JP2013123168A - On-vehicle communication equipment, its roadside equipment, on-vehicle communication lsi, and its roadside equipment lsi - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a communication apparatus to perform transmission power control which can maintain throughput as well as secure a service area in road-to-vehicle and vehicle-to-vehicle communications accessed by a CSMA/CA method.SOLUTION: In a communication apparatus, a road information database in which position information and vehicle density information are correlated to each other and a communication control unit are incorporated. The road information database outputs vehicle density information on the basis of position information which is input. The communication control unit controls transmission power on the basis of vehicle density information at its own position which is obtained by using the road information database. Since transmission power control is exercised so as to lower transmission power in an area where the vehicle density is high or raise transmission power in an area where the vehicle density is low without consuming throughput for communication to obtain the vehicle density information, communication with optimum transmission power necessary to secure a service area can be performed while maintaining throughput intact.

Description

  The present invention relates to a wireless communication apparatus, and more particularly to a technology that is effective when applied to an Intelligent Transport System (ITS).

  Wireless LAN (local area network) has been put into practical use by the technical standard IEEE802.11a (Non-Patent Document 1). This wireless LAN is a technical standard that assumes communication in a home or office.

  There is a technology that mounts wireless LAN devices in automobiles, communicates with roadside communication devices installed beside the road, and also communicates between vehicles, and the technical standard IEEE802.11p system has been proposed overseas (non-patented) Reference 2).

  In these, an access method called CSMA / CA (Carrier Sense Multiple Access with Collision Avoidance) is used, but a method for controlling the transmission power of the host vehicle is not defined.

  As a conventional technique for controlling transmission power, there is a technique for controlling transmission power by receiving road width, number of lanes, and weather from a database via a communication network (Patent Document 1).

JP 2008-227797 A

IEEE802.11a-1999, Part11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications: High-speed Physical Layer in the 5 GHz Band IEEE802.11p / D7.01 July 2009, Part11: Wireless LAN Medium Access Control (MAC) and Physical Layer (PHY) specifications, Amendment 7: Wireless Access for Vehicular Environments

  In road-to-vehicle communication and vehicle-to-vehicle communication accessed by the CSMA / CA method, when vehicles are densely populated, signal collisions occur frequently when the transmission power is large, and many vehicles must wait for communication to start. Data throughput is reduced. On the other hand, in the prior art disclosed in Patent Document 1, wireless transmission / reception is performed in order to obtain road information of the vehicle position, and road information is obtained via a communication network. There was a problem of increased traffic and reduced throughput.

  On the other hand, if the transmission power is lowered more than necessary, there is a problem that the communication distance is shortened and a sufficient service area cannot be secured.

  An object of the present invention is to provide a communication apparatus that performs transmission power control capable of both maintaining throughput and securing a service area in road-to-vehicle communication and vehicle-to-vehicle communication accessed by the CSMA / CA method.

  The above and other objects and novel features of the present invention will be apparent from the description of this specification and the accompanying drawings.

  The following is a brief description of an outline of typical inventions disclosed in the present application.

  That is, a communication device including a road information database in which position information and vehicle density information are associated with each other and a communication control unit, and the communication control unit inputs position information of a location where the communication control unit exists to the road information database. Thus, the communication device obtains the vehicle density information at its own position and controls the transmission power from the high frequency transmission / reception unit based on the obtained vehicle density information.

  The effects obtained by the representative ones of the inventions disclosed in the present application will be briefly described as follows.

  That is, it is possible to perform transmission power control that lowers transmission power in areas with high vehicle density and increases transmission power in areas with low vehicle density without consuming throughput by communication for obtaining vehicle density information. Thus, communication can be performed with optimum transmission power in order to secure a service area.

FIG. 1 is a block diagram illustrating an in-vehicle communication device according to the first embodiment. FIG. 2 is a diagram illustrating a road information database according to the first embodiment. FIG. 3 is a diagram illustrating a transmission power table according to the first embodiment. FIG. 4 is a block diagram illustrating an ITS roadside machine according to the second embodiment. FIG. 5 is a diagram illustrating the optimum transmission power when the vehicle density is high. FIG. 6 is a diagram illustrating the optimum transmission power when the vehicle density is low. FIG. 7 is a diagram illustrating an in-vehicle communication device LSI according to a third embodiment. FIG. 8 is a diagram showing an LSI for an ITS roadside machine according to the third embodiment. FIG. 9 is a diagram illustrating an ITS roadside device LSI according to the fourth embodiment. FIG. 10 is a diagram illustrating an on-vehicle communication device LSI according to a fifth embodiment.

1. First, an outline of a typical embodiment of the invention disclosed in the present application will be described. Reference numerals in the drawings referred to in parentheses in the outline description of the representative embodiments merely exemplify what are included in the concept of the components to which the reference numerals are attached.

[1] <In-vehicle communication device equipped with a database for obtaining vehicle density based on position information>
From a high frequency transmission / reception unit (11), a GPS reception unit (14), a road information database (13, 51) in which position information and vehicle density information are associated, and a communication control unit (12) that controls these The in-vehicle communication device (10), which operates as follows.

  The communication control unit inputs the position information (16) from the GPS receiving unit to the road information database (13, 51) to obtain vehicle density information (54) at the position of the own vehicle, and the vehicle density In accordance with the information, the high-frequency transmitter / receiver is controlled to vary the transmission power.

  Thereby, it is possible to perform communication with the optimum transmission power in order to secure the service area while maintaining the throughput.

[2] <In-vehicle communication device further provided with a transmission power table>
In item 1, the vehicle density information in the road information database is information (54) in which the vehicle density of a place on the map is classified into N stages (N is an integer of 2 or more) based on the traffic volume examined in advance. ). The position information in the road information database is latitude / longitude information (16) obtained from the GPS receiver. The road information database (51) associates the latitude / longitude information with the vehicle density information. The communication control unit has a table (55) in which the transmission power is classified into N stages and associated with the vehicle density information, and determines the transmission power (56) according to the latitude / longitude information.

  Thereby, transmission power can be determined at high speed from the obtained position information.

[3] <Vehicle density DB divided into four stages + vehicle-mounted communication device provided with transmission power table>
In Item 2, the road information database divides the vehicle density into four stages (54), and the communication control unit divides the transmission power into four stages (56) to control the high-frequency transceiver unit. The table is a 4: 4 table (55) in which a high transmission output is associated with a large vehicle density.

  Thereby, transmission power can be determined at higher speed.

[4] <ITS roadside machine>
An ITS composed of a high-frequency transmission / reception unit (11), a GPS reception unit (14), a road information database (13) in which position information and vehicle density information are associated, and a communication control unit (21) for controlling them. The roadside machine (30) operates as follows.

  The communication control unit inputs the position information (16) from the GPS receiving unit to the road information database, obtains vehicle density information (54) of the own roadside machine installation position, and according to the vehicle density information The obtained transmission power (56) is stored as an initial value, and the high frequency transmission / reception unit is controlled to transmit at the initial value of the transmission power.

  As a result, it is possible to provide an ITS roadside device that performs communication with the optimum transmission power in order to secure a service area while maintaining the throughput.

[5] <In-vehicle communication LSI>
A semiconductor memory (including a high-frequency transmission / reception unit (11) and a communication control unit (12), which stores the road information database in which the GPS reception unit (14) is associated with the position information and the vehicle density information ( 70) and operates in the following manner.

  The communication control unit inputs position information (16) from the GPS receiving unit to the road information database to obtain vehicle density information (54) of the own vehicle position, and according to the vehicle density information, The transmission power is varied by controlling the high frequency transmission / reception unit.

  As a result, it is possible to provide an in-vehicle communication LSI that performs communication with optimal transmission power in order to secure a service area while maintaining throughput.

[6] <LSI for ITS roadside machine>
A high-frequency transmission / reception unit (11) and a communication control unit (21); a GPS reception unit (14); and a semiconductor memory (70) storing the road information database in which position information and vehicle density information are associated with each other. The LSI is connected to and operates as follows.

  The communication control unit inputs the position information (16) from the GPS receiving unit to the road information database, obtains vehicle density information (54) of the own roadside machine installation position, and according to the vehicle density information The obtained transmission power (56) is stored as an initial value, and the high frequency transmission / reception unit is controlled to transmit at the transmission power initial value.

  As a result, it is possible to provide an ITS roadside device LSI that performs communication with optimum transmission power to maintain a service area while maintaining throughput.

[7] <GPS receiver on chip>
Item 5. The in-vehicle communication LSI according to Item 5 or the ITS roadside device LSI according to Item 6, comprising the GPS receiver.

  Thereby, the integration degree of the LSI can be increased and the cost can be reduced.

[8] <On-chip road information database>
The on-board communication LSI or the ITS roadside device LSI according to Item 7, including the semiconductor memory (70) storing the road information database.

  Thereby, the integration degree of the LSI can be further increased, and the cost can be further reduced.

2. Details of Embodiments Embodiments will be further described in detail.

  It will be described that there is an optimum transmission power capable of maintaining a high throughput according to the vehicle density on the road, which is the principle of the present invention.

Embodiment 1
First, it is well known that in the CSMA / CA system used in a wireless LAN, when the number of communication terminals increases, communication becomes congested and throughput decreases. When this is applied to in-vehicle mobile communications such as ITS, there is a relationship that the increase in the number of communication terminals = the increase in the number of communication vehicles = the increase in transmission power of the in-vehicle device. As the transmission power of the in-vehicle device increases, the range over which radio waves reach increases, so the number of terminals that can communicate increases.

  Based on the above, it will be explained that there exists optimum transmission power that can maintain high throughput according to the vehicle density on the road.

  FIG. 4 shows the distribution of vehicle density on the road. The vehicle density is divided into four stages: a commercial area 66, an urban area 67, a suburb 68, and a countryside / hill area not shown.

  In front of the railway station 64, there is a national road 61 (the thickest line in the figure) on one side of three lanes, and a prefectural road 62 on one side of two lanes intersects. Such a place (named commercial place 66) has a high traffic volume and a very high vehicle density. A place where the prefectural road 62 and the city road 63 (one lane on one side) intersect with the commercial area 66 has a slightly lower traffic volume and a medium vehicle density. This is named city area 67. Further, in a place (named suburb 68) located outside the urban area 67 with the commercial area 66 as the center, the city road 63 passes, the traffic volume is low, and the vehicle density is low.

  From this vehicle density information, the in-vehicle communication device reception sensitivity, and the transmission data transmission speed per user, the optimum transmission power capable of maintaining a high throughput can be calculated.

  A method for obtaining the optimum transmission power will be described with reference to FIGS. 5 and 6.

  FIG. 5 shows the optimum transmission power when the vehicle density is high (corresponding to an urban area 67 in FIG. 2 described later). On the right side, a graph showing the relationship of the number of accommodable users determined from traffic with respect to the transmission rate per user is shown, and on the left side, a graph showing the relationship of the accommodated number of subscribers in the cell to the transmission power Pt is shown. The wireless LAN system has operation modes in which the modulation speed is high, medium, and low, and the curve in the graph represents the correlation in each operation mode. In FIG. 5, the calculation is performed under the condition of vehicle density = 43 vehicles / km assuming the urban area 67.

  When the in-vehicle communication device communicates at 3 Mbps, it operates in the high-speed modulation mode, and the accommodable number of users determined from the traffic is found to be 48 from the curve on the right side of FIG. In the left of FIG. 5, it can be seen that in the same high-speed modulation mode, the transmission power Pt that can accommodate the 48 users is the “medium” level. This transmission power level is optimum, radio signal congestion occurs at transmission power higher than this level, and the number of users that can be accommodated decreases at low transmission power.

  Next, FIG. 6 shows the optimum transmission power when the vehicle density is low (corresponding to a suburb 68 in FIG. 2 described later). The vertical axis and horizontal axis of the right and left graphs are the same as those in FIG. 5, and the calculation is performed under the condition of vehicle density = 10 vehicles / km assuming the suburbs 68.

  When the in-vehicle communication device communicates at 3 Mbps, it operates in the high-speed modulation mode. From the curve in the graph on the right side of FIG. In the left of FIG. 6, in the same high-speed modulation mode, the transmission power Pt that can accommodate the 48 users is the “maximum” level.

  The “maximum” level is optimal when the vehicle density is low, and is different from the “medium” level when the vehicle density is very high. In other words, there is an optimum transmission output depending on the vehicle density.

  The present invention utilizes this principle, and obtains the vehicle density in FIG. 4 from the position information by GPS, obtains the vehicle density based on this, and determines the optimum transmission power. The positional information and the vehicle density are stored in a database as a correspondence relationship in advance, and the transmission power is controlled by referring to the database while moving.

  FIG. 2 shows a road information database according to an embodiment of the present invention. In FIG. 2, the road information database 51 stores latitude and longitude 16 representing position information, road data 53, and vehicle density 54 in association with each other. When the latitude / longitude 16 which is the position information is given, the vehicle density 54 at the point can be obtained. The vehicle density 54 is classified into four types, for example, a commercial area 66, an urban area 67, a suburb 68, and a countryside / hill area 69. The vehicle density corresponding to the road data can be calculated in advance from, for example, past statistical data, and a plurality of tables depending on changes due to time, day of the week, season, etc. may be prepared and appropriately replaced.

  FIG. 3 shows a transmission power table according to an embodiment of the present invention. The transmission power table 55 stores the transmission power Pt 56 in association with the vehicle density 54.

  Corresponding to the four sections of the vehicle density 54, the transmission power Pt56 has four levels of +0.0 dBm, +10 dBm, +20 dBm, and +30 dBm.

  An in-vehicle communication device according to an embodiment of the present invention is shown in FIG. In the in-vehicle communication device 10, 20 is a wireless LAN communication unit, 11 is a wireless LAN transmission / reception unit, 12 is a communication control unit, 13 is a road information DB (database), 14 is a GPS reception unit, 15 is a GPS antenna, and 16 is latitude / longitude. Data, 17 is a wireless LAN antenna, 18 is ITS transmission / reception data, and 19 is a PA control signal. Further, 31 is a car navigation control unit, 32 is a map DB (database), 33 is a terrestrial digital control unit, 34 is a terrestrial digital reception unit, 36 is map data, 37 is a terrestrial digital reception antenna, 38 is terrestrial digital video / audio data, Reference numeral 41 denotes a display unit, and 42 denotes display data. The PA control signal 19 is a signal for controlling a power amplifier (PA) in the wireless LAN transmission / reception unit 11 and controls transmission power and the like.

  In order to prevent a collision between the host vehicle and another vehicle, the wireless LAN communication unit 20 performs wireless communication with the wireless LAN communication unit of the other vehicle. This communicates by the ad hoc mode which is a communication method between wireless LAN apparatuses.

  The communication control unit 12 controls the GPS receiving unit 14 to know the latitude / longitude data 16. The car navigation control unit 31 normally operates as a car navigation system, and displays a map of the current position on the display unit 41.

  The in-vehicle communication device 10 according to the present embodiment inputs the latitude / longitude data 16 to the road information DB 13 and obtains the vehicle density 54. The communication control unit 12 obtains the transmission power Pt 56 from the vehicle density 54 based on the predetermined transmission power table 55, adjusts the transmission power by the PA control signal 19, and transmits it from the wireless LAN antenna 17.

  An example of the operation of the in-vehicle communication device 10 will be described with reference to FIGS. The own vehicle is traveling in a commercial area of a city. When the communication control unit 11 obtains the latitude / longitude data 16 = aaaa from the GPS reception unit, it can be seen from the road information DB 51 shown in FIG. The road information DB is based on whether it is an urban area or a suburb, whether a building is dense, whether the number of road lanes is one lane on one side or two lanes on one side, and the density of the vehicle is different for each region. Have as a table. The AA station is divided into commercial areas with high vehicle density. The communication control unit 11 obtains the transmission power Pt of the commercial district from the transmission power table 55 shown in FIG. 3, and outputs the PA control signal 19 so that the transmission power Pt = + 0.0 dBm.

  Thereafter, when the own vehicle moves from the city to the countryside, the communication control unit 11 obtains latitude / longitude data 16 = dddd from the GPS reception unit, and it is understood from the road information DB (FIG. 2) that it is included in the DD ranch. . The vehicle density 54 in this DD ranch is a countryside / hill region with a low vehicle density. The communication control unit 11 obtains the transmission power Pt of the countryside / hill region from the transmission power table 55 (FIG. 3), and outputs the PA control signal 19 so that the transmission power Pt = + 30 dBm.

  The road information DB 13 changes the range in which the road data 53 includes the latitude / longitude data 16 according to the vehicle density, that is, the area matching the AA station is narrow and the area matching the DD ranch is wide. Yes.

  Specifically, the commercial area is an area centered on a station or a downtown area, for example, an area having a radius of 3 to 5 km such as near Shinjuku Station in Tokyo or near Shibuya Station. In this region, the transmission power Pt = + 0.0 dBm is output so that the reach of radio waves is within a few hundred meters, thereby avoiding communication congestion.

  An urban area is a residential area within a 20-minute walk from a station, away from a downtown area, and is an area with a radius of 10 km. Corresponds to C3.3 Urban area described in Appendix C, Propagation Conditions of GSM05.05, which is the GSM mobile phone system standard. In this region, the transmission power Pt = + 10.0 dBm is output to make the radio wave reach within 1 km, thereby avoiding communication congestion.

  The suburb is an intermediate point between the residential area and the countryside, and is an area with a radius of 20 km. In this area, the transmission power Pt = + 20.0 dBm is output to reduce the reachable range of the radio wave to about 5 km and ensure a communicable distance.

  The countryside / hill region is a so-called countryside area of a mountainous area or a coastal area, and has a radius of 40 km. Corresponds to C3.1 Rural area described in Appendix C, Propagation Conditions of GSM05.05, which is the standard for GSM mobile phone systems. In this region, the transmission power Pt = + 30.0 dBm is output, so that the reachable range of radio waves is about 10 km, and the communicable distance is widened.

  In order to operate in this way, the in-vehicle communication device of the present invention reduces the transmission power in densely populated areas to prevent radio signal congestion and ITS data throughput reduction, and increases the transmission power in areas with few vehicles. By extending the communication distance, it is possible to maintain both throughput and service area.

  The radius, transmission power, radio wave reach distance, etc. in the region setting are merely examples, and can be determined as appropriate.

[Embodiment 2]
FIG. 7 shows an ITS roadside machine according to the second embodiment of the present invention. In FIG. 7, 30 is an ITS roadside machine, 21 is a roadside machine communication control part, and others are the same as FIG.

  The ITS roadside machine 30 is fixedly installed at an intersection or a roadside and communicates with a passing vehicle. The roadside machine communication control unit 21 communicates with a plurality of vehicles in an infrastructure mode that is a wireless LAN master-slave communication method.

  In the ITS roadside machine 30, as an initial operation, the roadside machine communication control unit 21 controls the GPS receiving unit 14 to know the latitude / longitude data 16. The latitude / longitude data 16 is input to the road information DB 13 to obtain the vehicle density 54. The communication control unit 12 obtains the transmission power Pt56 from the vehicle density 54 based on the predetermined transmission power table 55, and stores it as the initial transmission power value.

  Next, infrastructure mode transmission is performed with the initial transmission power value by adjusting the transmission power by the PA control signal 19. Thereafter, the transmission power is transmitted with the same value.

  The ITS roadside machine 30 is used in a fixed manner. However, when the roadside machine arrangement is changed, the initial operation is performed again, and the initial value of transmission power appropriate to the own position is stored.

  In order to operate in this way, the ITS roadside unit according to the present embodiment reduces transmission power in a densely populated area of the vehicle to prevent radio signal congestion and ITS data throughput reduction, and reduces transmission power in areas where there are few vehicles. It is possible to achieve both throughput maintenance and service area securing by increasing the communication distance.

  Although the initial value of the transmission power has been described as a single value, it is not necessary to be limited to a single value, and may be appropriately changed depending on time, day of the week, season, and other factors.

[Embodiment 3]
FIG. 8 shows an in-vehicle communication device LSI according to a third embodiment of the present invention. In FIG. 8, reference numeral 40 denotes an in-vehicle communication device LSI, 70 denotes a semiconductor memory in which a road information database is stored, and the others are the same as those in FIG.

The in-vehicle communication device LSI 40 includes a wireless LAN transceiver 11, a GPS receiver 14, and a communication controller 12.
The semiconductor memory 70 stores the road information of FIG. 2 as a database.

  In the in-vehicle communication device LSI 40, the communication control unit 12 controls the GPS receiving unit 14 to learn the latitude / longitude data 16 and inputs it to the semiconductor memory 70 to obtain the vehicle density 54.

  Thereafter, the operation is the same as in the first embodiment.

  In order to operate in this way, the LSI for in-vehicle communication device of the present invention lowers the transmission power in a crowded area of the vehicle to prevent radio signal congestion and a decrease in the ITS data throughput, and reduces the transmission power in an area where the vehicle is small. It is possible to achieve both throughput maintenance and service area securing by increasing the communication distance.

[Embodiment 4]
FIG. 9 shows an LSI for an ITS roadside machine according to a fourth embodiment of the present invention. In FIG. 9, 50 is an LSI for an ITS roadside machine, 70 is a semiconductor memory in which a road information database is stored, and the others are the same as in FIG.

  The ITS roadside device LSI 50 includes a wireless LAN transmission / reception unit 11, a GPS reception unit 14, and a roadside device communication control unit 21. The semiconductor memory 70 stores the road information of FIG. 2 as a database.

  In the ITS roadside machine LSI 50, the roadside machine communication control unit 21 controls the GPS receiving unit 14 to learn the latitude / longitude data 16 and inputs it to the semiconductor memory 70 to obtain the vehicle density 54.

  Thereafter, the operation is the same as in the second embodiment.

  In order to operate in this manner, the LSI for ITS roadside machine of the present invention lowers transmission power in densely populated areas to prevent radio signal congestion and ITS data throughput degradation, and reduces transmission power in areas with few vehicles. It is possible to achieve both throughput maintenance and service area securing by increasing the communication distance.

[Embodiment 5]
FIG. 10 shows an in-vehicle communication device LSI according to a fifth embodiment of the present invention. In FIG. 10, 60 is an in-vehicle communication device LSI, 35 is prefecture information output from the car navigation control unit 31, 52 is a prefecture buffer memory for storing a part of the road information DB 13, and the others are the same as in FIG. It is.

  The in-vehicle communication device LSI of the present invention optimally controls the transmission power by comparing the current position and road information. The fifth embodiment is an example in which this comparison processing is speeded up.

  When the car navigation control unit 31 of the car navigation system with the digital TV broadcast reception function moves beyond the reception area of the broadcasting station, the car navigation control unit 31 outputs the reception area information. In general, since the reception area of a broadcasting station is in units of prefectures, the reception area information is updated when moving across prefectures. Therefore, in this embodiment, it is described as prefecture information 35.

  The communication control unit 12 transfers only the corresponding information from the road information DB 13 to the prefecture buffer memory 52 based on the prefecture information 35.

  The communication control unit 12 searches the prefectural buffer memory 52 for transmission power that matches the latitude / longitude data 16 and sets it in the wireless LAN transmission / reception unit 11.

  Since it operates in this way, transmission power search can be realized at high speed.

  Although the invention made by the present inventor has been specifically described based on the embodiments, it is needless to say that the present invention is not limited thereto and can be variously modified without departing from the gist thereof.

  For example, the in-vehicle communication LSI and the ITS roadside device LSI according to the embodiment of the present invention may be configured to include a function of obtaining vehicle density from position information and controlling transmission power based on the vehicle density. The functional blocks formed in can be selected as appropriate. For example, the wireless LAN transmission / reception unit 11 and the communication control unit 12 may be configured, or the wireless LAN transmission / reception unit 11, the communication control unit 12, and the semiconductor memory 70 may be configured.

  Moreover, although the vehicle density and transmission power showed the example divided into four steps, the division | segmentation step can be determined suitably.

10 in-vehicle communication device 30 ITS roadside device 40 60 LSI for in-vehicle communication device
50 LSI for ITS roadside machine
70 Semiconductor memory 20 Wireless LAN communication unit 11 Wireless LAN transmission / reception unit 12 Communication control unit 13 Road information DB (database)
14 GPS receiver 31 Car navigation controller 32 Map DB (database)
33 terrestrial digital control unit 34 terrestrial digital reception unit 41 display unit 52 prefecture buffer memory 16 latitude / longitude data 19 PA control signal 51 road information database 54 vehicle density 55 transmission power table 56 optimum transmission power

Claims (8)

In an in-vehicle communication device including a high-frequency transmission / reception unit, a GPS reception unit, a road information database in which position information and vehicle density information are associated, and a communication control unit that controls these,
The communication control unit inputs position information from the GPS receiving unit to the road information database, obtains vehicle density information at the position of the host vehicle, and controls the high-frequency transmitting / receiving unit according to the vehicle density information. To change the transmission power,
In-vehicle communication device. In claim 1,
The vehicle density information in the road information database is information representing a vehicle density of a place on a map divided into N stages (N is an integer of 2 or more) based on a traffic volume examined in advance.
The location information of the road information database is latitude and longitude information obtained from the GPS receiver,
The road information database associates the latitude / longitude information with the vehicle density information,
The communication control unit has a table in which the transmission power is divided into N stages and associated with the vehicle density information, and determines the transmission power according to the latitude and longitude information.
In-vehicle communication device. In claim 2,
The road information database classifies the vehicle density into four stages,
The communication control unit divides the transmission power into four stages to control the high-frequency transmission / reception unit,
The table is a 4: 4 table in which a high transmission output is associated with a large vehicle density.
In-vehicle communication device. In an ITS roadside unit comprising a high-frequency transmission / reception unit, a GPS reception unit, a road information database in which position information and vehicle density information are associated, and a communication control unit that controls these,
The communication control unit inputs the position information from the GPS receiving unit to the road information database, obtains vehicle density information of the own roadside device installation position, and initially sets the transmission power obtained according to the vehicle density information. Storing as a value, transmitting the initial value of the transmission power by controlling the high-frequency transmitting and receiving unit,
ITS roadside machine. In-vehicle communication LSI configured to include a high-frequency transmission / reception unit and a communication control unit and operate by being connected to a GPS reception unit and a road information database in which position information and vehicle density information are associated with each other.
The communication control unit inputs position information from the GPS receiving unit to the road information database, obtains vehicle density information of the vehicle position, and controls the high-frequency transmission / reception unit according to the vehicle density information. Variable transmission power
In-vehicle communication LSI. In an ITS roadside equipment LSI that is configured to include a high-frequency transmission / reception unit and a communication control unit, and operates by being connected to a GPS reception unit and a road information database in which position information and vehicle density information are associated with each other.
The communication control unit inputs the position information from the GPS receiving unit to the road information database, obtains vehicle density information of the own roadside device installation position, and initially sets the transmission power obtained according to the vehicle density information. Storing as a value, transmitting the initial value of the transmission power by controlling the high-frequency transceiver unit,
LSI for ITS roadside machine. The in-vehicle communication LSI according to claim 5, comprising the GPS receiver.
In-vehicle communication LSI. The in-vehicle communication LSI according to claim 7, comprising a semiconductor memory storing the road information database.
In-vehicle communication LSI.

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