JP2003087152A - On-vehicle communication equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide passive on-vehicle communication equipment that can be configured small while keeping the communication performance satisfactory. SOLUTION: In this on-vehicle communication equipment 1, a modulator circuit 30 consists of a Schottky diode 32, a capacitor 34 and an impedance change setting circuit 36. In the on-vehicle communication equipment 1, a control circuit 72 inputs voltage for a reverse bias as a modulation signal to the Schottky diode 32 and power consumption needed when a down signal 114 is modulated is reduced. One terminal is shared by an input terminal for the down signal 114 and an output terminal for an up signal 116 in the modulation circuit 30, and one antenna 10 is shared by an antenna for receiving the down signal 114 and an antenna for transmitting the up signal 116.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle communication device mounted on a vehicle for utilizing a system such as an ETC (automatic toll collection system on a toll road).

[0002]

2. Description of the Related Art Conventionally, two-way communication has been performed between an on-vehicle communication device mounted on a vehicle and a roadside device installed near the traveling road of the vehicle to make the traveling of the vehicle smoother. Known systems include GPS, VICS, ETC, and the like.

There are two communication systems applied to such a system, namely, transmission of an uplink signal (uplink signal) from a vehicle-mounted communication device to a roadside device and transmission of a downlink signal from the roadside device to a vehicle-mounted communication device. By using the active method in which the in-vehicle communication device autonomously uses a signal in a frequency band different from the signal (downlink signal) and transmitting the uplink signal by modulating and returning the carrier signal in the downlink signal. There is a passive method to do.

FIG. 4 is a block diagram showing a general structure of a conventional vehicle-mounted communication device used in the passive system. As shown in FIG. 4, this in-vehicle communication device 100
Then, the downlink signal 11 transmitted from the roadside device (not shown)
0 is received by the receiving antenna 102, and the received downlink signal 110 is received by the distribution circuit 20 in the modulation circuit (mixer).
It is distributed to the 120 side and the detection circuit 40 side.

The downlink signal 110 is formed by modulating a carrier signal of a predetermined frequency by an inquiry signal to the vehicle-mounted communication device 100. In the detection circuit 40, the downlink signal distributed to the detection circuit 40 side by the distribution circuit 20. 110 is detected, and the interrogation signal from the roadside machine is extracted.

The interrogation signal extracted by the detection circuit 40 is input to the activation discrimination circuit 50. The start-up determination circuit 50 is constantly operating by being supplied with power from a power supply circuit 80 that generates a constant power supply voltage using an on-vehicle battery as a power supply, and a signal input from the detection circuit 40 is equal to or higher than a predetermined threshold power. If the vehicle (that is, the vehicle (that is, the in-vehicle communication device 100) enters the communication area where data communication with the roadside device is possible), the demodulation circuit 60 and the control circuit 70 are connected to the power supply circuit. Directly connected to 80, a start signal for turning on these power supplies is output to start the demodulation circuit 60 and the control circuit 70.

When the interrogation signal extracted by the detection circuit 40 is input to the demodulation circuit 60 which has been activated as described above, the interrogation signal is converted into a digital signal and amplified. In this way, the interrogation signal is sent to the demodulation circuit 6
After receiving the processing of 0, it is input to the control circuit 70 which is also activated and processed.

On the other hand, the control circuit 70 is in the period in which the portion including only the carrier signal, which is the period subsequent to the period in which the portion including the inquiry signal in the downlink signal 110 is transmitted, is transmitted. , And outputs a response signal (modulation signal) to the roadside machine. This response signal is input to the modulation circuit 120. In the modulation circuit 120, the downlink signal 110 (carrier signal) distributed to the modulation circuit 120 side by the distribution circuit 20 is modulated by this response signal, and goes up to the roadside machine. It is output as the signal 112. The upstream signal 112 is input to the transmission antenna 104 provided separately from the reception antenna 102, and is transmitted to the roadside device via the transmission antenna 104.

A matching circuit 132 is provided between the distribution circuit 20 and the modulation circuit 120 in the in-vehicle communication device 100.
Is provided with the amplifier circuit 130, and the modulator circuit 1
It is configured so that the strength of the carrier signal for generation of the upstream signal 112 input to 20 is amplified and the radio field strength of the upstream signal 112 transmitted to the roadside device can be made sufficient.

[0010]

By the way, in the above-mentioned conventional vehicle-mounted communication device 100, the one provided with the transistor as the modulation circuit 120 is generally used.
However, the modulation circuit 12 including such a transistor
4, the output terminal 126 for inputting the downlink signal 110 and the output terminal 126 for outputting the uplink signal 112 are separately provided in addition to the input terminal 122 for the modulation signal as shown in FIG. However, there is a problem that the number of terminals is large and it is difficult to downsize the circuit configuration of the vehicle-mounted communication device 100 accordingly.

In this case, the receiving antenna 102 is connected to the input terminal 124 side and the transmitting antenna 104 is connected to the output terminal 126 side separately from the receiving antenna 102 through a predetermined transmission line. Therefore, the receiving antenna 102 and the transmitting antenna 1
It is necessary to provide a predetermined space between the antenna No. 04 and the antenna No. 04 in order to secure isolation between the antennas 102 and 104.
Therefore, due to the constraint that a predetermined space must be provided between both antennas 102 and 104,
There is a certain limit to the extent to which the circuit configuration of the vehicle-mounted communication device 100 can be miniaturized.

The present invention has been made to solve the above problems, and an object of the present invention is to provide a passive type vehicle-mounted communication device which can be constructed in a small size while maintaining suitable communication performance. Is to provide.

[0013]

The vehicle-mounted communication device according to claim 1, which is an invention for achieving the above object, has an antenna for communication and a roadside device received by the antenna. And a modulation means for generating an upstream signal to be transmitted to the on-road unit by modulating the downstream signal from (1), and the modulation means has an impedance variable type modulation means.

Here, the variable impedance modulation means has a characteristic that the impedance is changed by receiving the input of the modulation signal for generating the upstream signal, and the down signal is input to the variable impedance modulation means. Then, the down signal is output as an up signal after being subjected to modulation corresponding to the impedance change. That is, the modulation degree of the downlink signal in the variable impedance modulation means is configured to change according to the degree of impedance change in the variable impedance modulation means.

The variable impedance modulation means uses the generated upstream signal for communication along the communication antenna side, that is, along the same path as the input path of the downstream signal to the variable impedance modulation means. It is configured to reflect and output to the antenna side.

Therefore, according to the vehicle-mounted communication device of the present invention,
The down signal input terminal and the up signal output terminal in the modulation means (impedance variable type modulation means) can be shared by one terminal, and since such sharing is possible, the conventional vehicle-mounted communication device can be used. In comparison with the above, the circuit configuration of the vehicle-mounted communication device can be downsized while maintaining the communication performance of the vehicle-mounted communication device as being suitable.

Further, in the vehicle-mounted communication device of the present invention, the modulation means (impedance variable type modulation means) has the above-mentioned configuration.
The up signal from the signal follows the reception path of the down signal in reverse,
It will be transmitted to the roadside device via the antenna used when receiving the downlink signal.

Therefore, in the vehicle-mounted communication device according to the present invention, it is possible to share the downlink signal receiving antenna and the uplink signal transmitting antenna by one antenna, and the conventional receiving antenna and transmitting antenna can be used. There is no problem that a predetermined space for ensuring isolation must be provided between them. From the fact that such a problem does not occur, according to the vehicle-mounted communication device of the present invention, compared with the conventional vehicle-mounted communication device, while maintaining the communication performance of the vehicle-mounted communication device to be suitable, The circuit configuration can be downsized.

Here, as the variable impedance modulation means, as described in claim 2, a diode functioning as the variable impedance modulation means may be used. Even in this case, the same effect as the vehicle-mounted communication device according to the first aspect can be obtained.

In this case, the bias voltage (specifically, the amount of change in the bias voltage) is input as a modulation signal to the diode as the variable impedance type modulation means. The diode may be arranged such that a forward bias voltage is applied as a modulation signal to the diode, or a reverse bias voltage is applied to the diode. It may be.

However, in order to reduce the power consumption necessary for operating the modulation means as much as possible, it is desirable that a reverse bias voltage is applied to the diode as a modulation signal. This is because, when a reverse bias voltage is applied, an extremely small current flows through the diode as compared with the case where a forward bias voltage is applied to the diode, so that the power consumption of the modulation means is reduced. This is because it will be reduced.

However, when the diode is made to function as the variable impedance type modulation means in this way, since the amount of change in the impedance of the diode due to the application of the bias voltage has a predetermined limit, the modulation degree of the down signal in the modulation means is It is limited depending on the limit amount of the impedance change amount.

Therefore, in the case where the aspect described in claim 2 is adopted, as described in claim 3, when the impedance of the diode as the impedance variable type modulation means changes in response to the input of the modulation signal, the modulation is performed. Impedance change amount setting means for setting the impedance change amount in the means to a predetermined change amount may be further provided for the modulation means. By doing so, it becomes possible to set the modulation degree of the downlink signal in the modulation means to a desired modulation degree irrespective of the characteristics of the diode.

On the other hand, in the case of a so-called passive type on-vehicle communication device such as the on-vehicle communication device of the present invention, a downlink signal whose radio field intensity is attenuated to some extent on the route from the roadside device to the on-vehicle communication device is used. Since an upstream signal is generated using the above, in order to realize suitable propagation of the upstream signal to the roadside device, as described in claim 4, the communication antenna is
It is preferable to include a gain improving means for improving the radio field intensity of the upstream signal.

Here, as the gain improving means, claim 5
As described in (1), a plurality of radiating elements included in the communication antenna may be provided. By doing so, the gain of the antenna is improved and the propagation of the upstream signal to the roadside device is favorably performed as compared with the case where the communication antenna is provided with only one radiating element.

Further, if the antenna gain is improved by providing a plurality of radiating elements as described above, an amplifier circuit for amplifying the radio wave intensity of the upstream signal is provided on the circuit forming the in-vehicle communication device as in the conventional in-vehicle communication device. Since it is possible to adopt a mode not provided in the above, when the amplifier circuit is omitted in this way, the circuit configuration of the vehicle-mounted communication device of the present invention can be further miniaturized by the amount of the amplifier circuit omitted. It will be possible.

In this case, in order to maximize the antenna gain, a plurality of radiating elements that the antenna has as gain improving means are provided at appropriate intervals according to the radio waves used by the in-vehicle communication device of the present invention for communication. It is desirable to place in. For example, when the communication antenna includes two radiating elements, the wavelength of the radio wave used for communication is λ,
It is desirable to dispose the two radiating elements with a spacing of λ / 2.

In order to make the antenna gain suitable as described above, the in-vehicle communication device of the present invention may be fixed to the license plate of the vehicle as described in claim 6. . That is, first, the mounting location of the in-vehicle communication device may be, for example, on the dashboard inside the windshield. In this case, the windshield is interposed between the in-vehicle communication device and the roadside device, and the transmission is performed. Since a part of radio waves is reflected by the windshield, the antenna gain may be reduced.

On the other hand, if the vehicle-mounted communication device of the present invention is attached to the portion facing the outside of the vehicle to prevent a part of the vehicle from intervening between the vehicle-mounted communication device and the roadside device, the vehicle-mounted communication device can be provided. It is possible to prevent the antenna gain from being reduced because a part of the vehicle, which may be a factor for reducing the antenna gain of the vehicle-mounted communication device, is not interposed between the device and the roadside device.

According to a sixth aspect of the present invention, the in-vehicle communication device is attached to a portion facing the outside of the vehicle.
If the in-vehicle communication device of the present invention is configured to be fixed to the license plate of the vehicle as described above, the in-vehicle communication device can be located at the end of the vehicle in the traveling direction (that is, the front license plate of the vehicle). When the vehicle-mounted communication device is fixed to the vehicle-mounted communication device, the vehicle-mounted communication device is located at the end in the traveling direction of the vehicle when the vehicle is traveling forward, and conversely, on the rear-side license plate of the vehicle. If the in-vehicle communication device is fixed to the vehicle, the in-vehicle communication device will be located at the end in the traveling direction of the vehicle when the vehicle is traveling rearward.) It is possible to set a short communication distance between the on-road communication device and the on-vehicle communication device that relatively approaches the vehicle from the direction side, and suitable bidirectional communication between the on-road device and the on-vehicle communication device of the present invention is possible. Becomes

[0031]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below with reference to the drawings. The passive-type on-vehicle communication device of the present embodiment functions via bidirectional communication between the on-vehicle communication device and a roadside device (not shown) installed near the traveling path of the vehicle.
It is applied to a system such as PS, VICS, ETC, or a parking lot management system that permits parking of a vehicle in a predetermined parking lot through communication between an in-vehicle communication device and a roadside device, It is configured to be fixed to a front license plate (not shown) of the vehicle.

Specifically, the vehicle-mounted communication device of this embodiment is
A case that also functions as a seal for the front license plate (a case at least a part of which is made of resin or the like that transmits radio waves, or at least a radiating element 12 described later).
A case configured such that a portion is exposed outside the case;
It is also provided (not shown) and is fixed to the front license plate by being housed in the case.

FIG. 1 is a block diagram showing the circuit configuration of the vehicle-mounted communication device 1 of this embodiment. As shown in FIG. 1, the in-vehicle communication device 1 includes an antenna 10 for communication and a distribution circuit 20.
, Modulation circuit 30, detection circuit 40, and start-up determination circuit 5
0, a demodulation circuit 60, a control circuit 72, and a battery (coin-type lithium battery or the like) mounted on a chip (not shown) on which the circuit forming the in-vehicle communication device 1 is arranged, and a constant power supply voltage is applied. And a power supply circuit 82 for generating.

Of the above, the distribution circuit 20 and the detection circuit 4
0, the start-up determination circuit 50, and the demodulation circuit 60 all have the same configurations as those described in FIG. 4, and therefore, the same reference numerals as those in FIG. In the following, a portion having a configuration different from that of the conventional vehicle-mounted communication device 100 shown in FIG. 4 will be mainly described below.

First, the conventional vehicle-mounted communication device 1 shown in FIG.
00 had two antennas 102 and 104,
In the case of the in-vehicle communication device 1 of this embodiment, one antenna 10
Equipped with only. The antenna 10 of the in-vehicle communication device 1 is
Each of the antennas 102, 1 in the conventional vehicle-mounted communication device 100 is composed of two radiating elements 12 and a feeder line 14 that connects the two radiating elements 12 and the distribution circuit 20.
Unlike 04, which has only one radiating element.

In this embodiment, bidirectional communication is performed between the on-road equipment and the in-vehicle communication device 1 using a 5.8 GHz radio wave as a carrier signal.
In order to maximize the antenna gain of the antenna 10 in the communication direction, a distance of λ / 2 is set between the two radiating elements 12, where the wavelength of the radio wave as a carrier signal is λ.

Further, the in-vehicle communication device 1 of this embodiment is not provided with the amplifier circuit 130 included in the conventional in-vehicle communication device 100, and the carrier signal generated by the on-road device is installed on the on-road device. The downlink signal 114 (downlink signal) modulated by the inquiry signal to the communication device 1 is the antenna 1
When received at 0 and distributed to the modulation circuit 30 side by the distribution circuit 20, the distributed downlink signal 114 is directly input to the modulation circuit 30.

The modulation circuit 30 comprises a Schottky diode 32, a capacitor 34, and an impedance change setting circuit 36. One end of the modulation circuit 30 is the distribution circuit 2
0, and the other end is connected to the control circuit 72.
As shown in FIG. 1, among these constituent elements of the modulation circuit 30, the impedance change setting circuit 36 is arranged at a position closest to the distribution circuit 20, and the impedance change setting circuit 36 is connected to a terminal on the opposite side of the distribution circuit 20. Is connected to the cathode of the Schottky diode 32, and the anode is grounded. One end of the cathode of the Schottky diode 32 is connected to the cathode and the other end thereof is connected to the control circuit 7.
The wiring connected to 2 is connected, and one end is grounded on this wiring that connects the Schottky diode 32 and the control circuit 72, and the other end of the wiring in which the capacitor 34 is arranged in the middle is connected to the other end. Further connected.

Next, with reference to the timing charts of FIGS. 2 and 3, the operation of the vehicle-mounted communication device 1 during the bidirectional communication between the road unit and the vehicle-mounted communication device 1 will be described in detail. Of the downlink signal 114 from the roadside device to the vehicle-mounted communication device 1 and the uplink signal 116 (uplink signal) from the vehicle-mounted communication device 1 to the roadside device, the downlink signal 114 is, as shown in FIG. In the interrogation signal period and the interrogation signal period, which are alternately arranged in series, in the interrogation signal period, the carrier signal generated by the roadside machine and continuously transmitted (5.8
(GHz) is modulated by the interrogation signal 114a from the roadside device to the in-vehicle communication device 1.

When a plurality of road vehicles are arranged adjacent to each other and the communication areas of the road vehicles partially overlap each other, one in-vehicle communication device 1 mounted in one vehicle is used. In order to be able to communicate with only one specific on-road unit, a plurality of on-road units can be used for the interrogation signal period (see FIG. 2A).
Interrogation signal 114 within a period corresponding to the broken line portion)
The transmission timing of a may be shifted, or the frequencies of carrier signals may be set to be different.

The vehicle (vehicle-mounted communication device 1) approaches the communication area where bidirectional communication with the roadside device is possible, and the interrogation signal 114a input to the start-up determination circuit 50 has received power equal to or higher than a predetermined threshold power. If it is determined by the start-up determination circuit 50, at that time t1, the start-up signal 118 for directly connecting the demodulation circuit 60 and the control circuit 72 to the power supply circuit 82 to turn on these power supplies is the start-up determination. It is output from the circuit 50 (see FIG. 2B).

After the time t1, the interrogation signal 114a extracted by the detection circuit 40 and input to the demodulation circuit 60.
Is converted into a digital signal and amplified, and then input to the control circuit 72 for processing (see FIG. 2C). Then, the control circuit 72 outputs the response signal 116a (modulation signal) to the roadside machine as the bias voltage (specifically, the amount of change in the bias voltage) in the response signal period after the input processing of the inquiry signal 114a, and the modulation circuit It is made to input into 30 (refer FIG.2 (d)).

When the bias voltage as the modulation signal is input to the Schottky diode 32, the impedance of the Schottky diode 32 changes according to the bias voltage. In the modulation circuit 30, the downlink signal 114 in the response signal period is utilized by utilizing this impedance change.
A modulation process (that is, a signal composed of only carrier signals) is performed.

Specifically, in this embodiment, there is no change in the bias voltage applied to the Schottky diode 32 from the control circuit 72 and no response signal is input (before the time T1 in FIG. 3 is reached). In the period), the impedance of the modulation circuit 30 viewed from the antenna 10 side is
The downlink signal 114 is configured to be totally reflected to the antenna 10 side with almost no modulation.

That is, in this case, the downlink signal 114 (see FIG. 3 (a)) input from the antenna 10 side is totally reflected to the antenna 10 side at the Schottky diode 32 while being hardly modulated. It is output from the antenna 10 portion to the roadside device as an upstream signal 116 (time T
Uplink signal 116 before 1 (see FIG. 3C)).

On the other hand, the input of the bias voltage (bias voltage change amount) as the response signal to the Schottky diode 32 is started, and the impedance of the Schottky diode 32 is changing (time T in FIG. 3).
In the period (1 to T2), the impedance of the modulation circuit 30 viewed from the antenna 10 side causes the downlink signal 114 to be totally reflected to the antenna 10 side in a state where the phase of the downlink signal 114 is changed by a predetermined degree. Is configured.

That is, in this case, the downlink signal 114 from the antenna 10 side undergoes phase modulation according to the response signal when totally reflected by the Schottky diode 32 portion, and thereafter, as the uplink signal 116, the antenna 10 portion. Is output to the roadside equipment (uplink signal 116 at time points T1 and T2).
(See FIG. 3 (c)).

Here, in the in-vehicle communication device 1 of this embodiment,
By arranging the impedance change setting circuit 36 in the modulation circuit 30, the downlink signal 11 is generated at time points T1 and T2.
4 is adjusted so that the degree of phase modulation received by 4 is approximately 180 ° (phase inversion). That is, first, the impedance change amount of the Schottky diode 32 due to the input of the response signal is determined by the Schottky diode 32.
Since there is a predetermined limit according to the characteristics of (1), there is a predetermined limit in the degree of phase modulation that the downlink signal 114 receives when only the Schottky diode 32 is arranged as the modulation circuit 30.

However, if the impedance change setting circuit 36 configured as a distributed constant circuit or a lumped constant circuit is arranged in the modulation circuit 30 as in the present embodiment, the impedance of the Schottky diode 32 causes the input of the response signal. When receiving and changing, the impedance change amount in the modulation circuit 30 can be set to a predetermined desired change amount irrespective of the characteristics of the Schottky diode 32. For example, as in the present embodiment, the downlink signal Modulation circuit 3 so that the degree of phase modulation 114 receives is approximately 180 °.
It is also possible to set an impedance change amount of 0.

A capacitor 34 is also provided in the modulation circuit 30 between the Schottky diode 32 and the control circuit 72 as described above. Therefore, the high frequency (5.8G) input from the antenna 10 side to the modulation circuit 30.
(Hz) downlink signal 114 is prevented from wrapping around to the control circuit 72 side.

As described above, in the vehicle-mounted communication device 1 of this embodiment, the downlink signal 114 is generated by using the bias voltage (the amount of change in bias voltage) output from the control circuit 72 to the Schottky diode 32 as a modulation signal. It is configured to perform modulation of (carrier signal).

Particularly, in the case of this embodiment, the cathode portion of the Schottky diode 32 is connected to one end of the wiring connecting the Schottky diode 32 and the control circuit 72, and the Schottky diode 32 is connected from the control circuit 72.
Is configured to be applied with a reverse bias voltage as a modulation signal.

Therefore, in the vehicle-mounted communication device 1 of this embodiment,
When a modulation signal is input from the control circuit 72 to the Schottky diode 32, only a very small current flows in the Schottky diode 32 portion.
Compared to the case where the modulation circuit 120 including a transistor is used to modulate the downlink signal like the conventional vehicle-mounted communication device 100, the power consumed by the modulation circuit 30 when modulating the downlink signal 114 (by extension, The power consumption of the vehicle-mounted communication device 1) can be reliably reduced.

As described above, in the vehicle-mounted communication device 1 of the present embodiment, the electric power required for modulating the downlink signal 114 is reduced as compared with the conventional one, so that the circuit forming the vehicle-mounted communication device 1 is arranged. The battery, which is a component of the power supply circuit 82 mounted on the mounted chip, can be downsized, and in turn, the circuit configuration of the vehicle-mounted communication device 1 can be downsized.

In the vehicle-mounted communication device 1 of this embodiment, the signal generated as the upstream signal 116 by the modulation circuit 30 is located on the antenna 10 side along the same path as the input path of the downstream signal 114 to the modulation circuit 30. Since the input terminal of the downlink signal 114 and the output terminal of the uplink signal 116 in the modulation circuit 30 are shared by one terminal, the modulation circuit 30 is configured to reflect and output the same. In comparison with the case of the conventional vehicle-mounted communication device 100 in which the input terminal of the down signal and the output terminal of the up signal in 120 are configured as separate terminals, the communication performance of the vehicle-mounted communication device 1 is maintained as being preferable. The circuit configuration of the vehicle-mounted communication device 1 can be downsized.

Further, in the vehicle-mounted communication device 1 of this embodiment, the antenna for receiving the downlink signal 114 and the uplink signal 1 are used as described above.
Since 16 antennas for transmission are shared by one antenna 10, there is a problem that a predetermined space for ensuring isolation must be provided between the receiving antenna 102 and the transmitting antenna 104 as in the conventional case. Also from this point, according to the vehicle-mounted communication device 1 of the present embodiment, the vehicle-mounted communication device 1 can maintain the communication performance of the vehicle-mounted communication device 1 as being preferable as compared with the conventional vehicle-mounted communication device 100. The circuit configuration of the device 1 can be downsized.

Furthermore, in the vehicle-mounted communication device 1 of the present embodiment, the antenna 10 has two radiating elements 12 arranged at intervals of λ / 2 (λ: wavelength of carrier signal). Therefore, each of the antennas 102, 104 provided with only one radiating element in the conventional vehicle-mounted communication device 100
Compared with, the antenna gain is improved.

Therefore, according to the vehicle-mounted communication device 1 of the present embodiment, the amplifier circuit 130 for amplifying the radio wave intensity of the upstream signal is not provided on the circuit forming the vehicle-mounted communication device unlike the conventional vehicle-mounted communication device 100. As a result, it is possible to preferably transmit the upstream signal 116 to the on-road device, and the amplifier circuit 130 can be omitted, so that the circuit configuration of the vehicle-mounted communication device 1 can be further downsized.

Further, in this embodiment, since the vehicle-mounted communication device 1 is configured to be fixed to the front license plate, the vehicle-mounted communication that is mounted and fixed on the dashboard inside the windshield as in the conventional case. Unlike the case of the device, there is no windshield or the like that may be a factor that reduces the antenna gain of the vehicle-mounted communication device between the vehicle-mounted communication device 1 and the roadside device, and when the vehicle is traveling forward. The vehicle-mounted communication device 1 is located at the end of the vehicle in the traveling direction.

Therefore, according to this embodiment, there is no inclusion such as a windshield between the vehicle-mounted communication device 1 and the roadside equipment,
Since the communication distance between the on-vehicle communication device 1 and the on-road device relatively approaching the vehicle from the traveling direction of the vehicle when the vehicle is running can be set to be short, the on-road communication device 1 and the on-vehicle communication device 1 can be set. Suitable bi-directional communication is possible.

In the above, the modulation circuit 30 corresponds to the modulation means of the present invention, and the Schottky diode 32.
Corresponds to the variable impedance modulation means of the present invention,
The impedance change setting circuit 36 corresponds to the impedance change amount setting means of the present invention, and the two radiating elements 12 in the antenna 10 correspond to the gain improving means of the present invention.

Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment.
Various aspects can be adopted. For example, in the above embodiment, the Schottky diode 32 is described as being used as the variable impedance type modulation means, but it goes without saying that another type of diode or the like may be used as the variable impedance type modulation means.

However, in the case of an in-vehicle communication device for performing communication using high frequency radio waves (e.g., 5.8 GHz radio waves) as in the above embodiment, in addition to the Schottky diode 32 having excellent high frequency characteristics, , PIN diodes or the like are preferably used as the variable impedance modulation means.

In the above embodiment, the antenna 10 has two
Although it has been described that one radiating element 12 is provided as the gain improving means, it may be configured to have three or more radiating elements 12 as the gain improving means. The radiating element 12 in the vehicle-mounted communication device 1 is usually formed using glass epoxy or the like, but may be formed using a Teflon (registered trademark) substrate or the like in order to improve the gain of the antenna 10.

Further, in the above-mentioned embodiment, the vehicle-mounted communication device 1 can be fixed to the front license plate, but it may be fixed to the rear license plate. With this configuration, when the vehicle is traveling rearward, the vehicle-mounted communication device 1 is located at the end portion in the traveling direction of the vehicle, and the vehicle-mounted communication with the roadside device located on the rear side of the vehicle is performed. Since the communication distance with the device 1 can be shortened, suitable bidirectional communication between the roadside device and the vehicle-mounted communication device 1 becomes possible.

[Brief description of drawings]

FIG. 1 is a block diagram illustrating a circuit configuration of an in-vehicle communication device according to an embodiment.

FIG. 2 is a timing chart showing the operation of the vehicle-mounted communication device and the roadside device according to the embodiment.

FIG. 3 is a timing diagram for explaining the operation of the modulation circuit of the vehicle-mounted communication device according to the embodiment.

FIG. 4 is a block diagram showing a circuit configuration of a conventional vehicle-mounted communication device.

[Explanation of symbols]

1 ... In-vehicle communication device, 10 ... Antenna, 12 ... Radiating element,
30 ... Modulation circuit, 32 ... Schottky diode, 36
... Impedance change setting circuit, 114 ... Down signal, 1
16 ... Uplink signal, 116a ... Response signal

Claims (6)

[Claims] 1. A vehicle comprising: a communication antenna; and a modulator that modulates a down signal received from the on-road unit by the antenna to generate an up signal to be transmitted to the on-road unit. An on-vehicle communication device mounted, wherein the modulating means changes impedance by receiving an input of a modulated signal for generating an upstream signal, and modulates a downstream signal input from the antenna according to the impedance change. Therefore, the vehicle-mounted communication device is provided with a variable impedance modulation unit that generates an upstream signal and reflects it toward the antenna. 2. The in-vehicle communication device according to claim 1, wherein the modulation means has a diode as the variable impedance modulation means. 3. The impedance change amount setting means for setting the impedance change amount in the modulation means to a predetermined change amount when the impedance of the diode changes in response to the input of the modulation signal. The vehicle-mounted communication device according to claim 2, further comprising: 4. The antenna has a gain improving means for improving a radio field intensity of the upstream signal transmitted from the antenna to the roadside device.
~ The in-vehicle communication device according to claim 3. 5. The vehicle-mounted communication device according to claim 4, wherein the antenna includes a plurality of radiating elements as the gain improving means. 6. The in-vehicle communication device according to claim 1, wherein the in-vehicle communication device is configured to be fixed to a license plate of a vehicle.