JP4678049B2 - Inter-vehicle communication device and access control method using inter-vehicle communication device - Google Patents

Description

  The present invention relates to an inter-vehicle communication device and an access control method using the inter-vehicle communication device. 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, high real-time properties are also required for the above communication characteristics.

  DSRC refers to short-range short-term communication used in ETC (Electronic Toll Collection System) and the like. However, the IVC system may use a communication band such as UHF (Ultra High Frequency) in addition to the DSRC. In view of this, development of a technology capable of realizing desired communication characteristics by efficiently using such a plurality of communication bands has been energetically advanced.

  Regarding vehicle-to-vehicle communication technology, Patent Document 1 below discloses a technology for calculating vehicle density based on a vehicle position, a traveling speed, and the like. Further, this document discloses a technique for transmitting time information used when periodically transmitting vehicle position data according to vehicle density. The technology described in this document is intended to detect a traffic jam condition using inter-vehicle communication and efficiently transmit vehicle information. In other words, the technique described in this document relates to a technique for determining a traffic situation based on vehicle position information and adjusting the frequency of periodic transmission according to the traffic situation.

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) JP 2007-143121 A

  As described above, when the vehicle density increases, the amount of communication traffic increases and the frequency of occurrence of communication failures increases. In addition, when the carrier detection multiple access (CSMA) method is adopted, when the vehicle density increases, the number of vehicles within the carrier sense range increases, thereby increasing communication failure due to frame collision. . Furthermore, if the carrier sense range is set wider than necessary, the number of vehicles subject to carrier sense increases, and when these vehicles transmit, the own vehicle cannot be transmitted, resulting in increased communication failure due to timeout.

  Accordingly, the present invention has been made in view of the above problems, and an object of the present invention is to improve communication quality by appropriately setting communication according to the vehicle density and the position of the host vehicle in the service area. It is an object of the present invention to provide a new and improved vehicle-to-vehicle communication device and an access control method using the vehicle-to-vehicle communication device.

In order to solve the above problems, according to an aspect of the present invention, there is provided a vehicle density detection means for detecting a vehicle density within a predetermined range based on the position of the host vehicle, which is an inter-vehicle communication device mounted on a vehicle. Carrier sense level setting means for setting a carrier sense level based on the vehicle density detected by the vehicle density detection means, and a reception signal level is set by the carrier sense level setting means before the frame is transmitted. Carrier sense execution means for determining whether the carrier sense level is below the carrier sense level , wherein the carrier sense level setting means sets the carrier sense level based on at least the distance from the approximate center of the intersection to the host vehicle. An inter-vehicle communication device is provided.

Further, the inter-vehicle communication device described above is based on position detection means for detecting the position of the own vehicle and whether or not the own vehicle exists within a predetermined service area based on the position of the own vehicle detected by the position detection means. And an area detecting means for detecting the above. The predetermined service area may be set to include the intersection. In this case, the carrier sense level setting means detects the vehicle within the predetermined service area detected by the position detecting means when the area detecting means determines that the host vehicle is present in the predetermined service area. The carrier sense level is set based on the position of the vehicle and the vehicle density.

  The inter-vehicle communication device includes a vehicle number calculation unit that calculates the number of vehicles within a range defined by a predetermined carrier sense radius based on the vehicle density detected by the vehicle density detection unit, and the vehicle number calculation. There may be further provided carrier sense radius changing means for changing the carrier sense radius so that the number of vehicles calculated by the means is smaller than the number of vehicles that can be accommodated in the predetermined band. In this case, the carrier sense level setting means sets the carrier sense level so that a vehicle within a range defined by the carrier sense radius after being changed by the carrier sense radius changing means becomes a target of carrier sense. .

In order to solve the above problem, according to another aspect of the present invention, there is provided an inter-vehicle communication device mounted on a vehicle, the position detecting unit for detecting the position of the host vehicle, and the position detecting unit. An area detecting means for detecting whether or not the own vehicle exists within a predetermined service area based on the position of the own vehicle, and determining that the own vehicle exists within the predetermined service area by the area detecting means; A carrier sense level setting means for setting a carrier sense level based on the position of the host vehicle in the predetermined service area detected by the position detection means, and a reception signal before the frame is transmitted. Carrier sense execution means for determining whether a level is lower than a carrier sense level set by the carrier sense level setting means; Wherein the predetermined service area is set so as to include an intersection, the carrier sense level setting means sets the carrier sense level on the basis of the approximate center of at least the intersection of the distance to the vehicle, inter-vehicle A communication device is provided.

  Further, the inter-vehicle communication device has a predetermined reception quality detected by the destination vehicle when the signal transmitted from the host vehicle and the signal transmitted from the other vehicle are transmitted to the destination vehicle of the frame. Interfering vehicle detection means for detecting the other vehicle that is of quality, distance from the other vehicle detected by the interference vehicle detection means to the approximate center of the intersection, and distance from the own vehicle to the approximate center of the intersection Carrier sense radius setting means for setting a value obtained by adding to the carrier sense radius. In this case, the carrier sense level setting means sets the carrier sense level so that a vehicle within a range defined by the carrier sense radius set by the carrier sense radius setting means becomes a carrier sense target.

  Further, the vehicle density detection means may be configured to detect the vehicle density based on a traveling speed of a vehicle located within the predetermined range.

  The vehicle density detection means may be configured to detect the vehicle density based on the number of frames received from another vehicle.

  The vehicle density detection means may be configured to detect the vehicle density based on position information exchanged with another vehicle.

In order to solve the above problem, according to another aspect of the present invention, there is provided an access control method using an inter-vehicle communication device mounted on a vehicle, wherein the vehicle density is within a predetermined range based on the position of the host vehicle. Vehicle density detection step, carrier sense level setting step in which the carrier sense level is set based on the vehicle density detected in the vehicle density detection step, and the received signal level before the frame is transmitted. look including a carrier sense execution step of whether below the carrier sense level set by the carrier sense level setting step is determined, the carrier sense level setting step, until the vehicle from substantially the center of at least the intersection wherein a step of setting the carrier sense level, the access control method according to the inter-vehicle communication apparatus is provided on the basis of the distance

In order to solve the above-described problem, according to another aspect of the present invention, there is provided an access control method using an inter-vehicle communication device mounted on a vehicle, the position detecting step of detecting the position of the host vehicle, An area detecting step for detecting whether or not the own vehicle is present in a predetermined service area based on the position of the own vehicle detected in the position detecting step; and the own vehicle is the predetermined service in the area detecting step. A carrier sense level setting step in which a carrier sense level is set based on the position of the host vehicle in the predetermined service area detected in the position detection step when it is determined that the frame exists, and a frame is transmitted Before being received, it is determined whether or not the received signal level is below the carrier sense level set in the carrier sense level setting step. Seen containing an execution step, a predetermined service area is set so as to include an intersection, the carrier sense level setting step, the carrier sense on the basis of substantially the center of at least the intersection of the distance to the vehicle An access control method by a vehicle-to-vehicle communication device that is a step of setting a level 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, communication quality can be improved by appropriately performing communication settings according to the vehicle density and the position of the host vehicle in the service area. In particular, communication quality can be improved by appropriately setting the carrier sense level or the number of retransmissions.

  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.

[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)
The service control means 12 is means for generating information (hereinafter referred to as notification information) to be notified to other vehicles in order to provide a predetermined service. This notification information includes information on the position and speed of the host vehicle, information on a predetermined service, and the like. As the predetermined service, for example, there is a service that warns the driver that another vehicle is approaching the host vehicle (hereinafter referred to as an approaching vehicle notification service).

  On the other hand, the service control means 12 acquires notification information generated by other vehicles (that is, information on the position and speed of other vehicles, information on a predetermined service, etc. (hereinafter, other vehicle information)). This other vehicle information is acquired using the inter-vehicle communication means 16 and is input to the service control means 12 via the data processing means 22. When providing the approaching vehicle notification service, the service control unit 12 determines whether or not the host vehicle and the other vehicle are approaching based on the acquired other vehicle information. When the distance between the vehicles is approaching, the service control unit 12 issues a warning to the driver as necessary.

  Not limited to the above example, the service control unit 12 acquires various other vehicle information, performs processing necessary to provide a predetermined service based on the acquired other vehicle information, and notifies the other vehicle. To generate notification information. This notification information is transmitted to other vehicles via the data processing means 22 and the inter-vehicle communication means 16.

(Vehicle group control means 14)
The vehicle group control unit 14 includes a data processing unit 22 and a vehicle group formation unit 24.

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

  Here, processing executed when notification information is transmitted will be described. The data processing means 22 makes the transmission destination of the notification information a vehicle in the vehicle group or all vehicles including vehicles outside the vehicle group according to the type of service provided by the service control means 12. Determine whether. At this time, the data processing means 22 makes the above determination 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 notification 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 notification information. When the transmission destination of the notification 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 notification information.

  Next, a process for receiving notification information transmitted from another vehicle will be described. The data processing unit 22 selects a vehicle that is a transmission source (acquisition destination) of the notification information as a vehicle in the vehicle group according to the type of service provided by the service control unit 12, or a vehicle outside the vehicle group To make all vehicles including At this time, the data processing means 22 makes the above determination according to whether or not the host vehicle is a master. For example, when the host vehicle is a master, depending on the type of notification 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 notification information. When the transmission source of the notification information is designated in this way, the designated transmission source information is input to the inter-vehicle communication means 16.

(Car group forming means 24)
The vehicle group formation means 24 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. . 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 separated vehicle as the master. Of course, the master setting method is not limited to this.

  A vehicle that is not the master among the vehicles that belong to the vehicle group is 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. In summary, the state of each vehicle is classified into three types of attributes: master, slave, and outside the vehicle group. In the following description, the attributes classified into these three types may be referred to as “state” of the vehicle. Information indicating the state of the host vehicle set by the vehicle group formation unit 24 (hereinafter, state information) is input to the data processing unit 22. The status information is referred to by the data processing unit 22 when the transmission destination or transmission source of the notification information is selected.

(Vehicle communication means 16)
When the notification information is input from the data processing unit 22, the inter-vehicle communication unit 16 adds information necessary for access control to the notification 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. On the other hand, the inter-vehicle communication means 16 receives the modulation signal of the notification information transmitted at a predetermined frequency from the transmission source selected by the data processing means 22 and demodulates the frame. Further, 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 controls formation of a vehicle group or entry / exit from the vehicle group. In addition, a vehicle state such as a master is set in the formed vehicle group. Furthermore, the transmission destination of the notification information necessary for providing the service or the transmission source of the notification information to be received is set according to the state of the host 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 vehicle-to-vehicle communication device 10 and the vehicle-to-vehicle communication devices 100, 200, 300, 400, 500, and 600 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, 200, 300, 400, 500, and 600.

  As shown in FIG. 2, the functions of the inter-vehicle communication devices 10, 100, 200, 300, 400, 500, 600 include, for example, a GPS receiver H12, a central processing unit (CPU) H14, a memory H16, a communication control unit H18, This is realized by hardware resources such as the RF front end circuit H20 and the 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. The memory H16 stores, for example, relative position information, area range information, own vehicle state information, vehicle number information, transmission / reception data, and the like. 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, and the like.

  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 transmission data is converted into an RF signal having a predetermined frequency and input to the antenna H22. The antenna H22 is a transmission / reception antenna for an RF signal output from the RF front end circuit H20.

  Heretofore, an example of a hardware configuration that can realize the functions of the inter-vehicle communication devices 10, 100, 200, 300, 400, 500, and 600 has been described. Next, a specific example of the service area will be described. The technology of the embodiment described later is assumed to be used in the vicinity of a service area as in a specific example described below, for example. However, it should be noted that the scope of application of the technology according to the embodiment is not limited to the following specific examples.

[About service area]
A setting example of the service area will be briefly described with reference to FIGS. FIG. 3 is a service area setting example (case (1)) for preventing a right turn accident at an intersection. FIG. 4 is a service area setting example (case (2)) for preventing encounter accidents at crossroads and preventing pedestrians jumping off at T-shaped roads.

  In addition to this, there are various application examples for setting the service area, such as for preventing frontal collision accidents, for preventing rear-end collisions, for preventing accidents involving left turn, and for preventing contact accidents when changing lanes. However, for convenience of explanation, only two specific cases (case (1) and case (2)) will be described, and description of the other cases will be omitted.

(About Case (1))
First, referring to FIG. FIG. 3 shows an intersection, a plurality of vehicles (C1, C2, C3, etc.), and a service area SA. First, attention is paid to the vehicles C1, C2, and C3 located near the center of the intersection. The vehicle C1 is a straight traveling vehicle. Vehicles C2 and C3 are right-turn vehicles. Under such circumstances, the driver of the right turn vehicle C2 can visually recognize the positions and movements of the vehicles C1 and C3. However, the driver of the right turn vehicle C2 may not be able to visually recognize that the straight vehicle C1 is coming from behind the right turn vehicle C3. Therefore, in such a situation, a collision between the straight traveling vehicle C1 and the right turn vehicle C2 may occur.

  In order to prevent such a collision accident, it is important to inform the driver of the right turn vehicle C2 of the presence of the straight traveling vehicle C1 in the above situation. For example, if a warning for notifying the existence of each other is given to both the straight-ahead vehicle C1 and the right-turn vehicle C2, there is an increased possibility that the above-described collision accident can be prevented. Furthermore, if the vehicle situation in the intersection is notified to the following vehicle of the straight traveling vehicle C1 or the right turn vehicle C2, the driver of each vehicle can recognize the current situation or predict an accident. Such a warning notification can be realized by using the inter-vehicle communication technology. Furthermore, if vehicle-to-vehicle communication is applied and control information for controlling brakes, accelerators, and the like is appropriately exchanged between the vehicles, each vehicle can automatically avoid a collision.

  From such a viewpoint, for example, as shown in FIG. 3, a service area SA that largely covers an intersection is set. In the example of FIG. 3, in order to realize a collision prevention service between a right-turn vehicle (for example, the vehicle C2) entering in the −X direction and a straight-ahead vehicle (for example, the vehicle C1) traveling in the X direction, The service area SA is set longer along the extended road. In the example of FIG. 3, the service area SA is set so that the center part of the intersection is largely covered, assuming a collision accident when turning right.

  The length of the service area SA is set based on the behavior of the vehicle, the braking distance, and the like. For example, the length of the service area SA is set in consideration of the length of the right turn lane, the position where the driver of the right turn vehicle takes the blinker, the distance from when the driver steps on the brake until the vehicle stops. More specifically, the service area SA is determined based on the section in which the right-turn vehicle displays a right-turn intention, the idle running distance of the vehicle, and the braking distance of the vehicle. Of course, the shape and size of the service area SA vary depending on the size and structure of the intersection, the number of lanes on the road, the presence or absence of pedestrian crossings, the form of signals, and the like.

(About Case (2))
Reference is now made to FIG. On the right side of FIG. 4 (close to the −X direction), a crossroad, a building, a wall, a plurality of vehicles (C1, C2, etc.), and a plurality of service areas SA1, SA2 are described. On the other hand, a T-shaped road, a vehicle C3, a pedestrian M1, and a plurality of service areas SA3 and SA4 are described on the left side (close to the X direction) in FIG. Case (2) assumes a smaller road than Case (1). A small road with a low visibility such as Case (2) has a higher probability of an accident than a high-visibility road such as a main road. Here, let's consider an example of setting a service area on such a road.

  First, pay attention to the vehicles C1 and C2 located near the center of the crossroads. Vehicles C1 and C2 are straight-ahead vehicles that go straight in the X direction and the Y direction, respectively. A crossing accident is likely to occur at the crossroads where the vehicles C1 and C2 are located. In particular, there are walls and high buildings along the road in the vicinity of the crossroads, and the vehicle C1 traveling straight in the X direction cannot be seen from the vehicle C2 traveling straight in the Y direction. This is an example.

  Usually, such a crossroad is equipped with a mirror, and the driver relies on the map reflected on the mirror. However, there are cases where the mirror is hidden by a tree, the sun is reflected, and the visibility is lowered, or the mirror is damaged in the first place. In such a case, the drivers of the vehicles C1 and C2 try to enter the crossroads carefully, paying attention to the presence or absence of vehicles entering the crossroads. However, if it is a road with a low traffic volume or the width of a road that intersects at a crossroad is usually different, the driver's attention may be lessened, which may lead to an unexpected collision. Even in such a case, if the positions and speeds of the vehicles C1 and C2 can be recognized, the possibility of a collision accident being prevented is increased.

  However, walls and buildings as shown in FIG. 4 generally shield radio waves. For this reason, when a communication method with high straightness such as DSRC is used, communication between the vehicles C1 and C2 often cannot be performed until a crossroad is reached. For this reason, the vehicles C1 and C2 cannot exchange vehicle information between the crossroads, and it is difficult to avoid a collision accident at the encounter. Therefore, a communication method using a frequency band that can bypass the shield by diffraction is used so that communication is possible even when there is a shield.

  Moreover, in order to be able to exchange vehicle information among as many vehicles as possible, it is necessary to consider the frequency band utilization efficiency. Therefore, a method of using a communication method capable of bypassing a shield in inter-vehicle group communication and using another communication method in in-vehicle communication is used. For example, a method of using DSRC for intra-vehicle communication and UHF for inter-vehicle communication is conceivable. This is because DSRC has high straightness and is suitable for communication within a local range, and UHF has a relatively small diffraction loss and is suitable for communication that bypasses the shield.

  When different communication methods are used for intra-vehicle communication and inter-vehicle communication, for example, as shown in FIG. 4, service areas SA1, SA2 are set for each road along the traveling direction of the vehicles C1, C2. . The lengths of the service areas SA1 and SA2 are set based on the braking distance of the vehicle. The lengths of the service areas SA1 and SA2 are set in consideration of, for example, the distance from when the driver steps on the brake until the vehicle stops. In particular, the length of the service area is preferably determined based on the idle running distance and the braking distance. If the lengths of the service areas SA1 and SA2 are determined based on the width of the road, the speed limit, etc., the length of the service area SA1 and the length of the service area SA2 may be different.

  In FIG. 4, the service area SA1 and the service area SA2 are drawn separately, but the service area is not necessarily divided, and an L-shaped service area may be set. By the way, the technology related to the inter-vehicle communication device 10 or the like is not applied only to the vehicle. For example, the safety of the pedestrian M1 can be enhanced by applying to a portable device such as a mobile phone held by the pedestrian M1.

  For example, as described on the left side of FIG. 4, when the pedestrian M1 jumps out of a narrow alley, a contact accident between the vehicle C3 and the pedestrian M1 is likely to occur. One reason for this is that it is difficult for the pedestrian M1 to visually recognize the vehicle C3. In addition, when the alley is narrow, the mirror may not be installed, or the child may suddenly jump out without looking at the mirror. In such a case, if the driver of the vehicle C3 is notified of information such as the position and traveling direction of the pedestrian M1, the possibility of preventing a contact accident in advance is increased. In consideration of such a situation, for example, it is preferable that service areas (SA3 and SA4) are also set in the vicinity of a narrow alley where the pedestrian M1 walks. However, it is assumed that the pedestrian M1 holds an electronic device (for example, a mobile phone) on which the functions of the inter-vehicle communication devices 10, 100, 200, 300, 400, 500, and 600 are mounted.

  The situation where the service area is set has been briefly described above. As described above, the service area is used for ensuring the safety of a moving body such as a vehicle or a pedestrian, and is set based on the moving characteristics of the moving body. The technique according to each embodiment of the present invention to be described later is suitably used in or near such a service area.

<First Embodiment>
First, a first embodiment of the present invention will be described. The present embodiment relates to a transmission data retransmission control method. In particular, the present embodiment relates to a technique for adjusting the number of retransmissions of transmission data according to the vehicle density. However, the vehicle density is detected using inter-vehicle communication. The retransmission control process is started, for example, at the timing when the host vehicle enters the service area.

[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 showing a functional configuration of the vehicle-to-vehicle communication device 100 according to the present embodiment. It is assumed that the inter-vehicle communication device 100 is mounted on a vehicle.

  As shown in FIG. 5, the inter-vehicle communication apparatus 100 mainly includes a service control unit 102, a vehicle position detection unit 104, a frequency setting unit 106, an inter-vehicle communication unit 108, a vehicle density estimation unit 110, a vehicle group. And control means 130.

(Service control means 102)
The service control unit 102 is a unit that generates notification information in order to provide a predetermined service. For example, the service control unit 102 acquires information on another vehicle, and executes processing necessary for realizing a predetermined service using the information. When the above processing is executed by the service control unit 102, notification information is generated as a result. This notification information includes information such as the position and speed of the host vehicle, or information used to provide a predetermined service. This notification information is input to the inter-vehicle communication unit 108 via the data processing unit 132 described later, and is transmitted to the other vehicle by the inter-vehicle communication unit 108.

  The service control unit 102 provides information indicating the range of the service area (hereinafter, area range information). For example, the service control unit 102 provides area range information to the area detection unit 138. For example, when the service area location information is stored in the memory H16 in association with the service content, the service control unit 102 reads the service area location information from the memory H16 according to the content of the service to be provided. Provided to the detecting means 138.

(Vehicle position detection means 104)
The vehicle position detection means 104 is a means for detecting the position of the host vehicle. For example, the position of the host vehicle is detected as an absolute position expressed by latitude and longitude. Such absolute position detection is realized by using the GPS receiver H12 or the like. Position information indicating the position of the host vehicle detected by the vehicle position detection unit 104 is input to the area detection unit 138.

(Frequency setting means 106)
The frequency setting means 106 is a means for setting a transmission / reception frequency used for intra-vehicle group communication and inter-vehicle group communication. Information on the transmission / reception frequency set by the frequency setting means 106 is input to the inter-vehicle communication means 108. In the following description, a frequency used for intra-vehicle group communication may be called an intra-vehicle group frequency, and a frequency used for inter-vehicle group communication may be called an inter-vehicle group frequency. Moreover, the function of the frequency setting means 106 is implement | achieved using the communication control part H18, central processing unit H14, memory H16, etc.

(Vehicle communication means 108)
The vehicle-to-vehicle communication means 108 is a means for generating a transmission frame by adding information necessary for access control to transmission information. For example, notification information is input to the inter-vehicle communication unit 108 from the data processing unit 132 described later. In this case, the inter-vehicle communication unit 108 generates a frame by adding information necessary for access control to the notification information input from the data processing unit 132. The frame generated by the inter-vehicle communication unit 108 is modulated by a predetermined modulation method and transmitted at the transmission frequency set by the frequency setting unit 106. At this time, the frame is periodically transmitted to other vehicles.

  On the other hand, the inter-vehicle communication means 108 is also means for receiving a modulation signal from another vehicle, demodulating the frame, and extracting received information from the frame. The inter-vehicle communication unit 108 receives the modulation signal at the reception frequency set by the frequency setting unit 106. Next, the vehicle-to-vehicle communication means 108 demodulates the frame from the received modulation signal, further removes information necessary for access control from the frame, and extracts notification information of other vehicles. The notification information extracted by the inter-vehicle communication unit 108 is input to the data processing unit 132. Note that the function of the vehicle-to-vehicle communication means 108 is realized by using the communication control unit H18, the RF front end circuit H20, and the like.

  Here, the frame configuration of the beacon frame transmitted by the inter-vehicle communication means 108 will be briefly described with reference to FIG. FIG. 6 is an explanatory diagram illustrating a configuration example of a beacon frame transmitted by the inter-vehicle communication unit 108.

  As shown in FIG. 6, the beacon frame includes a MAC header, a transmission source vehicle group ID, a transmission source vehicle ID, a transmission source vehicle position, the 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 transmitting the beacon frame. CRC is a Cyclic Redundancy Check (Cyclic Redundancy Check) code. This beacon frame is transmitted at a predetermined cycle. The beacon frame includes vehicle group management information such as the vehicle position of the host vehicle and the number of vehicles in the vehicle group. And a vehicle group is formed based on this beacon frame, the vehicle which enters into each vehicle group is determined, or the state of the own vehicle in a vehicle group is determined.

(Vehicle density estimation means 110)
Refer to FIG. 5 again. The vehicle density estimation means 110 is a means for estimating the vehicle density around the host vehicle. For example, the vehicle density estimating means 110 detects, for example, the traveling speed of the host vehicle or a vehicle located in the vicinity, and estimates that the vehicle density is low when the traveling speed is high, and the vehicle density is high when the traveling speed is low. Estimated. Normally, the driver travels with a greater distance between the vehicles as the traveling speed increases. As a result, the distance between the vehicles increases and the vehicle density decreases. For this reason, the vehicle density can be estimated as described above based on the traveling speed of the host vehicle or the surrounding vehicles. Note that the vehicle density may be estimated from the traveling speeds of both the traveling speed of the host vehicle and the traveling speeds of the surrounding vehicles. In addition, the information regarding the traveling speed of surrounding vehicles is acquired using inter-vehicle communication.

  Further, the vehicle density estimation means 110 may be configured to estimate the vehicle density based on the number of vehicle information received from other vehicles located around the host vehicle. In this case, the vehicle density estimation means 110 counts the number of receptions of vehicle information transmitted from the surrounding vehicles, estimates that the vehicle density is high when the number of receptions is large, and low when the number of receptions is small. Estimated. At this time, if the position information of each vehicle is included in the vehicle information, the vehicle density can be estimated based on the number of received vehicle information and the position information of each vehicle. Can be estimated. Note that the vehicle density estimated by the vehicle density estimation unit 110 as described above is input to the retransmission control unit 136.

(Vehicle group control means 130)
The vehicle group control means 130 includes data processing means 132, vehicle group formation means 134, retransmission control means 136, and area detection means 138. The function of the vehicle group control means 130 is realized using the central processing unit H14, the memory H16, the communication control unit H18, and the like.

(Data processing means 132)
The data processing unit 132 is a unit that selects a vehicle that is a transmission destination of the notification information when the notification information generated by the service control unit 102 is transmitted. The data processing unit 132 is also a unit that selects a vehicle that is a transmission source of the notification information when the notification information of the other vehicle is acquired. As described above, the notification information is input from the service control unit 102 to the data processing unit 132. Further, the data processing unit 132 is input with information on a vehicle group to which the host vehicle belongs, information on other vehicles included in the vehicle group, status information on the host vehicle, and the like from a vehicle group forming unit 134 described later.

  When the notification information is transmitted, the data processing unit 132 determines whether the transmission destination of the notification information should be a vehicle in the vehicle group based on the content of the notification information acquired from the service control unit 102 or Determine what the vehicle should be. For example, the data processing unit 132 refers to the notification information input from the service control unit 102 and selects a transmission destination based on the type of service, information on the own vehicle, information on other vehicles, or the like. The determination result by the data processing unit 132 is input to the inter-vehicle communication unit 108.

  Further, when the notification information is received from another vehicle, the data processing unit 132 refers to the notification information input from the service control unit 102 and sets the other vehicle that is the transmission source of the notification information as a vehicle in the vehicle group. Or whether the vehicle is out of the vehicle group. For example, the data processing unit 132 selects a transmission source based on the type of service, information on the own vehicle, information on other vehicles, or the like. The determination result by the data processing unit 132 is input to the inter-vehicle communication unit 108.

  When the host vehicle is a master, in addition to the vehicles in the vehicle group, vehicles belonging to other vehicle groups are also included in the transmission destination or transmission source of the notification information. Therefore, as described above, the process of selecting whether the notification information transmission destination or transmission source is a vehicle in the vehicle group or a vehicle outside the vehicle group is executed in consideration of the state of the host vehicle. The

(Car group forming means 134)
When the own vehicle belongs to the vehicle group, information on a service area where the own vehicle is located (hereinafter, area information) is input from the area detection unit 138 to the vehicle group forming unit 134. Based on the input information, the vehicle group forming means 134 forms a vehicle group with the own vehicle, enters the own vehicle into the already formed vehicle group, or selects the own vehicle from the belonging vehicle group. Let go. For example, when the position of the host vehicle is within the service area, the vehicle group forming unit 134 forms the vehicle group with the host vehicle or places the host vehicle in the vehicle group within the service area indicated in the area information. Let it enter. On the other hand, when the position of the host vehicle is outside the service area, the vehicle group forming unit 134 causes the host vehicle to leave the group of vehicles to which the vehicle group belongs.

  As described above, there are three types of vehicle states: master, slave, and outside the vehicle group. Therefore, the vehicle group formation means 134 sets the attribute of the own vehicle when the own vehicle enters the vehicle group or leaves the vehicle group. For example, a master attribute is set for a vehicle that belongs to a vehicle group and performs communication between the vehicle groups. Further, a slave attribute is set for a vehicle that belongs to a vehicle group but is not a master. Furthermore, attributes outside the vehicle group are set for vehicles that do not belong to the vehicle group.

  From the definition of the vehicle group, when the host vehicle is located in the service area, the host vehicle belongs to one of the vehicle groups. In this case, the state of the host vehicle is set to master or slave. For example, if the master exists in other vehicles belonging to the same vehicle group, the state of the own vehicle is set to slave. On the other hand, when the own vehicle is outside the service area, the own vehicle does not belong to the vehicle group. In this case, the state of the own vehicle is set outside the vehicle group. As described above, the state of the host vehicle set by the vehicle group formation unit 134 is input to the data processing unit 132.

(Retransmission control means 136)
Information relating to the vehicle density around the host vehicle estimated by the vehicle density estimation unit 110 is input to the retransmission control unit 136. In addition, the retransmission control unit 136 receives information related to the distance from the intersection detected by the area detection unit 138 described later to the host vehicle. For example, information indicating the distance between the intersection center and the host vehicle is input. Therefore, the retransmission control unit 136 performs retransmission control based on the input information. Specifically, when a frame transmitted via the vehicle-to-vehicle communication means 108 does not normally reach the transmission destination, or the frame is retransmitted at a predetermined time interval without performing arrival confirmation. . However, the retransmission control unit 136 adjusts the number of retransmissions according to the vehicle density around the host vehicle or the distance from the intersection.

  Here, the method of adjusting the number of retransmissions by the retransmission control unit 136 will be described in more detail with reference to FIGS. FIG. 7 is an explanatory diagram showing a method for setting the number of retransmissions based on the vehicle density. FIG. 8 is an explanatory diagram showing a method for setting the number of retransmissions based on the distance from the intersection.

(How to set the number of retransmissions based on vehicle density)
First, referring to FIG. In FIG. 7, the transmission source vehicle Ct of the frame and the transmission destination vehicle Cr of the frame are drawn. In the example of FIG. 7, the inter-vehicle group communication RO is assumed, but in the case of the intra-vehicle group communication RI, the number of retransmissions is similarly set. Case A is an example when the vehicle density is low. On the other hand, Case B is an example when the vehicle density is high.

  When the vehicle density is low as in case A, the amount of communication traffic is small, so that the communication quality can be improved by increasing the number of retransmissions. Further, when the vehicle density is high as in case B, the amount of communication traffic is large, so that it is possible to improve the throughput by suppressing the number of retransmissions. Furthermore, the following effects can also be considered in consideration of frame transmission using inter-vehicle communication and inter-vehicle group communication.

  When the vehicle density is low as in the case A, there are few vehicles that are shields between the transmission source vehicle Ct and the transmission destination vehicle Cr. In addition, since the number of vehicles that transmit frames is small, the amount of communication traffic is relatively small. However, when performing inter-group communication via the master, etc., if the vehicle density is low, the distance from the host vehicle to the master increases, so the received power decreases accordingly, bit errors increase, Communication failure due to frame collision is likely to occur. Therefore, when the vehicle density is low, the retransmission control unit 136 sets the number of retransmissions to a relatively large value. As a result, communication quality within the service area is improved.

  On the other hand, when the vehicle density is high as in the case B, there are many vehicles serving as shielding objects between the transmission source vehicle Ct and the transmission destination vehicle Cr. However, when a frame is transmitted to the master using a method of communicating between adjacent vehicles such as in-car communication, the influence of other vehicles interposed between the host vehicle and the master is small. Further, since the vehicle density is high, the distance between the vehicles is short, and the reception power of the adjacent vehicle is relatively large. Therefore, the possibility of communication failure between the host vehicle and the adjacent vehicle is relatively low. Therefore, when the vehicle density is high, the retransmission control unit 136 sets the number of retransmissions to a relatively small value. As a result, throughput can be improved.

(How to set the number of retransmissions based on the distance from the intersection)
Reference is now made to FIG. In FIG. 8, a transmission source vehicle Ct of a frame and a transmission destination vehicle Cr of the frame are drawn. In the example of FIG. 8, the inter-vehicle group communication RO is assumed, but the number of retransmissions is similarly set in the case of the intra-vehicle group communication RI. Case A is an example when the distance from the intersection is short. On the other hand, Case B is an example when the distance from the intersection is long. A reference point is drawn near the center of the intersection. This reference point is preferably set at the center of the intersection.

  As already described, the service assumed in the description of the present embodiment is, for example, an encounter collision accident prevention service for the purpose of preventing an accident in an intersection. In situations where such services are required, it is important to be able to communicate stably between vehicles traveling in different road directions.

  A vehicle having a short distance from the intersection as in case A has a short distance to a vehicle entering the intersection from a different direction. For this reason, the received power received by the destination vehicle Cr is relatively large and has interference resistance, so that it is difficult for bit errors to occur and communication failures due to frame collisions. That is, when the distance from the intersection is short, there is a high probability that the frame will normally reach in one transmission process, and frame transmission can be successful even if the number of frame retransmissions is small. Therefore, the retransmission control unit 136 sets the number of retransmissions to a relatively small value when the distance from the intersection is short.

  As described above, when the number of retransmissions is set appropriately, excessive frame retransmission processing is not performed, and communication traffic required by vehicles far from the intersection is wasted. Is effectively avoided. On the other hand, a vehicle with a long distance from the intersection as in Case B has a long distance from a vehicle entering the intersection from a different direction. For this reason, the received power received by the destination vehicle Cr is relatively small and susceptible to interference, so that bit errors and communication failures due to frame collisions are likely to occur. Therefore, the retransmission control unit 136 sets the number of retransmissions to a relatively large value when the distance from the intersection is far.

  As described above, by appropriately setting the number of retransmissions according to the distance from the intersection, services can be stably provided to vehicles in the service area provided near the intersection. As a result, services can be stably provided to vehicles located at a short distance from the intersection as well as to vehicles following the vehicle, resulting in encounter crashes and accompanying incidents. It is possible to prevent rear-end collisions and the like.

  Refer to FIG. 5 again. The retransmission control process as described above is executed when the host vehicle is located in the service area. That is, the retransmission control unit 136 acquires information indicating whether or not the host vehicle is located in the service area from the area detection unit 138 described later, and the above-described retransmission when the host vehicle enters the service area. Start control. By adopting such a configuration, it is possible to suppress the communication quality between vehicles located in the service area from being lowered to a predetermined level or less. In particular, services can be stably provided to vehicles in a position where there is a high risk of a collision accident.

  As already described, among vehicles located in the service area, there is a vehicle to which service should be preferentially provided. For example, a vehicle located near an intersection has a high possibility of a collision. Therefore, the vehicle information of other vehicles should be provided preferentially to the vehicle located near the intersection. Therefore, in the present embodiment, the retransmission control as described above is performed. Therefore, by performing the retransmission control as described above, the service is stably provided to the vehicles in the service area, and the occurrence probability of the collision accident due to the delay or failure of the service provision is prevented. be able to.

(Area detection means 138)
Position information of the host vehicle is input from the vehicle position detection unit 104 to the area detection unit 138. Further, area range information indicating the range of the service area is input from the service control unit 102 to the area detection unit 138. Therefore, the area detection unit 138 detects whether or not the host vehicle is located in the service area based on the input position information of the host vehicle and the area range information. For example, when the range of the service area is expressed by the absolute position, the area detecting unit 138 collates the absolute position indicated by the position information of the own vehicle with the area range information, so that the own vehicle is located in the service area. It can be judged whether or not.

  There may be a plurality of service areas. In this case, a plurality of area range information is input from the service control unit 102 to the area detection unit 138. In this case, the area detection means 138 collates a plurality of area range information with the position information of the own vehicle, and detects a service area including the own vehicle. In this way, the area detection unit 138 detects whether or not the host vehicle is included in the service area. Further, if the own vehicle is included in any service area, it is detected which service area is included. The result thus detected is input to the vehicle group forming means 134. The area detecting unit 138 detects the distance between the host vehicle and the intersection and inputs the distance to the retransmission control unit 136.

  Heretofore, the functional configuration of the inter-vehicle communication device 100 according to the present embodiment has been described. As described above, the inter-vehicle communication device 100 sets the number of retransmissions according to the vehicle density of the vehicles located around the host vehicle and the distance from the intersection to the host vehicle, and performs retransmission control of frame transmission based on the number of retransmissions. It can be carried out. Therefore, a stable service with a communication quality of a predetermined level or higher is provided to each vehicle located in the service area set near the intersection. As a result, the service is surely provided to the vehicle having a high collision risk located near the intersection, and the service is also appropriately provided to the following vehicle.

[Flow of data transmission processing]
Next, the flow of data transmission processing by the inter-vehicle communication device 100 will be described with reference to FIG. FIG. 9 is an explanatory diagram showing the overall flow of data transmission processing by the inter-vehicle communication device 100.

  As shown in FIG. 9, first, the data processing unit 132 determines the presence or absence of transmission data (S102). When there is no transmission data, the inter-vehicle communication device 100 determines whether or not to end a series of processes related to data transmission (S108). On the other hand, when there is transmission data, the inter-vehicle communication device 100 proceeds to the process of step S104. At this time, the data processing unit 132 instructs the retransmission control unit 136 to set the number of retransmissions. In step S104, the retransmission control unit 136 sets the number of retransmissions based on the vehicle density estimated by the vehicle density estimation unit 110 and the distance from the intersection detected by the area detection unit 138 (S104).

  Next, the vehicle-to-vehicle communication apparatus 100 proceeds to the process of step S106, and transmits transmission data using the vehicle-to-vehicle communication means 108 (S106). At this time, the vehicle-to-vehicle communication means 108 transmits data for the number of retransmissions set in step S104. Next, the inter-vehicle communication device 100 determines whether or not to end a series of processes related to data transmission (S108). If the series of processes is not terminated, the inter-vehicle communication device 100 proceeds to the process of step S102 again and repeats the processes of steps S102 to S108.

  The overall flow of data transmission processing by the inter-vehicle communication device 100 has been described above. As described above, the inter-vehicle communication device 100 is characterized by the method for setting the number of retransmissions. That is, the above-described data transmission process is characterized by the process in step S104. Note that the processing in step S104 is executed by the retransmission control means 136 by the method shown in FIGS.

  The first embodiment of the present invention has been described above. As described above, in the present embodiment, the number of retransmissions is set according to the vehicle density around the host vehicle and the distance from the intersection to the host vehicle, and retransmission control is performed based on the number of retransmissions. In particular, by setting the number of retransmissions by the method shown in FIGS. 7 and 8, a predetermined or higher communication quality is maintained for each vehicle in the service area set near the intersection. As a result, services are stably provided to each vehicle located within the service area, and collision accidents and the like that occur near intersections are effectively prevented.

[Modification 1: Distance from intersection only]
Here, a modification of the present embodiment will be briefly described with reference to FIG. FIG. 10 is an explanatory diagram illustrating a functional configuration of the vehicle-to-vehicle communication device 200 according to a modified example (hereinafter, modified example 1) of the present embodiment. However, components that are substantially the same as those in the vehicle-to-vehicle communication device 100 are denoted by the same reference numerals, and detailed description thereof is omitted.

(Functional configuration of inter-vehicle communication device 200)
As shown in FIG. 10, the inter-vehicle communication device 200 is mainly composed of service control means 102, vehicle position detection means 104, frequency setting means 106, inter-vehicle communication means 108, and vehicle group control means 130. The Further, the vehicle group control means 130 includes a data processing means 132, a vehicle group formation means 134, a retransmission control means 136, and an area detection means 138. The function of the vehicle group control means 130 is realized using the central processing unit H14, the memory H16, the communication control unit H18, and the like.

  As described above, the vehicle density estimation unit 110 is not provided in the inter-vehicle communication device 200. Therefore, the retransmission control unit 136 sets the number of retransmissions according to the distance from the intersection to the host vehicle, and performs retransmission control based on the number of retransmissions. That is, the retransmission control unit 136 sets the number of retransmissions based on the distance from the intersection input from the area detection unit 138 regardless of the vehicle density around the host vehicle. Thus, even when the number of retransmissions is set based only on the distance from the intersection, the communication quality for the vehicles in the service area can be improved by appropriately setting the number of retransmissions based on the method shown in FIG. Can be improved.

[Modification 2: Vehicle density only]
Next, a modification of the present embodiment will be briefly described with reference to FIG. FIG. 11 is an explanatory diagram showing a functional configuration of the vehicle-to-vehicle communication device 300 according to a modified example (hereinafter, modified example 2) of the present embodiment. However, components that are substantially the same as those in the vehicle-to-vehicle communication device 100 are denoted by the same reference numerals, and redundant description is omitted.

(Functional configuration of inter-vehicle communication device 300)
As shown in FIG. 11, the inter-vehicle communication device 300 mainly includes a service control unit 102, a frequency setting unit 106, an inter-vehicle communication unit 108, a vehicle density estimation unit 110, and a vehicle group control unit 130. The Further, the vehicle group control means 130 includes a data processing means 132, a vehicle group formation means 134, a retransmission control means 136, and an area detection means 138. The function of the vehicle group control means 130 is realized using the central processing unit H14, the memory H16, the communication control unit H18, and the like.

  As described above, the vehicle position detection unit 104 is not provided in the inter-vehicle communication device 300. Therefore, the retransmission control unit 136 sets the number of retransmissions according to the vehicle density, and performs retransmission control based on the number of retransmissions. That is, the retransmission control unit 136 sets the number of retransmissions based on the vehicle density input from the vehicle density estimation unit 110 regardless of the distance from the intersection to the host vehicle. Thus, even when the number of retransmissions is set based only on the vehicle density, the communication quality for the vehicles in the service area is improved by appropriately setting the number of retransmissions based on the method shown in FIG. be able to.

<Second Embodiment>
Next, a second embodiment of the present invention will be described. Unlike the first embodiment, the present embodiment relates to a technique for appropriately setting the carrier sense level according to the vehicle density and the distance from the intersection to the host vehicle. That is, in this embodiment, vehicle-to-vehicle communication using a carrier detection multiple access (CSMA) method is assumed.

(About CSMA method)
The CSMA method is a method in which before the own vehicle starts communication, the presence or absence of another vehicle communicating at that time is confirmed, and when the other vehicle is not communicating, the own vehicle starts communication. For example, communication of the host vehicle is started when it is confirmed that the channel is idle for a predetermined time or longer. In this method, since a plurality of vehicles share the same channel, it is necessary to control transmission timing so that a plurality of communications are not performed simultaneously.

  Therefore, when the channel is unused (other vehicles are not transmitting), the transmission process is executed after waiting for a predetermined time. If the channel is in use (the other vehicle is transmitting), it waits until the transmission of the other vehicle is completed (this time is not included in the predetermined waiting time). Control processing is performed so that transmission processing is executed after waiting for a predetermined time. As the predetermined time, for example, a certain minimum time plus a random waiting time is used. Thus, by using a random waiting time, a plurality of communications are prevented from being executed simultaneously after a predetermined time.

  In order to perform communication control as described above, it is necessary to detect the transmission state of other vehicles in the vicinity of the host vehicle. For example, the host vehicle can determine the channel usage status (transmission status of other vehicles) by detecting whether or not the received power level from surrounding vehicles exceeds a predetermined level. In particular, it is detected whether or not the received power level of a predetermined frequency exceeds a predetermined level. If the received signal level is higher than the predetermined level, it is determined that the channel is in use, and the host vehicle waits until the channel becomes unused. On the other hand, when the received signal level is lower than the predetermined level, it is determined that the channel is unused, and the host vehicle waits for the required time before transmitting the frame.

  That is, when the predetermined level is set high, the host vehicle performs frame transmission control without worrying too much about frame collision with surrounding vehicles. Conversely, when the predetermined level is set low, the host vehicle performs frame transmission control so as to avoid frame collisions with frames transmitted by neighboring vehicles as much as possible. Therefore, depending on the predetermined level setting method, the communication quality of surrounding vehicles may be greatly affected. Hereinafter, this predetermined level is referred to as a carrier sense level. In the present embodiment, a method is proposed in which the carrier sense level is appropriately set so that communication quality of a predetermined level or higher is maintained in each vehicle in the service area.

[Functional configuration of inter-vehicle communication apparatus 400]
First, the functional configuration of the inter-vehicle communication device 400 according to the present embodiment will be described with reference to FIG. FIG. 12 is an explanatory diagram illustrating a functional configuration example of the vehicle-to-vehicle communication device 400 according to the present embodiment. In this description, a method for setting the carrier sense level will be described. However, components that are substantially the same as those in the vehicle-to-vehicle communication device 100 according to the first embodiment described above are denoted by the same reference numerals, and detailed description thereof is omitted.

  As shown in FIG. 12, the inter-vehicle communication apparatus 400 mainly includes a service control unit 102, a vehicle position detection unit 104, a frequency setting unit 106, an inter-vehicle communication unit 108, a vehicle density estimation unit 110, a carrier sense. The level setting means 112 and the vehicle group control means 130 are comprised. Further, the vehicle group control means 130 includes a data processing means 132, a vehicle group formation means 134, and an area detection means 138. The function of the vehicle group control means 130 is realized using the central processing unit H14, the memory H16, the communication control unit H18, and the like.

  As described above, the inter-vehicle communication apparatus 400 according to the present embodiment is obtained by omitting the retransmission control unit 136 from the inter-vehicle communication apparatus 100 according to the first embodiment and newly adding the carrier sense level setting unit 112. . Therefore, the function of the carrier sense level setting unit 112 and the function of each unit related to the function will be mainly described.

(Carrier sense level setting means 112)
The carrier sense level setting unit 112 is a unit that adjusts the carrier sense level according to the vehicle density around the host vehicle and the distance from the intersection to the host vehicle. Information indicating the distance from the intersection detected by the area detection unit 138 to the host vehicle is input to the carrier sense level setting unit 112. Further, information indicating the vehicle density around the host vehicle is input to the carrier sense level setting unit 112 from the vehicle density estimation unit 110. When the own vehicle is located in the service area, the carrier sense level setting unit 112 sets the carrier sense level based on the input information. Information on the carrier sense level set by the carrier sense level setting means 112 is input to the inter-vehicle communication means 108.

  Here, the carrier sense level setting method according to the present embodiment will be described with reference to FIGS. 13 and 14. FIG. 13 is an explanatory diagram showing a carrier sense level setting method based on vehicle density. FIG. 14 is an explanatory diagram showing a carrier sense level setting method based on the distance from the intersection to the host vehicle.

(Setting method of carrier sense level based on vehicle density)
First, referring to FIG. In FIG. 13, the transmission source vehicle Ct of the frame and the transmission destination vehicle Cr of the frame are drawn. In the example of FIG. 13, the inter-vehicle group communication RO is assumed, but the carrier sense level is similarly set in the case of the intra-vehicle group communication RI. Case A is an example when the vehicle density is low. On the other hand, Case B is an example when the vehicle density is high.

  Similar to the first embodiment, the object of the present embodiment is to stably provide a communication environment of a predetermined quality or higher to each vehicle in a service area set near an intersection or the like.

  Here, let's introduce the quantity called the carrier sense radius as an index that defines the target of carrier sense. The carrier sense radius referred to here is a radius of a circle drawn around the host vehicle, and vehicles located within the circle are included in the carrier sense target. The relationship between the carrier sense radius and the carrier sense level is as follows.

  As already described, the carrier sense level is a threshold level for determining whether or not the host vehicle transmits a frame. In particular, when the destination vehicle is unspecified as in broadcast transmission, if the carrier sense level is low, the number of vehicles subject to interference increases, and the probability of time-out without frame transmission increases. Therefore, the number of vehicles within the carrier sense radius needs to be less than the number that can satisfy the predetermined communication quality. When the vehicle density is high as in the case B, it is necessary to reduce the radius of a circle centered on the own vehicle including a predetermined number of vehicles. Therefore, the received signal level that the host vehicle needs to detect for vehicles located within the circle is relatively higher than in the case where the vehicle density is low as in case A.

  Therefore, when the vehicle density is high as in case B, the carrier sense level corresponding to the predetermined carrier sense radius is relatively high. Conversely, when the vehicle density is low as in case A, the carrier sense radius can be increased compared to when the vehicle density is low, so the carrier sense level corresponding to the predetermined carrier sense radius is relatively low.

  By the way, the transmission power when the host vehicle transmits a frame is determined to some extent. In addition, a desired wave power to interference wave power ratio necessary for stably transmitting a frame to the transmission destination vehicle Cr is also determined. Therefore, when the destination vehicle is specific or when the destination vehicle is limited to a specific range, the carrier sense level of the transmission source vehicle is obtained as a desired desired signal power to interference signal power ratio in the destination vehicle. What is necessary is just to set it to the value more than the grade.

  As shown in FIG. 13, the carrier sense level setting means 112 sets the carrier sense level small when the vehicle density is low (case A), and sets the carrier sense level large when the vehicle density is high (case B). . However, the carrier sense level setting means 112 takes into account the propagation loss between the transmission source vehicle Ct and the transmission destination vehicle Cr and the propagation loss of the interference wave received by the transmission destination vehicle Cr, and the desired value in the transmission destination vehicle Cr. The carrier sense level is set to such a value that the desired signal power to interference signal power ratio can be obtained. With such a setting method, it is possible to improve communication quality without causing frame collision with other vehicles more than necessary.

  When the vehicle density is low as in the case A, there are few vehicles that are shields between the transmission source vehicle Ct and the transmission destination vehicle Cr. In addition, since the number of vehicles that transmit frames is small, the amount of communication traffic is relatively small. However, when performing inter-group communication via the master, etc., if the vehicle density is low, the distance from the host vehicle to the master increases, so the received power decreases accordingly, bit errors increase, Communication failure due to frame collision is likely to occur. Therefore, when the vehicle density is low, the carrier sense level setting unit 112 sets the carrier sense level to a relatively small value. As a result, communication quality within the service area is improved.

  On the other hand, when the vehicle density is high as in the case B, there are many vehicles serving as shielding objects between the transmission source vehicle Ct and the transmission destination vehicle Cr. However, when a frame is transmitted to the master using a method of communicating between adjacent vehicles such as in-car communication, the influence of other vehicles interposed between the host vehicle and the master is small. Further, since the vehicle density is high, the distance between the vehicles is short, and the reception power of the adjacent vehicle is relatively large. Therefore, the possibility of communication failure between the host vehicle and the adjacent vehicle is relatively low. Therefore, when the vehicle density is high, the carrier sense level setting unit 112 sets the carrier sense level to a relatively large value. As a result, throughput can be improved.

(How to set the carrier sense level based on the distance from the intersection)
Reference is now made to FIG. In FIG. 14, the transmission source vehicle Ct of the frame and the transmission destination vehicle Cr of the frame are drawn. In the example of FIG. 14, the inter-vehicle group communication RO is assumed. However, in the case of the intra-vehicle group communication RI, the carrier sense level is similarly set. Case A is an example when the distance from the intersection is short. On the other hand, Case B is an example when the distance from the intersection is long. A reference point is drawn near the center of the intersection. This reference point is preferably set at the center of the intersection.

  As already described, the service assumed in the description of the present embodiment is, for example, an encounter collision accident prevention service for the purpose of preventing an accident in an intersection. In situations where such services are required, it is important to be able to communicate stably between vehicles traveling in different road directions.

  A vehicle having a short distance from the intersection as in case A has a short distance to a vehicle entering the intersection from a different direction. Therefore, the reception power received by the destination vehicle Cr is relatively large and has interference resistance, and it is difficult for a bit error or a communication failure due to a frame collision to occur. Further, the propagation loss is small as the distance between the transmission source vehicle Ct and the transmission destination vehicle Cr is short. That is, when the distance from the intersection is short, there is a high probability that the transmission frame of the transmission source vehicle Ct will normally reach even when the interference wave power level is high.

  Therefore, when the distance from the intersection to the host vehicle is short as in case A, the carrier sense level setting means 112 increases the carrier sense level so that frame collision with other vehicles is allowed to some extent. On the contrary, when the distance from the intersection to the host vehicle is long as in the case B, the carrier sense level setting unit 112 sets the carrier sense level to be small and reduces the probability that a frame collision will occur with another vehicle. .

  More specifically, as shown in FIG. 15, the propagation loss between the reference point and the transmission source vehicle Ct is estimated from the distance Lc between the transmission source vehicle Ct and the transmission destination vehicle Cr, Estimate the desired wave power level. From this value and the desired signal power to interference signal power ratio that can satisfy the required communication quality, the required interference signal power is obtained, and then the propagation loss between the interference source vehicle Ci and the destination vehicle Cr is calculated. presume. Subsequently, the distance Li between the transmission source vehicle Ct and the interference source vehicle Ci is estimated by estimating the distance Li between the reference point and the interference source vehicle Ci. The carrier sense level setting means 112 sets the distance Lc + Li between the transmission source vehicle Ct and the interference source vehicle Ci as the carrier sense radius Lcs, and sets the carrier sense level corresponding to the carrier sense radius Lcs.

  With such a setting, when it is far from the intersection, the frame is transmitted at a timing at which the frame collision hardly occurs, and the probability that the frame reaches the transmission destination vehicle Cr is improved. Furthermore, when near the intersection, the frame is transmitted preferentially using the high interference resistance.

  As explained above, communication quality is improved by appropriately setting the carrier sense level according to the distance from the intersection, and services are stably provided to vehicles in the service area provided near the intersection. Become so. As a result, services are stably provided to vehicles located at a short distance from the intersection as well as to vehicles following the vehicle, such as encounter crashes and incidental rear-end crashes. It becomes possible to prevent.

  In addition, said carrier sense is performed when the own vehicle is located in a service area. That is, the carrier sense level setting unit 112 acquires information indicating whether or not the host vehicle is located in the service area from the area detection unit 138, and sets the above when the host vehicle enters the service area. Start processing. Further, processing such as carrier sense is executed using the vehicle-to-vehicle communication means 108. By adopting such a configuration, it is possible to suppress the communication quality between vehicles located in the service area from being lowered to a predetermined level or less. In particular, services can be stably provided to vehicles having a high risk of collision accidents.

[Flow of data transmission processing]
Next, the flow of data transmission processing by the inter-vehicle communication device 400 will be described with reference to FIG. FIG. 16 is an explanatory diagram showing the overall flow of data transmission processing by the inter-vehicle communication device 400.

  As shown in FIG. 14, first, the presence or absence of transmission data is determined by the data processing means 132 (S402). When there is no transmission data, the vehicle-to-vehicle communication device 400 determines whether or not to end a series of processes related to data transmission (S408). On the other hand, when there is transmission data, the inter-vehicle communication device 400 proceeds to the process of step S404. At this time, the data processing unit 132 instructs the carrier sense level setting unit 112 to set the carrier sense level.

  In step S404, the carrier sense level setting unit 112 sets the carrier sense level based on the vehicle density estimated by the vehicle density estimation unit 110 and the distance from the intersection detected by the area detection unit 138 (S104). Further, the inter-vehicle communication unit 108 starts the carrier sense operation based on the carrier sense level set by the carrier sense level setting unit 112.

  Next, the vehicle-to-vehicle communication device 400 proceeds to the process of step S406, and transmits transmission data using the vehicle-to-vehicle communication means 108 (S406). At this time, the inter-vehicle communication unit 108 transmits data while adjusting the transmission timing based on the carrier sense level set in step S404. Next, the inter-vehicle communication device 400 determines whether or not to end a series of processes related to data transmission (S408). If the series of processes is not terminated, the vehicle-to-car communication device 400 proceeds to the process of step S402 again, and repeats the processes of step S402 to step S408.

  The overall flow of data transmission processing by the inter-vehicle communication device 400 has been described above. As described above, the vehicle-to-vehicle communication device 400 is characterized by the carrier sense level setting method. That is, the above-described data transmission process is characterized by the process in step S404. Note that the process of step S404 is executed by the carrier sense level setting means 112 by the method shown in FIGS.

  The second embodiment of the present invention has been described above. As described above, in the present embodiment, the carrier sense level is set according to the vehicle density around the host vehicle and the distance from the intersection to the host vehicle, and the carrier sense is performed based on the carrier sense level. In particular, when the carrier sense level is set by the method shown in FIGS. 13 and 14, a predetermined or higher communication quality is maintained for each vehicle in the service area set near the intersection. As a result, services are stably provided to each vehicle located within the service area, and collision accidents and the like that occur near intersections are effectively prevented.

[Variation 3: Only the distance from the intersection]
Here, a modification of the present embodiment will be briefly described with reference to FIG. FIG. 17 is an explanatory diagram illustrating a functional configuration of the vehicle-to-vehicle communication device 500 according to a modified example (hereinafter, modified example 3) of the present embodiment. However, components that are substantially the same as those in the vehicle-to-vehicle communication device 400 are given the same reference numerals, and detailed description thereof is omitted.

(Functional configuration of inter-vehicle communication device 500)
As shown in FIG. 17, the inter-vehicle communication device 500 mainly includes a service control unit 102, a vehicle position detection unit 104, a frequency setting unit 106, an inter-vehicle communication unit 108, a carrier sense level setting unit 112, a vehicle And group control means 130. Further, the vehicle group control means 130 includes a data processing means 132, a vehicle group formation means 134, and an area detection means 138. The function of the vehicle group control means 130 is realized using the central processing unit H14, the memory H16, the communication control unit H18, and the like.

  As described above, the vehicle density estimation unit 110 is not provided in the inter-vehicle communication device 500. Therefore, the carrier sense level setting means 112 sets a carrier sense level according to the distance from the intersection to the host vehicle, and performs carrier sense based on the carrier sense level. That is, the carrier sense level setting unit 112 sets the carrier sense level based on the distance from the intersection input from the area detection unit 138 regardless of the vehicle density around the host vehicle. As described above, even when the carrier sense level is set based only on the distance from the intersection, the carrier sense level is appropriately set based on the method shown in FIG. Quality is improved.

[Variation 4: Vehicle density only]
Next, a modification of the present embodiment will be briefly described with reference to FIG. FIG. 18 is an explanatory diagram illustrating a functional configuration of the vehicle-to-vehicle communication device 600 according to a modified example (hereinafter, modified example 4) of the present embodiment. However, components that are substantially the same as those in the vehicle-to-vehicle communication device 400 are given the same reference numerals, and redundant description is omitted.

(Functional configuration of inter-vehicle communication device 600)
As shown in FIG. 18, the inter-vehicle communication device 600 mainly includes a service control unit 102, a frequency setting unit 106, an inter-vehicle communication unit 108, a vehicle density estimation unit 110, a carrier sense level setting unit 112, a vehicle And group control means 130. Further, the vehicle group control means 130 includes a data processing means 132 and a vehicle group formation means 134. The function of the vehicle group control means 130 is realized using the central processing unit H14, the memory H16, the communication control unit H18, and the like.

  As described above, the vehicle position detection unit 104 is not provided in the inter-vehicle communication device 600. Therefore, the carrier sense level setting unit 112 sets a carrier sense level according to the vehicle density, and performs carrier sense based on the carrier sense level. That is, the carrier sense level setting unit 112 sets the carrier sense level based on the vehicle density input from the vehicle density estimation unit 110 regardless of the distance from the intersection to the host vehicle. Thus, even when the carrier sense level is set based only on the vehicle density, the communication quality for the vehicles in the service area can be improved by appropriately setting the carrier sense level based on the method shown in FIG. Can be improved.

  Heretofore, the second embodiment of the present invention and its modifications have been described. As described above, the second embodiment of the present invention is based on the CSMA method. Therefore, in the case of a normal CSMA system, if the vehicle density is high, the number of vehicles within the carrier sense range defined by the carrier sense radius increases, and communication failures due to frame collisions increase. If the carrier sense radius is set to be larger than necessary, the number of vehicles subject to interference increases, and the probability of time-out without frame transmission increases. However, by setting the carrier sense level by the method shown in FIGS. 13, 14, etc., these problems are solved, and the communication quality is improved.

[Remarks]
The vehicle-to-vehicle communication unit 108 is an example of a carrier sense execution unit. The vehicle position detection unit 104 is an example of a position detection unit. The vehicle density estimation unit 110 is an example of a vehicle number calculation unit. The carrier sense level setting unit 112 is an example of a carrier sense radius changing unit, an interference vehicle detecting unit, and a carrier sense radius setting unit. The retransmission control unit 136 is an example of a retransmission number setting unit.

  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.

It is explanatory drawing which shows the function structural example of a general 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 the example of a specific setting of a service area. It is explanatory drawing which shows the example of a specific setting of a service area. It is explanatory drawing which shows the function structure of the vehicle-to-vehicle communication apparatus which concerns on 1st Embodiment of this invention. It is explanatory drawing which shows the structural example of the beacon frame which concerns on the embodiment. It is explanatory drawing which shows an example of the retransmission control method which concerns on the same embodiment. It is explanatory drawing which shows an example of the retransmission control method which concerns on the same embodiment. It is explanatory drawing which shows an example of the data transmission method which concerns on the same embodiment. It is explanatory drawing which shows the function structure of the vehicle-to-vehicle communication apparatus which concerns on the modification of the embodiment. It is explanatory drawing which shows the function structure of the vehicle-to-vehicle communication apparatus which concerns on the modification of the embodiment. It is explanatory drawing which shows the function structure of the vehicle-to-vehicle communication apparatus which concerns on 2nd Embodiment of this invention. It is explanatory drawing which shows the setting method of the carrier sense level which concerns on the same embodiment. It is explanatory drawing which shows the setting method of the carrier sense level which concerns on the same embodiment. It is explanatory drawing which shows the setting method of the carrier sense level which concerns on the embodiment. It is explanatory drawing which shows an example of the data transmission method which concerns on the same embodiment. It is explanatory drawing which shows the function structure of the vehicle-to-vehicle communication apparatus which concerns on the modification of the embodiment. It is explanatory drawing which shows the function structure of the vehicle-to-vehicle communication apparatus which concerns on the modification of the embodiment.

Explanation of symbols

100, 200, 300, 400, 500, 600 Inter-vehicle communication device 102 Service control means 104 Vehicle position detection means 106 Frequency setting means 108 Inter-vehicle communication means 110 Vehicle density estimation means 112 Carrier sense level setting means 130 Vehicle group control means 132 Data processing Means 134 Vehicle group formation means 136 Retransmission control means 138 Area detection means H12 GPS receiver H14 Central processing unit H16 Memory H18 Communication control unit H20 RF front end circuit H22 Antenna H24 Bus

Claims (10)

An inter-vehicle communication device mounted on a vehicle,
Vehicle density detection means for detecting a vehicle density within a predetermined range based on the position of the host vehicle;
Carrier sense level setting means for setting a carrier sense level based on the vehicle density detected by the vehicle density detection means;
Carrier sense execution means for determining whether a received signal level is lower than a carrier sense level set by the carrier sense level setting means before a frame is transmitted;
Equipped with a,
The carrier sense level setting means sets the carrier sense level based on at least the distance from the approximate center of the intersection to the host vehicle .
Inter-vehicle communication device. Position detecting means for detecting the position of the host vehicle;
Area detecting means for detecting whether or not the own vehicle exists in a predetermined service area based on the position of the own vehicle detected by the position detecting means;
Further comprising
The predetermined service area is set to include the intersection,
The carrier sense level setting means detects the position of the own vehicle within the predetermined service area detected by the position detecting means when the area detecting means determines that the own vehicle is present within the predetermined service area. And setting the carrier sense level based on the vehicle density,
The inter-vehicle communication device according to claim 1. Vehicle number calculation means for calculating the number of vehicles within a range defined by a predetermined carrier sense radius based on the vehicle density detected by the vehicle density detection means;
Carrier sense radius changing means for changing the carrier sense radius so that the number of vehicles calculated by the vehicle number calculating means is less than the number of vehicles that can be accommodated in a predetermined band;
Further comprising
The carrier sense level setting unit sets the carrier sense level so that a vehicle within a range defined by a carrier sense radius after being changed by the carrier sense radius changing unit is a target of carrier sense. The inter-vehicle communication device according to 1 or 2. An inter-vehicle communication device mounted on a vehicle,
Position detecting means for detecting the position of the host vehicle;
Area detecting means for detecting whether or not the own vehicle exists in a predetermined service area based on the position of the own vehicle detected by the position detecting means;
A carrier sense level is set based on the position of the own vehicle in the predetermined service area detected by the position detecting unit when the area detecting unit determines that the own vehicle is present in the predetermined service area. Carrier sense level setting means,
Carrier sense execution means for determining whether a received signal level is lower than a carrier sense level set by the carrier sense level setting means before a frame is transmitted;
Equipped with a,
The predetermined service area is set to include an intersection,
The carrier sense level setting means sets the carrier sense level based at least on the distance from the approximate center of the intersection to the host vehicle;
Inter-vehicle communication device. When the signal transmitted from the own vehicle and the signal transmitted from the other vehicle are transmitted to the transmission destination vehicle of the frame, the other vehicle in which the reception quality detected by the transmission destination vehicle becomes a predetermined quality. Interference vehicle detecting means for detecting;
Carrier sense radius setting means for setting a value obtained by adding the distance from the other vehicle detected by the interference vehicle detection means to the approximate center of the intersection and the distance from the own vehicle to the approximate center of the intersection as a carrier sense radius; ,
Further comprising
The carrier sense level setting means sets the carrier sense level so that a vehicle within a range defined by the carrier sense radius set by the carrier sense radius setting means is a target of carrier sense.
The inter-vehicle communication device according to claim 4. The vehicle density detecting means detects the vehicle density based on a traveling speed of a vehicle located within the predetermined range;
The inter-vehicle communication device according to any one of claims 1 to 3 . The vehicle density detection means detects the vehicle density based on the number of frames received from another vehicle.
The inter-vehicle communication device according to any one of claims 1 to 3 . The vehicle density detection means detects the vehicle density based on position information exchanged with another vehicle.
The inter-vehicle communication device according to any one of claims 1 to 3 . An access control method using an inter-vehicle communication device mounted on a vehicle,
A vehicle density detection step in which a vehicle density within a predetermined range based on the position of the host vehicle is detected;
A carrier sense level setting step in which a carrier sense level is set based on the vehicle density detected in the vehicle density detection step;
A carrier sense execution step of determining whether or not a received signal level is lower than a carrier sense level set in the carrier sense level setting step before a frame is transmitted;
Only including,
The carrier sense level setting step is a step of setting the carrier sense level based on at least the distance from the approximate center of the intersection to the host vehicle .
An access control method using an inter-vehicle communication device. An access control method using an inter-vehicle communication device mounted on a vehicle,
A position detection step in which the position of the host vehicle is detected;
An area detecting step for detecting whether or not the own vehicle is present in a predetermined service area based on the position of the own vehicle detected in the position detecting step;
A carrier sense level is set based on the position of the own vehicle in the predetermined service area detected in the position detection step when it is determined in the area detection step that the own vehicle is present in the predetermined service area. Carrier sense level setting process,
A carrier sense execution step of determining whether or not a received signal level is lower than a carrier sense level set in the carrier sense level setting step before a frame is transmitted;
Only including,
The predetermined service area is set to include an intersection,
The carrier sense level setting step is a step of setting the carrier sense level based on at least a distance from the approximate center of the intersection to the host vehicle.
An access control method using an inter-vehicle communication device.

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