JP4784669B2 - Inter-vehicle communication device, vehicle group management method, and communication control method - Google Patents

Description

  The present invention relates to an inter-vehicle communication device, a vehicle group management method, and a communication control method. In particular, the present invention relates to an inter-vehicle communication (IVC) system applicable to an advanced safety vehicle (ASV) and the like that are being developed for the purpose of improving safety.

  Recently, attention has been focused on a technology called inter-vehicle communication (IVC) in which vehicles directly communicate with each other without using an infrastructure such as a roadside device using an autonomous distributed control type wireless communication technology. The IVC is applied to, for example, ASV and is intended to provide a safe driving support service, an entertainment information service, and the like when the vehicle is traveling. In this regard, for example, the following Non-Patent Document 1 describes a DSRC (Dedicated Short Range Communications) type IVC system.

  This document mentions high speed, large capacity, high quality, wide service area, and high mobility as requirements for communication characteristics required for a DSRC type IVC system. In addition, in the DSRC type IVC system, it is required to promptly exchange information with a vehicle that enters the service area around the own vehicle or leaves the service area. Therefore, a high real-time property is required for the inter-vehicle communication. DSRC refers to short-range short-term communication used in ETC (Electronic Toll Collection System) and the like.

  In the above IVC system, it is assumed that individual vehicles directly communicate with each other. However, when such a method is used, when the vehicle density increases, the communication quality is deteriorated, and a predetermined service may not be provided. Therefore, a method has been devised in which a plurality of vehicles are grouped and communication between vehicles is realized in units of groups (hereinafter referred to as vehicle groups). In this method, for example, communication between vehicles in the same vehicle group is performed using a frequency band assigned for communication in the vehicle group, and communication between vehicles belonging to different vehicle groups is performed in communication between the vehicle groups. Communication is performed using the allocated frequency band.

  In recent years, the use of UHF (Ultra High Frequency) in addition to DSRC has been studied for IVC systems. In view of the propagation characteristics of the frequency band, UHF is used for inter-vehicle communication and DSRC is used for intra-vehicle communication. By using such a method, inter-vehicle communication is hierarchized into inter-vehicle communication and intra-vehicle communication, and the number of vehicles to be provided with services is increased while maintaining communication quality of a predetermined level or higher. Is possible.

Tokuda Kiyohito, “Realization of safety applications in a ubiquitous network environment by DSRC inter-vehicle communication system”, Oki Technical Review, October 2004 / No. 200, Vol. 71, no. 4 (http://www.oki.com/jp/Home/JIS/Books/KENKAI/n200/pdf/200_R07.pdf)

  In the above method, when performing communication between vehicle groups, communication is performed between vehicles (hereinafter referred to as masters) selected within each vehicle group. That is, each master collects the vehicle information transmitted by the vehicles in the vehicle group managed by the own vehicle and transmits it to the master managing other vehicle groups. Each master receives vehicle information sent from a master that manages other vehicle groups, and distributes the information to each vehicle in the own vehicle group. However, in an area where a large number of vehicles are crowded, such as in an urban area, a large amount of vehicle information is collected / distributed to each master via the intra-vehicle communication channel, and transmitted / received via the inter-vehicle communication channel. As a result, the communication traffic volume of each communication channel may exceed an allowable value. As a result, communication errors increase, and a situation in which a predetermined service cannot be provided occurs.

  Accordingly, the present invention has been made in view of the above problems, and an object of the present invention is to suppress an increase in the amount of communication traffic in the inter-vehicle group communication channel or the intra-vehicle group communication channel. Another object of the present invention is to provide a new and improved vehicle-to-vehicle communication device, vehicle group management method, and communication control method.

  In order to solve the above-described problem, according to one aspect of the present invention, the communication traffic amount of the in-vehicle communication channel used for communication between vehicles within the own vehicle group to which one or a plurality of vehicles including the own vehicle belong is determined. Intra-vehicle communication traffic amount detecting means for detecting the communication traffic amount of the inter-vehicle communication channel used for communication between the vehicle traffic detection means for detecting the vehicle and a vehicle belonging to another vehicle group different from the own vehicle group Detecting means; and vehicle number determining means for determining the maximum number of vehicles that are allowed to enter the vehicle group based on the communication traffic volume of the intra-vehicle group communication channel and the inter-vehicle group communication channel. An inter-vehicle communication device is provided.

  With this configuration, it is possible to manage the number of vehicles in the vehicle group in consideration of the communication traffic amount in the intra-vehicle communication channel and the communication traffic amount in the inter-vehicle communication channel. As a result, it becomes possible to avoid deterioration of communication quality as service provision becomes difficult, and a service of a predetermined quality or higher is maintained.

  The vehicle number determining means is configured to determine the maximum number of vehicles to a small value when the communication traffic volume of the intra-vehicle communication channel is large and the communication traffic volume of the inter-vehicle communication channel is small. May be. By adopting such a configuration, it is possible to prevent the communication traffic amount of the intra-vehicle communication channel from becoming too large and the communication quality of the intra-vehicle communication from deteriorating to a predetermined level or less.

  The vehicle number determining means is configured to determine the maximum number of vehicles to a large value when the communication traffic volume of the intra-vehicle communication channel is small and the communication traffic volume of the inter-vehicle communication channel is large. May be. By adopting such a configuration, it is possible to prevent the communication traffic volume of the inter-vehicle group communication channel from becoming excessively large and the communication quality of the inter-vehicle group communication from deteriorating to a predetermined level or less. Further, since the vehicle group becomes large, a vehicle having a better communication environment between the vehicle groups can be selected as a vehicle that carries the communication between the vehicle groups, and the quality of the communication between the vehicle groups can be further improved.

  In addition, the inter-vehicle communication device described above is a vehicle that refuses entry of a new vehicle into the host vehicle group when the number of vehicles in the host vehicle group reaches the maximum number of vehicles determined by the vehicle number determining means. A group management means may be further provided. Thus, the communication quality of in-vehicle communication is maintained at a predetermined level or more by suppressing entry of new vehicles using the vehicle group management means.

  The inter-vehicle communication device may further include a communication unit that generates a beacon frame including the maximum number of vehicles determined by the vehicle number determination unit and transmits the beacon frame at a predetermined time interval. . In this way, by transmitting the information on the maximum number of vehicles in the beacon frame and transmitting it, it becomes possible for other surrounding vehicles to determine whether or not they can enter the vehicle group.

  The in-vehicle communication traffic amount detecting means may be configured to detect the communication traffic amount based on the number of frames received through the in-vehicle communication channel. Further, the inter-vehicle communication traffic amount detecting means may be configured to detect the communication traffic amount based on the number of frames received through the inter-vehicle communication channel. Thus, by detecting the number of received frames of each communication channel, it is possible to easily estimate the communication traffic amount of both channels.

  The vehicle group management means monitors the maximum number of the vehicles determined by the vehicle number determination means and the number of vehicles in the own vehicle group, and the number of vehicles in the own vehicle group is the maximum number of the vehicles. When the number exceeds the number, the number of vehicles in the host vehicle group may be configured to be disengaged so that the number of vehicles in the host vehicle group is equal to or less than the maximum number of the vehicles. By adopting such a configuration, when the amount of communication traffic changes, the number of vehicles in the vehicle group can be dynamically changed, and the number of vehicles in the vehicle group appropriate for the communication traffic amount can be maintained. Become. As a result, communication quality is maintained.

  In order to solve the above-mentioned problem, according to another aspect of the present invention, communication of an in-vehicle communication channel used for communication between vehicles within the own vehicle group to which one or a plurality of vehicles including the own vehicle belong. In-vehicle communication traffic amount detecting means for detecting the traffic amount and between vehicle groups for detecting the communication traffic amount of the inter-vehicle communication channel used for communication between vehicles belonging to other vehicle groups different from the own vehicle group Communication traffic amount detection means, and the intra-vehicle communication channel or the inter-vehicle communication as a transmission channel used when transmitting information based on the communication traffic amount of the intra-vehicle communication channel and the inter-vehicle communication channel There is provided an inter-vehicle communication device comprising transmission channel selection means for selecting a channel.

  With such a configuration, it is possible to use different transmission channels in consideration of the amount of communication traffic in the intra-vehicle group communication channel and the amount of communication traffic in the inter-vehicle group communication channel. As a result, it becomes possible to avoid deterioration of communication quality as service provision becomes difficult, and a service of a predetermined quality or higher is maintained.

  Further, the transmission channel selection means, when the communication traffic amount of the intra-vehicle communication channel is small, and the communication traffic amount of the inter-vehicle communication channel is large, select the intra-vehicle communication channel as the transmission channel, The inter-vehicle communication channel may be selected when the communication traffic amount of the intra-vehicle communication channel is large and the communication traffic amount of the inter-vehicle communication channel is small. By adopting such a configuration, it is possible to prevent the communication traffic volume of the intra-vehicle communication channel from becoming too large and the communication quality of the intra-vehicle communication from deteriorating to a predetermined level or less. Further, the inter-vehicle group communication channel can be used effectively.

  The inter-vehicle communication apparatus may further include a transmission unit that transmits a frame at a frequency of the transmission channel selected by the transmission channel selection unit. By adopting such a configuration, it is possible to selectively use communication channels used when transmitting frames.

  In order to solve the above-mentioned problem, according to another aspect of the present invention, communication of an in-vehicle communication channel used for communication between vehicles within the own vehicle group to which one or a plurality of vehicles including the own vehicle belong. Intra-vehicle communication traffic amount detection step for detecting the traffic amount and between vehicle groups for detecting the communication traffic amount of the inter-vehicle communication channel used for communication between vehicles belonging to other vehicle groups different from the own vehicle group A communication traffic amount detecting step; and a vehicle number determining step for determining a maximum number of vehicles allowed to enter the own vehicle group based on the communication traffic amounts of the intra-vehicle group communication channel and the inter-vehicle group communication channel; A vehicle group management method is provided.

  In order to solve the above-mentioned problem, according to another aspect of the present invention, communication of an in-vehicle communication channel used for communication between vehicles within the own vehicle group to which one or a plurality of vehicles including the own vehicle belong. Intra-vehicle communication traffic amount detection step for detecting the traffic amount and between vehicle groups for detecting the communication traffic amount of the inter-vehicle communication channel used for communication between vehicles belonging to other vehicle groups different from the own vehicle group A communication traffic amount detection step, and the intra-vehicle communication channel or the inter-vehicle communication as a transmission channel used when transmitting information based on the communication traffic amount of the intra-vehicle communication channel and the inter-vehicle communication channel A transmission channel selection step of selecting a channel is provided.

  In order to solve the above problems, according to another aspect of the present invention, a program for causing a computer to realize the functions of the above-described inter-vehicle communication device can be provided. Furthermore, a computer-readable recording medium on which the program is recorded can be provided.

  As described above, according to the present invention, it is possible to suppress an increase in the amount of communication traffic in the vehicle group communication channel or the vehicle group communication channel.

It is explanatory drawing which shows the function structural example of the conventional inter-vehicle communication apparatus. It is explanatory drawing which shows the hardware structural example of a communication apparatus between vehicles. It is explanatory drawing which shows an example of the conventional inter-vehicle communication method. It is explanatory drawing which shows an example of the conventional inter-vehicle communication method. It is explanatory drawing which shows the function structural example of the inter-vehicle communication apparatus which concerns on 1st Embodiment of this invention. It is explanatory drawing which shows the packet structural example which concerns on the same embodiment. It is explanatory drawing which shows the determination method of the maximum vehicle number according to the communication traffic amount which concerns on the embodiment. It is explanatory drawing which shows the flow of the determination process of the maximum vehicle number according to the communication traffic amount which concerns on the embodiment. It is explanatory drawing which shows the function structural example of the inter-vehicle communication apparatus which concerns on 2nd Embodiment of this invention. It is explanatory drawing which shows the determination method of the transmission channel according to the communication traffic amount which concerns on the embodiment. It is explanatory drawing which shows the flow of the determination process of the transmission channel according to the communication traffic amount which concerns on the embodiment.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol.

[About the flow of explanation]
Here, the flow of explanation described below will be briefly described. First, the functional configuration of the conventional inter-vehicle communication device (10) will be described with reference to FIG. Next, a hardware configuration example for realizing the functions of the inter-vehicle communication device will be described with reference to FIG. Next, a conventional inter-vehicle communication method will be described with reference to FIGS. 3 and 4.

  Next, the functional configuration of the vehicle-to-vehicle communication device (100) according to the first embodiment of the present invention will be described with reference to FIG. Moreover, the vehicle-to-vehicle communication method according to the embodiment will be described in detail with reference to FIGS. Next, the functional configuration of the vehicle-to-vehicle communication device (200) according to the second embodiment of the present invention will be described with reference to FIG. The inter-vehicle communication method according to the embodiment will be described in detail with reference to FIGS. 10 and 11.

[Functional Configuration of Conventional Inter-Vehicle Communication Device 10]
First, prior to describing a preferred embodiment of the present invention, a functional configuration of a conventional inter-vehicle communication device 10 will be briefly described in order to clarify differences between the technology according to the embodiment and the conventional technology. . FIG. 1 is an explanatory diagram illustrating a functional configuration example of a conventional inter-vehicle communication device 10.

  As shown in FIG. 1, the inter-vehicle communication device 10 mainly includes a service control unit 12, a vehicle group control unit 14, and an inter-vehicle communication unit 16.

(Service control means 12)
First, the service control unit 12 will be described. The service control means 12 is means for generating information (hereinafter, vehicle information) to be notified to other vehicles in order to provide a predetermined service. The vehicle information includes information related to the position and speed of the host vehicle, information related to a predetermined service, and the like. Examples of the predetermined service include a service that warns the driver that another vehicle is approaching the host vehicle (hereinafter referred to as an approaching vehicle notification service). In the following description, vehicle information generated by the host vehicle may be referred to as host vehicle information.

  Further, the service control unit 12 acquires vehicle information generated by the other vehicle (that is, information about the position and speed of the other vehicle, information about a predetermined service, etc.). In the following description, vehicle information generated by other vehicles may be referred to as other vehicle information. The other vehicle information is acquired using the inter-vehicle communication unit 16 and is input to the service control unit 12 via the data processing unit 22. For example, when providing the approaching vehicle notification service, first, the service control unit 12 determines whether or not the own vehicle and the other vehicle are approaching based on the acquired other vehicle information. When it is determined that the distance between the host vehicle and the other vehicle is approaching, the service control unit 12 warns the driver as necessary.

  Not limited to the above example, the service control unit 12 acquires other vehicle information periodically or at a predetermined timing, and executes processing necessary to provide a predetermined service based on the acquired other vehicle information. . For example, the service control means 12 warns the driver that another vehicle is approaching. Moreover, the service control means 12 produces | generates the own vehicle information which should be notified to another vehicle. The own vehicle information generated by the service control unit 12 is transmitted to the other vehicle via the data processing unit 22 and the inter-vehicle communication unit 16.

(Vehicle group control means 14)
Next, the vehicle group control means 14 will be described. The vehicle group control unit 14 includes a data processing unit 22 and a vehicle group formation unit 24.

(Data processing means 22)
First, the data processing means 22 will be described. The data processing unit 22 selects a vehicle that is a transmission destination of the host vehicle information generated by the service control unit 12, and selects a vehicle that is a transmission source of other vehicle information to be acquired. As described above, the vehicle information generated by the host vehicle is input from the service control unit 12 to the data processing unit 22. Further, the data processing means 22 is inputted with information on the vehicle group to which the host vehicle belongs (hereinafter referred to as host vehicle group information) and vehicle information acquired from the vehicle included in the vehicle group from the vehicle group forming unit 24 described later. The

  When transmitting the own vehicle information, first, the data processing unit 22 selects the vehicle information transmission destination as a vehicle in the vehicle group according to the type of service provided by the service control unit 12, or the vehicle group. Judge whether to make all vehicles including outside vehicles. This determination is made according to whether or not the host vehicle is a master in the vehicle group. For example, when the host vehicle is a master, depending on the type of vehicle information, in addition to the vehicles in the vehicle group, vehicles belonging to other vehicle groups are also included in the transmission destination of the vehicle information. When the transmission destination of the vehicle information is designated in this way, the information on the designated transmission destination is input to the inter-vehicle communication means 16 together with the vehicle information.

  When receiving the other vehicle information, first, the data processing unit 22 selects the vehicle information transmission source (acquisition destination) as a vehicle in the vehicle group according to the type of service provided by the service control unit 12, or Alternatively, it is determined whether to make all vehicles including vehicles outside the vehicle group. This determination is made according to whether or not the host vehicle is a master. For example, when the host vehicle is a master, although depending on the type of vehicle information, in addition to the vehicles in the vehicle group, vehicles belonging to other vehicle groups are also included in the transmission source of the vehicle information. When the transmission source of the vehicle information is specified in this way, information for specifying the specified transmission source is input to the inter-vehicle communication means 16.

(Car group forming means 24)
Next, the vehicle group forming means 24 will be described. The vehicle group forming means 24 performs a process for forming a vehicle group with vehicles existing around the host vehicle, entering a previously formed vehicle group, or leaving the vehicle group. It is. Moreover, the vehicle group formation means 24 sets the vehicle (master) which performs communication between vehicle groups among the vehicles which belong to a vehicle group. For example, the vehicle group forming means 24 sets the vehicle that first formed the vehicle group as the master. Further, when the vehicle set as the master leaves, the vehicle group forming means 24 sets the vehicle that has entered next to the left vehicle as the master. By using such a method, the state where the master is always set in the vehicle group is maintained. Of course, the master setting method is not limited to this.

  In the following description, a vehicle that is not a master among vehicles belonging to a vehicle group may be referred to as a slave. That is, the attribute of the vehicle that belongs to the vehicle group but is not the master is set to the slave. When such an attribute is introduced, the state of each vehicle is classified into three types of attributes (hereinafter sometimes referred to as “state”): master, slave, and outside the vehicle group. Information (hereinafter, state information) indicating the state of the host vehicle set by the vehicle group forming unit 24 in this manner is input to the data processing unit 22. The status information is referred to by the data processing means 22 when the transmission destination or transmission source of the vehicle information is selected.

  For example, when the state of the host vehicle is a slave and the transmission destination vehicle is outside the vehicle group, the data processing means 22 selects the master as the transmission destination of the vehicle information. On the other hand, when the state of the host vehicle is a master and the transmission destination vehicle is outside the vehicle group, the data processing unit 22 selects the master of the other vehicle group as the transmission destination of the vehicle information. Of course, if the transmission destination vehicle is in the vehicle group, the data processing means 22 selects the vehicle as the transmission destination vehicle.

(Vehicle communication means 16)
Next, the inter-vehicle communication means 16 will be described. As described above, vehicle information is input from the data processing unit 22 to the inter-vehicle communication unit 16. When the vehicle information is input from the data processing unit 22, the inter-vehicle communication unit 16 adds information necessary for access control to the vehicle information and generates a frame. This frame is modulated at a predetermined frequency and transmitted to the destination vehicle selected by the data processing means 22. Further, the inter-vehicle communication unit 16 receives a modulation signal of vehicle information transmitted by the transmission source selected by the data processing unit 22 at a predetermined frequency, and demodulates the frame. The inter-vehicle communication unit 16 removes information necessary for access control from the demodulated frame and inputs the information to the data processing unit 22.

  The functional configuration of the conventional inter-vehicle communication device 10 has been described above. As described above, the inter-vehicle communication device 10 has a function of controlling formation of a vehicle group and entry / exit from the vehicle group. The inter-vehicle communication device 10 has a function of setting a vehicle state such as a master in the formed vehicle group. Furthermore, the inter-vehicle communication device 10 has a function of setting a transmission destination of vehicle information necessary for providing a service or a transmission source of vehicle information to be received according to the state of the own vehicle.

  Between vehicles equipped with such an inter-vehicle communication device 10, a vehicle group is formed as necessary, and communication within the vehicle group and communication between the vehicle groups are hierarchized. Therefore, the frequency utilization efficiency when information is transmitted and received between vehicles is improved, and the number of vehicles that can be accommodated in a predetermined frequency band is increased.

[Hardware configuration example]
Next, a hardware configuration capable of realizing the functions of the inter-vehicle communication device 10 and the inter-vehicle communication devices 100 and 200 described later will be described with reference to FIG. FIG. 2 is an explanatory diagram illustrating a hardware configuration example of the inter-vehicle communication devices 10, 100, and 200.

  As shown in FIG. 2, the functions of the inter-vehicle communication devices 10, 100, and 200 include, for example, a GPS receiver H 12, a central processing unit (CPU) H 14, a memory H 16, a communication control unit H 18, and an RF front end circuit. This is realized by hardware resources such as H20 and antenna H22. The central processing unit H14, the memory H16, and the communication control unit H18 are connected via a bus H24.

  The GPS receiver H12 is means for detecting the position of the host vehicle. The GPS receiver H12 is connected to the central processing unit H14. For example, the GPS receiver H12 detects the position of the host vehicle at each time and inputs it to the central processing unit H14. The central processing unit H14 is an arithmetic processing chip. For example, the central processing unit H14 executes predetermined processing using information related to the position of the host vehicle, and stores the processing result in the memory H16 or inputs the processing result to the communication control unit H18.

  As the memory H16, for example, a semiconductor memory such as a RAM (Random Access Memory) or a ROM (Read Only Memory), a magnetic recording medium, an optical recording medium, a magneto-optical recording medium, or the like is used. In the memory H16, for example, relative position information indicating a relative position between vehicles, area range information indicating an area where a service is provided, state information of the own vehicle, vehicle number information of the own vehicle group or another vehicle group, Transmission / reception data and the like are stored. Further, the memory H16 stores the distance from the intersection to the host vehicle estimated based on the information on the position of the host vehicle, the surrounding vehicle density, information used for retransmission control, information used for measurement of communication traffic, and the like. The

  The communication control unit H18 is a control chip that controls the RF front end circuit H20 and the like. The RF front end circuit H20 is a signal processing circuit for performing signal processing such as frequency conversion and signal amplification of an RF signal. For example, the RF front end circuit H20 converts transmission data into an RF signal having a predetermined frequency and outputs the RF signal to the antenna H22. The antenna H22 is a transmission / reception antenna for an RF signal output from the RF front end circuit H20.

  The example of the hardware configuration that can realize the functions of the inter-vehicle communication devices 10, 100, and 200 has been described above.

[Conventional vehicle-to-vehicle communication method]
Next, a conventional inter-vehicle communication method will be briefly described with reference to FIGS. FIG. 3 is an explanatory diagram showing a flow of vehicle information transmission processing in the conventional inter-vehicle communication method. FIG. 4 is an explanatory diagram showing the flow of beacon transmission processing in the conventional inter-vehicle communication method.

(Vehicle information transmission process)
First, referring to FIG. FIG. 3 shows the flow of processing executed when the inter-vehicle communication device 10 transmits vehicle information as the service starts. First, when the service is started, the inter-vehicle communication device 10 determines whether or not to transmit vehicle information of the host vehicle (S12). When the vehicle information is transmitted, the vehicle information is generated by the service control unit 12, and the transmission destination of the vehicle information is selected by the data processing unit 22. Then, the inter-vehicle communication device 10 proceeds to the process of step S14. On the other hand, when not transmitting vehicle information, the inter-vehicle communication apparatus 10 proceeds to the process of step S12 again and determines whether or not to transmit vehicle information.

  When it progresses to step S14, the inter-vehicle communication apparatus 10 transmits the vehicle information produced | generated by the service control means 12 to the transmission destination vehicle selected by the data processing means 22 (S14). At this time, together with the vehicle information generated by the service control means 12, information on the transmission destination selected by the data processing means 22 is input to the inter-vehicle communication means 16. This transmission destination information indicates, for example, whether the transmission destination is a vehicle in the host vehicle group or a vehicle in another vehicle group. Therefore, the vehicle-to-vehicle communication means 16 uses a communication channel used for in-vehicle communication (hereinafter referred to as an in-vehicle communication channel) or a communication channel used for inter-vehicle communication (hereinafter referred to as between vehicle groups) based on the input destination information. Select a communication channel. And the vehicle-to-vehicle communication means 16 transmits vehicle information on the selected communication channel.

  When the vehicle information is transmitted as described above, the inter-vehicle communication device 10 determines whether or not to end a series of processes related to the transmission of the vehicle information (S16). When ending the process, the inter-vehicle communication device 10 ends a series of processes related to transmission of vehicle information. On the other hand, when not terminating the process, the inter-vehicle communication device 10 proceeds to step S12 again and determines whether or not to transmit vehicle information. Thus, the vehicle-to-vehicle communication device 10 can transmit vehicle information efficiently by selectively using the intra-vehicle group communication channel and the inter-vehicle group communication channel according to the transmission destination.

  The above example assumes that the host vehicle is a master. If the host vehicle is a slave, the vehicle information needs to be transmitted to the vehicles in the other vehicle group via the master in order to transmit the vehicle information to the vehicles in the other vehicle group. Therefore, when the host vehicle is a slave, the inter-vehicle communication means 16 transmits vehicle information to the master or destination vehicle using the intra-vehicle communication channel. With such a configuration, the in-vehicle group communication channel and the inter-vehicle group communication channel can be used efficiently.

(About beacon transmission processing)
Reference is now made to FIG. FIG. 4 shows a flow of processing executed when the inter-vehicle communication device 10 transmits a beacon frame as the service starts. In the beacon frame, identification information of the own vehicle that is the transmission source of the frame, identification information of the vehicle group to which the own vehicle belongs, the number of vehicles in the vehicle group to which the own vehicle belongs, and the like are shown. Therefore, the inter-vehicle communication device 10 of each vehicle receives the information of the received beacon frame when forming the vehicle group by the vehicle group forming unit 24 or setting the entry into the vehicle group or the departure from the vehicle group. Refer to

  First, when the service is started, the inter-vehicle communication device 10 determines whether or not to transmit a beacon frame (S22). When transmitting a beacon frame, various information is generated by the service control unit 12 and input to the inter-vehicle communication unit 16. Then, the inter-vehicle communication means 16 adds information necessary for access control to the input information, and generates a beacon frame. The generated beacon frame is transmitted by the vehicle-to-vehicle communication means 16 (S24).

  When the beacon frame is transmitted, the inter-vehicle communication device 10 determines whether or not to end a series of processes related to the transmission of the beacon frame (S26). When ending the process, the inter-vehicle communication device 10 ends a series of processes related to transmission of the beacon frame. On the other hand, when not terminating the process, the inter-vehicle communication device 10 proceeds to step S22 again and determines whether or not to transmit a beacon frame. By transmitting the beacon frame in this way, it becomes possible to grasp the state of the vehicle and the vehicle group around which each vehicle exists, and the formation of the vehicle group and the entry into the vehicle group, or the vehicle group It is possible to efficiently leave the vehicle and eliminate the vehicle group. In the above description, the vehicle information and the beacon are transmitted as separate frames. However, the vehicle information and the beacon may be combined and transmitted as one frame.

  The conventional inter-vehicle communication method has been briefly described above. By using the above method, an efficient communication environment using a vehicle group can be realized. However, if a large number of vehicles are congested in a narrow area, or if all vehicles in the vehicle group transmit vehicle information to the master at the same time, the amount of communication traffic becomes very large, and a service of a predetermined quality It will be difficult to provide.

  Therefore, in a first embodiment described later, a method for imposing a limit on the number of vehicles in the vehicle group according to the communication traffic amount is proposed. Furthermore, in a second embodiment to be described later, a method for appropriately switching control of communication channels according to the amount of communication traffic is proposed. By using these methods, it is possible to improve the communication quality in a situation where vehicles such as an urban area are crowded.

<First Embodiment>
First, a first embodiment of the present invention will be described. The present embodiment is characterized in that the maximum number of vehicles in the vehicle group is determined according to the amount of communication traffic and the number of vehicles belonging to the vehicle group is limited.

[Functional configuration of inter-vehicle communication device 100]
First, the functional configuration of the inter-vehicle communication device 100 according to the present embodiment will be described with reference to FIG. FIG. 5 is an explanatory diagram illustrating a functional configuration example of the vehicle-to-vehicle communication device 100 according to the present embodiment.

  As shown in FIG. 5, the inter-vehicle communication device 100 mainly includes a service control unit 102, a vehicle group control unit 104, an inter-vehicle communication unit 106, and a communication traffic amount measuring unit 108. The main difference from the inter-vehicle communication apparatus 10 shown in FIG. 1 is the function of the vehicle group control means 104 and the presence of the communication traffic amount measuring means 108. The communication traffic volume measuring unit 108 is an example of the intra-vehicle communication traffic volume detection unit and the inter-vehicle communication traffic volume detection unit. The inter-vehicle communication unit 106 is an example of a communication unit.

(Service control means 102)
First, the service control unit 102 will be described. The service control means 102 is means for generating information (vehicle information) to be notified to other vehicles in order to provide a predetermined service. Further, the service control unit 102 acquires vehicle information (other vehicle information) generated by another vehicle via the inter-vehicle communication unit 106. The vehicle information includes information on the position or speed of the host vehicle, information on a predetermined service, and the like. For example, the service control unit 102 refers to other vehicle information together with information related to the own vehicle, and generates information (own vehicle information) necessary to provide a predetermined service. The own vehicle information generated by the service control unit 102 is transmitted to other vehicles via the data processing unit 112 and the inter-vehicle communication unit 106.

(Vehicle group control means 104)
Next, the vehicle group control means 104 will be described. The vehicle group control unit 104 includes a data processing unit 112, a vehicle group formation unit 114, and a vehicle number determination unit 116. The vehicle group forming unit 114 is an example of a vehicle group management unit.

(Data processing means 112)
First, the data processing means 112 will be described. The data processing unit 112 selects a vehicle that is a transmission destination of the host vehicle information generated by the service control unit 102, or selects a vehicle that is a transmission source of other vehicle information to be acquired. As described above, the host vehicle information is input from the service control unit 102 to the data processing unit 112. Further, the data processing unit 112 receives information on the vehicle group to which the host vehicle belongs (own vehicle group information) and vehicle information acquired from the vehicle included in the vehicle group from the vehicle group forming unit 114 described later.

  When transmitting the own vehicle information, first, the data processing unit 112 sets the transmission destination of the own vehicle information to a vehicle in the vehicle group according to the type of service provided by the service control unit 102, or It is determined whether to select all vehicles including vehicles outside the group. This determination is made according to whether or not the host vehicle is a master in the vehicle group. For example, when the host vehicle is a master, depending on the type of vehicle information, in addition to the vehicles in the vehicle group, vehicles belonging to other vehicle groups are also included in the transmission destination of the vehicle information. When the transmission destination of the vehicle information is designated in this way, the information on the designated transmission destination is input to the inter-vehicle communication means 106 together with the vehicle information.

  When receiving other vehicle information, first, the data processing unit 112 sets the vehicle information transmission source (acquisition destination) to a vehicle in the vehicle group according to the type of service provided by the service control unit 102, or Alternatively, it is determined whether to make all vehicles including vehicles outside the vehicle group. This determination is made according to whether or not the host vehicle is a master. For example, when the host vehicle is a master, although depending on the type of vehicle information, in addition to the vehicles in the vehicle group, vehicles belonging to other vehicle groups are also included in the transmission source of the vehicle information. When the transmission source of the vehicle information is designated in this way, information for specifying the designated transmission source is input to the inter-vehicle communication means 106.

(Car group forming means 114)
Next, the vehicle group forming means 114 will be described. The vehicle group formation means 114 is a means for performing a process for forming a vehicle group with vehicles existing around the host vehicle, entering a previously formed vehicle group, or leaving the vehicle group. It is. Moreover, the vehicle group formation means 114 sets the vehicle (master) which performs communication between vehicle groups among the vehicles which belong to a vehicle group. For example, the vehicle group forming means 114 sets the vehicle that first formed the vehicle group as the master. Further, when the vehicle set as the master leaves, the vehicle group forming unit 114 sets the vehicle that has entered next to the left vehicle as the master. The master setting method is not limited to this.

  When the master is set, transmission / reception of vehicle information between vehicle groups is executed through the master. For example, when vehicle information is transmitted from a slave toward a vehicle outside the vehicle group, the vehicle information is once transmitted from the slave to the master, and the vehicle information is transmitted from the master to a vehicle outside the vehicle group. In some cases, the vehicle information is relayed from the master of the own vehicle group to the master of the other vehicle group, and the vehicle information is transferred to the slave of the other vehicle group. By using such a method, intra-car group communication and inter-car group communication are properly used, which contributes to improving communication quality.

  Furthermore, the master manages the configuration of the vehicle group. This management is mainly performed by the master vehicle group forming means 114. For example, when the host vehicle is a master, the vehicle group forming unit 114 performs processing when another vehicle enters or leaves the host vehicle group. At this time, the vehicle group formation unit 114 manages the vehicle group configuration based on the maximum number of vehicles in the vehicle group determined by the vehicle number determination unit 116 described later. The maximum number of vehicles in the vehicle group is the maximum number of vehicles that can be accommodated in the host vehicle group. That is, the vehicle group formation unit 114 does not allow a new vehicle to enter when the number of vehicles in the host vehicle group has reached the maximum number of vehicles in the vehicle group determined by the vehicle number determination unit 116.

  With such a configuration, the number of vehicles in the host vehicle group is limited, so that the amount of information transmitted from the slave to the master using the intra-car group communication channel is limited to a predetermined value or less. As a result, the amount of communication traffic in the in-vehicle communication of the own vehicle group is suppressed to a predetermined value or less, and deterioration of service quality caused by an increase in the communication traffic amount of in-vehicle communication can be reduced. In addition, since the amount of information concentrated on the master is kept within an allowable range, a decrease in service quality accompanying an increase in the processing load on the master is also reduced.

  As described above, the vehicle group formation unit 114 manages the vehicle group based on the maximum number of vehicles in the vehicle group input from the vehicle number determination unit 116. At this time, the vehicle number determining means 116 not only restricts new vehicles entering the vehicle group, but also refers to the maximum number of vehicles determined by the vehicle number determining means 116 according to the change in the communication traffic volume. It is also possible to dynamically reduce the number of vehicles in the vehicle group. For example, when the communication traffic amount in the vehicle group increases and the vehicle number determination unit 116 notifies the maximum number of vehicles smaller than the number of vehicles currently present in the vehicle group, the vehicle group formation unit 114 Some vehicles are made to leave so that the number of vehicles is equal to or less than the notified maximum number of vehicles.

  In such a configuration, the vehicle group formation unit 114 refers to the maximum number of vehicles determined by the vehicle number determination unit 116 at a predetermined cycle or a predetermined timing. Note that the vehicle group forming unit 114 selects a vehicle that leaves the slave as much as possible without leaving the master in the vehicle group as much as possible. Further, as a selection method, for example, a method of accepting an entry request again from a slave in a vehicle group and sequentially accepting entry until reaching the maximum number of vehicles is conceivable. However, it may be configured such that vehicles that manage departure or entry are concentrated on the master, or each slave may be configured to autonomously determine departure or entry.

  In addition to the above, the determination criteria for the leaving vehicle may include the position of each vehicle, the number of vehicles that have established communication (number of links), randomness, and the like. Of course, these elements may be combined to select a leaving vehicle. In addition, assuming that the amount of communication traffic fluctuates frequently, when performing vehicle departure processing or vehicle group reconfiguration processing, a predetermined waiting time may be set before the detached vehicle can re-enter. It is preferable to set a different threshold value for the communication traffic volume serving as the reference for starting the entry process and a threshold value for the communication traffic volume serving as the execution start standard for the leaving process.

  Now, the state information of the host vehicle set by the vehicle group formation unit 114 is input to the data processing unit 112 and is referred to when the transmission destination or transmission source of the vehicle information is selected.

(Vehicle number determination means 116)
Next, the vehicle number determination means 116 will be described. The vehicle number determination means 116 is a means for determining the maximum number of vehicles in the host vehicle group according to the communication traffic volume measured by the communication traffic volume measurement means 108 described later. Information indicating the communication traffic volume of the in-vehicle group communication channel and the inter-vehicle group communication channel is input from the communication traffic amount measuring unit 108 to the vehicle number determining unit 116. Therefore, the vehicle number determination means 116 depends on the communication traffic volume of the intra-vehicle group channel (hereinafter referred to as intra-vehicle communication traffic amount) and the communication traffic amount of the inter-vehicle channel (hereinafter referred to as inter-vehicle communication traffic amount). Determine the maximum number of vehicles in your vehicle group.

(How to determine the maximum number of vehicles in a vehicle group according to the amount of communication traffic)
Here, a method for determining the maximum number of vehicles in the vehicle group according to the communication traffic amount by the vehicle number determination means 116 will be described with reference to FIG. FIG. 7 is an explanatory diagram showing a method for determining the maximum number of vehicles in the vehicle group according to the amount of communication traffic by the vehicle number determination means 116.

  In the example of FIG. 7, an encounter prevention support service at an intersection is assumed as an example of the safe driving support service. Each vehicle (A to G) is assumed to be transmitting its own vehicle information (position, speed, etc. of the own vehicle) by broadcast at a predetermined cycle. In the example of FIG. 7, a road on which six vehicles A to F are located is referred to as a priority side road, and a road on which one vehicle G is located is referred to as a regulation side road. In the following description, it is assumed that the vehicles A to F on the priority road and the vehicle G on the restriction road enter the intersection.

  In the vehicle group, it is assumed that a communication link is formed between adjacent vehicles. And communication performed between vehicles other than an adjacent vehicle shall be implement | achieved when the vehicle located in the middle of both vehicles transfers. For example, the communication between the vehicle A and the vehicle C is realized by the transfer of the vehicle B located between the vehicles A and C. With this configuration, when all the vehicles in the vehicle group try to transmit information to the vehicles outside the vehicle group at the same time, a large number of transfer processes (hops) occur, and communication within the vehicle group occurs. The amount of traffic becomes very large.

(Specific example: When the maximum number of vehicles is increased)
For example, in the case of FIG. 7A, when vehicle information is transmitted from the vehicle F to the vehicle G, the vehicle information is relayed in the order of the vehicles E, D, C, B, A, and G. In this example, the hop number H1 (F, G) when the vehicle information is transmitted from the vehicle F to the vehicle G is 6. However, it should be noted that the communication between the vehicle A and the vehicle G is the inter-group communication. Therefore, the number of hops H1 (F, A) = 6-1 = 5 due to intra-car group communication. Further, when all the vehicles in the vehicle group 1 transmit the vehicle information, the vehicle information is transmitted to the vehicle A in which five vehicles (B to F) are masters. G) is 15. That is, Ti1 (A, F) = H1 (F, A) + H1 (E, A) + H1 (D, A) + H1 (C, A) + H1 (B, A) = 5 + 4 + 3 + 2 + 1 = 15.

  Next, the traffic volume of the vehicle group communication will be described. The following three types of vehicle group communication methods are assumed. The first is i) a method of transmitting vehicle information of all vehicles in the vehicle group. The second is a method in which only a part of vehicles belonging to the vehicle group exchange vehicle information between the vehicle groups. Here, as an example, an encounter collision prevention support service is assumed, and only vehicle information of the leading vehicle in the vehicle group having a high risk of collision with another vehicle is transmitted. The third method is a method in which the master aggregates vehicle information transmitted from all vehicles in the vehicle group and transmits the vehicle information as one vehicle group information to the master of the other vehicle group. That is, only one vehicle group information is transmitted per vehicle group. Here, it is assumed that the size of the vehicle group information is the same as the size of the vehicle information per vehicle.

  In the case of i), since the vehicle information for six vehicles is transmitted by inter-vehicle group communication, the inter-vehicle communication traffic volume To1 (A, G) is 6, which is the same as the number of vehicles. In the case of ii), an inter-vehicle communication traffic amount To1 (A) = 1 is generated when transmitting information of the master (vehicle A) that is the leading vehicle in the vehicle group. In the case of iii), an inter-vehicle communication traffic amount To1 (Group) = 1 occurs when the vehicle group information of the vehicle group 1 is transmitted.

(Specific example: When the maximum number of vehicles is reduced)
On the other hand, when the vehicle group is divided by reducing the maximum number of vehicles in the vehicle group as shown in FIG. 7 (2), the number of hops H2 (F, G) when the vehicle information is transmitted from the vehicle F to the vehicle G is 3. (<H1 (F, G)). Accordingly, the number of hops H2 (F, D) by communication within the vehicle group = 3-1 = 2. Further, the in-vehicle communication traffic amount is 3 when the vehicle information is transmitted to the vehicle D which is the master of the two vehicles (E, F). That is, H2 (F, D) + H2 (E, D) = 2 + 1 = 3. Similarly, the in-vehicle communication traffic amount is 3 when the vehicle information is transmitted to the vehicle A in which the two vehicles (B, C) are masters. Therefore, the in-vehicle communication traffic volume Ti2 (A, F) = 3 + 3 = 6 (<Ti1 (A, F) = when the vehicle information of all the vehicles (A to F) belonging to the vehicle groups 1 and 2 is transmitted. 15).

  Assuming the above three methods as the vehicle group communication method, in the case of i), vehicle information for three vehicles (vehicles D, E, F) is transmitted by vehicle group communication. The traffic amount To2 is 3, which is the same as the number of vehicles. Similarly, when the vehicle information of the vehicles A, B, and C is transmitted by the inter-vehicle communication, the inter-vehicle communication traffic amount is 3, which is the same as the number of vehicles. Therefore, the inter-vehicle communication traffic amount To2 (A, G) = 3 + 3 = 6 (= To1 (A, G)) when the vehicle information of all the vehicles (A to F) belonging to the vehicle groups 1 and 2 is transmitted. It becomes. In the case of ii), an inter-vehicle communication traffic amount To2 (A + D) = 2 (> To1 (A) = 1) occurs when transmitting information of the master (vehicles A and D).

  In the case of iii), an inter-vehicle communication traffic amount To2 (Group) = 2 (> To1 (Group) = 1) is generated when the vehicle group information of the vehicle groups 1 and 2 is transmitted.

  As apparent from the comparison between FIGS. 7A and 7B, the balance between the inter-vehicle communication traffic volume and the intra-vehicle communication traffic volume is adjusted by controlling the maximum number of vehicles in the vehicle group. be able to. That is, if the maximum number of vehicles in the vehicle group is increased, the communication traffic amount in the vehicle group increases, but the communication traffic amount between the vehicle groups can be reduced. On the other hand, when the maximum number of vehicles in the vehicle group is reduced, the communication traffic amount between the vehicle groups increases, but the communication traffic amount in the vehicle group can be reduced.

  Therefore, the vehicle number determination means 116 reduces the maximum number of vehicles in the vehicle group when the communication traffic volume in the vehicle group is large. As a result, the number of hops in the communication route in the vehicle group is reduced, the number of times of transferring frames transmitted by other vehicles in the same vehicle group is reduced, and an increase in the communication traffic amount in the vehicle group can be suppressed. On the contrary, when the communication traffic amount between the vehicle groups is small, the vehicle number determination means 116 increases the maximum number of vehicles in the vehicle group. As a result, an increase in the amount of communication traffic between the vehicle groups can be suppressed. Further, by increasing the vehicle group, a vehicle that is less susceptible to the influence of the shielding object can be set as a master, and therefore, communication can be performed using a better inter-vehicle group communication environment.

  The vehicle number determining means 116 determines the maximum number of vehicles in the vehicle group based on the communication traffic volume, based on a predetermined calculation formula or by referring to a predetermined table, Determine the maximum number of vehicles in the group.

  An example of the predetermined calculation formula is shown below. Let Ta be the upper limit of the in-vehicle communication traffic volume that can satisfy the predetermined communication quality. The master of each vehicle group autonomously determines the maximum number of vehicles in the vehicle group so as to approach the upper limit of the communication traffic amount in the vehicle group. If the maximum number of vehicles in the vehicle group is Y, and the communication traffic volume in the vehicle group per vehicle group is Tg, Tg = 1 + 2 + ... + (Y−1) = (Y−1) × Y / 2 Become. Note that Tg is normalized by the amount of communication traffic per frame. Here, when the total number of vehicles is Na, the total number of vehicle groups is Ng = Na / Y. Since Ta = Tg × Ng, Y = 2Ta / Na + 1 is derived.

  Therefore, the master of each vehicle group can determine the maximum number of vehicles Y in the vehicle group by the following procedures (1) to (3). (1) The upper limit Ta of the in-vehicle communication traffic volume is set in advance (stored in a memory or the like). This value is determined by the radio system (modulation system, bandwidth, etc.). (2) The total number Na of vehicles that can communicate with the vehicle is obtained. It can be obtained from the number of frames received within a predetermined time (assuming that frames with the same transmission source are not counted repeatedly). (3) The maximum number of vehicles Y in the vehicle group is determined from Ta and Na.

  According to the above procedure, when the traffic volume in the vehicle group is large, the maximum number of vehicles in the vehicle group is set to a small value, and when the communication traffic amount in the vehicle group is small, the maximum number of vehicles in the vehicle group is determined to be a large value. It is possible. That is, when the amount of communication traffic in the vehicle group increases due to the merging of vehicles and exceeds the upper limit Tv, the master of each vehicle group keeps the communication traffic amount in the vehicle group at Tv so that the maximum number of vehicles in the vehicle group Decrease. On the other hand, when the amount of communication traffic in the vehicle group decreases due to the discreteness of the vehicle and falls below the upper limit Tv, the master of each vehicle group determines the maximum number of vehicles in the vehicle group so that the communication traffic amount in the vehicle group reaches Tv. Increase.

  As the predetermined table, for example, a table associating the total number Na of vehicles as shown in Table 1 below with the maximum number of vehicles Y in the vehicle group is used. This table is stored in the memory H16, for example. Of course, the specific value of the table and the specific shape of the calculation formula used when the vehicle number determination means 116 determines the number of vehicles in the vehicle group can be changed as appropriate.

  Now, in the case where only a part of the vehicles belonging to the vehicle group ii) exchanges vehicle information between the vehicle groups, or the vehicle information transmitted from all the vehicles in the vehicle group iii) is transmitted by the master. When the information is aggregated and transmitted to the master of another vehicle group as one vehicle group information, the following synergistic effect is obtained. In addition, when collecting vehicle information and producing | generating one vehicle group information, the master may be comprised so that the aggregated vehicle information may be combined or compressed and transmitted. As described above, when the in-vehicle communication traffic volume is large and the inter-vehicle communication traffic volume is small, the vehicle number determination means 116 decreases the maximum number of vehicles in the vehicle group. As the maximum number of vehicles in the vehicle group becomes smaller, an increase in the communication traffic volume in the vehicle group is suppressed, and in the above cases, more vehicle information can be transmitted through the inter-vehicle communication channel. A synergistic effect is possible.

  The function of the vehicle number determination unit 116 has been described above. As already described, information indicating the maximum number of vehicles in the vehicle group determined by the vehicle number determination unit 116 is input to the vehicle group formation unit 114. Then, the vehicle group forming unit 114 manages the number of vehicles in the vehicle group so as not to exceed the maximum number of vehicles determined by the vehicle number determining unit 116. Information indicating the maximum number of vehicles in the vehicle group determined by the vehicle number determination unit 116 is input to the inter-vehicle communication unit 106 through the vehicle group formation unit 114 and the data processing unit 112.

(Vehicle communication means 106)
The vehicle-to-vehicle communication means 106 will be described with reference to FIG. 5 again. As described above, vehicle information is input from the data processing unit 112 to the inter-vehicle communication unit 106. When the vehicle information is input from the data processing unit 112, the inter-vehicle communication unit 106 adds information necessary for access control to the vehicle information and generates a frame. This frame is modulated at a predetermined frequency and transmitted to the destination vehicle selected by the data processing means 112. For example, when the transmission destination is a vehicle in the vehicle group, the frame is modulated with the frequency of the communication channel in the vehicle group. Conversely, if the host vehicle is the master and the transmission destination is a vehicle outside the vehicle group, the frame is modulated at the frequency of the inter-vehicle communication channel.

  Further, the inter-vehicle communication unit 106 receives a modulation signal of vehicle information transmitted at a predetermined frequency by the transmission source selected by the data processing unit 112 and demodulates the frame. Then, the inter-vehicle communication unit 106 removes information necessary for access control from the demodulated frame and inputs the information to the data processing unit 112. Further, the inter-vehicle communication unit 106 notifies the communication traffic amount measuring unit 108 of information used for measuring the communication traffic. For example, the inter-vehicle communication unit 106 inputs a reception notification or a frame transmission waiting time (when CSMA (Carrier Sense Multiple Access) is assumed) to the communication traffic amount measuring unit 108 at the timing of receiving the frame.

(Beacon frame configuration)
Here, a frame configuration of a beacon frame transmitted and received by the inter-vehicle communication means 106 will be briefly described with reference to FIG. FIG. 6 is an explanatory diagram showing a configuration example of a beacon frame transmitted / received by the vehicle-to-vehicle communication unit 106.

  As shown in FIG. 6, the beacon frame includes a MAC header, a transmission source vehicle group ID, a transmission source vehicle ID, the number of vehicles in the vehicle group, the maximum number of vehicles in the vehicle group, and a CRC. The MAC header indicates the source MAC address. The transmission source vehicle group ID is identification information for specifying the transmission source vehicle group. The transmission source vehicle ID is identification information for specifying the transmission source vehicle. The number of vehicles in the vehicle group is the number of vehicles in the vehicle group at the time of transmission of the beacon frame. The maximum number of vehicles in the vehicle group is the maximum number of vehicles in the vehicle group determined by the vehicle number determination means 116.

  CRC is a Cyclic Redundancy Check (Cyclic Redundancy Check) code. This beacon frame is transmitted at a predetermined cycle. As described above, the vehicle position of the host vehicle, the number of vehicles in the vehicle group, the maximum number of vehicles in the vehicle group, and the like are included in the beacon frame as vehicle group management information. It becomes possible to manage the vehicle group. For example, each vehicle can determine whether or not it can enter the vehicle group managed by the master that transmitted the beacon frame. In addition, it replaces with the information on the maximum number of vehicles, and the information which shows the availability of entry into a vehicle group may be contained in the beacon frame.

  The function of the inter-vehicle communication unit 106 has been described above.

(Communication traffic volume measuring means 108)
With reference to FIG. 5 again, the communication traffic amount measuring means 108 will be described. The communication traffic volume measuring means 108 is a means for measuring the communication traffic volume. For example, the communication traffic amount measuring unit 108 measures the number of frames received by the inter-vehicle communication unit 106 within a predetermined time as the communication traffic amount. Naturally, it is considered that the larger the number of received frames, the greater the amount of communication traffic. Further, when CSMA is assumed as the media access method, the communication traffic volume measuring unit 108 measures the transmission waiting time as the communication traffic volume. In the case of CSMA, the transmission waiting time becomes longer as the communication channel is congested. Therefore, the communication traffic amount can be estimated from the length of the transmission waiting time.

  Note that the communication traffic amount measuring means 108 measures the communication traffic amount of the intra-vehicle communication channel and the communication traffic amount of the inter-vehicle communication channel. For example, the in-vehicle communication traffic amount can be estimated by counting the number of frames transmitted through the in-vehicle communication channel. Similarly, the amount of inter-vehicle communication traffic can be estimated by counting the number of frames transmitted through the inter-vehicle communication channel. Information on the in-vehicle communication traffic volume and the inter-vehicle communication traffic volume measured in this way is input to the vehicle number determining means 116. When this information is input, the vehicle number determination means 116 determines the maximum number of vehicles in the appropriate vehicle group according to the amount of communication traffic.

  The functional configuration of the inter-vehicle communication device 100 according to the first embodiment of the present invention has been described above. As described above, the inter-vehicle communication device 100 is characterized by detecting the communication traffic amount of each communication channel and determining the maximum number of vehicles in the vehicle group according to the detection result. In particular, the inter-vehicle communication device 100 maintains the communication quality at a predetermined level or higher by suppressing the maximum number of vehicles in the vehicle group so that the intra-vehicle communication traffic amount or the inter-vehicle communication traffic amount is effectively reduced. .

  In the above description, a configuration is shown in which the master determines the maximum number of vehicles in the vehicle group and notifies the maximum number of vehicles to other vehicles entering the vehicle group. However, a configuration in which the master notifies other vehicles of the maximum number of vehicles in the vehicle group is not essential. For example, another vehicle attempting to enter the vehicle group may be configured to autonomously determine the maximum number of vehicles in the vehicle group and determine whether to enter the vehicle group according to the maximum number of vehicles. . In this case, the information on the maximum number of vehicles is not included in the beacon frame, and the maximum number of vehicles is determined according to the amount of communication traffic measured by other vehicles trying to enter the vehicle group. Even with such a configuration, appropriate vehicle group management according to the amount of communication traffic is realized.

[Flow of processing by inter-vehicle communication device 100]
Here, with reference to FIG. 8, the flow of processing by the above-described inter-vehicle communication device 100 will be described. FIG. 8 is an explanatory diagram showing a flow of processing by the vehicle-to-vehicle communication device 100 described above.

  First, when the service is started, the inter-vehicle communication device 100 determines whether or not to transmit a beacon frame (S102). When transmitting a beacon frame, various types of information are generated by the service control unit 102 and input to the inter-vehicle communication unit 106. Further, the maximum number of vehicles in the vehicle group is determined by the vehicle number determination unit 116 based on the communication traffic amount measured by the communication traffic amount measurement unit 108 (S104). Information indicating the determined maximum number of vehicles in the vehicle group is input to the inter-vehicle communication means 106. Then, the inter-vehicle communication means 106 adds information necessary for access control to the input information, and generates a beacon frame. The generated beacon frame is transmitted by the vehicle-to-vehicle communication means 106 (S106).

  When the beacon frame is transmitted, the inter-vehicle communication device 100 determines whether or not to end a series of processes related to the transmission of the beacon frame (S108). When the process ends, the inter-vehicle communication device 100 ends a series of processes related to transmission of the beacon frame. On the other hand, when not terminating the process, the vehicle-to-vehicle communication device 100 proceeds to step S102 again and determines whether or not to transmit a beacon frame. By transmitting the beacon frame in this way, it becomes possible to know the number of vehicles around each individual vehicle, the state of the vehicle group, whether or not the beacon frame can enter the transmission source vehicle group, and communication traffic. Effective vehicle group management considering quantity is realized.

  The first embodiment of the present invention has been described above. As described above, communication traffic around the host vehicle is detected, and the maximum number of vehicles in the vehicle group is determined based on the detected value, thereby suppressing an increase in the communication traffic volume in the vehicle group or between the vehicle groups. can do. As a result, the communication quality can be maintained at a predetermined level or higher.

Second Embodiment
Next, a second embodiment of the present invention will be described. The present embodiment is characterized in that a communication channel used for transmission of vehicle information is determined according to the amount of communication traffic.

[Functional configuration of inter-vehicle communication device 200]
First, the functional configuration of the inter-vehicle communication device 200 according to the present embodiment will be described with reference to FIG. FIG. 9 is an explanatory diagram illustrating a functional configuration example of the vehicle-to-vehicle communication device 200 according to the present embodiment.

  As shown in FIG. 9, the inter-vehicle communication device 200 mainly includes a service control unit 102, a vehicle group control unit 202, an inter-vehicle communication unit 204, and a communication traffic amount measuring unit 108. The main difference from the inter-vehicle communication device 100 according to the first embodiment described above is the function of the vehicle group control means 202. Therefore, in the following, this difference will be mainly described, and detailed description will be given by attaching the same reference numerals to components having substantially the same function as the inter-vehicle communication device 100 according to the first embodiment. Is omitted. The communication traffic volume measuring unit 108 is an example of the intra-vehicle communication traffic volume detection unit and the inter-vehicle communication traffic volume detection unit. The inter-vehicle communication unit 204 is an example of a transmission unit.

(Vehicle group control means 202)
First, the vehicle group control means 202 will be described. The vehicle group control unit 202 includes a data processing unit 112, a vehicle group formation unit 114, and a transmission channel determination unit 212. The transmission channel determination unit 212 is an example of a transmission channel selection unit.

(Data processing means 112)
First, the data processing means 112 will be described. The data processing unit 112 selects a vehicle that is a transmission destination of the host vehicle information generated by the service control unit 102, or selects a vehicle that is a transmission source of other vehicle information to be acquired. The host vehicle information is input from the service control unit 102 to the data processing unit 112. Further, the data processing unit 112 receives information on the vehicle group to which the host vehicle belongs (own vehicle group information) and vehicle information acquired from the vehicle included in the vehicle group from the vehicle group forming unit 114 described later.

(Car group forming means 114)
Next, the vehicle group forming means 114 will be described. The vehicle group formation means 114 is a means for performing a process for forming a vehicle group with vehicles existing around the host vehicle, entering a previously formed vehicle group, or leaving the vehicle group. It is. Moreover, the vehicle group formation means 114 sets the vehicle (master) which performs communication between vehicle groups among the vehicles which belong to a vehicle group. Further, the master vehicle group forming means 114 manages the configuration of the vehicle group. For example, the vehicle group forming unit 114 performs processing when another vehicle enters or leaves the own vehicle group. However, in the present embodiment, unlike the first embodiment, the maximum number of vehicles in the vehicle group is not set and entry of new vehicles is not restricted.

(Transmission channel determination means 212)
Next, the transmission channel determination unit 212 will be described. The transmission channel determination unit 212 is a unit that determines a transmission channel based on the communication traffic volume measured by the communication traffic volume measurement unit 108. Information indicating the intra-group communication traffic volume and the inter-group communication traffic volume is input from the communication traffic volume measuring unit 108 to the transmission channel determination unit 212. Therefore, the transmission channel determination means 212 determines whether the transmission channel used for transmitting vehicle information is the inter-vehicle group communication channel or the intra-vehicle group communication channel based on the input information. Information on the transmission channel determined by the transmission channel determination unit 212 is input to the inter-vehicle communication unit 204.

(How to determine the transmission channel according to the amount of communication traffic)
Here, with reference to FIG. 10, the transmission channel determination method according to the communication traffic amount by the transmission channel determination means 212 will be described in more detail. FIG. 10 is an explanatory diagram showing a method for determining a transmission channel according to the amount of communication traffic by the transmission channel determination means 212.

  In the example of FIG. 10, an encounter prevention support service at an intersection is assumed as an example of a safe driving support service. Each vehicle (A to G) is assumed to be transmitting its own vehicle information (position, speed, etc. of the own vehicle) by broadcast at a predetermined cycle. In the example of FIG. 7, a road on which six vehicles A to F are located is referred to as a priority side road, and a road on which one vehicle G is located is referred to as a regulation side road. In the following description, it is assumed that the vehicles A to F on the priority road and the vehicle G on the restriction road enter the intersection.

  In the vehicle group, it is assumed that a communication link is formed between adjacent vehicles. And communication performed between vehicles other than an adjacent vehicle shall be implement | achieved when the vehicle located in the middle of both vehicles transfers. For example, the communication between the vehicle A and the vehicle C is realized by the transfer of the vehicle B located between the vehicles A and C. With this configuration, when all the vehicles in the vehicle group try to transmit information to the vehicles outside the vehicle group at the same time, a large number of transfer processes (hops) occur, and communication within the vehicle group occurs. The amount of traffic becomes very large.

(When the transmission channel is determined to be the in-vehicle communication channel)
For example, in the case of FIG. 10A, when vehicle information is transmitted from the vehicle F to the vehicle G, the vehicle information is relayed in the order of the vehicles E, D, C, B, A, and G. In this example, the hop number H1 (F, G) when the vehicle information is transmitted from the vehicle F to the vehicle G is 6. However, it should be noted that the communication between the vehicle A and the vehicle G is the inter-group communication. Therefore, the number of hops H1 (F, A) = 6-1 = 5 due to intra-car group communication. In addition, when all the vehicles in the vehicle group transmit vehicle information, the vehicle information is transmitted to the vehicle A in which five vehicles (B to F) are masters. ) Is 15. That is, Ti1 (A, F) = H1 (F, A) + H1 (E, A) + H1 (D, A) + H1 (C, A) + H1 (B, A) = 5 + 4 + 3 + 2 + 1 = 15.

(Specific example: When the transmission channel is determined as the inter-group communication channel)
On the other hand, when the slave vehicle is permitted to use the inter-vehicle communication channel as shown in FIG. 10 (2), the vehicle information may be transmitted directly from the vehicle F to the vehicle G using the inter-vehicle communication channel. It becomes possible. Therefore, the hop number H2 (F, G) when the vehicle information is transmitted from the vehicle F to the vehicle G is 1 (<H1 (F, G) = 6). Further, when each slave uses the vehicle group communication channel, the six vehicles (A to F) transmit vehicle information to the vehicle G through the vehicle group communication channel. Therefore, the communication traffic volume Ti2 (A, G) of the intra-vehicle communication channel is 0 (<Ti1 (A, G) = 15). However, compared with the case of FIG. 10 (1), the communication traffic volume between vehicle groups becomes large.

  As is clear from the comparison between FIGS. 10 (1) and 10 (2), the balance between the inter-vehicle communication traffic volume and the intra-vehicle communication traffic volume is adjusted by controlling the transmission channel used by each vehicle. be able to. That is, when the inter-vehicle communication channel is used as the transmission channel, the intra-vehicle communication traffic amount can be reduced although the inter-vehicle communication traffic amount increases. On the other hand, when the intra-vehicle communication channel is mainly used as the transmission channel, the intra-vehicle communication traffic amount increases, but the inter-vehicle communication traffic amount can be reduced.

  Therefore, the transmission channel determination means 212 uses the inter-vehicle communication channel as the transmission channel even when the own vehicle is a slave when the intra-vehicle communication traffic amount is large. By adopting such a configuration, the number of hops in the in-vehicle communication path is reduced, the number of times that vehicles other than the transmission source vehicle transfer frames is reduced, and an increase in the in-vehicle communication traffic volume can be suppressed. it can. On the other hand, when the in-vehicle communication traffic amount is small, the transmission channel determining means 212 selects the in-vehicle communication channel as the transmission channel when the own vehicle is a slave. With such a configuration, it is possible to suppress an increase in the amount of communication traffic between vehicle groups, and to transmit vehicle information using a master at a good position in the communication environment between vehicle groups.

  The function of the transmission channel determination unit 212 has been described above. Information indicating the transmission channel determined by the transmission channel determination unit 212 is input to the inter-vehicle communication unit 204.

(Vehicle communication means 204)
The vehicle-to-vehicle communication unit 204 will be described with reference to FIG. 9 again. As described above, vehicle information is input to the inter-vehicle communication unit 204 from the data processing unit 112. When the vehicle information is input from the data processing unit 112, the inter-vehicle communication unit 204 adds information necessary for access control to the vehicle information and generates a frame. This frame is modulated at a predetermined frequency and transmitted to the destination vehicle selected by the data processing means 112. At this time, the vehicle-to-vehicle communication unit 204 transmits the frame at the frequency of the transmission channel determined by the transmission channel determination unit 212. For example, when the vehicle group communication channel is selected as the transmission channel, the frame is transmitted at the frequency of the vehicle group communication channel even if the host vehicle is a slave.

(Communication traffic volume measuring means 108)
Next, the communication traffic amount measuring unit 108 will be described. The communication traffic volume measuring means 108 is a means for measuring the communication traffic volume. For example, the communication traffic amount measuring unit 108 measures the number of frames received by the inter-vehicle communication unit 204 within a predetermined time as the communication traffic amount. Naturally, it is considered that the larger the number of received frames, the greater the amount of communication traffic. Further, when CSMA is assumed as the media access method, the communication traffic volume measuring unit 108 measures the transmission waiting time as the communication traffic volume. In the case of CSMA, the transmission waiting time becomes longer as the communication channel is congested. Therefore, the communication traffic amount can be estimated from the length of the transmission waiting time. The amount of communication traffic measured in this way is input to the transmission channel determination means 212 and used for transmission channel determination processing.

  Heretofore, the functional configuration of the vehicle-to-vehicle communication device 200 according to the second embodiment of the present invention has been described. As described above, the inter-vehicle communication apparatus 200 is characterized in that it detects the communication traffic amount of each communication channel and determines the transmission channel according to the detection result. That is, the inter-vehicle communication device 200 maintains the communication quality at a predetermined level or more by determining the transmission channel so that the intra-vehicle group traffic traffic volume or the inter-vehicle communication traffic volume is effectively reduced.

[Flow of processing by inter-vehicle communication apparatus 200]
Here, the flow of processing performed by the above-described inter-vehicle communication device 200 will be described with reference to FIG. FIG. 11 is an explanatory diagram showing a flow of processing by the vehicle-to-vehicle communication device 200 described above.

  First, when the service is started, the inter-vehicle communication device 200 determines whether or not to transmit vehicle information (S202). When the vehicle information is transmitted, various types of information are generated by the service control unit 102 and input to the inter-vehicle communication unit 204. Further, based on the communication traffic volume measured by the communication traffic volume measuring unit 108, the transmission channel determining unit 212 determines the transmission channel (S204). Information indicating the determined transmission channel is input to the vehicle-to-vehicle communication means 204. Then, the inter-vehicle communication unit 204 adds information necessary for access control to the input information, and generates a frame. The generated frame is transmitted by the inter-vehicle communication unit 204 at the frequency of the transmission channel determined by the transmission channel determination unit 212 (S206).

  When the frame is transmitted, the inter-vehicle communication device 200 determines whether or not to end a series of processes related to the transmission of the vehicle information (S208). When ending the process, the inter-vehicle communication device 200 ends a series of processes related to transmission of vehicle information. On the other hand, when not terminating the process, the inter-vehicle communication device 200 proceeds to step S202 again and determines whether or not to transmit vehicle information. By transmitting vehicle information in this way, it becomes possible to grasp the number of vehicles around which individual vehicles exist and the state of the vehicle group. Further, by determining a transmission channel in consideration of the amount of communication traffic in step S204, communication quality exceeding a predetermined level is maintained.

  The second embodiment of the present invention has been described above. As described above, by detecting the communication traffic around the host vehicle and determining the transmission channel based on the detected value, an increase in the intra-vehicle communication traffic volume or the inter-vehicle communication traffic volume can be suppressed. As a result, the communication quality can be maintained at a predetermined level or higher.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to the example which concerns. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

  For example, in the above description, the configuration for determining the maximum number of vehicles in the vehicle group according to the communication traffic amount and the configuration for switching the transmission channel according to the communication traffic amount have been described separately. It is also possible to configure.

10, 100, 200 Inter-vehicle communication device 12, 102 Service control means 14, 104, 202 Vehicle group control means 16, 106, 204 Inter-vehicle communication means 108 Communication traffic volume measuring means 22, 112 Data processing means 24, 114 Vehicle group formation means 116 Vehicle number determination means 212 Transmission channel determination means H12 GPS receiver H14 Central processing unit H16 Memory H18 Communication control unit H20 RF front end circuit H22 Antenna H24 Bus

Claims (8)

In-vehicle communication traffic volume detection means for detecting the communication traffic volume of the in-vehicle communication channel used for communication between vehicles within the own vehicle group to which one or more vehicles including the own vehicle belong,
An inter-vehicle communication traffic amount detecting means for detecting an inter-vehicle communication channel communication traffic amount used for communication with a vehicle belonging to another vehicle group different from the own vehicle group;
Vehicle number determination means for determining the maximum number of vehicles allowed to enter the vehicle group based on the communication traffic volume of the intra-vehicle group communication channel and the inter-vehicle group communication channel;
Equipped with a,
The vehicle number determination means determines the maximum number of vehicles to a small value when the communication traffic volume of the intra-vehicle communication channel is large and the communication traffic volume of the inter-vehicle communication channel is small. Vehicle-to-vehicle communication device. In-vehicle communication traffic volume detection means for detecting the communication traffic volume of the in-vehicle communication channel used for communication between vehicles within the own vehicle group to which one or more vehicles including the own vehicle belong,
An inter-vehicle communication traffic amount detecting means for detecting an inter-vehicle communication channel communication traffic amount used for communication with a vehicle belonging to another vehicle group different from the own vehicle group;
Vehicle number determination means for determining the maximum number of vehicles allowed to enter the vehicle group based on the communication traffic volume of the intra-vehicle group communication channel and the inter-vehicle group communication channel;
Equipped with a,
The vehicle number determination means determines the maximum number of vehicles to a large value when the communication traffic volume of the intra-vehicle communication channel is small and the communication traffic volume of the inter-vehicle communication channel is large. Vehicle-to-vehicle communication device. The vehicle further comprises vehicle group management means for rejecting entry of a new vehicle into the vehicle group when the number of vehicles in the vehicle group reaches the maximum number of vehicles determined by the vehicle number determination unit. The inter-vehicle communication device according to claim 1 or 2 . The inter-vehicle space according to claim 3 , further comprising a communication unit that generates a beacon frame including the maximum number of vehicles determined by the vehicle number determination unit and transmits the beacon frame at a predetermined time interval. Communication device. The in-vehicle communication traffic amount detecting means detects the communication traffic amount based on the number of frames received through the in-vehicle communication channel,
The inter-vehicle communication device according to claim 3 , wherein the inter-vehicle communication traffic amount detecting means detects the communication traffic amount based on the number of frames received through the inter-vehicle communication channel. The vehicle group management means monitors the maximum number of the vehicles determined by the vehicle number determination means and the number of vehicles in the own vehicle group, and the number of vehicles in the own vehicle group determines the maximum number of vehicles. 4. The inter-vehicle communication device according to claim 3 , wherein when the number of vehicles exceeds the number of vehicles in the host vehicle group, the vehicles in the host vehicle group are separated so that the number of vehicles in the host vehicle group is equal to or less than the maximum number of the vehicles. Intra-vehicle communication traffic amount detection step for detecting the communication traffic amount of the intra-vehicle communication channel used for communication between vehicles within the own vehicle group to which one or more vehicles including the own vehicle belong, and
An inter-vehicle communication traffic amount detection step for detecting an inter-vehicle communication channel communication traffic amount used for communication with a vehicle belonging to another vehicle group different from the own vehicle group;
A vehicle number determination step for determining the maximum number of vehicles allowed to enter the vehicle group based on the communication traffic volume of the intra-vehicle group communication channel and the inter-vehicle group communication channel;
Only including,
The vehicle number determining step is a step of determining the maximum number of vehicles to a small value when the communication traffic volume of the intra-vehicle communication channel is large and the communication traffic volume of the inter-vehicle communication channel is small. A vehicle group management method as a feature. Intra-vehicle communication traffic amount detection step for detecting the communication traffic amount of the intra-vehicle communication channel used for communication between vehicles within the own vehicle group to which one or more vehicles including the own vehicle belong, and
An inter-vehicle communication traffic amount detection step for detecting an inter-vehicle communication channel communication traffic amount used for communication with a vehicle belonging to another vehicle group different from the own vehicle group;
A vehicle number determination step for determining the maximum number of vehicles allowed to enter the vehicle group based on the communication traffic volume of the intra-vehicle group communication channel and the inter-vehicle group communication channel;
Only including,
The vehicle number determination step is a step of determining the maximum number of vehicles to a large value when the communication traffic amount of the intra-vehicle communication channel is small and the communication traffic amount of the inter-vehicle communication channel is large. A vehicle group management method as a feature.

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