JP5206342B2 - Roadside communication device and wireless communication method - Google Patents

Description

  The present invention relates to, for example, a roadside communication device and a wireless communication method that are useful when implementing an Intelligent Transport System (ITS).

In recent years, for the purpose of promoting traffic safety and preventing traffic accidents, advanced road traffic systems that improve the safety of vehicles by receiving information from infrastructure devices installed on the road and utilizing this information have been studied. (For example, refer to Patent Document 1).
This traffic system is mainly composed of a plurality of roadside communication devices that are wireless communication devices on the infrastructure side, and in-vehicle communication devices (mobile communication devices) that are wireless communication devices mounted on each vehicle.

In this case, a combination of communication performed between communication subjects includes road-to-road communication between road-side communication devices, road-to-vehicle (or vehicle-road) communication between road-side communication devices and vehicle-mounted communication devices, and vehicle-mounted communication. Vehicle-to-vehicle communication performed between aircraft.
And the roadside communication device is installed near the intersection, for example, and the vehicle-mounted communication devices mounted on the vehicles entering the intersection perform wireless communication (vehicle-to-vehicle communication), thereby improving the safety of the vehicle at the intersection. Can do.

Japanese Patent No. 2806801

In the above-described intelligent road traffic system, in order to coexist each communication such as inter-vehicle communication, road-to-vehicle communication, and road-to-road communication, it becomes a problem how to perform communication control using the frequency band effectively. Therefore, it has been studied that multiple access is used to perform communication between roads, road vehicles, and vehicles within a limited band.
As this multi-access method, there are frequency division multiplexing (FDMA) and code division multiple access (CDMA), but only in-vehicle communication devices in areas where roadside communication devices are not installed. As a multi-access method for vehicle-to-vehicle communication that is assumed to be used in communication, it is preferable to adopt an autonomous random access method represented by CSMA (Carrier Sense Multiple Access), for example.

  However, for example, when performing inter-vehicle communication to improve vehicle safety at each intersection where urban roadside communication devices are installed, if the CSMA method is adopted for inter-vehicle communication, When the traffic volume increases and the number of in-vehicle communication devices increases, the usable frequency band is limited, causing the following problems.

That is, in the CSMA method, information cannot be transmitted while a radio wave (carrier wave) from another mobile communication device is being detected. Therefore, when the number of mobile communication devices increases in a limited frequency band, information may not be sufficiently transmitted / received in inter-vehicle communication.
Also, especially in urban areas, intersections are provided at relatively close distances, so even if mobile communication devices in the vicinity of each intersection perform vehicle-to-vehicle communication, they are transmitted from mobile communication devices at one intersection. The radio waves easily reach the mobile communication device at the other intersection, and the mobile communication device at the other intersection cannot transmit information.

  Accordingly, the present invention provides roadside communication that can increase the number of wireless communications that can be performed simultaneously within a limited radio resource even when the number of mobile communication devices that perform wireless communications using the carrier sense method increases. It is an object to provide an apparatus and a wireless communication method.

(1) The present invention is a roadside communication device that transmits information wirelessly to a mobile communication device that is used in an intelligent road traffic system and performs vehicle- to- vehicle communication using a carrier sense method. Storage means for storing command information for requesting a decrease in radio wave transmission output or a decrease in radio wave reception sensitivity during the vehicle-to-vehicle communication performed directly, and transmitting the stored command information to the mobile communication device The command information includes a radio wave transmission output during the vehicle-to-vehicle communication in response to an increase in reception level of the radio wave broadcast from the roadside communication device at the mobile communication device. It is information that requests to reduce the reception sensitivity of the radio wave .

According to the present invention, the roadside communicator transmits to the mobile communicator command information requesting a reduction in radio wave transmission output during inter-vehicle communication directly performed by the mobile communicators. The communication device receives the command information from the roadside communication device. When the mobile communication device that has received the command information reduces the transmission output of the radio wave during the inter-vehicle communication , the reach of the radio wave (carrier) can be narrowed, and the other mobile communication device that detects the carrier Becomes difficult to receive the radio waves. Therefore, it is possible to give an opportunity to allow transmit information to another mobile communication device, even if the number mobile communication device for performing inter-vehicle communication by the carrier sensing method is, at the same time inter-vehicle in a limited radio resource The number of mobile communication devices that can perform communication can be increased.

“ Vehicle-to-vehicle communication performed directly between mobile communicators” means that no roadside communicator is involved in the transmission and reception of information between mobile communicators. Means that wireless communication is performed by direct reception by the mobile communication device.

Alternatively, when the command information is information requesting a decrease in radio wave reception sensitivity during the vehicle-to-vehicle communication , one mobile communication device receives the command information and sets the reception sensitivity during the vehicle-to-vehicle communication. When it is lowered, it is difficult to receive radio waves (carriers) transmitted by other mobile communication devices when detecting carriers. Therefore, in the mobile communication device of the one having a reduced reception sensitivity, given the opportunity to be able to transmit information, even if the number mobile communication device for performing inter-vehicle communication by the carrier sensing method is limited radio resources It is possible to increase the number of mobile communication devices that can perform inter-vehicle communication at the same time.

The command information includes a radio wave transmission output or a radio wave reception sensitivity at the time of inter-vehicle communication according to an increase in a reception level of the radio wave broadcast from the roadside communication device at the mobile communication device. This is information requesting to lower the value.

Therefore , even if the mobile communication device enters the communication area where the roadside communication device is transmitting radio waves and receives command information, the mobile communication device receives the radio waves transmitted from the roadside communication device side. If the level is low, vehicle-to-vehicle communication with the mobile communication device is enabled without significantly reducing the radio wave transmission output or radio wave reception sensitivity. On the other hand, if the reception level of the radio wave transmitted from the roadside communication device is high, the vehicle-to-vehicle communication with the mobile communication device is possible even if the radio wave transmission output or radio wave reception sensitivity is greatly reduced. Is obtained.

( 2 ) Further, the command information further includes the vehicle-to-vehicle communication according to the congestion degree of the mobile communication device existing in a communication area where the roadside communication device is transmitting a radio wave. It is preferable that the information is a request to reduce the transmission output of the radio wave or the reception sensitivity of the radio wave.
When the mobile communication device is mounted on a vehicle, if the degree of congestion is high, the speed of the vehicle on which the mobile communication device is mounted becomes relatively slow, and vehicle-to-vehicle communication between mobile communication devices that are separated for traffic safety. The need to do is reduced. For this reason, as the degree of congestion increases, it is preferable to increase the degree to which the radio wave transmission output is reduced, or to increase the degree to which the radio wave reception sensitivity is reduced. Therefore, if information on the degree of congestion is acquired, the above-described adjustment can be made with respect to the degree to which radio wave transmission output is reduced or the radio wave reception sensitivity is reduced by the command information.

( 3 ) Further, the command information further requests to reduce the radio wave transmission output or the radio wave reception sensitivity in the inter-vehicle communication according to the type of vehicle on which the mobile communication device is mounted. It is preferable that the information be
When the vehicle on which the mobile communication device is mounted is an emergency vehicle, it is also possible to communicate with other mobile communication devices that are far away, and for example, it is preferable to notify other mobile communication devices of the approach information of the emergency vehicle. Moreover, it is preferable that the emergency vehicle is notified of travel information of other mobile communication devices that are far away. In this case, according to the type of vehicle on which the mobile communication device is mounted, the degree to which the radio wave transmission output is reduced may be reduced, or the degree to which the radio wave reception sensitivity is reduced may be reduced. Therefore, if information on the type of vehicle on which the mobile communication device is mounted is acquired, the degree to which the transmission output of radio waves is reduced or the reception sensitivity of radio waves is reduced by the command information as described above. Adjustment is possible.

( 4 ) Further, the command information further includes transmission of radio waves during the inter-vehicle communication according to a type of road in which a communication area, which is an area where the roadside communication device is transmitting radio waves, is set. It is preferably information that requests to reduce the output or the reception sensitivity of the radio wave.
When the mobile communicator is mounted on a vehicle and the type of road on which the vehicle travels is a road with a relatively high speed limit, the speed of the vehicle equipped with the mobile communicator increases. Since the travel distance becomes large, there is an increasing need to obtain information on a distant vehicle for traffic safety or to notify the distant vehicle of information on the own vehicle. In this case, depending on the type of road, the degree to which the radio wave transmission output is reduced should be reduced, or the degree to which the radio wave reception sensitivity is reduced should be reduced. Therefore, if information about the type of road in which the communication area is set is acquired, the degree to which radio wave transmission output is reduced or the radio wave reception sensitivity is reduced by the correspondence information is described above. Such adjustment is possible.

( 5 ) Further, the command information is information requesting to further reduce the radio wave transmission output or the radio wave reception sensitivity in the inter-vehicle communication according to the moving speed of the mobile communication device. Is preferred.
When the mobile communication device is mounted on a vehicle and the moving speed (traveling speed) of the vehicle increases, the moving distance per unit time increases. The need to notify the vehicle of the information of the own vehicle increases. In this case, it is preferable to reduce the degree to which the radio wave transmission output is reduced, or to reduce the degree to which the radio wave reception sensitivity is reduced, according to the moving speed. Therefore, if information about the moving speed of the mobile communication device (vehicle) is acquired, the degree of reducing the radio wave transmission output or the degree of reducing the radio wave reception sensitivity according to the correspondence information is as described above. Adjustment is possible.

( 6 ) Further, the command information further includes a radio wave transmission output or reception of the radio wave in the inter-vehicle communication according to an environment in a communication area where the roadside communication device is transmitting the radio wave. It is preferable that the information is required to reduce the sensitivity. If the mobile communication device is mounted on a vehicle and the environment in the communication area is bad, that is, if the driver's visibility is bad due to heavy rain or heavy fog, etc., for traffic safety. It is desirable to convey the surrounding information to the driver as soon as possible, and the need for obtaining information on a distant vehicle or notifying the distant vehicle of the information on the own vehicle increases. In this case, according to the environment in the communication area, the degree to which the radio wave transmission output is reduced may be reduced, or the degree to which the radio wave reception sensitivity is reduced may be reduced. Therefore, if information about the environment in the communication area is acquired, the correspondence information can be adjusted as described above with respect to the degree to which the radio wave transmission output is reduced or the radio wave reception sensitivity is reduced. .

( 7 ) Further, the present invention is used in an intelligent road traffic system in which vehicle-to-vehicle communication is performed between mobile communication devices by a carrier sense method, and road-to-vehicle communication is performed between the mobile communication device and a roadside communication device. In the wireless communication method, the roadside communication device is configured to reduce the transmission output of radio waves or the reception sensitivity of the radio waves during vehicle-to-vehicle communication directly between the mobile communication devices. The command information is a method of transmitting a request for reduction, and the command information is transmitted during the vehicle-to-vehicle communication according to an increase in a reception level of the radio wave broadcast from the roadside communication device at the mobile communication device. It is the information which requests | requires that the transmission output of this radio wave or the receiving sensitivity of the said radio wave should be reduced .

According to the present invention, the roadside communicator transmits to the mobile communicator command information requesting a reduction in radio wave transmission output during inter-vehicle communication directly performed by the mobile communicators. The communication device receives the command information from the roadside communication device. When the mobile communication device that has received the command information reduces the transmission output of the radio wave during the inter-vehicle communication , the reach of the radio wave (carrier) can be narrowed, and the other mobile communication device that detects the carrier Becomes difficult to receive the radio waves. Therefore, it is possible to give an opportunity to allow transmit information to another mobile communication device, even if the number mobile communication device for performing inter-vehicle communication by the carrier sensing method is, at the same time inter-vehicle in a limited radio resource The number of mobile communication devices that can perform communication can be increased.

Alternatively, when the command information is information requesting a decrease in radio wave reception sensitivity during the vehicle-to-vehicle communication , one mobile communication device receives the command information and sets the reception sensitivity during the vehicle-to-vehicle communication. When it is lowered, it is difficult to receive radio waves (carriers) transmitted by other mobile communication devices when detecting carriers. Therefore, in the mobile communication device of the one having a reduced reception sensitivity, given the opportunity to be able to transmit information, even if the number mobile communication device for performing inter-vehicle communication by the carrier sensing method is limited radio resources It is possible to increase the number of mobile communication devices that can perform inter-vehicle communication at the same time.

In each of the present inventions described above, the reason why attention is paid to roadside communication devices that are not directly involved in the communication between the mobile communication devices is as follows.
First, roadside communicators are considered to be installed at places where many mobile communicators are likely to gather (for example, at intersections in urban areas) and often distribute wireless information to mobile communicators. In this case, a large number of mobile communication devices that require wireless information from the roadside communication device (want to obtain wireless information) gather at a place where radio waves from the installed roadside communication device can be received. Therefore, within the radio wave reach of this roadside communication device, the number of mobile communication devices that can communicate at the same time can be increased by applying the devices as described in the present invention, so that mobile communication devices can communicate with each other using the carrier sense method. This is because a technical effect peculiar to the case of direct communication is found.
Second, in the communication area of a roadside communication device, transmission of radio waves of the roadside communication device is often given priority over mobile communication devices. In this case, while the roadside communication device is transmitting radio waves, The mobile communication device is difficult to transmit radio waves, and it is assumed that there are fewer opportunities for the mobile communication device to transmit radio waves compared to places where roadside communication devices are not installed. Therefore, the inventors have found a unique technical effect that the number of mobile communication devices that can simultaneously communicate within a limited time during which the roadside communication device does not transmit radio waves can be increased by the devices described in the present invention. It is.

  ADVANTAGE OF THE INVENTION According to this invention, even if the mobile communication apparatus which performs radio | wireless communication by a carrier sense system in the limited radio wave resource increases, the mobile communication apparatus which can perform radio | wireless communication simultaneously can be increased, and a roadside communication apparatus It becomes possible to make the communication system provided with

[Overall system configuration]
FIG. 1 is a schematic perspective view showing an overall configuration of an intelligent road traffic system (ITS).
As shown in FIG. 1, the intelligent traffic system includes a traffic signal 1, a roadside communication device 2, an in-vehicle communication device 3 (see FIGS. 2 and 3), a central device 4, and an in-vehicle communication device (mobile communication device) 3. Including vehicles 5 and the like.

Each traffic signal 1 is installed at each of a plurality of intersections Ci (i = 1 to 12 in the figure), and is connected to a router 8 via a communication line 7 such as a telephone line. This router 8 is connected to the central device 4 in the traffic control center.
The central device 4 constitutes a LAN (Local Area Network) with the traffic signal device 1 and the roadside communication device 2 of each intersection Ci included in the monitoring area under its control. Therefore, the central device 4 can perform bidirectional communication with each traffic signal 1 and each roadside communication device 2. The central device 4 may be installed on the road instead of the traffic control center.

  In FIG. 1 and FIG. 2, for simplification of illustration, only one signal lamp is depicted at each intersection Ci, but at each actual intersection Ci, at least 4 for ascending and descending roads intersecting each other. There are two signal lights.

[Wireless communication systems, etc.]
FIG. 2 is a road plan view showing a part of the monitoring area of the intelligent road traffic system.
In FIG. 2, each of two roads intersecting each other is illustrated as one lane on one side in the up and down directions, but the road structure is not limited to this.
As shown also in FIG. 2, the traffic system of this embodiment is wireless with a plurality of roadside communication devices 2 capable of wireless communication with the in-vehicle communication device 3, and with the other communication devices 2 and 3 by the carrier sense method. It is provided with an in-vehicle communication device 3 that is a kind of mobile radio transceiver that performs communication.

The plurality of roadside communication devices 2 are installed at each roadside intersection, and are attached to the pillars of the traffic signal device 2 in the examples of FIGS. 1 and 2. On the other hand, the in-vehicle communication device 3 is mounted on each vehicle 5 traveling on the road.
Each roadside communication device 2 has a communication area A in a predetermined range that extends around the roadside communication device 2, and can perform wireless communication with the in-vehicle communication device 3 of each vehicle 5 that travels in the communication area A. The communication area A is an area where the roadside communication device 2 is transmitting radio waves, and the in-vehicle communication device 3 is an area where the radio waves can be received.

  In the traffic system of this embodiment, wireless communication is used between the roadside communication devices 2 (roadside communication), and between the roadside communication device 2 and the vehicle-mounted communication device 3 (from “road” to “car”). Wireless communication is also used for both the vehicle-to-vehicle communication and the vehicle-to-vehicle communication devices 3 (vehicle-to-vehicle communication).

In this transportation system, the in-vehicle communication devices 3 perform direct wireless communication (vehicle-to-vehicle communication) by the carrier sense method even outside the communication area A of the roadside communication device 2. In the communication area A of the roadside communication device 2, direct wireless communication (vehicle-to-vehicle communication) is performed between the three by the carrier sense method.
In the present invention, “direct wireless communication” means that the roadside communication device 2 is not interposed in transmission / reception of information between the in-vehicle communication devices 3, and information transmitted from one in-vehicle communication device 3 It means that wireless communication is performed when the in-vehicle communication device 3 receives directly.

Each roadside communication device 2 that is centrally controlled by the central device 4 assigns time slots to be wirelessly transmitted by a time division multiplexing (TDMA) method. For this reason, the in-vehicle communication device 3 uses the remaining time slot for inter-vehicle communication by the CSMA method. That is, one in-vehicle communication device 3 performs wireless communication with another in-vehicle communication device 3 around the roadside communication device 2 by the carrier sense method.
Each roadside communication device 2 has a time synchronization function with other roadside communication devices 2 in order to control its own transmission timing.

[Roadside communication devices and in-vehicle communication devices]
FIG. 3 is a block diagram showing internal configurations of the roadside communication device 2 and the in-vehicle communication device 3.
The in-vehicle communication device 3 includes a wireless communication unit (transmission / reception unit) 31 connected to an antenna 30 for wireless communication, a control unit 32 including a processor that performs communication control on the communication unit 31, and the control unit 32. And a storage unit 33 including a storage device such as a ROM or a RAM connected thereto.
The wireless communication unit 31 can be configured to be normally used for wireless communication, and includes an oscillator, a modulator, a demodulator, an amplifier, and the like.
The storage unit 33 stores a computer program for communication control executed by the control unit 32, communication device IDs of the communication devices 2 and 3, and the like.

The control unit 32 of the in-vehicle communication device 3 causes the communication unit 31 to perform wireless communication using the carrier sense method for inter-vehicle communication. For this purpose, the detection unit 35 (described later) of the control unit 32 always senses the reception level of the predetermined carrier frequency in the communication unit 31, and performs radio transmission when the value is greater than or equal to a predetermined value. Instead, wireless transmission is performed only when the value is less than the predetermined value.
The transmission data transmitted by the in-vehicle communication device 3 includes a header, data, and a footer. The header includes a preamble and its own vehicle-mounted communication device ID (vehicle ID).

  The control unit 32 of the in-vehicle communication device 3 wirelessly transmits the current position information, speed information, and the like of the vehicle 5 from the communication unit 31 to the outside. For this reason, in the other vehicle 5 or the roadside communication device 2 that has received the position information, the speed information, and the like, for example, safe driving support control for avoiding a right-handed collision or a head-on collision can be performed.

On the other hand, the roadside communication device 2 includes a wireless communication unit (transmission / reception unit) 21 connected to an antenna 20 for wireless communication, a wired communication unit 22 that performs bidirectional communication with the central device 4, and a processor that performs communication control thereof. A control unit 23 including a CPU (Central Processing Unit) and the like, and a storage unit 24 including a storage device such as a ROM and a RAM connected to the control unit 23 are provided.
The wireless communication unit 21 can be configured to be normally used for wireless communication, and includes an oscillator, a modulator, a demodulator, an amplifier, and the like.
The storage unit 24 stores a computer program for communication control executed by the control unit 23, communication device IDs of the communication devices 2 and 3, and the like.

[Functions of the control unit of the roadside communication device and the control unit of the in-vehicle communication device]
The control unit 23 of the roadside communication device 2 causes the wireless communication unit 22 to perform wireless communication between roads and vehicles, between roads, and between roads by a time division multiplexing method. For this reason, the control unit 23 has a first time slot in which the roadside communication device 2 itself wirelessly transmits and a second time slot in which the in-vehicle communication device 3 allows wireless transmission as functional units achieved by executing the computer program. Are allocated in a time division manner at regular intervals.

Furthermore, the control unit 23 of the roadside communication device 2 includes a data transmission unit 23B that is a functional unit achieved by executing the computer program.
The data transmission unit 23B temporarily stores the acquired various information and traffic information such as traffic information of the central device 4 received by the wired communication unit 22 in the storage unit 24, and the information and the storage unit 24 have already been stored. The stored information is broadcasted to the in-vehicle communication device 2 via the wireless communication unit 21 and the antenna 20.

FIG. 4A is a diagram illustrating an example of a data format transmitted by the roadside communication device 2. The transmission data transmitted by the roadside communication device 2 (data transmission unit 23B) includes a header, data, and a footer. The header includes a preamble and its own roadside communication device ID. The data transmission unit 23B can include information stored in the storage unit 24 in a transmission signal, and the transmission data includes command information i and reference information j.
The command information i is information transmitted to the in-vehicle communication device 3 existing in the communication area A, and transmission of radio waves during wireless communication (vehicle-to-vehicle communication) directly performed by the in-vehicle communication devices 3. This is information requesting a decrease in output. The reference information j is information already stored in the storage unit 24, and a specific example will be described later.

  In FIG. 3, the control unit 32 of the in-vehicle communication device 3 includes a detection unit 35, an adjustment unit 36, and an information acquisition unit 37 as functional units executed by the computer program stored in the storage unit 33. The adjustment unit 36 in FIG. 3 is a transmission output adjustment unit 36 a that adjusts the transmission output of the transmission radio wave from the antenna 30. These functions will be described later.

<First embodiment>
FIG. 5A is an explanatory diagram for explaining the functions of the in-vehicle communication device 3 mounted on the roadside communication device 2 and the vehicle 5.
The detection unit 35 of the in-vehicle communication device 3 has a function of detecting that the in-vehicle communication device 3 has entered the communication area A of the roadside communication device 2. For this reason, the detection unit 35 constantly senses the reception level of the radio wave transmitted from the antenna 20 on the roadside communication device 2 side in the communication unit 31. And when the value is more than predetermined value, it can detect that the vehicle-mounted communication apparatus 3 approached in the communication area A of the said roadside communication apparatus 2 concerned. Furthermore, by referring to a specific bit (header) in the received signal, it can be seen that the signal transmission source is the roadside communication device 2.

On the other hand, since the command information i (see FIG. 4A) is included in the information transmitted to the communication area A by the data transmission unit 23B of the roadside communication device 2, the vehicle-mounted communication device 3 is installed. When the vehicle 5 has entered the communication area A, the in-vehicle communication device 3 receives the command information i.
When the in-vehicle communication device 3 receives the command information i, the transmission output adjustment unit 36a of the in-vehicle communication device 3 performs control to reduce the transmission output of radio waves for inter-vehicle communication so as to follow the command information i. The transmission output adjustment unit 36a can adjust the output of the transmission radio wave by controlling the amplifier (not shown) of the communication unit 31, for example.
Therefore, as shown in FIGS. 5A and 5B, when the in-vehicle communication device 3 receives the command signal i from the roadside communication device 2, the transmission output adjustment unit 36a of the in-vehicle communication device 3 Reduce the radio wave transmission output from the standard value.

Further, correspondence information (a function of the distance L and the transmission output) between the distance L and the transmission output as shown in FIG. 4B is transmitted from the roadside communication device 2 as the reference information j.
Therefore, the transmission output adjustment unit 36a of the in-vehicle communication device 3 that has received the command information i and the reference information j is within the communication area A as shown in FIGS. As the distance L between the antenna 20 of the roadside communication device 2 decreases, the radio wave transmission output is greatly reduced.

  For this purpose, the detection unit 35 of the in-vehicle communication device 3 obtains the distance L by grasping the current position of the vehicle 5 and the installation position of the antenna 20 from the GPS function provided in the in-vehicle communication device 3. The transmission output adjustment unit 36a acquires information on the distance L from the detection unit 35 and refers to the reference information j (FIG. 4B) (calculates based on the function of the distance L and the transmission output). Thus, the transmission output of the radio wave corresponding to the distance L is obtained, and processing for reducing the transmission output is performed.

As described above, when the reference information j is referred to, the command information i transmitted from the roadside communication device 2 is used for vehicle-to-vehicle communication 3 for vehicle-to-vehicle communication as the distance L decreases. This is information requesting to reduce the transmission output of the radio wave at.
In addition, since the roadside communication device 2 performs wireless communication with the in-vehicle communication device 3 in the communication area A, it is preferable that the command information i is information as described above. Even if the in-vehicle communication device 3 enters the communication area A and receives the command information i, if the in-vehicle communication device 3 is far from the roadside communication device 2 as shown in FIG. This is so that the roadside communication device 2 can receive the information from the in-vehicle communication device 3 without significantly reducing the above. On the other hand, when the in-vehicle communication device 3 approaches the road-side communication device 2, the road-side communication device 2 can be in a state in which wireless communication with the in-vehicle communication device 3 is possible even if the radio wave transmission output is greatly reduced.

  The reference information j may be a correspondence relationship in which the transmission output is reduced proportionally according to the distance L as shown by the solid line arrow in FIG. ), The transmission output may be reduced stepwise according to the distance L. When gradually reducing the transmission output adjustment unit 36a of the in-vehicle communication device 3, the transmission output of the radio wave is gradually reduced as shown in FIG.

  In addition, the command information i transmitted from the roadside communication device 2 increases the reception level Q of the radio wave transmitted from the roadside communication device 2 in the in-vehicle communication device 3 as shown in FIG. Accordingly, the information may be information requesting to reduce the transmission output of radio waves in the in-vehicle communication device 3 for inter-vehicle communication. In order to set the command information i to such information, the roadside communication device 2 uses the reference level j as the reference information j, as shown in FIG. Correspondence information (a function of reception level Q and transmission output) is transmitted.

  In this case, even if the in-vehicle communication device 3 enters the communication area A and receives the command information i, if the reception level Q is low, the road-side communication device 2 does not significantly reduce the radio wave transmission output. 3 can be received. On the other hand, if the reception level Q is high, the wireless communication with the in-vehicle communication device 3 can be performed even if the transmission output of the radio wave in the in-vehicle communication device 3 is greatly reduced.

  Then, the transmission output adjustment unit 36a of the in-vehicle communication device 3 that has received the command information i and the reference information j follows the in-vehicle communication within the communication area A as shown in FIG. As the reception level Q in the device 3 increases, the radio wave transmission output is greatly reduced.

Therefore, as described above, the detection unit 35 of the in-vehicle communication device 3 always senses the reception level in order to determine whether the in-vehicle communication device 3 has entered the communication area A. From the detection unit 35, the transmission output adjustment unit 36a acquires information on the reception level.
The transmission output adjustment unit 36a acquires information on the reception level from the detection unit 35 and refers to the reference information j (FIG. 4C) (calculates based on a function of the reception level Q and the transmission output). Thereby, the transmission output of the radio wave according to the reception level Q in the in-vehicle communication device 3 is obtained, and processing for reducing the transmission output is performed.

  Note that the radio wave reception level Q in the in-vehicle communication device 3 increases from a position away from the antenna 20 toward the vicinity of the antenna 20 (directly below position). For this reason, the transmission output adjustment unit 36a greatly reduces the transmission output of radio waves as it approaches the antenna 20.

  Also in this case, the reference information j may be a correspondence relationship that proportionally decreases the transmission output in accordance with the reception level Q, as indicated by the solid line arrow in FIG. The transmission output may be reduced stepwise according to the reception level Q, as indicated by the dashed arrow in FIG. In the case of stepwise reduction, the transmission output adjustment unit 36a of the in-vehicle communication device 3 decreases the radio wave transmission output stepwise as shown in FIG.

Further, in FIGS. 5B, 5C, and 5D, the radio wave transmission output is decreased while changing according to the distance L or the reception level Q, but as shown in FIG. 5E. In addition, when the in-vehicle communication device 3 receives the command information i, the transmission output adjustment unit 36a of the in-vehicle communication device 3 reduces the transmission output of the radio wave from the antenna 30 to a predetermined value and maintains the state. You may make it do. That is, when the command information i is received, the radio wave transmission output may be lowered to a certain value.
Alternatively, as shown in FIG. 5 (f), when the in-vehicle communication device 3 receives the command information i, the radio wave transmission output from the antenna 30 is reduced to a predetermined value, and then the reference is made. On the basis of the information j, the radio wave transmission output may be changed while being changed according to the distance L or the reception level Q.

  When the in-vehicle communication device 3 leaves the communication area A, the detection unit 35 of the in-vehicle communication device 3 can detect this, and when this is detected, the transmission output adjustment unit 36a outputs the radio wave transmission output. The normal state before entering the communication area A (a constant output state) is restored.

Alternatively, the roadside communication device 2 may include application time information about the time for which the decrease in transmission output is continued in the command information i. In this case, the in-vehicle communication device 3 that has received the command information i reduces the radio wave transmission output for that time, and autonomously restores the radio wave transmission output when the time has elapsed.
Alternatively, instead of the application time information, application travel distance information related to a distance traveled by reducing radio wave transmission output may be used. In this case, the distance is set to the range of the communication area A. Then, the in-vehicle communication device 3 that has received the command information i including the applicable travel distance information reduces the radio wave transmission output only while traveling the distance, and autonomously transmits the radio wave transmission output after finishing the travel of the distance. To return.

  Or, the roadside communication device 2 has information about the range of its own communication area A in advance, or has learned the range of its own communication area A through communication with the in-vehicle communication device 3, When the individual communication is possible between the road and the vehicle, the control unit 23 predicts the timing when the in-vehicle communication device 3 exits the communication area A based on the information of the range of the communication area A, and outputs the transmission output at the timing. Recovery command information for returning to the normal state may be transmitted to the communication area A. When the in-vehicle communication device 3 receives the restoration command information, the transmission output adjustment unit 36a restores the radio wave transmission output.

  According to the roadside communication device 2 configured as described above, the roadside communication device 2 is mounted on the vehicle-mounted communication device 3 that exists in the communication area A and has a function capable of reducing the transmission output of radio waves. 5, since the command information i is transmitted, the in-vehicle communication device 3 receives the command information i when entering the communication area A. The in-vehicle communication device 3 of one vehicle 5 that has received the command information i reduces the transmission output of radio waves for inter-vehicle communication, so that the reach range of the radio waves (carriers) It can be made narrower.

For this reason, the in-vehicle communication device 3 of another vehicle 5 in the vicinity of the one vehicle 5 receives the radio wave, but the in-vehicle communication device 3 of another vehicle 5 that is a little further away does not receive the radio wave, The in-vehicle communication device 3 of the other vehicle 5 can emit information.
Therefore, even if the frequency band allocated to the transportation system is limited (for example, 10 MHz) or even if the number of in-vehicle communication devices 3 (vehicles 5) increases in the communication area A, radio waves may be emitted simultaneously. The number of in-vehicle communication devices 3 that can be used increases, and the number of in-vehicle communication devices 3 that perform road-to-road communication increases, so that the communication can be actively performed.

  In particular, when the radio frequency used in the traffic system is relatively low, for example, in the UHF band (720 MHz band), the radio wave tends to be diffracted and reach farther as the frequency is lower. Therefore, when the transmission output of the radio wave from the in-vehicle communication device 3 is constant and the transmission output is set to be large in order to effectively execute the inter-vehicle communication in the mountainous area, the roadside communication device 2 is installed in the urban area. When the intersections are provided at a relatively close distance, even if the vehicle-to-vehicle communication is performed at each intersection, the radio wave transmitted from the in-vehicle communication device 3 at one intersection is at the other intersection. The in-vehicle communication device 3 can easily receive, and the in-vehicle communication device 3 at the other intersection may not be able to transmit information. However, according to the present invention, the communication area of one in-vehicle communication device 3 can be reduced, and such a phenomenon can be suppressed.

<Second embodiment>
In the first embodiment, the command information i is information requesting a reduction in the transmission output of radio waves for vehicle-to-vehicle communication. In the second embodiment, the command information i is in-vehicle for vehicle-to-vehicle communication. This is information requesting a decrease in radio wave reception sensitivity in the communication device 3. For this purpose, the adjustment unit 36 of the in-vehicle communication device 3 is a reception sensitivity adjustment unit 36b that adjusts the sensitivity of the received radio wave by the antenna 30, as shown in FIG. The other detection units 35 and the like are the same as those in the first embodiment.

In this second embodiment, as shown in FIGS. 7A and 7B, when the vehicle 5 equipped with the in-vehicle communication device 3 enters the communication area A of the roadside communication device 2, the in-vehicle communication device 3 is The command information i is received.
When the in-vehicle communication device 3 receives the command information i, the reception sensitivity adjusting unit 36b of the in-vehicle communication device 3 performs control to reduce the reception sensitivity of radio waves for inter-vehicle communication so as to follow the command information i. The reception sensitivity adjustment unit 36b can adjust the reception sensitivity by controlling an amplifier (not shown) of the communication unit 31, for example.
Therefore, as shown in FIG. 7B, when the in-vehicle communication device 3 receives the command signal i from the roadside communication device 2, the reception sensitivity adjustment unit 36b sets the reception sensitivity of the radio wave at the antenna 30 to a standard value. Reduce from.

  Further, as in the first embodiment, the command information i is transmitted to the in-vehicle communication device 3 for inter-vehicle communication as the distance L between the antenna 20 of the roadside communication device 2 and the in-vehicle communication device 3 decreases. It can be information requesting to reduce the radio wave reception sensitivity. For this purpose, the roadside communication device 2 only needs to transmit the reference information j (FIG. 4B), and the reception sensitivity adjustment unit 36b is proportional (FIG. 7B) as the distance L decreases. The reception sensitivity of the radio wave can be lowered step by step (see FIG. 7C).

Alternatively, as in the first embodiment, the command information i is transmitted to the vehicle-mounted communication device for vehicle-to-vehicle communication as the reception level Q of the radio wave transmitted from the roadside communication device 2 in the vehicle-mounted communication device 3 increases. 3 may be information requesting to reduce the radio wave reception sensitivity. For this purpose, the roadside communication device 2 only needs to transmit the reference information j (FIG. 4C), and the reception sensitivity adjustment unit 36b decreases the reception sensitivity of the radio wave as the reception level Q increases. (See FIG. 7D).
Furthermore, as shown in FIG. 7E, when the in-vehicle communication device 3 receives the command information i, the reception sensitivity adjustment unit 36b reduces the reception sensitivity of the radio wave by the antenna 30 to a predetermined value. And may maintain that state.

In the second embodiment, the roadside communication device 2 communicates with each other with respect to the vehicle 5 equipped with the vehicle-mounted communication device 3 that exists in the communication area A and has a function of reducing the radio wave reception sensitivity. Command information i for requesting a decrease in radio wave reception sensitivity is transmitted. Thus, when one in-vehicle communication device 3 receives the command information i and decreases the reception sensitivity for inter-vehicle communication, when the one in-vehicle communication device 3 detects a carrier, the other in-vehicle communication device 3 3 becomes difficult to receive the radio wave (carrier) transmitted.
For this reason, the in-vehicle communication device 3 whose reception sensitivity is lowered receives the radio wave transmitted by the in-vehicle communication device 3 of another vehicle 5 in the vicinity, but the radio wave of the in-vehicle communication device 3 of the other vehicle 5 that is a little away is received. The in-vehicle communication device 3 that cannot receive and has reduced reception sensitivity will have more opportunities to emit information.

Therefore, even if the frequency band allocated to the transportation system is limited (for example, 10 MHz) or even if the number of in-vehicle communication devices 3 (vehicles 5) increases in the communication area A, radio waves may be emitted simultaneously. The number of in-vehicle communication devices 3 that can be used increases, and the number of in-vehicle communication devices 3 that perform road-to-road communication increases, so that the communication can be actively performed.
The reception sensitivity of the in-vehicle communication device 3 is restored by the same means as in the first embodiment.

<Third embodiment>
The configuration of the roadside communication device 2 is the same as that of the first or second embodiment, but the roadside communication device 2 determines the transmission output of radio waves for vehicle-to-vehicle communication or the reception sensitivity of the radio waves. Transmits command information requesting to be selected and lowered.
In the in-vehicle communication device 3, as illustrated in FIG. 8, the adjustment unit 36 includes both functions of the transmission output adjustment unit 36 a and the reception sensitivity adjustment unit 36 b. The control unit 32 further includes a selection unit 38 that allows any one of the transmission output adjustment unit 36a and the reception sensitivity adjustment unit 36b to function. The functions of the detection unit 35, the transmission output adjustment unit 36a, and the reception sensitivity adjustment unit 36b are the same as those described in the above embodiment.

The selection unit 38 selects one of the transmission output adjustment unit 36a and the reception sensitivity adjustment unit 36b according to the communication status between vehicles or road vehicles. To describe a specific example, the detection unit 35 can detect reception sensitivity (C / N (Carrier to Noise Ratio), RSSI (Receive Signal Strength Indication)) in addition to detecting reception sensitivity. Therefore, the selection unit 38 executes the selection process based on the reception quality detected by the detection unit 35.
For example, when there is a lot of noise in wireless communication (when reception / reception quality is poor), it is preferable to select the reception sensitivity adjustment unit 36b to function. Thereby, the influence of noise can be suppressed.

  By the communication system provided with the roadside communication device 2 and the in-vehicle communication device 3 of each embodiment configured as described above, the roadside communication device 2 and the in-vehicle communication device in the communication area A of the roadside communication device 2 installed on the roadside. 3, and a vehicle-to-vehicle communication method in which direct vehicle-to-vehicle communication is performed in the communication area A by the carrier sense method is used in the in-vehicle communication in which the roadside communication device 2 exists in the communication area A. This is performed by transmitting to the machine 3 command information i for requesting a decrease in transmission output of radio waves for inter-vehicle communication or a decrease in reception sensitivity of the radio waves.

[About adjustment of transmission output and reception sensitivity]
In each said embodiment, when the roadside communication apparatus 2 transmits the reference information j and the vehicle-mounted communication apparatus 3 receives the reference information j, the vehicle-mounted communication apparatus 3 is based on the reference information j. Depending on the distance L, the degree of reduction in the transmission output of radio waves for vehicle-to-vehicle communication or the degree of reduction in reception sensitivity of the radio waves is adjusted, and the reduction process is performed (vehicle-side processing).
However, in the present invention, the roadside communication device 2 may determine the degree of decrease in the transmission output of radio waves for vehicle-to-vehicle communication or the degree of decrease in reception sensitivity of the radiowaves (roadside processing). For this roadside processing, the control unit 23 of the roadside communication device 2 needs to have an adjustment unit 23C having the same function as the adjustment unit 36 of the in-vehicle communication device 3. However, in this case, the roadside communication device 2 may not transmit the reference information j to the communication area A.

  In the case of roadside processing, the control unit 23 of the roadside communication device 2 acquires, for example, information on the distance L (by inter-road communication), and adjusts the roadside communication device 2 based on the acquired information and reference information j. The unit 23C determines the degree of reduction in the transmission output of radio waves for vehicle-to-vehicle communication or the degree of reduction in reception sensitivity of the radio waves. Then, the roadside communication device 2 transmits command information i including information on the determined degree of decrease to the in-vehicle communication device 3 in the communication area A. The in-vehicle communication device 3 that has received the command information i may reduce the transmission output of the radio wave according to the determined degree according to the command information i.

  In the following, the roadside communication device 2 also transmits the reference information j to determine the degree of reduction in the transmission output of radio waves for vehicle-to-vehicle communication or the degree of reduction in reception sensitivity of the radio waves. 3 is performed (that is, the on-vehicle side processing).

In each of the above embodiments, the adjustment unit 36 of the in-vehicle communication device 3 further adjusts the transmission output based on other criteria other than the distance L and the reception level Q, and adjusts the reception sensitivity. can do.
For this purpose, the roadside communication device 2 further has reference information j2 shown as a table in FIGS. 9 and 10. The reference information j2 is stored in the storage unit 24 of the roadside communication device 2.
The reference information j2 is information in which various determination criteria such as the degree of congestion in the communication area A are associated with the degree of decrease in transmission output (degree of decrease in reception sensitivity). In FIGS. 9 and 10, only the degree of decrease in transmission output is shown as a representative.

  Specifically, the reference information j2 includes the type of road in which the communication area A is set, the congestion level of the in-vehicle communication device 3 existing in the communication area A, the vehicle 5 in which the in-vehicle communication device 3 is mounted. Transmission based on one of the conditions of the traveling speed, the type of the vehicle 5 on which the in-vehicle communication device 3 is mounted, and the environment in the communication area A, or a combination of two or more of these conditions This is information for determining the degree of decrease in output.

  The roadside communication device 2 transmits the command information i to the communication area A, and the degree of decrease in the radio wave transmission output in the in-vehicle communication device 3 is determined based on the reference information j2. i is the type of road where the communication area A is set, the congestion level of the in-vehicle communication device 3 existing in the communication area A, the traveling speed of the vehicle 5 in which the in-vehicle communication device 3 is mounted, the in-vehicle communication device 3 Depending on the type of vehicle 5 on which the vehicle is mounted and one of the environments in the communication area A or a combination of two or more of these, the transmission output of radio waves for inter-vehicle communication is This is information requesting to be lowered.

  In addition, the control unit 32 of the in-vehicle communication device 3 includes the information acquisition unit 37 as a function unit, and the control unit 23 of the roadside communication device 2 similarly includes an information acquisition unit 23D as a function unit (for example, FIG. 3), which will be described later, these information acquisition units can acquire various types of information.

  Then, the process of determining the degree of decrease in the transmission output by the adjustment unit 36 is performed in accordance with the degree of decrease in the transmission output (reception received from the received reference information j2 and the information acquired by the information acquisition unit 37). This is done by extracting the degree of sensitivity reduction. The adjustment unit 36 can adjust the transmission output (adjust the reception sensitivity) according to the degree.

A specific example will be described.
The storage unit 24 of the roadside communication device 2 stores road type information related to the type of road for which the communication area A is set as the reference information j2 (FIG. 9). The types of roads are, for example, ordinary roads, automobile-only roads, and the like, and it is assumed that the speed limit is set higher on automobile-only roads than on ordinary roads.

For example, in FIG. 4, the roadside communication device 2 transmits the road type information to the communication area A in addition to the command information i and the reference information j2. When the in-vehicle communication device 3 enters the communication area A, the information acquisition unit 37 of the in-vehicle communication device 3 acquires these information via the communication unit 31.
And the adjustment part 36 of the vehicle-mounted communication apparatus 3 adjusts the degree which reduces the transmission output of the electromagnetic wave from the antenna 30 based on the said road classification information and reference information j2 (FIG. 9) according to the command information i. (Or adjust the degree to which the reception sensitivity of the radio wave by the antenna 30 is lowered).

  Specifically, according to the road type information acquired by the information acquisition unit 37, when the road type is an automobile-only road with a relatively high speed limit, the speed of the vehicle 5 equipped with the in-vehicle communication device 3 is Because the speed increases, the travel distance per unit time increases, and the necessity of performing vehicle-to-vehicle communication between vehicles separated for driving assistance and traffic safety increases. That is, it is necessary to obtain information on a distant vehicle or notify the distant vehicle of the information on the own vehicle. For this reason, in order to make the communication area of the in-vehicle communication device 3 relatively wide, the adjustment unit 36 reduces the degree of reduction in the radio wave transmission output. That is, according to the reference information j2 in FIG. 9, the normal transmission output is reduced to about “medium”. On the other hand, when the road type is a general road, according to the reference information j2 in FIG. 9, the normal transmission output is reduced to “small” which is smaller than “medium”.

Further, the roadside communication device 2 monitors the signals from the surrounding vehicle-mounted communication devices 3, so that the information acquisition unit 23D of the roadside communication device 2 grasps the number of vehicle-mounted communication devices 3 present in the surroundings. It is possible to obtain congestion information on the degree of congestion of the mobile communication devices 3 existing in the communication area A.
Therefore, in addition to the command information i and the reference information j2, the congestion information is also transmitted from the roadside communication device 2, and the information acquisition unit 37 of the in-vehicle communication device 3 can acquire these information by road-to-vehicle communication. .
And the adjustment part 36 of the vehicle-mounted communication apparatus 3 adjusts the degree which reduces the transmission output of the electromagnetic wave from the antenna 30 based on the said congestion information and reference information j2 (FIG. 9) according to the command information i ( Or, the degree to which the reception sensitivity of the radio wave by the antenna 30 is lowered is adjusted).

  Specifically, the adjustment unit 36 makes a determination based on the congestion information. If the degree of congestion is high, the speed of the vehicle 5 on which the in-vehicle communication device 3 is mounted becomes relatively slow. Therefore, the necessity of performing wireless communication between the in-vehicle communication devices 3 separated from each other is reduced. For this reason, as the degree of congestion increases, the degree to which the radio wave transmission output is reduced is increased, the radio wave transmission output is greatly reduced (or the degree to which the radio wave reception sensitivity is reduced is increased, and the radio wave reception sensitivity is increased. Greatly reduced).

Further, the information acquisition unit 37 of the in-vehicle communication device 3 can acquire speed information related to the traveling speed of the vehicle 5 from a vehicle speed sensor (not shown) provided in the vehicle 5.
In this case, the command information i and the reference information j2 are transmitted from the roadside communication device 2, and the information acquisition unit 37 of the in-vehicle communication device 3 can acquire these information by road-to-vehicle communication.
And the adjustment part 36 of the roadside communication apparatus 2 adjusts the degree which reduces the transmission output of the electromagnetic wave from the antenna 30 based on the said speed information and reference information j2 (FIG. 9) according to the command information i ( Or, the degree to which the reception sensitivity of the radio wave by the antenna 30 is lowered is adjusted).

  Specifically, when the traveling speed of the vehicle 5 increases, the travel distance per unit time increases, so the need for inter-vehicle communication between the distant vehicles 5 for driving assistance and traffic safety increases. . That is, it is necessary to obtain information on a distant vehicle or notify the distant vehicle of the information on the own vehicle. For this reason, in order to make the communication area of the in-vehicle communication device 3 relatively wide, the adjustment unit 36 reduces the degree of reducing the radio wave transmission output based on the speed information (or reduces the radio wave reception sensitivity). Reduce the degree).

Further, when the in-vehicle communication device 3 is mounted on the vehicle 5, the vehicle type information regarding the vehicle type is stored in the storage unit 33 of the in-vehicle communication device 3. Note that the types of vehicles include general vehicles and emergency vehicles as shown in FIG. The information acquisition unit 37 can acquire vehicle type information from the storage unit 33.
In this case, the command information i and the reference information j2 are transmitted from the roadside communication device 2, and the information acquisition unit 37 of the in-vehicle communication device 3 can acquire these information by road-to-vehicle communication.
And the adjustment part 36 of the roadside communication apparatus 2 is the degree which reduces the transmission output of the electromagnetic wave from the antenna 30 based on the said vehicle classification information and reference information j2 (FIG. 10 (a)) according to the command information i. (Or adjust the degree to which the reception sensitivity of the radio wave by the antenna 30 is lowered).

Specifically, when the vehicle 5 equipped with the in-vehicle communication device 3 is an emergency vehicle such as a patrol car or an ambulance, communication with the in-vehicle communication device 3 of another remote vehicle 5 is possible, and the approach information of the emergency vehicle It is preferable to notify (information indicating that an emergency vehicle is approaching) to another mobile communication device. In addition, as an emergency vehicle equipped with the in-vehicle communication device 3, it is preferable that travel information (information indicating that the vehicle is traveling) of another vehicle 5 (the in-vehicle communication device 3) that is distant is also notified.
Therefore, when the vehicle type information is an emergency vehicle, the adjustment unit 36 of the in-vehicle communication device 3 reduces the transmission output of the radio wave in order to relatively widen the communication area of the in-vehicle communication device 3 mounted on the emergency vehicle. The degree should be reduced, and the normal transmission output should be reduced to the “medium” level (or the degree to which the radio wave reception sensitivity is reduced should be reduced).

The information acquisition unit 23D of the roadside communication device 2 can acquire environment information from the sensor 40 that detects the environment of the communication area A. The sensor 40 can detect the amount of rainfall and the degree of fog.
Therefore, in addition to the command information i and the reference information j2, the environmental information is also transmitted from the roadside communication device 2, and the information acquisition unit 37 of the in-vehicle communication device 3 can acquire these information by road-to-vehicle communication. .
And the adjustment part 36 of the vehicle-mounted communication apparatus 3 sets the degree which reduces the transmission output of the electromagnetic wave from the antenna 30 based on the acquired said environment information and reference information j2 (FIG.10 (b)) according to the command information i. Adjust (or adjust the degree to which the reception sensitivity of radio waves by the antenna 30 is lowered).

Specifically, when the environment around the roadside communication device 2 is bad, that is, when the driver's visibility is bad due to heavy rain, heavy fog, etc., the necessity of performing vehicle-to-vehicle communication between the distant vehicles 5 increases. That is, it is desirable to convey the surrounding information to the driver as soon as possible for traffic safety, and the necessity of obtaining information on a distant vehicle or notifying the distant vehicle of the information on the own vehicle increases. For this reason, when the roadside communication device 2 acquires environmental information related to the surrounding environment by the sensor 40, the in-vehicle communication device 3 can receive this environmental information by road-to-vehicle communication.
In this case, when the environment information is bad, the adjustment unit 36 of the in-vehicle communication device 3 preferably reduces the degree of reduction of the radio wave transmission output according to the received environmental information. Decrease it to the “medium” level (or reduce the degree of decrease in radio wave reception sensitivity).

In addition, with respect to the present invention, the embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is not meant to be described above, but is intended to include all modifications within the meaning and scope equivalent to the scope of the claims.
For example, in the above-described embodiment, the mobile communication device has been described as the in-vehicle communication device 3 (a mobile communication device for a vehicle mounted on the vehicle 5), but the mobile communication device may be mounted on a device other than the vehicle. May have.
Moreover, although the case where the transmission unit of the present invention is configured by the function of the control unit 23 (data transmission unit 23B) has been described in the above embodiment, the transmission unit of the present invention includes the wireless communication unit 21 and the control unit 23 ( It can be configured by at least one of the functions of the data transmission unit 23B).

It is a schematic perspective view which shows the whole structure of an intelligent road traffic system. It is a top view which shows a part of intelligent traffic system. It is a block diagram which shows the internal structure of a roadside communication apparatus and a vehicle-mounted communication apparatus. It is a figure which shows an example of the information which a roadside communication apparatus transmits. It is explanatory drawing for demonstrating the function of a roadside communication apparatus and a vehicle-mounted communication apparatus. It is a block diagram which shows the internal structure of a roadside communication apparatus and a vehicle-mounted communication apparatus. It is explanatory drawing for demonstrating the function of a roadside communication apparatus and a vehicle-mounted communication apparatus. It is a block diagram which shows the internal structure of a roadside communication apparatus and a vehicle-mounted communication apparatus. It is explanatory drawing explaining the reference information as a table | surface. It is explanatory drawing explaining the reference information as a table | surface.

Explanation of symbols

2 Roadside communication equipment 3 Onboard communication equipment (mobile communication equipment)
5 vehicle 23B data transmission part (transmission means)
24 storage unit (storage means)
A Communication area i Command information L Distance Q Reception level

Claims (7)

A roadside communication device that transmits information wirelessly to a mobile communication device that is used in an intelligent road traffic system and performs vehicle- to- vehicle communication using a carrier sense method.
Storage means for storing command information for requesting a decrease in radio wave transmission output or a decrease in radio wave reception sensitivity during the inter-vehicle communication performed directly between the mobile communication devices;
Transmission means for transmitting the stored command information to the mobile communication device ,
The command information reduces the radio wave transmission output or the radio wave reception sensitivity during the inter-vehicle communication in response to an increase in the reception level of the radio wave broadcast from the roadside communication device at the mobile communication device. A roadside communication device characterized in that the information is requested to be executed. The command information further includes transmission of radio waves during the vehicle-to-vehicle communication according to the degree of congestion of the mobile communication device existing in a communication area that is an area where the roadside communication device is transmitting radio waves. The roadside communication device according to claim 1 , which is information requesting to reduce output or reception sensitivity of the radio wave. The instruction information further wherein according to the type of vehicle in which the mobile communication device is mounted is information requesting to reduce the reception sensitivity of the transmission power or the radio wave of a radio wave during the inter-vehicle communication according Item 3. A roadside communication device according to item 1 or 2 . The command information further includes the transmission output of the radio wave during the vehicle-to-vehicle communication or the radio wave according to the type of road in which the communication area that is the area where the roadside communication device is transmitting the radio wave is set. The roadside communication device according to any one of claims 1 to 3 , wherein the roadside communication device is information requesting to reduce reception sensitivity. The instruction information further according to the moving speed of the mobile communication device, according to claim 1-4 which is information for requesting to reduce the reception sensitivity of the transmission power or the radio wave of a radio wave during the inter-vehicle communication The roadside communication device according to any one of the above. The command information further reduces the radio wave transmission output or the radio wave reception sensitivity in the inter-vehicle communication according to the environment in the communication area where the roadside communication device is transmitting radio waves. The roadside communication device according to any one of claims 1 to 5 , wherein the roadside communication device is information requested to the device. With the inter-vehicle communication is performed by the carrier sensing method by the mobile communication device together, the road-vehicle communication is performed by said mobile communication device and the roadside communication device, a wireless communication method used in intelligent transportation systems,
The roadside communication device sends command information requesting the mobile communication device to reduce the transmission output of radio waves or decrease the reception sensitivity of the radio waves during vehicle-to-vehicle communication performed directly between the mobile communication devices. Is a way to send
The command information reduces the radio wave transmission output or the radio wave reception sensitivity during the inter-vehicle communication in response to an increase in the reception level of the radio wave broadcast from the roadside communication device at the mobile communication device. A wireless communication method characterized in that the information is information requested to be executed.

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