Method and apparatus for relay UE selection and reselection in UE-to-UE scenarios

Abstract

This disclosure provides a method and apparatus for selecting and reselecting a relay UE in a UE-to-UE scenario. The method includes: a first UE determining candidate relay UEs based on first selection criteria; and the first UE determining a target relay UE to be selected or reselected based on the candidate relay UEs. The first selection criteria include any one of the following: selecting a relay UE whose terminal identifier is included in a notification message or neighbor cell 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) meets a threshold condition as a candidate relay UE; and selecting a relay UE whose terminal identifier is included in a notification message or neighbor cell list, and whose SL-RSRP or SD-RSRP meets a threshold condition as a candidate relay UE. By implementing this disclosure, the problem of selecting and reselecting relay UEs in a UE-to-UE scenario can be solved, thereby ensuring normal communication of the terminal device.

Description

Technical Field

[0001] This disclosure relates to the field of communication technology, and in particular to a method and apparatus for selecting and reselecting relay UEs in a UE-to-UE scenario. Background Technology

[0002] To support direct communication between terminal equipment (also called user equipment, UE) and other UEs, a direct communication method (also called sidelink, SL) is introduced, with the interface between UEs being PC-5. Based on the correspondence between sending and receiving UEs, three transmission modes are supported on the sidelink: unicast, multicast, and broadcast. The sending UE transmits Sidelink Control Information (SCI) on the PSCCH (Physical Sidelink Control Channel) and a second-stage SCI on the PSSCH (Physical Sidelink Shared Channel), which carries the resource location of the transmitted data and source and destination identifiers. Upon receiving the SCI, the receiving UE determines whether to receive the corresponding data and which process to receive based on the source and destination UE identifiers. In a unicast connection, each UE corresponds to a destination identifier; in multicast, each UE can belong to one or more groups, each group corresponding to a destination identifier; and in broadcast, all UEs correspond to at least one destination identifier.

[0003] A UE can communicate with a base station without directly connecting to it, but instead through a relay of another UE. The UE not directly connected to the base station is called a remote UE, and the UE providing relay functionality is called a relay UE. One scenario is that UE A can connect to UE B without directly connecting to UE B, but instead through a relay of UE C. In this case, UE A and UE B are remote UEs, and UE C, providing relay functionality, is the relay UE. All UEs communicate with each other via sidelink unicast. This architecture is called U2U (UE to UE, terminal to terminal) relay.

[0004] However, there is currently a lack of effective means for selecting and reselecting relay UEs in U2U scenarios. Summary of the Invention

[0005] This disclosure provides a method and apparatus for selecting and reselecting a relay UE in a UE-to-UE scenario. It can be applied to vehicle-to-everything (V2X) communication, long-term evolution-vehicle (LTE-V) communication, vehicle-to-vehicle (V2V) communication, or intelligent driving, intelligent connected vehicles, and other fields. By selecting or reselecting a target relay UE through relay selection conditions, it can solve the problem of how to select and reselect a relay UE in a UE-to-UE (U2U) scenario, thereby ensuring normal communication of the terminal device.

[0006] In a first aspect, embodiments of this disclosure provide a relay UE selection and reselection method for a terminal UE-to-UE scenario, the method being executed by a first UE, the method comprising:

[0007] Candidate relay UEs are determined based on the first selection criteria;

[0008] Based on the candidate relay UEs, determine the target relay UE to be selected or reselected;

[0009] The first selection condition includes any one of the following:

[0010] Select a relay UE that includes the terminal identifier of the second UE in the notification message or the neighbor cell list as a candidate relay UE; wherein, the second UE is the target communication UE of the first UE, and the first UE communicates with the second UE through the relay UE;

[0011] Relay UEs that meet the threshold conditions for either the sidelink communication reference signal received power (SL-RSRP) or the sidelink discovery reference signal received power (SD-RSRP) are selected as candidate relay UEs.

[0012] Select a relay UE that includes the terminal identifier of the second UE in the notification message or the neighbor cell list, and whose SL-RSRP or SD.RSRP meets the threshold conditions as a candidate relay UE.

[0013] In this technical solution, the first UE can select or reselect the target relay UE according to the relay selection conditions, which can solve the problem of how to select and reselect the relay UE in the UE-to-UE (U2U) scenario, thereby ensuring the normal communication of the terminal device.

[0014] In one implementation, the relay UE that satisfies the threshold condition for the SL-RSRP or SD-RSRP includes any one of the following:

[0015] A relay UE whose SL-RSRP or SD-RSRP with the first UE meets the first threshold condition;

[0016] A relay UE whose SL-RSRP or SD-RSRP with the second UE meets the second threshold condition;

[0017] A relay UE whose SL-RSRP or SD-RSRP with the first UE meets a first threshold condition and whose SL-RSRP or SD-RSRP with the second UE meets a second threshold condition.

[0018] In one possible implementation, the SL-RSRP or SD-RSRP satisfies a threshold condition, including: 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 at least one hysteresis parameter value of the predefined threshold.

[0019] In one possible implementation, the predefined threshold includes a first predefined threshold and a second predefined threshold, wherein the first predefined threshold is a minimum threshold and the second predefined threshold is a maximum threshold; and wherein...

[0020] The SL-RSRP or SD-RSRP being greater than or equal to a predefined threshold includes:

[0021] 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;

[0022] The SL.RSRP or SD-RSRP being greater than at least one hysteresis parameter value of the predefined threshold includes:

[0023] The SL.RSRP or SD-RSRP is greater than at least one hysteresis parameter value of the first predefined threshold and less than at least one hysteresis parameter value of the second predefined threshold.

[0024] In one implementation, determining the selected or reselected target relay UE based on the candidate relay UEs includes: selecting one candidate relay UE from the candidate relay UEs as the target relay UE; or selecting multiple relay UEs from the candidate relay UEs as the target relay UE.

[0025] Secondly, this disclosure provides another method for relay UE selection and reselection in a terminal UE-to-UE scenario: the method is executed by a first UE, and the method includes:

[0026] Candidate relay UEs are determined based on the second selection criteria;

[0027] Based on the candidate relay UEs, determine the target relay UE to be selected or reselected;

[0028] The second selection condition includes any one of the following:

[0029] The relay UE that satisfies the first threshold condition between the first UE and the relay UE is selected as the candidate relay UE;

[0030] A relay UE is selected as a candidate relay UE if 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.

[0031] Wherein, the first UE is the source remote UE in the terminal UE to UE scenario, and the second UE is the target remote UE in the terminal UE to UE scenario.

[0032] In this technical solution, the source and remote UEs can select or reselect the target relay UE based on the relay selection conditions of the source and remote UEs. This can solve the problem of how to select and reselect the relay UE in UE-to-UE (U2U) scenarios, thereby ensuring the normal communication of terminal devices.

[0033] In one implementation, determining the candidate relay UE based on the second selection condition includes:

[0034] A discovery request message is sent from at least one first relay UE to the second UE;

[0035] Receive a discovery response message sent by at least one second relay UE; wherein, the at least one second relay UE is a relay UE selected by the second UE from the at least one first relay UE whose SL-RSRP or SD-RSRP with the second UE meets a second threshold condition;

[0036] From the at least one second relay UE, all second relay UEs whose SL-RSRP or SD-RSRP with the first UE meets the first threshold condition are selected as the candidate relay UEs.

[0037] In one possible implementation, determining the candidate relay UE based on the second selection condition includes:

[0038] Obtain the SL-RSRP or SD-RSRP between the second UE and the relay UE;

[0039] All relay UEs whose SL-RSRP or SD-RSRP with the first UE meets the first threshold condition and whose SL-RSRP or SD-RSRP with the second UE meets the second threshold condition are selected as candidate relay UEs.

[0040] In one possible implementation, determining the selected or reselected target relay UE based on the candidate relay UEs includes:

[0041] Based on the implementation, a candidate relay UE is selected from the candidate relay UEs as the target relay UE;

[0042] Alternatively, multiple relay UEs may be selected as the target relay UE from the candidate relay UEs.

[0043] Thirdly, embodiments of this disclosure provide another method for relay UE selection and reselection in a terminal UE-to-UE scenario, the method being executed by a second UE, the method comprising:

[0044] Receive at least one discovery request message sent by a first relay UE;

[0045] From the at least one first relay UE, select the relay UE whose SL-RSRP or SD-RSRP with the second UE satisfies the second threshold condition as the second relay UE;

[0046] The second relay UE sends a discovery response message to the first UE; the second relay UE is used by the first UE to select and reselect relay UEs.

[0047] Wherein, the first UE is the source remote UE in the terminal UE to UE scenario, and the second UE is the target remote UE in the terminal UE to UE scenario.

[0048] In this technical solution, the target remote UE can select or reselect a relay UE based on the relay selection conditions of the target remote UE to forward the discovery response message. Then, based on the relay UE selected or reselected by the target remote UE, the source remote UE can filter relay UEs that meet the relay selection conditions of the source remote UE as candidate relay UEs. This can solve the problem of how to select and reselect relay UEs in UE-to-UE (U2U) scenarios, thereby ensuring the normal communication of terminal devices.

[0049] Fourthly, embodiments of this disclosure provide another method for relay UE selection and reselection in a terminal UE-to-UE scenario, wherein the method is executed by a second UE, and the method includes:

[0050] Candidate relay UEs are determined based on the third selection criterion;

[0051] Based on the candidate relay UEs, determine the target relay UE to be selected or reselected;

[0052] The third selection condition includes any one of the following:

[0053] The relay UE that satisfies the second threshold condition between the second UE and the relay UE is selected as the candidate relay UE;

[0054] A relay UE is selected as a candidate relay UE if 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.

[0055] Wherein, the first UE is the source remote UE in the terminal UE to UE scenario, and the second UE is the target remote UE in the terminal UE to UE scenario.

[0056] In this technical solution, the target remote UE can select or reselect the target relay UE according to the relay selection conditions of the target remote UE. This can solve the problem of how to select and reselect the relay UE in the UE-to-UE (U2U) scenario, thereby ensuring the normal communication of the terminal device.

[0057] In one implementation, determining the candidate relay UE based on the third selection condition includes:

[0058] Receive a discovery request message sent by at least one third relay UE; wherein, the at least one third relay UE is a relay UE selected by the first UE whose SL-RSRP or SD-RSRP with the first UE meets a first threshold condition;

[0059] From the at least one third relay UE, all third relay UEs whose SL-RSRP or SD-RSRP with the second UE meets the second threshold condition are selected as the candidate relay UEs.

[0060] In one implementation, determining the candidate relay UE based on the third selection condition includes:

[0061] Obtain the SL-RSRP or SD-RSRP between the first UE and the relay UE;

[0062] All relay UEs whose SL-RSRP or SD-RSRP with the first UE meets the first threshold condition and whose SL-RSRP or SD-RSRP with the second UE meets the second threshold condition are selected as candidate relay UEs.

[0063] In one possible implementation, determining the selected or reselected target relay UE based on the candidate relay UEs includes:

[0064] Based on the implementation, a candidate relay UE is selected from the candidate relay UEs as the target relay UE;

[0065] Alternatively, multiple relay UEs may be selected as the target relay UE from the candidate relay UEs.

[0066] Fifthly, embodiments of this disclosure provide another method for relay UE selection and reselection in a terminal UE-to-UE scenario, the method being executed by a first UE, the method comprising:

[0067] The relay UE whose SL-RSRP or SD-RSRP with the first UE meets the first threshold condition is selected as the third relay UE;

[0068] The third relay UE sends a discovery request message to the second UE; the third relay UE is used by the second UE to select and reselect relay UEs.

[0069] Wherein, the first UE is the source remote UE in the terminal UE to UE scenario, and the second UE is the target remote UE in the terminal UE to UE scenario.

[0070] In this technical solution, the source remote UE can select or reselect a relay UE based on the relay selection conditions of the source remote UE to forward the discovery response message. Then, the target remote UE can filter the relay UEs that meet the relay selection conditions of the target remote UE as candidate relay UEs based on the relay UEs selected or reselected by the source remote UE. This can solve the problem of how to select and reselect relay UEs in UE-to-UE (U2U) scenarios, thereby ensuring the normal communication of terminal devices.

[0071] Sixthly, embodiments of this disclosure provide a method for triggering relay terminal selection and reselection in a UE-to-UE scenario, the method being executed by a terminal device, the method comprising:

[0072] In response to the sidelink communication reference signal received power SL-RSRP or sidelink discovery reference signal received power SD-RSRP between the terminal device and other terminal devices satisfying the triggering conditions for relay terminal selection and reselection, relay terminal selection or reselection is triggered.

[0073] In this technical solution, if the terminal device determines that the SL-RSRP or SD-RSRP between the terminal device and other terminal devices meets the triggering conditions for relay terminal selection and reselection, the relay terminal selection or reselection is triggered. This can solve the problem of selecting and reselecting the relay UE in UE-to-UE (U2U) scenarios, thereby ensuring normal communication of the terminal device.

[0074] In one implementation, the SL-RSRP or SD-RSRP satisfies the triggering conditions for relay terminal selection and reselection, including:

[0075] The SL-RSRP or SD-RSRP is less than or equal to a predefined threshold;

[0076] Alternatively, the SL-RSRP or SD-RSRP is less than at least one hysteresis parameter value of a predefined threshold.

[0077] In one possible implementation, the terminal device is the source remote terminal in the UE-to-UE scenario, and the other terminal devices are the target remote terminals in the UE-to-UE scenario.

[0078] In one possible implementation, the terminal device is the target remote terminal in the UE-to-UE scenario, and the other terminal devices are the source remote terminals in the UE-to-UE scenario.

[0079] In one possible implementation, the terminal device is a source remote terminal or a target remote terminal in the UE-to-UE scenario, and the other terminal devices are relay terminals in the UE-to-UE scenario.

[0080] In a seventh aspect, embodiments of this disclosure provide a communication device that implements some or all of the functions of the terminal device described in the first aspect above. For example, the communication device may have the functions of some or all of the embodiments in this disclosure, or it may have the functions of any one embodiment in this disclosure implemented individually. The functions may be implemented by hardware or by hardware executing corresponding software. The hardware or software includes one or more units or modules corresponding to the above functions.

[0081] In one implementation, the communication device may include a transceiver module and a processing module, the processing module being configured to support the communication device in performing the corresponding functions described in the above method. The transceiver module supports communication between the communication device and other devices. The communication device may also include a storage module, coupled to the transceiver module and the processing module, which stores necessary computer programs and data for the communication device.

[0082] As an example, the processing module can be a processor, the transceiver module can be a transceiver or a communication interface, and the storage module can be a memory.

[0083] Eighthly, embodiments of this disclosure provide another communication device that has some or all of the functions of the terminal device described in the method example of the second aspect above. For example, the communication device may have the functions of some or all of the embodiments in this disclosure, or it may have the functions of any one embodiment in this disclosure implemented individually. The functions may be implemented by hardware or by hardware executing corresponding software. The hardware or software includes one or more units or modules corresponding to the above functions.

[0084] In one implementation, the communication device may include a transceiver module and a processing module, the processing module being configured to support the communication device in performing the corresponding functions described in the above method. The transceiver module is used to support communication between the communication device and other devices. The communication device may also include a storage module, which is coupled to the transceiver module and the processing module, and stores the necessary computer programs and data of the communication device.

[0085] Ninthly, embodiments of this disclosure provide another communication device that has some or all of the functions of the terminal device described in the example of the method described in the third aspect above. For example, the communication device may have the functions of some or all of the embodiments in this disclosure, or it may have the functions of implementing any one embodiment of this disclosure individually. The functions may be implemented by hardware or by hardware executing corresponding software. The hardware or software includes one or more units or modules corresponding to the above functions.

[0086] In a tenth aspect, embodiments of this disclosure provide another communication device that has some or all of the functions of the terminal device described in the example of the method described in the fourth aspect above. For example, the communication device may have the functions of some or all of the embodiments in this disclosure, or it may have the functions of implementing any one embodiment of this disclosure individually. The functions may be implemented by hardware or by hardware executing corresponding software. The hardware or software includes one or more units or modules corresponding to the above functions.

[0087] Eleventhly, embodiments of this disclosure provide another communication device that has some or all of the functions of the terminal device described in the fifth aspect above. For example, the communication device may have some or all of the functions in the embodiments of this disclosure, or it may have the functions of implementing any one embodiment of this disclosure individually. The functions may be implemented by hardware or by hardware executing corresponding software. The hardware or software includes one or more units or modules corresponding to the above functions.

[0088] In a twelfth aspect, embodiments of this disclosure provide another communication device that has some or all of the functions of the terminal device described in the sixth aspect above. For example, the communication device may have some or all of the functions in the embodiments of this disclosure, or it may have the functions of implementing any one embodiment of this disclosure individually. The functions may be implemented by hardware or by hardware executing corresponding software. The hardware or software includes one or more units or modules corresponding to the above functions.

[0089] In a thirteenth aspect, embodiments of this disclosure provide a communication device including a processor that, when the processor invokes a computer program in memory, executes the method described in the first aspect.

[0090] In a fourteenth aspect, embodiments of this disclosure provide a communication device including a processor that, when the processor invokes a computer program in memory, executes the method described in the second aspect above.

[0091] In a fifteenth aspect, embodiments of this disclosure provide a communication device including a processor that, when the processor invokes a computer program in memory, executes the method described in the third aspect above.

[0092] In a sixteenth aspect, embodiments of this disclosure provide a communication device including a processor that, when the processor invokes a computer program in memory, executes the method described in the fourth aspect above.

[0093] In a seventeenth aspect, embodiments of this disclosure provide a communication device including a processor that, when the processor invokes a computer program in memory, executes the method described in the fifth aspect above.

[0094] In an eighteenth aspect, embodiments of this disclosure provide a communication device including a processor that, when the processor invokes a computer program in memory, executes the method described in the sixth aspect above.

[0095] In a nineteenth aspect, embodiments of this disclosure provide a communication device including a processor and a memory storing a computer program; the processor executes the computer program stored in the memory to cause the communication device to perform the method described in the first aspect above.

[0096] In a twentieth aspect, embodiments of this disclosure provide a communication device including a processor and a memory, the memory storing a computer program; the processor executes the computer program stored in the memory to cause the communication device to perform the method described in the second aspect above.

[0097] In a twentieth aspect, embodiments of this disclosure provide a communication device including a processor and a memory, the memory storing a computer program; the processor executes the computer program stored in the memory to cause the communication device to perform the method described in the third aspect above.

[0098] In a twentieth aspect, embodiments of this disclosure provide a communication device including a processor and a memory, the memory storing a computer program; the processor executes the computer program stored in the memory to cause the communication device to perform the method described in the fourth aspect above.

[0099] In a twentieth aspect, embodiments of this disclosure provide a communication device including a processor and a memory, the memory storing a computer program; the processor executes the computer program stored in the memory to cause the communication device to perform the method described in the fifth aspect above.

[0100] In a twentieth aspect, embodiments of this disclosure provide a communication device including a processor and a memory storing a computer program; the processor executes the computer program stored in the memory to cause the communication device to perform the method described in the sixth aspect above.

[0101] In a twentieth aspect, embodiments of this disclosure provide a communication device including a processor and an interface circuit. The interface circuit is configured to receive code instructions and transmit them to the processor, which is configured to execute the code instructions to cause the device to perform the method described in the first aspect above.

[0102] In a twentieth aspect, embodiments of this disclosure provide a communication device including a processor and an interface circuit. The interface circuit is configured to receive code instructions and transmit them to the processor, which is configured to execute the code instructions to cause the device to perform the method described in the second aspect above.

[0103] In a twentieth aspect, embodiments of this disclosure provide a communication device including a processor and an interface circuit. The interface circuit is configured to receive code instructions and transmit them to the processor, which is configured to execute the code instructions to cause the device to perform the method described in the third aspect above.

[0104] In a twentieth aspect, embodiments of this disclosure provide a communication device including a processor and an interface circuit. The interface circuit is configured to receive code instructions and transmit them to the processor, which is configured to execute the code instructions to cause the device to perform the method described in the fourth aspect above.

[0105] In a twentieth aspect, embodiments of this disclosure provide a communication device including a processor and an interface circuit. The interface circuit is configured to receive code instructions and transmit them to the processor, which is configured to execute the code instructions to cause the device to perform the method described in the fifth aspect above.

[0106] In a thirtieth aspect, embodiments of this disclosure provide a communication device including a processor and an interface circuit. The interface circuit is configured to receive code instructions and transmit them to the processor, which is configured to execute the code instructions to cause the device to perform the method described in the sixth aspect above.

[0107] In a thirty-first aspect, embodiments of this disclosure provide a computer-readable storage medium for storing instructions for use by the aforementioned terminal device, which, when executed, cause the terminal device to perform the method described in the first aspect.

[0108] In a thirty-second aspect, embodiments of this disclosure provide a readable storage medium for storing instructions for use by the aforementioned terminal device, which, when executed, cause the network device to perform the method described in the second aspect.

[0109] In a thirty-third aspect, embodiments of this disclosure provide a readable storage medium for storing instructions for use by the aforementioned terminal device, which, when executed, cause the network device to perform the method described in the third aspect.

[0110] In a thirty-fourth aspect, embodiments of this disclosure provide a readable storage medium for storing instructions for use by the aforementioned terminal device, which, when executed, cause the network device to perform the method described in the fourth aspect above.

[0111] In a thirty-fifth aspect, embodiments of this disclosure provide a readable storage medium for storing instructions for use by the aforementioned terminal device, which, when executed, cause the network device to perform the method described in the fifth aspect.

[0112] In a thirty-sixth aspect, embodiments of this disclosure provide a readable storage medium for storing instructions for use by the aforementioned terminal device, which, when executed, cause the network device to perform the method described in the sixth aspect.

[0113] In a thirty-seventh aspect, this disclosure also provides a computer program product including a computer program that, when run on a computer, causes the computer to perform the method described in the first aspect above.

[0114] In a thirty-eighth aspect, this disclosure also provides a computer program product including a computer program that, when run on a computer, causes the computer to perform the method described in the second aspect above.

[0115] In a thirty-ninth aspect, this disclosure also provides a computer program product including a computer program, which, when run on a computer, causes the computer to perform the method described in the third aspect above.

[0116] In a fortieth aspect, this disclosure also provides a computer program product including a computer program that, when run on a computer, causes the computer to perform the method described in the fourth aspect above.

[0117] In the forty-first aspect, this disclosure also provides a computer program product including a computer program that, when run on a computer, causes the computer to perform the method described in the fifth aspect above.

[0118] In a forty-second aspect, this disclosure also provides a computer program product including a computer program, which, when run on a computer, causes the computer to perform the method described in the sixth aspect above.

[0119] In a forty-third aspect, this disclosure provides a computer program that, when run on a computer, causes the computer to perform the methods described above. Attached Figure Description

[0120] To more clearly illustrate the technical solutions in the embodiments or background art of this disclosure, the accompanying drawings used in the embodiments or background art of this disclosure will be described below.

[0121] Figure 1 This is a flowchart illustrating a relay UE selection and reselection method for a terminal UE to UE scenario provided in this disclosure embodiment;

[0122] Figure 2 A flowchart illustrating another relay UE selection and reselection method for a terminal UE-to-UE scenario provided in this disclosure embodiment;

[0123] Figure 3 A flowchart illustrating another relay UE selection and reselection method for a terminal UE-to-UE scenario provided in this disclosure embodiment;

[0124] Figure 4 A flowchart illustrating another relay UE selection and reselection method for a terminal UE-to-UE scenario provided in this disclosure embodiment;

[0125] Figure 5 A flowchart illustrating yet another relay UE selection and reselection method for a terminal UE-to-UE scenario provided in this disclosure embodiment;

[0126] Figure 6 A flowchart of a method for triggering relay terminal selection and reselection in a UE-to-UE scenario provided by embodiments of this disclosure;

[0127] Figure 7 This is a schematic diagram of the structure of a communication device provided in an embodiment of this disclosure.

[0128] Figure 8 This is a schematic diagram of another communication device provided in an embodiment of this disclosure. Detailed Implementation

[0129] The embodiments of this disclosure are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this disclosure, and should not be construed as limiting this disclosure. In the description of this disclosure, unless otherwise stated, " / " means "or," for example, A / B can mean A or B; "and / or" in this document is merely a description of the relationship between related objects, indicating that three relationships can exist, for example, A and / or B can represent: A existing alone, A and B existing simultaneously, and B existing alone.

[0130] The terminology used in this disclosure is for the purpose of describing particular embodiments only and is not intended to be limiting of the present disclosure. The singular forms “a” and “the” as used in this disclosure and the appended claims are also intended to include the plural forms, unless the context clearly indicates otherwise.

[0131] It should be understood that although the terms first, second, third, etc., may be used to describe various information in embodiments of this disclosure, such information should not be limited to these terms. These terms are only used to distinguish information of the same type from one another. For example, first information may also be referred to as second information without departing from the scope of embodiments of this disclosure, and similarly, second information may also be referred to as first information. Depending on the context, the words “if” and “suppose” as used herein may be interpreted as “when”, “when”, or “in response to a determination”.

[0132] Embodiments of this disclosure are described in detail below, with examples of embodiments illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain this disclosure, and should not be construed as limiting this disclosure.

[0133] To support direct communication between terminal equipment (also called user equipment, UE) and other UEs, a direct communication method (also called sidelink, SL) is introduced, with the interface between UEs being PC-5. Based on the correspondence between the sending and receiving UEs, three transmission modes are supported on the sidelink: unicast, multicast, and broadcast. The sending UE transmits Sidelink Control Information (SCI) on the PSCCH (Physical Sidelink Control Channel) and a second-stage SCI on the PSSCH (Physical Sidelink Shared Channel), which carries the resource location of the transmitted data and source and destination identifiers. Upon receiving the SCI, the receiving UE determines whether to receive the corresponding data and which process it corresponds to based on the source and destination UE identifiers within it. In a unicast connection, each UE corresponds to a destination identifier. In a multicast connection, each UE can belong to one or more groups, and each group corresponds to a destination identifier. In a broadcast connection, all UEs correspond to at least one destination identifier.

[0134] A UE can communicate with a base station without directly connecting to it, but instead through a relay of another UE. The UE not directly connected to the base station is called a remote UE, and the UE providing relay functionality is called a relay UE. One scenario is that UE A can connect to UE B without directly connecting to UE B, but instead through a relay of UE C. In this case, UE A and UE B are remote UEs, and UE C, providing relay functionality, is the relay UE. All UEs communicate with each other via sidelink unicast. This architecture is called U2U (UE to UE, terminal to terminal) relay.

[0135] However, there is currently a lack of effective means for selecting and reselecting relay UEs in U2U scenarios.

[0136] Therefore, this disclosure provides a method and apparatus for selecting and reselecting a relay UE in a UE-to-UE scenario. By having the source remote UE or the target remote UE select or reselect the relay UE according to relay selection conditions, the problem of how to select and reselect the relay UE in a UE-to-UE (U2U) scenario can be solved, thereby ensuring normal communication of the terminal device.

[0137] It should be noted that the terminal (also called terminal device) in the embodiments of this disclosure is an entity on the user side used to receive or transmit signals, such as a mobile phone. Terminal devices can also be called terminal equipment, user equipment (UE), mobile station (MS), mobile terminal (MT), etc. Terminal devices can be vehicles with communication functions, smart cars, mobile phones, wearable devices, tablets, computers with wireless transceiver capabilities, virtual reality (VR) terminal devices, augmented reality (AR) terminal devices, wireless terminal devices in industrial control, wireless terminal devices in self-driving, wireless terminal devices in remote medical surgery, wireless terminal devices in smart grids, wireless terminal devices in transportation safety, wireless terminal devices in smart cities, wireless terminal devices in smart homes, etc. The embodiments of this disclosure do not limit the specific technology or device form used in the terminal device.

[0138] The following description, in conjunction with the accompanying drawings, details the relay UE selection and reselection method and apparatus provided in this disclosure for UE-to-UE scenarios.

[0139] Please see Figure 1 , Figure 1 This is a flowchart illustrating a relay UE selection and reselection method for a terminal UE-to-UE scenario provided by an embodiment of this disclosure. It should be noted that this method can be executed by a first UE. Figure 1 As shown, the method may include, but is not limited to, the following steps.

[0140] In step 101, candidate relay UEs are determined according to the first selection criteria.

[0141] In embodiments of this disclosure, the first selection condition may include any one of the following items 1) to 3):

[0142] 1) Select the relay UE that includes the terminal identifier of the second UE in the notification message or the neighbor cell list as the candidate relay UE;

[0143] 2) Select relay UEs that meet the threshold conditions of SL-RSRP (Sidelink Reference Signal Receiving Power) or SD-RSRP (Sidelink Discovery Reference Signal Receiving Power) as candidate relay UEs;

[0144] 3) Select a relay UE that includes the terminal identifier of the second UE in the notification message or the neighbor cell list, and whose SL-RSRP or SD-RSRP meets the threshold conditions as a candidate relay UE.

[0145] In this embodiment, taking a relay UE whose first selection condition includes the terminal identifier of the second UE in the notification message or neighbor cell list as a candidate relay UE as an example, 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 terminal identifier of the second UE is included in the notification message or neighbor cell list as a candidate relay UE. One possible implementation of the terminal identifier of the second UE is the source layer 2 address of the second UE, or the application layer identifier, but other implementations are not limited. Optionally, the second UE is the target communication UE of the first UE, and the first UE communicates with the second UE through the relay UE.

[0146] It should be noted that for U2U scenarios, there are two modes for sending discovery request messages: Mode A and Mode B. In Mode A, the U2U relay UE periodically broadcasts a notification message. This notification message carries the terminal identifier of the target terminal, or the target terminal's terminal identifier is included in the neighbor cell list within the notification message. The source terminal listens for the notification message and selects a U2U relay UE as its relay UE. As an example, in Mode A, if the first UE needs to determine that the notification message broadcast by the relay terminal contains the terminal identifier of the second UE, then the first UE can consider that relay terminal as a candidate relay UE.

[0147] In this embodiment, taking the first selection condition including selecting a relay UE that meets the threshold condition of SL-RSRP or SD-RSRP as a candidate relay UE as an example, 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 that meets the threshold condition of SL-RSRP or SD-RSRP as a candidate relay UE.

[0148] In this embodiment, taking a relay UE that has a terminal identifier of the second UE included in the notification message or the neighbor cell list, and whose SL-RSRP or SD-RSRP meets the threshold condition as a candidate relay UE as an example, 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 that has a terminal identifier of the second UE included in the notification message or the neighbor cell list, and whose SL-RSRP or SD-RSRP meets the threshold condition as a candidate relay UE.

[0149] In embodiments of this disclosure, the threshold condition for SL-RSRP or SD-RSRP to satisfy the threshold condition may include: SL-RSRP or SD-RSRP being greater than or equal to a predefined threshold; or SL-RSRP or SD-RSRP being greater than at least one hysteresis parameter value of the predefined threshold. For example, SL-RSRP or SD-RSRP can be understood as the signal strength of the sidelink between the first UE and the relay UE. The first UE can select a relay UE whose signal strength with the first UE satisfies the threshold condition as a candidate relay UE. For instance, the first UE can select a relay UE whose signal strength with the first UE is greater than or equal to the 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 at least one hysteresis parameter value of the predefined threshold as a candidate relay UE. In one possible implementation, the network device only configures a predefined threshold, then the threshold condition for SL-RSRP or SD-RSRP to satisfy the threshold condition can be that SL-RSRP or SD-RSRP is greater than or equal to the predefined threshold. In another possible implementation, the network device is configured with predefined threshold and hysteresis parameter values. If the SL-RSRP or SD-RSRP satisfies the threshold condition, then the SL-RSRP or SD-RSRP is greater than at least one predefined threshold hysteresis parameter value.

[0150] It should be noted that in some embodiments of this disclosure, if the SL-RSRP and SD-RSRP between terminals can be obtained, the obtained SL-RSRP can be compared with a predefined threshold, or the obtained SD-RSRP can be compared with a predefined threshold, or the UE can select one of SL-RSRP / SD-RSRP for comparison with the predefined threshold. If the terminal cannot obtain the SL-RSRP between terminals and can only obtain the SD-RSRP between terminals, then the terminal uses the obtained SD-RSRP to compare with the predefined threshold. If the terminal cannot obtain the SD-RSRP between terminals and can only obtain the SL-RSRP between terminals, then the terminal uses the obtained SL-RSRP to compare with the predefined threshold.

[0151] For example, if the SL-RSRP and SD-RSRP between the first UE and the relay UE can be obtained, the first UE can compare the obtained SL-RSRP with a predefined threshold to determine whether the threshold condition is met; alternatively, the first UE can compare the obtained SD-RSRP with a predefined threshold to determine whether the threshold condition is met; or, the first UE can select one of the SL-RSRP and SD-RSRP to compare with the predefined threshold to determine whether the threshold condition is met. If the first UE cannot obtain the SL-RSRP between the first UE and the relay UE, and can only obtain the SD-RSRP between the first UE and the relay UE, then the first UE compares the obtained SD-RSRP with the predefined threshold to determine whether the threshold condition is met. If the first UE cannot obtain the SD-RSRP between the first UE and the relay UE, and can only obtain the SL-RSRP between the first UE and the relay UE, then the first UE compares the obtained SL-RSRP with the predefined threshold to determine whether the threshold condition is met.

[0152] It should be noted that, in the embodiments of this disclosure, the predefined threshold can be configured or pre-configured to the terminal device through network device configuration. If the terminal device is in-coverage, it can obtain the predefined threshold configured by the network device through dedicated RRC signaling or SIB. If the terminal device is out-of-coverage, it can obtain the predefined threshold through pre-configuration.

[0153] In embodiments of this disclosure, the predefined threshold includes a first predefined threshold and a second predefined threshold, wherein the first predefined threshold is a minimum threshold and the second predefined threshold is a maximum threshold. In embodiments of this disclosure, the SL-RSRP or SD-RSRP being greater than or equal to the predefined threshold may include: 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. The SL-RSRP or SD-RSRP being greater than at least one hysteresis parameter value of the predefined threshold may include: SL-RSRP or SD-RSRP being greater than at least one hysteresis parameter value of the first predefined threshold and less than at least one hysteresis parameter value of the second predefined threshold.

[0154] In one possible implementation, the network device can be configured with two predefined thresholds, such as a first predefined threshold and a second predefined threshold. The first UE can select 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 as a candidate relay UE. In another possible implementation, the first UE can select a relay UE whose SL-RSRP or SD-RSRP is greater than at least one hysteresis parameter value of the first predefined threshold and less than at least one hysteresis parameter value of the second predefined threshold as a candidate relay UE.

[0155] In some embodiments of this disclosure, a relay UE that satisfies the threshold conditions for SL-RSRP or SD-RSRP includes any one of the following items 1) to 3):

[0156] 1) A relay UE whose SL-RSRP or SD-RSRP with the first UE meets the first threshold condition;

[0157] 2) A relay UE whose SL-RSRP or SD-RSRP with the second UE meets the second threshold condition;

[0158] 3) A relay UE whose SL-RSRP or SD-RSRP with the first UE meets the first threshold condition and whose SL-RSRP or SD-RSRP with the second UE meets the second threshold condition.

[0159] In embodiments of this disclosure, taking the selection condition including selecting relay UEs whose SL-RSRP or SD-RSRP meets a threshold condition, wherein the relay UEs whose SL-RSRP or SD-RSRP meets the threshold condition include relay UEs whose SL-RSRP or SD-RSRP with the first UE meets the first threshold condition as an example, the first UE can select relay UEs whose SL-RSRP or SD-RSRP with the first UE meets the first threshold condition as candidate relay UEs. In one implementation, the network device can configure a predefined threshold, and the first UE can select relay UEs whose SL-RSRP or SD-RSRP with the first UE is greater than or equal to the predefined threshold as candidate relay UEs; or, the first UE can select relay UEs whose SL-RSRP or SD-RSRP with the first UE is greater than at least one hysteresis parameter value of the predefined threshold as candidate relay UEs. In another implementation, the network device can configure two predefined thresholds, such as a minimum threshold and a maximum threshold. As one example of a possible implementation, the first UE can select a relay UE whose SL-RSRP or SD-RSRP with respect to it is greater than or equal to a minimum threshold and less than or equal to a maximum threshold as a candidate relay UE. As another example of a possible implementation, the first UE can select a relay UE whose SL-RSRP or SD-RSRP with respect to it is greater than at least one hysteresis parameter value of the minimum threshold and less than at least one hysteresis parameter value of the maximum threshold as a candidate relay UE.

[0160] In embodiments of this disclosure, taking the selection condition including choosing a relay UE whose SL-RSRP or SD-RSRP meets a threshold condition, wherein the relay UE whose SL-RSRP or SD-RSRP meets the threshold condition includes a relay UE whose SL-RSRP or SD-RSRP with the second UE meets a second threshold condition as an example, the first UE can select a relay UE whose SL-RSRP or SD-RSRP with the second UE meets the second threshold condition as a candidate relay UE. In one implementation, the network device can configure a predefined threshold, and the first UE can select a relay UE whose SL-RSRP or SD-RSRP with the second UE is greater than or equal to the predefined threshold as a candidate relay UE, or the first UE can select a relay UE whose SL-RSRP or SD-RSRP with the second UE is greater than at least one hysteresis parameter value of the predefined threshold as a candidate relay UE. In another implementation, the network device can configure two predefined thresholds, such as a minimum threshold and a maximum threshold. As one example of a possible implementation, the first UE can select a relay UE whose SL-RSRP or SD-RSRP with the second UE is greater than or equal to a minimum threshold and less than or equal to a maximum threshold as a candidate relay UE. As another example of a possible implementation, the first UE can select a relay UE whose SL-RSRP or SD-RSRP with the second UE is greater than at least one hysteresis parameter value above the minimum threshold and less than at least one hysteresis parameter value below the maximum threshold as a candidate relay UE.

[0161] In embodiments of this disclosure, taking the selection condition including selecting a relay UE whose SL-RSRP or SD-RSRP meets a threshold condition, wherein the relay UE whose SL-RSRP or SD-RSRP meets the threshold condition includes a relay UE whose SL-RSRP or SD-RSRP with the first UE meets the first threshold condition and whose SL-RSRP or SD-RSRP with the second UE meets the second threshold condition as an example, the first UE can select a relay UE whose SL-RSRP or SD-RSRP with the first UE meets the first threshold condition and whose SL-RSRP or SD-RSRP with the second UE meets the second threshold condition as a candidate relay UE.

[0162] In one implementation, the network device can be configured with a predefined threshold. A first UE can select a relay UE whose SL-RSRP or SD-RSRP with the first UE is greater than or equal to the predefined threshold and whose SL-RSRP or SD-RSRP with the second UE is greater than or equal to 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 at least one hysteresis parameter value of the predefined threshold and whose SL-RSRP or SD-RSRP with the second UE is greater than at least one hysteresis parameter value of the predefined threshold as a candidate relay UE.

[0163] In another implementation, the network device can be configured with two predefined thresholds, such as a minimum threshold and a maximum threshold. As an example of a possible implementation, the SL-RSRP or SD-RSRP between the first UE and the relay UE can satisfy the first threshold condition as follows: 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; the SL-RSRP or SD-RSRP between the second UE and the relay UE can satisfy the second threshold condition as follows: 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 can satisfy the first threshold condition as follows: the SL-RSRP or SD-RSRP between the first UE and the relay UE is greater than at least one hysteresis parameter value of the lowest threshold and less than at least one hysteresis parameter value of the highest threshold; the SL-RSRP or SD-RSRP between the second UE and the relay UE can satisfy the second threshold condition as follows: the SL-RSRP or SD-RSRP between the second UE and the relay UE is greater than at least one hysteresis parameter value of the lowest threshold and less than at least one hysteresis parameter value of the highest threshold.

[0164] In step 102, the target relay UE to be selected or reselected is determined based on the candidate relay UEs.

[0165] In one possible implementation, the first UE may select a candidate relay UE from among the candidate relay UEs as the selected or reselected target relay UE. For example, the first UE may randomly select a candidate relay UE from among the candidate relay UEs as the selected or reselected target relay UE.

[0166] In another possible implementation, the first UE may select multiple candidate relay UEs as the target relay UE for selection or reselection based on the implementation.

[0167] Optionally, in some embodiments of this disclosure, the first UE can be a source remote UE in a U2U relay scenario, and the second UE can be a target remote UE in a U2U relay scenario.

[0168] Taking the example that the first UE can be the source remote UE in a U2U relay scenario and the second UE can be the 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:

[0169] 1) The notification message or neighbor cell list includes the terminal identifier of the target remote UE;

[0170] 2) The SL-RSRP / SD-RSRP between the source remote UE and the relay UE is greater than or equal to a predefined threshold or greater than at least one hysteresis parameter value of the predefined threshold;

[0171] 3) The SL-RSRP / SD-RSRP between the target remote UE and the relay UE is greater than or equal to a predefined threshold or greater than at least one hysteresis parameter value of the predefined threshold.

[0172] As an example, for mode A, the source remote UE needs to determine that the notification message / neighbor cell list broadcast by the relay UE contains the terminal identifier of the target remote UE. One possible implementation of the target remote UE's terminal identifier is the source layer 2 address of the target remote UE; another possible implementation is the application layer identifier, but other implementations are not limited. Additionally, SL-RSRP / SD-RSRP needs to meet preset conditions. These conditions can be met only between the source remote UE and the relay UE, only between the target remote UE and the relay UE, or simultaneously between both the source remote UE and the relay UE. Meeting these preset conditions can be greater than or equal to a predefined threshold or greater than at least one hysteresis parameter value. This hysteresis parameter value can be a threshold offset or a delay.

[0173] In one implementation, the network device can be configured with two predefined thresholds: a minimum threshold and a maximum threshold. As an example, the SL-RSRP / SD-RSRP between the source remote UE and the relay UE can satisfy the preset conditions as follows: 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, 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.

[0174] As an example, the SL-RSRP / SD-RSRP between the target remote UE and the relay UE can meet the preset conditions as follows: the SL-RSRP / SD-RSRP between the target 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 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.

[0175] After determining the candidate relay UEs, the source and remote UEs can determine the selected or reselected target relay UE based on the candidate relay UEs. As one example of a possible implementation, the source and remote UEs can randomly select one candidate relay UE from the candidate relay UEs as the selected or reselected target relay UE. As another example of a possible implementation, the source and remote UEs can select multiple candidate relay UEs from the candidate relay UEs as the selected or reselected target relay UE.

[0176] Optionally, in some embodiments of this disclosure, the first UE can be a target remote UE in a U2U relay scenario, and the second UE can be a source remote UE in a U2U relay scenario.

[0177] Taking the example that the first UE can be the target remote UE in a U2U relay scenario and the second UE can be the source remote UE in a U2U relay scenario, the target remote UE can select a relay UE that meets at least one of the following conditions 1) to 3) as a candidate relay UE:

[0178] 1) The notification message or neighbor cell list includes the terminal identifier of the source remote UE;

[0179] 2) The SL-RSRP / SD-RSRP between the source remote UE and the relay UE is greater than or equal to a predefined threshold or greater than at least one hysteresis parameter value of the predefined threshold;

[0180] 3) The SL-RSRP / SD-RSRP between the target remote UE and the relay UE is greater than or equal to a predefined threshold or greater than at least one hysteresis parameter value of the predefined threshold.

[0181] As an example, for mode A, the target remote UE needs to determine that the notification message broadcast by the relay UE contains the terminal identifier of the source remote UE. One possible implementation of the source remote UE's terminal identifier is the source layer 2 address of the source remote UE, and another possible implementation is the application layer identifier, but other implementations are not limited. In addition, SL-RSRP / SD-RSRP also needs to meet preset conditions. These conditions can be met only between the source remote UE and the relay UE, only between the target remote UE and the relay UE, or simultaneously between both the source remote UE and the relay UE. The SL-RSRP / SD-RSRP meeting the preset conditions can be greater than or equal to a predefined threshold or greater than at least one hysteresis parameter value. This hysteresis parameter value can be a threshold offset or a delay.

[0182] In one implementation, the network device can be configured with two predefined thresholds: a minimum threshold and a maximum threshold. As an example, the SL-RSRP / SD-RSRP between the source remote UE and the relay UE can satisfy the preset conditions as follows: 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, 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.

[0183] As an example, the SL-RSRP / SD-RSRP between the target remote UE and the relay UE can meet the preset conditions as follows: the SL-RSRP / SD-RSRP between the target 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 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.

[0184] After determining the candidate relay UEs, the target remote UE can select or reselect the target relay UE based on the candidate relay UEs. As one possible implementation example, the target remote UE can randomly select one candidate relay UE from the candidate relay UEs as the selected or reselected target relay UE. As another possible implementation example, the target remote UE can select multiple candidate relay UEs from the candidate relay UEs as the selected or reselected target relay UE.

[0185] By implementing the embodiments of this disclosure, the first UE can select or reselect the target relay UE according to the relay selection conditions, which can solve the problem of how to select and reselect the relay UE in the UE-to-UE (U2U) scenario, thereby ensuring the normal communication of the terminal device.

[0186] It should be noted that for U2U scenarios, there are two modes for sending discovery request messages: Mode A and Mode B. In Mode B, if there are multiple U2U relay UEs, the source remote UE or the target remote UE selects one or more U2U relay UEs as relay UEs. The following will describe the implementation of the first UE selecting and reselecting the relay UE in Mode B, using an example. Please refer to [link to example]. Figure 2 , Figure 2 This is a flowchart illustrating another relay UE selection and reselection method for a terminal UE-to-UE scenario provided by an embodiment of this disclosure. It should be noted that this method can be executed by a first UE. In one implementation, the first UE in this embodiment can be a source remote UE in a U2U scenario, and the second UE in this embodiment can be a target remote UE in a U2U scenario. Figure 2 As shown, the method may include, but is not limited to, the following steps.

[0187] In step 201, candidate relay UEs are determined according to the second selection criteria.

[0188] In embodiments of this disclosure, the second selection condition may include any one of the following items 1) to 2):

[0189] 1) Select the relay UE whose SL-RSRP or SD-RSRP between the first UE and the relay UE meets the first threshold condition as the candidate relay UE;

[0190] 2) Select the relay UEs whose SL-RSRP or SD-RSRP between the first UE and the relay UE meets the first threshold condition and whose SL-RSRP or SD-RSRP between the second UE and the relay UE meets the second threshold condition as candidate relay UEs.

[0191] Optionally, in embodiments of this disclosure, taking the second selection condition including 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, 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 as an example, the source remote UE may 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.

[0192] In one possible implementation, the first UE sends a discovery request message to the second UE through at least one first relay UE; the first UE receives a discovery response message sent by the second UE through at least one second relay UE; wherein, the at least one second relay UE is a relay UE selected by the second UE from at least one first relay UE whose SL-RSRP or SD-RSRP with the second UE satisfies a second threshold condition; the first UE selects all second relay UEs from at least one second relay UE whose SL-RSRP or SD-RSRP with the first UE satisfies the first threshold condition as candidate relay UEs. The implementation methods for satisfying the second threshold condition in SL-RSRP or SD-RSRP between the second UE and the relay UE, and the implementation methods for satisfying the first threshold condition in SL-RSRP or SD-RSRP between the first UE and the relay UE, can be implemented using any of the methods in the various embodiments of this disclosure, and are not limited herein, nor will they be described in detail.

[0193] For example, in mode B, the source remote UE sends a discovery request message to the second UE through at least one first relay UE. The target remote UE receives the discovery request message forwarded by at least one first relay UE. The target remote UE can select a relay UE from the at least one first relay UE whose SL-RSRP or SD-RSRP with the target remote UE is greater than or equal to a predefined threshold as the second relay UE, or the target remote UE can select a relay UE from the at least one first relay UE whose SL-RSRP or SD-RSRP with the target remote UE is greater than at least one hysteresis parameter value of a predefined threshold as the second relay UE. The target remote UE forwards a discovery response message through the second relay UE. The source remote UE receives the discovery response message sent by the target remote UE through at least one second relay UE. The source remote UE selects all second relay UEs whose SL-RSRP or SD-RSRP is greater than or equal to a predefined threshold from the at least one second relay UE as candidate relay UEs; or, the source remote UE selects all second relay UEs whose SL-RSRP or SD-RSRP is greater than at least one predefined threshold hysteresis parameter value from the at least one second relay UE as candidate relay UEs.

[0194] Optionally, in embodiments of this disclosure, taking a second selection condition including 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 the second UE and the relay UE satisfies a second threshold condition as a candidate relay UE, 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 as an example, the source remote UE selects 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 as a candidate relay UE.

[0195] 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.

[0196] As one possible implementation example, the first UE can select all relay UEs whose SL-RSRP or SD-RSRP with the first UE meets a first threshold condition as a first candidate relay UE set; from the first candidate relay UE set, select all relay UEs whose SL-RSRP or SD-RSRP with the second UE meets a second threshold condition as candidate relay UEs. As another possible implementation example, the first UE can select all relay UEs whose SL-RSRP or SD-RSRP with the second UE meets a second threshold condition as a candidate relay UE set, and from this candidate relay UE set, select all relay UEs whose SL-RSRP or SD-RSRP with the first UE meets the first threshold condition as the candidate relay UEs.

[0197] Optionally, the first UE can obtain the SL-RSRP or SD-RSRP between the second UE and the relay UE through the discovery signal of the relay UE or other means. The implementation methods for satisfying the second threshold condition in the SL-RSRP or SD-RSRP between the second UE and the relay UE, and the implementation methods for satisfying the first threshold condition in the SL-RSRP or SD-RSRP between the first UE and the relay UE, can be implemented using any of the methods in the various embodiments of this disclosure. No limitation is imposed here, and further details will not be provided.

[0198] For example, in mode B, the source remote UE can obtain the SL-RSRP or SD-RSRP between the target remote UE and the relay UE through the relay UE's discovery signal or other means. The source remote UE selects all relay UEs whose SL-RSRP or SD-RSRP with the source remote UE meets a first threshold condition and whose SL-RSRP or SD-RSRP with the target remote UE meets a second threshold condition as candidate relay UEs.

[0199] In step 202, the target relay UE to be selected or reselected is determined based on the candidate relay UEs.

[0200] In one possible implementation, the first UE may select one candidate relay UE as the target relay UE from among the candidate relay UEs. In another possible implementation, the first UE may select multiple relay UEs as the target relay UE from among the candidate relay UEs. Optionally, the first UE sends a discovery request message to the second UE through the target relay UE.

[0201] By implementing the embodiments of this disclosure, the target remote UE can select a relay UE that meets the conditions to forward the discovery response message, and the source remote UE can select a relay UE that meets the conditions as a candidate relay UE from the relay UEs that forward the discovery response message. This enables the source remote UE to select or reselect the target relay UE, which can solve the problem of how to select and reselect the relay UE in UE-to-UE (U2U) scenarios, thereby ensuring the normal communication of the terminal device.

[0202] It is understandable that the above Figure 2 The illustrated embodiment describes the implementation of the relay UE selection and reselection method for a terminal UE-to-UE scenario according to the embodiments of this disclosure from the perspective of a first UE. This disclosure also proposes a relay UE selection and reselection method for a terminal UE-to-UE scenario, which will be implemented below from the perspective of a second UE. Please refer to [link to relevant documentation]. Figure 3 , Figure 3 This is a flowchart illustrating another relay UE selection and reselection method for a terminal UE-to-UE scenario provided by an embodiment of this disclosure. It should be noted that this method can be executed by a second UE. In this embodiment, the first UE is the source remote UE in the terminal UE-to-UE scenario, and the second UE is the target remote UE in the terminal UE-to-UE scenario. Figure 3 As shown, the method may include, but is not limited to, the following steps.

[0203] In step 301, a discovery request message sent by the first UE through at least one first relay UE is received.

[0204] In one implementation, for mode B, the target remote UE receives a discovery request message forwarded by at least one first relay UE.

[0205] In step 302, from at least one first relay UE, a relay UE whose SL-RSRP or SD-RSRP satisfies the second threshold condition with the second UE is selected as the second relay UE.

[0206] In the embodiments of this disclosure, the implementation method for satisfying the second threshold condition in SL-RSRP or SD-RSRP between the second UE and the relay UE can be implemented in any of the embodiments of this disclosure, and no limitation is made here, nor will it be described in detail.

[0207] In step 303, a discovery response message is sent to the first UE based on the second relay UE; the second relay UE is used by the first UE to select and reselect relay UEs.

[0208] In one implementation, the target remote UE discovers a response message to the source remote UE through a second relay UE. Upon receiving the discovery response message forwarded by the second relay UE, the source remote UE selects relay UEs from the second relay UE whose SL-RSRP or SD-RSRP with the source remote UE satisfies a first threshold condition as candidate relay UEs. Based on its UE implementation, the source remote UE determines one or more relay UEs from the candidate relay UEs as the selected or reselected target relay UE. The implementation method for ensuring that 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 implemented using any of the methods described in the various embodiments of this disclosure, and is not limited thereto, nor will it be elaborated further.

[0209] By implementing the embodiments of this disclosure, the target remote UE can select or reselect a relay UE based on the relay selection conditions of the target remote UE to forward the discovery response message. Then, based on the relay UE selected or reselected by the target remote UE, the source remote UE can filter relay UEs that meet the relay selection conditions of the source remote UE as candidate relay UEs. This can solve the problem of how to select and reselect relay UEs in UE-to-UE (U2U) scenarios, thereby ensuring normal communication of terminal devices.

[0210] It should be noted that, for Mode B, if there are multiple U2U relay UEs, either the source remote UE or the target remote UE selects one U2U relay UE as the relay UE. The following will describe the implementation method of the second UE selecting and reselecting the relay UE in Mode B, with reference to an embodiment. Please refer to... Figure 4 , Figure 4This is a flowchart illustrating another relay UE selection and reselection method for a terminal UE-to-UE scenario provided by an embodiment of this disclosure. It should be noted that this method can be executed by a second UE. In one implementation, the first UE in this embodiment can be a source remote UE in a U2U scenario, and the second UE in this embodiment can be a target remote UE in a U2U scenario. Figure 4 As shown, the method may include, but is not limited to, the following steps.

[0211] In step 401, a candidate relay UE is determined based on the third selection condition.

[0212] The third selection condition includes any one of the following items 1) to 2):

[0213] 1) Select the relay UE whose SL-RSRP or SD-RSRP between the second UE and the relay UE meets the second threshold condition as the candidate relay UE;

[0214] 2) Select the relay UEs whose SL-RSRP or SD-RSRP between the first UE and the relay UE meets the first threshold condition and whose SL-RSRP or SD-RSRP between the second UE and the relay UE meets the second threshold condition as candidate relay UEs.

[0215] Optionally, in embodiments of this disclosure, taking the third selection condition including 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, 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 as an example, the target remote UE may select a relay UE whose SL-RSRP or SD-RSRP between it and the target remote UE satisfies the second threshold condition as a candidate relay UE.

[0216] In one possible implementation, the second UE receives a discovery request message sent by the first UE through at least one third relay UE; wherein the at least one third relay UE is a relay UE selected by the first UE whose SL-RSRP or SD-RSRP with the first UE satisfies a first threshold condition; the second UE selects all third relay UEs whose SL-RSRP or SD-RSRP with the second UE satisfies a second threshold condition from the at least one third relay UE as candidate relay UEs. The implementation methods for satisfying the second threshold condition in SL-RSRP or SD-RSRP between the second UE and the relay UE, and the implementation methods for satisfying the first threshold condition in SL-RSRP or SD-RSRP between the first UE and the relay UE, can be implemented using any of the methods in the various embodiments of this disclosure, and are not limited herein, nor will they be described in detail.

[0217] For example, in mode B, the source remote UE selects a relay UE whose SL-RSRP or SD-RSRP with it meets a first threshold condition as a third relay UE. The source remote UE then sends a discovery request message to the target remote UE through the third relay UE. Upon receiving the discovery request message forwarded by the third relay UE, the target remote UE selects all third relay UEs whose SL-RSRP or SD-RSRP with it meets a second threshold condition as candidate relay UEs.

[0218] Optionally, in embodiments of this disclosure, taking a third selection condition including 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 the second UE and the relay UE satisfies a second threshold condition as a candidate relay UE, 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 as an example, the target remote UE selects a relay UE whose SL-RSRP or SD-RSRP between itself and the target remote UE satisfies the second threshold condition and whose SL-RSRP or SD-RSRP between itself and the source remote UE satisfies the first threshold condition as a candidate relay UE.

[0219] In one possible implementation, the second UE obtains the SL-RSRP or SD-RSRP between the first UE and the relay UE. The second UE can select all relay UEs whose SL-RSRP or SD-RSRP with the second UE meets a second threshold condition and whose SL-RSRP or SD-RSRP with the first UE meets a first threshold condition as candidate relay UEs.

[0220] As one possible implementation example, the second UE can select all relay UEs whose SL-RSRP or SD-RSRP with the first UE meets a second threshold condition as a second candidate relay UE set. From this second candidate relay UE set, the second UE selects all relay UEs whose SL-RSRP or SD-RSRP with the first UE meets a first threshold condition as candidate relay UEs. As another possible implementation example, the second UE can select all relay UEs whose SL-RSRP or SD-RSRP with the second UE meets a second threshold condition from this candidate relay UE set as candidate relay UEs.

[0221] Optionally, the second UE can obtain the SL-RSRP or SD-RSRP between the first UE and the relay UE through the discovery signal of the relay UE or other means. The implementation methods for satisfying the second threshold condition in the SL-RSRP or SD-RSRP between the second UE and the relay UE, and the implementation methods for satisfying the first threshold condition in the SL-RSRP or SD-RSRP between the first UE and the relay UE, can be implemented using any of the methods in the various embodiments of this disclosure. No limitation is imposed here, and further details will not be provided.

[0222] For example, in Mode B, the target remote UE can obtain the SL-RSRP or SD-RSRP between the source remote UE and the relay UE through the relay UE's discovery signal or other means. The target remote UE selects all relay UEs whose SL-RSRP or SD-RSRP with the target remote UE meets a second threshold condition and whose SL-RSRP or SD-RSRP with the source remote UE meets a first threshold condition as candidate relay UEs.

[0223] In step 402, the target relay UE to be selected or reselected is determined based on the candidate relay UEs.

[0224] In one possible implementation, the second UE may select one candidate relay UE as the target relay UE from among the candidate relay UEs. In another possible implementation, the second UE may select multiple relay UEs as the target relay UE from among the candidate relay UEs. Optionally, the second UE sends a discovery response message to the first UE through the target relay UE.

[0225] By implementing the embodiments of this disclosure, the source remote UE can select a relay UE that meets the conditions to forward the discovery request message, and the target remote UE can select a relay UE that meets the conditions from the relay UEs forwarding the discovery request message as a candidate relay UE. This enables the target remote UE to select or reselect the target relay UE, which can solve the problem of how to select and reselect the relay UE in the UE-to-UE (U2U) scenario, thereby ensuring the normal communication of the terminal device.

[0226] It is understandable that the above Figure 4 The illustrated embodiment describes the implementation of the relay UE selection and reselection method for a terminal UE-to-UE scenario from the second UE side. This disclosure also proposes a relay UE selection and reselection method for a terminal UE-to-UE scenario; the implementation of this method from the first UE side will be described below. Please refer to... Figure 5 , Figure 5This is a flowchart illustrating another relay UE selection and reselection method for a terminal UE-to-UE scenario provided by an embodiment of this disclosure. It should be noted that this method can be executed by a first UE. In this embodiment, the first UE is the source remote UE in the terminal UE-to-UE scenario, and the second UE is the target remote UE in the terminal UE-to-UE scenario. Figure 5 As shown, the method may include, but is not limited to, the following steps.

[0227] In step 501, a relay UE whose SL-RSRP or SD-RSRP with the first UE satisfies the first threshold condition is selected as the third relay UE.

[0228] The implementation method for satisfying the first threshold condition in SL-RSRP or SD-RSRP between the first UE and the relay UE can be implemented in any of the embodiments of this disclosure. No limitation is made here, and it will not be described in detail.

[0229] In one implementation, the source remote UE selects a relay UE whose SL-RSRP or SD-RSRP with the source remote UE satisfies a first threshold condition as the third relay UE.

[0230] In step 502, a discovery request message is sent to the second UE based on the third relay UE; the third relay UE is used by the second UE to select and reselect relay UEs.

[0231] In one implementation, the source remote UE sends a discovery request message to the target remote UE through a third relay UE. Upon receiving the discovery request message forwarded by the third relay UE, the target remote UE selects relay UEs whose SL-RSRP or SD-RSRP with it meets a second threshold condition as candidate relay UEs. The target remote UE then selects one or more relay UEs from the candidate relay UEs as the selected or reselected target relay UE.

[0232] By implementing the embodiments of this disclosure, the source remote UE can select or reselect a relay UE based on the relay selection conditions of the source remote UE to forward the discovery request message. Then, the target remote UE can filter the relay UEs that meet the relay selection conditions of the target remote UE as candidate relay UEs based on the relay UEs selected or reselected by the source remote UE. This can solve the problem of how to select and reselect relay UEs in UE-to-UE (U2U) scenarios, thereby ensuring the normal communication of terminal devices.

[0233] This disclosure also provides a method for triggering relay terminal selection and reselection in a UE-to-UE scenario. Please refer to [link to relevant documentation]. Figure 6 , Figure 6This is a flowchart illustrating a method for triggering relay terminal selection and reselection in a UE-to-UE scenario, as provided in this disclosure. It should be noted that this method can be executed by a terminal device. Figure 6 As shown, the method may include, but is not limited to, the following steps.

[0234] In step 601, in response to the side link communication reference signal received power SL-RSRP or side link discovery reference signal received power SD-RSRP between the terminal device and other terminal devices satisfying the triggering conditions for relay terminal selection and reselection, the terminal device triggers relay terminal selection or reselection.

[0235] In one implementation, the SL-RSRP or SD-RSRP satisfies the triggering conditions for relay terminal selection and reselection, including: 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 at least one hysteresis parameter value of the predefined threshold. Optionally, the terminal device can determine the SL-RSRP or SD-RSRP between itself and other terminal devices, and compare the SL-RSRP or SD-RSRP with the predefined threshold to determine whether the SL-RSRP or SD-RSRP between itself and other terminal devices satisfies the triggering conditions for relay terminal selection and reselection.

[0236] In one implementation, if the SL-RSRP and SD-RSRP between the terminal device and other terminal devices can be obtained, the obtained SL-RSRP can be compared with a predefined threshold; alternatively, the obtained SD-RSRP can be compared with a predefined threshold; or the UE can select one of SL-RSRP / SD-RSRP for comparison with the predefined threshold. If the terminal cannot obtain the SL-RSRP between the terminal device and other terminal devices, and can only obtain the SD-RSRP between terminals, then the terminal compares the obtained SD-RSRP with the predefined threshold. If the terminal cannot obtain the SD-RSRP between the terminal device and other terminal devices, and can only obtain the SL-RSRP between the terminal device and other terminal devices, then the terminal compares the obtained SL-RSRP with the predefined threshold.

[0237] It should be noted that, in the embodiments of this disclosure, the predefined threshold can be configured or pre-configured to the terminal device through network device configuration. If the terminal device is in-coverage, it can obtain the predefined threshold configured by the network device through dedicated RRC signaling or SIB. If the terminal device is out-of-coverage, it can obtain the predefined threshold through pre-configuration.

[0238] In one possible implementation, the terminal device can be a source remote terminal in the UE-to-UE scenario, and other terminal devices can be target remote terminals in the UE-to-UE scenario.

[0239] As an example of a possible implementation, the source remote terminal determines the SL-RSRP or SD-RSRP between itself and the target remote terminal, and compares the SL-RSRP or SD-RSRP with a predefined threshold to determine whether the SL-RSRP or SD-RSRP between the source remote terminal and the target remote terminal meets the triggering conditions 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 less than or equal to a predefined threshold, or if the SL-RSRP or SD-RSRP is less than at least one hysteresis parameter value of the predefined threshold, then the source remote terminal triggers relay terminal selection. The implementation of relay terminal selection by the source remote terminal can be carried out using any of the methods described in the various embodiments of this disclosure, and is not limited thereto, nor will it be elaborated further.

[0240] In another possible implementation, the terminal device is the target remote terminal in the UE-to-UE scenario, and the other terminal devices are the source remote terminals in the UE-to-UE scenario.

[0241] 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, and compares the SL-RSRP or SD-RSRP with a predefined threshold to determine whether the SL-RSRP or SD-RSRP between the target remote terminal and the source remote terminal meets the triggering conditions 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 less than or equal to a predefined threshold, or if the SL-RSRP or SD-RSRP is less than at least one hysteresis parameter value of the predefined threshold, then the target remote terminal triggers relay terminal selection. The implementation of the target remote terminal selecting the relay terminal can be carried out using any of the methods described in the various embodiments of this disclosure, and is not limited thereto, nor will it be elaborated further.

[0242] In another possible implementation, the terminal device is the source terminal in the UE-to-UE scenario, and the other terminal devices are relay terminals in the UE-to-UE scenario.

[0243] As an example of a possible implementation, the source terminal determines the SL-RSRP or SD-RSRP between itself and the relay terminal, and compares this SL-RSRP or SD-RSRP with a predefined threshold to determine whether the SL-RSRP or SD-RSRP between the source terminal and the relay terminal meets the triggering conditions for relay terminal selection and reselection. For example, if the SL-RSRP or SD-RSRP between the source terminal and the relay terminal is less than or equal to the predefined threshold, or if the SL-RSRP or SD-RSRP is less than at least one hysteresis parameter value of the predefined threshold, then the source terminal triggers relay terminal reselection. The implementation of relay terminal reselection by the source terminal can be carried out using any of the methods described in the various embodiments of this disclosure, and is not limited thereto, nor will it be elaborated further.

[0244] In another possible implementation, the terminal device is the source remote terminal and the target remote terminal in the UE-to-UE scenario, and the other terminal devices are the relay terminals in the UE-to-UE scenario.

[0245] As an example of a possible implementation, the target remote terminal determines the SL-RSRP or SD-RSRP between itself and the relay terminal, and compares this SL-RSRP or SD-RSRP with a predefined threshold to determine whether the SL-RSRP or SD-RSRP between the target remote terminal and the relay terminal meets the triggering conditions for relay terminal selection and reselection. For example, if the SL-RSRP or SD-RSRP between the target remote terminal and the relay terminal is less than or equal to the predefined threshold, or if the SL-RSRP or SD-RSRP is less than at least one hysteresis parameter value of the predefined threshold, then the target remote terminal triggers relay terminal reselection. The implementation of the target remote terminal reselecting the relay terminal can be carried out using any of the methods described in the various embodiments of this disclosure, and is not limited thereto, nor will it be elaborated further.

[0246] By implementing the embodiments of this disclosure, if the terminal device determines that the SL-RSRP or SD-RSRP between the terminal device and other terminal devices meets the triggering conditions for relay terminal selection and reselection, the relay terminal selection or reselection can be triggered, thereby solving the problem of selecting and reselecting the relay UE in UE-to-UE (U2U) scenarios, and thus ensuring normal communication of the terminal device.

[0247] In the embodiments provided above, the methods provided by this disclosure are described from the perspective of terminal devices (such as the aforementioned first UE and second UE). To implement the functions of the methods provided in the embodiments of this disclosure, the terminal device (such as the aforementioned first UE and second UE) may include hardware structures and software modules, implementing the above functions in the form of hardware structures, software modules, or a combination of hardware structures and software modules. One of the above functions may be executed in the form of hardware structures, software modules, or a combination of hardware structures and software modules.

[0248] Please see Figure 7 This is a schematic diagram of the structure of a communication device 70 provided in an embodiment of this disclosure. Figure 7 The communication device 70 shown may include a transceiver module 701 and a processing module 702. The transceiver module 701 may include a sending module and / or a receiving module. The sending module is used to implement the sending function, and the receiving module is used to implement the receiving function. The transceiver module 701 can implement both sending and / or receiving functions.

[0249] The communication device 70 may be a terminal device (such as the first UE and the second UE in the aforementioned method embodiments), a device in the terminal device, or a device that can be used in conjunction with the terminal device.

[0250] Communication device 70 is a terminal device (as described above) Figure 1 In the illustrated embodiment (first UE): the processing module 702 is used to determine candidate relay UEs according to a first selection condition; the processing module 702 is also used to determine the selected or reselected target relay UE based on the candidate relay UEs. The first selection condition includes any one of the following: selecting a relay UE whose terminal identifier is included in the notification message or neighbor cell 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) meets a threshold condition as a candidate relay UE; selecting a relay UE whose terminal identifier is included in the notification message or neighbor cell list, and whose SL-RSRP or SD-RSRP meets a threshold condition as a candidate relay UE. The second UE is the target communication UE of the first UE, and the first UE communicates with the second UE through the relay UE.

[0251] In one implementation, a relay UE whose SL-RSRP or SD-RSRP meets a threshold condition includes any one of the following: a relay UE whose SL-RSRP or SD-RSRP with a first UE meets a first threshold condition; a relay UE whose SL-RSRP or SD-RSRP with a second UE meets a second threshold condition; and a relay UE whose SL-RSRP or SD-RSRP with a first UE meets the first threshold condition and whose SL-RSRP or SD-RSRP with a second UE meets the second threshold condition.

[0252] In one implementation, SL-RSRP or SD-RSRP satisfies a threshold condition, including: SL-RSRP or SD-RSRP being greater than or equal to a predefined threshold; or SL-RSRP or SD-RSRP being greater than at least one hysteresis parameter value of the predefined threshold.

[0253] In one possible implementation, the predefined thresholds include a first predefined threshold and a second predefined threshold, wherein the first predefined threshold is a minimum threshold and the second predefined threshold is a maximum threshold; and wherein SL-RSRP or SD-RSRP is greater than or equal to the predefined thresholds, including: 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. SL-RSRP or SD-RSRP is greater than at least one hysteresis parameter value of the predefined thresholds, including: SL-RSRP or SD-RSRP is greater than at least one hysteresis parameter value of the first predefined threshold and less than at least one hysteresis parameter value of the second predefined threshold.

[0254] In one possible implementation, the processing module 702 is specifically used to: select one candidate relay UE as the target relay UE from among the candidate relay UEs based on the implementation; or, select multiple relay UEs as the target relay UE from among the candidate relay UEs based on the implementation.

[0255] Communication device 70 is a terminal device (as described above) Figure 2In the illustrated embodiment (first UE): the processing module 702 is used to determine candidate relay UEs according to a second selection condition; the processing module 702 is also used to determine the selected or reselected target relay UE based on the candidate relay UEs. The second selection condition includes any one of the following: 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; 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 the second threshold condition as a candidate relay UE. The first UE is the source remote UE in the terminal UE-to-UE scenario, and the second UE is the target remote UE in the terminal UE-to-UE scenario.

[0256] In one implementation, transceiver module 701 is configured to send a discovery request message to a second UE via at least one first relay UE. Transceiver module 701 is also configured to receive a discovery response message sent by at least one second relay UE; wherein the at least one second relay UE is a relay UE selected by the second UE from at least one first relay UE that satisfies a second threshold condition with respect to the second UE's SL-RSRP or SD-RSRP. Processing module 702 is configured to select all second relay UEs from the at least one second relay UE that satisfy the first threshold condition with respect to the first UE's SL-RSRP or SD-RSRP as candidate relay UEs.

[0257] In one possible implementation, processing module 702 is used to obtain the SL-RSRP or SD-RSRP between the second UE and the relay UE. Processing module 702 is also used to select all relay UEs whose SL-RSRP or SD-RSRP with the first UE satisfy a first threshold condition as a first candidate relay UE set, and from the first candidate relay UE set, select all relay UEs whose SL-RSRP or SD-RSRP with the second UE satisfy a second threshold condition as candidate relay UEs.

[0258] In one possible implementation, the processing module 702 is specifically used to: select one candidate relay UE as the target relay UE from among the candidate relay UEs based on the implementation; or, select multiple relay UEs as the target relay UE from among the candidate relay UEs based on the implementation.

[0259] Communication device 70 is a terminal device (as described above) Figure 3In the illustrated embodiment (second UE): the transceiver module 701 is used to receive a discovery request message sent by at least one first relay UE. The processing module 702 is used to select, from at least one first relay UE, a relay UE whose SL-RSRP or SD-RSRP satisfies a second threshold condition with the second UE as the second relay UE. The transceiver module 701 is also used to send a discovery response message to the first UE based on the second relay UE; the second relay UE is used by the first UE to select and reselect relay UEs. Wherein, the first UE is the source remote UE in the terminal UE to UE scenario, and the second UE is the target remote UE in the terminal UE to UE scenario.

[0260] Communication device 70 is a terminal device (as described above) Figure 4 In the illustrated embodiment (second UE): Processing module 702 is used to determine candidate relay UEs according to a third selection condition. Processing module 702 is also used to determine the selected or reselected target relay UE based on the candidate relay UEs. The third selection condition includes any one of the following: 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; 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 the second UE and the relay UE satisfies a second threshold condition as a candidate relay UE. Wherein, the first UE is the source remote UE in the terminal UE-to-UE scenario, and the second UE is the target remote UE in the terminal UE-to-UE scenario.

[0261] In one implementation, the transceiver module 701 is configured to receive a discovery request message sent by at least one third relay UE; wherein the at least one third relay UE is a relay UE selected by the first UE whose SL-RSRP or SD-RSRP satisfies a first threshold condition with the first UE. The processing module 702 is configured to select all third relay UEs from the at least one third relay UE whose SL-RSRP or SD-RSRP satisfies a second threshold condition with the second UE as candidate relay UEs.

[0262] In one possible implementation, processing module 702 is further configured to obtain the SL-RSRP or SD-RSRP between the first UE and the relay UE. 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 candidate relay UE set. From the second candidate relay UE set, processing module 702 selects all relay UEs whose SL-RSRP or SD-RSRP with the first UE satisfies a first threshold condition as candidate relay UEs.

[0263] In one implementation, the processing module 702 is specifically used to: select one candidate relay UE as the target relay UE from among the candidate relay UEs based on the implementation; or, select multiple relay UEs as the target relay UE from among the candidate relay UEs based on the implementation.

[0264] Communication device 70 is a terminal device (as described above) Figure 5 In the illustrated embodiment (first UE): the processing module 702 is used to select a relay UE whose SL-RSRP or SD-RSRP with the first UE meets a first threshold condition as the third relay UE. The transceiver module 701 is used to send a discovery request message to the second UE based on the third relay UE; the third relay UE is used by the second UE to select and reselect relay UEs. Wherein, the first UE is the source remote UE in the terminal UE-to-UE scenario, and the second UE is the target remote UE in the terminal UE-to-UE scenario.

[0265] Communication device 70 is a terminal device (such as...) Figure 6 In the terminal device shown in the embodiment: the processing module 702 is used to trigger relay terminal selection or reselection in response to the side link communication reference signal received power SL-RSRP or side link discovery reference signal received power SD-RSRP between the terminal device and other terminal devices satisfying the triggering conditions for relay terminal selection and reselection.

[0266] In one implementation, SL-RSRP or SD-RSRP satisfies the triggering conditions for relay terminal selection and reselection, including: SL-RSRP or SD-RSRP being less than or equal to a predefined threshold; or SL-RSRP or SD-RSRP being less than at least one hysteresis parameter value of the predefined threshold.

[0267] In one implementation, the terminal device is a source remote terminal in the UE-to-UE scenario, and other terminal devices are target remote terminals in the UE-to-UE scenario; or, the terminal device is a target remote terminal in the UE-to-UE scenario, and other terminal devices are source remote terminals 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 other terminal devices are relay terminals in the UE-to-UE scenario.

[0268] Regarding the apparatus in the above embodiments, the specific manner in which each module performs its operation has been described in detail in the embodiments related to the method, and will not be elaborated upon here.

[0269] Please see Figure 8 , Figure 8This is a schematic diagram of another communication device 80 provided in this embodiment. The communication device 80 can be a terminal device (such as the first UE and the second UE in the foregoing method embodiments), or a chip, chip system, or processor that supports the terminal device in implementing the above methods. This device can be used to implement the methods described in the above method embodiments, and for details, please refer to the description in the above method embodiments.

[0270] The communication device 80 may include one or more processors 801. The processor 801 may be a general-purpose processor or a dedicated processor, such as a baseband processor or a central processing unit (CPU). The baseband processor can be used to process communication protocols and communication data, while the CPU can be used to control the communication device (e.g., base station, baseband chip, terminal equipment, terminal equipment chip, DU or CU, etc.), execute computer programs, and process data from the computer programs.

[0271] Optionally, the communication device 80 may further include one or more memories 802, which may store a computer program 804. The processor 801 executes the computer program 804 to cause the communication device 80 to perform the methods described in the above method embodiments. Optionally, the memory 802 may also store data. The communication device 80 and the memory 802 may be provided separately or integrated together.

[0272] Optionally, the communication device 80 may also include a transceiver 805 and an antenna 806. The transceiver 805 may be referred to as a transceiver unit, transceiver, or transceiver circuit, etc., and is used to implement the transmission and reception functions. The transceiver 805 may include a receiver and a transmitter. The receiver may be referred to as a receiver or receiving circuit, etc., and is used to implement the receiving function; the transmitter may be referred to as a transmitter or transmitting circuit, etc., and is used to implement the transmitting function.

[0273] Optionally, the communication device 80 may further include one or more interface circuits 807. The interface circuits 807 are used to receive code instructions and transmit them 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.

[0274] Communication device 80 is a terminal device (as described above) Figure 1 The first UE in the illustrated embodiment: processor 801 is used to execute Figure 1 Steps 101 and 102 in the process.

[0275] Communication device 80 is a terminal device (as described above) Figure 2 The first UE in the illustrated embodiment: processor 801 is used to execute Figure 2 Steps 201 and 202 in the process.

[0276] Communication device 80 is a terminal device (as described above) Figure 3 The second UE in the illustrated embodiment: transceiver 805 is used to perform Figure 3 Steps 301 and 303 in the process. Processor 801 is used to execute... Figure 3 Step 302 in the process.

[0277] Communication device 80 is a terminal device (as described above) Figure 4 The second UE in the illustrated embodiment: processor 801 is used to execute Figure 4 Steps 401 and 402 in the process.

[0278] Communication device 80 is a terminal device (as described above) Figure 5 The first UE in the illustrated embodiment: processor 801 is used to execute Figure 5 Step 501 in the process. Transceiver 805 is used to perform... Figure 5 Step 502 in the process.

[0279] Communication device 80 is a terminal device (as described above) Figure 6 The terminal device in the illustrated embodiment: Processor 801 is used to execute Figure 6 Step 601 in the process.

[0280] In one implementation, the processor 801 may include a transceiver for implementing receive and transmit functions. For example, the transceiver may be a transceiver circuit, an interface, or an interface circuit. The transceiver circuit, interface, or interface circuit for implementing receive and transmit functions may be separate or integrated. The aforementioned transceiver circuit, interface, or interface circuit can be used for reading and writing code / data, or it can be used for transmitting or relaying signals.

[0281] In one implementation, processor 801 may store a computer program that runs on processor 801, causing communication device 80 to perform the methods described in the above method embodiments. The computer program may be embedded in processor 801; in this case, processor 801 may be implemented in hardware.

[0282] In one implementation, the communication device 80 may include circuitry capable of performing the functions of transmitting, receiving, or communicating as described in the foregoing method embodiments. The processor and transceiver described in this disclosure can be implemented on integrated circuits (ICs), analog ICs, radio frequency integrated circuits (RFICs), mixed-signal ICs, application-specific integrated circuits (ASICs), printed circuit boards (PCBs), electronic devices, etc. The processor and transceiver can also be manufactured using various IC process technologies, such as complementary metal-oxide-semiconductor (CMOS), n-metal-oxide-semiconductor (NMOS), positive-channel metal-oxide-semiconductor (PMOS), bipolar junction transistors (BJTs), bipolar CMOS (BiCMOS), silicon-germanium (SiGe), gallium arsenide (GaAs), etc.

[0283] The communication device described in the above embodiments may be a terminal device (such as the first UE and the second UE in the foregoing method embodiments), but the scope of the communication device described in this disclosure is not limited thereto, and the structure of the communication device may vary. Figure 8 The communication device may be a standalone device or part of a larger device. For example, the communication device may be:

[0284] (1) Independent integrated circuit IC, or chip, or chip system or subsystem;

[0285] (2) A collection of one or more ICs, optionally including storage components for storing data and computer programs;

[0286] (3) ASIC, such as modem;

[0287] (4) Modules that can be embedded in other devices;

[0288] (5) Receivers, terminal equipment, smart terminal equipment, cellular phones, wireless equipment, handheld devices, mobile units, vehicle-mounted equipment, network equipment, cloud equipment, artificial intelligence equipment, etc.

[0289] (6) Others, etc.

[0290] Those skilled in the art will also understand that the various illustrative logical blocks and steps listed in the embodiments of this disclosure can be implemented by electronic hardware, computer software, or a combination of both. Whether such functionality is implemented in hardware or software depends on the specific application and the overall system design requirements. Those skilled in the art can implement the described functionality using various methods for each specific application, but such implementation should not be construed as exceeding the scope of protection of the embodiments of this disclosure.

[0291] This disclosure also provides a readable storage medium having instructions stored thereon that, when executed by a computer, implement the functions of any of the above method embodiments.

[0292] This disclosure also provides a computer program product that, when executed by a computer, implements the functions of any of the above method embodiments.

[0293] In the above embodiments, implementation can be achieved, in whole or in part, through software, hardware, firmware, or any combination thereof. When implemented in software, it can be implemented, in whole or in part, as a computer program product. The computer program product includes one or more computer programs. When the computer program is loaded and executed on a computer, all or part of the processes or functions described in the embodiments of this disclosure are generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer program can be stored in a computer-readable storage medium or transferred from one computer-readable storage medium to another. For example, the computer program can be transferred from one website, computer, server, or data center to another via wired (e.g., coaxial cable, fiber optic, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium accessible to a computer or a data storage device such as a server or data center that integrates one or more available media. The available media may be magnetic media (e.g., floppy disks, hard disks, magnetic tapes), optical media (e.g., high-density digital video discs (DVDs)), or semiconductor media (e.g., solid-state disks (SSDs)).

[0294] Those skilled in the art will understand that the various numerical designations such as "first," "second," etc., used in this disclosure are merely for the convenience of description and are not intended to limit the scope of the embodiments of this disclosure, nor do they indicate the order of events.

[0295] At least one of the features described in this disclosure can also be described as one or more, and multiple features can be two, three, four or more, and this disclosure does not impose any limitations. In the embodiments of this disclosure, for a technical feature, the technical features in that technical feature are distinguished by "first", "second", "third", "A", "B", "C" and "D", etc., and there is no sequential order or size order among the technical features described by "first", "second", "third", "A", "B", "C" and "D".

[0296] The correspondences shown in the tables of this disclosure can be configured or predefined. The values ​​of the information in each table are merely examples and can be configured to other values; this disclosure is not limiting. When configuring the correspondences between information and parameters, it is not necessarily required to configure all the correspondences shown in each table. For example, the correspondences shown in some rows of the tables in this disclosure may not be configured. Furthermore, appropriate modifications and adjustments can be made based on the above tables, such as splitting, merging, etc. The names of the parameters shown in the headers of the above tables can also use other names that the communication device can understand, and the values ​​or representations of the parameters can also be other values ​​or representations that the communication device can understand. In the implementation of the above tables, other data structures can also be used, such as arrays, queues, containers, stacks, linear lists, pointers, linked lists, trees, graphs, structures, classes, heaps, hash tables, or hash tables, etc.

[0297] The predefined terms in this disclosure can be understood as defined, predefined, stored, pre-stored, pre-negotiated, pre-configured, solidified, or pre-burned.

[0298] Those skilled in the art will recognize that the units and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this disclosure.

[0299] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0300] The above description is merely a specific embodiment of this disclosure, but the scope of protection of this disclosure is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this disclosure should be included within the scope of protection of this disclosure. Therefore, the scope of protection of this disclosure should be determined by the scope of the claims.

Claims

1. A method for selecting and reselecting a relay UE in a UE-to-UE scenario, characterized in that, The method is executed by a first UE, and the method includes: Candidate relay UEs are determined based on the second selection criteria; Based on the candidate relay UEs, determine the target relay UE to be selected or reselected; The second selection condition includes: The relay UE whose SD-RSRP between the first UE and the relay UE meets the first threshold condition is selected as the candidate relay UE; The step of determining candidate relay UEs based on the second selection criteria includes: A discovery request message is sent from at least one first relay UE to the second UE; Receive a discovery response message sent by at least one second relay UE; wherein, the at least one second relay UE is a relay UE selected by the second UE from the at least one first relay UE whose SD-RSRP with the second UE meets a second threshold condition; From the at least one second relay UE, a second relay UE whose SD-RSRP with the first UE meets a first threshold condition is selected as the candidate relay UE; Wherein, the first UE is the source remote UE in the terminal UE to UE scenario, and the second UE is the target remote UE in the terminal UE to UE scenario.

2. The method as described in claim 1, characterized in that, The step of determining the selected or reselected target relay UE based on the candidate relay UEs includes: Based on the implementation, a candidate relay UE is selected from the candidate relay UEs as the target relay UE; Alternatively, multiple relay UEs may be selected as the target relay UE from the candidate relay UEs.

3. The method as described in claim 1, characterized in that, The method further includes: In response to the sidelink communication reference signal received power SL-RSRP or sidelink discovery reference signal received power SD-RSRP between the first UE and other terminal devices satisfying the triggering conditions for relay terminal selection and reselection, relay terminal selection or reselection is triggered. The SL-RSRP or SD-RSRP satisfies the triggering conditions for relay terminal selection and reselection, including: the SL-RSRP or SD-RSRP is less than or equal to a predefined threshold; Wherein, the other terminal device is the target remote terminal in the UE-to-UE scenario, or the other terminal device is the relay terminal in the UE-to-UE scenario.

4. The method as described in claim 1, characterized in that, The method further includes: The first threshold condition for the SD-RSRP between the first UE and the relay UE to satisfy the first threshold condition includes: the 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; The second threshold condition for the SD-RSRP between the second UE and the relay UE to satisfy the second threshold condition includes: the 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.

5. The method as described in claim 1, characterized in that, The method further includes: The first threshold condition for the SD-RSRP between the first UE and the relay UE to satisfy the first threshold condition includes: the SD-RSRP between the first UE and the relay UE is greater than at least one hysteresis parameter value of the lowest threshold and less than at least one hysteresis parameter value of the highest threshold; The second threshold condition is met for the SD-RSRP between the second UE and the relay UE: the SD-RSRP between the second UE and the relay UE is greater than at least one hysteresis parameter value of the minimum threshold and less than at least one hysteresis parameter value of the maximum threshold.

6. The method as described in claim 5, characterized in that, The hysteresis parameter value is either threshold bias or hysteresis.

7. The method according to any one of claims 1 to 6, characterized in that, The minimum and maximum thresholds are configured by the network device.

8. A method for selecting and reselecting a relay UE in a UE-to-UE scenario, characterized in that, The method is executed by a second UE, and the method includes: Receive at least one discovery request message sent by a first relay UE; From the at least one first relay UE, select the relay UE whose SD-RSRP with the second UE satisfies the second threshold condition as the second relay UE; The second relay UE sends a discovery response message to the first UE; the second relay UE is used by the first UE to select and reselect a relay UE, wherein the candidate relay UE of the first UE is the relay UE among the second relay UEs whose SD-RSRP with the first UE meets the first threshold condition, and the candidate relay UE is used by the first UE to determine the target relay UE to be selected or reselected; Wherein, the first UE is the source remote UE in the terminal UE to UE scenario, and the second UE is the target remote UE in the terminal UE to UE scenario.

9. The method as described in claim 8, characterized in that: The second relay UE is used to select and reselect the relay UE when the sidelink communication reference signal received power SL-RSRP or sidelink discovery reference signal received power SD-RSRP between the first UE and other terminal devices meets the triggering conditions for relay terminal selection and reselection. The SL-RSRP or SD-RSRP satisfies the triggering conditions for relay terminal selection and reselection, including: the SL-RSRP or SD-RSRP is less than or equal to a predefined threshold; Wherein, the other terminal device is the target remote terminal in the UE-to-UE scenario, or the other terminal device is the relay terminal in the UE-to-UE scenario.

10. The method as described in claim 8, characterized in that, The SD-RSRP between the second relay UE and the first UE satisfies the first threshold condition as follows: the SD-RSRP between the second relay UE and the first UE is greater than or equal to the minimum threshold and less than or equal to the maximum threshold; The second threshold condition for the SD-RSRP between the first relay UE and the second UE to satisfy the SD-RSRP includes: the SD-RSRP between the first relay UE and the second UE is greater than or equal to the minimum threshold and less than or equal to the maximum threshold.

11. The method as described in claim 8, characterized in that, The method further includes: The SD-RSRP between the second relay UE and the first UE satisfies the first threshold condition as follows: the SD-RSRP between the second relay UE and the first UE is greater than at least one hysteresis parameter value of the lowest threshold and less than at least one hysteresis parameter value of the highest threshold; The second threshold condition is met for the SD-RSRP between the first relay UE and the second UE: the SD-RSRP between the first relay UE and the second UE is greater than at least one hysteresis parameter value of the minimum threshold and less than at least one hysteresis parameter value of the maximum threshold.

12. The method as described in claim 11, characterized in that, The hysteresis parameter value is either threshold bias or hysteresis.

13. The method according to any one of claims 8 to 12, characterized in that, The minimum and maximum thresholds are configured by the network device.

14. A method for selecting and reselecting a relay UE in a UE-to-UE scenario, characterized in that, The method is executed by a second UE, and the method includes: Candidate relay UEs are determined based on the third selection criterion; Based on the candidate relay UEs, determine the target relay UE to be selected or reselected; The third selection condition includes: A relay UE is selected as a candidate relay UE if 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. The step of determining candidate relay UEs based on the third selection condition includes: Receive a discovery request message sent by at least one third relay UE; wherein, the at least one third relay UE is a relay UE selected by the first UE whose SL-RSRP or SD-RSRP with the first UE meets a first threshold condition; From the at least one third relay UE, a third relay UE whose SL-RSRP or SD-RSRP with the second UE satisfies the second threshold condition is selected as the candidate relay UE; Wherein, the first UE is the source remote UE in the terminal UE to UE scenario, and the second UE is the target remote UE in the terminal UE to UE scenario.

15. The method as described in claim 14, characterized in that, The step of determining the selected or reselected target relay UE based on the candidate relay UEs includes: Based on the implementation, a candidate relay UE is selected from the candidate relay UEs as the target relay UE; Alternatively, multiple relay UEs may be selected as the target relay UE from the candidate relay UEs.

16. The method as described in claim 14, characterized in that, In response to the sidelink communication reference signal received power SL-RSRP or sidelink discovery reference signal received power SD-RSRP between the second UE and other terminal devices meeting the triggering conditions for relay terminal selection and reselection, relay terminal selection or reselection is triggered. The SL-RSRP or SD-RSRP satisfies the triggering conditions for relay terminal selection and reselection, including: the SL-RSRP or SD-RSRP is less than or equal to a predefined threshold; Wherein, the other terminal device is the target remote terminal in the UE-to-UE scenario, or the other terminal device is the relay terminal in the UE-to-UE scenario.

17. The method as described in claim 14, characterized in that, The method further includes: The first threshold condition is met for the SL-RSRP or SD-RSRP between the first UE and the relay UE: 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. The second threshold condition is met for the SL-RSRP or SD-RSRP between the second UE and the relay UE: 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.

18. The method as described in claim 14, characterized in that, The method further includes: The first threshold condition is met for the SL-RSRP or SD-RSRP between the first UE and the relay UE: the SL-RSRP or SD-RSRP between the first UE and the relay UE is greater than at least one hysteresis parameter value of the lowest threshold and less than at least one hysteresis parameter value of the highest threshold. The second threshold condition is met for the SL-RSRP or SD-RSRP between the second UE and the relay UE: the SL-RSRP or SD-RSRP between the second UE and the relay UE is greater than at least one hysteresis parameter value of the minimum threshold and less than at least one hysteresis parameter value of the maximum threshold.

19. The method as described in claim 18, characterized in that, The hysteresis parameter value is either threshold bias or hysteresis.

20. The method according to any one of claims 14 to 19, characterized in that, The minimum and maximum thresholds are configured by the network device.

21. A method for selecting and reselecting a relay UE in a UE-to-UE scenario, characterized in that, The method is executed by a first UE, and the method includes: The relay UE whose SL-RSRP or SD-RSRP with the first UE meets the first threshold condition is selected as the third relay UE; The third relay UE sends a discovery request message to the second UE; the third relay UE is used by the second UE to select and reselect a relay UE; the candidate relay UE of the second UE is the third relay UE whose SL-RSRP or SD-RSRP with the second UE meets the second threshold condition; the candidate relay UE of the second UE is used by the second UE to determine the target relay UE to be selected or reselected. Wherein, the first UE is the source remote UE in the terminal UE to UE scenario, and the second UE is the target remote UE in the terminal UE to UE scenario.

22. The method as described in claim 21, characterized in that, The method further includes: The first threshold condition is met for the SL-RSRP or SD-RSRP between the first UE and the relay UE: 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. The second threshold condition is met for the SL-RSRP or SD-RSRP between the second UE and the third relay UE: 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.

23. The method as described in claim 21, characterized in that, The method further includes: The first threshold condition is met for the SL-RSRP or SD-RSRP between the first UE and the relay UE: the SL-RSRP or SD-RSRP between the first UE and the relay UE is greater than at least one hysteresis parameter value of the lowest threshold and less than at least one hysteresis parameter value of the highest threshold. The second threshold condition is met for the SL-RSRP or SD-RSRP between the second UE and the relay UE: the SL-RSRP or SD-RSRP between the second UE and the relay UE is greater than at least one hysteresis parameter value of the minimum threshold and less than at least one hysteresis parameter value of the maximum threshold.

24. The method as described in claim 23, characterized in that, The hysteresis parameter value is either threshold bias or hysteresis.

25. The method according to any one of claims 21 to 24, characterized in that, The minimum and maximum thresholds are configured by the network device.

26. A communication device, characterized in that, include: The processing module is used to determine candidate relay UEs based on the second selection criteria; The processing module is further configured to determine the selected or reselected target relay UE based on the candidate relay UE; The second selection condition includes: The relay UE whose SD-RSRP between the first UE and the relay UE meets the first threshold condition is selected as the candidate relay UE; The communication device is also used for: A discovery request message is sent from at least one first relay UE to the second UE; Receive a discovery response message sent by at least one second relay UE; wherein, the at least one second relay UE is a relay UE selected by the second UE from the at least one first relay UE whose SD-RSRP with the second UE meets a second threshold condition; From the at least one second relay UE, a second relay UE whose SD-RSRP with the first UE meets a first threshold condition is selected as the candidate relay UE; Wherein, the first UE is the source remote UE in the terminal UE to UE scenario, and the second UE is the target remote UE in the terminal UE to UE scenario.

27. A communication device, characterized in that, include: The transceiver module is used to receive discovery request messages sent by at least one first relay UE; The processing module is configured to select, from the at least one first relay UE, a relay UE whose SD-RSRP with the second UE satisfies a second threshold condition as the second relay UE; The transceiver module is further configured to send a discovery response message to the first UE based on the second relay UE; the second relay UE is used by the first UE to select and reselect a relay UE, wherein the candidate relay UE of the first UE is the relay UE among the second relay UEs whose SD-RSRP with the first UE meets the first threshold condition, and the candidate relay UE is used by the first UE to determine the target relay UE to be selected or reselected. Wherein, the first UE is the source remote UE in the terminal UE to UE scenario, and the second UE is the target remote UE in the terminal UE to UE scenario.

28. A communication device, characterized in that, include: The processing module is used to determine candidate relay UEs based on the third selection condition; The processing module is further configured to determine the selected or reselected target relay UE based on the candidate relay UE; The third selection condition includes: A relay UE is selected as a candidate relay UE if the SL-RSRP or SD-RSRP between the first UE and the relay UE meets the first threshold condition and the SL-RSRP or SD-RSRP between the second UE and the relay UE meets the second threshold condition. The step of determining candidate relay UEs based on the third selection condition includes: Receive a discovery request message sent by at least one third relay UE; wherein, the at least one third relay UE is a relay UE selected by the first UE whose SL-RSRP or SD-RSRP with the first UE meets a first threshold condition; From the at least one third relay UE, a third relay UE whose SL-RSRP or SD-RSRP with the second UE satisfies the second threshold condition is selected as the candidate relay UE; Wherein, the first UE is the source remote UE in the terminal UE to UE scenario, and the second UE is the target remote UE in the terminal UE to UE scenario.

29. A communication device, characterized in that, include: The processing module is used to select a relay UE whose SL-RSRP or SD-RSRP with the first UE meets a first threshold condition as the third relay UE; The transceiver module is used to send a discovery request message to the second UE based on the third relay UE; the third relay UE is used by the second UE to select and reselect a relay UE, and the candidate relay UE of the second UE is the third relay UE whose SL-RSRP or SD-RSRP with the second UE meets the second threshold condition. The candidate relay UE of the second UE is used by the second UE to determine the target relay UE to be selected or reselected. Wherein, the first UE is the source remote UE in the terminal UE to UE scenario, and the second UE is the target remote UE in the terminal UE to UE scenario.

30. A communication device, characterized in that, The device includes a processor and a memory, the memory storing a computer program, the processor executing the computer program stored in the memory to cause the device to perform the method as described in any one of claims 1 to 7.

31. A communication device, characterized in that, The device includes a processor and a memory, the memory storing a computer program, the processor executing the computer program stored in the memory to cause the device to perform the method as described in any one of claims 8 to 13.

32. A communication device, characterized in that, The device includes a processor and a memory, the memory storing a computer program, the processor executing the computer program stored in the memory to cause the device to perform the method as described in any one of claims 14 to 20.

33. A communication device, characterized in that, The device includes a processor and a memory, the memory storing a computer program, the processor executing the computer program stored in the memory to cause the device to perform the method as described in any one of claims 21 to 25.

34. A computer-readable storage medium for storing instructions that, when executed, cause the method as described in any one of claims 1 to 7 to be implemented.

35. A computer-readable storage medium for storing instructions that, when executed, cause the method of any one of claims 8 to 13 to be implemented.

36. A computer-readable storage medium for storing instructions that, when executed, cause the method of any one of claims 14 to 20 to be implemented.

37. A computer-readable storage medium for storing instructions that, when executed, cause the method of any one of claims 21 to 25 to be implemented.

38. A communication system, comprising a network device and at least one of a first UE and a second UE; characterized in that: The first UE performs the method as described in any one of claims 1 to 7; The second UE performs the method as described in any one of claims 8 to 13.

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