Communication device, control method, and program

Abstract

This technology provides a way to appropriately switch communication paths between terminal devices between paths where relay devices may be involved. [Solution] A communication device according to one aspect of the present disclosure is a communication device that operates as a terminal device, comprising: a decision means that decides to switch the communication method by which the communication device communicates with another terminal device between a first communication method that communicates with the other terminal device via a base station and a second communication method that communicates with the other terminal device without going through a base station; and a transmission means that transmits a signal relating to a relay device that relays communication between the communication device and the other terminal device using the second communication method, in response to the decision means deciding to switch the communication method between the first communication method and the second communication method.

Description

Technical Field

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

Background Art

[0002] In the 3rd Generation Partnership Project (3GPP (registered trademark): 3rd Generation Partnership Project), cellular communication standards (also referred to as 3GPP standards) have been formulated. In recent years, the formulation of the specifications of 3GPP's LTE (Long Term Evolution) and NR (New Radio) has been progressing.

[0003] In 3GPP, a specification has been formulated to switch the communication path (or communication) between UEs (User Equipment) between a path (Uu path) connected via a base station and a path (PC5 path) connected directly. Note that a UE may be referred to as a terminal device or simply a terminal.

[0004] Patent Document 1 discloses a technique for switching the connection between terminals from a direct connection to a connection via a base station.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] 3GPP is also working on the specification of 5G ProSe (Proximity-based services) UE-to-UE Relay. UE-to-UE Relay is a mechanism in Sidelink communication, where two terminal devices (End UEs) communicate directly without going through a base station, and the communication path between the terminal devices is relayed by a relay device (UE-to-UE Relay terminal).

[0007] Therefore, it is assumed that the communication path between UEs will be switched between paths in which a UE-to-UE Relay terminal (or a candidate thereof) may intervene. However, the operation related to switching between paths in which a UE-to-UE Relay terminal may intervene is not specified and is not clearly defined. Note that a UE-to-UE Relay terminal is sometimes also called a Sidelink Relay terminal, relay UE, or Relay.

[0008] Meanwhile, 3GPP is also working on the specifications for 5G ProSe UE-to-NE Relay. UE-to-NE Relay is a system in which terminal equipment and relay equipment (UE-to-NE Relay terminals) communicate via Sidelink, and the communication path (or communication) between the End UE and the base station is relayed by the UE-to-NE Relay terminal.

[0009] Therefore, it is assumed that the communication path between UEs will be switched between paths in which a UE-to-NE Relay terminal (or a candidate thereof) may intervene. However, the operation related to switching between paths in which a UE-to-NE Relay terminal may intervene is not specified and is not clearly defined. Note that a UE-to-NE Relay terminal is also sometimes called a Sidelink Relay terminal, relay UE, or Relay. [Means for solving the problem]

[0010] One aspect of this disclosure, in view of the above, aims to provide a technology for appropriately switching communication paths between terminal devices between paths in which relay devices may be interposed.

[0011] A communication device according to one aspect of the present disclosure is a communication device operating as a terminal device, comprising: a decision means for deciding whether to switch the communication method used by the communication device to communicate with another terminal device between a first communication method, which communicates with the other terminal device via a base station, and a second communication method, which communicates with the other terminal device without going through a base station; and a transmission means for transmitting a signal relating to a relay device that relays communication between the communication device and the other terminal device using the second communication method, in response to the decision means deciding to switch the communication method between the first communication method and the second communication method. [Effects of the Invention]

[0012] According to one aspect of this disclosure, the communication path between terminal devices can be appropriately switched between paths in which a relay device may be involved. [Brief explanation of the drawing]

[0013] [Figure 1] This figure shows an example configuration of a communication system according to the first embodiment of this disclosure. [Figure 2] This is a block diagram showing an example of the functional configuration of a terminal device according to an embodiment. [Figure 3] This figure shows an example of the functional configuration of a Sidelink Relay terminal device according to an embodiment. [Figure 4] This is a sequence diagram showing an example of the process when switching from a Uu path to a relay path using a discovery request message, according to the first embodiment. [Figure 5] This is a sequence diagram showing an example of the process when switching from a Uu path to a relay path using a discovery announcement message, according to the first embodiment. [Figure 6] This flowchart shows an example of the process used when a terminal device determines whether to switch from a Uu path to a relay path, according to the embodiment. [Figure 7] This is a sequence diagram showing an example of the process when switching from a relay path to a Uu path according to the first embodiment. [Figure 8]It is a sequence diagram showing a processing example when switching from a relay path to a Uu path after determining whether it is directly connectable to a PC5 in accordance with a first embodiment. [Figure 9] It is a flowchart showing a processing example when determining a switch from a relay path to another PC5 path or a Uu path by a terminal device in accordance with an embodiment. [Figure 10] It is a diagram showing a configuration example of a communication system according to a second embodiment of the present disclosure. [Figure 11] It is a sequence diagram showing a processing example when switching from a UE-to-NE relay path (Uu path) to a UE-to-UE relay path (PC5 path) in accordance with a second embodiment. [Figure 12] It is a sequence diagram showing a processing example when switching from a UE-to-UE relay path (PC5 path) to a UE-to-NE relay path (Uu path) in accordance with a second embodiment. [Figure 13] It is a diagram showing a configuration example of a communication system according to a third embodiment of the present disclosure. [Figure 14] It is a sequence diagram showing a processing example when switching from a UE-to-NE relay path (Uu path) to a UE-to-UE relay path (PC5 path) in accordance with a third embodiment. [Figure 15] It is a sequence diagram showing a processing example when switching from a UE-to-UE relay path (PC5 path) to a UE-to-NE relay path (Uu path) in accordance with a third embodiment. [Embodiments for Carrying Out the Invention]

[0014] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the content described in the claims. Although a plurality of features are described in the embodiments, not all of these plurality of features are essential to the present disclosure, and the plurality of features may be arbitrarily combined. Further, in the accompanying drawings, the same or similar configurations may be given the same reference numerals, and redundant explanations may be omitted.

[0015] [First Embodiment] (System Configuration) FIG. 1 is a diagram showing a configuration example of a communication system according to an embodiment of the present disclosure. In the communication system shown in FIG. 1 according to the present embodiment, proximity-based services (ProSe) that enable UEs to communicate directly with each other are provided. ProSe may be called D2D (Device-to-Device) service. This makes it possible, for example, to improve frequency utilization efficiency and overall throughput, and to reduce power consumption of UEs. The UEs described below support ProSe and may be called ProSe UEs or ProSe-capable UEs.

[0016] Note that, in the present embodiment, the description is made with respect to 5G, but the present disclosure is also applicable to beyond 5G (for example, next-generation mobile communication systems such as 5G Advanced and 6G, LTE, LTE-Advanced, combinations thereof, etc.).

[0017] As shown in FIG. 1, an exemplary communication system includes UE-1 (101), UE-2 (102), UE-to-UE Relay terminal (103), NG-RAN (104), 5GC (105), and Data Network (105).

[0018] UE-1 (101) and UE-2 (102) are terminals having a communication function with a base station and a direct communication (Sidelink communication) function with other terminals in a 5G mobile communication network (or 5G mobile communication system). The communication between UE-1 (101) and UE-2 (102) and the base station (for example, NG-RAN (104)) is performed via the Uu path. The communication between UE-1 (101) and UE-2 (102) and other terminals (for example, UE-to-UE Relay terminal (103)) is performed via the PC5 path.

[0019] The UE-to-UE Relay terminal (103) is a relay device (relay terminal) that relays Sidelink communication between terminals and extends the coverage of Sidelink communication.

[0020] NG-RAN(104) is a base station in a 5G mobile communication network that communicates wirelessly with terminals. NG-RAN is an abbreviation for Next Generation Radio Access Network.

[0021] 5GC(105) is the 5G core network that controls 5G mobile communications. 5GC is an abbreviation for 5th Generation Core Network.

[0022] The Data Network (106) is an external network such as the Internet that connects to the 5G mobile communication network.

[0023] As will be explained in detail below, UE-1(101) decides to switch the communication method used by UE-1(101) to communicate with UE-2(102) as follows: UE-1(101) decides to switch the communication method between a first communication method that communicates with UE-2(102) via NG-RAN(104) and a second communication method that communicates with UE-2(102) without using NG-RAN(104). Alternatively, UE-1(101) decides to switch the communication method between the two second communication methods. The communication method used by UE-1(101) to communicate with UE-2(102) via the Uu path is an example of the first communication method. The communication method used by UE-1(101) to communicate with UE-2(102) via the PC5 path is an example of the second communication method. The communication method in which UE-1(101) communicates directly with UE-2(102) via the PC5 path is an example of a third communication method. "Communication method" may be rephrased as "connection method," "connection method," "connection method," etc.

[0024] Furthermore, as will be explained in detail below, UE-1(101) transmits the following signals in response to its decision to switch as described above. Specifically, UE-1(101) transmits signals relating to the UE-to-UE Relay terminal(103) that relays communication between UE-1(101) and UE-2(102) using the second communication method. The discovery request message (a signal for searching for the relay device) described below is an example of a signal relating to the UE-to-UE Relay terminal(103). Also, the disconnection request message (a disconnection signal for disconnecting communication with the relay device) described below is an example of a signal relating to the UE-to-UE Relay terminal(103).

[0025] (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.

[0026] 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 remaining functions configured in software. When a functional block is configured in software, the processors constituting the control and decision units 201 and 301 described in Figures 2 and 3 below execute a control program to realize the functions stored in the storage units 202 and 302 described below. This provides the functionality of the functional block.

[0027] Figure 2 is a block diagram showing an example of the functional configuration of terminal devices (UE-1(101) and UE-2(102)) according to this embodiment.

[0028] As shown in Figure 2, each of UE-1(101) and UE-2(102) includes a control / decision unit 201, a storage unit 202, a message generation unit 203, and a message analysis unit 204. Each of UE-1(101) and UE-2(102) also includes a Sidelink Relay connection processing unit 205, a PC5 communication processing unit 206, a wireless communication unit 207, and a Uu communication processing unit 208.

[0029] The control and decision unit 201 is composed of, for example, a processor such as a CPU or MPU, an application-specific integrated circuit (ASIC), a digital signal processor (DSP), a field-programmable gate array (FPGA), etc. CPU is an abbreviation for Central Processing Unit, and MPU is an abbreviation for Micro Processing Unit. The control and decision unit 201 performs control and decision-making related to the operation of UE-1 (101) and UE-2 (102) by executing, for example, a program stored in the memory unit 202. The control and decision unit 201 is an example of a decision means, a judgment means, etc.

[0030] The storage unit 202 is configured to include, for example, memory such as ROM (Read Only Memory) and RAM (Random Access Memory). The storage unit 202 stores various information such as a program for processing described later, information used by the control / decision unit 201 for control and decision-making, and information related to communication (for example, communication parameters for wireless communication). In addition to memory such as ROM and RAM, the storage unit 202 may also be configured to include storage media such as flexible disks, hard disks, optical disks, magneto-optical disks, CD-ROMs, CD-Rs, magnetic tapes, non-volatile memory cards, and DVDs. CD is an abbreviation for Compact Disc, CD-R is an abbreviation for Compact Disc Recordable, and DVD is an abbreviation for Digital Versatile Disc.

[0031] The message generation unit 203 is composed of a general-purpose processor such as a CPU (for example, implemented as a program), a dedicated processing circuit, etc. The message generation unit 203 generates signals and messages to be transmitted to other UEs and base stations. Such signals and messages include discovery request messages (shown as UE-to-UE Relay Discovery Solicitation messages). These signals and messages also include response messages to discovery request messages (shown as UE-to-UE Relay Discovery Response messages). These signals and messages also include path switch request messages (shown as Path Switch Request messages), response messages to path switch request messages (shown as Path Switch Response messages), disconnection request messages (shown as Disconnect Request messages), response messages to disconnection request messages (shown as Disconnect Response messages), and response messages to connection setting change request messages (shown as Link Modification Accept messages).

[0032] The message analysis unit 204 is composed of a general-purpose processor such as a CPU (for example, implemented as a program), a dedicated processing circuit, etc. The message analysis unit 204 analyzes signals and messages received from other UEs and base stations. Such signals and messages include discovery request messages, response messages to discovery request messages, etc. Such signals and messages also include discovery announcement messages (shown as a UE-to-UE Relay Discovery Announcement message), etc. Such signals and messages also include path switching request messages, response messages to path switching request messages, etc. Such signals and messages also include disconnection request messages, response messages to disconnection request messages, connection setting change request messages (shown as a Link Modification Request), etc.

[0033] The Sidelink Relay connection processing unit 205 is configured to include hardware for performing wireless communication (for example, compliant with the 3GPP cellular communication standard). The Sidelink Relay connection processing unit 205 may be configured by a general-purpose processor such as a CPU (for example, implemented as a program). The Sidelink Relay connection processing unit 205 performs the process of UE-1 (101) and UE-2 (102) connecting to the Sidelink Relay terminal device.

[0034] The PC5 communication processing unit 206 is configured to include hardware for performing wireless communication (for example, in accordance with the 3GPP cellular communication standard). The PC5 communication processing unit 206 may be configured by a general-purpose processor such as a CPU (for example, implemented as a program). The PC5 communication processing unit 206 performs transmission and reception processing when performing PC5 communication (Sidelink communication) with other UEs. The PC5 communication processing unit 206 performs the processing of sending messages related to PC5 communication, generated by the message generation unit 203, to other UEs, and the processing of receiving messages related to PC5 communication from other UEs. The PC5 communication processing unit 206 is an example of a transmission means, a reception means, etc.

[0035] The wireless communication unit 207 is configured to include hardware for performing wireless communication (for example, in accordance with the 3GPP cellular communication standard). The wireless communication unit 207 may be configured with a general-purpose processor such as a CPU (for example, implemented as a program). The wireless communication unit 207 performs common processing for wireless communication with other UEs and base stations, which is performed by the PC5 communication processing unit 206 and the Uu communication processing unit 208 for transmission and reception processing.

[0036] The Uu communication processing unit 208 is configured to include hardware for performing wireless communication (for example, in accordance with the 3GPP cellular communication standard). The Uu communication processing unit 208 may be configured by a general-purpose processor such as a CPU (for example, implemented as a program). The Uu communication processing unit 208 performs transmission and reception processing when performing Uu communication with a base station. The Uu communication processing unit 208 performs the processing of sending messages related to Uu communication, generated by the message generation unit 203, to the base station, and the processing of receiving messages related to Uu communication from the base station.

[0037] Any two or more of the Sidelink Relay connection processing unit 205, PC5 communication processing unit 206, wireless communication unit 207, and Uu communication processing unit 208 may be configured as an integrated unit.

[0038] Figure 3 is a block diagram showing an example of the functional configuration of a Sidelink Relay terminal device (UE-to-UE Relay terminal (103)) according to this embodiment.

[0039] As shown in Figure 3, the UE-to-UE Relay terminal (103) comprises a control / decision unit 301, a storage unit 302, a message generation unit 303, and a message analysis unit 304. The UE-to-UE Relay terminal (103) also comprises a Sidelink Relay connection processing unit 305, a PC5 communication processing unit 306, a wireless communication unit 307, and a Uu communication processing unit 308.

[0040] The control and decision unit 301 is composed of, for example, a processor such as a CPU or MPU, an ASIC, a DSP, or an FPGA. The control and decision unit 301 performs control and decision-making related to the operation of the UE-to-UE Relay terminal (103) by, for example, executing a program stored in the memory unit 302.

[0041] The storage unit 302 is configured to include, for example, memory such as ROM or RAM. The storage unit 302 stores various information such as a program for processing described later, information used by the control / decision unit 301 for control and decision-making, and information related to communication (for example, communication parameters for wireless communication). In addition to memory such as ROM or RAM, the storage unit 302 may also be configured to include storage media such as flexible disks, hard disks, optical disks, magneto-optical disks, CD-ROMs, CD-Rs, magnetic tapes, non-volatile memory cards, and DVDs.

[0042] The message generation unit 303 is comprised of a general-purpose processor such as a CPU (for example, implemented as a program), a dedicated processing circuit, etc. The message generation unit 303 generates signals and messages to be transmitted to other UEs or base stations. Such signals and messages include discovery request messages, response messages to discovery request messages, discovery announcement messages, etc. These signals and messages also include disconnection request messages, response messages to disconnection request messages, connection setting change request messages, etc.

[0043] The message analysis unit 304 consists of a general-purpose processor such as a CPU (for example, implemented as a program), dedicated processing circuits, etc. The message analysis unit 304 analyzes signals and messages received from other UEs and base stations. Such signals and messages include discovery request messages, response messages to discovery request messages, disconnection request messages, response messages to disconnection request messages, and response messages to connection setting change request messages.

[0044] The Sidelink Relay connection processing unit 305 is configured to include hardware for performing wireless communication (for example, in accordance with the 3GPP cellular communication standard). The Sidelink Relay connection processing unit 305 may be configured by a general-purpose processor such as a CPU (for example, implemented as a program). The Sidelink Relay connection processing unit 305 performs the process of connecting the UE-to-UE Relay terminal (103) with UE-1 (101) and UE-2 (102).

[0045] The PC5 communication processing unit 306 is configured to include hardware for performing wireless communication (for example, in accordance with the 3GPP cellular communication standard). The PC5 communication processing unit 306 may be configured by a general-purpose processor such as a CPU (for example, implemented as a program). The PC5 communication processing unit 306 performs transmission and reception processing when performing PC5 communication (Sidelink communication) with other UEs. The PC5 communication processing unit 306 performs the processing of sending messages related to PC5 communication, generated by the message generation unit 303, to other UEs, and the processing of receiving messages related to PC5 communication from other UEs.

[0046] The wireless communication unit 307 is configured to include hardware for performing wireless communication (for example, in accordance with the 3GPP cellular communication standard). The wireless communication unit 307 may be configured with a general-purpose processor such as a CPU (for example, implemented as a program). The wireless communication unit 307 performs common processing for wireless communication with other UEs and base stations, which is performed by the PC5 communication processing unit 306 and the Uu communication processing unit 308 for transmission and reception processing.

[0047] The Uu communication processing unit 308 is configured to include hardware for performing wireless communication (for example, in accordance with the 3GPP cellular communication standard). The Uu communication processing unit 308 may be configured by a general-purpose processor such as a CPU (for example, implemented as a program). The Uu communication processing unit 308 performs transmission and reception processing when performing Uu communication with a base station. The Uu communication processing unit 308 performs the processing of sending messages related to Uu communication, generated by the message generation unit 303, to the base station, and the processing of receiving messages related to Uu communication from the base station.

[0048] Any two or more of the Sidelink Relay connection processing unit 305, PC5 communication processing unit 306, wireless communication unit 307, and Uu communication processing unit 308 may be configured as an integrated unit.

[0049] The functional configuration example of the Sidelink Relay terminal device (UE-to-UE Relay terminal (103)) according to this embodiment has been described in detail above with reference to Figure 3. Hereinafter, the UE-to-NE Relay terminal described later may also have the same or similar functional configuration. That is, the UE-to-NE Relay-1 terminal (107) and the UE-to-NE Relay-2 terminal (108) according to the second and third embodiments may also have the same or similar functional configuration.

[0050] The message generation unit 303 of the UE-to-NE Relay-1 terminal (107) and the UE-to-NE Relay-2 terminal (108) generates signals and messages to be transmitted to other UEs and base stations. Such signals and messages include response messages to discovery request messages (shown as the UE-to-NE Relay Discovery Response message). These signals and messages also include response messages to path switching request messages and response messages to disconnection request messages.

[0051] The message analysis unit 304 of the UE-to-NE Relay-1 terminal (107) and the UE-to-NE Relay-2 terminal (108) analyzes signals and messages received from other UEs and base stations. Such signals and messages include discovery request messages (shown as the UE-to-NE Relay Discovery Solicitation message). These signals and messages also include path switching request messages and disconnection request messages.

[0052] (Example of processing) Next, using the sequence diagrams shown in Figures 4 and 5, we will explain an example of the process when switching communication between UE-1 (101) and UE-2 (102) from the Uu path via the base station to the relay path via the UE-to-UE Relay terminal (103).

[0053] The sequence diagram in Figure 4 shows an example (Model B) where the UE searches for UE-to-UE Relay terminals used in the relay path using discovery request messages (an example of a search signal for searching for relay devices) issued by the UE. The sequence diagram in Figure 5 shows an example (Model A) where the UE-to-UE Relay terminals used in the relay path are discovered using discovery announcement messages issued by the UE-to-UE Relay terminals.

[0054] Figure 4 is a sequence diagram showing an example of the process when switching from a Uu path to a relay path using a discovery request message.

[0055] In the F401, UE-1 (101) and UE-2 (102) communicate with each other via a Uu path through the base station.

[0056] In F402, UE-1 (101) assesses the situation and decides to switch communication with UE-2 (102) from the currently used Uu path to another path (relay path). A detailed example of F402's processing (situation assessment) will be described later.

[0057] In F403a, UE-1 (101) searches for UE-2 (102) via PC5 communication (discovery). If UE-2 (102) cannot be found as a result of the search, or if UE-1 (101) determines that the communication conditions are poor, it searches for a UE-to-UE Relay terminal (103) that relays PC5 communication between UE-1 (101) and UE-2 (102). This search is performed by the processing described in F403b to F403e below, and it is assumed that the UE-to-UE Relay terminal (103) is found during the search.

[0058] In F403b, UE-1(101) sends a discovery request message.

[0059] In F403c, the UE-to-UE Relay terminal (103), upon receiving a discovery request message transmitted from UE-1 (101), adds information and forwards the discovery request message.

[0060] In F403d, UE-2 (102), upon receiving a discovery request message from the UE-to-UE Relay terminal (103), sends a response message to the discovery request message.

[0061] In the F403e, the UE-to-UE Relay terminal (103), upon receiving a response message from UE-2 (102), adds information and sends a response message.

[0062] Note that the searches in F403b to F403e may be performed before the search in F403a.

[0063] In F404, UE-1 (101) performs the connection process with the UE-to-UE Relay terminal (103) found during the search.

[0064] In F405, the UE-to-UE Relay terminal (103) performs the connection process with UE-2 (102).

[0065] In F406, UE-1 (101) performs the connection process with UE-2 (102) via the UE-to-UE Relay terminal (103).

[0066] In F407, UE-1 (101) and UE-2 (102) switch from transmitting and receiving information via the Uu path through the base station to transmitting and receiving information via a relay path through the UE-to-UE Relay terminal (103).

[0067] After switching to the relay path, UE-1(101) checks in F408a whether communication via the base station is being used by other applications, etc. If it determines that a connection to the base station is no longer necessary, it disconnects (or terminates) the connection.

[0068] After switching to the relay path, UE-2(102) checks in F408b whether communication via the base station is being used by other applications, etc. If it determines that a connection to the base station is no longer necessary, it disconnects (or terminates) the connection.

[0069] In the F409, UE-1 (101) and UE-2 (102) communicate with each other via a relay path through the UE-to-UE Relay terminal (103).

[0070] Figure 5 is a sequence diagram showing an example of the process when switching from a Uu path to a relay path using a discovery announcement message.

[0071] F401 and F402 are as described using Figure 4, so their explanation will be omitted.

[0072] In F403a, UE-1 (101) searches for UE-2 (102) via PC5 communication. Here, UE-1 (101) and UE-2 (102) can recognize the presence of the UE-to-UE Relay terminal (103) through the discovery announcement messages shown in F503b and F503c, respectively. The discovery announcement message is transmitted by the UE-to-UE Relay terminal (103). Therefore, UE-1 (101) (and / or UE-2 (102)) can use this discovery announcement message to decide whether to switch to the relay path. As will be described later, in F407, the communication path is switched from the Uu path to the relay path. Therefore, prior to this switchover, UE-1 (101) and UE-2 (102) have received a discovery announcement message from the same UE-to-UE Relay terminal (103) which is either a relay device or a candidate relay device.

[0073] When UE-1(101) decides to switch to the relay path, F503d sends a path switching request message to UE-2(102) requesting a switch from the Uu path to the PC5 path. F503e sends a response message (acknowledgment or acceptance message) to UE-1(101) in response to the path switching request message.

[0074] F404 to F409 are as explained using Figure 4, so their explanation will be omitted.

[0075] Figure 6 is a flowchart showing an example of the process performed by UE-1(101) when deciding to switch from the Uu path to the relay path in F402 of the sequence diagram shown in Figure 4.

[0076] In S601, UE-1(101) determines whether UE-2(102), which is communicating via the Uu path, is close enough to UE-1(101) to enable direct PC5 communication or communication via the UE-to-UE Relay terminal. This determination is made based on location information relating to UE-1(101), UE-2(102), and the UE-to-UE Relay terminal. Additionally or alternatively, this determination may be made based on communication quality information relating to UE-1(101), UE-2(102), and the UE-to-UE Relay terminal (received power, received SNR, received error rate, etc.). SNR is an abbreviation for Signal-to-Noise Ratio.

[0077] If UE-1(101) determines that UE-2(102) is not adjacent to UE-1(101) (No in S601), it returns to S601. On the other hand, if UE-1(101) determines that UE-2(102) is adjacent to UE-1(101) (Yes in S601), it proceeds to S602.

[0078] In S602, UE-1(101) determines whether the communication quality between UE-1(101) and the base station currently connected to form the Uu path has deteriorated (for example, to below a threshold). The communication quality may be RSRP (SD-RSRP, SL-RSRP, etc.), RSSI, RSRQ, etc. Communication quality may also be interpreted as signal strength. RSRP is an abbreviation for Reference Signal Received Power. SD-RSRP is an abbreviation for Sidelink Discovery RSRP, and SL-RSRP is an abbreviation for Sidelink RSRP. RSSI is an abbreviation for Received Signal Strength Indicator. RSRQ is an abbreviation for Reference Signal Received Quality. Good (high) communication quality between communication devices means that the communication conditions between communication devices are good.

[0079] If UE-1(101) determines that the communication quality has deteriorated (Yes in S602), it proceeds to S606. On the other hand, if UE-1(101) determines that the communication quality has not deteriorated (No in S602), it proceeds to S603.

[0080] In S603, UE-1(101) determines whether the traffic being transmitted and received between UE-1(102) and UE-2(102) via the Uu path is increasing (for example, above a threshold). Alternatively, in S603, UE-1(101) determines whether it is predicted that the traffic being transmitted and received between UE-1(102) and UE-2(102) via the Uu path will increase (for example, above a threshold within a predetermined time or at a predetermined time). Traffic may be reinterpreted as throughput, transmission speed, bandwidth, etc.

[0081] If UE-1(101) determines that traffic is increasing or is expected to increase (Yes in S603), it proceeds to S606. On the other hand, if UE-1(101) determines that traffic is not increasing or is not expected to increase (it is not expected to increase) (No in S603), it proceeds to S604.

[0082] In S604, UE-1(101) determines whether it is running or running a service (or application) that requires low-latency communication with UE-2(102) (referred to as a low-latency service; for example, a URLLC service). In other words, UE-1(101) determines the operational status or execution status of the low-latency service that is running or will be run with UE-2(102). URLLC is an abbreviation for Ultra-Reliable and Low Latency Communications.

[0083] If UE-1(101) is running or has determined to run a low-latency service (Yes in S604), it proceeds to S606. On the other hand, if UE-1(101) is not running or has determined not to run a low-latency service (No in S604), it proceeds to S605.

[0084] In S605, UE-1(101) determines whether the battery level of UE-1(101) or UE-2(102) is low (for example, below a threshold). In other words, UE-1(101) determines whether it has enough battery power to continue communication via the Uu path through the base station. UE-1(101) and UE-2(102) exchange information about the battery levels of their respective devices through communication via the Uu path through the base station.

[0085] If UE-1(101) determines that the battery level is low (Yes in S605), it proceeds to S606. On the other hand, if UE-1(101) determines that the battery level is not low (No in S604), it returns to S601.

[0086] In S606, UE-1(101) decides to switch from the Uu path to the relay path based on the decision result ("Yes") in one of S602 to S605. The flow then ends.

[0087] As explained above, it becomes possible to switch communication between UEs from communication via a base station (communication via the Uu path) to communication via a relay UE without going through a base station (communication via the PC5 path through the Relay). This expands the range over which high-speed, low-power direct communication can be used between nearby UEs. In this way, communication between terminal devices, which may involve relay devices, can be appropriately switched between communication via a base station and communication without going through a base station.

[0088] Next, using the sequence diagrams shown in Figures 7 and 8, we will explain an example of the process when switching communication between UE-1 (101) and UE-2 (102) from the relay path via the UE-to-UE Relay terminal (103) to another path. The other path is the Uu path via the base station, the relay path via a UE-to-UE Relay terminal other than the UE-to-UE Relay terminal (103), or the direct PC5 path.

[0089] The sequence diagram in Figure 7 shows an example of when UE-1(101) decides to switch from the relay path to the Uu path. The sequence diagram in Figure 8 shows an example of when UE-1(101) tries to see if PC5 communication with UE-2(102) is possible via another PC5 path before switching from the relay path to the Uu path. In this case, if UE-1(101) does not find an alternative PC5 path, it decides to switch to the Uu path and performs the switching operation.

[0090] Figure 7 is a sequence diagram showing an example of the process when switching from a relay path to a Uu path.

[0091] In the F701, UE-1 (101) and UE-2 (102) communicate with each other via a relay path through the UE-to-UE Relay terminal (103).

[0092] In F702, UE-1(101) assesses the situation and decides to switch communication with UE-2(102) from the currently used relay path to another path (in this case, the Uu path). A detailed example of F702's processing (situation assessment) will be described later.

[0093] In F703a, UE-1(101) sends a path switching request message to UE-2(102) to request a switch from the relay path (PC5 path) to another path (in this case, the Uu path). In F703b, UE-2(102) sends a response message (acknowledgment or acceptance message) to UE-1(101) in response to the path switching request message.

[0094] UE-1(101) in F704a determines the connection status with the base station and establishes a connection with the base station as needed.

[0095] UE-2(102) in F704b determines the connection status with the base station and establishes a connection with the base station as necessary.

[0096] When UE-1(101) and UE-2(102) each connect to the base station, F705 operates as follows: UE-1(101) and UE-2(102) switch the communication path between UE-1(101) and UE-2(102) from the relay path (PC5 path) to the Uu path via the base station.

[0097] In F706a, UE-1(101) sends a disconnection request message to the UE-to-UE Relay terminal(103) to request the disconnection of the connection or communication with the UE-to-UE Relay terminal(103). The disconnection request message to request the disconnection of the connection or communication with the UE-to-UE Relay terminal(103) is an example of a disconnection signal for disconnecting communication with the relay device. In F706b, the UE-to-UE Relay terminal(103) sends a response message (acknowledgment or acceptance message) to the disconnection request message to UE-1(101).

[0098] The UE-to-UE Relay terminal (103) sends a disconnection request message to UE-2 (102) via F707a, if necessary, to request the disconnection of the connection or communication with UE-2 (102). The UE-2 (102) sends a response message (acknowledgment or acceptance message) to the UE-to-UE Relay terminal (103) via F707b, if necessary.

[0099] The UE-to-UE Relay terminal (103) sends a connection setting change request message to UE-2 (102) via F708a, if necessary, to request a change in the connection settings with UE-2 (102). The UE-2 (102) sends a response message (acknowledgment or acceptance message) to the UE-to-UE Relay terminal (103) via F708b, if necessary, to the connection setting change request message.

[0100] In the F709, UE-1 (101) and UE-2 (102) communicate with each other via a Uu path through the base station.

[0101] Figure 8 is a sequence diagram showing an example of the process when switching from the relay path to the Uu path after determining whether a direct PC5 connection is possible.

[0102] In the F701, UE-1 (101) and UE-2 (102) communicate with each other via a relay path through the UE-to-UE Relay terminal (103).

[0103] In F802a, UE-1(101) decides to switch paths from the current relay path via the UE-to-UE Relay terminal(103). More specifically, UE-1(101) decides to search for alternative PC5 paths, such as other relay paths or direct PC5 paths between terminals.

[0104] In F802b, UE-1 (101) searches for an alternative UE-to-UE Relay terminal other than the UE-to-UE Relay terminal (103) currently connected to the relay path.

[0105] UE-1(101) searches for UE-2(102) in the F802c by transmitting a search signal for a direct (PC5) connection with UE-2(102) to determine if a direct PC5 connection with UE-2(102) is possible. The search signal for a direct (PC5) connection with UE-2(102) may also be called a search signal for searching for UE-2(102).

[0106] Note that the search in F802c may be performed before the search in F802b.

[0107] Detailed processing examples for F802a to F802c will be described later.

[0108] In this example, it is assumed that no alternative UE-to-UE Relay terminal was found in F802b, and UE-2(102) was not found in F802c, so UE-1(101) proceeds to F703a.

[0109] F703a to F709 are as explained using Figure 7, so their explanation will be omitted.

[0110] Note that the search in F802c may be performed before the search in F802b.

[0111] Detailed processing examples for F802a to F802c will be described later.

[0112] If UE-1(101) does not find UE-2(102), it proceeds to F703a.

[0113] F703a to F704b are as explained using Figure 7, so their explanation will be omitted.

[0114] As detailed in Figure 9, path switching can also involve switching to other PC5 paths besides the Uu path. An example of this process is as follows.

[0115] In the step replacing F705, UE-1(101) and UE-2(102) switch the communication path between UE-1(101) and UE-2(102) from the relay path (PC5 path) to another path (another PC5 path or a Uu path via the base station).

[0116] Furthermore, in the step replacing F709, UE-1(101) and UE-2(102) communicate with each other via another path (an alternative PC5 path or a Uu path via the base station).

[0117] Figure 9 is a flowchart showing an example of the processing performed by UE-1(101) when deciding to switch from a relay path to another PC5 path or Uu path in F802a to F802c in the sequence diagram shown in Figure 8.

[0118] In S901, UE-1(101) determines whether UE-1(101) and UE-2(102) have moved too far apart for direct PC5 connection and relay path connection via UE-to-UE Relay terminal to be possible. This determination is made based on location information of UE-1(101), UE-2(102), and UE-to-UE Relay terminal(103). Additionally or alternatively, this determination may be made based on communication quality information (received power, received SNR, received error rate, etc.) of UE-1(101), UE-2(102), and UE-to-UE Relay terminal(103).

[0119] If UE-1(101) determines that UE-1(101) and UE-2(102) have moved further apart (Yes in S901), it proceeds to S907. On the other hand, if UE-1(101) determines that UE-1(101) and UE-2(102) have not moved further apart (No in S901), it proceeds to S902.

[0120] In S902, UE-1(101) determines whether the low-latency service that was running between UE-1(101) and UE-2(102) has ended (the operational status or execution status of the low-latency service).

[0121] If UE-1(101) determines that the low-latency service has ended (Yes in S902), it proceeds to S907. On the other hand, if UE-1(101) determines that the low-latency service has not ended (No in S902), it proceeds to S903.

[0122] In S903, UE-1(101) determines whether the traffic being sent and received between UE-1(101) and UE-2(102) has decreased sufficiently (for example, to below a threshold) on the Uu path.

[0123] If UE-1(101) determines that traffic has decreased (Yes in S903), it proceeds to S907. On the other hand, if UE-1(101) determines that traffic has not decreased (No in S903), it proceeds to S904.

[0124] In S904, UE-1(101) determines whether the communication quality between UE-1(101) and the UE-to-UE Relay terminal(103) has deteriorated (for example, to below a threshold). The communication quality may be RSRP (SD-RSRP, SL-RSRP, etc.), RSSI, RSRQ, etc.

[0125] If UE-1(101) determines that the communication quality has deteriorated (Yes in S904), it proceeds to S905. On the other hand, if UE-1(101) determines that the communication quality has not deteriorated (No in S904), it returns to S901.

[0126] In S904, UE-1(101) determines whether it can connect to UE-2(102) via an alternative relay path through a different UE-to-UE Relay terminal other than the one currently connected via the relay path, or via a direct PC5 path.

[0127] If UE-1(101) determines that it can connect to UE-2(102) (Yes in S905), it proceeds to S906. On the other hand, if UE-1(101) determines that it cannot connect to UE-2(102) (No in S905), it proceeds to S907.

[0128] In S906, UE-1(101) decides which of the other relay paths and / or direct PC5 paths to use. Then the flow ends.

[0129] In addition, in S906, UE-1(101) may select or determine the switched path, for example, as follows:

[0130] UE-1(101) obtains the first communication quality of the direct PC5 connection path to UE-2(102) and the second communication quality of the alternative UE-to-UE Relay terminal path to UE-2(102). Based on the first and second communication quality, UE-1(101) selects a path to connect (communicate) with UE-2(102) from the direct PC5 connection path and the alternative UE-to-UE Relay terminal path. There may be multiple alternative UE-to-UE Relay terminals (candidate relay devices). In that case, there are multiple second communication quality levels corresponding to each of the multiple alternative UE-to-UE Relay terminals (candidate relay devices). Here, the communication quality of a path may mean all the communication quality levels between the connected communication devices (UE, UE-to-UE Relay terminal) included in the path. Selecting a route to connect to UE-2(102) based on the communication quality of the routes may include provisionally selecting a route in which all of the communication quality parameters are within a predetermined range (for example, above a threshold). Furthermore, selecting a route to connect to UE-2(102) based on the communication quality of the routes may also include selecting the route with the best communication quality within the predetermined range from one or more provisionally selected routes as the route to connect to UE-2(102).

[0131] In S907, UE-1(101) decides to switch from the relay path to the Uu path based on the decision result (Yes) in any of S901-S903 or the decision result (No) in S905. The flow then ends.

[0132] Furthermore, the process performed by UE-1(101) in F702 in the sequence diagram shown in Figure 7 to determine whether to switch from the relay path to the Uu path is also executed as shown in Figure 9. However, in this case, blocks S905 and S906 do not exist in Figure 9, and the Yes branch in block S904 leads to block S907. Then, in S907, UE-1(101) decides to switch from the relay path to the Uu path based on the decision result (Yes) in any of S901 to S904.

[0133] As explained above, depending on the situation of communication via a relay UE without going through a base station (communication via the PC5 path through the Relay), it becomes possible to switch to communication via a more appropriate path.

[0134] [Second Embodiment] The first embodiment described path switching in a communication system where a UE-to-UE Relay terminal exists. In contrast, the second embodiment describes path switching in a communication system where a UE-to-NE Relay terminal may exist. Note that if the configuration and processing in the second embodiment are the same as or similar to those in the first embodiment, the explanation may be omitted.

[0135] Figure 10 shows an example configuration of a communication system according to a second embodiment of the present disclosure. The communication system shown in Figure 10 is the same as the communication system shown in Figure 1, but with the addition of a UE-to-NE Relay-1 terminal (107). In the example shown in Figure 10, the UE-to-NE Relay-1 terminal (107) relays the communication of UE-1 (101) and connects to the base station. The UE-to-NE Relay-1 terminal (107) is a relay device (relay terminal) that connects to the terminal via the PC5 path and to the base station (for example, NG-RAN (104)) via the Uu path, and relays Sidelink communication from the terminal.

[0136] The following describes an example of the process when switching communication between UE-1 (101) and UE-2 (102) from the Uu path to a relay path via the UE-to-UE Relay terminal (103), using the sequence diagram shown in Figure 11. This Uu path is a Uu path via a base station that is relayed by the UE-to-NE Relay-1 terminal (107).

[0137] In F1101, UE-1 (101) and UE-2 (102) communicate with each other via a Uu path relayed by a base station via a UE-to-NE Relay terminal (107).

[0138] In F1102, UE-2 (102) assesses the situation and decides to switch communication with UE-1 (101) from the currently used Uu path to another path (relay path). A detailed example of the processing in F1102 (situation assessment) is the same as the explanation above using Figure 6, so the explanation is omitted.

[0139] In F1103a, UE-2 (102) searches for (discovers) UE-1 (101) via PC5 communication. If UE-1 (101) is not found or the communication conditions are poor, UE-2 (102) searches for a UE-to-UE Relay terminal (103) that relays PC5 communication between UE-1 (101) and UE-2 (102). This search is performed by the processes in F1103b and F1103c below, and it is assumed that the UE-to-UE Relay terminal (103) is found.

[0140] In F1103b, UE-2(102) sends a discovery request message.

[0141] In F1103c, the UE-to-UE Relay terminal (103), upon receiving a discovery request message from UE-2 (102), sends a response message to the discovery request message.

[0142] Note that the searches performed by F1103b and F1103c may be performed before the searches performed by F1103a.

[0143] In F1104, UE-2 (102) performs the connection process with the UE-to-UE Relay terminal (103) found during the search.

[0144] When UE-2(102) decides to switch to the relay path, in F1105a it sends a path switching request message to UE-1(101) requesting a switch from the Uu path to the PC5 path. This Uu path is the Uu path via the base station, which is relayed by the UE-to-NE Relay-1 terminal(107). In F1105b, UE-1(101) sends a response message (acknowledgment or acceptance message) to UE-2(102) in response to the path switching request message.

[0145] When UE-1(101) receives a path switching request message from UE-2(102), it searches for a UE-to-UE Relay terminal(103) that relays PC5 communication between UE-1(101) and UE-2(102). This search is performed by the following processes F1106a and F1106b, and it is assumed that the UE-to-UE Relay terminal(103) is found.

[0146] In F1106a, UE-1(101) sends a discovery request message.

[0147] In F1106b, the UE-to-UE Relay terminal (103), upon receiving a discovery request message from UE-1 (101), sends a response message to the discovery request message.

[0148] In F1107, UE-1 (101) performs the connection process with the UE-to-UE Relay terminal (103) found during the search.

[0149] In F1108, UE-1 (101) performs the connection process with UE-2 (102) via the UE-to-UE Relay terminal (103).

[0150] In F1109a, UE-2(102) sends a path switching request message to the UE-to-UE Relay terminal(103) to request a switch to the PC5 path. In F1109b, the UE-to-UE Relay terminal(103) sends a response message (acknowledgment or acceptance message) to UE-2(102) in response to the path switching request message.

[0151] In F1110a, UE-2(102) sends a path switching request message to the UE-to-NE Relay-1 terminal(107) to request a switch from the Uu path to the PC5 path. This Uu path is the Uu path via the base station that is relayed by the UE-to-NE Relay-1 terminal(107). In F1110b, the UE-to-NE Relay-1 terminal(107) sends a response message (acknowledgment or acceptance message) to the path switching request message to UE-2(102).

[0152] In F1111, UE-1 (101) and UE-2 (102) switch from sending and receiving information via the Uu path to sending and receiving information via a relay path through the UE-to-UE Relay terminal (103).

[0153] After switching to the relay path via the UE-to-UE Relay terminal (103), the UE-to-NE Relay-1 terminal (107) operates as follows in F1112: The UE-to-NE Relay-1 terminal (107) determines whether communication via the base station is being used by other applications, etc., and if it determines that a connection to the base station is unnecessary, it disconnects (or terminates) the connection.

[0154] After switching to the relay path, UE-2(102) checks in F1113 whether communication via the base station is being used by other applications, etc. If it determines that a connection to the base station is no longer necessary, it disconnects (or terminates) the connection.

[0155] In F1114, UE-1 (101) and UE-2 (102) communicate with each other via a relay path through the UE-to-UE Relay terminal (103).

[0156] Figure 12 is a sequence diagram showing an example of the process when switching from a relay path via a UE-to-UE Relay terminal (103) to a Uu path via a base station relayed by a UE-to-NE Relay-1 terminal (107).

[0157] In F1201, UE-1 (101) and UE-2 (102) communicate with each other via a relay path through a UE-to-UE Relay terminal (103).

[0158] In F1202, UE-2 (102) assesses the situation and decides to switch communication with UE-1 (101) from the currently used relay path to another path. In this example, UE-2 (102) decides to switch communication with UE-1 (101) to the Uu path via the base station relayed by the UE-to-NE Relay-1 terminal (107). A detailed example of the processing (situation assessment) in F1202 is the same as the explanation above using Figure 9, so the explanation is omitted.

[0159] In F1203a, UE-2(102) sends a path switching request message to UE-1(101) to request a switch from the relay path (PC5 path) to the Uu path. This Uu path is the Uu path via the base station, which is relayed by the UE-to-NE Relay-1 terminal(107). In F1203b, UE-1(101) sends a response message (acknowledgment or acceptance message) to UE-2(102) in response to the path switching request message.

[0160] UE-2(102) determines the connection status with the base station in F1204 and establishes a connection with the base station as needed.

[0161] In F1205a, UE-1 (101) sends a discovery request message via PC5 communication to search for (discover) the UE-to-NE Relay-1 terminal (107).

[0162] In F1205b, the UE-to-NE Relay-1 terminal (107), upon receiving a discovery request message from UE-1 (101), sends a response message to the discovery request message.

[0163] In F1206, UE-1 (101) performs the connection process with the UE-to-NE Relay-1 terminal (107) found during the search.

[0164] In F1207a, UE-1(101) sends a path switching request message to the UE-to-NE Relay-1 terminal(107) to request a switch from the relay path (PC5 path) to the Uu path. This Uu path is the Uu path via the base station that is relayed by the UE-to-NE Relay-1 terminal(107). In F1207b, the UE-to-NE Relay-1 terminal(107) sends a response message (acknowledgment or acceptance message) to the path switching request message to UE-1(101).

[0165] The UE-to-NE Relay-1 terminal (107) determines the connection status with the base station in F1208 and connects to the base station as necessary.

[0166] In F1209a, UE-2 (102) sends a path switching request message to the UE-to-UE Relay terminal (103) to request a switch from the relay path (PC5 path) to the Uu path. This Uu path is the Uu path via the base station, which is relayed by the UE-to-NE Relay-1 terminal (107). In F1209b, the UE-to-UE Relay terminal (103) sends a response message (acknowledgment or acceptance message) to the path switching request message to UE-2 (102).

[0167] Note that while Figure 12 shows an example where UE-2 (102) sends a path switching request message to the UE-to-UE Relay terminal (103), UE-1 (101) may also send the path switching request message.

[0168] When UE-2(102) and UE-to-NE Relay-1 terminal(107) each connect to the base station, UE-1(101) and UE-2(102) operate in F1210 as follows: UE-1(101) and UE-2(102) switch the communication path between UE-1(101) and UE-2(102) from the relay path (PC5 path) to the Uu path via the base station, which is relayed by the UE-to-NE Relay-1 terminal(107).

[0169] In F1211a, UE-1(101) sends a disconnection request message to the UE-to-UE Relay terminal(103) to request the disconnection of the connection or communication with the UE-to-UE Relay terminal(103). The disconnection request message to request the disconnection of the connection or communication with the UE-to-UE Relay terminal(103) is an example of a disconnection signal for disconnecting communication with a relay device. In F1211b, the UE-to-UE Relay terminal(103) sends a response message (acknowledgment or acceptance message) to the disconnection request message to UE-1(101).

[0170] In F1212a, UE-2(102) sends a disconnection request message to the UE-to-UE Relay terminal(103) to request the disconnection of the connection or communication with the UE-to-UE Relay terminal(103). The disconnection request message to request the disconnection of the connection or communication with the UE-to-UE Relay terminal(103) is an example of a disconnection signal for disconnecting communication with the relay device. In F1212b, the UE-to-UE Relay terminal(103) sends a response message (acknowledgment or acceptance message) to the disconnection request message to UE-2(102).

[0171] Note that while Figure 12 shows an example where both UE-1 (101) and UE-2 (102) send disconnection request messages, either one of the UEs may send a disconnection request message, as shown in F706a and F708b in Figure 8.

[0172] In F1213, UE-1 (101) and UE-2 (102) communicate with each other via a Uu path relayed by a base station via a UE-to-NE Relay-1 terminal (107).

[0173] As explained above, it becomes possible to appropriately switch between communication between UEs (Unified Element Users) between communication via a base station (Uu path) and communication without a base station (PC5 path).

[0174] [Third Embodiment] The second embodiment described path switching in a communication system where one UE-to-NE Relay terminal may exist. In contrast, the third embodiment describes path switching in a communication system where two UE-to-NE Relay terminals may exist. Note that if the configuration and processing in the third embodiment are the same as or similar to the configuration and processing in the first or second embodiment, the explanation may be omitted.

[0175] Figure 13 is a diagram showing an example configuration of a communication system according to a third embodiment of this disclosure. The communication system shown in Figure 13 is the same as the communication system shown in Figure 10, with the addition of a UE-to-NE Relay-2 terminal (108). In the example shown in Figure 13, the UE-to-NE Relay-2 terminal (108) relays the communication of the UE-2 (102) and connects to the base station. The UE-to-NE Relay-2 terminal (108) is a relay device (relay terminal) that connects to the terminal via the PC5 path and to the base station (for example, NG-RAN (104)) via the Uu path, and relays Sidelink communication from the terminal.

[0176] The following describes an example of the process when switching communication between UE-1 (101) and UE-2 (102) from the Uu path to a relay path via the UE-to-UE Relay terminal (103), using the sequence diagram shown in Figure 14. This Uu path is a base station-based Uu path relayed by the UE-to-NE Relay-1 terminal (107) to which UE-1 (101) is connected, and the UE-to-NE Relay-2 terminal (108) to which UE-2 (102) is connected. That is, the UE-to-NE Relay-1 terminal (107) relays the communication of UE-1 (101) and connects to the base station, and the UE-to-NE Relay-2 terminal (108) relays the communication of UE-2 (102) and connects to the base station.

[0177] In F1401, UE-1 (101) and UE-2 (102) communicate with each other via a Uu path relayed by the UE-to-NE Relay-1 terminal (107) and the UE-to-NE Relay-2 terminal (108) through the base station.

[0178] In F1402, UE-2 (102) assesses the situation and decides to switch communication with UE-1 (101) from the currently used Uu path to another path (relay path). A detailed example of the processing in F1402 (situation assessment) is the same as the explanation above using Figure 6, so the explanation is omitted.

[0179] In F1403a, UE-2(102) searches for (discovers) UE-1(101) via PC5 communication. If UE-1(101) is not found or the communication conditions are poor, UE-2(102) searches for a UE-to-UE Relay terminal(103) that relays PC5 communication between UE-1(101) and UE-2(102). This search is performed by the processes in F1403b and F1403c below, and it is assumed that the UE-to-UE Relay terminal(103) is found.

[0180] In F1403b, UE-2(102) sends a discovery request message.

[0181] In F1403c, the UE-to-UE Relay terminal (103), upon receiving a discovery request message from UE-2 (102), sends a response message to the discovery request message.

[0182] Note that the searches performed by F1403b and F4103c may be performed before the searches performed by F1403a.

[0183] In F1404, UE-2 (102) performs the connection process with the UE-to-UE Relay terminal (103) found during the search.

[0184] When UE-2(102) decides to switch to the relay path, in F1405a it sends a path switching request message to UE-1(101) requesting a switch from the Uu path to the PC5 path. This Uu path is the Uu path via the base station, which is relayed by the UE-to-NE Relay-1 terminal (107) and the UE-to-NE Relay-2 terminal (108). In F1405b, UE-1(101) sends a response message (acknowledgment or acceptance message) to UE-2(102) in response to the path switching request message.

[0185] When UE-1(101) receives a path switching request message from UE-2(102), it searches for a UE-to-UE Relay terminal(103) that relays PC5 communication between UE-1(101) and UE-2(102). This search is performed by the following processes F1406a and F1406b, and it is assumed that the UE-to-UE Relay terminal(103) is found.

[0186] In F1406a, UE-1(101) sends a discovery request message.

[0187] In F1406b, the UE-to-UE Relay terminal (103), upon receiving a discovery request message from UE-1 (101), sends a response message to the discovery request message.

[0188] In F1407, UE-1 (101) performs the connection process with the UE-to-UE Relay terminal (103) found during the search.

[0189] In F1408, UE-1 (101) performs the connection process with UE-2 (102) via the UE-to-UE Relay terminal (103).

[0190] In F1409a, UE-2(102) sends a path switching request message to the UE-to-UE Relay terminal(103) to request a switch to the PC5 path. In F1409b, the UE-to-UE Relay terminal(103) sends a response message (acknowledgment or acceptance message) to UE-2(102) in response to the path switching request message.

[0191] In F1410a, UE-2(102) sends a path switching request message to the UE-to-NE Relay-1 terminal (107) to request a switch from the Uu path to the PC5 path. This Uu path is the Uu path via the base station, which is relayed by the UE-to-NE Relay-1 terminal (107) and the UE-to-NE Relay-2 terminal (108). In F1410b, the UE-to-NE Relay-1 terminal (107) sends a response message (acknowledgment or acceptance message) to the path switching request message to UE-2(102).

[0192] In F1411a, UE-2(102) sends a path switching request message to the UE-to-NE Relay-2 terminal (108) to request a switch from the Uu path to the PC5 path. This Uu path is the Uu path via the base station, which is relayed by the UE-to-NE Relay-1 terminal (107) and the UE-to-NE Relay-2 terminal (108). In F1411b, the UE-to-NE Relay-2 terminal (108) sends a response message (acknowledgment or acceptance message) to the path switching request message to UE-2(102).

[0193] Figure 14 shows an example where UE-2 (102) sends path switching request messages to the UE-to-UE Relay terminal (103), the UE-to-NE Relay-1 terminal (107), and the UE-to-NE Relay-2 terminal (108). However, UE-1 (101) may also send path switching request messages to each of these terminals.

[0194] In F1412, UE-1 (101) and UE-2 (102) switch from sending and receiving information via the Uu path to sending and receiving information via a relay path through the UE-to-UE Relay terminal (103).

[0195] After switching to the relay path via the UE-to-UE Relay terminal (103), the UE-to-NE Relay-1 terminal (107) operates as follows in F1413: The UE-to-NE Relay-1 terminal (107) determines whether communication via the base station is being used by other applications, etc., and if it determines that a connection to the base station is unnecessary, it disconnects (or terminates) the connection.

[0196] After switching to the relay path via the UE-to-UE Relay terminal (103), the UE-to-NE Relay-2 terminal (108) operates as follows in F1414: The UE-to-NE Relay-2 terminal (108) determines whether communication via the base station is being used by other applications, etc., and if it determines that a connection to the base station is unnecessary, it disconnects (or terminates) the connection.

[0197] In F1415, UE-1 (101) and UE-2 (102) communicate with each other via a relay path through the UE-to-UE Relay terminal (103).

[0198] Figure 15 is a sequence diagram showing an example of the process when switching from a relay path via a UE-to-UE Relay terminal (103) to a Uu path. This Uu path is a Uu path via a base station that is relayed by a UE-to-NE Relay-1 terminal (107) and a UE-to-NE Relay-2 terminal (108).

[0199] In F1501, UE-1 (101) and UE-2 (102) communicate with each other via a relay path through a UE-to-UE Relay terminal (103).

[0200] In F1502, UE-2(102) assesses the situation and decides to switch communication with UE-1(101) from the currently used relay path to another path. In this example, UE-2(102) decides to switch communication with UE-1(101) to the Uu path via the base station, which is relayed by the UE-to-NE Relay-1 terminal (107) and the UE-to-NE Relay-2 terminal (108). A detailed example of the processing (situation assessment) in F1502 is the same as the explanation above using Figure 9, so the explanation is omitted.

[0201] In F1503a, UE-2(102) sends a path switching request message to UE-1(101) to request a switch from the relay path (PC5 path) to the Uu path. This Uu path is the base station-based Uu path relayed by the UE-to-NE Relay-1 terminal (107) and the UE-to-NE Relay-2 terminal (108). In F1503b, UE-1(101) sends a response message (acknowledgment or acceptance message) to UE-2(102) in response to the path switching request message.

[0202] In F1504a, UE-2 (102) sends a discovery request message via PC5 communication to search for (discover) the UE-to-NE Relay-2 terminal (108).

[0203] In F1504b, the UE-to-NE Relay-2 terminal (108), upon receiving a discovery request message from UE-2 (102), sends a response message to the discovery request message.

[0204] In F1505, UE-2 (102) performs the connection process with the UE-to-NE Relay-2 terminal (108) found during the search.

[0205] In F1506a, UE-2(102) sends a path switching request message to the UE-to-NE Relay-2 terminal(108) to request a switch from the relay path (PC5 path) to the Uu path. This Uu path is the Uu path via the base station that is relayed by the UE-to-NE Relay-2 terminal(108) (and the UE-to-NE Relay-1 terminal(107)). In F1506b, the UE-to-NE Relay-2 terminal(108) sends a response message (acknowledgment or acceptance message) to the path switching request message to UE-2(102).

[0206] The UE-to-NE Relay-2 terminal (108) determines the connection status with the base station in F1507 and establishes a connection with the base station as necessary.

[0207] In F1508a, UE-1 (101) sends a discovery request message via PC5 communication to search for (discover) the UE-to-NE Relay-1 terminal (107).

[0208] In F1508b, the UE-to-NE Relay-1 terminal (107), upon receiving a discovery request message from UE-1 (101), sends a response message to the discovery request message.

[0209] In F1509, UE-1 (101) performs the connection process with the UE-to-NE Relay-1 terminal (107) found during the search.

[0210] In F1510a, UE-1(101) sends a path switching request message to the UE-to-NE Relay-1 terminal(107) to request a switch from the relay path (PC5 path) to the Uu path. This Uu path is the base station-based Uu path relayed by the UE-to-NE Relay-1 terminal(107) (and the UE-to-NE Relay-2 terminal(108)). In F1510b, the UE-to-NE Relay-1 terminal(107) sends a response message (acknowledgment or acceptance message) to the path switching request message to UE-1(101).

[0211] The UE-to-NE Relay-1 terminal (107) determines the connection status with the base station at F1511 and connects to the base station as necessary.

[0212] In F1512a, UE-2 (102) sends a path switching request message to the UE-to-UE Relay terminal (103) to request a switch from the relay path (PC5 path) to the Uu path. This Uu path is the base station-based Uu path relayed by the UE-to-NE Relay-1 terminal (107) and the UE-to-NE Relay-2 terminal (108). In F1512b, the UE-to-UE Relay terminal (103) sends a response message (acknowledgment or acceptance message) to the path switching request message to UE-2 (102).

[0213] Note that while Figure 15 shows an example where UE-2 (102) sends a path switching request message to the UE-to-UE Relay terminal (103), UE-1 (101) may also send the path switching request message.

[0214] When the UE-to-NE Relay-1 terminal (107) and the UE-to-NE Relay-2 terminal (108) each connect to the base station, in F1513, UE-1 (101) and UE-2 (102) operate as follows: UE-1 (101) and UE-2 (102) switch the communication path between UE-1 (101) and UE-2 (102) from the relay path (PC5 path) to the Uu path. This Uu path is the Uu path via the base station, relayed by the UE-to-NE Relay-1 terminal (107) and the UE-to-NE Relay-2 terminal (108).

[0215] In F1211a, UE-1(101) sends a disconnection request message to the UE-to-UE Relay terminal(103) to request the disconnection of the connection or communication with the UE-to-UE Relay terminal(103). The disconnection request message to request the disconnection of the connection or communication with the UE-to-UE Relay terminal(103) is an example of a disconnection signal for disconnecting communication with a relay device. In F1211b, the UE-to-UE Relay terminal(103) sends a response message (acknowledgment or acceptance message) to the disconnection request message to UE-1(101).

[0216] In F1514a, UE-1(101) sends a disconnection request message to the UE-to-UE Relay terminal(103) to request the disconnection of the connection or communication with the UE-to-UE Relay terminal(103). The disconnection request message to request the disconnection of the connection or communication with the UE-to-UE Relay terminal(103) is an example of a disconnection signal for disconnecting communication with a relay device. In F1514b, the UE-to-UE Relay terminal(103) sends a response message (acknowledgment or acceptance message) to the disconnection request message to UE-1(101).

[0217] In F1515a, UE-2(102) sends a disconnection request message to UE-to-UE Relay terminal(103) to request the disconnection of connection or communication with UE-to-UE Relay terminal(103). The disconnection request message to request the disconnection of connection or communication with UE-to-UE Relay terminal(103) is an example of a disconnection signal for disconnecting communication with a relay device. In F1515b, UE-to-UE Relay terminal(103) sends a response message (acknowledgment or acceptance message) to UE-2(102) in response to the disconnection request message.

[0218] Note that while Figure 15 shows an example where both UE-1 (101) and UE-2 (102) send disconnection request messages, either one of the UEs may send a disconnection request message, as shown in F706a and F708b in Figure 8.

[0219] In F1516, UE-1 (101) and UE-2 (102) communicate with each other via a Uu path relayed by the UE-to-NE Relay-1 terminal (107) and the UE-to-NE Relay-2 terminal (108) through a base station.

[0220] As explained above, it becomes possible to appropriately switch between communication between UEs (Unified Element Users) between communication via a base station (Uu path) and communication without a base station (PC5 path).

[0221] [Other embodiments] The above describes an example of switching from a Uu path to a relay path with reference to Figure 6. However, this disclosure is not limited to this example. UE-1(101) may select or determine a path to connect (communicate) with UE-2(102) from a direct PC5 connection path to UE-2(102) (if possible) and a path via a UE-to-UE Relay terminal (103) to UE-2(102). Specifically, UE-1(101) obtains a first communication quality for the direct PC5 connection path to UE-2(102) and a second communication quality for the path via a UE-to-UE Relay terminal (103) to UE-2(102). Based on the first and second communication qualities, UE-1(101) selects a path to connect with UE-2(102) from the direct PC5 connection path and the path via a UE-to-UE Relay terminal (103). Here, the communication quality of a route may refer to the overall communication quality between each connected communication device (UE, UE-to-UE Relay terminal) included in the route. Selecting a route to connect to UE-2(102) based on the communication quality of a route may include provisionally selecting a route in which all of the communication qualities are within a predetermined range (for example, above a threshold). Furthermore, selecting a route to connect to UE-2(102) based on the communication quality of a route may also include selecting the route with the best communication quality within the predetermined range from one or more provisionally selected routes as the route to connect to UE-2(102).

[0222] In the second and third embodiments, examples were described in which UE-2(102) switches communication with UE-1(101) via a relay path (PC5 path) to a Uu path via a base station by directly connecting to the base station or via a relay terminal. In this case, UE-2(102) may decide (or determine) whether to connect directly to the base station or via a relay terminal, depending on the situation. UE-2(102) may make this decision in the same manner as described in Figure 6 or Figure 9. Specifically, UE-2(102) may make this decision based on communication quality, the operating status of low-latency services, the battery level of UE-2(102) and the relay terminal, etc. For example, UE-2(102) may decide to connect to the base station via a relay terminal if the communication quality with the base station deteriorates, if a low-latency service is being performed, or if the battery level of UE-2 is low.

[0223] Some of the messages described in the embodiments above may be included in other messages. For example, a Path Switch Request message may be included in a Link Modification Request message.

[0224] This disclosure can also be implemented by supplying a program that implements one or more of the functions of the embodiments described above to a system or device via a network or storage medium, and by having one or more processors in the computer of that system or device read and execute the program. Furthermore, this disclosure can also be implemented by a circuit (e.g., an ASIC or FPGA) that implements one or more functions.

[0225] 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 this disclosure.

[0226] The names of the functional units, messages, parameters, fields, etc., described in the embodiments described above are examples and may be changed to other names.

[0227] The order of the processing procedures, sequences, flowcharts, etc., in the embodiments described above is not limited to the specific order presented, and may be rearranged or additional steps may be added, as long as they are not contradictory. For example, in Figure 6, the order of S602 to S605 may be changed, or one to three blocks from S602 to S605 may be omitted. Also, if the judgment result in two or more of S602 to S605 is Yes, UE-1(101) may proceed to S606. Also, for example, in Figure 9, the order of S902 and S904 may be changed, or one of the blocks from S902 and S904 may be omitted. Also, if the judgment result in both S902 and S904 is Yes, UE-1(101) may proceed to S907. Furthermore, for example, in Figure 9, if blocks S905 and S906 do not exist, the order of S902 to S904 may be changed, or one or two of the blocks S902 to S904 may be absent. Also, if blocks S905 and S906 do not exist, UE-1(101) may proceed to S907 if the judgment result in two or more of the blocks S902 to S904 is Yes.

[0228] The matters described in the above embodiments may be incorporated into other embodiments, insofar as they do not contradict each other.

[0229] Furthermore, the following additional information is disclosed regarding the above embodiments.

[0230] [Note 1] A communication device that operates as a terminal device, A decision means for determining whether to switch the communication method used by the communication device to communicate with other terminal devices between a first communication method, which communicates with the other terminal devices via a base station, and a second communication method, which communicates with the other terminal devices without going through a base station. In response to the determination means deciding to switch the communication method between the first communication method and the second communication method, a transmitting means transmits a signal relating to a relay device that relays communication between the communication device and the other terminal device using the second communication method. A communication device having the following features.

[0231] [Note 2] The communication device as described in Appendix 1, wherein, in response to the decision means deciding to switch the communication method from the first communication method to the second communication method, the transmitting means transmits a search signal for searching for the relay device as a signal relating to the relay device.

[0232] [Note 3] The communication device according to Appendix 1 or 2, wherein the determination means determines to switch the communication method between the first communication method and the second communication method based on the operating status of a service or application used between the communication device and the other terminal device.

[0233] [Note 4] The communication device according to any one of the appendices 1 to 3, wherein the determination means determines to switch the communication method from the first communication method to the second communication method based on the communication quality between the communication device and the base station in the first communication method.

[0234] [Note 5] The communication device according to any one of the appendices 1 to 4, wherein the determination means determines to switch the communication method from the first communication method to the second communication method based on the remaining battery level of the communication device or the other terminal device.

[0235] [Note 6] Selection means for selecting a route to communicate with the other terminal device from the direct connection route and the route via the relay device, based on the communication quality of the direct connection route to the other terminal device and the communication quality of the route to the other terminal device via the relay device. A communication device as described in Appendix 2, further comprising the above.

[0236] [Note 7] Receiving means that receive a discoverer announcement message from the relay device together with the other terminal device before the communication method is switched from the first communication method to the second communication method. A communication device as described in any of the appendices 1 to 6, further comprising the above.

[0237] [Note 8] The communication device according to any one of the appendices 1 to 7, wherein, in response to the determination means deciding to switch the communication method from the second communication method via the relay device to the first communication method, the second communication method via another relay device, or a third communication method that directly connects to another terminal device, the transmission means transmits a disconnection signal for disconnecting communication with the relay device as a signal relating to the relay device.

[0238] [Note 9] The communication device according to any one of the appendices 1 to 8, wherein the determination means determines, based on the communication quality between the communication device and the relay device, to switch the communication method from the second communication method via the relay device to the first communication method, the second communication method via another relay device, or a third communication method that directly connects to the other terminal device.

[0239] [Note 10] The communication device according to any one of the appendices 1 to 9, wherein, before the decision means decides to switch the communication method from the second communication method via the relay device to the first communication method, the second communication method via another relay device, or a third communication method that directly connects to the other terminal device, the transmitting means transmits a search signal for direct connection to the other terminal device.

[0240] [Note 11] Receiving means for receiving a response signal to the search signal from the other terminal device, A determination means for determining that the communication device can be directly connected to the other terminal device based on the response signal, A communication device as described in Appendix 10, further comprising the above.

[0241] [Note 12] Selection means for selecting a communication path to the other terminal device from the direct connection path and the path via a relay device other than the relay device, based on the communication quality of the direct connection path to the other terminal device and the communication quality of the path to the other terminal device via a relay device other than the relay device. A communication device as described in Appendix 11, further comprising the above.

[0242] [Note 13] The communication device as described in Appendix 1, wherein the first communication method is either a first form in which the communication device is directly connected to a base station and communicates with the other terminal device, or a second form in which the communication device is connected to a base station via another relay device and communicates with the other terminal device.

[0243] [Note 14] The communication device as described in Appendix 13, wherein the transmitting means transmits a search signal for searching for another relay device before transmitting a signal related to the relay device.

[0244] [Note 15] A communication device operating as a terminal device decides to switch the communication method by which the communication device communicates with other terminal devices between a first communication method, which communicates with the other terminal device via a base station, and a second communication method, which communicates with the other terminal device without going through a base station. The communication device, in response to deciding to switch the communication method between the first communication method and the second communication method, transmits a signal related to a relay device that relays communication between the communication device and the other terminal device using the second communication method. A control method including

[0245] [Note 16] A program for causing the computer of a communication device operating as a terminal device to execute the control method described in Appendix 15. [Explanation of symbols]

[0246] 101 UE-1 (Terminal) 102 UE-2 (Terminal) 103 UE-to-UE Relay Terminal (Relay Terminal) 104 NG-RAN (base station) 105 5GC (Core Network) 106 Data Network (External Network) 107 UE-to-NE Relay-1 terminal (relay terminal) 108 UE-to-NE Relay-2 terminal (relay terminal)

Claims

1. A communication device that operates as a terminal device, A decision means for determining whether to switch the communication method used by the communication device to communicate with other terminal devices between a first communication method, which communicates with the other terminal devices via a base station, and a second communication method, which communicates with the other terminal devices without going through a base station. In response to the determination means deciding to switch the communication method between the first communication method and the second communication method, a transmitting means transmits a signal relating to a relay device that relays communication between the communication device and the other terminal device using the second communication method. A communication device having the following features.

2. The communication device according to claim 1, wherein, in response to the decision means deciding to switch the communication method from the first communication method to the second communication method, the transmitting means transmits a search signal for searching for the relay device as a signal relating to the relay device.

3. The communication device according to claim 1, wherein the determination means determines to switch the communication method between the first communication method and the second communication method based on the operating state of a service or application used between the communication device and the other terminal device.

4. The communication device according to claim 1, wherein the determination means determines to switch the communication method from the first communication method to the second communication method based on the communication quality between the communication device and the base station in the first communication method.

5. The communication device according to claim 1, wherein the determination means determines to switch the communication method from the first communication method to the second communication method based on the remaining battery level of the communication device or the other terminal device.

6. Selection means for selecting a route to communicate with the other terminal device from the direct connection route and the route via the relay device, based on the communication quality of the direct connection route to the other terminal device and the communication quality of the route to the other terminal device via the relay device. The communication device according to claim 2, further comprising the above.

7. Receiving means that receive a discoverer announcement message from the relay device together with the other terminal device before the communication method is switched from the first communication method to the second communication method. The communication device according to claim 1, further comprising the following:

8. The communication device according to claim 1, wherein, in response to the determination means deciding to switch the communication method from the second communication method via the relay device to the first communication method, the second communication method via another relay device, or a third communication method that directly connects to another terminal device, the transmission means transmits a disconnection signal for disconnecting communication with the relay device as a signal relating to the relay device.

9. The communication device according to claim 1, wherein the determination means determines, based on the communication quality between the communication device and the relay device, to switch the communication method from the second communication method via the relay device to the first communication method, the second communication method via another relay device, or a third communication method that directly connects to the other terminal device.

10. The communication device according to claim 1, wherein, before the decision means decides to switch the communication method from the second communication method via the relay device to the first communication method, the second communication method via another relay device, or a third communication method that directly connects to the other terminal device, the transmitting means transmits a search signal for direct connection to the other terminal device.

11. Receiving means for receiving a response signal to the search signal from the other terminal device, A determination means for determining that the communication device can be directly connected to the other terminal device based on the response signal, The communication device according to claim 10, further comprising the above.

12. Selection means for selecting a communication path to the other terminal device from the direct connection path and the path via a relay device other than the relay device, based on the communication quality of the direct connection path to the other terminal device and the communication quality of the path to the other terminal device via a relay device other than the relay device. The communication device according to claim 11, further comprising the above.

13. The communication device according to claim 1, wherein the first communication method is either a first form in which the communication device is directly connected to a base station and communicates with the other terminal device, or a second form in which the communication device is connected to a base station via another relay device and communicates with the other terminal device.

14. The communication device according to claim 13, wherein the transmitting means transmits a search signal for searching for another relay device before transmitting a signal related to the relay device.

15. A communication device operating as a terminal device decides to switch the communication method by which the communication device communicates with other terminal devices between a first communication method, which communicates with the other terminal device via a base station, and a second communication method, which communicates with the other terminal device without going through a base station. The communication device, in response to deciding to switch the communication method between the first communication method and the second communication method, transmits a signal related to a relay device that relays communication between the communication device and the other terminal device using the second communication method. A control method including

16. A program for causing a computer of a communication device operating as a terminal device to execute the control method described in claim 15.

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