios and ensuring normal communication of terminal devices.

[0028] In one implementation, the SL-RSRP or SD-RSRP meeting the trigger conditions for relay terminal selection and reselection includes the SL-RSRP or SD-RSRP being less than or equal to a predefined threshold, or the SL-RSRP or SD-RSRP being less than a predefined threshold by at least one hysteresis parameter value.

[0029] In one alternative implementation, the terminal device is a source remote terminal in the UE-to-UE scenario, and the other terminal device is a target remote terminal in the UE-to-UE scenario.

[0030] In one alternative implementation, the terminal device is a target remote terminal in the UE-to-UE scenario, and the other terminal device is a source remote terminal in the UE-to-UE scenario.

[0031] In one alternative implementation, the terminal device is a source remote terminal or a target remote terminal in the UE-to-UE scenario, and the other terminal device is a relay terminal in the UE-to-UE scenario.

[0032] According to a seventh aspect, an embodiment of the present disclosure provides a communication device, the communication device having some or all of the functions of a terminal device that implements the method described in the first aspect above. For example, the functions of the communication device may include some or all of the functions of the embodiments of the present disclosure, or may include the function of implementing any one of the embodiments of the present disclosure alone. The functions can be implemented by hardware, or can be implemented by the hardware executing corresponding software. The hardware or software includes one or more units or modules corresponding to the above functions.

[0033] In one implementation, the structure of the communication device may include a transceiver module and a processing module, the processing module being configured to support the communication device to perform the corresponding functions of the above method. The transceiver module supports communication between the communication device and other devices. The communication device may further include a storage module, the storage module being used to combine the transceiver module and the processing module, and storing computer programs and data required for the communication device.

[0034] As an example, the processing module may be a processor, the transmitting and receiving module may be a transceiver or a communication interface, and the storage module may be a memory.

[0035] According to an eighth aspect, an embodiment of the present disclosure provides a communication device, the communication device having some or all of the functions of a terminal device that implements the method described in the second aspect above. For example, the functions of the communication device may include some or all of the functions of the embodiments of the present disclosure, or may include the function of implementing any one of the embodiments of the present disclosure alone. The functions can be implemented by hardware, or can be implemented by the hardware executing corresponding software. The hardware or software includes one or more units or modules corresponding to the above functions.

[0036] In one implementation, the structure of the communication device may include a transceiver module and a processing module, the processing module being configured to support the communication device to perform the corresponding functions of the above method. The transceiver module supports communication between the communication device and other devices. The communication device may further include a storage module, the storage module being used to combine the transceiver module and the processing module, and storing computer programs and data required for the communication device.

[0037] According to a ninth aspect, an embodiment of the present disclosure provides a communication device, the communication device having some or all of the functions of a terminal device that implements the method described in the third aspect above. For example, the functions of the communication device may include some or all of the functions of the embodiments of the present disclosure, or may include the function of implementing any one of the embodiments of the present disclosure alone. The functions can be implemented by hardware, or can be implemented by the hardware executing corresponding software. The hardware or software includes one or more units or modules corresponding to the above functions.

[0038] According to a tenth aspect, an embodiment of the present disclosure provides a communication device, the communication device having some or all of the functions of a terminal device that implements the method described in the fourth aspect above. For example, the functions of the communication device may include some or all of the functions of the embodiments of the present disclosure, or may include the function of implementing any one of the embodiments of the present disclosure alone. The functions can be implemented by hardware, or can be implemented by the hardware executing corresponding software. The hardware or software includes one or more units or modules corresponding to the above functions.

[0039] According to an eleventh aspect, an embodiment of the present disclosure provides a communication device, the communication device having some or all of the functions of a terminal device that implements the method described in the fifth aspect above. For example, the functions of the communication device may include some or all of the functions of the embodiments of the present disclosure, or may include the function of independently implementing any one of the embodiments of the present disclosure. The functions can be implemented by hardware, or can be implemented by the hardware executing corresponding software. The hardware or software includes one or more units or modules corresponding to the above functions.

[0040] According to a twelfth aspect, an embodiment of the present disclosure provides a communication device, the communication device having some or all of the functions of a terminal device that implements the method described in the sixth aspect above. For example, the functions of the communication device may include some or all of the functions of the embodiments of the present disclosure, or may include the function of implementing any one of the embodiments of the present disclosure alone. The functions can be implemented by hardware, or can be implemented by the hardware executing corresponding software. The hardware or software includes one or more units or modules corresponding to the above functions.

[0041] According to a thirteenth aspect, an embodiment of the present disclosure provides a communication device, the communication device including a processor, the processor executing the method according to the first aspect above when calling a computer program in a memory.

[0042] According to a fourteenth aspect, an embodiment of the present disclosure provides a communication device, the communication device including a processor, the processor executing the method according to the second aspect above when calling a computer program in a memory.

[0043] According to a fifteenth aspect, an embodiment of the present disclosure provides a communication device, the communication device including a processor, the processor executing the method according to the third aspect above when calling a computer program in a memory.

[0044] According to a sixteenth aspect, an embodiment of the present disclosure provides a communication device, the communication device including a processor, the processor executing the method according to the fourth aspect above when calling a computer program in a memory.

[0045] According to a seventeenth aspect, an embodiment of the present disclosure provides a communication device, the communication device including a processor, the processor executing the method according to the fifth aspect above when calling a computer program in a memory.

[0046] According to an eighteenth aspect, an embodiment of the present disclosure provides a communication device, the communication device including a processor, the processor executing the method according to the sixth aspect above when calling a computer program in a memory.

[0047] According to a nineteenth aspect, an embodiment of the present disclosure provides a communication device, the communication device including a processor and a memory, wherein a computer program is stored in the memory, and the processor executes the computer program stored in the memory to cause the communication device to perform the method according to the first aspect above.

[0048] According to a twentieth aspect, an embodiment of the present disclosure provides a communication device, the communication device including a processor and a memory, wherein a computer program is stored in the memory, and the processor executes the computer program stored in the memory to cause the communication device to perform the method according to the second aspect above.

[0049] According to a twenty-first aspect, an embodiment of the present disclosure provides a communication device, the communication device including a processor and a memory, wherein a computer program is stored in the memory, and the processor executes the computer program stored in the memory to cause the communication device to perform the method according to the third aspect above.

[0050] According to a twenty-second aspect, an embodiment of the present disclosure provides a communication device, the communication device including a processor and a memory, wherein a computer program is stored in the memory, and the processor executes the computer program stored in the memory to cause the communication device to perform the method according to the fourth aspect above.

[0051] According to a twenty-third aspect, an embodiment of the present disclosure provides a communication device, the communication device including a processor and a memory, wherein a computer program is stored in the memory, and the processor executes the computer program stored in the memory to cause the communication device to perform the method according to the fifth aspect above.

[0052] According to a twenty-fourth aspect, an embodiment of the present disclosure provides a communication device, the communication device including a processor and a memory, wherein a computer program is stored in the memory, and the processor executes the computer program stored in the memory to cause the communication device to perform the method according to the sixth aspect above.

[0053] According to a twenty-fifth aspect, an embodiment of the present disclosure provides a communication device, the device including a processor and an interface circuit, the interface circuit receiving and transmitting code instructions to the processor, and the processor executing the code instructions to cause the device to perform the method according to the first aspect above.

[0054] According to a twenty-sixth aspect, an embodiment of the present disclosure provides a communication device, the device including a processor and an interface circuit, the interface circuit receiving and transmitting code instructions to the processor, and the processor executing the code instructions to cause the device to perform the method according to the second aspect above.

[0055] According to a twenty-seventh aspect, an embodiment of the present disclosure provides a communication device, the device including a processor and an interface circuit, the interface circuit receiving and transmitting code instructions to the processor, and the processor executing the code instructions to cause the device to perform the method according to the third aspect above.

[0056] According to a twenty-eighth aspect, an embodiment of the present disclosure provides a communication device, the device including a processor and an interface circuit, the interface circuit receiving and transmitting code instructions to the processor, and the processor executing the code instructions to cause the device to perform the method according to the fourth aspect above.

[0057] According to a twenty-ninth aspect, an embodiment of the present disclosure provides a communication device, the device including a processor and an interface circuit, the interface circuit receiving and transmitting code instructions to the processor, and the processor executing the code instructions to cause the device to perform the method according to the fifth aspect above.

[0058] According to a thirtieth aspect, an embodiment of the present disclosure provides a communication device, the device including a processor and an interface circuit, the interface circuit receiving and transmitting code instructions to the processor, and the processor executing the code instructions to cause the device to perform the method according to the sixth aspect above.

[0059] According to a thirty-first aspect, an embodiment of the present disclosure provides a computer-readable storage medium for storing instructions for use in the above terminal device, the instructions, when executed, causing the terminal device to perform the method according to the first aspect above.

[0060] According to a thirty-second aspect, an embodiment of the present disclosure provides a computer-readable storage medium for storing instructions for use in the above terminal device, the instructions, when executed, causing the network device to perform the method according to the second aspect above.

[0061] According to a thirty-third aspect, an embodiment of the present disclosure provides a computer-readable storage medium for storing instructions for use in the above terminal device, the instructions, when executed, causing the network device to perform the method according to the third aspect above.

[0062] According to a thirty-fourth aspect, an embodiment of the present disclosure provides a computer-readable storage medium for storing instructions for use in the above terminal device, the instructions, when executed, causing the network device to perform the method according to the fourth aspect above.

[0063] According to a thirty-fifth aspect, an embodiment of the present disclosure provides a computer-readable storage medium for storing instructions for use in the above terminal device, the instructions, when executed, causing the network device to perform the method according to the fifth aspect above.

[0064] According to a thirty-sixth aspect, an embodiment of the present disclosure provides a computer-readable storage medium for storing instructions for use in the above terminal device, the instructions, when executed, causing the network device to perform the method according to the sixth aspect above.

[0065] According to a thirty-seventh aspect, the present disclosure further provides a computer program product comprising a computer program which, when executed on a computer, causes the computer to perform the method according to the first aspect above.

[0066] According to a thirty-eighth aspect, the present disclosure further provides a computer program product comprising a computer program which, when executed on a computer, causes the computer to perform the method according to the second aspect above.

[0067] According to a thirty-ninth aspect, the present disclosure further provides a computer program product comprising a computer program which, when executed on a computer, causes the computer to perform the method according to the third aspect above.

[0068] According to a fortieth aspect, the present disclosure further provides a computer program product comprising a computer program which, when run on a computer, causes the computer to perform the method according to the fourth aspect above.

[0069] According to a forty-first aspect, the present disclosure further provides a computer program product comprising a computer program which, when executed on a computer, causes the computer to perform the method according to the fifth aspect above.

[0070] According to a forty-second aspect, the present disclosure further provides a computer program product comprising a computer program which, when executed on a computer, causes the computer to perform the method according to the sixth aspect above.

[0071] According to a forty-third aspect, the present disclosure provides a computer program which, when run on a computer, causes the computer to carry out the above method. [Brief explanation of the drawings]

[0072] In order to more clearly describe the technical solutions in the embodiments or background art of the present disclosure, the following describes the drawings that need to be used in the embodiments or background art of the present disclosure. [Figure 1] 1 is a schematic flowchart of a relay UE selection and reselection method in a terminal (UE)-to-UE scenario provided by an embodiment of the present disclosure; [Figure 2] 10 is a flowchart of a relay UE selection and reselection method in another terminal (UE)-to-UE scenario provided by an embodiment of the present disclosure. [Figure 3] 10 is a flowchart of a relay UE selection and reselection method in another terminal (UE)-to-UE scenario provided by an embodiment of the present disclosure. [Figure 4] 10 is a flowchart of a relay UE selection and reselection method in another terminal (UE)-to-UE scenario provided by an embodiment of the present disclosure. [Figure 5] 10 is a flowchart of a relay UE selection and reselection method in another terminal (UE)-to-UE scenario provided by an embodiment of the present disclosure. [Figure 6] 1 is a flowchart of a method for triggering relay terminal selection and reselection in a terminal (UE)-to-UE scenario provided by an embodiment of the present disclosure. [Figure 7] FIG. 1 is a schematic configuration diagram of a communication device provided by an embodiment of the present disclosure. [Figure 8] FIG. 10 is a schematic configuration diagram of another communication device provided by an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0073] Hereinafter, embodiments of the present disclosure will be described in detail. Examples of the embodiments are illustrated in the accompanying drawings, in which the same or similar reference numerals throughout the drawings indicate the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are intended to illustrate the present disclosure and should not be construed as limiting the present disclosure. In the description of the present disclosure, unless otherwise specified, " / " means "or." For example, "A / B" can represent either A or B. In this specification, "and / or" is used only to describe the relationship between related objects and indicates that three relationships are possible. For example, "A and / or B" can represent three situations: A exists alone, A and B exist simultaneously, or B exists alone.

[0074] The terms used in the embodiments of the present disclosure are used to describe particular embodiments and are not intended to limit the embodiments of the present disclosure. Unless the context clearly indicates otherwise, the singular forms "a," "an," and "the" used in the embodiments of the present disclosure and the appended claims are intended to include the plural forms.

[0075] Although various pieces of information may be described using terms such as first, second, and third in the embodiments of the present disclosure, these pieces of information should not be limited to these terms. These terms are used only to distinguish between pieces of information of the same type. For example, first information may be referred to as second information without departing from the scope of the embodiments of the present disclosure. Similarly, second information may be referred to as first information. Depending on the context, the terms "when" and "in response to" used herein may be understood as "at the time of" or "on the occasion of" or "in response to determining."

[0076]

[0023] The following detailed description of the embodiments of the present disclosure will be given, and examples of the embodiments are shown in the drawings, in which the same or similar reference numerals throughout indicate the same or similar elements. The embodiments described below with reference to the accompanying drawings are illustrative and are intended to explain the present disclosure, but cannot be understood as limiting the present disclosure.

[0077] To support direct communication between terminal devices (also known as user equipment, or UEs), the direct connection communication (also known as sidelink, or SL) communication method has been introduced, and the interface between UEs is PC-5. Sidelink supports three transmission methods: unicast, multicast, and broadcast, depending on the correspondence between the transmitting and receiving UEs. The transmitting UE transmits sidelink control information (SCI) on the physical sidelink control channel (PSCCH) and the second-stage SCI on the physical sidelink shared channel (PSSCH). This SCI includes the resource location for data transmission and source and target identifiers. After receiving the SCI, the receiving UE determines whether to receive the corresponding data and which process to use based on the source UE and destination UE identifiers contained therein. In a unicast connection, each UE corresponds to one destination identifier; in a multicast connection, each UE may belong to one or more groups, each group corresponding to one destination identifier; and in a broadcast connection, all UEs correspond to at least one destination identifier.

[0078] A UE can communicate with a base station through the relay of another UE without directly connecting to the base station. Here, a UE not connected to a base station is called a remote UE, and a UE providing relay functionality is called a relay UE. One scenario is when UE A does not directly connect to UE B, but instead can connect to UE B through the relay of UE C. Here, UE A and UE B are remote UEs, and UE C providing relay functionality is a relay UE, and all UEs communicate via sidelink unicast. This architecture is called U2U (UE to UE, terminal to terminal) relay.

[0079] However, the related art currently lacks an effective means for relay UE selection and reselection in U2U scenarios.

[0080] Therefore, the embodiments of the present disclosure provide a method and apparatus for selecting and reselecting a relay UE in a terminal (UE)-to-UE scenario, in which a source remote UE or a target remote UE selects or reselects a relay UE based on relay selection conditions, thereby solving the problem of how to select and reselect a relay UE in a UE-to-UE (U2U) scenario and ensuring normal communication of terminal devices.

[0081] Note that a terminal (also referred to as a terminal device) in the embodiments of the present disclosure is a user-side entity for receiving or transmitting signals, such as a mobile phone. The terminal device may also be referred to as a terminal, user equipment (UE), mobile station (MS), mobile terminal (MT), etc. The terminal device may be an automobile with a communication function, a smart car, a mobile phone, a wearable device, a tablet, a personal computer with a wireless transmission / reception function, a virtual reality (VR) terminal device, an augmented reality (AR) terminal device, a wireless terminal device for industrial control, a wireless terminal device for self-driving, a wireless terminal device for remote medical surgery, a wireless terminal device for smart grid, a wireless terminal device for transportation safety, a wireless terminal device for smart city, a wireless terminal device for smart home, etc. The embodiments of the present disclosure do not limit the specific technology adopted by the terminal device and the specific device configuration.

[0082] Hereinafter, a method and apparatus for relay UE selection and reselection in a terminal (UE)-to-UE scenario provided by the present disclosure will be described in detail in conjunction with the accompanying drawings.

[0083] Referring to Figure 1, Figure 1 is a schematic flowchart of a relay UE selection and reselection method in a terminal (UE)-to-UE scenario provided by an embodiment of the present disclosure, which can be performed by a first UE. As shown in Figure 1, the method may include, but is not limited to, the following steps:

[0084] In step 101, candidate relay UEs are determined based on a first selection condition.

[0085] Here, in the embodiment of the present disclosure, the first selection condition may include any one of the following 1) to 3). 1) selecting a relay UE that includes a terminal identifier of the second UE in the notification message or neighbor list as a candidate relay UE; 2) Selecting a relay UE whose SL-RSRP (Sidelink Reference Signal Receiving Power) or SD-RSRP (Sidelink Discovery Reference Signal Receiving Power) satisfies a threshold condition as a candidate relay UE; 3) Selecting a relay UE that includes the terminal identifier of the second UE in the notification message or neighbor list and whose SL-RSRP or SD-RSRP meets the threshold condition as a candidate relay UE.

[0086] In this embodiment, for example, the first selection condition includes selecting a relay UE that includes the terminal identifier of the second UE in the notification message or neighbor list as a candidate relay UE. The first UE can select a relay UE that satisfies the first condition as a candidate relay UE, i.e., the first UE can select a relay UE that includes the terminal identifier of the second UE in the notification message or neighbor list as a candidate relay UE. One possible implementation form of the terminal identifier of the second UE is the source Layer 2 address or application layer identifier of the second UE, but other implementation forms are also limited. Optionally, the second UE is a target communication UE of the first UE, and the first UE communicates with the second UE through the relay UE.

[0087] For U2U scenarios, there are two modes for transmitting discovery request messages: Mode A and Mode B. In Mode A, a U2U relay UE periodically broadcasts a notification message, which carries the terminal identifier of the target terminal, or the neighbor list of the notification message carries the terminal identifier of the target terminal. The source terminal monitors the notification messages and selects one U2U relay UE as the relay UE. As an example, for Mode A, the first UE needs to determine that the notification message broadcast by the relay terminal carries the terminal identifier of the second UE, and the first UE can select the relay terminal as a candidate relay UE.

[0088] In this embodiment, for example, the first selection condition includes selecting a relay UE whose SL-RSRP or SD-RSRP meets a threshold condition as a candidate relay UE, and the first UE can select a relay UE that meets the first condition as a candidate relay UE, that is, the first UE can select a relay UE whose SL-RSRP or SD-RSRP meets a threshold condition as a candidate relay UE.

[0089] In this embodiment, for example, the first selection condition includes selecting a relay UE that includes the terminal identifier of the second UE in the notification message or neighbor list and whose SL-RSRP or SD-RSRP satisfies a threshold condition as a candidate relay UE, so that the first UE can select a relay UE that satisfies the first condition as a candidate relay UE, i.e., the first UE can select a relay UE that includes the terminal identifier of the second UE in the notification message or neighbor list and whose SL-RSRP or SD-RSRP satisfies a threshold condition as a candidate relay UE.

[0090] In an embodiment of the present disclosure, the SL-RSRP or SD-RSRP satisfying the threshold condition may include the SL-RSRP or SD-RSRP being equal to or greater than a predefined threshold, or the SL-RSRP or SD-RSRP being greater than a predefined threshold by at least one hysteresis parameter value. For example, the SL-RSRP or SD-RSRP can be understood as a signal strength of a sidelink between a first UE and a relay UE, and the first UE can select a relay UE whose signal strength with the first UE satisfies a threshold condition as a candidate relay UE. For example, the first UE can select a relay UE whose signal strength with the first UE is equal to or greater than a predefined threshold as a candidate relay UE, or the first UE can select a relay UE whose signal strength with the first UE is greater than a predefined threshold by at least one hysteresis parameter value as a candidate relay UE. In an alternative implementation form, if the network device configures only a predefined threshold, the SL-RSRP or SD-RSRP satisfying the threshold condition may be the SL-RSRP or SD-RSRP being greater than or equal to the predefined threshold. In another alternative implementation, if the network device sets predefined threshold and hysteresis parameter values, the SL-RSRP or SD-RSRP satisfying the threshold condition may be that the SL-RSRP or SD-RSRP is greater than the predefined threshold by at least one hysteresis parameter value.

[0091] Note that in some embodiments of the present disclosure, when the SL-RSRP and SD-RSRP between terminals can be acquired, the UE may compare the acquired SL-RSRP with a predefined threshold, or may compare the acquired SD-RSRP with a predefined threshold, or the UE may select one of the SL-RSRP / SD-RSRP and compare it with a predefined threshold. When the UE cannot acquire the SL-RSRP between terminals and can acquire only the SD-RSRP between terminals, the UE compares the acquired SD-RSRP with the predefined threshold. When the UE cannot acquire the SD-RSRP between terminals and can acquire only the SL-RSRP between terminals, the UE compares the acquired SL-RSRP with the predefined threshold.

[0092] For example, if the first UE can acquire the SL-RSRP and SD-RSRP between the first UE and the relay UE, the first UE can compare the acquired SL-RSRP with a predefined threshold to determine whether a threshold condition is met, or the first UE can compare the acquired SD-RSRP with a predefined threshold to determine whether a threshold condition is met, or the first UE can select one of the SL-RSRP and the SD-RSRP and compare it with a predefined threshold to determine whether a threshold condition is met. If the first UE cannot acquire the SL-RSRP between the first UE and the relay UE but can acquire only the SD-RSRP between the first UE and the relay UE, the first UE can compare the acquired SD-RSRP with the predefined threshold to determine whether a threshold condition is met. If the first UE cannot acquire the SD-RSRP between the first UE and the relay UE but can acquire only the SL-RSRP between the first UE and the relay UE, the first UE can compare the acquired SL-RSRP with the predefined threshold to determine whether a threshold condition is met.

[0093] In addition, in the embodiments of the present disclosure, the predefined threshold may be set or preset in the terminal device by a network device. When the terminal device is in-coverage, the terminal device can obtain the predefined threshold set by the network device using specific RRC signaling or SIB. When the terminal device is out-of-coverage, the terminal device can obtain the predefined threshold by pre-configuration.

[0094] In an embodiment of the present disclosure, the predefined thresholds include a first predefined threshold and a second predefined threshold, where the first predefined threshold is a lowest threshold and the second predefined threshold is a highest threshold. In an embodiment of the present disclosure, the SL-RSRP or SD-RSRP being equal to or greater than the predefined threshold may include the SL-RSRP or SD-RSRP being equal to or greater than the first predefined threshold and equal to or less than the second predefined threshold. The SL-RSRP or SD-RSRP being greater than the predefined threshold by at least one hysteresis parameter value may include the SL-RSRP or SD-RSRP being greater than the first predefined threshold by at least one hysteresis parameter value and less than the second predefined threshold by at least one hysteresis parameter value.

[0095] In one alternative implementation, the network device can set two predefined thresholds, for example, a first predefined threshold and a second predefined threshold, and the first UE can select as a candidate relay UE a relay UE whose SL-RSRP or SD-RSRP is greater than or equal to the first predefined threshold and less than or equal to the second predefined threshold. In another alternative implementation, the first UE can select as a candidate relay UE a relay UE whose SL-RSRP or SD-RSRP is greater than the first predefined threshold by at least one hysteresis parameter value and less than the second predefined threshold by at least one hysteresis parameter value.

[0096] In some embodiments of the present disclosure, the relay UEs whose SL-RSRP or SD-RSRP meets the threshold condition include any of the following 1) to 3). 1) A relay UE whose SL-RSRP or SD-RSRP between it and the first UE satisfies a first threshold condition; 2) A relay UE whose SL-RSRP or SD-RSRP between it and a second UE satisfies a second threshold condition; 3) A relay UE whose SL-RSRP or SD-RSRP with the first UE satisfies the first threshold condition and whose SL-RSRP or SD-RSRP with the second UE satisfies the second threshold condition.

[0097] In an embodiment of the present disclosure, the first selection condition is to select a relay UE whose SL-RSRP or SD-RSRP satisfies a threshold condition, and the relay UE whose SL-RSRP or SD-RSRP satisfies the threshold condition includes a relay UE whose SL-RSRP or SD-RSRP with a first UE satisfies the first threshold condition. The first UE can select a relay UE whose SL-RSRP or SD-RSRP with the first UE satisfies the first threshold condition as a candidate relay UE. In one implementation, the network device can set a predefined threshold, and the first UE can select a relay UE whose SL-RSRP or SD-RSRP with the first UE is equal to or greater than the predefined threshold as a candidate relay UE. Alternatively, the first UE can select a relay UE whose SL-RSRP or SD-RSRP with the first UE is greater than the predefined threshold by at least one hysteresis parameter value as a candidate relay UE. In another implementation, the network device can set two predefined thresholds, for example, a lowest threshold and a highest threshold. As an example of one possible implementation, the first UE may select as a candidate relay UE a relay UE whose SL-RSRP or SD-RSRP between itself and the first UE is greater than or equal to a minimum threshold and less than or equal to a maximum threshold. As an example of another possible implementation, the first UE may select as a candidate relay UE a relay UE whose SL-RSRP or SD-RSRP between itself and the first UE is greater than the minimum threshold by at least one hysteresis parameter value and less than the maximum threshold by at least one hysteresis parameter value.

[0098] In an embodiment of the present disclosure, for example, the first selection condition is to select a relay UE whose SL-RSRP or SD-RSRP satisfies a threshold condition, and the relay UE whose SL-RSRP or SD-RSRP satisfies the threshold condition includes a relay UE whose SL-RSRP or SD-RSRP with a second UE satisfies a second threshold condition. The first UE can select, as a candidate relay UE, a relay UE whose SL-RSRP or SD-RSRP with the second UE satisfies the second threshold condition. In one implementation, the network device can set a predefined threshold, and the first UE can select, as a candidate relay UE, a relay UE whose SL-RSRP or SD-RSRP with the second UE is equal to or greater than the predefined threshold. Alternatively, the first UE can select, as a candidate relay UE, a relay UE whose SL-RSRP or SD-RSRP with the second UE is greater than the predefined threshold by at least one hysteresis parameter value. In another implementation, the network device can set two predefined thresholds, for example, a minimum threshold and a maximum threshold. As an example of one possible implementation, the first UE may select as a candidate relay UE a relay UE whose SL-RSRP or SD-RSRP between itself and the second UE is greater than or equal to a minimum threshold and less than or equal to a maximum threshold. As an example of another possible implementation, the first UE may select as a candidate relay UE a relay UE whose SL-RSRP or SD-RSRP between itself and the second UE is greater than the minimum threshold by at least one hysteresis parameter value and less than the maximum threshold by at least one hysteresis parameter value.

[0099] In an embodiment of the present disclosure, the first selection condition is to select a relay UE whose SL-RSRP or SD-RSRP satisfies a threshold condition, and here the relay UE whose SL-RSRP or SD-RSRP satisfies the threshold condition includes a relay UE whose SL-RSRP or SD-RSRP with a first UE satisfies the first threshold condition and whose SL-RSRP or SD-RSRP with a second UE satisfies the second threshold condition. For example, the first UE can select a relay UE whose SL-RSRP or SD-RSRP with the first UE satisfies the first threshold condition and whose SL-RSRP or SD-RSRP with the second UE satisfies the second threshold condition as a candidate relay UE.

[0100] In one implementation, the network device can set one predefined threshold, and the first UE can select as a candidate relay UE a relay UE whose SL-RSRP or SD-RSRP between the first UE and the second UE is greater than or equal to the predefined threshold, or the first UE can select as a candidate relay UE a relay UE whose SL-RSRP or SD-RSRP between the first UE and the second UE is greater than or equal to the predefined threshold by at least one hysteresis parameter value.

[0101] In another implementation, the network device may set two predefined thresholds, for example, one minimum threshold and one maximum threshold. As an example of one possible implementation, the SL-RSRP or SD-RSRP between the first UE and the relay UE satisfying the first threshold condition may be that the SL-RSRP or SD-RSRP between the first UE and the relay UE is greater than or equal to the minimum threshold and less than or equal to the maximum threshold, and the SL-RSRP or SD-RSRP between the second UE and the relay UE satisfying the second threshold condition may be that the SL-RSRP or SD-RSRP between the second UE and the relay UE is greater than or equal to the minimum threshold and less than or equal to the maximum threshold. As an example of another possible implementation, the SL-RSRP or SD-RSRP between the first UE and the relay UE satisfying the first threshold condition may be that the SL-RSRP or SD-RSRP between the first UE and the relay UE is greater than the lowest threshold by at least one hysteresis parameter value and less than the highest threshold by at least one hysteresis parameter value, and the SL-RSRP or SD-RSRP between the second UE and the relay UE satisfying the second threshold condition may be that the SL-RSRP or SD-RSRP between the second UE and the relay UE is greater than the lowest threshold by at least one hysteresis parameter value and less than the highest threshold by at least one hysteresis parameter value.

[0102] In step 102, a target relay UE to be selected or reselected is determined based on the candidate relay UEs.

[0103] In one possible implementation, the first UE may, based on implementation, select one candidate relay UE from among the candidate relay UEs to be the target relay UE to be selected or reselected. For example, based on implementation, the first UE may, randomly select one candidate relay UE from among the candidate relay UEs to be the target relay UE to be selected or reselected.

[0104] In another alternative implementation, the first UE may select multiple candidate relay UEs from among the candidate relay UEs to be the target relay UE to be selected or reselected, based on implementation.

[0105] Optionally, in some embodiments of the present disclosure, the first UE may be a source remote UE in a U2U relay scenario, and the second UE may be a target remote UE in a U2U relay scenario.

[0106] For example, the first UE may be a source remote UE in a U2U relay scenario, and the second UE may be a target remote UE in a U2U relay scenario. The source remote UE can select a relay UE that satisfies at least one of the following conditions 1) to 3) as a candidate relay UE: 1) The notification message or neighbor list includes the terminal identifier of the target remote UE; 2) The SL-RSRP / SD-RSRP between the source remote UE and the relay UE is equal to or greater than a predefined threshold or is greater than the predefined threshold by at least one hysteresis parameter value; 3) The SL-RSRP / SD-RSRP between the target remote UE and the relay UE is equal to or greater than a predefined threshold or is greater than the predefined threshold by at least one hysteresis parameter value.

[0107] For example, in Mode A, the source remote UE needs to determine that the terminal identifier of the target remote UE is included in the notification message / neighbor list broadcast by the relay UE. The terminal identifier of the target remote UE can be the source Layer 2 address of the target remote UE or an application layer identifier, but other implementations are not limited thereto. The SL-RSRP / SD-RSRP also needs to satisfy a predetermined condition. Here, only the SL-RSRP / SD-RSRP between the source remote UE and the relay UE can satisfy the predetermined condition, or only the SL-RSRP / SD-RSRP between the target remote UE and the relay UE can satisfy the predetermined condition, or both the SL-RSRP / SD-RSRP between the source remote UE and the relay UE and the SL-RSRP / SD-RSRP between the target remote UE and the relay UE can satisfy the predetermined condition. Here, the SL-RSRP / SD-RSRP satisfies the predetermined condition when it is equal to or greater than a predefined threshold or is greater than the predefined threshold by at least one hysteresis parameter value. Here, the hysteresis parameter value may be a threshold offset or a hysteresis.

[0108] In one implementation, the network device can set two predefined thresholds, for example, one minimum threshold and one maximum threshold. As an example, the SL-RSRP / SD-RSRP between the source remote UE and the relay UE satisfying the predefined condition may be that the SL-RSRP / SD-RSRP between the source remote UE and the relay UE is greater than or equal to the minimum threshold and less than or equal to the maximum threshold, or that the SL-RSRP / SD-RSRP between the source remote UE and the relay UE is greater than the minimum threshold by at least one hysteresis parameter value and less than the maximum threshold by at least one hysteresis parameter value.

[0109] As an example, the SL-RSRP / SD-RSRP between the target remote UE and the relay UE satisfying the preset condition may be that the SL-RSRP / SD-RSRP between the target remote UE and the relay UE is greater than or equal to a minimum threshold and less than or equal to a maximum threshold, or that the SL-RSRP / SD-RSRP between the target remote terminal and the relay terminal is greater than the minimum threshold by at least one hysteresis parameter value and less than the maximum threshold by at least one hysteresis parameter value.

[0110] After determining the candidate relay UEs, the source remote UE can determine the target relay UE to be selected or reselected based on the candidate relay UEs. As an example of a possible implementation, the source remote UE can randomly select one candidate relay UE from the candidate relay UEs based on implementation to be the target relay UE to be selected or reselected. As another example of a possible implementation, the source remote UE can select multiple candidate relay UEs from the candidate relay UEs based on implementation to be the target relay UE to be selected or reselected.

[0111] Optionally, in some embodiments of the present disclosure, the first UE may be a target remote UE in a U2U relay scenario, and the second UE may be a source remote UE in a U2U relay scenario.

[0112] For example, the first UE may be a target remote UE in a U2U relay scenario, and the second UE may be a source remote UE in a U2U relay scenario. The target remote UE can select a relay UE that satisfies at least one of the following conditions 1) to 3) as a candidate relay UE: 1) The notification message or neighbor list includes the terminal identifier of the source remote UE; 2) The SL-RSRP / SD-RSRP between the source remote UE and the relay UE is equal to or greater than a predefined threshold or is greater than the predefined threshold by at least one hysteresis parameter value; 3) The SL-RSRP / SD-RSRP between the target remote UE and the relay UE is equal to or greater than a predefined threshold or is greater than the predefined threshold by at least one hysteresis parameter value.

[0113] For example, in Mode A, the target remote UE needs to determine that the notification message broadcast by the relay UE includes the terminal identifier of the source remote UE. The terminal identifier of the source remote UE can be the source Layer 2 address of the source remote UE or an application layer identifier, but other implementations are not limited thereto. The SL-RSRP / SD-RSRP also needs to satisfy a predetermined condition, where only the SL-RSRP / SD-RSRP between the source remote UE and the relay UE satisfies the predetermined condition, or only the SL-RSRP / SD-RSRP between the target remote UE and the relay UE satisfies the predetermined condition, or both the SL-RSRP / SD-RSRP between the source remote UE and the relay UE and the SL-RSRP / SD-RSRP between the target remote UE and the relay UE satisfies the predetermined condition. The SL-RSRP / SD-RSRP satisfying the predetermined condition can be equal to or greater than a predefined threshold or at least one hysteresis parameter value greater than the predefined threshold. The hysteresis parameter value can be a threshold offset or hysteresis.

[0114] In one implementation, the network device can set two predefined thresholds, for example, one minimum threshold and one maximum threshold. As an example, the SL-RSRP / SD-RSRP between the source remote UE and the relay UE satisfying the predefined condition may be that the SL-RSRP / SD-RSRP between the source remote UE and the relay UE is greater than or equal to the minimum threshold and less than or equal to the maximum threshold, or that the SL-RSRP / SD-RSRP between the source remote UE and the relay UE is greater than the minimum threshold by at least one hysteresis parameter value and less than the maximum threshold by at least one hysteresis parameter value.

[0115] As an example, the SL-RSRP / SD-RSRP between the target remote UE and the relay UE satisfying the preset condition may be that the SL-RSRP / SD-RSRP between the target remote UE and the relay UE is greater than or equal to a minimum threshold and less than or equal to a maximum threshold, or that the SL-RSRP / SD-RSRP between the target remote terminal and the relay terminal is greater than the minimum threshold by at least one hysteresis parameter value and less than the maximum threshold by at least one hysteresis parameter value.

[0116] After determining the candidate relay UEs, the target remote UE can determine a target relay UE to be selected or reselected based on the candidate relay UEs. As an example of a possible implementation, the target remote UE can randomly select one candidate relay UE from the candidate relay UEs based on implementation to be the target relay UE to be selected or reselected. As another example of a possible implementation, the target remote UE can select multiple candidate relay UEs from the candidate relay UEs based on implementation to be the target relay UE to be selected or reselected.

[0117] By implementing the embodiments of the present disclosure, the first UE selects or reselects a target relay UE based on the relay selection conditions, thereby solving the problem of how to select and reselect a relay UE in a UE-to-UE (U2U) scenario and ensuring normal communication of the terminal device.

[0118] Note that for the U2U scenario, there are two modes for transmitting discovery request messages: Mode A and Mode B. In Mode B, if there are multiple U2U relay UEs, the source remote UE or target remote UE selects one or more U2U relay UEs as relay UEs. Hereinafter, an implementation of the first UE selecting and reselecting a relay UE in Mode B will be described in conjunction with an embodiment. Referring to FIG. 2, FIG. 2 is a flowchart of another method for relay UE selection and reselection in a terminal (UE)-to-UE scenario provided by an embodiment of the present disclosure. Note that the method can be performed by the first UE. In one implementation, the first UE in this embodiment may be a source remote UE in the U2U scenario, and the second UE in this embodiment may be a target remote UE in the U2U scenario. As shown in FIG. 2, the method may include, but is not limited to, the following steps:

[0119] In step 201, candidate relay UEs are determined based on a second selection condition.

[0120] Here, in the embodiment of the present disclosure, the second selection condition may include any one of the following 1) to 2). 1) selecting a relay UE whose SL-RSRP or SD-RSRP between the first UE and the relay UE satisfies a first threshold condition as a candidate relay UE; 2) Selecting a relay UE as a candidate relay UE, where the SL-RSRP or SD-RSRP between the first UE and the relay UE satisfies a first threshold condition, and the SL-RSRP or SD-RSRP between the second UE and the relay UE satisfies a second threshold condition.

[0121] Optionally, in an embodiment of the present disclosure, the second selection condition includes selecting a relay UE whose SL-RSRP or SD-RSRP between the first UE and the relay UE satisfies a first threshold condition as a candidate relay UE, and the first UE may be a source remote UE in a U2U scenario, and the second UE may be a target remote UE in a U2U scenario. For example, the source remote UE can select a relay UE whose SL-RSRP or SD-RSRP between the source remote UE and the relay UE satisfies the first threshold condition as a candidate relay UE.

[0122] In one possible implementation, a first UE transmits a discovery request message to a second UE via at least one first relay UE, and the first UE receives a discovery response message transmitted by the second UE via at least one second relay UE, where the at least one second relay UE is a relay UE selected by the second UE from among the at least one first relay UE, the SL-RSRP or SD-RSRP between the second UE and the first UE satisfies a second threshold condition, and the first UE selects, from among the at least one second relay UE, all second relay UEs whose SL-RSRP or SD-RSRP between the first UE and the second UE satisfies the first threshold condition as candidate relay UEs. Here, the implementation in which the SL-RSRP or SD-RSRP between the second UE and the relay UE satisfies the second threshold condition and the implementation in which the SL-RSRP or SD-RSRP between the first UE and the relay UE satisfies the first threshold condition can be realized by any of the embodiments of the present disclosure, and description thereof will be omitted herein for brevity.

[0123] For example, in Mode B, the source remote UE transmits a discovery request message to a second UE via at least one first relay UE. The target remote UE receives the discovery request message forwarded by the at least one first relay UE. The target remote UE can select, from the at least one first relay UE, a relay UE whose SL-RSRP or SD-RSRP between the target remote UE and the source remote UE is equal to or greater than a predefined threshold, as a second relay UE. Alternatively, the target remote UE selects, from the at least one first relay UE, a relay UE whose SL-RSRP or SD-RSRP between the target remote UE and the source remote UE is greater than a predefined threshold by at least one hysteresis parameter value, as a second relay UE. The target remote UE forwards a discovery response message via the second relay UE. The source remote UE receives the discovery response message sent by the target remote UE via the at least one second relay UE. The source remote UE selects, from the at least one second relay UE, all second relay UEs whose SL-RSRP or SD-RSRP with the source remote UE is equal to or greater than a predefined threshold as candidate relay UEs, or the source remote UE selects, from the at least one second relay UE, all second relay UEs whose SL-RSRP or SD-RSRP with the source remote UE is greater than a predefined threshold by at least one hysteresis parameter value as candidate relay UEs.

[0124] Optionally, in an embodiment of the present disclosure, the second selection condition includes selecting, as a candidate relay UE, a relay UE whose SL-RSRP or SD-RSRP between the first UE and the relay UE satisfies a first threshold condition and whose SL-RSRP or SD-RSRP between the second UE and the relay UE satisfies a second threshold condition, and the first UE may be a source remote UE in a U2U scenario, and the second UE may be a target remote UE in a U2U scenario. For example, the source remote UE selects, as a candidate relay UE, a relay UE whose SL-RSRP or SD-RSRP between the source remote UE and the relay UE satisfies the first threshold condition and whose SL-RSRP or SD-RSRP between the target remote UE and the relay UE satisfies the second threshold condition.

[0125] In one possible implementation, the first UE obtains the SL-RSRP or SD-RSRP between the second UE and the relay UE, and selects all relay UEs whose SL-RSRP or SD-RSRP with the first UE satisfies a first threshold condition and whose SL-RSRP or SD-RSRP with the second UE satisfies a second threshold condition as candidate relay UEs.

[0126] As an example of one possible implementation, the first UE may, based on implementation, select all relay UEs whose SL-RSRP or SD-RSRP between themselves and the first UE satisfies a first threshold condition as a first candidate relay UE set, and select all relay UEs whose SL-RSRP or SD-RSRP between themselves and the second UE satisfies a second threshold condition from the first candidate relay UE set as candidate relay UEs. As an example of another possible implementation, the first UE may, based on implementation, select all relay UEs whose SL-RSRP or SD-RSRP between themselves and the second UE satisfies a second threshold condition as one candidate relay UE set, and select all relay UEs whose SL-RSRP or SD-RSRP between themselves and the first UE satisfies the first threshold condition from the candidate relay UE set as the candidate relay UEs.

[0127] Alternatively, the first UE may acquire the SL-RSRP or SD-RSRP between the second UE and the relay UE through a discovery signal of the relay UE or in another manner. Here, the implementation in which the SL-RSRP or SD-RSRP between the second UE and the relay UE satisfies the second threshold condition and the implementation in which the SL-RSRP or SD-RSRP between the first UE and the relay UE satisfies the first threshold condition may be implemented in any of the embodiments of the present disclosure, and the present disclosure is not limited thereto and will not be described further.

[0128] For example, in Mode B, the source remote UE can acquire the SL-RSRP or SD-RSRP between the target remote UE and the relay UE through the discovery signal of the relay UE or other methods, and the source remote UE selects as candidate relay UEs all relay UEs whose SL-RSRP or SD-RSRP with the source remote UE satisfies a first threshold condition and whose SL-RSRP or SD-RSRP with the target remote UE satisfies a second threshold condition.

[0129] In step 202, a target relay UE to be selected or reselected is determined based on the candidate relay UEs.

[0130] In one alternative implementation, the first UE may select one candidate relay UE from the candidate relay UEs as the target relay UE based on implementation. In another alternative implementation, the first UE may select multiple relay UEs from the candidate relay UEs as the target relay UE based on implementation. Optionally, the first UE sends a discovery request message to the second UE via the target relay UE.

[0131] By implementing the embodiments of the present disclosure, the target remote UE selects a relay UE that meets the conditions and forwards the discovery response message to it, and the source remote UE selects a relay UE that meets the conditions from the relay UEs that forwarded the discovery response message as a candidate relay UE, thereby realizing the source remote UE to select or reselect the target relay UE, which solves the problem of how to select and reselect a relay UE in a UE-to-UE (U2U) scenario and ensures normal communication of the terminal device.

[0132] It should be understood that the embodiment shown in FIG. 2 above describes an implementation of a relay UE selection and reselection method in a terminal (UE)-to-UE scenario according to an embodiment of the present disclosure from the perspective of a first UE. An embodiment of the present disclosure further proposes a relay UE selection and reselection method in a terminal (UE)-to-UE scenario, and the implementation of the relay UE selection and reselection method in a terminal (UE)-to-UE scenario will be described below from the perspective of a second UE. Referring to FIG. 3, FIG. 3 is a flowchart of another relay UE selection and reselection method in a terminal (UE)-to-UE scenario provided by an embodiment of the present disclosure. Note that the method can be performed by a second UE. In this embodiment, the first UE is a source remote UE in the terminal (UE)-to-UE scenario, and the second UE is a target remote UE in the terminal (UE)-to-UE scenario. As shown in FIG. 3, the method may include, but is not limited to, the following steps:

[0133] In step 301, receive a discovery request message sent by a first UE via at least one first relay UE.

[0134] In one implementation, in Mode B, the target remote UE receives a discovery request message forwarded via at least one first relay UE.

[0135] In step 302, from among the at least one first relay UE, a relay UE whose SL-RSRP or SD-RSRP with a second UE satisfies a second threshold condition is selected as a second relay UE.

[0136] Here, in the embodiments of the present disclosure, the realization form in which the SL-RSRP or SD-RSRP between the second UE and the relay UE satisfies the second threshold condition can be realized in any of the embodiments of the present disclosure, and is not limited to this here, and no explanation will be given.

[0137] In step 303, send a discovery response message to the first UE based on the second relay UE, which is used by the first UE to select and reselect a relay UE.

[0138] In one implementation, the target remote UE sends a discovery response message to the source remote UE via a second relay UE. The source remote UE receives the discovery response message forwarded through the second relay UE, and selects relay UEs from the second relay UEs whose SL-RSRP or SD-RSRP between the source remote UE and the second relay UE satisfies a first threshold condition as candidate relay UEs. The source remote UE determines one or more relay UEs from the candidate relay UEs as target relay UEs to be selected or reselected based on UE implementation. Here, the implementation in which the SL-RSRP or SD-RSRP between the source remote UE (i.e., the first UE) and the relay UE satisfies the first threshold condition can be realized in any of the embodiments of the present disclosure, and is not limited thereto, and description thereof will be omitted.

[0139] By implementing the embodiments of the present disclosure, the target remote UE selects or reselects a relay UE based on the relay selection conditions of the target remote UE to transmit a discovery response message, and the source remote UE selects relay UEs that meet the relay selection conditions of the source remote UE based on the relay UEs selected or reselected by the target remote UE to set them as candidate relay UEs, thereby solving the problem of how to select and reselect relay UEs in UE-to-UE (U2U) scenarios and ensuring normal communication of terminal devices.

[0140] In Mode B, if there are multiple U2U relay UEs, the source remote UE or target remote UE selects one U2U relay UE as the relay UE. Hereinafter, a second UE selection and reselection relay UE implementation in Mode B will be described in conjunction with an embodiment. Referring to FIG. 4, FIG. 4 is a flowchart of another relay UE selection and reselection method in a terminal (UE)-to-UE scenario provided by an embodiment of the present disclosure. Note that the method can be performed by a second UE. In one implementation, the first UE in this embodiment may be a source remote UE in a U2U scenario, and the second UE in this embodiment may be a target remote UE in a U2U scenario. As shown in FIG. 4, the method may include, but is not limited to, the following steps:

[0141] In step 401, candidate relay UEs are determined based on a third selection condition.

[0142] Here, the third selection condition includes any one of the following 1) to 2). 1) selecting a relay UE whose SL-RSRP or SD-RSRP between the second UE and the relay UE satisfies a second threshold condition as a candidate relay UE; 2) Selecting a relay UE as a candidate relay UE, where the SL-RSRP or SD-RSRP between the first UE and the relay UE satisfies a first threshold condition, and the SL-RSRP or SD-RSRP between the second UE and the relay UE satisfies a second threshold condition.

[0143] Optionally, in an embodiment of the present disclosure, the third selection condition includes selecting a relay UE whose SL-RSRP or SD-RSRP between the second UE and the relay UE satisfies the second threshold condition as a candidate relay UE, and taking the example that the first UE may be a source remote UE in a U2U scenario and the second UE may be a target remote UE in a U2U scenario, the target remote UE can select a relay UE whose SL-RSRP or SD-RSRP between the target remote UE and the relay UE satisfies the second threshold condition as a candidate relay UE.

[0144] In one possible implementation, the second UE receives a discovery request message sent by the first UE via at least one third relay UE, where the at least one third relay UE is a relay UE selected by the first UE and whose SL-RSRP or SD-RSRP between the first UE and the second UE satisfies a first threshold condition, and the second UE selects, from the at least one third relay UE, all third relay UEs whose SL-RSRP or SD-RSRP between the second UE and the second UE satisfies a second threshold condition as candidate relay UEs. Here, the implementation in which the SL-RSRP or SD-RSRP between the second UE and the relay UE satisfies the second threshold condition and the implementation in which the SL-RSRP or SD-RSRP between the first UE and the relay UE satisfies the first threshold condition can be implemented in any of the embodiments of the present disclosure, and the present disclosure is not limited to this and will not be described further.

[0145] For example, in Mode B, the source remote UE selects as third relay UEs relay UEs whose SL-RSRP or SD-RSRP between itself and the source remote UE satisfies a first threshold condition, and the source remote UE transmits a discovery request message to the target remote UE via the third relay UE. The target remote UE receives the discovery request message forwarded via the third relay UE, and selects as candidate relay UEs all third relay UEs whose SL-RSRP or SD-RSRP between itself and the target remote UE satisfies a second threshold condition from the third relay UEs.

[0146] Optionally, in an embodiment of the present disclosure, the third selection condition includes selecting, as a candidate relay UE, a relay UE whose SL-RSRP or SD-RSRP between the first UE and the relay UE satisfies a first threshold condition and whose SL-RSRP or SD-RSRP between the second UE and the relay UE satisfies a second threshold condition. For example, the first UE may be a source remote UE in a U2U scenario, and the second UE may be a target remote UE in a U2U scenario. The target remote UE selects, as a candidate relay UE, a relay UE whose SL-RSRP or SD-RSRP between the target remote UE satisfies the second threshold condition and whose SL-RSRP or SD-RSRP between the target remote UE and the source remote UE satisfies the first threshold condition.

[0147] In one alternative implementation, the second UE obtains the SL-RSRP or SD-RSRP between the first UE and the relay UE, and the second UE can select as candidate relay UEs all relay UEs whose SL-RSRP or SD-RSRP between the second UE and the relay UE satisfies a second threshold condition and whose SL-RSRP or SD-RSRP between the second UE and the first UE satisfies a first threshold condition.

[0148] As an example of one possible implementation, the second UE may select, based on implementation, all relay UEs whose SL-RSRP or SD-RSRP between themselves and the second UE satisfies a second threshold condition as a second candidate relay UE set. The second UE selects, from the second candidate relay UE set, all relay UEs whose SL-RSRP or SD-RSRP between themselves and the first UE satisfies a first threshold condition as candidate relay UEs. As another example of a possible implementation, based on implementation, the second UE may select, as one candidate relay UE set, all relay UEs whose SL-RSRP or SD-RSRP between themselves and the first UE satisfies a first threshold condition, and select, from the candidate relay UE set, all relay UEs whose SL-RSRP or SD-RSRP between themselves and the second UE satisfies a second threshold condition as the candidate relay UEs.

[0149] Alternatively, the second UE may acquire the SL-RSRP or SD-RSRP between the first UE and the relay UE through a discovery signal of the relay UE or in another manner. Here, the implementation in which the SL-RSRP or SD-RSRP between the second UE and the relay UE satisfies the second threshold condition and the implementation in which the SL-RSRP or SD-RSRP between the first UE and the relay UE satisfies the first threshold condition may be implemented in any of the embodiments of the present disclosure, and the present disclosure is not limited thereto, and description thereof will be omitted.

[0150] For example, in Mode B, the target remote UE can acquire the SL-RSRP or SD-RSRP between the source remote UE and the relay UE through the discovery signal of the relay UE or other methods, and selects as candidate relay UEs all relay UEs whose SL-RSRP or SD-RSRP with the target remote UE satisfies the second threshold condition and whose SL-RSRP or SD-RSRP with the source remote UE satisfies the first threshold condition.

[0151] In step 402, a target relay UE to be selected or reselected is determined based on the candidate relay UEs.

[0152] In one alternative implementation, the second UE may select one candidate relay UE from the candidate relay UEs as the target relay UE based on implementation. In another alternative implementation, the second UE may select multiple relay UEs from the candidate relay UEs as the target relay UE based on implementation. Optionally, the second UE transmits a discovery response message to the first UE via the target relay UE.

[0153] By implementing the embodiments of the present disclosure, the source remote UE selects a relay UE that meets the conditions and forwards the discovery request message to it, and the target remote UE selects a relay UE that meets the conditions from the relay UEs that forwarded the discovery request message as a candidate relay UE, thereby realizing the target remote UE to select or reselect the target relay UE, which solves the problem of how to select and reselect a relay UE in a UE-to-UE (U2U) scenario and ensures normal communication of terminal devices.

[0154] It should be understood that the embodiment shown in FIG. 4 above describes an implementation of a relay UE selection and reselection method in a terminal (UE)-to-UE scenario according to an embodiment of the present disclosure from the perspective of a second UE. An embodiment of the present disclosure further proposes a relay UE selection and reselection method in a terminal (UE)-to-UE scenario, and the implementation of the relay UE selection and reselection method in a terminal (UE)-to-UE scenario will be described below from the perspective of a first UE. Referring to FIG. 5, FIG. 5 is a flowchart of another relay UE selection and reselection method in a terminal (UE)-to-UE scenario provided by an embodiment of the present disclosure. Note that the method can be performed by a first UE. In this embodiment, the first UE is a source remote UE in the terminal (UE)-to-UE scenario, and the second UE is a target remote UE in the terminal (UE)-to-UE scenario. As shown in FIG. 5, the method may include, but is not limited to, the following steps:

[0155] In step 501, a relay UE whose SL-RSRP or SD-RSRP between itself and the first UE satisfies a first threshold condition is selected as a third relay UE.

[0156] Here, the implementation form in which the SL-RSRP or SD-RSRP between the first UE and the relay UE satisfies the first threshold condition can be implemented in any of the embodiments of the present disclosure, and is not limited to this here, and no explanation will be given.

[0157] In one implementation, the source remote UE selects a relay UE whose SL-RSRP or SD-RSRP between itself and the source remote UE satisfies a first threshold condition as a third relay UE.

[0158] In step 502, send a discovery request message to the second UE based on the third relay UE, which is used by the second UE to select and reselect the relay UE.

[0159] In one implementation, the source remote UE sends a discovery request message to the target remote UE via a third relay UE, the target remote UE receives the discovery request message forwarded via the third relay UE, the target remote UE selects relay UEs whose SL-RSRP or SD-RSRP between the source remote UE and the target remote UE satisfies a second threshold condition as candidate relay UEs, and the target remote UE selects one or more relay UEs from the candidate relay UEs as target relay UEs to be selected or reselected.

[0160] By implementing the embodiments of the present disclosure, the source remote UE selects or reselects a relay UE based on the relay selection conditions of the source remote UE to forward the discovery request message, and the target remote UE selects relay UEs that meet the relay selection conditions of the target remote UE based on the relay UEs selected or reselected by the source remote UE to set them as candidate relay UEs, thereby solving the problem of how to select and reselect relay UEs in UE-to-UE (U2U) scenarios and ensuring normal communication of terminal devices.

[0161] An embodiment of the present disclosure further provides a method for triggering selection and reselection of a relay terminal in a terminal (UE)-to-UE scenario. Referring to FIG. 6, FIG. 6 is a flowchart of a method for triggering selection and reselection of a relay terminal in a terminal (UE)-to-UE scenario provided by an embodiment of the present disclosure. Note that the method can be performed by a terminal device. As shown in FIG. 6, the method may include, but is not limited to, the following steps:

[0162] In step 601, the terminal device triggers the selection or reselection of a relay terminal in response to the sidelink communication reference signal received power (SL-RSRP) or the sidelink discovery reference signal received power (SD-RSRP) between the terminal device and another terminal device satisfying the trigger condition for the selection and reselection of a relay terminal.

[0163] In one implementation, the SL-RSRP or SD-RSRP satisfying the trigger condition for relay terminal selection and reselection includes the SL-RSRP or SD-RSRP being less than or equal to a predefined threshold, or the SL-RSRP or SD-RSRP being less than a predefined threshold by at least one hysteresis parameter value. Optionally, the terminal device can determine the SL-RSRP or SD-RSRP between the terminal device and another terminal device, and compare the SL-RSRP or SD-RSRP with a predefined threshold to determine whether the SL-RSRP or SD-RSRP between the terminal device and another terminal device satisfies the trigger condition for relay terminal selection and reselection.

[0164] In one implementation, when the SL-RSRP and SD-RSRP between the terminal device and another terminal device can be acquired, the acquired SL-RSRP may be compared with a predefined threshold, or the acquired SD-RSRP may be compared with a predefined threshold, or the UE may select one of the SL-RSRP / SD-RSRP and compare it with a predefined threshold. When the terminal cannot acquire the SL-RSRP between the terminal device and another terminal device and can acquire only the SD-RSRP between the terminals, the terminal compares the acquired SD-RSRP with the predefined threshold. When the terminal cannot acquire the SD-RSRP between the terminal device and another terminal device and can acquire only the SL-RSRP between the terminal device and another terminal device, the terminal compares the acquired SL-RSRP with the predefined threshold.

[0165] In addition, in the embodiments of the present disclosure, the predefined threshold may be set or preset in the terminal device by a network device. When the terminal device is in-coverage, the terminal device can obtain the predefined threshold set by the network device using specific RRC signaling or SIB. When the terminal device is out-of-coverage, the terminal device can obtain the predefined threshold by pre-configuration.

[0166] In one alternative implementation, the terminal device may be a source remote terminal in a UE-to-UE scenario, and the other terminal device may be a target remote terminal in a UE-to-UE scenario.

[0167] As an example of a possible implementation, a source remote terminal determines the SL-RSRP or SD-RSRP between the source remote terminal and a target remote terminal, compares the SL-RSRP or SD-RSRP with a predefined threshold, and determines whether the SL-RSRP or SD-RSRP between the source remote terminal and the target remote terminal satisfies a trigger condition for relay terminal selection and reselection. For example, if the SL-RSRP or SD-RSRP between the source remote terminal and the target remote terminal is equal to or less than the predefined threshold, or if the SL-RSRP or SD-RSRP is smaller than the predefined threshold by at least one hysteresis parameter value, the source remote terminal triggers the selection of a relay terminal. Here, the implementation in which the source remote terminal selects a relay terminal can be implemented in any of the embodiments of the present disclosure, and is not limited thereto, and description thereof will be omitted here.

[0168] In another alternative implementation, the terminal device is a target remote terminal in a UE-to-UE scenario, and the other terminal device is a source remote terminal in a UE-to-UE scenario.

[0169] As an example of a possible implementation, the target remote terminal determines the SL-RSRP or SD-RSRP between the source remote terminal and the target remote terminal, compares the SL-RSRP or SD-RSRP with a predefined threshold, and determines whether the SL-RSRP or SD-RSRP between the target remote terminal and the source remote terminal satisfies the trigger condition for relay terminal selection and reselection. For example, if the SL-RSRP or SD-RSRP between the source remote terminal and the target remote terminal is equal to or less than the predefined threshold, or if the SL-RSRP or SD-RSRP is smaller than the predefined threshold by at least one hysteresis parameter value, the target remote terminal triggers the selection of a relay terminal. Here, the implementation in which the target remote terminal selects a relay terminal can be implemented in any of the embodiments of the present disclosure, and is not limited thereto, and description thereof will be omitted here.

[0170] In another possible implementation, the terminal device is a source remote terminal in a UE-to-UE scenario, and the other terminal device is a relay terminal in a UE-to-UE scenario.

[0171] As an example of a possible implementation, the source remote terminal determines the SL-RSRP or SD-RSRP between the source remote terminal and the relay terminal, compares the SL-RSRP or SD-RSRP with a predefined threshold, and determines whether the SL-RSRP or SD-RSRP between the source remote terminal and the relay terminal satisfies the trigger condition for relay terminal selection and reselection. For example, if the SL-RSRP or SD-RSRP between the source remote terminal and the relay terminal is equal to or less than the predefined threshold, or if the SL-RSRP or SD-RSRP is smaller than the predefined threshold by at least one hysteresis parameter value, the source remote terminal triggers reselection of the relay terminal. Here, the implementation of the source remote terminal reselecting the relay terminal can be implemented in any of the embodiments of the present disclosure, and is not limited thereto, and description thereof will be omitted here.

[0172] In another possible implementation, the terminal device is a source remote terminal and a target remote terminal in a UE-to-UE scenario, and the other terminal device is a relay terminal in a UE-to-UE scenario.

[0173] As an example of a possible implementation, the target remote terminal determines the SL-RSRP or SD-RSRP between the target remote terminal and a relay terminal, compares the SL-RSRP or SD-RSRP with a predefined threshold, and determines whether the SL-RSRP or SD-RSRP between the target remote terminal and a relay terminal satisfies the trigger condition for relay terminal selection and reselection. For example, if the SL-RSRP or SD-RSRP between the target remote terminal and a relay terminal is equal to or less than the predefined threshold, or if the SL-RSRP or SD-RSRP is smaller than the predefined threshold by at least one hysteresis parameter value, the target remote terminal triggers reselection of the relay terminal. Here, the implementation of the target remote terminal reselecting the relay terminal can be implemented in any of the embodiments of the present disclosure, and is not limited thereto, and description thereof will be omitted here.

[0174] By implementing the embodiments of the present disclosure, if a terminal device determines that the SL-RSRP or SD-RSRP between the terminal device and another terminal device satisfies the trigger conditions for relay terminal selection and reselection, the problem of relay UE selection and reselection in a UE-to-UE (U2U) scenario can be solved by triggering relay terminal selection or reselection, and normal communication of the terminal device can be ensured.

[0175] In the above embodiments provided by the present disclosure, the methods provided by the embodiments of the present disclosure are described from the perspective of terminal devices (e.g., the first UE and second UE described above). To realize each function of the methods provided by the above embodiments of the present disclosure, the terminal devices (e.g., the first UE and second UE described above) may include a hardware structure or a software module, and realize each of the above functions in the form of a hardware structure, a software module, or a combination of a hardware structure and a software module. Some of the above functions can be performed in the form of a hardware structure, a software module, or a combination of a hardware structure and a software module.

[0176] 7, which is a schematic structural diagram of a communication device 70 provided by an embodiment of the present disclosure. The communication device 70 shown in FIG. 7 may include a transceiver module 701 and a processing module 702. The transceiver module 701 may include a transmitting module and / or a receiving module, where the transmitting module realizes a transmitting function and the receiving module realizes a receiving function, and the transceiver module 701 may realize a transmitting function and / or a receiving function.

[0177] The communication device 70 may be a terminal device (for example, the first UE and the second UE in the above-described method embodiment), may be a device in the terminal device, or may be a device usable in conjunction with the terminal device.

[0178] When the communication device 70 is a terminal device (e.g., a first UE in the embodiment shown in FIG. 1 ), the processing module 702 determines a candidate relay UE based on a first selection condition, and the processing module 702 further determines a target relay UE to be selected or reselected based on the candidate relay UE. Here, the first selection condition includes any one of the following: selecting a relay UE that includes a terminal identifier of the second UE in a notification message or a neighbor list as a candidate relay UE; selecting a relay UE whose sidelink communication reference signal received power (SL-RSRP) or sidelink discovery reference signal received power (SD-RSRP) satisfies a threshold condition as a candidate relay UE; and selecting a relay UE that includes a terminal identifier of the second UE in a notification message or a neighbor list and whose SL-RSRP or SD-RSRP satisfies a threshold condition as a candidate relay UE. Here, the second UE is a target communication UE of the first UE, and the first UE communicates with the second UE via the relay UE.

[0179] In one implementation, a relay UE whose SL-RSRP or SD-RSRP satisfies a threshold condition includes any one of a relay UE whose SL-RSRP or SD-RSRP with a first UE satisfies a first threshold condition, a relay UE whose SL-RSRP or SD-RSRP with a second UE satisfies a second threshold condition, and a relay UE whose SL-RSRP or SD-RSRP with a first UE satisfies a first threshold condition and whose SL-RSRP or SD-RSRP with a second UE satisfies a second threshold condition.

[0180] In one implementation, the SL-RSRP or SD-RSRP meeting the threshold condition includes the SL-RSRP or SD-RSRP being greater than or equal to a predefined threshold, or the SL-RSRP or SD-RSRP being greater than a predefined threshold by at least one hysteresis parameter value.

[0181] In one alternative implementation, the predefined thresholds include a first predefined threshold and a second predefined threshold, where the first predefined threshold is a lowest threshold and the second predefined threshold is a highest threshold, and where SL-RSRP or SD-RSRP being equal to or greater than the predefined thresholds includes SL-RSRP or SD-RSRP being equal to or greater than the first predefined threshold and equal to or less than the second predefined threshold, and SL-RSRP or SD-RSRP being greater than the predefined thresholds by at least one hysteresis parameter value includes SL-RSRP or SD-RSRP being greater than the first predefined threshold by at least one hysteresis parameter value and less than the second predefined threshold by at least one hysteresis parameter value.

[0182] In one selectable implementation, the processing module 702 specifically selects one candidate relay UE from the candidate relay UEs as a target relay UE based on implementation, or selects multiple relay UEs from the candidate relay UEs as target relay UEs based on implementation.

[0183] When the communication device 70 is a terminal device (e.g., the first UE in the embodiment shown in FIG. 2 above), the processing module 702 determines a candidate relay UE based on a second selection condition, and the processing module 702 further determines a target relay UE to be selected or reselected based on the candidate relay UE. Here, the second selection condition includes any one of: selecting a relay UE whose SL-RSRP or SD-RSRP between the first UE and the relay UE satisfies a first threshold condition as a candidate relay UE; or selecting a relay UE whose SL-RSRP or SD-RSRP between the first UE and the relay UE satisfies the first threshold condition and whose SL-RSRP or SD-RSRP between the second UE and the relay UE satisfies a second threshold condition as a candidate relay UE. Here, the first UE is a source remote UE in a terminal (UE)-to-UE scenario, and the second UE is a target remote UE in a terminal (UE)-to-UE scenario.

[0184] In one implementation, the transceiver module 701 transmits a discovery request message to a second UE via at least one first relay UE. The transceiver module 701 further receives a discovery response message transmitted from at least one second relay UE, where the at least one second relay UE is a relay UE selected by the second UE from among the at least one first relay UE, the SL-RSRP or SD-RSRP with the second UE satisfying a second threshold condition. The processing module 702 selects, from among the at least one second relay UE, all second relay UEs whose SL-RSRP or SD-RSRP with the first UE satisfy the first threshold condition as candidate relay UEs.

[0185] In one alternative implementation, the processing module 702 obtains the SL-RSRP or SD-RSRP between the second UE and the relay UE, and further selects all relay UEs whose SL-RSRP or SD-RSRP with the first UE satisfies a first threshold condition as a first set of candidate relay UEs, and selects all relay UEs from the first set of candidate relay UEs whose SL-RSRP or SD-RSRP with the second UE satisfies a second threshold condition as candidate relay UEs.

[0186] In one selectable implementation, the processing module 702 specifically selects one candidate relay UE from the candidate relay UEs as a target relay UE based on implementation, or selects multiple relay UEs from the candidate relay UEs as target relay UEs based on implementation.

[0187] When the communication device 70 is a terminal device (e.g., the second UE in the embodiment shown in FIG. 3 above), the transceiver module 701 receives a discovery request message sent from at least one first relay UE. The processing module 702 selects, from the at least one first relay UE, a relay UE whose SL-RSRP or SD-RSRP with the second UE satisfies a second threshold condition as a second relay UE. The transceiver module 701 further transmits a discovery response message to the first UE based on the second relay UE, and the second relay UE is used by the first UE to select and reselect a relay UE. Here, the first UE is a source remote UE in a terminal (UE)-to-UE scenario, and the second UE is a target remote UE in a terminal (UE)-to-UE scenario.

[0188] When the communication device 70 is a terminal device (e.g., the second UE in the embodiment shown in FIG. 4 ), the processing module 702 determines a candidate relay UE based on a third selection condition. The processing module 702 further determines a target relay UE to be selected or reselected based on the candidate relay UE. Here, the third selection condition includes any one of: selecting a relay UE for which the SL-RSRP or SD-RSRP between the second UE and the relay UE satisfies a second threshold condition as a candidate relay UE; and selecting a relay UE for which the SL-RSRP or SD-RSRP between the first UE and the relay UE satisfies the first threshold condition and the SL-RSRP or SD-RSRP between the second UE and the relay UE satisfies the second threshold condition as a candidate relay UE. Here, the first UE is a source remote UE in a terminal (UE)-to-UE scenario, and the second UE is a target remote UE in a terminal (UE)-to-UE scenario.

[0189] In one implementation, the transceiver module 701 receives a discovery request message sent from at least one third relay UE, where the at least one third relay UE is a relay UE selected by the first UE and whose SL-RSRP or SD-RSRP with the first UE satisfies a first threshold condition. The processing module 702 selects, from the at least one third relay UE, all third relay UEs whose SL-RSRP or SD-RSRP with the second UE satisfies a second threshold condition as candidate relay UEs.

[0190] In one alternative implementation, the processing module 702 further obtains an SL-RSRP or SD-RSRP between the first UE and the relay UE. The processing module 702 selects all relay UEs whose SL-RSRP or SD-RSRP with the second UE satisfies a second threshold condition as a second set of candidate relay UEs. The processing module 702 selects all relay UEs whose SL-RSRP or SD-RSRP with the first UE satisfies a first threshold condition from the second set of candidate relay UEs as candidate relay UEs.

[0191] In one implementation, the processing module 702 specifically selects one candidate relay UE from the candidate relay UEs as a target relay UE based on implementation, or selects multiple relay UEs from the candidate relay UEs as target relay UEs based on implementation.

[0192] When the communication device 70 is a terminal device (for example, the first UE in the embodiment shown in FIG. 5 above), the processing module 702 selects a relay UE whose SL-RSRP or SD-RSRP with the first UE satisfies a first threshold condition as a third relay UE. The transceiver module 701 sends a discovery request message to the second UE based on the third relay UE, and the third relay UE is used by the second UE to select and reselect a relay UE. Here, the first UE is a source remote UE in a terminal (UE)-to-UE scenario, and the second UE is a target remote UE in a terminal (UE)-to-UE scenario.

[0193] In the case where the communication device 70 is a terminal device (the terminal device in the embodiment shown in FIG. 6 ): the processing module 702 triggers the selection or reselection of a relay terminal in response to the sidelink communication reference signal received power (SL-RSRP) or the sidelink discovery reference signal received power (SD-RSRP) between the terminal device and another terminal device satisfying the trigger condition for the selection and reselection of a relay terminal.

[0194] In one implementation, the SL-RSRP or SD-RSRP meeting the trigger conditions for relay terminal selection and reselection includes the SL-RSRP or SD-RSRP being less than or equal to a predefined threshold, or the SL-RSRP or SD-RSRP being less than a predefined threshold by at least one hysteresis parameter value.

[0195] In one implementation, the terminal device is a source remote terminal in a UE-to-UE scenario and the other terminal device is a target remote terminal in a UE-to-UE scenario, or the terminal device is a target remote terminal in a UE-to-UE scenario and the other terminal device is a source remote terminal in a UE-to-UE scenario, or the terminal device is a source remote terminal or a target remote terminal in a UE-to-UE scenario and the other terminal device is a relay terminal in a UE-to-UE scenario.

[0196] Regarding the apparatus in the above-described embodiment, the specific method by which each module performs an operation is described in detail in the embodiment relating to the method, but will not be described in detail here.

[0197] Referring to Figure 8, Figure 8 is a schematic diagram of another communication device 80 provided by an embodiment of the present disclosure. The communication device 80 may be a terminal device (e.g., the first UE and the second UE in the above-mentioned method embodiment), or may be a chip, a chip system, a processor, etc. that supports the implementation of the above-mentioned method by the terminal device. The device may be used to implement the method described in the above-mentioned method embodiment, and for details, please refer to the description of the above-mentioned method embodiment.

[0198] The communication device 80 may include one or more processors 801. The processor 801 may be a general-purpose processor or a special-purpose processor. For example, it may be a baseband processor or a central processor. The baseband processor may be used to process communication protocols and communication data, and the central processing unit may be used to control a communication device (e.g., a base station, a baseband chip, a terminal device, a terminal device chip, a DU or CU, etc.), execute a computer program, and process data of the computer program.

[0199] Optionally, the communication device 80 may further include one or more memories 802 capable of storing computer programs 804, and the processor 801 executes the computer programs 804 so that the communication device 80 performs the methods described in the above method embodiments. Optionally, data may be further stored in the memory 802. The communication device 80 and the memory 802 may be provided separately or integrated.

[0200] Optionally, the communication device 80 may further include a transceiver 805 and an antenna 806. The transceiver 805 may be referred to as a transmitting / receiving unit, a transceiver, or a transmitting / receiving circuit for realizing a transmitting / receiving function. The transceiver 805 may include a receiver and a transmitter, and the receiver may be referred to as a receiver or a receiving circuit for realizing a receiving function, and the transmitter may be referred to as a transmitter or a transmitting circuit for realizing a transmitting function.

[0201] Optionally, the communication device 80 may further include one or more interface circuits 807. The interface circuits 807 are used to receive and transmit code instructions to the processor 801. The processor 801 executes the code instructions to cause the communication device 80 to perform the methods described in the above method embodiments.

[0202] When the communication device 80 is a terminal device (for example, the first UE in the embodiment shown in FIG. 1 above): the processor 801 executes step 101 and step 102 in FIG.

[0203] When the communication device 80 is a terminal device (for example, the first UE in the embodiment shown in FIG. 2 above): the processor 801 executes step 201 and step 202 in FIG.

[0204] When the communication device 80 is a terminal device (for example, the second UE in the embodiment shown in FIG. 3 above): the transceiver 805 performs steps 301 and 303 in FIG. 3. The processor 801 performs step 302 in FIG. 3.

[0205] When the communication device 80 is a terminal device (for example, the second UE in the embodiment shown in FIG. 4 above): the processor 801 executes step 401 and step 402 in FIG.

[0206] When the communication device 80 is a terminal device (for example, the first UE in the embodiment shown in FIG. 5 above): the processor 801 performs step 501 in FIG. 5. The transceiver 805 performs step 502 in FIG.

[0207] When the communication device 80 is a terminal device (for example, the terminal device in the embodiment shown in FIG. 6 above), the processor 801 executes step 601 in FIG.

[0208] In one embodiment, the processor 801 may include a transceiver for implementing receiving and transmitting functions. For example, the transceiver may be a transmitting and receiving circuit, an interface, or an interface circuit. The transmitting and receiving circuit, interface, or interface circuit for implementing the receiving and transmitting functions may be separate or integrated. The transmitting and receiving circuit, interface, or interface circuit may be used to read or write code or data, or the transmitting and receiving circuit, interface, or interface circuit may be used to transmit or communicate signals.

[0209] In one implementation, the processor 801 may store a computer program that, when executed on the processor 801, causes the communication device 80 to perform the methods described in the above method embodiments. The computer program may be hardened within the processor 801, in which case the processor 801 may be implemented by hardware.

[0210] In one implementation, the communication device 80 may include circuitry capable of performing the transmitting, receiving, or communicating functions of the method embodiments described above. The processors and transceivers described in this disclosure may be implemented in an integrated circuit (IC), an analog IC, a radio frequency integrated circuit (RFIC), a hybrid signal IC, an application specific integrated circuit (ASIC), a printed circuit board (PCB), an electronic device, or the like. The processors and transceivers may also be fabricated in various IC process technologies, such as complementary metal oxide semiconductor (CMOS), n-type metal oxide semiconductor (NMOS), p-type metal oxide semiconductor (PMOS), bipolar junction transistor (BJT), bipolar CMOS (BiCMOS), silicon germanium (SiGe), or gallium arsenide (GaAs).

[0211] The communication devices described in the above embodiments may be terminal devices (e.g., the first UE and the second UE in the above method embodiments), but the scope of the communication devices described in the present disclosure is not limited thereto, and the structure of the communication devices may not be limited to that shown in FIG. 8. The communication device may be an independent device or part of a larger device. For example, the communication device may be as follows: (1) An independent integrated circuit IC, or chip, or chip system or subsystem; (2) having a set of one or more ICs, optionally including a memory component for storing data, computer programs; (3) ASICs such as modems, (4) Modules that can be incorporated into other devices; (5) Receivers, terminal devices, smart terminal devices, mobile phones, wireless devices, handhelds, mobile units, in-vehicle devices, network-side devices, cloud devices, artificial intelligence devices, etc. (6) Others.

[0212] Those skilled in the art can also understand that various illustrative logical blocks and steps described in the embodiments of the present disclosure can be realized by electronic hardware, computer software, or a combination of both. Whether such functions are realized by hardware or software is determined by the specific application and the overall system design requirements. Those skilled in the art can realize the described functions using various methods for each specific application, but this implementation should not be understood as exceeding the scope of protection of the embodiments of the present disclosure.

[0213] The present disclosure further provides a computer-readable storage medium having stored thereon instructions that, when executed by a computer, implement the functionality of any of the method embodiments described above.

[0214] The present disclosure further provides a computer program product that, when executed by a computer, implements the functionality of any of the above method embodiments.

[0215] The above-described embodiments may be implemented in whole or in part by software, hardware, firmware, or any combination thereof. When implemented using software, they may be implemented in whole or in part in the form of a computer program product. The computer program product includes one or more computer programs. The processes or functions according to the above-described embodiments of the present disclosure are generated in whole or in part when the computer programs are loaded and executed by a computer. The computer may be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer program may be stored on a computer-readable storage medium or transmitted from one computer-readable storage medium to another; for example, the computer program may be transmitted from one website, computer, server, or data center to another via wire (e.g., coaxial cable, fiber optic, digital subscriber line (DSL)) or wireless (e.g., infrared, radio, microwave, etc.). The computer-readable storage medium may be any available medium accessible by a computer, or may include a data storage device such as a server, data center, or the like integrated with one or more available media. The available medium may be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape), an optical medium (e.g., digital video disc (DVD)), or a semiconductor medium (e.g., solid state disk (SSD)).

[0216] Those skilled in the art will understand that the various numerals such as first, second, etc. in the present disclosure are merely for the convenience of explanation and do not limit the scope of the embodiments of the present disclosure, nor do they represent priority.

[0217] At least one of the features of the present disclosure may be described as one or more, and the more may be two, three, four or more, and is not limited to the present disclosure. In the embodiments of the present disclosure, for one technical feature, the technical features in the technical feature category are distinguished by "first," "second," "third," "A," "B," "C," and "D," etc., and there is no order of precedence or chronology between the technical features described as "first," "second," "third," "A," "B," "C," and "D."

[0218] The correspondences shown in each table in the present disclosure may be set or predefined. The values ​​of the information in each table are merely examples and may be set to other values ​​and are not limited to the present disclosure. When setting the correspondences between information and each parameter, it is not necessary to set all of the correspondences shown in each table. For example, in the tables of the present disclosure, the correspondences shown by certain rows may not be set. As another example, appropriate transformations such as splitting and merging can be performed based on the above tables. The names of the parameters shown in the titles of the above tables may be other names understandable by the communication device, and the values ​​or representation methods of the parameters may be other values ​​or representation methods understandable by the communication device. The above tables may be implemented using other data structures, such as arrays, queues, containers, stacks, linear tables, pointers, link tables, trees, diagrams, structures, classes, heaps, hash lists, or hash tables.

[0219] Predefined in this disclosure can be understood as defined, predefined, stored, prestored, prenegotiated, pre-set, hardened, or pre-baked.

[0220] Those skilled in the art will recognize that the units and algorithm steps of each example described in the embodiments disclosed herein can be realized in electronic hardware or a combination of computer software and electronic hardware. Whether a function is implemented in hardware or software is determined by the specific application and design constraints of the technical solution. Those skilled in the art may realize the described functions using different methods for each specific application, but such realization should not be considered beyond the scope of the present disclosure.

[0221] As will be apparent to those skilled in the art, for convenience and brevity of description, the specific operating processes of the above-described systems, devices and units may refer to the corresponding processes in the above-described method embodiments, and the description thereof will be omitted here.

[0222] As described above, the present disclosure only covers specific embodiments, but the scope of protection of the present disclosure is not limited thereto, and those skilled in the art can easily imagine that modifications or replacements within the technical scope disclosed in the present disclosure should fall within the scope of protection of the present disclosure. Therefore, the scope of protection of the present disclosure should be determined based on the scope of protection of the claims.

Claims

1. 1. A method for relay UE selection and reselection in a terminal (UE) to UE scenario, the method being performed by a first UE, the method comprising: determining candidate relay UEs based on a first selection condition; determining a target relay UE to be selected or reselected based on the candidate relay UE; The first selection condition is: selecting a relay UE including a terminal identifier of a second UE in a notification message or a neighbor list as a candidate relay UE, wherein the second UE is a target communication UE of the first UE, and the first UE communicates with the second UE via the relay UE; selecting, as candidate relay UEs, relay UEs whose sidelink communication reference signal received power (SL-RSRP) or sidelink discovery reference signal received power (SD-RSRP) meet a threshold condition; selecting a relay UE that includes a terminal identifier of the second UE in the notification message or the neighbor list and whose SL-RSRP or SD-RSRP satisfies a threshold condition as a candidate relay UE; A method for relay UE selection and reselection in a UE-to-UE scenario, comprising:

2. A relay UE whose SL-RSRP or SD-RSRP satisfies a threshold condition: a relay UE whose SL-RSRP or SD-RSRP between the first UE and the relay UE satisfies a first threshold condition; a relay UE whose SL-RSRP or SD-RSRP between the relay UE and the second UE satisfies a second threshold condition; a relay UE whose SL-RSRP or SD-RSRP between the first UE and the relay UE satisfies a first threshold condition and whose SL-RSRP or SD-RSRP between the second UE and the relay UE satisfies a second threshold condition; The method of claim 1, wherein the relay UE selection and reselection in a UE-to-UE scenario is

3. The SL-RSRP or SD-RSRP satisfies the threshold condition. the SL-RSRP or SD-RSRP is greater than or equal to a predefined threshold; or the SL-RSRP or SD-RSRP is greater than the predefined threshold by at least one hysteresis parameter value. The method of claim 1, wherein the relay UE selection and reselection in a UE-to-UE scenario is

4. the predefined thresholds include a first predefined threshold and a second predefined threshold, the first predefined threshold being a lowest threshold and the second predefined threshold being a highest threshold; The SL-RSRP or SD-RSRP being equal to or greater than a predefined threshold the SL-RSRP or SD-RSRP is greater than or equal to the first predefined threshold and less than or equal to the second predefined threshold; The SL-RSRP or SD-RSRP being greater than the predefined threshold by at least one hysteresis parameter value, the SL-RSRP or SD-RSRP being greater than the first predefined threshold by at least one hysteresis parameter value and less than the second predefined threshold by at least one hysteresis parameter value. The method of claim 3, wherein the relay UE selection and reselection in a UE-to-UE scenario is

5. determining a target relay UE to be selected or reselected based on the candidate relay UEs, Based on implementation, selecting one candidate relay UE from the candidate relay UEs as the target relay UE; Alternatively, based on implementation, selecting a plurality of relay UEs from the candidate relay UEs as the target relay UE. The method of claim 1, wherein the relay UE selection and reselection in a UE-to-UE scenario is

6. 1. A method for relay UE selection and reselection in a terminal (UE) to UE scenario, the method being performed by a first UE, the method comprising: determining candidate relay UEs based on a second selection condition; determining a target relay UE to be selected or reselected based on the candidate relay UE; The second selection condition is Selecting a relay UE, in which SL-RSRP or SD-RSRP between the first UE and the relay UE satisfies a first threshold condition, as a candidate relay UE; selecting, as a candidate relay UE, a relay UE in which SL-RSRP or SD-RSRP between the first UE and the relay UE satisfies a first threshold condition and SL-RSRP or SD-RSRP between the second UE and the relay UE satisfies a second threshold condition; The first UE is a source remote UE in the terminal (UE) to UE scenario, and the second UE is a target remote UE in the terminal (UE) to UE scenario; A method for relay UE selection and reselection in a UE-to-UE scenario, comprising:

7. The step of determining candidate relay UEs based on the second selection condition includes: sending a discovery request message to the second UE via at least one first relay UE; receiving a discovery response message transmitted from at least one second relay UE, wherein the at least one second relay UE is a relay UE selected by the second UE from among the at least one first relay UE, and whose SL-RSRP or SD-RSRP between the second UE and the at least one second relay UE satisfies a second threshold condition; selecting, from the at least one second relay UE, all second relay UEs whose SL-RSRP or SD-RSRP between the first UE and the second relay UE satisfies a first threshold condition as the candidate relay UEs; The method of claim 6, wherein the relay UE selection and reselection in a UE-to-UE scenario is

8. The step of determining candidate relay UEs based on the second selection condition includes: obtaining a SL-RSRP or SD-RSRP between the second UE and a relay UE; selecting, as the candidate relay UEs, all relay UEs whose SL-RSRP or SD-RSRP between the first UE and the relay UE satisfies a first threshold condition and whose SL-RSRP or SD-RSRP between the second UE and the relay UE satisfies a second threshold condition; The method of claim 6, wherein the relay UE selection and reselection in a UE-to-UE scenario is

9. determining a target relay UE to be selected or reselected based on the candidate relay UEs, Based on implementation, selecting one candidate relay UE from the candidate relay UEs as the target relay UE; Alternatively, based on implementation, selecting a plurality of relay UEs from the candidate relay UEs as the target relay UE. The method for relay UE selection and reselection in a UE-to-UE scenario according to any one of claims 6 to 8.

10. 1. A method for relay UE selection and reselection in a terminal (UE) to UE scenario, the method being performed by a second UE, the method comprising: receiving a discovery request message sent from at least one first relay UE; selecting, from the at least one first relay UE, a relay UE whose SL-RSRP or SD-RSRP between the first relay UE and the second relay UE satisfies a second threshold condition, as a second relay UE; transmitting a discovery response message to the first UE based on the second relay UE, the second relay UE being used by the first UE to select and reselect a relay UE; The first UE is a source remote UE in the terminal (UE) to UE scenario, and the second UE is a target remote UE in the terminal (UE) to UE scenario; A method for relay UE selection and reselection in a UE-to-UE scenario, comprising:

11. 1. A method for relay UE selection and reselection in a terminal (UE) to UE scenario, the method being performed by a second UE, the method comprising: determining candidate relay UEs based on a third selection condition; determining a target relay UE to be selected or reselected based on the candidate relay UE; The third selection condition is: Selecting a relay UE, in which SL-RSRP or SD-RSRP between the second UE and the relay UE satisfies a second threshold condition, as a candidate relay UE; selecting a relay UE, in which SL-RSRP or SD-RSRP between the first UE and the relay UE satisfies a first threshold condition, and SL-RSRP or SD-RSRP between the second UE and the relay UE satisfies a second threshold condition, as a candidate relay UE; The first UE is a source remote UE in the terminal (UE) to UE scenario, and the second UE is a target remote UE in the terminal (UE) to UE scenario; A method for relay UE selection and reselection in a UE-to-UE scenario, comprising:

12. determining a candidate relay UE based on the third selection condition, receiving a discovery request message transmitted from at least one third relay UE, the at least one third relay UE being a relay UE selected by the first UE and having a SL-RSRP or SD-RSRP between the first UE and the third relay UE satisfying a first threshold condition; selecting, from the at least one third relay UE, all third relay UEs whose SL-RSRP or SD-RSRP between the third relay UE and the second UE satisfies a second threshold condition as the candidate relay UEs; The method of claim 11, wherein the relay UE selection and reselection in a UE-to-UE scenario is

13. determining a candidate relay UE based on the third selection condition, obtaining a SL-RSRP or SD-RSRP between the first UE and a relay UE; selecting, as the candidate relay UEs, all relay UEs whose SL-RSRP or SD-RSRP between the first UE and the relay UE satisfies a first threshold condition and whose SL-RSRP or SD-RSRP between the second UE and the relay UE satisfies a second threshold condition; The method of claim 11, wherein the relay UE selection and reselection in a UE-to-UE scenario is

14. determining a target relay UE to be selected or reselected based on the candidate relay UEs, Based on implementation, selecting one candidate relay UE from the candidate relay UEs as the target relay UE; Alternatively, based on implementation, selecting a plurality of relay UEs from the candidate relay UEs as the target relay UE. The method for relay UE selection and reselection in a UE-to-UE scenario according to any of claims 11 to 13.

15. 1. A method for relay UE selection and reselection in a terminal (UE) to UE scenario, the method being performed by a first UE, the method comprising: selecting a relay UE whose SL-RSRP or SD-RSRP between the first UE and the relay UE satisfies a first threshold condition as a third relay UE; transmitting a discovery request message to the second UE based on the third relay UE, the third relay UE being used by the second UE to select and reselect a relay UE; The first UE is a source remote UE in the terminal (UE) to UE scenario, and the second UE is a target remote UE in the terminal (UE) to UE scenario; A method for relay UE selection and reselection in a UE-to-UE scenario, comprising:

16. 1. A method for triggering relay terminal selection and reselection in a terminal (UE)-to-UE scenario, the method being performed by a terminal device, the method comprising: triggering selection or reselection of a relay terminal in response to a sidelink communication reference signal received power (SL-RSRP) or a sidelink discovery reference signal received power (SD-RSRP) between the terminal device and another terminal device satisfying a trigger condition for selection and reselection of a relay terminal; A method for triggering relay UE selection and reselection in a UE-to-UE scenario, comprising:

17. The SL-RSRP or SD-RSRP satisfies the trigger conditions for relay terminal selection and reselection, the SL-RSRP or SD-RSRP is less than or equal to a predefined threshold; or the SL-RSRP or SD-RSRP is less than a predefined threshold by at least one hysteresis parameter value.

17. The method of claim 16, wherein the method triggers relay UE selection and reselection in a UE-to-UE scenario.

18. The terminal device is a source remote terminal in the UE-to-UE scenario, and the other terminal device is a target remote terminal in the UE-to-UE scenario, or Or, the terminal device is a target remote terminal in the UE-to-UE scenario, and the other terminal device is a source remote terminal in the UE-to-UE scenario; Or, the terminal device is a source remote terminal or a target remote terminal in the UE-to-UE scenario, and the other terminal device is a relay terminal in the UE-to-UE scenario.

18. A method for triggering relay UE selection and reselection in a UE-to-UE scenario according to claim 16 or 17.

19. A communication device, comprising: a processing module; The processing module determines candidate relay UEs based on a first selection condition; The processing module further determines a target relay UE to be selected or reselected based on the candidate relay UE; The first selection condition is: Selecting a relay UE including a terminal identifier of a second UE in a notification message or a neighbor list as a candidate relay UE, wherein the second UE is a target communication UE of a first UE, and the first UE communicates with the second UE via the relay UE; selecting, as candidate relay UEs, relay UEs whose sidelink communication reference signal received power (SL-RSRP) or sidelink discovery reference signal received power (SD-RSRP) meet a threshold condition; selecting a relay UE that includes a terminal identifier of the second UE in the notification message or the neighbor list and whose SL-RSRP or SD-RSRP satisfies a threshold condition as a candidate relay UE; A communication device comprising:

20. A communication device, comprising: a processing module; The processing module determines candidate relay UEs based on a second selection condition; The processing module further determines a target relay UE to be selected or reselected based on the candidate relay UE; The second selection condition is Selecting a relay UE, in which the SL-RSRP or SD-RSRP between the first UE and the relay UE satisfies a first threshold condition, as a candidate relay UE; selecting, as a candidate relay UE, a relay UE in which SL-RSRP or SD-RSRP between the first UE and the relay UE satisfies a first threshold condition and SL-RSRP or SD-RSRP between the second UE and the relay UE satisfies a second threshold condition; The first UE is a source remote UE in the terminal (UE) to UE scenario, and the second UE is a target remote UE in the terminal (UE) to UE scenario; A communication device comprising:

21. A communication device, a transceiver module for receiving a discovery request message sent from at least one first relay UE; a processing module for selecting, from the at least one first relay UE, a relay UE whose SL-RSRP or SD-RSRP with a second UE satisfies a second threshold condition, as a second relay UE; The transceiver module further transmits a discovery response message to the first UE based on the second relay UE, and the second relay UE is used by the first UE to select and reselect a relay UE; The first UE is a source remote UE in the terminal (UE) to UE scenario, and the second UE is a target remote UE in the terminal (UE) to UE scenario; A communication device comprising:

22. A communication device, comprising: a processing module; The processing module determines candidate relay UEs based on a third selection condition; The processing module further determines a target relay UE to be selected or reselected based on the candidate relay UE; The third selection condition is: Selecting a relay UE, in which the SL-RSRP or SD-RSRP between the second UE and the relay UE satisfies a second threshold condition, as a candidate relay UE; selecting a relay UE, in which SL-RSRP or SD-RSRP between the first UE and the relay UE satisfies a first threshold condition, and SL-RSRP or SD-RSRP between the second UE and the relay UE satisfies a second threshold condition, as a candidate relay UE; The first UE is a source remote UE in the terminal (UE) to UE scenario, and the second UE is a target remote UE in the terminal (UE) to UE scenario; A communication device comprising:

23. A communication device, a processing module for selecting a relay UE whose SL-RSRP or SD-RSRP with the first UE satisfies a first threshold condition as a third relay UE; a transceiver module for transmitting a discovery request message to a second UE based on the third relay UE, the third relay UE including a transceiver module used by the second UE to select and reselect a relay UE; The first UE is a source remote UE in the terminal (UE) to UE scenario, and the second UE is a target remote UE in the terminal (UE) to UE scenario; A communication device comprising:

24. A communication apparatus applied to a terminal device, a processing module for triggering selection or reselection of a relay terminal in response to a sidelink communication reference signal received power (SL-RSRP) or a sidelink discovery reference signal received power (SD-RSRP) between the terminal device and another terminal device satisfying a trigger condition for selection and reselection of the relay terminal; A communication device comprising:

25. A communication device, a processor and a memory, a computer program stored in the memory, and the processor executes the computer program stored in the memory to cause the communication device to perform the method according to any one of claims 1 to 5; A communication device comprising:

26. A communication device, a processor and a memory, a computer program stored in the memory, and the processor executes the computer program stored in the memory to cause the communication device to perform the method according to any one of claims 6 to 9; A communication device comprising:

27. A communication device, a processor and a memory, A computer program is stored in the memory, and the processor executes the computer program stored in the memory to cause the communication device to perform the method of claim 10. A communication device comprising:

28. A communication device, a processor and a memory, a computer program stored in the memory, and the processor executes the computer program stored in the memory to cause the communication device to perform the method according to any one of claims 11 to 14; A communication device comprising:

29. A communication device, a processor and a memory, A computer program is stored in the memory, and the processor executes the computer program stored in the memory to cause the communication device to perform the method of claim 15. A communication device comprising:

30. A communication device, a processor and a memory, A computer program is stored in the memory, and the processor executes the computer program stored in the memory to cause the communication device to perform the method according to any one of claims 16 to 18. A communication device comprising:

31. A computer-readable storage medium having instructions stored thereon, When said instructions are executed, the method according to any one of claims 1 to 5 is achieved. A computer-readable storage medium comprising:

32. A computer-readable storage medium having instructions stored thereon, When said instructions are executed, the method according to any one of claims 6 to 9 is achieved. A computer-readable storage medium comprising:

33. A computer-readable storage medium having instructions stored thereon, When the instructions are executed, the method of claim 10 is achieved. A computer-readable storage medium comprising:

34. A computer-readable storage medium having instructions stored thereon, When said instructions are executed, a method according to any one of claims 11 to 14 is achieved. A computer-readable storage medium comprising:

35. A computer-readable storage medium having instructions stored thereon, When the instructions are executed, the method of claim 15 is achieved. A computer-readable storage medium comprising:

36. A computer-readable storage medium having instructions stored thereon, When said instructions are executed, the method according to any one of claims 16 to 18 is achieved. A computer-readable storage medium comprising:

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