Communication device, control method, and program

Abstract

A communication device that operates as a terminal device, the communication device including: a determination means that determines to switch a communication scheme in which the communication device communicates with another terminal device, between a first communication scheme in which the communication device communicates with the other terminal device via a base station, and a second communication scheme in which the communication device communicates with the other terminal device not via the base station; and a transmission means that, after the determination means determines to switch the communication scheme from the first communication scheme to the second communication scheme, transmits a search signal for searching for a terminal device that operates as a relay device that relays communication, under the second communication scheme, between the communication device and the other terminal device.

Description

Communication device, control method, and program

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

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

[0003] In 3GPP, a specification has been established 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 the 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.

[0005] Japanese Patent Application Laid-Open No. 2016-106449

[0006] In 3GPP, the standardization of 5G ProSe (Proximity-based services) UE-to-UE Relay is also under development. UE-to-UE Relay is a mechanism in which, in sidelink communication where two terminal devices (End UEs) communicate directly without going through a base station, 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 can be switched between paths where a UE-to-UE Relay terminal (or its candidate) can be interposed. However, the operation related to the switching between paths where a UE-to-UE Relay terminal can be interposed is not defined and is not clear. Note that the UE-to-UE Relay terminal may also be referred to as a Sidelink Relay terminal, a relay UE, a Relay, etc.

[0008] Meanwhile, 3GPP is also working on the specification of 5G ProSe UE-to-NE Relay. UE-to-NE Relay is a system in which a terminal device and a relay device (UE-to-NE Relay terminal) communicate via Sidelink, and the UE-to-NE Relay terminal relays the communication path (or communication) between End UE and the base station. NE is an abbreviation for Network, and UE-to-NE Relay as described below means UE-to-Network Relay.

[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 the UE-to-NE Relay terminal is also sometimes called a Sidelink Relay terminal, relay UE, or Relay.

[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 a relay device may be involved.

[0011] 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 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 search signal to search for a terminal device that operates as a relay device for relaying communication between the communication device and the other terminal device using the second communication method, after the decision means has decided to switch the communication method from the first communication method to the second communication method.

[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.

[0013] This figure shows an example configuration of a communication system according to the first embodiment of this disclosure. This block diagram shows an example of the functional configuration of a terminal device according to the embodiment. This figure shows an example of the functional configuration of a Sidelink Relay terminal device according to the embodiment. This sequence diagram shows an example of processing when switching from a Uu path to a relay path using a discovery request message according to the first embodiment. This sequence diagram shows an example of processing when switching from a Uu path to a relay path using a discovery announcement message according to the first embodiment. This flowchart shows an example of processing when a terminal device determines whether to switch from a Uu path to a relay path according to the embodiment. This sequence diagram shows an example of processing when switching from a relay path to a Uu path according to the first embodiment. This sequence diagram shows an example of processing when switching from a relay path to a Uu path after determining whether direct PC5 connection is possible according to the first embodiment. This flowchart shows an example of processing when a terminal device determines whether to switch from a relay path to another PC5 path or a Uu path according to the embodiment. This figure shows an example configuration of a communication system according to the second embodiment of this disclosure. This is a sequence diagram showing an example of processing when switching from a UE-to-NE relay path (Uu path) to a UE-to-UE relay path (PC5 path) according to the second embodiment. This is a sequence diagram showing an example of processing when switching from a UE-to-UE relay path (PC5 path) to a UE-to-NE relay path (Uu path) according to the second embodiment. This is a diagram showing an example of the configuration of a communication system according to the third embodiment of this disclosure. This is a sequence diagram showing an example of processing when switching from a UE-to-NE relay path (Uu path) to a UE-to-UE relay path (PC5 path) according to the third embodiment. This is a sequence diagram showing an example of processing when switching from a UE-to-UE relay path (PC5 path) to a UE-to-NE relay path (Uu path) according to the third embodiment.

[0014] The embodiments will be described in detail below with reference to the attached drawings. Note that the following embodiments do not limit the scope of the claims. While the embodiments describe multiple features, not all of these features are essential to this disclosure, and the features may be combined in any way. Furthermore, in the attached drawings, the same or similar configurations are given the same reference numerals, and redundant descriptions may be omitted.

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

[0016] Although this embodiment describes 5G, this disclosure is also applicable to other technologies (for example, next-generation mobile communication systems such as 5G Advanced and 6G, LTE, LTE-Advanced, and combinations thereof).

[0017] As shown in Figure 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 that have the function of communicating with a base station in a 5G mobile communication network (or 5G mobile communication system) and the function of direct communication (Sidelink communication) with other terminals. Communication between UE-1 (101) and UE-2 (102) and a base station (e.g., NG-RAN (104)) is performed via the Uu path. Communication between UE-1 (101) and UE-2 (102) and other terminals (e.g., 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] 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 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 signal in response to its decision to switch as described above. Specifically, UE-1 (101) transmits a signal 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 a 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, while the other functions are 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 programs for processing described later, information used by the control and 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 Solution message). These signals and messages also include response messages to discovery request messages (shown as UE-to-UE Relay Discovery Response message). Furthermore, these signals and messages also include path switching request messages (shown as Path Switch Request) and response messages to path switching request messages (shown as Path Switch Response). Furthermore, such signals and messages include disconnection request messages (disconnect request shown in the diagram) and response messages to disconnection request messages (disconnect response shown in the diagram). These signals and messages also include response messages to connection setting change request messages (link modification acceptance shown in the diagram).

[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 UE-to-UE Relay Discovery Announcement message). 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 Link Modification Request).

[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 with 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, compliant 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, compliant 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 the 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 the 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, an FPGA, etc. 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 storage 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 and 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 a flexible disk, hard disk, optical disk, magneto-optical disk, CD-ROM, CD-R, magnetic tape, non-volatile memory card, or DVD.

[0042] The message generation unit 303 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 303 generates signals and messages to be transmitted to other UEs and 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 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 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 (e.g., compliant with the 3GPP cellular communication standard). The Sidelink Relay connection processing unit 305 may be constituted by a general-purpose processor such as a CPU (e.g., realized as a program). The Sidelink Relay connection processing unit 305 performs the process of connecting the UE-to-UE Relay terminal (103) to the UE-1 (101) and the UE-2 (102).

[0045] The PC5 communication processing unit 306 is configured to include hardware for performing wireless communication (e.g., compliant with the 3GPP cellular communication standard). The PC5 communication processing unit 306 may be constituted by a general-purpose processor such as a CPU (e.g., realized 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 transmission processing of the message related to PC5 communication generated by the message generation unit 303 to other UEs, and the reception processing of the message related to PC5 communication from other UEs.

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

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

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

[0049] As described above, using FIG. 3, the functional configuration example of the Sidelink Relay terminal device (UE-to-UE Relay terminal (103)) according to the present embodiment has been described in detail. Here, the UE-to-NE Relay terminal described later can also have the same or similar functional configuration. That is, the UE-to-NE Relay-1 terminal (107) according to the second embodiment and the third embodiment and the UE-to-NE Relay-2 terminal (108) according to the third embodiment can also have the same or similar functional configuration.

[0050] The message generation units 303 of the UE-to-NE Relay-1 terminal (107) and the UE-to-NE Relay-2 terminal (108) generate signals, messages, etc. to be transmitted to other UEs and base stations. Such signals, messages, etc. include response messages to discovery request messages (the illustrated UE-to-NE Relay Discovery Response message), etc. Also, such signals, messages, etc. include response messages to path switching request messages, response messages to disconnection request messages, etc.

[0051] The message analysis units 304 of the UE-to-NE Relay-1 terminal (107) and the UE-to-NE Relay-2 terminal (108) analyze signals, messages, etc. received from other UEs and base stations. Such signals, messages, etc. include discovery request messages (the illustrated UE-to-NE Relay Discovery Solicitation message), etc. Also, such signals, messages, etc. include path switching request messages, disconnection request messages, etc.

[0052] (Processing Example) 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 a UE searches for a UE-to-UE Relay terminal used in a relay path using a discovery request message (an example of a search signal for searching for a relay device) issued by the UE. The sequence diagram in Figure 5 shows an example (Model A) where a UE-to-UE Relay terminal used in a relay path is discovered using a discovery announcement message issued by the UE-to-UE Relay terminal.

[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 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) is not 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 from F403b to F403e below, and it is assumed that the UE-to-UE Relay terminal (103) is found in the search.

[0058] In F403b, UE-1 (101) transmits 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 transmitted from the UE-to-UE Relay terminal (103), transmits a response message to the discovery request message.

[0061] In 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 a 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 connection processing with UE-2 (102).

[0065] In F406, UE-1 (101) performs connection processing 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 the relay path through the UE-to-UE Relay terminal (103).

[0067] After switching to the relay path, UE-1 (101) determines in F408a 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.

[0068] After switching to the relay path, UE-2(102) determines in F408b 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.

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

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

[0071] F401 and F402 are as explained 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) by 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 (affirmative 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 processing performed by UE-1 (101) when deciding to switch from the Uu path to the relay path at F402 in 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 (received power, received SNR, received error rate, etc.) relating to UE-1 (101), UE-2 (102), and the UE-to-UE Relay terminal. SNR is an abbreviation for Signal-to-Noise Ratio.

[0077] If UE-1 (101) determines that UE-2 (102) is not close 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 close 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, for example, RSRP (SD-RSRP, SL-RSRP, etc.), RSSI, RSRQ, etc. The 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 the 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 it 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 it 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 a 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 determines that it will run a low-latency service (Yes in S604), it proceeds to S606. On the other hand, if UE-1 (101) is not running or determines that it will not 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 there is enough battery power to continue communication via the Uu path through the base station. UE-1(101) and UE-2(102) exchange information regarding 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 any 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 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, where a relay device may be involved, 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, an example of the process for 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 will be explained. 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 shown in Figure 7 illustrates an example where UE-1 (101) decides to switch from the relay path to the Uu path. The sequence diagram shown in Figure 8 illustrates an example where UE-1 (101) tries to determine 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 executes 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 F701, UE-1 (101) and UE-2 (102) communicate with each other via a relay path through a 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 (affirmative or acceptance message) to UE-1 (101) in response to the path switching request message.

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

[0095] UE-2(102) determines the connection status with the base station in F704b 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 connection or communication with the UE-to-UE Relay terminal (103). The disconnection request message to request the disconnection of 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 UE-1 (101) in response to the disconnection request message.

[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 disconnection request message via F707b, if necessary, to the UE-to-UE Relay terminal (103).

[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 connection setting change request message to the UE-to-UE Relay terminal (103) via F708b, if necessary.

[0100] In 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 connection to PC5 is possible.

[0102] In F701, UE-1 (101) and UE-2 (102) communicate with each other via a relay path through a 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 an alternative PC5 path, such as another relay path or a direct PC5 path 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 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), proceed 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 may involve switching to a PC5 path other than the Uu path. An example of the process in this case 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 a 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 to connect directly to the PC5 and via a relay path through 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 (103). Additionally or alternatively, this determination may be made based on communication quality information (received power, received SNR, received error rate, etc.) relating to UE-1 (101), UE-2 (102), and the 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) via 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, for example, 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 another relay path through an alternative UE-to-UE Relay terminal other than the UE-to-UE Relay terminal 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 a first communication quality for the direct PC5 connection route to UE-2 (102) and a second communication quality for the route via an alternative UE-to-UE Relay terminal to UE-2 (102). Based on the first and second communication quality, UE-1 (101) selects a route to connect (communicate) with UE-2 (102) from the direct PC5 connection route and the route via the alternative UE-to-UE Relay terminal. 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 route may mean all of the communication quality between each of the connected communication devices (UE, UE-to-UE Relay terminals) 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 quality levels 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).

[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 to 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 determination result (Yes) in any of S901 to S904.

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

[0134] [Second Embodiment] In the first embodiment, path switching in a communication system where a UE-to-UE Relay terminal exists was described. 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 the configuration and processing in the first embodiment, the description 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 a Uu path to a relay path via a 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 a 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 through 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 UE-1 (101) via PC5 communication (discovery). If UE-1 (101) is not found as a result of the search, or if UE-2 (102) 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 following processes F1103b and F1103c, and it is assumed that a UE-to-UE Relay terminal (103) is found.

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

[0141] In F1103c, the UE-to-UE Relay terminal (103), upon receiving a discovery request message transmitted from UE-2 (102), transmits 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 a 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, F1105a sends a path switching request message to UE-1 (101) 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). 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 a UE-to-UE Relay terminal (103) is found.

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

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

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

[0149] In F1108, UE-1 (101) performs connection processing 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] At 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 a Uu path via the base station that is relayed by the UE-to-NE Relay-1 terminal (107). At F1110b, the UE-to-NE Relay-1 terminal (107) sends a response message (affirmation 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 via the UE-to-UE Relay terminal (103).

[0153] After switching to the relay path via the UE-to-NE Relay-1 terminal (107) 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, 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) determines in F1113 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.

[0155] In F1114, UE-1 (101) and UE-2 (102) communicate with each other via a relay path through a 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 of F1202 (situation assessment) 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 a Uu path via the base station that 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 at F1204 and establishes a connection with the base station as necessary.

[0161] In F1205a, UE-1 (101) sends a discovery request message via PC5 communication and searches for (discovers) 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 transmitted from UE-1 (101), transmits a response message to the discovery request message.

[0163] In F1206, UE-1 (101) performs a 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 a 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 UE-1 (101) in response to the path switching request message.

[0165] The UE-to-NE Relay-1 terminal (107) determines the connection status with the base station at 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 a Uu path via the base station that 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 UE-2 (102) in response to the path switching request message.

[0167] In Figure 12, an example is shown in which UE-2 (102) sends a path switching request message to the UE-to-UE Relay terminal (103), but 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 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 connection or communication with the UE-to-UE Relay terminal (103). The disconnection request message to request the disconnection of 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 F1211b, the UE-to-UE Relay terminal (103) sends a response message (acknowledgment or acceptance message) to UE-1 (101) in response to the disconnection request message.

[0170] In F1212a, UE-2 (102) sends a disconnection request message to the UE-to-UE Relay terminal (103) to request the disconnection of connection or communication with the UE-to-UE Relay terminal (103). The disconnection request message to request the disconnection of 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] Although Figure 12 shows an example where both UE-1 (101) and UE-2 (102) send disconnection request messages, as in Figure 8 with F706a and F708b, only one of the UEs may send a disconnection request message.

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

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

[0174] [Third Embodiment] In the second embodiment, path switching in a communication system where one UE-to-NE Relay terminal may exist was described. 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 description may be omitted.

[0175] Figure 13 shows an example configuration of a communication system according to a third embodiment of the present 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 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 a base station via a UE-to-NE Relay-1 terminal (107) and a UE-to-NE Relay-2 terminal (108).

[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 UE-1 (101) via PC5 communication (discovery). If UE-1 (101) is not found as a result of the search, or if UE-2 (102) 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 following processes F1403b and F1403c, and it is assumed that a UE-to-UE Relay terminal (103) is found.

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

[0181] In F1403c, the UE-to-UE Relay terminal (103), upon receiving a discovery request message transmitted from UE-2 (102), transmits 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 a 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) to request a switch from the Uu path to the PC5 path. This Uu path is a Uu path via the base station that 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) transmits a discovery request message.

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

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

[0189] In F1408, UE-1 (101) performs connection processing 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] UE-2 (102) sends a path switching request message to the UE-to-NE Relay-1 terminal (107) in F1410a to request a switch from the Uu path to the PC5 path. This Uu path is a Uu path via the base station that 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 a 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). 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 in which 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 via the UE-to-UE Relay terminal (103).

[0195] After switching to the relay path via the UE-to-NE Relay-1 terminal (107) 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, 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 a 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 of F1502 (situation assessment) 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 a 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 and searches for (discovers) 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 a 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 a 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 at F1507 and connects to the base station as necessary.

[0207] In F1508a, UE-1 (101) sends a discovery request message via PC5 communication and searches for (discovers) 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 transmitted from UE-1 (101), transmits a response message to the discovery request message.

[0209] In F1509, UE-1 (101) performs a 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 a Uu path via the base station that is 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 a 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 UE-2 (102) in response to the path switching request message.

[0213] In Figure 15, an example is shown in which UE-2 (102) sends a path switching request message to the UE-to-UE Relay terminal (103), but 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 connection or communication with the UE-to-UE Relay terminal (103). The disconnection request message to request the disconnection of 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 F1211b, the UE-to-UE Relay terminal (103) sends a response message (acknowledgment or acceptance message) to UE-1 (101) in response to the disconnection request message.

[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 the relay device. In F1514b, the UE-to-UE Relay terminal (103) sends a response message (acknowledgment or acceptance message) to UE-1 (101) in response to the disconnection request message.

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

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

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

[0221] [Other Embodiments] In the above, an example of switching from a Uu path to a relay path was described 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 path of direct PC 5 connection to UE-2 (102) (if possible) and a path via the UE-to-UE Relay terminal (103) to UE-2 (102). Specifically, UE-1 (101) obtains a first communication quality of the path of direct PC 5 connection to UE-2 (102) and a second communication quality of the path via the UE-to-UE Relay terminal (103) to UE-2 (102). Then, UE-1 (101) selects a route to connect to UE-2 (102) from the direct PC5 connection route and the route via the UE-to-UE Relay terminal (103) based on the first and second communication quality. Here, the communication quality of a route may mean all of the communication quality between each of the connected communication devices (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 respective communication quality levels 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 by connecting via a Relay terminal. In this case, UE-2 (102) may decide (or determine) whether to connect directly to the base station or connect 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 when the communication quality with the base station deteriorates, when a low-latency service is being performed, or when 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 (for example, 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 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 omitted. 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 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] The present invention is not limited to the embodiments described above, and various modifications and variations are possible without departing from the spirit and scope of the invention. Accordingly, the following claims are attached to make the scope of the invention public.

[0230] This application claims priority based on Japanese Patent Application No. 2024-194901, filed on 7 November 2024, and Japanese Patent Application No. 2025-078589, filed on 9 May 2025, and all of the contents of those applications are incorporated herein by reference.

[0231] 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 compliant with the 3GPP (3rd Generation Partnership Project) standard, comprising: a decision means for deciding 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 other terminal devices without going through a base station; and a transmission means for transmitting a search signal to search for a terminal device that operates as a relay device for relaying communication between the communication device and the other terminal devices using the second communication method, after the decision means has decided to switch the communication method from the first communication method to the second communication method.

2. 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 operating status of a service or application used between the communication device and the other terminal device.

3. 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.

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 remaining battery level of the communication device or the other terminal device.

5. The communication device according to any one of claims 1 to 4, further comprising a receiving means for receiving a response signal to the search signal from a terminal device operating as the relay device.

6. The communication device according to any one of claims 1 to 5, characterized in that the search signal is a UE-to-UE Relay Discovery Solution message.

7. The communication device according to claim 5, characterized in that the response signal is a UE-to-UE Relay Discovery Response message.

8. After switching the communication method from the first communication method to the second communication method, the determination means further decides to switch the communication method from the second communication method via the relay device to the first communication method based on the communication quality between the communication device and the terminal device acting as the relay device, according to any one of claims 1 to 7.

9. The communication device according to claim 8, wherein, in response to the decision means deciding to switch the communication method from the second communication method via a terminal device acting as a relay device to the first communication method, the transmitting means transmits a disconnection signal for disconnecting communication with the relay device as a signal relating to the relay device.

10. A communication device operating as a terminal device, comprising: a decision means for deciding to switch the communication method by which the communication device communicates with another terminal device between a first communication method in which the communication device communicates with the other terminal device via a base station and a second communication method in which the communication device communicates with the other terminal device via a terminal device operating as a relay device without going through a base station; and a transmission means for transmitting a request signal to a terminal device operating as a relay device that relays communication between the communication device and the other terminal device using the second communication method, after the decision means has decided to switch the communication method from the second communication method to the first communication method.

11. The communication device according to claim 10, wherein, before the decision means decides to switch the communication method from the second communication method via a terminal device acting as a relay device to the first communication method, the transmitting means transmits a search signal for direct connection with the other terminal device.

12. The communication device according to claim 11, further comprising: receiving means for receiving a response signal to the search signal from the other terminal device; and determining means for determining, based on the response signal, that the communication device can be directly connected to the other terminal device.

13. The communication device according to claim 11, further comprising a selection means for selecting a route to communicate with the other terminal device from the direct connection route and the route via other relay devices other than the relay device, based on the communication quality of the direct connection route and the communication quality of the route to the other terminal device via other relay devices other than the relay device.

14. The communication device according to claim 1 or 10, 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.

15. A control method comprising: a step of a communication device operating as a terminal device deciding 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; and a step of the communication device, after deciding to switch the communication method from the first communication method to the second communication method, transmitting a search signal to search for a terminal device that operates as a relay device to relay communication between the communication device and the other terminal device using the second communication method.

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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