COMMUNICATION DEVICE, COMMUNICATION METHOD, CONTROL CIRCUIT AND STORAGE MEDIUM

Abstract

A communication device (1) has a function of directly communicating with a communication terminal, which is another communication device, and comprises: a base station search unit (31) that searches for base stations with which direct communication is possible; a communication control unit (33) that performs a connection process for connecting to base stations searched by the base station search unit (31) to construct redundantly configured communication paths;and a communication terminal search unit (32) that searches for the communication terminal connected to a base station, and in a case where the number of established direct communications with base stations is less than the number required to establish the redundantly configured communication paths, the communication control unit (33) establishes indirect communication with a base station via a communication terminal searched by the communication terminal search unit (32) to establish redundantly configured communication paths.;

Description

Area

[0001] The present disclosure relates to a communication device, a communication method, a control circuit and a storage medium. background

[0002] One possible means of achieving fully automated driving of a motor vehicle in a specific environment (Level 4 automated driving) is dynamic mapping, in which dynamic information, including the situation of a surrounding mobile object, is superimposed on a three-dimensional map as static information. The communication required to implement dynamic mapping must be highly reliable compared to normal communication. Therefore, within the framework of the 3rd Generation Partnership Project (3GPP) (registered trademark), a redundant configuration was investigated in which a communication device installed in a motor vehicle communicates with multiple base stations, and highly reliable communication can be realized by transmitting dynamic information over multiple paths.

[0003] On the other hand, a redundant configuration with multiple base stations cannot be realized due to communication environment, reception capacity, geographical constraints, and the like. In this case, communication interruption and fallback operation, or emergency operation, are considered. In the case of communication interruption and fallback operation, sufficient reliability cannot be guaranteed, so an alternative redundancy means is required.

[0004] As a technique for solving this problem, Non-Patent Literature 1 discloses a redundant configuration in which direct communication with a base station and indirect communication with the base station via a relay by another mobile station are combined. List of cited publicationsNon-patent literature

[0005] Non-patent literature 1: 3GPP TR 23.700-33, "Study on system enhancement for Proximity based Services(ProSe) in the 5G System(5GS); Phase 2" SummaryTechnical task

[0006] However, the technique described in Non-Patent Literature 1 can realize indirect communication only through a mobile station designated by a base station, and Non-Patent Literature 1 does not describe a method for selecting a mobile station that performs a relay process to realize indirect communication by a mobile station that requires implementing a redundant configuration. In a case where a mobile station for realizing indirect communication is not directly selected by a communication device installed in a vehicle with dynamic mapping, the provision of dynamic information is delayed due to the influence of a communication delay, and the delay required for dynamic mapping cannot be achieved.

[0007] The present disclosure has been made in view of the foregoing, and an object thereof is to provide a communication apparatus which, in a case of realizing a redundant configuration of communication paths by combining direct communication and indirect communication, realizes a communication system in which a mobile station requesting to realize a redundant configuration can select a relay station which performs a relay process of the indirect communication. Solution to the problem

[0008] To solve the problems described above and achieve the object, the present disclosure is a communication device having a function of directly communicating with a communication terminal that is another communication device. The communication device includes: a base station search unit for searching for base stations with which direct communication is possible; a communication control unit for performing a connection process for connecting to base stations searched by the base station search unit to establish redundantly configured communication paths; and a communication terminal search unit for searching the communication terminal connected to a base station.In a case where the number of established direct communications with base stations is less than the number required to establish the redundantly configured communication paths, the communication control unit establishes indirect communication with a base station via the communication terminal searched by the communication terminal search unit to establish redundantly configured communication paths. Advantageous effects of the invention

[0009] The communication device according to the present disclosure achieves an effect that, in a case of realizing a redundant configuration of communication paths by combining direct communication and indirect communication, a communication system can be realized in which a mobile station aiming to realize a redundant configuration can select a relay station that performs a relay process of the indirect communication. Brief description of the drawings Fig. 1 is a diagram showing an exemplary configuration of a communication system according to a first embodiment. Fig. 2 is a diagram showing an example of a functional block configuration of a communication device according to the first embodiment that realizes mobile stations. Fig. 3 is a diagram showing an example of an operation flow of the communication system according to the first embodiment. Fig. 4 is a flowchart showing an example of an operation of the mobile station according to the first embodiment. Fig. 5 is a diagram showing an exemplary configuration of a communication system according to a second embodiment. Fig. 6 is a diagram showing an example of an operation flow of the communication system according to the second embodiment. Fig. 7 is a diagram showing an example of an operation flow of a communication system according to a third embodiment. Fig. 8 is a flowchart showing an example of an operation of the mobile station according to the third embodiment. Fig. 9 is a diagram showing an exemplary configuration of a communication system according to a fourth embodiment. Fig. 10 is a diagram showing an example of an operation flow of the communication system according to the fourth embodiment. Fig. 11 is a flowchart showing an example of an operation of the mobile station according to the fourth embodiment. Fig. 12 is a diagram showing an example configuration of a processing circuit in a case where a communication unit of the communication device is realized by a processor and a memory. Description of embodiments

[0010] Hereinafter, a communication apparatus, a communication method, and a storage medium according to embodiments of the present disclosure will be described in detail with reference to the drawings. First embodiment.

[0011] Fig. 1 is a diagram showing an example configuration of a communication system 101 according to a first embodiment. The communication system 101 is a 5G communication system, specifically, a 5G communication system in which the indirect communication function described in Non-Patent Literature 1 is implemented and capable of establishing a redundant configuration using the indirect communication function.

[0012] The communication system 101 includes the base stations 11-1 and 11-2 and the mobile stations 12 and 13. The mobile stations 12 and 13 have the function of conducting direct communication without going through a base station and can be operated as relay stations that forward signals between a connected base station and a remote station of the direct communication. It should be noted that in Fig. 1, of the components of the communication system 101, only the components necessary to describe the first embodiment are shown. For example, base stations other than base stations 11-1 and 11-2, mobile stations other than mobile stations 12 and 13, a core network to which base stations 11-1 and 11-2 are connected, and the like are not shown.

[0013] The base station 11-1 is a base station that is in direct communication with the mobile station 12. The base station 11-2 is a base station that is in direct communication with the mobile station 13, but is in a state in which it is unable to conduct direct communication with the mobile station 12.

[0014] The mobile station 12 is a mobile station that aims to realize a redundant configuration of communication paths, and is a mobile object such as a motor vehicle on which the communication device according to the first embodiment is installed. That is, the mobile station 12 includes a mobile object and a communication device installed on the mobile object. The mobile station 12 is a mobile station that requests mission-critical communication, for example, dynamic mapping. The mobile station 12 attempts to realize a redundant configuration, but cannot perform direct communication with a plurality of base stations, and attempts to realize the redundant configuration through indirect communication via surrounding mobile stations in combination.In the present embodiment, the mobile station 12 is in a state where direct communication with the base station 11-1 can be performed, but direct communication with the base station 11-2 cannot be performed. Therefore, the mobile station 12 performs indirect communication with the base station 11-2 via the mobile station 13 capable of direct communication with the base station 11-2.

[0015] Similar to mobile station 12, mobile station 13 includes a mobile object and a communication device installed on the mobile object. Mobile station 13 communicates directly with base station 11-2 and functions as a relay station, performing a relay process when mobile station 12 indirectly communicates with base station 11-2.

[0016] Fig. 2 is a diagram showing an example of a functional block configuration of a communication device 1 according to the first embodiment, which realizes the mobile stations 12 and 13.

[0017] As in Fig. 2, the communication device 1 according to the first embodiment includes a wireless unit 20 that transmits and receives a wireless signal to and from another communication device, and a communication unit 30 that performs transmission and reception of a control signal and a data signal to and from another communication device via the wireless unit 20, and the like. The communication device 1 is configured to be capable of simultaneously communicating with a plurality of other communication devices. That is, the wireless unit 20 can simultaneously transmit wireless signals to and from a plurality of other communication devices, and the communication unit 30 can simultaneously communicate with a plurality of other communication devices.The communication unit 30 includes a base station search unit 31 that searches for a base station with which direct communication can be performed, a communication terminal search unit 32 that searches for a communication terminal with which direct communication can be performed, such as a mobile object on which another communication device is installed, and a communication control unit 33 that controls communication operations with the base station and the communication terminal.

[0018] It should be noted that the communication device 1 in each of the mobile stations 12 and 13 performs communication processes with the base stations 11-1 and 11-2 and the like that have a communication function, but in order not to make the description too complicated, the mobile stations 12 and 13 are described in the following description as subjects that perform the communication processes.

[0019] Next, a function of the communication system 101 will be described. Specifically, a function is described in which the mobile station 12 Fig. 1 by combining direct communication with the base station 11-1 and indirect communication with the base station 11-2 via the mobile station 13.

[0020] Fig. 3 is a diagram showing an example of an operation flow of the communication system 101 according to the first embodiment. In detail, Fig. 3 is a sequence diagram illustrating an example of an operation in which, when the mobile station 12 establishes redundant communication paths between the mobile station 12 and the base station 11, indirect communication with the base station 11-2 led by the mobile station 12 is started, thereby providing redundancy of the communication paths.

[0021] In the Fig. 3, the mobile station 12 first transmits a direct communication request to the base stations 11-1 and 11-2 to realize a redundant configuration by direct communication (step S11).

[0022] At this time, only the base station 11-1, in response to the direct communication request from the mobile station 12, accepts the request and returns a direct communication authorization to the mobile station 12, and direct communication is established between them (step S12). Note that, apart from the base stations 11-1 and 11-2, no other base stations are located within an area where the mobile station 12 can perform direct communication. Fig. 3, the base station 11-2 does not transmit a response signal to the mobile station 12, but may return a response signal rejecting the direct communication request. In a case where the response signal rejecting the direct communication request is not transmitted from the base station 11-2, when a certain period of time has elapsed since the transmission of the direct communication request in step S11, the mobile station 12 determines that the direct communication request is rejected.

[0023] Since direct communication with the base station 11-2 cannot be established, the mobile station 12 establishes a redundant configuration with indirect communication in combination. Then, the mobile station 12 searches for surrounding mobile stations and selects a mobile station from the found mobile stations to which a request for indirect communication is to be made (step S13). While searching for surrounding mobile stations, the mobile station 12 also collects information about base stations to which the mobile stations are connected. That is, the mobile station 12 acquires, from each of the mobile stations found through the search, information about the base station with which the found mobile station has established direct communication.

[0024] Here, the mobile station 12 selects the mobile station 13 connected to the base station 11-2. The mobile station 12 sends a direct communication request containing a request for indirect communication with the base station 11-2 to the selected mobile station 13 (step S14). Note that the direct communication request transmitted by the mobile station 12 in step S14 is a request for direct communication with the mobile station 13.

[0025] The mobile station 13 accepts the direct communication request received from the mobile station 12 and sends a relay communication request for data directed to the mobile station 12 to the base station 11-2 with which the mobile station 13 directly communicates (step S15). Note that there may be a case where the mobile station 13 rejects the direct communication request from the mobile station 12, but an operation in the case of rejection is not covered by the present disclosure, and therefore, the description thereof is omitted. Similarly, there may be a case where the base station 11-2 rejects the relay communication request from the mobile station 13, but an operation in the case of rejection is not covered by the present disclosure, and therefore, the description thereof is omitted.

[0026] The base station 11-2 accepts the relay communication request received from the mobile station 13 and returns a relay communication permission (step S16). Upon receiving the relay communication permission from the base station 11-2, the mobile station 13 transmits to the mobile station 12 a direct communication permission for the direct communication request from the mobile station 12 (step S17). At this time, the mobile station 13 also transmits a permission for the indirect communication request with the base station 11-2. That is, in step S17, the mobile station 13 transmits to the mobile station 12 the direct communication permission including the permission for the indirect communication request with the base station 11-2. As a result, indirect communication is established between the base station 11-2 and the mobile station 12 via the mobile station 13.

[0027] Through the operation described above, the mobile station 12, which has not been able to realize a redundant configuration by direct communication with the base station 11-2, can select a suitable mobile station 13 from the surrounding mobile stations and establish indirect communication with the base station 11-2 via the selected mobile station 13.

[0028] Here, an operation of the mobile station 12 of the communication system 101 according to the first embodiment is as shown in a flowchart of Fig. 4 shown. Fig. 4 is a flowchart showing an example of an operation of the mobile station shown in FIG. 12 of the first embodiment.

[0029] In a case where the mobile station 12 establishes a redundant communication path to the base station, the mobile station 12 first searches for base stations located within an area where direct communication can be performed (step S1). Specifically, the base station search unit 31 transmits a base station search signal and receives a response signal thereto, thereby finding base stations with which direct communication can be performed.

[0030] Next, the mobile station 12 performs a connection process for connecting to base stations (step S2). Specifically, the communication control unit 33 selects two base stations that can be used to establish redundant communication paths among the base stations found by the base station search unit 31, and performs a process for connecting to the two selected base stations. In a case where the number of base stations found by the base station search unit 31 is three or more, the communication control unit 33 selects, for example, two base stations with good wireless communication quality, for example, two base stations from which high-power signals are received. Note that the selection method is not limited to this.

[0031] If the connection to the two base stations is successful (step S3: Yes), the mobile station 12 was able to establish the redundant configuration of the communication paths by direct communication with the two base stations and thus terminates the operation.

[0032] If the connection to the two base stations is unsuccessful, that is, if the connection to at least one of the two selected base stations has failed (step S3: No), the mobile station 12 searches for communication terminals (step S4). Specifically, the communication terminal search unit 32 searches for communication terminals, which are surrounding mobile stations or the like, with which direct communication can be performed. Note that the communication terminal does not have to be a mobile station, but may also be, for example, a roadside unit installed on a road. When searching for communication terminals, the communication terminal search unit 32 collects information about base stations with which the found communication terminals have established direct communication.

[0033] From the communication terminals found in step S4, the mobile station 12 selects a communication terminal to which operation as a relay station that performs a relaying process is requested, and performs a connection process to connect to the base station via the selected communication terminal (step S5). Specifically, the communication control unit 33 selects a communication terminal directly connected to the base station, with which the communication control unit 33 failed to establish a connection in step S2, and requests the selected communication terminal to operate as a relay station that realizes indirect communication with the base station.In a case where there are a plurality of communication terminals directly connected to the base station and to which the communication control unit 33 could not establish a connection in step S2, the communication control unit 33 selects any one of the communication terminals. In this case, the communication control unit 33 selects a communication terminal capable of realizing indirect communication with good communication quality, for example, based on the quality of the wireless communication between the mobile station 12 and each communication terminal and the quality of the wireless communication between each communication terminal and the base station. When the connection with the selected communication terminal is completed and indirect communication with the base station via the selected communication terminal is possible, the mobile station 12 terminates the operation.

[0034] Note that in a case where the number of base stations found in step S1 is three or more and connection to the two base stations selected in step S2 has failed, the mobile station 12 may again select a base station as the connection destination and perform the connection process again. The mobile station 12 executes step S4 in a case where connection has been attempted to all the base stations found in step S1 and the number of base stations to which connection has been successful is one or less. Moreover, in a case where connection to all the base stations to which connection was attempted in step S2 fails, that is, in a case where there is no base station with which direct communication can be performed, the mobile station 12 may establish two communication paths using indirect communication with the base station in step S5.

[0035] In the above-described step S5, the mobile station 12 selects the communication terminal directly connected to the base station whose connection failed in step S2 and requests the selected communication terminal to operate as a relay station, but may also select a communication terminal directly connected to a base station other than the base station whose connection failed in step S2. For example, the mobile station 12 may preferentially select a communication terminal capable of realizing indirect communication with good communication quality, regardless of whether the communication terminal is a communication terminal directly connected to the base station whose connection failed in step S2.

[0036] As described above, in the communication system 101 according to the present embodiment, in a case where the mobile station 12 aiming at redundancy of communication paths cannot realize a redundant configuration by establishing direct communication with each of the plurality of base stations, the mobile station 12 searches for a communication terminal that has established direct communication with the base station and establishes direct communication with a communication terminal that has been found, thereby establishing indirect communication with the base station via the communication terminal to establish a redundant configuration.Consequently, in a case where the redundant configuration of the communication paths is realized by using indirect communication, the mobile station 12 can select a communication terminal that operates as a relay station and performs a relay process of the indirect communication. Second embodiment.

[0037] Fig. 5 is a diagram showing an example configuration of a communication system 102 according to a second embodiment. The communication system 102 has a similar configuration to the communication system 101 according to the first embodiment, but the base station with which the mobile station 12 performs indirect communication is different from that of the first embodiment. Specifically, in the communication system 102 according to the second embodiment, the mobile station 12 performs indirect communication with the base station 11-1 via the mobile station 13. That is, the mobile station 12 performs indirect communication with the base station 11-1 via the mobile station 13 while performing direct communication with the base station 11-1.

[0038] Fig. 6 is a diagram showing an example of an operation flow of the communication system 102 according to the second embodiment. In detail, Fig. 6 is a sequence diagram illustrating an example of an operation in which, when the mobile station 12 establishes redundant communication paths between the mobile station 12 and the base station, indirect communication with the base station 11-1, which is conducted by the mobile station 12, is started, thereby providing redundancy of the communication paths. In Fig. 6 are the same processes as those in the workflow of the communication system 101 according to the first embodiment of Fig. 3 are identified by the same step numbers. The descriptions of the processes that have the same step numbers as in Fig. 3 are not repeated.

[0039] In the communication system 102, since the mobile station 13 receiving the direct communication request including the indirect communication request from the mobile station 12 is connected to the base station 11-1, the mobile station 13 transmits to the base station 11-1 a forwarding communication request for data directed to the mobile station 12 (step S15a). The base station 11-1 accepts the forwarding communication request received from the mobile station 13 and returns a forwarding communication permission (step S16a).

[0040] Since the operation of the mobile station 12 is similar to that of the first embodiment, a description thereof will not be repeated.

[0041] By operating as explained above, when the mobile station 12 which has not been able to realize the redundant configuration by direct communication selects a suitable mobile station from the surrounding mobile stations, even in a case where the mobile station 12 selects another mobile station 13 connected to the same base station as that to which the mobile station 12 is connected, a plurality of communication paths can be prepared and the redundant configuration can be realized. Third embodiment.

[0042] The configuration of a communication system according to a third embodiment is similar to that in the first embodiment. In the communication system according to the third embodiment, after a mobile station realizes a redundant configuration through direct communication and indirect communication with base stations, the mobile station again attempts to establish direct communication with a base station with which direct communication could not be established. In a case where direct communication can be established, the mobile station terminates the indirect communication and switches to a redundant configuration through the two direct communications.

[0043] Fig. Fig. 7 is a diagram showing an example of an operation flow of the communication system according to the third embodiment. In the Fig. In the example shown in Figure 7, the communication system consists of base station #1, base station #2, a mobile station, and a relay station. Fig. 7, base station #1 corresponds to base station 11-1 of the first embodiment, and base station #2 corresponds to base station 11-2 of the first embodiment. The mobile station corresponds to mobile station 12 of the first embodiment, and the relay station corresponds to mobile station 13 of the first embodiment. The mobile station performs direct communication with base station #1 and performs indirect communication with base station #2 via the relay station.

[0044] As in Fig. As shown in Figure 7, the mobile station transmits a direct communication request to base station #2 at a predetermined time while indirectly communicating with base station #2 via the relay station (step S31). For example, the mobile station periodically transmits the direct communication request to base station #2 until direct communication with base station #2 is established. Step S31 is a process similar to step S11 shown in Fig. 3, and the like.

[0045] In a case where base station #2 can accept the direct communication request, base station #2 returns a direct communication authorization to the mobile station (step S32). Consequently, direct communication is established between the mobile station and base station #2. When direct communication with base station #2 is established, the mobile station determines to stop indirect communication with base station #2 and sends a direct communication stop request, including a request to stop indirect communication with base station #2, to the relay station (step S33). The relay station transmits a relay communication stop request to base station #2 in indirect communication with the mobile station (step S34).Base station #2, which has received the relay communication stop request, accepts the request and returns a relay communication stop permission to the relay station (step S35). Upon receiving the relay communication permission from base station #2, the relay station transmits to the mobile station a direct communication stop permission for the direct communication stop request from the mobile station (step S36). At this time, the relay station also transmits a permission to stop indirect communication with base station #2. That is, in step S36, the relay station transmits to the mobile station the direct communication stop permission, including the permission to stop indirect communication with base station #2. Consequently, the indirect communication between the mobile station and base station #2 via the relay station ends.

[0046] An operation of the mobile station according to the present embodiment is as shown in a flowchart of Fig. 8 shown. Fig. Fig. 8 is a flowchart showing an example of an operation of the mobile station according to the third embodiment. In Fig. 8 are the same processes as in the flow chart of Fig. 4, which shows the operation of the mobile station 12 according to the first embodiment, with the same step numbers as in Fig. 4. The descriptions of the processes that have the same step numbers as those in Fig. 4 (the processes of steps S1 to S5) are not repeated.

[0047] After executing the process of step S5, the mobile station according to the third embodiment performs a connection process to connect to the base station (step S6). In step S6, the mobile station performs a connection process to connect to the base station with which direct communication could not be established by the connection process performed in step S2. If the connection to the base station is successful, that is, if direct communication with the base station is established (step S7: Yes), the mobile station terminates indirect communication with the base station via the communication terminal operating as a relay station (step S8), and the operation ends. If the connection to the base station failed (step S7: No), the mobile station returns to step S6 and performs the connection process to connect to the base station again.

[0048] As described above, according to the present embodiment, after implementing the redundant configuration using indirect communication, the mobile station again executes the process of establishing direct communication with the base station with which direct communication could not be established at a predetermined timing, and in a case where direct communication can be established, the mobile station terminates the indirect communication. Therefore, it is possible to transition from a redundant configuration using a combination of direct communication and indirect communication to a redundant configuration using only direct communication.

[0049] Note that in the present embodiment, the process of establishing direct communication is performed again for the base station for which direct communication failed. However, the mobile station may search for surrounding base stations, and if it finds a base station with which direct communication could not be established, the mobile station may perform the process of establishing direct communication with the found base station again. Fourth embodiment.

[0050] Fig. 9 is a diagram showing an example configuration of a communication system 103 according to a fourth embodiment. The communication system 103 is a 5G communication system similar to the communication system 101 according to the Fig. 1 is similar to the first embodiment shown. In Fig. 9, the components that are the same as those of the communication system 101 according to the first embodiment are designated by the same reference numerals.

[0051] The communication system 103 includes the base stations 11-1 and 11-2, the mobile station 12, which establishes redundantly configured communication paths, and the mobile stations 13-1 and 13-2, which operate as relay stations in the redundantly configured communication paths to be established by the mobile station 12.

[0052] In the communication system 103, the mobile station 12 establishes a communication path with each of the base stations 11-1 and 11-2, but cannot establish direct communication with the base station 11-2. Therefore, the mobile station 12 establishes indirect communication with the base station 11-2 via each of the mobile stations 13-1 and 13-2. A difference between the communication system 103 and the communication system 101 according to the first embodiment is that an indirect communication path is duplicated.

[0053] Fig. 10 is a diagram showing an example of an operation flow of the communication system 103 according to the fourth embodiment. In Fig. 10 are the same processes as those in the workflow of the communication system 101 according to the first embodiment of Fig. 3 are identified by the same step numbers. The descriptions of the processes that have the same step numbers as in Fig. 3 are not repeated.

[0054] After receiving the direct communication permission from the base station 11-1 in step S12, the mobile station 12 selects a plurality of mobile stations to each of which a request for indirect communication is to be made (step S13a). Specifically, the mobile station 12 selects two of the mobile stations 13-1 and 13-2 as mobile stations to each of which a request for indirect communication is to be made. In a case where it is possible to select only a single mobile station to which a request for indirect communication is to be made, the mobile station 12 selects a single mobile station to which a request for indirect communication is to be made. In this case, the operation is similar to that in the first embodiment.

[0055] The mobile station 12 sends to the selected mobile stations 13-1 and 13-2 a direct communication request containing a request for indirect communication with the base station 11-2 (step S14a).

[0056] The mobile stations 13-1 and 13-2 accept the direct communication request received from the mobile station 12 and send to the base station 11-2 with which the mobile stations 13-1 and 13-2 directly communicate, a relay communication request for data directed to the mobile station 12 (steps S15-1 and S15-2).

[0057] The base station 11-2 accepts the relay communication requests received from the mobile stations 13-1 and 13-2 and returns relay communication permissions (steps S16-1 and S16-2). Upon receiving the relay communication permission from the base station 11-2, the mobile stations 13-1 and 13-2 each transmit to the mobile station 12 a direct communication permission for the direct communication request from the mobile station 12 (steps S17-1 and S17-2). At this time, the mobile stations S13-1 and S13-2 each also transmit a permission for the indirect communication request with the base station 11-2. That is, in step S17-1, the mobile station 13-1 transmits to the mobile station 12 the direct communication permission including the permission for the indirect communication request with the base station 11-2.In step S17-2, the mobile station 13-2 transmits to the mobile station 12 the direct communication authorization, including the authorization for requesting indirect communication with the base station 11-2. Consequently, indirect communication via the mobile station 13-1 and indirect communication via the mobile station 13-2 are established between the base station 11-2 and the mobile station 12.

[0058] Through the above-described operation, the mobile station 12, which could not realize the redundant configuration by direct communication, selects a plurality of appropriate mobile stations from the surrounding mobile stations to establish indirect communication, and a stronger redundant configuration than that of the first embodiment can be realized.

[0059] An operation of the mobile station 12 according to the present embodiment is as shown in a flowchart of Fig. 11 shown. Fig. Fig. 11 is a flowchart showing an example of an operation of the mobile station 12 according to the fourth embodiment. In Fig. 11 are the same processes as in the flow chart of Fig. 4, which shows the operation of the mobile station 12 according to the first embodiment, with the same step numbers as those in Fig. 4. The descriptions of the processes that have the same step numbers as in Fig. 4 are not repeated.

[0060] After searching for communication terminals in step S4, the mobile station 12 according to the fourth embodiment selects, from the communication terminals found in step S4, a plurality of communication terminals to each of which a request to operate as a relay station performing a relaying process is made, and performs a connection process for connecting to the base station 11-2 via the selected plurality of communication terminals (step S5a). Specifically, the mobile station 12 selects the mobile stations 13-1 and 13-2 and performs a connection process for connecting to the base station 11-2.

[0061] As described above, in the communication system 103 according to the present embodiment, in a case where direct communication with a base station cannot be established and indirect communication is established, the mobile station 12 selects a plurality of mobile stations from the mobile stations found by performing a search, and establishes a plurality of indirect communications via the respective selected mobile stations. Consequently, it is possible to realize communication with higher reliability than the communication system 101 according to the first embodiment in which the redundant configuration is realized by using a single indirect communication instead of direct communication.

[0062] It should be noted that in the Fig. In the communication system 103 shown in FIG. 9, both the mobile station 13-1 and the mobile station 13-2 operating as relay stations are connected to the base station 11-2, but this connection is not limited to this connection form. At least one of the mobile station 13-1 and the mobile station 13-2 may be connected to the base station 11-1. That is, the mobile station 13-1 and the mobile station 13-2 operating as relay stations may be connected to the same base station as the one to which the mobile station 12 requesting the indirect communication is connected, or they may be connected to a different base station. Furthermore, a base station to which the mobile station 13-1 is connected and a base station to which the mobile station 13-2 is connected may be different from each other.

[0063] Next, a hardware configuration of the communication device 1 constituting the mobile station 12 described in each embodiment will be described. The wireless unit 20 of the communication device 1 is realized by a transceiver. The communication unit 30 of the communication device 1 is realized by a processing circuit, which is dedicated hardware, specifically, a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), or a processing circuit obtained by combining these.

[0064] Furthermore, the processing circuit that realizes the communication unit 30 of the communication device 1 may be a control circuit having a processor that executes a program stored in a working memory. Fig. 12 is a diagram showing an example configuration of a processing circuit in a case where the communication unit 30 of the communication device 1 is realized by a processor and a RAM. A processor 91 is a central processing unit (CPU, also referred to as a central processing device, processing device, arithmetic device, microprocessor, microcomputer, processor, and digital signal processor (DSP)) or the like. A RAM 92 is, for example, a random access memory (RAM), a read-only memory (ROM), a flash memory, an erasable programmable read-only memory (EPROM), or an electrically erasable programmable read-only memory (EEPROM (registered trademark)).

[0065] The communication unit 30 of the communication device 1, that is, the base station search unit 31, the communication terminal search unit 32, and the communication control unit 33, are realized by the processor 91 and the working memory 92. That is, programs for operating as the base station search unit 31, the communication terminal search unit 32, and the communication control unit 33 are stored in the working memory 92, and the processor 91 reads and executes the programs, thereby realizing the communication unit 30 of the communication device 1.

[0066] It should be noted that some of the components of the communication unit 30 of the communication device 1 can be realized by dedicated hardware, while the remaining components can be realized by the Fig.12 and the working memory 92. In a case where some or all of the components of the communication unit 30 of the communication device 1 are realized by the processor 91 and the working memory 92, programs stored in the working memory 92 can be provided to a user or the like, for example, in a state where they are written into a storage medium such as a compact disc (CD)-ROM or a digital versatile disc (DVD)-ROM, or they can be provided via a network.

[0067] The configurations described above are merely examples and can be combined with other known technologies. The embodiments can be combined with each other, and some configurations can be omitted or modified without departing from the core concept. For example, in each embodiment, the number of base stations with which the mobile station 12 establishes direct communication is two, but the number of base stations with which the mobile station establishes direct communication may be three or more. List of reference symbols

[0068] 1 communication device; 11-1, 11-2 base station; 12, 13, 13-1, 13-2 mobile station; 20 wireless unit; 30 communication unit; 31 base station search unit; 32 communication terminal search unit; 33 communication control unit; 101, 102, 103 communication system.

Claims

[1] A communication device having a function of directly communicating with a communication terminal which is another communication device, the communication device comprising: a base station search unit to search for base stations with which direct communication is possible; a communication control unit for performing a connection process for connecting to base stations searched by the base station search unit to establish redundantly configured communication paths; and a communication terminal searching unit for searching the communication terminal connected to a base station, wherein in a case where the number of established direct communications with base stations is less than the number required to establish the redundantly configured communication paths, the communication control unit establishes indirect communication with a base station via the communication terminal searched by the communication terminal search unit to establish redundantly configured communication paths. [2] Communication device according to claim 1, wherein the communication terminal search unit collects information about a base station to which the searched communication terminal is connected, and the communication control unit selects a communication terminal that performs a relay process of indirect communication based on the information about the base station collected by the communication terminal search unit. [3] The communication device according to claim 2, wherein the communication control unit selects a communication terminal directly connected to a base station for which establishment of direct communication has failed from among the communication terminals searched by the communication terminal search unit, and establishes indirect communication via the selected communication terminal. [4] The communication device according to any one of claims 1 to 3, wherein after the establishment of the indirect communication, the communication control unit executes a connection process for establishing direct communication with a base station, and in a case where the direct communication with the base station is successfully established, the communication control unit terminates the indirect communication. [5] The communication device according to any one of claims 1 to 4, wherein the communication control unit selects a plurality of communication terminals from the communication terminals searched by the communication terminal search unit, and establishes a plurality of indirect communications each via one of the plurality of selected communication terminals. [6] A communication method performed by a communication device having a function of directly communicating with a communication terminal which is another communication device, the communication method comprising: a base station search step of searching for base stations with which direct communication is possible; a communication control step of performing a connection process for connecting to base stations searched for in the base station search step to establish redundantly configured communication paths; and a communication terminal searching step of searching for the communication terminal connected to a base station, wherein in the communication control step, in a case where a number of established direct communications with base stations is less than a number required for establishing the redundantly configured communication paths, indirect communication with a base station is established via a communication terminal searched for in the communication terminal search step to establish redundantly configured communication paths. [7] A control circuit that controls a communication device having a function of directly communicating with a communication terminal that is another communication device, the control circuit causing the communication device to perform: a base station search step of searching for base stations with which direct communication is possible; a communication control step of performing a connection process for connecting to base stations searched for in the base station search step to establish redundantly configured communication paths; and a communication terminal searching step of searching for the communication terminal connected to a base station, wherein in a case where a number of established direct communications with base stations is less than a number required to establish the redundantly configured communication paths, the communication control step comprises a process of establishing indirect communication with a base station via a communication terminal searched for in the communication terminal search step to establish redundantly configured communication paths. [8] A storage medium storing a program for controlling a communication device having a function of directly communicating with a communication terminal which is another communication device, the program causing the communication device to execute: a base station search step of searching for base stations with which direct communication is possible; a communication control step of performing a connection process for connecting to base stations searched for in the base station search step to establish redundantly configured communication paths; and a communication terminal searching step of searching for the communication terminal connected to a base station, wherein in a case where a number of established direct communications with base stations is less than a number required to establish the redundantly configured communication paths, the communication control step comprises a process of establishing indirect communication with a base station via a communication terminal searched for in the communication terminal search step to establish redundantly configured communication paths.

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