COMMUNICATION TERMINAL DEVICE, RELAY DECISION PROGRAM, AND RELAY DECISION METHOD

Abstract

The communication terminal device (101) is mounted on a vehicle (301). When the vehicle (301) enters the information sharing area (31A), the communication terminal device (101) calculates a cost value of 1 or more indicating an index value of whether the vehicle should become a relay station that relays groupcast data received from other vehicles present in the information sharing area (31A) based on an attribute that should be shared by multiple vehicles present in the information sharing area (31A). The communication terminal device (101) determines for itself whether it should become a relay station based on the calculated cost value of 1 or more.

Description

[Technical field]

[0001] The present disclosure relates to a communication terminal device, a relay determination program, and a relay determination method for performing inter-vehicle communication. [Background technology]

[0002] When turning right at an intersection, entering a road from an intersection with poor visibility or a parking lot, etc., there is a risk of overlooking approaching moving objects such as motorcycles, bicycles, and pedestrians that slip through the blind spot formed by other passing vehicles. If moving object detection information on the side of the vehicle detected by a sensor mounted on another vehicle can be shared with surrounding vehicles using vehicle-to-vehicle communication, it will be possible to issue a warning to vehicles turning right at an intersection before the moving object approaches. Therefore, vehicle-to-vehicle communication can support safe driving. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2010-259103 A

[0004] Patent Document 1 describes a technology for selecting a vehicle as a relay vehicle whose difference from the average speed of a vehicle group is equal to or less than a threshold. This technology eliminates the need to frequently reselect vehicles to relay, and reduces the amount of communication and processing required to select a relay vehicle. However, for example, if some of the vehicles that belonged to a vehicle group until approaching an intersection stop in a right-turn lane, the speed difference between the vehicle and the other vehicles in the group becomes large, so the vehicle will be removed from the group and information sharing will become impossible. Also, a vehicle stopped in the oncoming lane at an intersection waiting to turn right is traveling in a different direction. Patent Document 1 does not disclose a method for sharing information with such a vehicle group in the oncoming lane.

[0005] Furthermore, in an information sharing area including an intersection, a stopped vehicle may be more suitable for relaying. However, Patent Document 1 does not disclose or suggest using a stopped vehicle as a relay station. For example, a vehicle waiting to turn right attempts to build a network for sharing information with a vehicle traveling in the oncoming lane in order to obtain moving object detection information in a blind spot from a vehicle in the oncoming lane. At this time, since the vehicle in the oncoming lane moves through the information sharing area and drives away, it is necessary to keep updating the vehicle information present in the information sharing area. In that case, communication traffic due to procedures such as vehicle detection increases. In vehicle-to-vehicle communication, there is a method for determining a relay vehicle called UE-to-UE Relay discovery, which is specified in ProSe. However, in order to determine a relay vehicle, it is necessary to repeatedly execute the relay vehicle discovery procedure each time a vehicle moves through an information sharing area. Furthermore, the procedure for determining the relay vehicle requires that not only vehicles waiting to turn right but all vehicles traveling in the information sharing area frequently execute the relay vehicle determination procedure, which leads to an increase in communication traffic. Summary of the Invention [Problem to be solved by the invention]

[0006] The present disclosure aims to provide a vehicle-to-vehicle communication system that relays broadcast notifications transmitted via group cast, while suppressing an increase in traffic within an information sharing area, and allows broadcast notifications to be shared up to the edges of the information sharing area. [Means for solving the problem]

[0007] The communication terminal device of the present disclosure is mounted on a vehicle. A communication terminal device according to the present disclosure includes: a cost calculation unit that calculates, when a vehicle enters an information sharing area designated as an area in which a plurality of vehicles should share information, a cost value of 1 or more that indicates an index value of whether a vehicle should become a relay station that relays groupcast data received from other vehicles present in the information sharing area, based on an attribute that a plurality of vehicles present in the information sharing area should have in common; a relay determination unit that determines whether a node should become the relay station based on the calculated one or more cost values; Equipped with. Effect of the Invention

[0008] The communication terminal device according to the present disclosure includes a cost calculation unit and a relay determination unit. By installing the communication terminal device in each vehicle of a plurality of vehicles, it is possible to provide a vehicle-to-vehicle communication system that suppresses an increase in traffic and relays a broadcast notification transmitted by groupcast, enabling the broadcast notification to be shared to the edge of an information sharing area. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a block diagram of a communication terminal device 101 according to the first embodiment. [Diagram 2] FIG. 1 is a diagram showing an overview of an inter-vehicle communication system 200 according to a first embodiment. [Diagram 3] FIG. 1 is a diagram according to the first embodiment, showing information sharing area information 30A, information sharing area information 30B, information sharing area information 30C, . . . stored in the information sharing area storage unit 3. [Figure 4] FIG. 2 is a sequence diagram showing the operation of the communication terminal device 101 according to the first embodiment. [Diagram 5] FIG. 10 is a flowchart showing details of step S24, which is an operation of the cost calculation unit 10, in the diagram of the first embodiment. [Figure 6] FIG. 11 is a diagram showing an example in which a groupcast broadcast notification is relayed as a result of the cost calculation unit 10 determining whether or not relaying is required in the first embodiment. [Figure 7] FIG. 11 is a flowchart showing the operation of a communication terminal device according to the first embodiment and the first modified example. [Figure 8] FIG. 10 is a diagram of the first embodiment, showing a sequence of Group Member Discover in the relay vehicle determination procedure defined in ProSe. [Figure 9] FIG. 11 is a flowchart illustrating the operation of a communication terminal device according to the first embodiment and a second modified example. [Figure 10] FIG. 11 is a diagram of the first embodiment, illustrating data relay by a communication terminal device of the inter-vehicle communication system 200 in a second modification. [Figure 11] In the diagram of the first embodiment, a hardware configuration of a communication terminal device 101 is shown. [Figure 12] FIG. 1 is a diagram of the first embodiment, showing a configuration in which the functions of a communication terminal device 101 are realized by hardware. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] In the description of the embodiments and the drawings, the same elements and corresponding elements are designated by the same reference numerals. Descriptions of elements with the same reference numerals will be omitted or simplified as appropriate. In the following embodiments, the word "part" may be interpreted as a "circuit," "step," "procedure," "process," or "circuitry" as appropriate.

[0011] Embodiment 1 The first embodiment described below can use the techniques described in the following reference documents 1 and 2. Note that 3GPP is a registered trademark. [Reference 1] 3GPP TR 23.700-33 Study on system enhancement for Proximity based Services(ProSe) in the 5G System(5GS); Phase 2 (Release 18)

[0012] [Reference 2] 3GPP TS 23.287 Architecture enhancements for 5G System (5GS) to support Vehicle-to-Everything (V2X) services (Release 17)

[0013] Reference 1 is one of the standardization specifications for vehicle-to-vehicle communications by 3GPP. Reference 2 shows one of the standardization specifications that specifies d services for V2X communication by 3GPP. Reference 2 specifies Groupcast as a means of broadcast notification. In the first embodiment, this Groupcast can be used.

[0014] A vehicle-to-vehicle communication system 200 and a communication terminal device according to the first embodiment will be described with reference to Fig. 1 to Fig. 12. In the following first embodiment, the communication terminal device may be described as a relay station, and a vehicle may be described as a relay station, but these two descriptions have the same meaning.

[0015] A plurality of vehicles appear in the inter-vehicle communication system 200 described in the first embodiment. Seven vehicles, vehicle 301 to vehicle 307, are shown as the plurality of vehicles, but seven is an example and the number of vehicles is not limited. The plurality of vehicles are equipped with communication terminal devices. The vehicle 301 is equipped with a communication terminal device 101. The vehicle 302 is equipped with a communication terminal device 102, And so on The vehicle 30i is equipped with a communication terminal device 10i. For purposes of explanation, the multiple vehicles are identified as vehicle 301, vehicle 302, . . . In addition, the communication terminals are differentiated as communication terminal 101, communication terminal 102, . . . , but the multiple communication terminals have the same configuration.

[0016] ***Configuration Description*** 1 is a block diagram of a communication terminal device 101. The communication terminal device 101 includes a wireless communication unit 1, a network control unit 2, an information sharing area storage unit 3, a position monitoring unit 4, a position acquisition unit 5, a transmission request unit 6, a sensor information acquisition unit 7, a received frame monitoring unit 8, a relay determination unit 9, a cost calculation unit 10, a speed acquisition unit 11, a traveling direction acquisition unit 12, a time acquisition unit 13, a specification storage unit 14, and a number storage unit 15.

[0017] The information sharing area storage unit 3, the specification storage unit 14, and the number storage unit 15 are realized by the auxiliary storage device 130 described later. The functions of the wireless communication unit 1, the network control unit 2 to the time acquisition unit 13 are realized by the processor 110 executing a relay determination program 131, as described later.

[0018] FIG. 2 shows an overview of the inter-vehicle communication system 200. FIG. 2 shows lanes 401, 402, 403, 404, and 405. In FIG. 2, a vehicle 301 that has entered an information sharing area 31A on lane 402 is currently located at a position P(t). The information sharing area 31A is an area where a plurality of vehicles present therein should share information. The information sharing area 31A will be described later in the description of the information sharing area storage unit 3. The description will be focused on the communication terminal device 101 mounted on the vehicle 301 that is about to enter the information sharing area 31A. The communication terminal devices mounted on the other vehicles also operate in the same manner as the communication terminal device 101. (1) When entering the information sharing area 31A, the communication terminal devices of all vehicles perform the same network settings. (2) The communication terminal device 101 that enters the information sharing area 31A transmits, by groupcast, a broadcast notification that stores information detected by a sensor mounted on the vehicle 301. The communication terminal devices that have completed the same network settings in the information sharing area 31A can receive broadcast notifications from other communication terminal devices. (3) The communication terminal device 101 in the information sharing area 31A determines whether relaying is required. (4) A communication terminal device 101 that is determined to satisfy the requirements for a relay station becomes a relay station itself and transfers broadcast notifications received from other communication terminal devices 101 by groupcast.

[0019] (Information sharing area memory unit 3) The information sharing area storage unit 3 stores information on the information sharing area. 3 shows the information sharing area information 30A, information sharing area information 30B, information sharing area information 30C, ... stored in the information sharing area storage unit 3. For each information sharing area, the information sharing area information 30A, information sharing area information 30B, information sharing area information 30C, ... is registered in the information sharing area storage unit 3. The information sharing area information 30A will be explained. The information sharing area information 30B, information sharing area information 30C, ... is the same as the information sharing area information 30A.

[0020] The information sharing area information is an area in which communication terminal devices located in the information sharing area can share sensor information, alarms, and the like by broadcasting information. The information sharing area information 30A includes an information sharing area 31A, a network setting 32A, shared information 33A, a weighting coefficient 34A, and a cost calculation threshold 35A. The threshold 35A may be displayed as a threshold TH(35A). The information sharing area information 30A may include information other than the information sharing area 31A to the weighting coefficient 34A.

[0021] The information included in the information sharing area information 30A can be stored in advance in the information sharing area storage unit 3. Alternatively, the information included in the information sharing area information 30A may be acquired by distribution from an information providing server via network communication or by distribution from a roadside device when the vehicle 301 enters the information sharing area 31A. Alternatively, the information included in the information sharing area information 30A may be acquired by distribution from an information providing server via network communication or by distribution from a roadside device when the vehicle 301 is in the vicinity of the information sharing area 31A.

[0022] The information contained in the information sharing area information 30A will be described below. (1) The information sharing area 31A refers to an area where multiple vehicles share information. The information sharing area 31A can be designated by the public institution that manages the area if it is public land, or by the owner that manages the area if it is private land. If the information sharing area 31A is a rectangular area, the four corners can be designated by position coordinates P1, P2, P3, and P4. (Latitude, longitude, altitude) can be used as the position coordinates (X, Y, Z) of the information sharing area 31A. By including altitude in the position coordinates, it is possible to distinguish between an elevated road and a ground road, for example. (2) Network settings 32A are information required for network settings in information sharing area 31A. In Fig. 3, a frequency channel, a bandwidth, and a groupcast ID are shown as examples of network settings 32A. The groupcast ID becomes a destination address. (3) The shared information 33A indicates information to be shared between vehicles present in the information sharing area 31A. In Fig. 3, the shared information 33A indicates a sensor type and an alarm type. Sensor detection information specified by the sensor type is shared, and an alarm specified by the alarm type is shared. That is, the communication terminal device 101 transmits the sensor detection information and the alarm by groupcast in the information sharing area 31A. (4) Weighting coefficient 34A is a coefficient used by cost calculation unit 10 in cost calculation using Equation 1 described later.

[0023] ***Explanation of Operation*** 4 is a sequence diagram showing the operation of the communication terminal device 101 mounted on the vehicle 301. The operation of the communication terminal device 101 will be described with reference to FIG. 4. The operation of the communication terminal device 101 corresponds to a relay determination method. The operation of the communication terminal device 101 is executed by a relay determination program 131.

[0024] <Step S11> In step S11, the location monitoring unit 4 acquires the current location from the location acquisition unit 5. The location monitoring unit 4 searches the information sharing area storage unit 3 and checks which information sharing area the communication terminal device 101 is approaching based on the acquired current location. In this example, the communication terminal device 101 is approaching the information sharing area 31A.

[0025] <Step S12> In step S12, the position monitoring unit 4 acquires, from the information sharing area storage unit 3, the information sharing area information 30A of the information sharing area 31A that the current position is approaching or entering.

[0026] <Step S13> In step S13, the location monitoring unit 4 passes the network setting information 32A of the information sharing area 31A to the network control unit 2, and instructs the network control unit 2 to perform network settings.

[0027] <Step S14> In step S14, the location monitoring unit 4 issues a transmission start command to the sensor information acquisition unit 7 to specify shared information 33A indicating the sensor type and alarm type to be shared in the information sharing area 31A and to instruct the sensor information acquisition unit 7 to transmit these upon detection.

[0028] <Step S15, Step S16> In step S15, when the current location passes through the information sharing area 31A, the location monitoring unit 4 commands the network control unit 2 to cancel the network setting used in the information sharing area 31A. In step S16, the location monitoring unit 4 issues a transmission end command to the sensor information acquisition unit 7 to end the transmission of the specified sensor type and alarm type.

[0029] <Step S17, Step S18> In step S17, the network control unit 2 performs network settings for the wireless communication unit 1 according to the network setting information 32A passed in step S13 from the location monitoring unit 4. In step S18, if the network control unit 2 receives a network setting cancellation command in step S15, it cancels the network setting 32A related to the information sharing area 31A for the wireless communication unit 1. When canceling the network setting, the original network setting used before entering the information sharing area 31A may be restored.

[0030] <Step S19> In step S19, the sensor information acquisition unit 7, in accordance with the transmission start command from the position monitoring unit 4 in step S14, passes the sensor data or alarm data to the transmission request unit 6 each time the specified sensor data or alarm data occurs until a transmission end command is issued.

[0031] <Step S20> In step S20, the transmission request unit 6 stores the sensor data or alarm data passed from the sensor information acquisition unit 7 in a broadcast notification message, passes it to the wireless communication unit 1, and requests groupcast transmission from the wireless communication unit 1. In addition, the transmission request unit 6 passes received frames from other communication terminal devices passed from the relay determination unit 9 to the wireless communication unit 1, as described below, and requests groupcast transmission.

[0032] <Steps S21 to S23> The following steps are relay determination. In step S21, the relay determination unit 9 acquires the information sharing area information 30A via the network control unit 2. In step S22, the relay determination unit 9 acquires, from the received frame monitoring unit 8, a broadcast notification received by groupcast from another vehicle located in the information sharing area 31A. In step S23, upon acquiring the broadcast notification, the relay determination unit 9 passes the information sharing area 31A and weighting coefficient 34A to the cost calculation unit 10 and requests calculation of the total cost value CT.

[0033] <Step S24> In step S24, the cost calculation unit 10 calculates the total cost value CT. The calculation of the total cost value CT by the cost calculation unit 10 will be described later. The cost calculation unit 10 calculates the total cost value CT in response to a request from the relay determination unit 9, and passes the total cost value CT to the relay determination unit 9.

[0034] <Step S25, Step S26> In step S25, the relay determination unit 9 obtains the total cost value CT from the cost calculation unit 10. If the total cost value CT is equal to or greater than the threshold value TH (35A), the relay determination unit 9 determines to relay the broadcast notification received from another vehicle. The relay determination unit 9 obtains this threshold value TH (35A) from the information sharing area information 30A shown in Fig. 3. If it is determined to relay, in step S26, the relay determination unit 9 requests the transmission request unit 6 to transmit the broadcast notification received from the other vehicle by group cast.

[0035] FIG. 5 is a flowchart showing details of step S24, which is the operation of the cost calculation unit 10. With reference to FIG. 5, a calculation method of the total cost value CT by the cost calculation unit 10 will be described. The cost calculation unit 10 has various cost calculation functions for relay station determination. One of the features of the cost calculation unit 10 is that it uses a weighting coefficient for each cost value to reflect characteristics such as the time period and local circumstances in the cost value. When the relay function is enabled, that is, when the vehicle communication terminal device 101 becomes a relay station, the Relay Discovery procedure indicated by ProSe may be executed. Alternatively, the procedure may be omitted and the signal may be forwarded unconditionally.

[0036] When the vehicle 301 enters the information sharing area 31A designated as an area where multiple vehicles should share information, the cost calculation unit 10 performs the following process. Based on an attribute that multiple vehicles located in the information sharing area 31A should have in common, the cost calculation unit 10 calculates a cost value Ci of 1 or more that indicates an index value of whether the vehicle should become a relay station that relays groupcast data received from other vehicles present in the information sharing area 31A. Based on the calculated cost value Ci of 1 or more, the relay determination unit 9 determines whether the communication terminal device 101 should become a relay station. This will be specifically described below.

[0037] 5, the cost calculation unit 10 calculates a sustainability cost value, an efficiency cost value, a communication performance cost value, and a surrounding number cost value. In step S245, the cost calculation unit 10 calculates a total cost value CT using the sustainability cost value, the efficiency cost value, the communication performance cost value, and the surrounding number cost value based on Equation 1 described later.

[0038] As shown in steps S246 to S248, the relay determination unit 9 enables the relay function when the total cost value CT exceeds the threshold value TH (35A), and does not enable the relay function when the total cost value CT is equal to or less than the threshold value TH (35A). In this way, the relay determination unit 9 compares the total cost value CT, which is the sum of cost values ​​equal to or greater than 1, with the threshold value TH (35A), and determines whether the communication terminal device 101 should become a relay station based on the comparison result.

[0039] The following is a specific description of how the cost calculation unit 10 calculates the total cost value CT. The operation of the cost calculation unit 10 is as follows. The cost calculation unit 10 acquires the information of the information sharing area 31A and the weighting coefficient 34A via the relay determination unit 9 (step S23).

[0040] The cost calculation unit 10 acquires various values ​​necessary for calculating Equation 1 described later from the position acquisition unit 5, the speed acquisition unit 11, the traveling direction acquisition unit 12, the current time acquisition unit 13, the specification storage unit 14, and the number storage unit 15. The cost calculation unit 10 calculates a total cost value CT for determining relay station requirements using these various values ​​and the weighting coefficient 34A. The cost calculation unit 10 calculates the total cost value CT in steps S241 to S245 of FIG. 5.

[0041] Each element for determining whether the communication terminal device 101 becomes a relay station is a cost value C(t) at the current time t. When the total cost value CT(t) exceeds a threshold TH (35A), the communication terminal device 101 performs an operation as a relay station. The following formula 1 shows an example of calculation of the total cost value CT(t). The cost calculation unit 10 calculates a sustainability cost value C1(t), an efficiency cost value C2(t), a communication performance cost value C3(t), and a surrounding number cost value C4(t) for each element of sustainability, efficiency, communication performance, and the number of surrounding devices. Furthermore, the cost calculation unit 10 multiplies the cost value Ci(t) by a weighting coefficient ai (i=1, 2, 3, 4) as the priority of each element. The sum of all the cost values ​​Ci(t)*ai taking the priority into consideration is the total cost value CT(t) shown in formula 1. * in formula 1 indicates multiplication. Total cost value CT(t) = Σ[Ci(t)*ai] =C1(t)*a1+C2(t)*a2+C3(t)*a3+C4(t)*a4 (Formula 1) C1(t): persistence cost value at current time t, a1: persistence coefficient C2(t): Efficiency cost value at current time t, a2: Efficiency coefficient C3(t): communication performance cost value at current time t, a3: communication performance coefficient C4(t): Cost value of number of surrounding vehicles at current time t, a4: Coefficient of number of surrounding vehicles

[0042] The cost values ​​of each element are explained below.

[0043] (Persistence cost value C1) The cost calculation unit 10 calculates a predicted staying time ΔT(t) of the vehicle 301 in the information sharing area 31A using the vehicle's position P, speed V, and traveling direction D as attributes. The cost calculation unit 10 calculates a first cost value C1 equivalent to the predicted staying time ΔT(t) from the predicted staying time ΔT(t). This will be specifically described below. The persistence is a predicted residence time ΔT(t) that the vehicle 301 equipped with the communication terminal device 101 is predicted to stay in the currently passing information sharing area 31A at the current time t. The predicted residence time ΔT is calculated from the information sharing area 31A, the position P(t) of the vehicle 301, the speed V(t) of the vehicle 301, and the traveling direction D(t) of the vehicle 301. FIG. 2 shows the position P(t), speed V(t), and traveling direction D(t) of the vehicle 301, and position coordinates P1, P2, P3, and P4 as the information sharing area 31A. The persistence cost value C1(t) is calculated from the predicted residence time ΔT(t). The persistence cost value C1(t) is a cost value equivalent to the predicted residence time ΔT(t). The persistence cost value C1(t) is C1(△T(t))=C1(31A,P(t),V(t),D(t)) This can be expressed as follows. 31A: Information sharing area 31A P(t): Position of the vehicle 301 at the current time t V(t): the speed of the vehicle 301 at the current time t D(t): Direction of travel of the vehicle 301 at the current time t An example of a method for calculating the persistence cost value C1(t) is shown below. The persistence cost value C1(t) is the ratio of the predicted residence time ΔT(t) to the reference value ΔTS(t) as shown in the following formula. C1(t)=△T(t) / △TS(t) Here, for the reference value ΔTS(t), for example, the following (a) or (b) can be used. (a) The reference value △TS(t) is the time it takes to pass through the area in the direction of travel at the legal speed. (b) A value specified by the information sharing area information 30A is used for the reference value ΔTS(t). When using the value specified by the information sharing area information 30A in (b), it is assumed that the reference value ΔTS(t) is registered in the information sharing area information 30A. The above is an example of a method for calculating the persistence cost value C1(t).

[0044] The longer the predicted residence time ΔT(t), the larger the persistence cost value C1 becomes, and the more advantageous it becomes as a relay station requirement for the communication terminal device 101.

[0045] The cost calculation unit 10 acquires the position coordinates P(t) of the vehicle 100 from the position acquisition unit 5, acquires the speed V(t) from the speed acquisition unit 11, acquires the traveling direction D(t) from the traveling direction acquisition unit 12, and acquires the current time from the time acquisition unit 13. The cost calculation unit 10 also acquires the information sharing area 31A and the weighting coefficient 34A from the relay determination unit 9. The cost calculation unit 10 uses these to calculate a predicted residence time ΔT(t) at the current time t, and calculates a persistence cost value C1(t) from the predicted residence time ΔT(t).

[0046] (Efficiency cost value C2) The cost calculation unit 10 determines the communication range 101C of the communication terminal device 101 as an attribute, calculates the difference ΔL(t) between the information sharing area 31A and the communication range 101C, and calculates a second cost value C2 equivalent to the difference ΔL(t) from the difference ΔL(t). A specific description will be given below. The efficiency is the following difference ΔL(t) at the current time t. The difference ΔL(t) will be described with reference to FIG. 2. The vehicle 301 shown by the solid line in FIG. 2 is in a state immediately before stopping in order to proceed from the lane 402 to the lane 405. The cost calculation unit 10 calculates the remaining distance L1(t) from the position P(t) of the vehicle 301 to the edge of the information sharing area 31A in which the vehicle 301 is currently traveling. The cost calculation unit 10 can calculate the remaining distance L1(t) from the information sharing area 31A and P(t). The edge of the information sharing area 31A is determined according to the system design of the inter-vehicle communication system 200. In the example of FIG. 2, the edge of the information sharing area 31A is the position P4 that is the farthest from the position P(t) of the vehicle 301. Therefore, the remaining distance L1(t) is the distance between the position P(t) of the vehicle 301 and the position P4 of the information sharing area 31A.

[0047] Next, the cost calculation unit 10 calculates the difference ΔL(t) between the remaining distance L1(t) and the communication range 101C of the communication terminal device 101 mounted on the vehicle 301. Here, the communication range 101C is the communication range 101C of the communication terminal device 101 mounted on the vehicle 301. The communication range 101C is recorded as one of the specifications in the specification storage unit 14 based on the installation state of the communication terminal device 101 on the vehicle 301. In the example of FIG. 2, the difference ΔL(t) is the distance between the remaining distance L1(t) and a point 407 on the communication range 101C in the direction of the remaining distance L1(t).

[0048] The efficiency cost value C2(t) is calculated from the difference ΔL(t). The efficiency cost value C2(t) is a cost value equivalent to the difference ΔL(t). The smaller the difference ΔL(t), the higher the efficiency cost value C2, which is more advantageous as a relay station requirement. As described above, the cost calculation unit 10 calculates the difference ΔL(t) from the information sharing area 31A and the position P(t) of the vehicle 301, and calculates the efficiency cost value C2(t) using the difference ΔL(t). Since the difference ΔL(t) is determined from the information sharing area 31A and the communication range 101C, the efficiency cost value C2(t) can be expressed as C2(31A, 101C). An example of a method for calculating the efficiency cost value C2(t) is shown below. The efficiency cost value C2(t) is the reciprocal of the absolute value of the difference ΔL(t) as shown in the following formula. C2(t)=1 / |△L(t)| The above is an example of the method for calculating the efficiency cost value C2(t).

[0049] (Communication performance cost value C3) The cost calculation unit 10 determines a communication performance value of the communication terminal device 101 as an attribute, and calculates a third cost value C3 corresponding to the communication performance value from the communication performance value. Specific explanations will be given below. The communication performance is the communication range 101C of the communication terminal device 101 mounted on the vehicle 301. The cost calculation unit 10 calculates a communication performance cost value C3 from the communication range 101C. The communication performance cost value C3 is calculated from the communication range 101C. The communication performance cost value C3 is a cost value corresponding to the communication range 101C. The wider the communication range 101C, the higher the communication performance cost value C3 becomes, and the more advantageous it is as a relay station requirement. The communication range 101C may be indicated by transmission output, antenna installation height depending on the vehicle class, advantageousness of visibility depending on the vehicle class, etc. The cost calculation unit 10 may calculate the communication performance cost value C3 from these data. The cost calculation unit 10 acquires information such as the communication range 101C or the above-mentioned "transmission output, antenna installation height depending on the vehicle class, advantageousness of visibility depending on the vehicle class" from the specification storage unit 14. The cost calculation unit 10 calculates the communication performance cost value C3 using these information. The communication performance cost value C3(t) can be expressed as C3(101C). An example of a method for calculating the communication performance cost value C3(t) is shown below. The communication performance cost value C3(t) is the ratio of the communication range 101C to the "reference value of the communication range" as shown in the following formula. C3(t) = communication range 101C / reference value of communication range Here, the reference value for the communication range may be, for example, the following (a) or (b). (a) Value based on the standard specifications of vehicle models that are widely distributed (e.g., ordinary passenger cars). (b) The value specified in information sharing area information 30A. In addition, in the case where the value specified in (b) the information sharing area information 30A is used, that "value" is registered in the information sharing area information 30A. The above is an example of the method for calculating the communication performance cost value C3(t).

[0050] (Cost value of surrounding vehicles C4) The cost calculation unit 10 identifies the number of detected vehicles detected to be present around the vehicle 301 in the information sharing area 31A as an attribute, and calculates a fourth cost value C4 corresponding to the number of vehicles from the number of vehicles. A specific description will be given below. The number of surrounding vehicles is the number of surrounding communication terminal devices that can directly communicate with vehicle 301. Cost calculation unit 10 determines the cost value from the number of surrounding vehicles. The surrounding number cost value C4 is calculated from the number of surrounding vehicles. The surrounding number cost value C4 is a cost value corresponding to the number of surrounding vehicles. The greater the number of surrounding vehicles, the higher the cost value of communication performance, which is advantageous as a relay station requirement. Regarding the number of surrounding vehicles, received frame monitoring unit 8 monitors packets transmitted from each communication terminal device, and stores the address of the source communication terminal device in number storage unit 15. Cost calculation unit 10 acquires the value of the number of surrounding vehicles from number storage unit 15. Cost calculation unit 10 calculates the surrounding number cost value C4 using the acquired number of surrounding vehicles. An example of a method for calculating the surrounding vehicle number cost value C4 is shown below. The surrounding vehicle number cost value C4 is the ratio of the "surrounding vehicle number" acquired from the vehicle number storage unit 15 to the "reference value of the surrounding maximum vehicle number" as shown in the following formula. C4 = Number of surrounding vehicles / Maximum number of surrounding vehicles Here, the reference value for the number of surrounding vehicles can be, for example, the following (a) or (b). (a) Number of vehicles that can be placed within the area of ​​communication coverage (passenger cars of the same class) (b) Value specified by information sharing area information 30A Incidentally, when (b) a value designated in the information sharing area information 30A is used, it is assumed that the "value" is registered in the information sharing area information 30A. The above is an example of the method for calculating the peripheral vehicle number cost value C4.

[0051] (Weighting coefficient) The cost calculation unit 10 weights the cost values ​​equal to or greater than 1. This will be specifically described below. The weighting coefficients a1, a2, a3, and a4 of each element shown in Equation 1 can be determined according to at least one of the traffic conditions in the information sharing area 31A and the characteristics of the time period. When the weighting coefficients are determined according to the characteristics of the time period, the cost calculation unit 10 obtains the current time from the current time acquisition unit 13, and calculates the cost value using the weighting coefficients given to the time period to which the obtained current time belongs. The time period to which the current time belongs can be specified by the weighting coefficient 34A of the information sharing area information 30A. The weighting coefficient 34A for the information sharing area 31A can be obtained in advance through various acquisition routes such as roadside devices around the information sharing area 31A and servers on the Internet, and can be stored in the information sharing area storage unit 3. The weighting coefficient 34A may also be updated non-periodically. When the weighting coefficient 34A is updated non-periodically, the position monitoring unit 4 may obtain the latest value of the weighting coefficient 34A when approaching the information sharing area 31A, and store and update the weighting coefficient 34A in the information sharing area storage unit 3.

[0052] 6 shows an example in which a groupcast broadcast notification is relayed as a result of the cost calculation unit 10 determining whether or not relaying is required. FIG. 6 corresponds to FIG. (1) Vehicles 301 and 302 are determined as relay stations. Vehicle 301 is determined as a relay station because it stops for a while in lane 402 shown in Fig. 2 and the continuity cost value C1 contributes to it. Vehicle 302 is determined as a relay station because it is a large vehicle and the efficiency cost value C2 and communication performance cost value C3 contribute to it. (2) Fig. 6 shows a communication range 101C of communication terminal device 101, a communication range 102C of communication terminal device 102, and a communication range 103C of communication terminal device 103. The communication range is the reach of Groupcast. (3) In Fig. 6, communication terminal device 103 transmits data 103d by groupcast, and communication terminal device 102 and communication terminal device 101 autonomously relay data 103d. Note that relaying by communication terminal device 104 to communication terminal device 106 is omitted. Data 103d is relayed as follows. (3.1) The vehicle 303 transmits data 103d. (3.2) Data 103d is received by vehicles 302, 304, and 305, which are located in communication range 103C. (3.3) Since vehicle 302 is a relay station, data 103d is relayed to vehicles 301, 303, and 305, which are located in communication range 102C. (3.3) Since vehicle 301 is a relay station, data 103d is relayed to vehicles 302 and 306 located in communication range 101C.

[0053] ***Advantages of the First Embodiment*** In the first embodiment, the cost calculation unit 10 of the communication terminal device 101 determines whether the communication terminal device 101 should become a relay station by the operation shown in Fig. 5. Therefore, the communication terminal device 101 can eliminate the trouble of searching for surrounding communication terminal devices and exchanging information on their positional relationships each time. Then, the communication terminal devices 101, 102, etc. individually determine whether relay is required based on Fig. 5, and only the communication terminal device that determines YES in step S246 becomes a relay station that relays the groupcast. This makes it possible to reduce communication traffic used to update information for determining a relay station. Furthermore, since each communication terminal autonomously determines whether relaying is required, relaying can be performed promptly.

[0054] <Variation 1> FIG. 7 is a flowchart showing the operation of the communication terminal device of the first modification. In the communication terminal device 101 of the first variant example, the relay determination unit 9 compares the received total cost value, which is an index value received from other vehicles and is an index value indicating whether another vehicle should become a relay station, with the total cost value CT, which is the sum of cost values ​​of 1 or more, and determines whether the communication terminal device 101 should become a relay station based on the comparison result. Variation 1 of the communication terminal device will be described with reference to Fig. 7. The communication terminal device 101 will be described as a representative. The communication terminal device 101 performs the same process up to the calculation of the total cost value CT of the relay station requirements. That is, steps S241 to S245 in Fig. 7 are the same as those in the flowchart in Fig. 5.

[0055] When the cost calculation unit 10 calculates the total cost value CT, in step S301 the relay determination unit 9 requests the transmission request unit 6 to transmit the total cost value CT to inform surrounding vehicles. In step S302, the transmission request unit 6 commands the wireless communication unit 1 to transmit. In step S303, the wireless communication unit 1 transmits a broadcast notification of the total cost value CT by groupcast.

[0056] When a communication terminal device 101 receives a broadcast notification of a total cost value CT from a surrounding communication terminal device, the received frame monitoring unit 8 checks the contents of the broadcast notification, and if the total cost value CT is included, the total cost value CT is stored in the number memory unit 15. 7, the relay determination unit 9 compares the total cost value CT for the vehicle 301 with the cost values ​​of other vehicles stored in the vehicle count storage unit 15. Only when the total cost value CT for the vehicle 301 is higher than the cost values ​​of the other vehicles, the relay determination unit 9 determines the communication terminal device 101 to be a relay station and executes relaying (step S305), and does not relay otherwise (step S306).

[0057] Fig. 8 shows a Group Member Discover sequence of a relay vehicle determination procedure defined in ProSe. Each communication terminal device may announce its own total cost value in the sequence shown in Fig. 8. In Fig. 8, the total cost value CT of the communication terminal device 103 is 15, which is the highest, so that the communication terminal device 103 is selected as a relay station. The relay station executes UE-to-UE Relay Discovery.

[0058] ***Effects of Modification 1*** In the first modification, the number of relay stations can be further reduced to a minimum compared to the first embodiment, and therefore, the effect of further reducing communication traffic can be obtained.

[0059] <Variation 2> Fig. 9 is a flow chart for explaining the operation of the communication terminal device of the modified example 2. The communication terminal device of the modified example 2 will be explained with reference to Fig. 9. Fig. 9 is based on the modified example 1. In communication terminal device 101 of modification 2, when relay determination unit 9 receives groupcast data from another vehicle after determining that communication terminal device 101 should become a relay station, relay determination unit 9 checks whether the groupcast data satisfies the data relay conditions. Only when the groupcast data satisfies the data relay conditions, relay determination unit 9 relays the groupcast data. This will be specifically described below.

[0060] In the communication terminal device of the modified example 2, even in the case of a relay station, the broadcast notification is relayed only when the designated data relay condition is satisfied. In other words, even in the case of a relay station, the communication terminal device of the modified example 2 does not relay the broadcast notification when the data relay condition is not satisfied. The separately determined data relay condition is, for example, a condition that the data relayed by the vehicle 301 is limited to data received from a vehicle traveling behind the vehicle 301. As in the modified example 1, the cost calculation unit 10 calculates the total cost value CT. In FIG. 9, steps S241 to S245 are the same as the flowchart in FIG. 5. As in the communication terminal device of the modified example 1, the communication terminal device of the modified example 2 may narrow down the relay stations by informing the surrounding vehicles of the total cost value CT. The communication terminal device described below is the communication terminal device 101.

[0061] When a situation arises where groupcast communication is to be performed due to the occurrence of a detection event from the sensor information acquisition unit 7, the transmission request unit 6 stores the data relay conditions for the notification direction and the location coordinates of the sender in a broadcast notification and causes the wireless communication unit 1 to transmit the same in groupcast (steps S302A, 303A). The data relay conditions are assumed to be included in advance in the information sharing area information 30A. As an example of the data relay conditions, if the sensor information is to be disseminated from the rear to the front in the vehicle travel direction, the transmission request unit 6 stores the azimuth angle value corresponding to the front as a data relay condition in the broadcast notification. If the sensor information is to be disseminated from the front to the rear in the vehicle travel direction, the transmission request unit 6 stores the azimuth angle value corresponding to the rear as a data relay condition in the broadcast notification.

[0062] When communication terminal device 101 is a relay station, before relaying a broadcast notification by groupcast transmission, in step S401, relay determination unit 9 determines whether the broadcast notification satisfies the data relay conditions. That is, when a broadcast notification to be relayed is received from another communication terminal device located in the transmission specified direction (forward in the traveling direction) of the data relay conditions from the position of communication terminal device 101, relay determination unit 9 determines that the broadcast notification does not need to be relayed and does not relay the broadcast notification (NO in step S401). On the other hand, when a broadcast notification to be relayed is received from another communication terminal device that is not located in the transmission direction specified by the data relay condition (forward in the direction of travel) relative to the position of communication terminal device 101, relay determination unit 9 determines that the data relay is satisfied and relays the broadcast notification by group cast (YES in step S401). If the relay determination unit 9 determines that the data relay conditions are met, then, at the time of relaying, the transmission request unit 6 rewrites the source location coordinates of the data relay conditions contained in the received broadcast notification with the location coordinates of the communication terminal device 101, and then relays the broadcast notification by group cast (steps S402A, S403A).

[0063] ***Effects of Modification 2*** Fig. 10 shows data relay by the communication terminal device of the inter-vehicle communication system 200 in the second modification, and corresponds to Fig. 6. As shown in Fig. 10, the broadcast notification is autonomously relayed only in the specified transmission direction, so that relay in the opposite direction where notification is not required can be omitted. That is, in the example of Fig. 10, data is relayed from the rear to the front with respect to the vehicle travel direction. Therefore, in the second modification, it is possible to obtain an effect of further suppressing communication traffic occurring within the information sharing area 31A compared to the communication terminal device 101 in the first embodiment and the first modification.

[0064] <Hardware configuration of communication terminal device> 11 shows a hardware configuration of the communication terminal device 101. The hardware configuration of the communication terminal device 101 will be described with reference to FIG.

[0065] The communication terminal device 101 is a computer. The communication terminal device 101 includes a processor 110. The communication terminal device 101 includes multiple pieces of hardware in addition to the processor 110. The multiple pieces of hardware are a main memory device 120, an auxiliary memory device 130, an input interface 140, an output interface 150, and a communication interface 160. The processor 110 is connected to the other hardware via a signal line 170 and controls the other hardware.

[0066] The communication terminal device 101 includes, as functional elements, a wireless communication unit 1, a network control unit 2, a position monitoring unit 4, a position acquisition unit 5, a transmission request unit 6, a sensor information acquisition unit 7, a received frame monitoring unit 8, a relay determination unit 9, a cost calculation unit 10, a speed acquisition unit 11, a traveling direction acquisition unit 12, and a time acquisition unit 13. The functions of the wireless communication unit 1, the network control unit 2, the position monitoring unit 4, the position acquisition unit 5, the transmission request unit 6, the sensor information acquisition unit 7, the received frame monitoring unit 8, the relay determination unit 9, the cost calculation unit 10, the speed acquisition unit 11, the traveling direction acquisition unit 12, and the time acquisition unit 13 are realized by a relay determination program 131.

[0067] The processor 110 is a device that executes a relay determination program 131. The processor 110 executes the relay determination program 131 to realize the functions of a wireless communication unit 1, a network control unit 2, a position monitoring unit 4, a position acquisition unit 5, a transmission request unit 6, a sensor information acquisition unit 7, a received frame monitoring unit 8, a relay determination unit 9, a cost calculation unit 10, a speed acquisition unit 11, a traveling direction acquisition unit 12, and a time acquisition unit 13. The processor 110 is an IC (Integrated Circuit) that performs arithmetic processing. Specific examples of the processor 110 are a CPU (Central Processing Unit), a DSP (Digital Signal Processor), and a GPU (Graphics Processing Unit).

[0068] Specific examples of the main memory device 120 include a static random access memory (SRAM) and a dynamic random access memory (DRAM). The main memory device 120 holds the results of calculations by the processor 110.

[0069] The auxiliary storage device 130 is a storage device that stores data in a non-volatile manner. A specific example of the auxiliary storage device 130 is a hard disk drive (HDD). The auxiliary storage device 130 may also be a portable recording medium. Examples of portable recording media include a Secure Digital (SD) memory card, a NAND flash, a flexible disk, an optical disk, a compact disk, a Blu-ray (Blu-ray) disk, and a digital versatile disk (DVD). The auxiliary storage device 130 stores a relay determination program 131. The auxiliary storage device 130 also realizes the information sharing area storage unit 3, the specification storage unit 14, and the number storage unit 15.

[0070] The input interface 140 is a port through which data is input from each device. The output interface 150 is connected to various devices. The output interface 150 is a port through which the processor 110 outputs data to the various devices. The communication interface 160 is a communication port through which the processor communicates with other communication terminal devices 101. The communication interface 160 is also a communication port through which the processor communicates with various sensors.

[0071] The processor 110 loads the relay determination program 131 from the auxiliary storage device 130 to the main storage device 120. The processor 110 reads the loaded relay determination program 131 from the main storage device 120 and executes it. In addition to the relay determination program 131, an OS (Operating System) is also stored in the main storage device 120. The processor 110 executes the relay determination program 131 while executing the OS. The communication terminal device 101 may include a plurality of processors that replace the processor 110. These plurality of processors share the execution of the relay determination program 131. Each processor is a device that executes the relay determination program 131, just like the processor 110. Data, information, signal values, and variable values ​​used, processed, or output by the relay determination program 131 are stored in the main storage device 120, the auxiliary storage device 130, or a register or cache memory in the processor 110.

[0072] The relay determination program 131 is a program that causes a computer to execute each process, procedure, or step of the wireless communication unit 1, network control unit 2, position monitoring unit 4, position acquisition unit 5, transmission request unit 6, sensor information acquisition unit 7, received frame monitoring unit 8, relay determination unit 9, cost calculation unit 10, speed acquisition unit 11, traveling direction acquisition unit 12, and time acquisition unit 13, where "part" is replaced with "processing," "procedure," or "step."

[0073] The relay determination method is a method carried out by the communication terminal device 101, which is a computer, executing the relay determination program 131. The relay determination program 131 may be provided in a state stored in a computer-readable recording medium, or may be provided as a program product.

[0074] <Hardware configuration supplement> 11, the functions of the communication terminal device 101 are realized by software. However, the functions of the communication terminal device 101 may be realized by hardware. Fig. 12 shows a configuration in which the functions of the communication terminal device 101 are realized by hardware. The electronic circuit 500 in Fig. 12 is a dedicated electronic circuit that realizes the functions of the wireless communication unit 1, the network control unit 2, the information sharing area storage unit 3, the position monitoring unit 4, the position acquisition unit 5, the transmission request unit 6, the sensor information acquisition unit 7, the received frame monitoring unit 8, the relay determination unit 9, the cost calculation unit 10, the speed acquisition unit 11, the traveling direction acquisition unit 12, the time acquisition unit 13, the specification storage unit 14, and the number storage unit 15 of the communication terminal device 101. The electronic circuit 500 is connected to a signal line 501. Specifically, the electronic circuit 500 is a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, a logic IC, a GA, an ASIC, or an FPGA. GA is an abbreviation for Gate Array. ASIC is an abbreviation for Application Specification Integrated Circuit. FPGA is an abbreviation for Field-Programmable Gate Array. The functions of the components of the communication terminal device 101 may be realized by one electronic circuit, or may be realized by distributing them among multiple electronic circuits. Also, some of the functions of the components of the communication terminal device 101 may be realized by electronic circuits, and the remaining functions may be realized by software.

[0075] Each of the processor 110 and the electronic circuit 500 is also called a processing circuitry or a circuitry. In the communication terminal device 101, the functions of the wireless communication unit 1, the network control unit 2, the information sharing area storage unit 3, the position monitoring unit 4, the position acquisition unit 5, the transmission request unit 6, the sensor information acquisition unit 7, the received frame monitoring unit 8, the relay determination unit 9, the cost calculation unit 10, the speed acquisition unit 11, the traveling direction acquisition unit 12, the time acquisition unit 13, the specification storage unit 14, and the number storage unit 15 may be realized by the circuitry.

[0076] The embodiment and modified examples 1 and 2 of the present disclosure have been described above. Some of these embodiments and modified examples 1 and 2 may be combined and implemented. Also, any one or some of them may be partially implemented. Note that the present disclosure is not limited to the above embodiment and modified examples 1 and 2, and various modifications are possible as necessary. [Explanation of symbols]

[0077] 1 wireless communication unit, 2 network control unit, 3 information sharing area storage unit, 4 position monitoring unit, 5 position acquisition unit, 6 transmission request unit, 7 sensor information acquisition unit, 8 received frame monitoring unit, 9 relay determination unit, 10 cost calculation unit, 11 speed acquisition unit, 12 direction acquisition unit, 13 time acquisition unit, 14 specification storage unit, 15 number of vehicles storage unit, 110 processor, 120 main storage unit, 130 auxiliary storage unit, 140 input interface, 150 output interface, 160 communication interface, 170 signal line, 101, 102, 103, 104, 105, 106, 107 communication terminal device, 101C, 102C, 103C communication range, 103d data, 200 vehicle-to-vehicle communication system, 301, 302, 303, 304, 305, 306, 307 Vehicles, 401,402,403,403,405 Lanes, 406 Points, 500 Electronic circuits, 501 Signal lines.

Claims

1. In a communication terminal device mounted on a vehicle, a cost calculation unit that calculates, when a vehicle enters an information sharing area designated as an area in which a plurality of vehicles should share information, one or more cost values ​​indicating an index value of whether a vehicle should become a relay station that relays groupcast data received from other vehicles present in the information sharing area, based on an attribute that the plurality of vehicles present in the information sharing area should have in common; a relay determination unit that determines whether a node should become the relay station based on the calculated one or more cost values; Equipped with The cost calculation unit A communication terminal device that calculates a predicted residence time of the vehicle in the information sharing area using the position, speed, and direction of travel of the vehicle as the attributes, and calculates a first cost value corresponding to the predicted residence time from the predicted residence time.

2. In a communication terminal device mounted on a vehicle, a cost calculation unit that calculates, when a vehicle enters an information sharing area designated as an area in which a plurality of vehicles should share information, one or more cost values ​​indicating an index value of whether a vehicle should become a relay station that relays groupcast data received from other vehicles present in the information sharing area, based on an attribute that the plurality of vehicles present in the information sharing area should have in common; a relay determination unit that determines whether a node should become the relay station based on the calculated one or more cost values; Equipped with The cost calculation unit The communication terminal determines a communication range of the communication terminal as the attribute, calculates a difference between the information sharing area and the communication range, and calculates a second cost value corresponding to the difference from the difference.

3. The cost calculation unit 3. The communication terminal device according to claim 1, further comprising: a communication performance value of the communication terminal device as the attribute; and a third cost value corresponding to the communication performance value is calculated from the communication performance value.

4. The cost calculation unit The communication terminal device according to claim 1 or claim 2, further comprising: identifying the number of detected vehicles detected to be present around the vehicle in the information sharing area as the attribute; and calculating a fourth cost value corresponding to the number from the number.

5. The cost calculation unit 3. The communication terminal device according to claim 1, wherein the one or more cost values ​​are weighted.

6. The relay determination unit is 3. The communication terminal device according to claim 1, further comprising: a total cost value, which is a sum of the one or more cost values, compared with a threshold value; and a determination as to whether the communication terminal device should become the relay station based on a comparison result.

7. The relay determination unit is A communication terminal device as described in claim 1 or 2, which compares a received total cost value, which is an index value for whether the other vehicle should become a relay station and is an index value received from the other vehicle, with a total cost value, which is the sum of the one or more cost values, and determines whether the other vehicle should become a relay station based on the comparison result.

8. The relay determination unit is 3. The communication terminal device according to claim 1, wherein when groupcast data is received from the other vehicle after it has been determined that the vehicle should become the relay station, the communication terminal device checks whether the groupcast data satisfies a data relay condition, and relays the groupcast data only if the groupcast data satisfies the data relay condition.

9. A communication terminal device, which is a computer mounted on a vehicle, a cost calculation process for calculating, when a vehicle enters an information sharing area designated as an area in which a plurality of vehicles should share information, one or more cost values ​​indicating an index value of whether a vehicle should become a relay station that relays groupcast data received from other vehicles present in the information sharing area, based on an attribute that the plurality of vehicles present in the information sharing area should have in common; a relay determination process for determining whether a station should become the relay station based on the calculated one or more cost values; A relay determination program for executing In the cost calculation process, A relay determination program that calculates a predicted residence time of the vehicle in the information sharing area using the position, speed, and direction of travel of the vehicle as the attributes, and calculates a first cost value equivalent to the predicted residence time from the predicted residence time.

10. A communication terminal device, which is a computer mounted on a vehicle, a cost calculation process for calculating, when a vehicle enters an information sharing area designated as an area in which a plurality of vehicles should share information, one or more cost values ​​indicating an index value of whether a vehicle should become a relay station that relays groupcast data received from other vehicles present in the information sharing area, based on an attribute that the plurality of vehicles present in the information sharing area should have in common; a relay determination process for determining whether a station should become the relay station based on the calculated one or more cost values; A relay determination program for executing In the cost calculation process, a relay determination program that determines a communication range of the communication terminal device as the attribute, calculates a difference between the information sharing area and the communication range, and calculates a second cost value corresponding to the difference from the difference.

11. A communication terminal device which is a computer mounted on a vehicle, When a vehicle enters an information sharing area designated as an area in which a plurality of vehicles should share information, one or more cost values ​​are calculated based on attributes that a plurality of vehicles located in the information sharing area should have in common, which indicate an index value as to whether the vehicle should become a relay station that relays groupcast data received from other vehicles present in the information sharing area; A relay determination method for determining whether a station should become a relay station based on the calculated one or more cost values, The communication terminal device, A relay determination method that calculates a predicted residence time of the vehicle in the information sharing area using the position, speed, and direction of travel of the vehicle as the attributes, and calculates a first cost value corresponding to the predicted residence time from the predicted residence time.

12. A communication terminal device which is a computer mounted on a vehicle, When a vehicle enters an information sharing area designated as an area in which a plurality of vehicles should share information, one or more cost values ​​are calculated based on attributes that a plurality of vehicles located in the information sharing area should have in common, which indicate an index value as to whether the vehicle should become a relay station that relays groupcast data received from other vehicles present in the information sharing area; A relay determination method for determining whether a station should become a relay station based on the calculated one or more cost values, The communication terminal device, A relay determination method that determines a communication range of the communication terminal device as the attribute, calculates a difference between the information sharing area and the communication range, and calculates a second cost value corresponding to the difference from the difference.

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