AU2002300905B2

AU2002300905B2 - Vehicular communication device

Info

Publication number: AU2002300905B2
Application number: AU2002300905A
Authority: AU
Inventors: Yoshimune Konishi; Takashi Sakurai
Original assignee: Denso Corp
Current assignee: Denso Corp
Priority date: 2001-09-17
Filing date: 2002-09-06
Publication date: 2004-11-18
Anticipated expiration: 2022-09-06
Also published as: CN1178407C; CN1405989A; JP2003087152A

Description

AUSTRALIA

PATENTS ACT 1990 COMPLETE SPECIFICATION Name of Applicant: Address for Service: Invention Title: DENSO CORPORATION DAVIES COLLISON CAVE Patent Attorneys 1 Nicholson Street, Melbourne, Victoria 3000 Australia "Vehicular communication device" The following statement is a full description of this invention, including the best method of performing it known to us: -1- FIELD OF THE INVENTION The present invention relates to a vehicular communication device mounted in a vehicle for use in communications systems such as ETC (Electronic Toll Collection).

BACKGROUND OF THE INVENTION Systems such as GPS, VICS and ETC are known as systems for two-way communication between communication devices mounted in vehicles and roadside devices installed in proximity to the road on which the vehicle travels to ensure vehicle travel proceeds smoothly.

Two kinds of communications methods are applicable to these kind of systems. One method is the active method, wherein the vehicular communication device autonomously transmits an uplink signal to the roadside device and the roadside device transmits a downlink signal at a different frequency to the vehicular communication device. The other method is the passive method, wherein the uplink signal is sent back by modulating the carrier wave signal of the downlink signal.

The block diagram in FIG.4 shows a typical structure of the vehicular communication device of the related art utilized by the passive method. A vehicular communication device 100 shown in FIG. 4, receives by way of a receiver antenna 102 a downlinksignal 110 transmitted from a roadside device (not shown).

The received downlink signal 110 is then supplied to a mixer 120 and a wave detector 40 by a dividing network -lA- The carrier wave of the downlink signal 110 sent on a specified frequency is modulated by an interrogator signal sent to the vehicular communication device 100. In the wave detector the downlink signal 110 from the dividing network 20 is detected by the wave detector 40 and the interrogator signal from the roadside device is extracted.

The interrogator signal extracted by the wave detector is input to a start detector 50. Power is supplied to the start detector 50 for constant operation by a fixed voltage generated by the vehicle battery serving as the power supply. When the signal input from the detector circuit 40 exceeds a specified power threshold, in other words when determined that the vehicle (vehicular communication device 100) has entered an area allowing data communication with the roadside device, a demodulator and a control circuit 70 directly connect to a power supply a start signal to turn on these power supplies is output, and the demodulator 60 and control circuit 70 are started up.

When the interrogator signal detected by the wave detector 40 is input to the demodulator 60 started up as described above, the interrogator signal is both converted to a digital signal and amplified. After being processed in this way by the demodulator 60, the interrogator signal is also input to the control circuit 70 and processed.

The control circuit 70 on the other hand, outputs a response signal (modulation signal) to the roadside device, in the period where the section containing only the carrier signal is sent following the period with the portion containing the interrogator signal in the downlink signal.

-2- This response signal is input to the mixer 120, modulates the downlink signal 110 (carrier signal) and is branched to the mixer 120 by the dividing network 20, and output (modulated carrier) as an uplink signal 112 to the roadside device. The uplink signal 112 is input to a transmitter antenna 104 installed separately from the receiver antenna 102, and sent to the roadside device by way of the transmitter antenna 104.

In the vehicular communication device 100, an amplifier 130 including a matching circuit 132 is installed between the dividing network 20 and the mixer 120. The amplifier 130 amplifies the strength of the carrier signal for the uplink signal 112 input to the mixer 120, and is capable of increasing the field intensity of the uplink signal 112 sent to the roadside device.

Transistors are generally used in the mixer 120.

In the mixer 120 comprised of transistors, besides having a mixer signal input terminal 122, the mixer 120 also has a separate input terminal 124 to input the downlink signal 110, and a separate output terminal 127 to output the uplink signal 112, so that there are many terminals, causing that configuring the vehicular communication device 100 as a compact circuit is impossible.

Also in this circuit structure, the receiver antenna 102 is connected to the input terminal 124 side via the specified transmission path, and the antenna 104 is connected to the terminal 126 side separate from the receiver antenna 102 making it necessary to place a specified space gap to keep both antennas 102 and 104 isolated from one another. Therefore the restrictions caused by having to install both antennas 102 and P:\OPERDH2569743 spa2.doc-07/09/04 104 at a specified gap from each other limits the extent, to which the circuit structure of the vehicular communication device 100 could be reduced.

SUMMARY OF THE INVENTION In accordance with the invention, there is provided a vehicular communication device having: an antenna; and a modulation means for generating an uplink signal to transmit to a roadside device by modulating a downlink signal received from the roadside device by the communication antenna, wherein the modulation means has an impedance variable modulation means for varying the impedance in response to an input of a modulation signal and modulating the downlink signal input from the antenna according to the varied impedance to generate and reflect an uplink signal to the antenna, wherein the impedance variable modulation means is a diode, and wherein the modulation means further has an impedance setting means, comprising a distributed constant circuit or concentrated constant circuit, for setting the amount of impedance variation in the modulation means to a preestablished amount, when impedance of the diode changes in response to the input of the modulation signal.

BRIEF DESCRIPTION OF THE DRAWINGS The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description made with reference to the accompanying drawings. In the drawings: FIG. 1 is a block diagram showing a vehicular communication device according to the embodiment of the present invention; FIG. 2 is a timing diagram showing the operation of the vehicular communication device and a roadside device according to the embodiment; FIG. 3 is a timing diagram showing the operation of the mixer of the vehicular communication device according to the embodiment; and FIG. 4 is a block diagram showing a vehicular communication device according to the related art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT A passive type vehicular communication device of the present embodiment can be utilized in systems such as GPS, VICS, ETC that operate by two-way communication with a roadside device installed in proximity to the path driven by the vehicle, and also can be utilized in parking control systems that permit vehicles to park in specified parking lots by communication with a roadside device. This vehicular communication device can be fastened to the front license plate (not shown) of the vehicle.

More specifically, the vehicular communication device of the present embodiment, also comprises a case functioning as a seal on the front of the license plate, that is, a case comprised of radio wave transmitting material on at least one portion, or case comprised at least of a radiating element 12 section exposed outside of the case (not shown) and secured to the front license plate stored within the case.

In FIG. 1, a vehicular communication device 1 shown in FIG. 1 is made up of a communication antenna 10, a dividing circuit a mixer 30, a wave detector 40, a start detector 50, a demodulator 60, a control circuit 72, and a power supply 82 for generating a fixed voltage constituted by a battery (for example button type lithium battery) mounted on a chip (not shown) containing the circuits constituting above circuits.

The dividing circuit 20, wave detector 40, start detector 50, and demodulator 60 are all the same as described with reference to FIG. 4, so the same reference numerals are attached and their explanation omitted or simplified. The following description will mainly explain the structure as differing from the vehicular communication device 100 of the related art shown in FIG. 4.

The vehicular communication device 1 of the present embodiment contains only one antenna 10. The antenna 10 of vehicular communication device 1 is comprised of a feeder line 14 connecting between two radiating elements 12 and the dividing circuit 20. The present embodiment utilizes an 8 GHz radio wave as the carrier wave signal for two-way communication between the roadside device and vehicular communication device 1. The two radiating elements 12 are installed to have a mutual gap of X /2 as the carrier signal (RF) wavelength to attain maximum gain in the direction that the antenna 10 communicates in.

A downlink signal 114 constituted by a carrier signal generated by the roadside device modulated by an interrogator signal is sent to the vehicular communication device 1, received by the antenna 10, and directly input to the mixer 30 when supplied by the dividing circuit 30. The mixer 30 is comprised of a Schottky diode 32, a capacitor 34, and an impedance setter 36.

One end of the mixer 30 connects to the dividing circuit 20 and the other end connects to the control circuit 72.

Among these components comprising the mixer 30 as shown in FIG. 1, the impedance setter 36 is in a position closest to the dividing circuit 20. The cathode of the Schottky diode 32 is connected to the dividing circuit 20 of impedance setter 36 and opposite side terminal, and the anode is grounded. A wire connects the cathode of the Schottky diode 32 to the impedance setter 36 at one end and to the control circuit 72 on the other end. One end of the wire connecting the Schottky diode 32 and control circuit 72 is grounded and a portion along the wire is further grounded at the capacitor 34.

The operation of the vehicular communication device 1 during two-way communication with the roadside device is explained next using the timing charts in FIG. 2 and FIG. 3.

Of the downlink signal 114 sent from the roadside device to the vehicular communication device i, and the uplink signal 116 sent from the vehicular communication device 1 to the roadside device, the downlink signal 114 sent from the roadside device to the vehicular communication device i, as shown in FIG. 2 is a carrier signal (5.8 GHz) continuously generated by the roadside device and modulated by the interrogator signal 114a in the interrogator signal period Tint among the interrogator and response signal period Tres occurring alternately along a time axis.

Multiple roadside devices are adjacently installed and when a portion of their roadside communication zones mutually overlap, the transmit timing of the interrogator signal 114a may be shifted within the interrogator signal period Tint (period -7equivalent to dashed line in Fig. of the multiple roadside devices or a different carrier signal frequency may be set so that one vehicular communication device 1 installed in one vehicle will communicate only with the designated roadside device.

As the vehicle (vehicular communication device 1) approaches a communication zone capable of two-way communications with the roadside device, and the start detector determines that the power of the signal received from the interrogator signal 114a input to the detector 50 has exceeded a specified threshold, the demodulator 60 and control circuit 72 are at that time point 1 directly connected to the power supply 82 and their (60 and 72) power turned on by a start signal 118 output from the start detector 50 (Fig. 2 From time point tl onwards, the interrogator signal 114a extracted by the wave detector 40 and input to the demodulator is converted to a digital signal, amplified and then input to the control circuit 72 for processing (Fig. 2 In the reply signal period after input processing of interrogator signal 114a, the control circuit 72 then outputs the reply signal 116a (modulation signal) for the roadside device as a bias voltage (more specifically, the change in bias voltage) and it (bias voltage) is input to the mixer 30 (Fig. 2 When the modulated signal is input to the Schottky diode 32 as a bias voltage, the impedance of the Schottky diode 32 varies according to the applicable bias voltage. In the modulator this change in impedance is utilized during the reply signal period, to modulate the downlink signal 14 (in other words, a signal comprised of only a carrier signal).

-8- More specifically, in this embodiment there is no change in the bias voltage applied to the Schottky diode 32 from the control circuit 27, and in the period with no reply signal input (period in FIG. 3 prior to reaching time point Ti) the mixer 30 impedance as seen from the antenna 10 is full reflected to the antenna 10 side unchanged, with virtually no modulation of downlink signal 114.

In other words, in this case the downlink signal 114 (FIG. input from the antenna 10 side, is fully reflected at the antenna 10 side by the Schottky diode 32 section unchanged, with hardly any modulation, and output as the uplink signal 116 to the roadside device from the antenna 10 section (uplink signal 116 prior to time point T1 (FIG. However, input of a bias voltage (amount of change in bias voltage) as the reply signal to the Schottky diode 32 commences, and in the period that the impedance of Schottky diode 32 changes, (period of time point T1 T2 in FIG. 3) the impedance of the mixer circuit 30 as seen from antenna 10 side is changed just to a specified extent of the downlink signal 114 phase and fully reflected to the antenna 10 side.

In other words, in this case, when the downlink signal 114 from the antenna 10 side is fully reflected by the Schottky diode 32 section, the phase is modulated according to the reply signal, and (the downlink signal) output from antenna 10 to the roadside device as uplink signal 116 (uplink signal 116 period of time point T1 T2 in FIG. The vehicular communication device 1 of the present embodiment is installed with the impedance setter 36 in the mixer circuit 30 so that the downlink signal 114 is adjusted during time point T1 T2 to be phase-modulated by approximately 180 degrees (phase reversal). In other words, since there is a specific limit (due to the Schottky diode 32 characteristics) on the change in impedance in Schottky diode 32 received from input of the reply signal, there is a specified limit on the amount of phase modulation of downlink signal 114 when the mixer consists of only the Schottky diode 32.

However, if the mixer circuit 30 contains an impedance setting circuit 36 comprised of a distributed constant circuit or concentrated (lumped) constant circuit as in the present embodiment, then, when the impedance of the Schottky diode 32 varies upon input of the reply signal, the change in impedance in mixer 30 can be set to a desired pre-established amount without having to depend on the characteristics of Schottky diode 32.

In the present embodiment for example, the amount of impedance of the mixer 30 can be set so that the downlink signal 114 receives a phase modulation of approximately 180 degrees.

The capacitor 34 is installed at a point between the Schottky diode 32 and control circuit 72 in the mixer 30. The high frequency (5.8 GHz) downlink signal 114 input to the mixer from the antenna 10 side is therefore blocked from entering the control circuit 72 side.

The vehicular communication device 1 thus modulates the downlink signal 114 (carrier signal) by utilizing the bias voltage (amount of change in bias voltage), and the control circuit 72 outputs to the Schottky diode 32 as the modulation signal.

In particular in this embodiment, the cathode portion of the Schottky diode 32 is connected to one end of the wire connecting the control circuit 72 and Schottky diode 32. A reverse bias voltage is applied as the modulation signal to the Schottky diode 32 from the control circuit 72.

Therefore, when the modulation signal is input to the Schottky diode 32 from the control section 72 in the vehicular communication device i, only an extremely small quantity of electrical current flows into the Schottky diode 32, so that the amount of electrical power consumed in the mixer 30 when modulating the downlink signal 114 is definitely reduced compared to the vehicular communication device 100 of the related art that modulates the downlink signal using a mixer 20 made up of transistors.

In the vehicular communication device i, the electrical power required when modulating the downlink signal 114 is reduced compared to the related art. The battery constituting the fundamental component of the power supply 82 mounted on the chip comprising the vehicular communication device 1 can therefore be made small, and so to the same extent, the circuit making up the vehicular communication device 1 can also be made small.

Also in the vehicular communication device i, the signal generated as the downlink signal 116 by the mixer 30 travels the same path as the input path of download signal 114 to the mixer 30 and is reflected to the antenna 10 side and output. The output terminal of upload signal 116 and the input terminal 114 of download signal 114 in the mixer 30 jointly use one terminal so that compared to the configuration of the vehicular communication device 100 having the output terminal for the uplink -11signal and the input terminal for the downlink signal in the mixer 120 as separate terminals, the circuit of the vehicular communication device 1 can be made small while maintaining satisfactory communications performance.

The vehicular communication device 1 also jointly uses one antenna 10 as the receiver antenna for the downlink signal 114 and transmitter antenna for the uplinksignal 116. Therefore, the circuit of the vehicular communication device 1 of the present embodiment can be made small while maintaining satisfactory communications performance.

In the vehicular communication device 1, the antenna has two radiating elements 12 installed to have a mutual gap of t/2 (1 wavelength of carrier signal) so that the antenna gain is improved compared to the antennas 102, 104 of the vehicular communication device 100 of the related art having only one radiating element. Therefore, unlike the vehicular communication device 100 of the related art, the vehicular communication device 1 can still satisfactorily transmit the uplink signal 116 to the roadside device, even if not installed with an amplifier for amplifying the radio wave intensity of the uplink signal. The circuit configuring the vehicular communication device 1 can therefore be made even smaller to the extent that the amplifier is omitted.

The vehicular communication device 1 is attached to the front license plate so that unlike the vehicular communication device 100 of the related art attached for example to the dashboard on the inner side of the front glass, there is no front windshield glass present between the vehicular communication device 1 and -12the roadside device to cause a drop in antenna gain. When the vehicle is moving in the forward direction, the vehicular communication device 1 is therefore positioned on the (vehicle) edge in the direction of vehicle forward movement.

Therefore, there is no front glass between the roadside device and vehicular communication device 1, so satisfactory two-way communication between the roadside device 1 and vehicular communication device 1 can be achieved because the roadside device becomes relatively nearer to the front of the vehicle moving in the forward direction so the communication distance between the roadside device and vehicular communication device 1 can to that extent be set shorter.

The mixer 30 operates as a modulation means. The Schottky diode 32 operates as an impedance variable modulation means. The impedance setter 36 operates as an impedance setting means. The two radiating elements 12 in the antenna 10 operate as a gain booster means.

The present invention is not limited by this embodiment and may be implemented in variety of forms.

In place of the Schottky diode 32, other types of diodes may of course also be utilized as the impedance variable modulation means. However, when the vehicular communication device utilizes high frequency radio waves (5.8 GHz, etc.) for communication, then preferably, besides the schottky diode 32 having excellent high frequency characteristics, diodes such as PIN diodes may be used as the impedance variable modulation means.

The antenna 10 having two radiating elements 12 as the gain booster means may have three or more radiating elements 12.

-13- The radiating elements 12 in the vehicular communication device 1 are usually formed utilizing glass epoxy, however the radiating elements 12 may also be formed from a teflon substrate in order to improve the gain of the antenna 1.

The vehicular communication device 1 may be attached to the rear license plate. By attaching it to the rear license plate, when the vehicle travels in the rearward direction, the communication distance between the vehicular communication device 1 and a roadside device installed at a position rearward of the vehicle can be shortened and to that extent (shorter distance) the roadside device and vehicular communication device 1 are capable of satisfactory two-way communications.

Throughout this specification and the claims which follow, unless the context requires otherwise, the word "comprise", and variations such as "comprises" and "comprising", will be understood to imply the inclusion of a stated integer or step or group of integers or steps but not the exclusion of any other integer or step or group of integers or steps.

The reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that that prior art forms part of the common general knowledge in Australia.

-14-

Claims

2. A vehicular communication device according to claim i, wherein the antenna has a gain booster means for increasing the radio wave intensity of the uplink signal for transmission to the roadside device from the antenna.
3. A vehicular communication device according to claim 1 or 2, wherein the antenna is attached to a vehicle license plate.
4. A vehicular communication device substantially as hereinbefore described with reference to Figures 1 to 3 of the drawings. DATED 7 September 2004 DENSO CORPORATION By DAVIES COLLISON CAVE Patent Attorneys for the applicant