Communication device, relay device, control method and program

Abstract

This technology provides a way to properly locate communication terminals. [Solution] A communication device according to one aspect of the present disclosure is a 3GPP-compliant communication device that connects to other communication devices via one or more relay devices, and comprises a transmitting means for transmitting a signal for searching for the other communication devices, the signal including information indicating that the signal is to be relayed to the other communication devices, and identification information indicating a connection service provided by the relay device.

Description

Technical Field

[0001] The present disclosure relates to a communication device, a relay device, a control method, and a program.

Background Art

[0002] In recent years, the specifications of LTE (Long Term Evolution) of 3GPP (registered trademark) (3rd Generation Partnership Project) and the next generation (NR (New Radio)) have been in progress. Among these, a standard specification called Sidelink communication (hereinafter referred to as Sidelink) has been established. This specification realizes direct wireless communication between communication terminals using an interface called PC5. A communication terminal is also called a terminal device, a terminal, a UE (User Equipment), etc.

[0003] In Proximity based Services (ProSe), which is the communication standard of NR's Sidelink, a procedure for searching for neighboring UEs is defined by 3GPP. This procedure is called 5G ProSe Direct Discovery or simply Direct Discovery. In this specification and the drawings, "search" may be replaced with "retrieve", "discover", "discovery", etc.

[0004] Furthermore, 3GPP is promoting the formulation of a specification for expanding the communication range of Sidelink by means of a Sidelink relay function that relays Sidelink communication via a relay device (relay UE). At this time, a means for a communication terminal (remote UE or end UE) having a function of connecting communication terminals to each other through the Sidelink relay function to search for neighboring relay UEs is defined.

[0005] Patent Document 1 describes a system that collects information on nearby relayable communication terminals in advance, and when a request is received from the discovering communication terminal (Discoverer end UE), the following is performed: First, it is determined whether the information of the terminal to be discovered (Discoveree end UE) in the request matches the collected terminal information. If they match, relaying between the Discoverer end UE and the Discoveree end UE is initiated to reduce the delay required for discovery. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] International Publication No. 2021 / 132498 [Overview of the project] [Problems that the invention aims to solve]

[0007] Direct Discovery searches for nearby UEs (Unified Element Users), but if the target UE is not nearby, there is no way to extend the search range via relay UEs. Therefore, it was necessary to use 5G ProSe UE-to-UE Relay Discovery to search for the target UE. 5G ProSe UE-to-UE Relay Discovery is a procedure for searching for nearby relay UEs. UE-to-UE is also written as U2U. However, when using this method, it first checks for the absence of nearby UEs using Direct Discovery, so it cannot be used when low latency is required.

[0008] One aspect of this disclosure aims to provide a technology for appropriately searching for a communication terminal, in view of at least one of the above-mentioned problems. [Means for solving the problem]

[0009] A communication device according to one aspect of the present disclosure is a 3GPP-compliant communication device that connects to other communication devices via one or more relay devices, and comprises a transmitting means for transmitting a signal for searching for the other communication devices, the signal including information indicating that the signal is to be relayed to the other communication devices, and identification information indicating a connection service provided by the relay device. [Effects of the Invention]

[0010] According to one aspect of the present invention, it becomes possible to appropriately search for communication terminals. [Brief explanation of the drawing]

[0011] [Figure 1] A diagram showing the configuration of the communication system in the first embodiment. [Figure 2] A diagram showing the configuration of the communication system in the second and third embodiments. [Figure 3] A diagram showing the configuration of the communication system in the fourth, fifth, and sixth embodiments. [Figure 4] A diagram showing the functional configuration of the Discoverer end UE in an embodiment. [Figure 5] A diagram showing the functional configuration of the relay UE in the embodiment. [Figure 6] A diagram showing the functional configuration of the Discoveree end UE in an embodiment. [Figure 7] Sequence diagram in the first embodiment. [Figure 8] A diagram showing the message format in the first embodiment. [Figure 9] Flowchart in the first embodiment. [Figure 10] Sequence diagram in the second embodiment. [Figure 11] A diagram showing the message format in the second embodiment. [Figure 12] Flowchart in the second embodiment. [Figure 13]Figure showing the relay path selected by the Discoverer end UE in the second embodiment. [Figure 14] Sequence diagram in the third embodiment. [Figure 15] Figure showing the message format in the third embodiment. [Figure 16] Flowchart in the third embodiment. [Figure 17] Figure showing the relay path selected by the Discoverer end UE in the third embodiment. [Figure 18] Sequence diagram in the fourth embodiment. [Figure 19] Figure showing the message format in the fourth embodiment. [Figure 20] Flowchart of Solicitation message transmission in the fourth embodiment. [Figure 21] Flowchart of Solicitation message transmission in the fourth embodiment. [Figure 22] Flowchart of Response message transmission in the fourth, fifth, and sixth embodiments. [Figure 23] Sequence diagram in the fifth embodiment. [Figure 24] Figure showing the message format in the fifth embodiment. [Figure 25] Flowchart of Solicitation message transmission in the fifth embodiment. [Figure 26] Figure showing the relay path selected by the Discoverer end UE in the fifth embodiment. [Figure 27] Sequence diagram in the sixth embodiment. [Figure 28] Figure showing the message format in the sixth embodiment. [Figure 29] Flowchart of Solicitation message transmission in the sixth embodiment. [Figure 30]A diagram showing the relay path selected by the Discoverer end UE in the sixth embodiment. [Modes for carrying out the invention]

[0012] [First Embodiment] (System Configuration) Figure 1 shows an example of the system configuration according to this embodiment. In Figure 1, end UE-A101, end UE-B102, end UE-D104, and end UE-E105 are terminals with Sidelink communication functionality. Relay UE-C103 is connected to end UE-A101 via Sidelink communication and is a terminal with the function of relaying communication between end UE-A101 and other end UEs (U2U relay function). Reference numeral 106 indicates the range of the radio waves from end UE-A101, and reference numeral 107 indicates the range of the radio waves from relay UE-C103.

[0013] End UE-A101, acting as a Discoverer, can perform 5G ProSe Direct Discovery (Model B) to search for End UE-B102, which will act as the Discoveree (Target UE). Furthermore, by using this embodiment, End UE-A101 can search for End UE-D104 and UE-E105, which are located outside the range of End UE-A101's radio waves. Specifically, End UE-A101 can search for UE-D104 and UE-E105 by relaying the Direct Discovery signal using the U2U relay function of relay UE-C103.

[0014] (Functional configuration of the device) Next, the functional configuration of the communication device according to this embodiment will be described. Note that the configuration of the functional blocks described below is merely an example.

[0015] Some (and sometimes all) of the functional blocks described may be replaced by other functional blocks that perform similar functions, some functional blocks may be omitted, or further functional blocks may be added. Also, one functional block shown in the following description may be divided into multiple functional blocks, or multiple functional blocks may be integrated into one functional block. Furthermore, only some of the functional blocks may be configured in hardware, with the other functions configured in software. When a functional block is configured in software, the processors constituting the control units 401, 501, and 601 described later execute control programs to realize the functions stored in the storage units 402, 502, and 602 described later. This provides the functionality of the functional block.

[0016] Figure 4 is a block diagram showing an example of the functional configuration of the Discoverer end UE-A101 in this embodiment.

[0017] The Discoverer end UE-A101 includes a control unit 401, a storage unit 402, a signal strength measurement unit 403, a Discoverer processing unit 404, a message generation processing unit 405, a message analysis processing unit 406, and a wireless communication unit 407.

[0018] The control unit 401 controls the operation of the end UE-A101. The memory unit 402 stores information used by the control unit 401 for control and information related to communication. The signal strength measurement unit 403 measures the signal strength (SD-RSRP) from the discovery signal sent from the relay UE. SD-RSRP is an abbreviation for Sidelink Discovery Reference Signal Received Power. The Discoverer processing unit 404, as a Discoverer, performs processing related to discovery of neighboring end UEs and discovery in relaying to end UEs via the relay UE. The message generation processing unit 405 generates messages necessary for discovery of relay UEs and end UEs. The message analysis processing unit 406 analyzes messages received from relay UEs and end UEs. The wireless communication unit 407 transmits and receives information wirelessly with relay UEs and end UEs via relay UEs. The wireless communication unit 407 performs the transmission processing of messages generated by the message generation processing unit 405. The message analysis processing unit 406 also performs the analysis processing of messages received by the wireless communication unit 407.

[0019] Figure 5 is a block diagram showing an example of the functional configuration of relay UE-C103 in this embodiment.

[0020] The relay UE-C103 includes a control unit 501, a storage unit 502, a signal strength measurement unit 503, a U2U Relay processing unit 504, a message generation processing unit 505, a message analysis processing unit 506, and a wireless communication unit 507.

[0021] The control unit 501 controls the operation of the relay UE-C103. The memory unit 502 stores information used by the control unit 501 for control and information related to communication. The signal strength measurement unit 503 measures the signal strength (SD-RSRP) from the discovery signal sent from the end UE. The U2U Relay processing unit 504 performs relay and discovery processing for communication between end UEs. The message generation processing unit 505 generates messages necessary for U2U relay discovery. The message analysis processing unit 506 analyzes messages received from the end UE. The wireless communication unit 507 sends and receives information wirelessly with the end UE. The wireless communication unit 507 performs the transmission processing of messages generated by the message generation processing unit 505. The message analysis processing unit 506 also performs the analysis processing of messages received by the wireless communication unit 507.

[0022] Figure 6 is a block diagram showing an example of the functional configuration of the Discoveree end UE-B102, UE-D104, and UE-E105 in this embodiment.

[0023] The Discoveree end UE-B102, for example, includes a control unit 601, a storage unit 602, a signal strength measurement unit 603, a Discoveree processing unit 604, a message generation processing unit 605, a message analysis processing unit 606, and a wireless communication unit 607.

[0024] The control unit 601 controls the operation of the Discoveree end UE-B102 and other devices. The memory unit 602 stores information used by the control unit 601 for control and information related to communication. The signal strength measurement unit 603 measures the signal strength (SD-RSRP) from the discovery signal sent from the Discoverer end UE or relay UE. The Discoveree processing unit 604, acting as the Discoveree, performs discovery processing in direct communication with neighboring end UEs, or discovery processing in relaying with end UEs via relay UEs. The message generation processing unit 605 generates messages necessary for discovery by relay UEs and end UEs. The message analysis processing unit 606 analyzes messages received from the Discoverer end UE or relay UE. The wireless communication unit 607 sends and receives information wirelessly with the Discoverer end UE or relay UE. The wireless communication unit 607 performs transmission processing for messages generated by the message generation processing unit 605. The message analysis processing unit 606 also performs analysis processing for messages received by the wireless communication unit 607.

[0025] In subsequent embodiments, the functional configuration of the Discoverer end UE is the same as that shown in Figure 4, the functional configuration of the relay UE is the same as that shown in Figure 5, and the functional configuration of the Discoveree end UE is the same as that shown in Figure 6.

[0026] (Example of processing) The operation of this embodiment will be explained using the operation sequence diagram shown in Figure 7, the message format shown in Figure 8, and the flowchart shown in Figure 9.

[0027] Figure 7 shows an example sequence in which a Discoverer end UE uses the Direct Discovery procedure to perform discovery with neighboring end UEs and end UEs within the relay UE's coverage via a relay UE. Figure 9 similarly shows an example flowchart in this embodiment. Figure 8 shows an example message format of the information contained in the Direct Discovery Solicitation message and Direct Discovery Response message in this embodiment. The Direct Discovery Solicitation message is also simply called the Solicitation message, and the Direct Discovery Response message is also simply called the Response message. In the example shown in Figure 8, the Direct Discovery Solicitation messages are 5G ProSe Direct Discovery Solicitation messages 801 and 804. Also in the example shown in Figure 8, the Direct Discovery Response message is 5G ProSe Direct Discovery Response message 808.

[0028] In this embodiment and subsequent embodiments, message transmission and reception and decision processing shown in sequences and flowcharts are realized by the respective control units shown in Figures 4, 5, and 6 executing control programs stored in the memory unit. Some processing is realized in cooperation with the functional blocks described in Figures 4, 5, and 6.

[0029] In Figures 7, 8, and 9, end UE-A101 operates as follows to discover the Discoveree end UE: End UE-A101 broadcasts a 5G ProSe Direct Discovery Solicitation message 801 (F701, S901, S902, S903, S904). At this time, the application running on end UE-A101 decides to extend the search range using the relay function of the U2U relay and adds the following to the Solicitation message 801: The application adds a Relay indication 802, which indicates a relay instruction, and a Relay service code 803, which is identification information indicating the connection service provided by the relay UE that is available to the end UE. The Relay indication is a field that indicates whether or not to relay. A Relay indication (value of 1) indicates that the Solicitation message should be relayed to the end UE being sought. A Relay indication (value of 1) can also be said to be information to request or instruct the relay UE to forward or relay the Solicitation message to the end UE being sought. Here, the Relay service code is a unique identifier for the Sidelink relay service, determined at a higher layer and configured in each UE during provisioning. The Relay service code may be configured by a PCF present on the 5G core network, or it may be obtained from non-volatile memory within the UE or from information embedded in the SIM card. PCF is an abbreviation for Policy Service Function.

[0030] When relay UE-C103 receives Solicitation message 801 (S905), it checks whether a Relay indication exists in message 801 (S906), and if not, it rejects message 801. If a Relay Indication exists in message 801 and its value is 1, meaning it is permissible to relay, relay UE-C103 operates as follows: Relay UE-C103 checks whether the Relay service code in message 801 matches the code of its own terminal. If they match, relay UE-C103 decides to broadcast (forward or relay) the 5G ProSe Direct Discovery Solicitation message 804. Depending on the operational status of the relay UE, relay UE-C103 may decide not to send the message. If relay UE-C103 sends message 804, it operates as follows: In other words, relay UE-C103 sets the value of Relay indication 805 to 0 and adds its own User info ID as UE-to-UE Relay UE Info 807 to message 804 (F703, S908). Here, a value of 0 for Relay indication 805 means that relaying is not possible.

[0031] Discoveree end UE-D104 and UE-E105 receive the 5G ProSe Direct Discovery Solicitation message 804 (S909). At this time, end UE-D104 and UE-E105 check whether a U2U relay UE info 807 exists in message 804 (S910). If it exists, end UE-D104 and UE-E105 can determine that this message was relayed by a relay UE. That is, the User info ID in the U2U relay UE info indicates that the relay UE indicated by that ID relayed this message. This also applies to subsequent embodiments. After this, end UE-D104 and UE-E105 check whether the Relay service code in message 804 matches the code of their own terminal (S912), and if they match, they check the ProSe query code as before. If the verification confirms that the terminal is the target of the discovery, end UE-D104 and UE-E105 create and send a 5G ProSe Direct Discovery Response message 808 (F704, F706). Here, each Discoveree end UE adds a Relay service code 809 to the Response message 808. Each Discoveree end UE also adds its own Application layer ID as Target discoveree end UE info 810 to the Response message 808. In addition, each Discoveree end UE obtains U2U relay UE info 807 from the Solicitation message 804 and adds the obtained U2U relay UE info 807 to message 808 (811). Here, the Application layer ID is an identifier of the Discoveree end UE determined and set by the higher layer. The Target discoveree end UE info 810 may also store the User info ID, which is a unique identifier of the UE and is also set by the higher layer.

[0032] On the other hand, the Discoveree end UE-B102, being within the coverage of end UE-A101, directly receives Solicitation message 801 from end UE-A101 (F701, S909). At this time, end UE-B102 checks whether U2U relay UE info 807 exists in message 801 (S910). If it does not exist, end UE-B102 determines that it has received a conventional 5G ProSe Direct Discovery Solicitation message and proceeds to check the ProSe query code. If the check reveals that its own terminal is the target of the search, end UE-B102 sends a 5G ProSe Direct Discovery Response message to the source, Discoverer end UE-A101 (S911).

[0033] Relay UE-C103 issues a timer after sending Solicitation message 804 and accepts response messages from end UEs until the timer expires. During this time, relay UE-C103 receives Response messages 808 from end UE-D104 and UE-E105 (F704, F706, S914). Relay UE-C103 then forwards the received message 808 to end UE-A101, the source of Solicitation message 804 (F705, F707, S915).

[0034] End UE-A101 issues a timer after sending Solicitation message 801 and accepts response messages from relay UEs until the timer expires. During this time, End UE-A101 receives a Response message from relay UE-C103 (F705, F707, S916).

[0035] In this embodiment, end UE-A101 receives three response messages. These response messages are from end UE-B102, end UE-D104, and end UE-E105, respectively. End UE-A101 can select the Discoveree end UE from among end UE-B102, end UE-D104, and end UE-E105 based on metadata included in the response message (F708, S917).

[0036] According to this embodiment, the end UE-A101 can discover target UEs over a wider area by utilizing the relay function of the relay UE, in addition to nearby end UEs.

[0037] In this embodiment and subsequent embodiments, instead of SD-RSRP, RSRQ, RSSI, CQI, etc., measured from the discovery signal may be used as the signal strength measured. RSRQ is an abbreviation for Reference Signal Received Quality. RSSI is an abbreviation for Received Signal Strength Indicator. CQI is an abbreviation for Channel Quality Indicator.

[0038] [Second Embodiment] (System Configuration) Figure 2 shows an example of the system configuration according to this embodiment. The difference from the first embodiment is that there are multiple (2) relay UEs. In Figure 2, relay UE-F201, like relay UE-C103, is a terminal that has the function of relaying communication between end UE-A101 and other end UEs (U2U relay function). Also, reference numeral 206 indicates the range of radio waves from relay UE-C103 and relay UE-F201. Otherwise, it is the same as the configuration example shown in Figure 1.

[0039] (Example of processing) The operation of this embodiment will be explained using the operation sequence diagram shown in Figure 10, the message format shown in Figure 11, and the flowchart shown in Figure 12.

[0040] Figure 10 shows an example sequence in which a Discoverer end UE uses the Direct Discovery procedure to perform discovery with neighboring end UEs and end UEs within the relay UE's coverage via a relay UE. Figure 12 similarly shows an example flowchart in this embodiment. Figure 11 shows an example message format of the information contained in a direct discovery response message in this embodiment. In the example shown in Figure 11, the direct discovery response message is a 5G ProSe Direct Discovery Response message 1101.

[0041] The difference between this embodiment and the first embodiment is that in this embodiment, the relay path (communication path) can be selected by adding signal strength (SD-RSRP) to the discovery signal (response message) used in the first embodiment. The relay path refers to the combination of the relay UE and the target UE.

[0042] End UE-A101 broadcasts a 5G ProSe Direct Discovery Solicitation message 801, similar to the first embodiment (F1001, S901, S902, S903, S904). Here, the neighboring End UE-B102 responds to message 801 by measuring the signal strength (SD-RSRP) of message 801 and sending a Response message containing the signal strength value (F1002, S909, S1201, S910, S911).

[0043] Next, relays UE-C103 and UE-F201 receive message 801 and broadcast Solicitation message 804, similar to the first embodiment (F1003, F1008, S905, S906, S907).

[0044] Next, the Discoveree end UE-D104 and UE-E105 receive Solicitation message 804, and measure the signal strength (SD-RSRP) of message 804 (S1201). Then, as in the first embodiment, end UE-D104 and UE-E105 proceed to verify the U2U relay UE info (S910) and the Relay service code (S912). After that, end UE-D104 and UE-E105 create a 5G ProSe Direct Discovery Response message 1101. Then, end UE-D104 and UE-E105 send the Response message 1101 to the source relay UE (F1004, F1005, F1009, F1010, S1202). At this time, end UE-D104 and UE-E105 include the measured signal strength in the Response message 1101 (S1202). In this embodiment, the Information Element name is set to SD-RSRP of Target discoveree end UE1102, and the Range can be set from 0 to 127. The actual value (in dBm) is the value obtained by subtracting 156 from that value.

[0045] Relays UE-C103 and UE-F201, upon receiving Response message 1101, forward the message to end UE-A101, the source of message 801 (F1006, F1007, F1011, F1012, S914, S915).

[0046] End UE-A101, having received the above Response message from relays UE-C103 and UE-F201, measures the signal strength (SD-RSRP) of the above Response message (S1203).

[0047] Figure 13 shows an example of the results obtained by combining the signal strength obtained from the message received by UE-A101 in this embodiment, the User info id of the relay UE, and the Application layer ID of the Discoveree end UE. From these results, end UE-A101 can select the relay path (combination of relay UE and end UE) for communication with the Discoveree end UE (F1013, S1204). In this example, for patterns 0 to 2, the signal strength between UE-A101 and UE-B102 is low, and the signal strength between relay UE-C and end UE-D104 or end UE-E105 is low. Therefore, it can be seen that if these patterns are selected, long-term communication may not be possible. For this reason, end UE-A101 can select pattern 3, which is the combination of relay UE-F201 and end UE-D104. In addition to signal strength, the selection priority may be changed based on information such as metadata, as in the conventional method. Metadata is arbitrary information set by the upper layer and is stored in the 5G ProSe Direct Discovery Response message. For example, information such as the identifier of the Discoveree end UE (Application layer ID or User info ID) and location information may be set by the upper layer. In addition, the neighboring UE, end UE-B102, may be identified by the Layer-2 ID used as the source and destination unicast addresses in Sidelink communication.

[0048] [Third Embodiment] (Example of processing) The operation of this embodiment will be explained using the operation sequence diagram shown in Figure 14, the message format shown in Figure 15, and the flowchart shown in Figure 16. The system configuration in this embodiment is shown in Figure 2, the same as in the second embodiment.

[0049] Figure 14 shows an example sequence in which a Discoverer end UE uses the Direct Discovery procedure to perform discovery with neighboring end UEs and end UEs within the relay UE's coverage via a relay UE. Figure 16 similarly shows an example flowchart in this embodiment. Figure 15 shows an example message format of the information contained in the Direct Discovery Solicitation message and Direct Discovery Response message in this embodiment. In the example shown in Figure 15, the Direct Discovery Solicitation message is a 5G ProSe Direct Discovery Solicitation message 1501. Also in the example shown in Figure 15, the Direct Discovery Response message is a 5G ProSe Direct Discovery Response message 1503.

[0050] The difference between this embodiment and the second embodiment is that this embodiment uses delay information instead of signal strength to select the relay path.

[0051] End UE-A101 broadcasts a 5G ProSe Direct Discovery Solicitation message 801, similar to the first embodiment (F1001, S901, S902, S903, S904). Here, the neighboring End UE-B102 responds to message 801 by sending a Response message (F1401, S909, S1603, S910, S911). The Response message includes Accumulated delay info 1504, which indicates the cumulative delay time. End UE-B102 calculates the delay time of the Solicitation message 801 and stores the calculated delay time information (delay information) in Accumulated delay info 1504 (S1603, S1604).

[0052] Next, relays UE-C103 and UE-F201 receive message 801 and broadcast Solicitation message 1501, similar to the first embodiment (F1402, F1407, S1601, S906, S907, S1602). At this time, relays UE-C103 and UE-F201 calculate the delay time of the Solicitation message 801 (S1601). Then, relays UE-C103 and UE-F201 store information indicating the calculated delay time (delay information) in Accumulated delay info 1502 (S1602).

[0053] Next, the Discoveree end UE-D104 and UE-E105 receive Solicitation message 1501, and here, similar to the relay UE, calculate the delay time (S909, S1603). Then, end UE-D104 and UE-E105 proceed to check the U2U relay UE info (S910) and the Relay service code (S912). After that, end UE-D104 and UE-E105 create 5G ProSe Direct Discovery Response message 1503. Then, end UE-D104 and UE-E105 send Response message 1503 to the source relay UE (F1403, F1404, F1408, F1409, S1605). In this case, end UE-D104 and UE-E105 add the delay time calculated as described above to the delay time indicated by Accumulated delay info1502 in Solicitation message 1501 (S1605). Then, end UE-D104 and UE-E105 include the cumulative delay information showing the result of the addition in Response message 1503 (1504) (S1605).

[0054] Relays UE-C103 and UE-F201, upon receiving Response message 1503, forward the message to end UE-A101, the source of message 801 (F1405, F1406, F1410, F1411, S914, S915).

[0055] End UE-A101 receives the above Response message from relay UE-C103 and UE-F201 (S916). Then, End UE-A101 selects a relay path (combination of relay UE and end UE) based on the above Response message (F1412, S1606).

[0056] Figure 17 shows an example of the result obtained by combining the cumulative delay time obtained from the message received by UE-A101 in this embodiment, the User info id of the relay UE, and the Application layer ID of the Discoveree end UE. From this result, end UE-A101 can select a relay path (combination of relay UE and end UE) to communicate with the Discoveree end UE (F1412, S1606). In this example, the patterns with the smallest delay are patterns 1 and 2, and since pattern 1 does not go through the relay UE and has fewer hops than pattern 2, pattern 1 can be selected. In addition to delay time, the selection priority may be changed by information such as metadata, as in the conventional method. Furthermore, the neighboring UE, end UE-B102, may be identified by the Layer-2 ID used as the source / destination unicast address in Sidelink communication. In addition to delay information, the signal strength information element shown in the second embodiment may be added to each discovery signal (response message) and used to determine the relay path.

[0057] [Fourth Embodiment] (System Configuration) Figure 3 shows an example of the system configuration according to this embodiment. In Figure 3, end UE-A301, end UE-E305, and end UE-F306 are terminals with Sidelink communication functionality. Relay UE-B302, relay UE-C303, and relay UE-D304 are terminals that have the function of relaying communication between end UE-A301 and end UE-E305 or end UE-F306 over multiple hops. Reference numeral 307 indicates the range of the radio waves from end UE-A301, reference numeral 308 indicates the range of the radio waves from relay UE-B302 and relay UE-C303, and reference numeral 309 indicates the range of the radio waves from relay UE-D304.

[0058] End UE-A301, acting as a Discoverer, uses 5G ProSe Direct Discovery to discover neighboring UEs. By using this embodiment, End UE-A301 can search for End UE-E305 and UE-F306, which are located outside the range of End UE-A301's radio waves. Specifically, End UE-A301 can search for UE-E305 and UE-F306 by relaying the Direct Discovery signal using the U2U relay function of relays UE-B302, UE-C303, and UE-D304.

[0059] (Functional configuration of the device) Regarding the functional configuration of the communication device according to this embodiment, the end UE-A301 has the same configuration as the Discoverer end UE in the first embodiment, as shown in Figure 4. The relay UE-B302, UE-C303, and UE-D304 have the same configuration as the relay UE in the first embodiment, as shown in Figure 5. The U2U Relay processing unit 504 is equipped with a multi-hop relay function. Furthermore, the end UE-E305 and UE-F306 have the same configuration as the Discoveree end UE in the first embodiment, as shown in Figure 6.

[0060] (Example of processing) The operation of the fourth embodiment will be explained using the operation sequence diagram shown in Figure 18, the message format shown in Figure 19, and the flowcharts shown in Figures 20, 21, and 22.

[0061] Figure 19 shows an example of a message format corresponding to multi-hop relay in this embodiment. The 5G ProSe Direct Discovery Solicitation messages 1901 and 1904 contain Relay service codes 1903 and 1906, similar to the embodiments described above. The 5G ProSe Direct Discovery Solicitation messages 1901 and 1904 also contain Hop Limits 1902 and 1905, indicating the maximum number of hops. The Solicitation message 1904 created by the relay UE includes a List of U2U relay UE info 1907, which is a list of the relay UE's User info IDs.

[0062] First, the Discoverer end UE-A301 determines the maximum number of hops allowed (Hop Limit). Then, the end UE-A301 broadcasts the 5G ProSe Direct Discovery Solicitation message 1901 (F1801, S2001, S2002, S2003, S2004). Here, the Hop Limit stored in message 1901 is N, which is a value greater than or equal to 2.

[0063] The nearby relay UE-B302 receives the Solicitation message 1901 (S2005). Relay UE-B302 checks whether a Hop Limit exists in message 1901 (S2006). If it does, relay UE-B302 determines that multi-hop relaying is being requested and decreases the Hop Limit value by 1. If the updated Hop Limit value is 0 or less, relay UE-B302 rejects message 1901 (S2006). In other words, in this embodiment, the Hop Limit is used in the same way as the so-called Time to Live (TTL). Therefore, in this case, the Hop Limit indicates the number of times the Solicitation message can be relayed or forwarded.

[0064] Next, relay UE-B302 checks whether the Relay service code in message 1901 matches the code of its own terminal (S2007). If they do not match, it discards message 1901. On the other hand, if they do match, relay UE-B302 checks whether a List of U2U relay UE info exists in message 1901. If it does, it confirms that its own ID is not in that list (S2008). This confirmation (determination) is for the purpose of preventing loops. In this case, since the list does not exist, relay UE-B302 does not discard message 1901 and proceeds to the next process (S2009).

[0065] Next, relay UE-B302 updates the received 5G ProSe Direct Discovery Solicitation message (S2009). The information to be updated is the addition of its own User info ID to the List of U2U relay UE info and the updated Hop Limit (value reduced by 1) as described above (S2109). Relay UE-B302 then broadcasts the updated Solicitation message 1904 (F1802, S2010).

[0066] In this embodiment, the Solicitation message 1904 sent from relay UE-B302 reaches relays UE-C303 and UE-D304 (F1802). For ease of explanation, the sequence diagram shown in Figure 18 is described separately from the route via relays UE-B302 and UE-C303, and the route via relays UE-B302 and UE-D304. Processing in each route is assumed to be performed asynchronously.

[0067] Relays UE-C303 and UE-D304, upon receiving Solicitation message 1904, operate in the same manner as relay UE-B302 as follows: Relays UE-C303 and UE-D304 update and verify the Hop Limit (S2006), verify the Relay service code (S2007), and verify that their own ID is not in the list (S2008). Then, relays UE-C303 and UE-D304 add their own User info ID to the List of U2U relay UE info in the Solicitation message (S2009). Relays UE-C303 and UE-D304 also update the Hop Limit in the Solicitation message (-1) (S2009). Next, relays UE-C303 and UE-D304 broadcast the updated Solicitation message 1904 (F1803, F1810, S2010).

[0068] In this embodiment, the Solicitation message 1904 sent from relays UE-C303 and UE-D304 arrives at Discoveree end UE-E305 and UE-F306 (F1803, F1810, S2011). At this time, end UE-E305 and UE-F306 check whether a List of U2U relay UE info 1907 exists in message 1904 (S2012). If it does not exist, end UE-E305 and UE-F306 determine that they have received a conventional 5G ProSe Direct Discovery Solicitation message and proceed to check the ProSe query code. If the check reveals that their own terminal is the target of the search, end UE-E305 and UE-F306 send a 5G ProSe Direct Discovery Response message to the sender of the Solicitation message (S2013).

[0069] In this embodiment, the message contains a List of U2U relay UE info1907, and the ID of relay UE-C303 or UE-D304 is included in the list. Therefore, end UE-E305 and UE-F306 proceed to verify the relay service code (S2014).

[0070] If the Relay service code in message 1904 matches the code of the local terminal, end UE-E305 and UE-F306 check the ProSe query code (S2015). If end UE-E305 and UE-F306 determine that their local terminal is the target of the search, they create a Response message 1908. Then, end UE-E305 and UE-F306 send Response message 1908 to the sender as a response to Solicitation message 1904 (F1804, F1807, F1811, F1814, S2015). At this time, end UE-E305 and UE-F306 store their own Relay service code 1909 in Response message 1908 (S2015). Furthermore, end UE-E305 and UE-F306 store their Application layer ID as Target discoveree end UE Info1910 in Response message 1908 (S2015). Also, end UE-E305 and UE-F306 add the List of U2U relay UE info1907 from the received Solicitation message 1904 to Response message 1908 (1911) (S2015).

[0071] The process shown in Figure 20 has been explained above.

[0072] On the other hand, the flowchart shown in Figure 21 is a flowchart of a pattern in which the handling of the Hop Limit in the 5G ProSe Direct Discovery Solicitation message is changed. In the process shown in Figure 21, the Hop Limit was used in the same way as the so-called Time to Live (TTL). On the other hand, in the process shown in Figure 22, the value of the Hop Limit is not updated and is set to a fixed value indicating the maximum number of hops. Therefore, in this case, the Hop Limit indicates the maximum number of relays or transmissions allowed for the Solicitation message. Then, the decision of whether to reject the Solicitation message 1904 is made by comparing it with the list length of the List of U2U relay UE info 1907. Specifically, relay UEs 302, 303, and 304 check whether the List of U2U relay UE info 1907 exists in the received Solicitation message. If it exists, relay UEs 302, 303, and 304 check whether the Hop Limits 1902 and 1905 are greater than the list length of the List of U2U relay UE info 1907 (S2101). Relays UE302, 303, and 304 terminate processing (i.e., discard the message) if the value is not large, and if it is large, they perform the same processing as from S2006 onwards in Figure 20. However, relays UE302, 303, and 304 do not update the Hop limit value stored in the Solicitation message 1904 that they send (S2102).

[0073] The flowchart shown in Figure 22 illustrates the processes that follow those shown in Figures 20 and 21.

[0074] After sending Solicitation message 1904, relays UE302, 303, and 304 issue a timer to wait for a response, allowing them to receive a response signal (response message) until the timer expires. The response signal in this case is 5G ProSe Direct Discovery Response message 1908.

[0075] Relay UE303 and 304 receive Response message 1908 from Discoveree end UE305 and 306 (F1804, F1807, F1811, F1814, S2202). Then, relay UE303 and 304 forward message 1908 to relay UE-B302, the source of Solicitation message 1904 (F1805, F1808, F1812, F1815, S2203).

[0076] Relay UE-B302 receives Response message 1908 from relays UE303 and 304 (F1805, F1808, F1812, F1815, S2202). Relay UE-B302 then forwards message 1908 to Discoverer end UE-A301, the source of Solicitation message 1901 (F1806, F1809, F1813, F1816, S2203).

[0077] Meanwhile, after sending the Solicitation message 1901, the Discoverer end UE-A301 issues a timer to wait for a response and waits for a response signal (response message) until the timer expires. The response signal here is the 5G ProSe Direct Discovery Response message 1908. In this embodiment, the end UE-A301 receives the Response message 1908 from the relay UE-B302 (F1806, F1809, F1813, F1816, S2201).

[0078] In this embodiment, end UE-A101 receives four response messages. These response messages are two response messages via the route through relay UE-B302 and UE-C303, and two response messages via the route through relay UE-B302 and UE-D304. End UE-A101 can select a Discoveree end UE from among Discoveree end UE-D305 and UE-F306 based on metadata included in the response message (S2204).

[0079] According to this embodiment, the end UE-A101 can use 5G ProSe Direct Discovery to discover target UEs over a wider area, not only neighboring end UEs, but also by utilizing the multi-hop relay function of relay UEs.

[0080] [Fifth Embodiment] (Example of processing) The operation of this embodiment will be explained using the operation sequence diagram shown in Figure 23, the message format shown in Figure 24, and the flowchart shown in Figure 25. The system configuration and device function configuration in this embodiment will be described as being the same as in the fourth embodiment.

[0081] (Example of processing) The difference between this embodiment and the fourth embodiment is that, in this embodiment, by adding signal strength (SD-RSRP) to the discovery signal (response message) used in the fourth embodiment, the relay path can be selected even in a multi-hop relay. The relay path refers to the combination of the relay UE and the target UE.

[0082] Figure 24 shows an example of the message format used in this embodiment. The 5G ProSe Direct Discovery Solicitation message sent by the Discoverer end UE-A301 is similar to message 1901 in the fourth embodiment shown in Figure 19.

[0083] In this embodiment, the 5G ProSe Direct Discovery Solicitation message 2401 is used as the direct discovery request message sent by the relay UE. In the fourth embodiment, the List of U2U relay UE info was a list of the relay UE's User info IDs. In contrast, in this embodiment, the List of U2U relay UE info is a list of fields (2402, 2406) that combine the User info ID and SD-RSRP as U2U relay UE info 2407.

[0084] Furthermore, in this embodiment, the 5G ProSe Direct Discovery Response message 2403 is used as the direct discovery response message. In this message format as well, the List of U2U relay UE info is a list of fields that combine the User info ID and SD-RSRP as U2U relay UE info 2407 (2405, 2406). In addition, a field for storing the SD-RSRP value measured by the target UE is added as SD-RSRP of Target discoveree end UE 2404.

[0085] End UE-A301 broadcasts the 5G ProSe Direct Discovery Solicitation message 1901, similar to the fourth embodiment (F2301, S2001, S2002, S2003, S2004).

[0086] Next, relay UE-B302 receives Solicitation message 1901 (S2501). At this time, relay UE-B302 measures the SD-RSRP from the received message 1901 (S2501). Relay UE-B302 confirms that it is a multi-hop message, as in the fourth embodiment (S2006), checks the Relay service code (S2007), and confirms the existence of a list and that its own ID is not in the list (S2008).

[0087] Next, relay UE-B302 broadcasts Solicitation message 2401 (F2302, S2010). In this message, relay UE-B302 includes its own User info ID, the SD-RSRP measured as described above, and the Hop Limit minus 1 (S2502).

[0088] When relays UE-C303 and UE-D304 receive Solicitation message 2401, they similarly measure the SD-RSRP from the received message 2401 (S2501). Then, relays UE-C303 and UE-D304 operate in the same way as UE-B302 as follows: Relays UE-C303 and UE-D304 check for messages indicating multi-hop (S2006), check the relay service code (S2007), and check for the existence of a list and that their own ID is not in the list (S2008).

[0089] Next, relays UE-C303 and UE-D304 broadcast Solicitation message 2401 (F2303, F2310, S2010). At this time, relays UE-C303 and UE-D304 include their own User info ID, the SD-RSRP measured as described above, and the Hop Limit subtracted by 1 in message 2401 (S2502).

[0090] Next, the Discoveree end UE-E305 and UE-F306 receive the Solicitation message 2401, and measure the message signal strength (SD-RSRP) (S2503). Then, as in the fourth embodiment, the end UE-E305 and UE-F306 proceed to verify the U2U relay UE info (S2012) and the Relay service code (S2014). After that, the end UE-E305 and UE-F306 create the 5G ProSe Direct Discovery Response message 2403 (S2504). In message 2403, the end UE-E305 and UE-F306 store the SD-RSRP value measured as described above in the SD-RSRP of target discoveree end UE field 2404. Furthermore, end UE-E305 and UE-F306 include their Relay service code and Application layer ID in Response message 2403 (1909, 1910), as in other embodiments. Also, end UE-E305 and UE-F306 include the List of U2U relay UE info stored in Solicitation message 2401 in Response message 2403 (2405), as in other embodiments. Subsequently, end UE-E305 and UE-F306 send Response message 2403 to the source relay UE (F2304, F2307, F2311, F2314, S2504).

[0091] The subsequent processing is the same as that shown in Figure 22.

[0092] Relays UE303 and 304 receive Response message 2403 from Discoveree end UE305 and 306 (F2304, F2307, F2311, F2314, S2202). Then, relays UE303 and 304 forward message 2403 to relay UE-B302, the source of Solicitation message 2401 (F2305, F2308, F2312, F2315, S2203).

[0093] Relay UE-B302 receives Response message 2403 from relays UE303 and 304 (F2305, F2308, F2312, F2315, S2202). Relay UE-B302 then forwards message 2403 to Discoverer end UE-A301, the source of Solicitation message 1901 (F2306, F2309, F2313, F2316, S2203).

[0094] Subsequently, the end UE-A301 checks the Response messages received before the response waiting timer expires and selects the relay UE and end UE from among the UEs that were involved in sending the Response messages (F2317, S2204).

[0095] Figure 26 shows an example of the results obtained by combining the signal strength from the message received by UE-A301 in this embodiment, the User info id of the relay UE, and the Application layer ID of the Discoveree end UE. From these results, end UE-A101 can select the relay path (combination of relay UE and end UE) for communication with the Discoveree end UE (F2317, S2204). In this example of results, for patterns 1 and 2, the SD-RSRP value measured by relay UE-C303 is low, and the signal strength between relay UE-B302 and relay UE-C303 is low. Therefore, it can be seen that if these patterns are selected, long-term communication may not be possible. For this reason, end UE-A101 selects a pattern other than these. Comparing patterns 3 and 4, it can be seen that the SD-RSRP value measured by end UE-F306 is lower than the SD-RSRP value measured by end UE-E305. Therefore, end UE-A301 can select relay path pattern 3, which is a combination of relay UE-B302, relay UE-D304, and end UE-E305.

[0096] Similar to the second embodiment, the selection priority may be changed based on information such as metadata, in addition to signal strength, as in the conventional method. Metadata is arbitrary information set by the upper layer and is stored in the 5G ProSe Direct Discovery Response message. For example, information such as the identifier of the Discoveree end UE (Application layer ID or User info ID) and location information may be set by the upper layer.

[0097] [Sixth Embodiment] (Example of processing) The operation of the sixth embodiment will be explained using the operation sequence diagram shown in Figure 27, the message format shown in Figure 28, and the flowchart shown in Figure 29. The system configuration and device function configuration in the sixth embodiment will be described as being the same as those in the fourth and fifth embodiments.

[0098] The difference between this embodiment and the fifth embodiment is that this embodiment uses delay information instead of signal strength to select the relay path.

[0099] Figure 28 shows an example of the message format used in this embodiment. In this embodiment, the 5G ProSe Direct Discovery Solicitation message 2801 is used as the direct discovery request message sent by the Discoverer end UE. In this embodiment, the 5G ProSe Direct Discovery Solicitation message 2807 is used as the direct discovery request message sent by the relay UE. In this embodiment, the 5G ProSe Direct Discovery Response message 2816 is used as the direct discovery response message.

[0100] In the fourth and fifth embodiments, the only field related to multi-hop was Hop Limit. In contrast, in this embodiment, in addition to Hop Limit 2806, 2813, the following fields (a) to (d) are added to the message: (a) Multi-hop indication 2803, 2810 indicating whether or not to perform multi-hop relay; (b) Hop Count 2804, 2812, 2820 indicating the hop count (the number of times the message has been forwarded (or relayed), or the number of relay UEs that forwarded (or relayed) the message); (c) Max delay allowed 2806, 2814 indicating the maximum allowable delay (the maximum cumulative delay allowed when sending or forwarding (or relaying) the message); (d) Accumulated delay info 2815, 2821 indicating the cumulative delay (the cumulative delay when sending or forwarding (or relaying) the message). Also in this embodiment, List of U2U relay UE info 2809, 2819 is a list of User info IDs of relay UEs. A Multi-hop indication (value of 1) indicates that the Solicitation message should be relayed to the target end UE. A Multi-hop indication (value of 1) can also be described as information requesting or instructing a relay UE to forward or relay the Solicitation message to the target end UE.

[0101] First, the Discoverer end UE-A301 determines that multi-hop is enabled and the maximum number of hops is N (an integer greater than or equal to 2). Then, the end UE-A301 creates and broadcasts the 5G ProSe Direct Discovery Solicitation message 2801 (F2701, S2001, S2002, S2901, S2004).

[0102] Relay UE-B302 receives Solicitation message 2801, similar to the fifth embodiment. Relay UE-B302 checks whether a Multi-hop indication exists in the received Solicitation message 2801 and whether its value is 1, indicating a multi-hop instruction (S2901). If a Multi-hop indication exists and its value is 1, Relay UE-B302 then checks whether the Relay service code in message 2801 matches the code of its own terminal (S2007). If they match, Relay UE-B302 calculates the delay time of Solicitation message 2801 and adds information indicating the calculated delay time (delay information) to Accumulated delay info (S2902). Next, Relay UE-B302 determines whether to relay the message. If the following conditions are met, Relay UE-B302 determines that multi-hop is possible and continues the relay process (S2903). The conditions are that the Hop Limit exceeds the Hop Count in message 2801 plus 1, and that the Max delay allowed exceeds the cumulative delay time indicated by the Accumulated delay info above. Relay UE-B302 also checks whether a List of U2U relay UE info exists in message 2801, and if so, confirms that its own ID is not in the list (S2008). This confirmation (determination) is for the purpose of preventing loops. In this case, the list does not exist, so relay UE-B302 does not reject message 2801 and proceeds to the next process (S2904).

[0103] Next, relay UE-B302 creates a 5G ProSe Direct Discovery Solicitation message 2807 (S2904). The information updated in Solicitation message 2807 from the received Solicitation message 2801 is as follows: the updated information is its own User info ID added to the List of U2U relay UE info, and the updated Hop Count and Accumulated delay info. Relay UE-B302 broadcasts the created Solicitation message 2807 (F2702, S2010).

[0104] The Solicitation message 2807 sent from relay UE-B302 reaches relays UE-C303 and UE-D304 (F2702). Note that, similar to Figure 23, the sequence diagram in Figure 27 is divided into two routes for ease of explanation: one via relays UE-B302 and UE-C303, and the other via relays UE-B302 and UE-D304. Processing for each route is assumed to be asynchronous.

[0105] Upon receiving message 2807, relays UE-C303 and UE-D304, like relay UE-B302, check whether a multi-hop indication exists and whether its value is 1, indicating a multi-hop instruction (S2006). Then, relays UE-C303 and UE-D304 perform the following: check the relay service code (S2007), update and check the Accumulated delay info and Hop Count (S2902, S2903), and confirm that their own ID is not in the list (S2008). Subsequently, relays UE-C303 and UE-D304 add their own User info ID to the List of U2U relay UE info in Solicitation message 2807 (S2904). Relays UE-C303 and UE-D304 also update the Hop Count and Accumulated delay info in the Solicitation message (S2904). Next, relays UE-C303 and UE-D304 broadcast the updated Solicitation message 2807 (F2703, F2710, S2010).

[0106] The Solicitation message 2807 sent from relay UE-C303 and UE-D304 reaches Discoveree end UE-E305 and UE-F306 (F2703, F2710, S2011). End UE-E305 and UE-F306, as in other embodiments, check whether a List of U2U relay UE info exists in the received message 2807 (S2012). If it does not exist, end UE-E305 and UE-F306 determine that they have received a conventional 5G ProSe Direct Discovery Solicitation message and proceed to check the ProSe query code. If the check reveals that their terminal is the target of the search, end UE-E305 and UE-F306 send a 5G ProSe Direct Discovery Response message to the source (S2013).

[0107] In this embodiment, since a List of U2U relay UE info exists and its list length is 1 or more, end UE-E305 and UE-F306 check whether the Relay service codes match (S2014). If they match, end UE-E305 and UE-F306 create a 5G ProSe Direct Discovery Response message 2816 as a response signal to the Solicitation message (S2905). At that time, end UE-E305 and UE-F306 store their own Relay service code and User info ID in the Response message 2816 (2817, 2818) (S2905). In addition, end UE-E305 and UE-F306 add the List of U2U relay UE info stored in the Solicitation message 2807 to the Response message 2816 (2819) (S2905). In this embodiment, in addition to the above, end UE-E305 and UE-F306 also add Hop Count 2820 and Accumulate delay info 2821 to Response message 2816 (S2905). Each Discoveree end UE305 and 306 transmits the created Response message 2816 as a response signal to relay UE303 and 304 (F2704, F2707, F2711, F2714, S2905).

[0108] The process shown in Figure 29 has been described above. The subsequent processes are almost the same as those in the fourth and fifth embodiments shown in Figure 22. The difference is that the forwarded Response message includes Hop Count and Accumulated delay info (F2705, F2706, F2708, F2709, F2712, F2713, F2715, F2716).

[0109] Subsequently, the end UE-A301 checks the Response received before the response waiting timer expires and selects the relay UE and end UE from among the UEs that participated in sending the Response message (F2717, S2204).

[0110] Figure 30 shows an example of the result obtained by combining the cumulative delay time obtained from the message received by UE-A301 in this embodiment, the User info id of the relay UE, and the Application layer ID of the Discoveree end UE. In this example of the result, end UE-A101 can select the combination of relay UE-B302, relay UE-C303, and end UE-F306, which is pattern 2 with the shortest cumulative delay time (F2717, S2204).

[0111] In the fourth, fifth, and sixth embodiments, no end UEs were present in the vicinity (within the coverage of end UE-A301), but as in the first, second, and third embodiments, end UEs may be present in the vicinity. Furthermore, end UE-A301 may use information contained in the response message received from the neighboring end UE to select the target UE, adding it to the resulting example. The neighboring UE, end UE-B102, may be identified by its Layer-2 ID, which is used as the source / destination unicast address in Sidelink communication.

[0112] In the fifth embodiment, the relay UE measures the SD-RSRP when it receives a Response message and stores the SD-RSRP value in the Response message. In the sixth embodiment, the relay UE may measure the SD-RSRP when it receives a Solicitation message and store the SD-RSRP value in each discovery signal. In this case, the aspect of signal strength may also be used in the selection decision, and the end UE-A301 may select the target UE and the relay UE path leading to it based on the signal strength as well.

[0113] Similar to the third embodiment, the selection priority may be changed based on information such as metadata, in addition to delay information, as in the conventional method.

[0114] Note that the unit of "Length" in the message formats shown in Figures 8, 11, 15, 19, 24, and 28 is Octet.

[0115] [Other embodiments] The above embodiments describe examples where the number of Discoveree end UEs is two or three. However, the number of Discoveree end UEs is not limited to the above. There may be one Discoveree end UE, two or three Discoveree end UEs, or four or more Discoveree end UEs.

[0116] In the above embodiment, an example was described in which the number of hops for the relay UE is 2. However, the number of hops is not limited to the above. There may be 3 or more hops. Also, in the above embodiment, there is one relay UE for the first hop, but there may be multiple relay UEs. Similarly, for the relay UE for the second hop, there may be one relay UE or multiple relay UEs.

[0117] The relay path selected by the Discoverer end UE may, in addition to or instead of SD-RSRP, be prioritized for the path with fewer hops if such a path exists. That is, the Discoverer end UE may also select the relay path based on the number of times request or response messages have been transferred between the Discoveree end UE and the Discoverer end UE.

[0118] Furthermore, the relay path selected by the Discoverer end UE may prioritize the relay path with less Accumulated delay info, in addition to or instead of SD-RSRP and / or hop count. That is, the Discoverer end UE may select the relay path based (furthermore) on the cumulative delay time for the transfer of request or response messages between the Discoveree end UE and the Discoverer end UE.

[0119] Furthermore, in the above embodiment, the relay UE measures the SD-RSRP upon receiving a request message and stores the measured SD-RSRP in the request message. However, the relay UE can also measure the SD-RSRP upon receiving a response message and store the measured SD-RSRP in the response message.

[0120] In S2903 in Figure 29, two conditions were described: one related to the Hop Limit, and the other related to Max delay allowed and Accumulated delay info. However, only one of these two conditions may be used. In this case, the fields related to the unused condition (Hop Limit, or Max delay allowed and Accumulated delay info) do not need to be present in the message. Also, if the conditions related to Max delay allowed and Accumulated delay info are not used, S2902 does not need to be executed.

[0121] In the above-described method, a program that implements one or more of the functions of the above-described embodiment is supplied to a system or device via a network or storage medium. This can also be implemented by one or more processors in the computer of that system or device reading and executing the program. Furthermore, it can also be implemented by a circuit that implements one or more functions (for example, an Application Specific Integrated Circuit (ASIC)).

[0122] This disclosure is not limited to the embodiments described above, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, the claims are attached to make the scope of this disclosure public.

[0123] In the above, the signal name is described as "5G ProSe Direct Discovery Solicitation message," but the signal name is not limited to this. The signal name may simply be "Direct Discovery Solicitation message," or "ProSe Direct Discovery Solicitation message." Furthermore, the signal name may also be "6G ProSe Direct Discovery Solicitation message." Such a Solicitation message (direct discovery request message or signal) is an example of a message or signal used to discover a communication device (end UE). The communication device (end UE) to be discovered is indicated, for example, by the ProSe query code within the message or signal.

[0124] Furthermore, although the signal name is described as "5G ProSe Direct Discovery Response message" above, the signal name is not limited to this. The signal name may simply be "Direct Discovery Response message" or "ProSe Direct Discovery Response message." In addition, the signal name may be "6G ProSe Direct Discovery Response message." Such a Response message (Direct Discovery Response message or signal) is an example of a response message or signal to a message or signal for discovering a communication device (end UE).

[0125] With respect to each of the embodiments described above, the following additional information is disclosed.

[0126] [Note 1] A communication device compliant with the 3GPP standard that connects to other communication devices via one or more relay devices, A communication device comprising a transmitting means for transmitting a signal for searching for the aforementioned other communication device, the signal including information indicating that the signal is to be relayed to the aforementioned other communication device, and identification information indicating a connection service provided by the relay device.

[0127] [Note 2] The communication device as described in Appendix 1, wherein the aforementioned information is indicated by a field indicating whether or not to perform relaying or whether or not to perform multi-hop relaying.

[0128] [Note 3] The communication device according to Appendix 1 or 2, wherein the signal further includes a field indicating the maximum number of transmissions of the signal that are permitted.

[0129] [Note 4] The communication device according to any one of the appendices 1 to 3, wherein the signal further includes a field indicating the number of times the signal can be transmitted.

[0130] [Note 5] The communication device according to any one of the appendices 1 to 5, wherein the signal further includes a field indicating the number of times the signal has been transmitted.

[0131] [Note 6] The communication device according to any one of the appendices 1 to 5, wherein the signal further includes a field indicating the maximum cumulative delay time allowed when transmitting or forwarding the signal.

[0132] [Note 7] Receiving means for receiving a response signal to the aforementioned signal, A communication device according to any one of the appendices 1 to 6, further comprising: a selection means for selecting a communication path for communicating with the other communication device based on the response signal.

[0133] [Note 8] A relay device compliant with the 3GPP standard that relays signals between a first communication device and a second communication device, Receiving means for receiving a signal from the first communication device or another first relay device for searching for the second communication device, the signal including information indicating that the signal is relayed to the second communication device and identification information indicating a connection service provided by the relay device, A relay device comprising: a transmitting means for transferring the aforementioned signal to the second communication device or another second relay device.

[0134] [Note 9] The relay device described in Appendix 8, wherein the aforementioned information is indicated by a field indicating whether or not to perform relaying or whether or not to perform multi-hop relaying.

[0135] [Note 10] The relay device according to Appendix 8 or 9, wherein the signal to be transmitted further includes identification information of the relay device.

[0136] [Note 11] The relay device according to any one of appendices 8 to 10, further comprising a field indicating the maximum number of times the signal is allowed to be transmitted.

[0137] [Note 12] The relay device according to any one of appendices 8 to 11, further comprising a field indicating the number of times the signal can be transmitted.

[0138] [Note 13] The relay device according to any one of appendices 8 to 12, further comprising a field indicating the number of times the signal has been transmitted.

[0139] [Note 14] The relay device according to any one of appendices 8 to 13, further comprising a field indicating the maximum cumulative delay time allowed when transmitting or forwarding the signal.

[0140] [Note 15] The relay device according to any one of appendices 8 to 14, wherein the signal further includes a field indicating the cumulative delay time when transmitting or forwarding the signal.

[0141] [Note 16] The system further includes a measuring means for measuring the signal strength from the received signal, The relay device according to any one of appendices 8 to 15, further comprising a field indicating the signal strength, to be transmitted.

[0142] [Note 17] The receiving means receives a response signal to the signal from the second communication device or the second other relay device. The transmitting means is a relay device according to any one of the appendices 8 to 16, which transfers the response signal to the first communication device or the first other relay device.

[0143] [Note 18] A communication device compliant with the 3GPP standard that connects to other communication devices via one or more relay devices, Receiving means for receiving a signal from the relay device for searching for the communication device, the signal being transmitted from the other communication device via the relay device, A communication device comprising a transmitting means for transmitting a response signal to the aforementioned signal to the relay device.

[0144] [Note 19] The communication device described in Appendix 18, wherein the signal includes information indicating that the relay device relayed the signal.

[0145] [Note 20] The communication device described in Appendix 18 or 19, wherein the response signal includes identification information of the communication device.

[0146] [Note 21] The communication device according to any one of appendices 18 to 20, wherein the response signal includes identification information indicating a connection service provided by the relay device.

[0147] [Note 22] The communication device according to any one of appendices 18 to 21, wherein the response signal includes a field indicating the number of times the signal has been transmitted.

[0148] [Note 23] The communication device according to any one of appendices 18 to 22, wherein the response signal includes a field indicating the cumulative delay time when transmitting or forwarding the signal.

[0149] [Note 24] The communication device according to any one of appendices 18 to 23, wherein the response signal includes a field indicating identification information of the relay device.

[0150] [Note 25] The communication device according to any one of appendices 18 to 24, wherein the response signal includes a field indicating the signal strength measured by the relay device from the signal.

[0151] [Note 26] The system further comprises a measuring means for measuring signal intensity from the aforementioned signal, The communication device according to any one of appendices 18 to 25, wherein the response signal includes a field indicating the signal strength.

[0152] [Note 27] A control method for a communication device compliant with the 3GPP standard that connects to other communication devices via one or more relay devices, A control method comprising the step of transmitting a signal for searching for the aforementioned other communication device, the signal comprising information indicating that the signal is to be relayed to the aforementioned other communication device, and identification information indicating a connection service provided by the relay device.

[0153] [Note 28] A control method for a relay device compliant with the 3GPP standard that relays signals between a first communication device and a second communication device, The steps of receiving a signal from the first communication device or another first relay device for searching for the second communication device, the signal including information indicating that the signal is relayed to the second communication device and identification information indicating a connection service provided by the relay device, A control method comprising the step of transferring the signal to the second communication device or a second other relay device.

[0154] [Note 29] A control method for a communication device compliant with the 3GPP standard that connects to other communication devices via one or more relay devices, The relay device receives a signal for searching for the communication device, which has been transmitted from the other communication device via the relay device. A control method comprising the step of transmitting a response signal to the aforementioned signal to the relay device.

[0155] [Note 30] A computer in a 3GPP-compliant communication device that connects to other communication devices via one or more relay devices, A program for performing a process of transmitting a signal for searching for the aforementioned other communication device, the signal comprising information indicating that the signal is to be relayed to the aforementioned other communication device, and identification information indicating a connection service provided by the relay device.

[0156] [Note 31] The computer of the relay device, which is compliant with the 3GPP standard and relays signals between the first communication device and the second communication device, Processing to receive a signal from the first communication device or another first relay device for searching for the second communication device, the signal including information indicating that the signal is relayed to the second communication device and identification information indicating a connection service provided by the relay device, A program for performing the process of transferring the aforementioned signal to the second communication device or another second relay device.

[0157] [Note 32] A computer in a 3GPP-compliant communication device that connects to other communication devices via one or more relay devices, The relay device receives a signal for searching for the communication device, which has been transmitted from the other communication device via the relay device. A program for causing a device to perform the process of transmitting a response signal to the aforementioned signal to the relay device. [Explanation of symbols]

[0158] 101 Discoverer End UE-A 102 Discoveree End UE-B 103 Relay UE-C 104 Discoveree End UE-D 105 Discoveree End UE-E

Claims

1. A communication device compliant with the 3GPP standard that connects to other communication devices via one or more relay devices, A communication device comprising a transmitting means for transmitting a signal for searching for the aforementioned other communication device, the signal including information indicating that the signal is to be relayed to the aforementioned other communication device, and identification information indicating a connection service provided by the relay device.

2. The communication device according to claim 1, wherein the information is indicated by a field indicating whether or not to perform relaying or whether or not to perform multi-hop relaying.

3. The communication device according to claim 1, wherein the signal further includes a field indicating the maximum number of transmissions of the signal that are permitted.

4. The communication device according to claim 1, wherein the signal further includes a field indicating the number of times the signal can be transmitted.

5. The communication device according to claim 1, wherein the signal further includes a field indicating the number of times the signal has been transmitted.

6. The communication device according to claim 1, wherein the signal further includes a field indicating the maximum cumulative delay time that is permissible when transmitting or forwarding the signal.

7. Receiving means for receiving a response signal to the aforementioned signal, The communication device according to claim 1, further comprising: selection means for selecting a communication path for communicating with the other communication device based on the response signal.

8. A relay device compliant with the 3GPP standard that relays signals between a first communication device and a second communication device, Receiving means for receiving a signal from the first communication device or another first relay device for searching for the second communication device, the signal including information indicating that the signal is relayed to the second communication device and identification information indicating a connection service provided by the relay device, A relay device comprising: a transmitting means for transferring the aforementioned signal to the second communication device or another second relay device.

9. The relay device according to claim 8, wherein the information is indicated by a field indicating whether or not to perform relaying or whether or not to perform multi-hop relaying.

10. The relay device according to claim 8, wherein the signal to be transmitted further includes identification information of the relay device.

11. The relay device according to claim 8, wherein the signal further includes a field indicating the maximum number of times the signal is allowed to be transmitted.

12. The relay device according to claim 8, wherein the signal further includes a field indicating the number of times the signal can be transmitted.

13. The relay device according to claim 8, wherein the signal further includes a field indicating the number of times the signal has been transmitted.

14. The relay device according to claim 8, wherein the signal further includes a field indicating the maximum cumulative delay time that is permissible when transmitting or forwarding the signal.

15. The relay device according to claim 8, wherein the signal further includes a field indicating the cumulative delay time when transmitting or forwarding the signal.

16. The system further includes a measuring means for measuring the signal strength from the received signal, The relay device according to claim 8, wherein the signal to be transmitted further includes a field indicating the signal strength.

17. The receiving means receives a response signal to the signal from the second communication device or the second other relay device. The relay device according to claim 8, wherein the transmitting means transfers the response signal to the first communication device or the first other relay device.

18. A communication device compliant with the 3GPP standard that connects to other communication devices via one or more relay devices, Receiving means for receiving a signal from the relay device for searching for the communication device, the signal being transmitted from the other communication device via the relay device, A communication device comprising a transmitting means for transmitting a response signal to the aforementioned signal to the relay device.

19. The communication device according to claim 18, wherein the signal includes information indicating that the relay device relayed the signal.

20. The communication device according to claim 18, wherein the response signal includes identification information of the communication device.

21. The communication device according to claim 18, wherein the response signal includes identification information indicating a connection service provided by the relay device.

22. The communication device according to claim 18, wherein the response signal includes a field indicating the number of times the signal has been transmitted.

23. The communication device according to claim 18, wherein the response signal includes a field indicating the cumulative delay time when transmitting or forwarding the signal.

24. The communication device according to claim 18, wherein the response signal includes a field indicating identification information of the relay device.

25. The communication device according to claim 18, wherein the response signal includes a field indicating the signal strength measured by the relay device from the signal.

26. The system further comprises a measuring means for measuring signal intensity from the aforementioned signal, The communication device according to claim 18, wherein the response signal includes a field indicating the signal strength.

27. A control method for a communication device compliant with the 3GPP standard that connects to other communication devices via one or more relay devices, A control method comprising the step of transmitting a signal for searching for the aforementioned other communication device, the signal comprising information indicating that the signal is to be relayed to the aforementioned other communication device, and identification information indicating a connection service provided by the relay device.

28. A control method for a relay device compliant with the 3GPP standard that relays signals between a first communication device and a second communication device, The steps of receiving a signal from the first communication device or another first relay device for searching for the second communication device, the signal including information indicating that the signal is relayed to the second communication device and identification information indicating a connection service provided by the relay device, A control method comprising the step of transferring the signal to the second communication device or a second other relay device.

29. A control method for a communication device compliant with the 3GPP standard that connects to other communication devices via one or more relay devices, The relay device receives a signal for searching for the communication device, which has been transmitted from the other communication device via the relay device. A control method comprising the step of transmitting a response signal to the aforementioned signal to the relay device.

30. A computer in a communication device compliant with the 3GPP standard that connects to other communication devices via one or more relay devices, A program for performing a process of transmitting a signal for searching for the aforementioned other communication device, the signal comprising information indicating that the signal is to be relayed to the aforementioned other communication device, and identification information indicating a connection service provided by the relay device.

31. The computer of the relay device compliant with the 3GPP standard, which relays signals between the first communication device and the second communication device, Processing to receive a signal from the first communication device or another first relay device for searching for the second communication device, the signal including information indicating that the signal is relayed to the second communication device and identification information indicating a connection service provided by the relay device, A program for performing the process of transferring the aforementioned signal to the second communication device or another second relay device.

32. A computer in a communication device compliant with the 3GPP standard that connects to other communication devices via one or more relay devices, The relay device receives a signal for searching for the communication device, which has been transmitted from the other communication device via the relay device. A program for causing a device to perform the process of transmitting a response signal to the aforementioned signal to the relay device.

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