JP2010118907A - Mobile communication equipment and radio communication method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide mobile communication equipment capable of increasing the number of times for simultaneously performing radio communication in limited radio wave resources even if the number of pieces of mobile communication equipment for performing radio communication by carrier sense systems is increased. <P>SOLUTION: The mobile communication equipment performs radio communication to other in-vehicle communication systems 3 by the carrier sense systems. The mobile communication equipment includes: a detection section 35 for detecting the approach of a roadside communication system 2 into a communication area A; and an adjustment section 36 for reducing a transmission output of a radio wave from an antenna 30 when the detection section 35 detects the approach of the roadside communication system into the communication area A. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to, for example, a mobile 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-mentioned 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 by effectively using the frequency band. 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.

  Therefore, the present invention provides a mobile communication that can increase the number of wireless communications that can be simultaneously performed within a limited radio wave resource even when the number of mobile communications 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 mobile communication device that performs radio communication with other mobile communication devices by a carrier sense method, and is in a communication area that is an area where roadside communication devices installed on the roadside are transmitting radio waves. A detection unit that detects entry, and an adjustment unit that lowers the transmission output of radio waves from the antenna or reduces reception sensitivity of radio waves when the detection unit detects entry into the communication area. It is characterized by.

  According to the present invention, when wireless communication is performed between mobile communication devices by the carrier sense method, when entering the communication area of the roadside communication device, the adjustment unit reduces the transmission output of the radio wave from the antenna. The reach of the radio wave (carrier) can be narrowed, and it becomes difficult for other mobile communication devices that detect the carrier to receive the radio wave. For this reason, it is possible to give an opportunity to transmit information to other mobile communication devices, and even if mobile communication devices increase around roadside communication devices, wireless communication can be performed simultaneously within limited radio resources. It is possible to increase the number of mobile communication devices that can be used.

  Alternatively, when the radio wave reception sensitivity is lowered by the adjustment unit of the present invention, it is difficult to receive radio waves (carriers) transmitted by other mobile communication devices when carrier detection is performed. For this reason, mobile communication devices with reduced reception sensitivity are given the opportunity to transmit information, and even if there are more mobile communication devices around roadside communication devices, wireless communication can be performed simultaneously within limited radio resources. It is possible to increase the number of mobile communication devices that can perform the communication.

  The detection unit can detect, for example, that it has entered the communication area when it can receive a radio wave transmitted from a roadside communication device, or it can detect itself with a GPS function provided in the mobile communication device. It is possible to detect that the current position has entered the communication area by determining whether or not the position of the self is present in the communication area stored in advance.

(2) Further, the adjustment unit reduces the radio wave transmission output or the radio wave reception sensitivity as the distance to the roadside communication device decreases within the communication area of the roadside communication device. Is preferred.
In this case, if it is within the communication area of the roadside communication device but is far from the roadside communication device, radio communication with the roadside communication device can be performed without significantly reducing the radio wave transmission output or reception sensitivity. On the other hand, if it is close to a roadside communication device, a state in which wireless communication with the roadside communication device can be obtained even if the transmission output or reception sensitivity of radio waves is greatly reduced.

(3) Alternatively, the adjustment unit reduces the radio wave transmission output or receives the radio wave as the reception level of the radio wave transmitted from the roadside communication device increases within the communication area of the roadside communication device. It is preferable to reduce the sensitivity.
In this case, if the reception level of the radio wave transmitted from the roadside communication device is low, wireless communication with the roadside communication device can be performed without significantly reducing the radio wave transmission output or reception sensitivity. On the other hand, if the reception level of the radio wave transmitted from the roadside communication device is high, the wireless communication with the roadside communication device can be achieved even if the transmission output or reception sensitivity of the radio wave is greatly reduced.

  (4) Further, the present invention is a mobile communication device that performs wireless communication with another mobile communication device by a carrier sense method, the detection unit detecting a distance from a roadside communication device installed on the roadside, and the detection And an adjusting unit that reduces the radio wave transmission output or the radio wave reception sensitivity as the distance detected by the unit decreases.

  According to the present invention, when wireless communication is performed between mobile communication devices by the carrier sense method, the transmission output of the radio wave from the antenna is reduced by the adjustment unit as the distance from the roadside communication device decreases. Therefore, the reach of the radio wave (carrier) can be narrowed, and it becomes difficult for other mobile communication devices that detect the carrier to receive the radio wave. For this reason, it is possible to give an opportunity to transmit information to other mobile communication devices, and even if mobile communication devices increase around roadside communication devices, wireless communication can be performed simultaneously within limited radio resources. It is possible to increase the number of mobile communication devices that can be used.

  Alternatively, when the radio wave reception sensitivity is lowered by the adjustment unit of the present invention, it is difficult to receive radio waves (carriers) transmitted by other mobile communication devices when carrier detection is performed. For this reason, mobile communication devices with reduced reception sensitivity are given the opportunity to transmit information, and even if there are more mobile communication devices around roadside communication devices, wireless communication can be performed simultaneously within limited radio resources. It is possible to increase the number of mobile communication devices that can perform the communication.

  (5) In addition, the present invention is a mobile communication device that performs wireless communication with another mobile communication device by a carrier sense method, and detects a reception level of a radio wave transmitted from a roadside communication device installed on the roadside. And an adjustment unit that reduces the radio wave transmission output or the radio wave reception sensitivity as the reception level detected by the detection unit increases.

  According to the present invention, when wireless communication is performed between mobile communication devices by the carrier sense method, the adjustment unit causes the radio wave from the antenna to be received as the reception level of the radio wave transmitted from the roadside communication device increases. Since the transmission output is reduced, the reach of the radio wave (carrier) can be narrowed, and it becomes difficult for other mobile communication devices that detect the carrier to receive the radio wave. For this reason, there are many opportunities to be able to transmit information to other mobile communication devices, and even if the number of mobile communication devices increases around roadside communication devices, wireless communication can be performed simultaneously within limited radio wave resources. The number of mobile communication devices that can be increased.

  Alternatively, when the radio wave reception sensitivity is lowered by the adjustment unit of the present invention, it is difficult to receive radio waves (carriers) transmitted by other mobile communication devices when carrier detection is performed. For this reason, mobile communication devices with reduced reception sensitivity have more opportunities to transmit information, and even if mobile communication devices increase around roadside communication devices, wireless communication can be performed within limited radio resources. The number of mobile communication devices that can be performed can be increased.

(6) Moreover, each said mobile communication apparatus is further equipped with the information acquisition part which acquires the congestion information regarding the congestion degree of the mobile communication apparatus which exists around the said roadside communication apparatus, The said adjustment part was acquired. It is preferable to adjust the degree of reducing the radio wave transmission output or the degree of reducing the radio wave reception sensitivity based on the congestion information.
When this 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 wireless communication is performed between mobile communication devices that are separated for traffic safety. Since the necessity becomes low, it is better to increase the degree to reduce the radio wave transmission output as the degree of congestion increases, or to increase the degree to reduce the radio wave reception sensitivity. According to the above, such adjustment is possible.

(7) The mobile communication device further includes an information acquisition unit that acquires vehicle type information related to a type of a vehicle on which the mobile communication device is mounted, and the adjustment unit includes the acquired vehicle type information. Based on this, it is preferable to adjust the degree of reducing the radio wave transmission output or the degree of reducing the radio wave reception sensitivity.
For example, when the vehicle on which the mobile communication device of the present invention is mounted is an emergency vehicle, communication with other mobile communication devices that are far away is possible, and for example, approach information of the emergency vehicle is notified to other mobile communication devices. It is also preferable for emergency vehicles to be notified of travel information of other mobile communication devices that are far away. Therefore, in this case, the adjustment unit may reduce the degree to which the radio wave transmission output is reduced based on the vehicle type information, or may reduce the degree to which the radio wave reception sensitivity is reduced. According to the above, such adjustment is possible.

(8) The mobile communication device further includes an information acquisition unit that acquires road type information related to a type of a moving road, and the adjustment unit transmits radio waves based on the acquired road type information. It is preferable to adjust the degree of lowering the output or the degree of lowering the radio wave reception sensitivity.
When this mobile communicator is mounted on a vehicle and the road type is a road with a relatively high speed limit, the speed of the vehicle equipped with the mobile communicator increases, so the travel distance per unit time increases. Therefore, there is an increasing need for obtaining information on a distant vehicle for traffic safety or notifying the distant vehicle of information on the own vehicle. Therefore, in this case, the adjustment unit may reduce the degree to which the radio wave transmission output is reduced based on the road type information, or reduce the degree to which the radio wave reception sensitivity is reduced. According to the above, such adjustment is possible.

(9) The mobile communication device further includes an information acquisition unit that acquires speed information related to a moving speed of the mobile communication device, and the adjustment unit transmits radio waves based on the acquired speed information. It is preferable to adjust the degree of lowering the output or the degree of lowering the radio wave reception sensitivity.
When this mobile communicator is mounted on a vehicle, the moving speed of the mobile communicator consists of the traveling speed of the vehicle. And when the speed of a vehicle equipped with a mobile communication device increases, the distance traveled per unit time increases, so you can get information on a distant vehicle for traffic safety or send information about your vehicle to a distant vehicle. Increased need for notification. Therefore, in this case, the adjustment unit should reduce the degree of reducing the radio wave transmission output based on the speed information, or reduce the degree of reduction of the radio wave reception sensitivity. Such an adjustment is possible.

(10) The mobile communication device may further include an information acquisition unit that acquires environment information about an environment around the roadside communication device, and the adjustment unit may be configured to receive radio waves based on the acquired environment information. It is preferable to adjust the degree of reducing the transmission output or the degree of reducing the radio wave reception sensitivity.
When this mobile communication device is installed in a vehicle and the surrounding environment of the roadside communication device is bad, that is, when the driver's visibility is poor due to heavy rain, heavy fog, etc., to convey the surrounding information to the driver as soon as possible for traffic safety This is desirable, and there is an increased need for obtaining information on a distant vehicle and notifying the distant vehicle of information on the own vehicle. Therefore, in this case, the adjustment unit should reduce the degree of reducing the radio wave transmission output based on the environmental information, or reduce the degree of reduction of the radio wave reception sensitivity. Such an adjustment is possible.

  (11) Further, the present invention is a wireless communication method for performing wireless communication between mobile communication devices by a carrier sense method, and when the mobile communication device approaches a roadside communication device installed on a roadside, the mobile communication device The transmission characteristic of the radio wave from the antenna connected to the machine is reduced or the reception sensitivity of the radio wave is reduced.

  According to the present invention, when wireless communication is performed between mobile communication devices using the carrier sense method, when the mobile communication device approaches the roadside communication device, the radio wave transmission output from the antenna connected to the mobile communication device is reduced. Since it is lowered, the reach of the radio wave (carrier) can be narrowed, and it becomes difficult for other mobile communication devices that detect the carrier to receive the radio wave. For this reason, it is possible to give an opportunity to transmit information to other mobile communication devices, and even if mobile communication devices increase around roadside communication devices, wireless communication can be performed simultaneously within limited radio resources. It is possible to increase the number of mobile communication devices that can be used.

  Alternatively, according to the present invention, when the mobile communication device approaches the roadside communication device, the radio wave reception sensitivity is reduced. Therefore, when detecting a carrier, it is difficult to receive the radio wave (carrier) transmitted by another mobile communication device. Become. For this reason, mobile communication devices with reduced reception sensitivity are given the opportunity to transmit information, and even if there are more mobile communication devices around roadside communication devices, wireless communication can be performed simultaneously within limited radio resources. It is possible to increase the number of mobile communication devices that can perform the communication.

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 this mobile communication It becomes possible to make a communication system equipped with a machine useful.

[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, only one signal lamp is depicted at each intersection Ci for simplification of illustration, 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 of a predetermined range extending around the roadside communication device 2 and can communicate with the in-vehicle communication device 3 of each vehicle 5 traveling 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).

Each roadside communication device 2 that is centrally controlled by the central device 4 assigns time slots to be wirelessly transmitted by the central device 4 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 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 (CPU) that performs communication control thereof. A central processing unit) and a storage unit 24 connected to the control unit 23, such as a ROM or a RAM.
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.

  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.

Further, the control unit 23 of the roadside communication device 2 includes a data transfer unit 23B that is a functional unit achieved by executing the computer program.
The data transfer unit 23B temporarily stores traffic information such as traffic jam information of the central device 4 received by the wired communication unit 22 in the storage unit 24, and transmits the traffic information to the in-vehicle communication device 2 via the wireless communication unit 21. Broadcast transmission.

On the other hand, 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. And a storage unit 33 including a storage device such as a ROM or a RAM connected to the storage unit 32.
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 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.

[Functions of the control unit of the in-vehicle communication device]
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.

<First embodiment>
FIG. 4A is an explanatory diagram for explaining the function of the in-vehicle communication device 3 mounted on the vehicle 5. The detection unit 35 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 in the received signal, it can be seen that the signal transmission source is the roadside communication device 2. When detecting the entry of the roadside communication device 2 into the communication area A, the detection unit 35 generates an entry signal.

  The transmission output adjustment unit 36 a performs control to reduce the transmission output of the radio wave from the antenna 30 by receiving the entry signal from the detection unit 35. 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 illustrated in FIG. 4B, when the detection unit 35 detects that the in-vehicle communication device 3 has entered the communication area A, the transmission output adjustment unit 36 a Decrease the transmission power from the standard value.

  Further, as shown in FIGS. 4A and 4B, the transmission output adjustment unit 36a responds as the distance L between the roadside communication device 2 (antenna 20) in the communication area A becomes smaller. The transmission output of radio waves has been greatly reduced. For this purpose, the detection unit 35 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 storage unit 33 stores correspondence information (function of the distance L and the transmission output) that associates the distance L with the value of the radio wave transmission output. The transmission output adjusting unit 36a can obtain (calculate) the transmission output of the radio wave according to the distance L based on the correspondence information (function) by acquiring information on the distance L from the detecting unit 35. Then, processing for reducing the transmission output is performed.

  As a mode in which the transmission output adjustment unit 36a reduces the transmission output of radio waves, it can be proportionally reduced according to the distance L as shown in FIG. Or you may reduce in steps according to the distance L like FIG.4 (c).

  Further, since the in-vehicle communication device 3 performs wireless communication with the roadside communication device 2 in the communication area A of the roadside communication device 2, as illustrated in FIGS. 4B and 4C, the transmission output adjustment unit 36a. However, in the communication area A, it is preferable to greatly reduce the transmission output of radio waves as the distance L to the roadside communication device 2 (antenna 20) decreases. As a result, if the in-vehicle communication device 3 is located in the communication area A of the roadside communication device 2 but is far from the roadside communication device 2, the transmission output of the radio wave is not reduced so much. The information can be received by the roadside communication device 2. On the other hand, when the in-vehicle communication device 3 is close to the roadside communication device 2, even if the transmission output of the radio wave is greatly reduced, wireless communication with the roadside communication device 2 can be achieved.

Further, as described above, since the detection unit 35 constantly senses the reception level in order to determine whether or not the in-vehicle communication device 3 has entered the communication area A, the transmission output adjustment unit 36a The information regarding the reception level can be acquired from 35.
Therefore, in addition to adjusting the transmission output of the radio wave according to the distance L, the transmission output adjustment unit 36a, in the communication area A, as the reception level of the radio wave transmitted from the roadside communication device 2 increases, The radio wave transmission output may be greatly reduced based on the correspondence information. The correspondence information is information (a function of the reception level and the transmission output) that associates the reception level of the radio wave transmitted from the roadside communication device 2 with the value of the radio wave transmission output, and is stored in the storage unit 33. Yes.

In addition, the reception level of the radio wave transmitted from the antenna 20 on the roadside communication device 2 side 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.
Even in this case, the transmission output adjustment unit 36a may decrease the transmission output of the radio wave proportionally as the reception level of the radio wave increases as shown in FIG. As shown in d), it may be lowered step by step as the radio wave reception level increases.

  Further, since the in-vehicle communication device 3 performs wireless communication with the roadside communication device 2 in the communication area A of the roadside communication device 2, the transmission output adjustment unit 36a is connected to the communication area A as shown in FIG. In particular, it is preferable to greatly reduce the transmission output of radio waves as the reception level of radio waves transmitted from the roadside communication device 2 increases. As a result, the in-vehicle communication device 3 is located in the communication area A of the roadside communication device 2, but if the reception level of the radio wave transmitted from the roadside communication device 2 is low, the in-vehicle communication device 3 transmits the radio wave. An attempt is made to maintain wireless communication between the in-vehicle communication device 3 and the roadside communication device 2 without reducing the output so much. On the other hand, if the reception level of the radio wave transmitted from the roadside communication device 2 is high, the wireless communication with the roadside communication device 2 can be made possible even if the transmission output of the radio wave is greatly reduced.

  Further, in FIGS. 4B, 4C, and 4D, the radio wave transmission output is lowered while being changed according to the distance L to the roadside communication device 2 (antenna 20) or the reception level. As shown in e), the transmission output adjustment unit 36a determines the transmission output of the radio wave from the antenna 30 when the detection unit 35 detects that the in-vehicle communication device 3 has entered the communication area A. The value may be lowered to maintain this state. That is, when entering communication area A, the radio wave transmission output may be lowered to a certain value.

Alternatively, as shown in FIG. 4 (f), when the detection unit 35 detects that the in-vehicle communication device 3 has entered the communication area A, the transmission output of the radio wave from the antenna 30 is set to a predetermined value. Then, it may be lowered while changing the transmission output of the radio wave according to the distance L or the reception level.
When the in-vehicle communication device 3 leaves the communication area A, the detection unit 35 can detect this, and when this is detected, the transmission output adjustment unit 36a converts the radio wave transmission output into the communication area A. It returns to the normal state before entering (constant output state).

  A plurality of vehicles 5 equipped with the mobile communication device 3 configured as described above travels around the roadside communication device 2 and wirelessly communicates between the in-vehicle communication devices 3 of these vehicles 5 by the carrier sense method (between vehicles). 4 (a), when the in-vehicle communication device 3 of one vehicle 5 enters the communication area A of the roadside communication device 2, the transmission output of the in-vehicle communication device 3 is performed. The adjustment unit 36a can reduce the reach of the radio wave (carrier) by reducing the transmission output of the radio wave from the antenna 30 as compared with that before entering the communication area A.

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 traffic system is limited (for example, 10 MHz) or even if the number of in-vehicle communication devices 3 (vehicles 5) existing around the roadside communication device 2 is increased, At the same time, the number of in-vehicle communication devices 3 that can emit radio waves increases, the number of roadside communication increases, and 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 adjustment unit 36 of the in-vehicle communication device 3 is the transmission output adjustment unit 36a that adjusts the transmission output of the transmission radio wave. However, the adjustment unit 36 is based on the antenna 30 as shown in FIG. The reception sensitivity adjustment unit 36b that adjusts the sensitivity of the reception radio wave may be used. The other detection units 35 and the like are the same as those in the first embodiment.

  In this case, as shown in FIGS. 6A and 6B, when the detection unit 35 detects that the in-vehicle communication device 3 has entered the communication area A, the reception sensitivity adjustment unit 36b Decrease reception sensitivity. The reception sensitivity adjustment unit 36b can adjust the reception sensitivity by adjusting an amplifier (not shown) of the communication unit 31, for example. The reception sensitivity adjustment unit 36b performs control to reduce the reception sensitivity from a standard value by receiving the entry signal from the detection unit 35. The storage unit 33 of the in-vehicle communication device 3 stores correspondence information that associates the distance L with the radio wave reception sensitivity.

  Similarly to the first embodiment, also in this second embodiment, the reception sensitivity adjustment unit 36b reduces the distance L between the roadside communication device 2 and the communication area A of the roadside communication device 2. Accordingly, the radio wave reception sensitivity can be reduced proportionally (see FIG. 6B) or stepwise (see FIG. 6C). Alternatively, as in the first embodiment, the reception sensitivity adjustment unit 36b decreases the reception sensitivity of radio waves in the communication area A as the reception level of radio waves transmitted from the roadside communication device 2 increases. It is also possible (see FIG. 6D).

  Furthermore, as shown in FIG. 6E, the reception sensitivity adjustment unit 36b receives the radio wave reception sensitivity when the detection unit 35 detects that the in-vehicle communication device 3 has entered the communication area A. May be lowered to a predetermined value and maintained in that state.

  By reducing the reception sensitivity of the radio wave by the reception sensitivity adjustment unit 36b of the second embodiment, when the in-vehicle communication device 3 detects the carrier, the radio wave (carrier) transmitted by the other in-vehicle communication device 3 is received. It becomes difficult to do. 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 traffic system is limited (for example, 10 MHz) or even if the number of in-vehicle communication devices 3 (vehicles 5) existing around the roadside communication device 2 is increased, At the same time, the number of in-vehicle communication devices 3 that can emit radio waves increases, the number of roadside communication increases, and the communication can be actively performed.
When the in-vehicle communication device 3 leaves the communication area A, the detection unit 35 can detect this, and when this is detected, the transmission output adjustment unit 36a converts the radio wave transmission output into the communication area A. It returns to the normal state before entering (constant output state).

<Third embodiment>
In the in-vehicle communication device 3 of the first and second embodiments, the in-vehicle communication device 3 is connected to the roadside communication device 2 in order for the transmission output adjustment unit 36a or the reception sensitivity adjustment unit 36b to adjust the transmission output or reception sensitivity of the transmission radio wave. In the communication area A.
However, in the third embodiment, as shown in FIGS. 7A and 7B, the transmission output adjustment unit 36a as the adjustment unit 36 outputs the transmission output of the transmission radio wave regardless of the inside or outside of the communication area A. adjust. 7A and 7B show a case where the transmission output of the transmission radio wave is adjusted from outside the communication area A. The configuration of the in-vehicle communication device 3 is the same as that shown in FIG.

For this purpose, the detection unit 35 of the in-vehicle communication device 3 has a function of detecting the distance L to the roadside communication device 2. The detection unit 35 obtains the distance L by the GPS function provided in the in-vehicle communication device 3 (as described above), for example.
And the transmission output adjustment part 36a of the vehicle-mounted communication apparatus 3 acquires the information about the said distance L from the detection part 35 continuously, and according to the said distance L becoming small, the transmission output of the electromagnetic wave from the antenna 30 is carried out. Reduce. In this case, the storage unit 33 of the in-vehicle communication device 3 stores correspondence information that associates the distance L with the radio wave transmission output, and the transmission output adjustment unit 36a transmits the transmission output based on the correspondence information. Can be reduced.

Further, as a mode of reducing the radio wave transmission output, it may be reduced proportionally or stepwise in accordance with the distance L as shown in FIG. 7B or 7C.
Furthermore, as illustrated in FIG. 7D, when the detection unit 35 detects that the distance L between the roadside communication device 2 has reached a certain value (La), the transmission output adjustment unit 36 a The transmission output of radio waves from the antenna 30 may be reduced to a predetermined value and maintained in that state.

<Fourth embodiment>
In the fourth embodiment, when the adjustment unit 36 is a reception sensitivity adjustment unit 36b, as shown in FIGS. 8A and 8B, the reception sensitivity adjustment unit 36b of the in-vehicle communication device 3 performs the detection. Information about the distance L to the roadside communication device 2 may be continuously acquired from the unit 35, and the radio wave reception sensitivity may be reduced as the distance L decreases. Note that the decrease in reception sensitivity may be proportional (see FIG. 8B) or stepwise (see FIG. 8C). In this case, the configuration of the in-vehicle communication device 3 is the same as that shown in FIG.

<Fifth embodiment>
In the fifth embodiment, regardless of the inside or outside of the communication area A, the transmission output adjustment unit 36a adjusts the transmission output of the transmission radio wave according to the reception level of the signal transmitted from the roadside communication device 2. The configuration of the in-vehicle communication device 3 is the same as that shown in FIG.
For this purpose, the detection unit 35 of the in-vehicle communication device 3 detects the reception level of the radio wave transmitted from the roadside communication device 2.

However, in this fifth embodiment, even if the reception level is not large enough to receive information from the roadside communication device 2 (information that can be used for traffic support), the reception level is low (so that information cannot be received). Even so, the detection unit 35 can detect. That is, the vehicle-mounted communication device 3 can receive weak radio waves from the roadside communication device 2 even outside the communication area A (distance La) set so that road-to-vehicle communication is effectively performed.
And the transmission output adjustment part 36a of the vehicle-mounted communication apparatus 3 acquires the information regarding the value of a reception level from the detection part 35 continuously, and according to the said reception level detected by the detection part 35 becoming large, FIG. As illustrated in (a), (b), (c), and (d), the transmission output adjustment unit 36a reduces the transmission output of the radio wave from the antenna 30.

<Sixth embodiment>
Further, as the sixth embodiment, when the adjustment unit 36 is the reception sensitivity adjustment unit 36b, the reception sensitivity adjustment unit 36b of the in-vehicle communication device 3 continuously acquires information on the value of the reception level from the detection unit 35. The radio wave reception sensitivity may be lowered as the reception level detected by the detection unit 35 increases. Note that the decrease in reception sensitivity may be proportional (FIG. 8B) or stepwise (FIG. 8C). In this case, the configuration of the in-vehicle communication device 3 is the same as that shown in FIG.

<Seventh embodiment>
As shown in FIG. 11, the adjustment unit 36 may have both functions of the transmission output adjustment unit 36 a and the reception sensitivity adjustment unit 36 b. In this case, the control unit 32 It 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.

  The vehicle-to-vehicle communication method executed by the carrier sense method around the roadside communication device 2 installed on the roadside by the vehicle-mounted communication device 3 of each embodiment configured as described above, the vehicle-mounted communication device 3 is the roadside communication device. When the value approaches 2, the transmission output of the radio wave from the antenna 30 connected to the in-vehicle communication device 3 is reduced, or the reception sensitivity of the radio wave is reduced.

[About adjustment of transmission output and reception sensitivity]
In each of the above embodiments, the adjustment unit 36 of the in-vehicle communication device 3 adjusts the transmission output by the transmission output adjustment unit 36a and the reception sensitivity adjustment unit 36b by adjusting the reception sensitivity, using other conditions as criteria. Or you may.
That is, the adjustment unit 36 is mounted with the type of road on which the vehicle 5 on which the in-vehicle communication device 3 is mounted travels, the congestion level of the in-vehicle communication device 3 existing around the roadside communication device 2, and the in-vehicle communication device 3. One of the conditions of the speed at which the vehicle 5 moves, the type of the vehicle 5 on which the in-vehicle communication device 3 is mounted, and the environment around the roadside communication device 2, or two or more of these conditions Combined matters are used as further criteria.

In order to use these as determination criteria, the storage unit 33 of the in-vehicle communication device 3 stores information (hereinafter referred to as reference information) shown as a table in FIGS. 9 and 10. The reference information is information in which various determination criteria 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.
And the control part 32 of the vehicle-mounted communication apparatus 3 is provided with the said information acquisition part 37, and although demonstrated later, this information acquisition part 37 can acquire various information (for example, refer FIG. 3).
The adjustment unit 36 extracts, from the reference information, the degree of decrease in transmission output (degree of decrease in reception sensitivity) that matches the information acquired by the information acquisition unit 37, and according to the degree Transmission output can be adjusted (reception sensitivity can be adjusted).

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 on which the roadside communication device 2 is installed as the reference information. 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, when the in-vehicle communication device 3 enters the communication area A of the roadside communication device 2, the information acquisition unit 37 of the in-vehicle communication device 3 is communicated from the roadside communication device 2 via the communication unit 31 by road-to-vehicle communication. Then, the road type information relating to the type of road that is running is acquired.
And the adjustment part 36 which the control part 32 of the vehicle-mounted communication apparatus 3 has is based on the said road classification information which the information acquisition part 37 acquired, and the said reference information (FIG. 9) which the memory | storage part 33 has memorize | stored. Based on this, the degree to which the radio wave transmission output from the antenna 30 is reduced (or the degree to which the radio wave reception sensitivity is lowered) is adjusted.

  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 to which the radio wave transmission output is reduced. That is, according to the reference information in FIG. 9, the normal transmission output is reduced to about “medium”. On the other hand, when the type of road is a general road, according to the reference information in FIG. 9, the normal transmission output is reduced to “small” which is smaller than “medium”.

Further, the roadside communication device 2 can grasp the number of vehicle-mounted communication devices 3 existing in the vicinity by monitoring signals from the vehicle-mounted communication devices 3 in the vicinity. For this reason, the roadside communication device 2 can obtain the congestion information regarding the congestion degree of the mobile communication devices existing around the roadside communication device 2. Then, the information acquisition part 37 of the vehicle-mounted communication apparatus 3 can acquire the said congestion information via the communication part 31 from the roadside communication apparatus 2 by road-to-vehicle communication.
Then, the adjustment unit 36 reduces the transmission output of the radio wave from the antenna 30 based on the congestion information acquired by the information acquisition unit 37 and the reference information (FIG. 9) stored in the storage unit 33. (Or adjust the degree of decrease in radio wave reception sensitivity).

  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 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 adjustment unit 36 reduces the transmission output of the radio wave from the antenna 30 based on the speed information acquired by the information acquisition unit 37 and the reference information (FIG. 9) stored in the storage unit 33. Adjust the degree (or adjust the degree to reduce the reception sensitivity of the radio wave).

  Specifically, when the traveling speed of the vehicle 5 increases, the distance traveled per unit time increases, so the need for inter-vehicle communication between the distant vehicles 5 for driving support 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.
Therefore, the adjusting unit 36 adjusts the degree of reducing the radio wave transmission output (or adjusting the degree of reducing the radio wave reception sensitivity) based on the vehicle type information.

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 roadside communication device 2 can acquire environmental information from a sensor that detects the environment around the place where the roadside communication device 2 is installed. The sensor can detect the amount of rainfall and the degree of fog.
Therefore, when the in-vehicle communication device 3 enters the communication area A of the roadside communication device 2, the information acquisition unit 37 of the in-vehicle communication device 3 is connected to the roadside via the communication unit 31 by road-to-vehicle communication from the roadside communication device 2. Environmental information related to the environment around the communication device 2 is acquired.
And the adjustment part 36 which the control part 32 of the vehicle-mounted communication apparatus 3 has is the said environment information which the information acquisition part 37 acquired, and the said reference information which the memory | storage part 33 has memorize | stored (FIG.10 (b)) The degree to which the radio wave transmission output from the antenna 30 is reduced is adjusted (or the degree to which the radio wave reception sensitivity 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, the in-vehicle communication device 3 can receive this environmental information by road-to-vehicle communication.
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, and the normal transmission output is about “medium”. (Or it is better to 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 vehicle-mounted communication device 3 (the vehicle mobile communication device mounted on the vehicle 5) has been described. However, the mobile communication device of the present invention may be mounted on a device other than the vehicle. You may have.

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 explanatory drawing for demonstrating the function of 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 vehicle-mounted communication apparatus. It is explanatory drawing for demonstrating the function of a vehicle-mounted communication apparatus. It is explanatory drawing for demonstrating the function of a vehicle-mounted communication apparatus. It is explanatory drawing explaining the information memorize | stored in the memory | storage part as a table | surface. It is explanatory drawing explaining the information memorize | stored in the memory | storage part as a table | surface. It is a block diagram which shows the internal structure of a roadside communication apparatus and a vehicle-mounted communication apparatus.

Explanation of symbols

1 traffic signal 2 roadside communication device 3 in-vehicle communication device (mobile communication device)
5 Vehicle 30 Antenna 31 Wireless communication unit 32 Control unit 33 Storage unit 35 Detection unit 36 Adjustment unit 36a Transmission output adjustment unit 36b Reception sensitivity adjustment unit 37 Information acquisition unit A Communication area L Distance

Claims (11)

A mobile communication device that performs wireless communication with another mobile communication device using a carrier sense method,
A detection unit that detects that a roadside communication device installed on the roadside has entered a communication area that is an area transmitting radio waves, and an antenna that detects that the detection unit has entered the communication area. A mobile communication device comprising: an adjustment unit that reduces a transmission output of radio waves from the radio or a reception sensitivity of radio waves.   2. The adjustment unit according to claim 1, wherein, in the communication area of the roadside communication device, the transmission unit decreases a radio wave transmission output or decreases a radio wave reception sensitivity as the distance to the roadside communication device decreases. Mobile communication device.   The adjustment unit reduces a radio wave transmission output or a radio wave reception sensitivity as a reception level of a radio wave transmitted from the roadside communication device increases in a communication area of the roadside communication device. Item 2. The mobile communication device according to Item 1. A mobile communication device that performs wireless communication with another mobile communication device using a carrier sense method,
A detection unit that detects a distance to a roadside communication device installed on the roadside, and reduces the transmission output of radio waves from the antenna or the reception sensitivity of radio waves as the distance detected by the detection unit decreases. A mobile communication device comprising: an adjustment unit; A mobile communication device that performs wireless communication with another mobile communication device using a carrier sense method,
A detection unit that detects a reception level of a radio wave transmitted from a roadside communication device installed on a roadside; and a radio wave transmission output from an antenna is reduced or increased according to an increase in the reception level detected by the detection unit A mobile communication device comprising: an adjustment unit that reduces the reception sensitivity of the mobile communication device. An information acquisition unit for acquiring congestion information related to the degree of congestion of mobile communication devices existing around the roadside communication device;
The said adjustment part adjusts the degree to which the transmission output of a radio wave is reduced or the degree to which the reception sensitivity of a radio wave is reduced based on the acquired said congestion information. The mobile communication device described in 1. An information acquisition unit for acquiring vehicle type information related to the type of vehicle on which the mobile communication device is mounted;
The said adjustment part adjusts the degree which reduces the transmission output of an electromagnetic wave, or the degree which reduces the receiving sensitivity of an electromagnetic wave based on the acquired said vehicle classification information. The mobile communication device described. An information acquisition unit for acquiring road type information related to the type of road to be moved;
The said adjustment part adjusts the degree which reduces the transmission output of an electromagnetic wave based on the acquired said road classification information, or the degree which reduces the receiving sensitivity of an electromagnetic wave to any one of Claims 1-7. The mobile communication device described. An information acquisition unit that acquires speed information related to the moving speed of the mobile communication device;
The said adjustment part adjusts the degree which reduces the transmission output of a radio wave, or the degree which reduces the reception sensitivity of a radio wave based on the acquired said speed information. Mobile communication equipment. An information acquisition unit for acquiring environmental information related to the environment around the roadside communication device;
The said adjustment part adjusts the degree which reduces the transmission output of an electromagnetic wave, or the degree which reduces the receiving sensitivity of an electromagnetic wave based on the acquired said environment information. Mobile communication equipment. A wireless communication method for performing wireless communication between mobile communication devices using a carrier sense method,
When the mobile communication device approaches a roadside communication device installed on the roadside, the radio communication output from the antenna connected to the mobile communication device is reduced or the reception sensitivity of the radio wave is reduced. Wireless communication method.

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