JPH02183182A - Roadside beacon method - Google Patents

Abstract

PURPOSE:To make it unnecessary to adjust a threshold value etc. and to reduce cost of a device mounted in a motor vehicle by comparing the phase between a transmitting data frame of a first modulated wave signal and an amplitude modulated signal performing a second modulation in a receiver device. CONSTITUTION:A split beam antenna 18 is provided with antenna elements each having a different main-radiating direction. A first modulated wave signal formed through modulation on the basis of a transmitting data frame is divided into two by a data modulator 12, and each divided signal is subjected to amplitude-modulation by a modulation signal synchronous with the transmitting data frame and having a phase opposite to that of the transmitting data frame, whereby a second modulated wave signal is obtained. The second modulated wave signal is supplied to the two elements so that the phase thereof becomes the same as that of the first modulated wave signal. A receiver device mounted in a motor vehicle receives a transmission signal from the antenna 18 and extracts amplitude-modulated components, with demodulating the first modulated wave signal and restoring the transmission data frame. At the same time, the receiver device reproduces a modulated signal synchronous with the transmission data frame, and compares the phase of the modulated signal with that of the amplitude-modulated components, whereby the position of an antenna at the road side is obtained.

Description

[Detailed Description of the Invention] Industrial Application Fields The present invention relates to a roadside beacon system, and more specifically, to a roadside beacon system that is used to calibrate a vehicle position in a navigation system that displays the current position of a vehicle. Conventional technology for a new roadside beacon system> As shown in Figure 9, conventional technology has been to install a small computer and display device (5L) in a vehicle, and store the information in a storage device such as a compact disk. A display device (51) reads out road map data.
In addition to displaying vehicle speed data from the vehicle speed sensor,
The position of the vehicle at each point in time is calculated and the direction of travel is determined by inputting the direction data from the direction sensor and the direction sensor, and based on these calculation results and judgment results, the road displayed on the display device (51) is calculated. So-called navigation systems have come to be provided in which a display (52) indicating a vehicle is added to a corresponding portion of a map.

If such a navigation system is used, the current location and driving direction of the vehicle can be easily identified visually, and the vehicle can be reliably reached the destination without getting lost.

However, in the navigation system with the above configuration, errors that the vehicle speed sensor and direction sensor inevitably have accumulate as the traveling distance increases, and when the traveling distance exceeds a predetermined distance (however, this predetermined distance (It is determined by the degree of error of the vehicle speed sensor and direction sensor in each vehicle, fluctuations in the atmospheric conditions at the location of each sensor, etc., and is not necessarily a constant distance), and the vehicle display position (52) on the display device (51). ) will deviate significantly from the actual position of the vehicle, making it impossible for the vehicle to function as intended, resulting in a situation where the vehicle gets lost.

In order to solve such problems, roadside antennas (53) are installed on the road transportation network at predetermined distances shorter than the distance at which the cumulative error is greater than or equal to a predetermined value. A signal containing data and road direction data is radiated only in a relatively narrow range, and the above signal is received by an antenna attached to the vehicle and input into a computer. Based on the received signal, the vehicle position and driving direction are determined. It has been proposed to use a so-called roadside beacon method that calibrates the data to correct data.

If such a roadside beacon method is adopted, it is possible to display information based on accurate position data and azimuth data while the accumulated error is always below a predetermined value, thereby demonstrating the original performance of the navigation system. In particular, by installing the roadside antenna (53) near railway tracks, at railroad crossings, etc., where large errors are likely to occur in the direction sensor, errors caused by external factors can be avoided. It has the advantage of being able to be calibrated effectively.

In the roadside beacon system with the above configuration, a roadside antenna with highly directional properties constantly radiates signals containing position data and road direction data, and a vehicle passes through an area covered by the radiated signals. Therefore, by increasing the area covered by the transmitted signal, the signal reception position relative to the roadside antenna can be adjusted. There is a problem that the deviation becomes large and a sufficient calibration effect cannot be achieved.

To explain in more detail, the basic function of the roadside beacon method is to provide signals containing position data and road direction data to vehicles equipped with a navigation system, but the following functions can also be added to the roadside beacon system. This is required for effective use of the beacon method. In other words, ■ Assist the smooth operation of vehicles by providing the navigation system with additional traffic information such as road congestion, construction, and other road usage conditions around the location where the roadside antenna is installed. , ■ Add detailed map information, including residential locations and personal names, around the locations where roadside antennas are installed.
To make it easier to reach the final destination, ■ To improve the road map displayed by a display device by adding road map information covering a fairly wide range, including the locations where roadside antennas are installed, and providing it to the navigation system. The plan is to update the system to provide additional services such as smooth operation to remote areas.
If such additional services are to be provided, it is essential to expand the transmission band using the signals radiated from the roadside antenna and to expand the area covered by the transmitted signals.

When the transmission area is expanded and the area covered by the transmitted signal is expanded as described above, the deviation of the signal reception position from the installation position of the roadside antenna becomes large, and the original purpose of A problem arises in that position calibration cannot be performed accurately due to the influence of the above-mentioned deviation.

In order to solve such problems, the applicant has already filed Japanese Patent Application Nos. 82-154922 and 62-255.
No. 589 proposes a roadside beacon system.

In the roadside beacon system according to the earlier application, the roadside antenna is configured with two antenna elements with different main radiation directions, and the roadside beacon system transmits a signal in which various data components are carried using a first modulation method such as PSK, FSX, or ASK modulation. is divided into two, and the divided signals are subjected to amplitude modulation with opposite phases to each other (second modulation method), position data is loaded, and power is fed to each antenna element so that the first modulation component is in phase. west,
On the vehicle side, the amplitude modulation component is extracted to perform position detection, and the first modulation component is extracted to restore various data.

The inventors of this invention use the above-mentioned clever roadside beacon system,
This made it possible to implement a roadside beacon system.

<Problems to be Solved by the Invention> By the way, the receiving devices in these earlier applications are as shown in FIG.
And as shown in FIG.
49), a peak hold circuit (37), a level determination circuit (40), a position detection gate circuit (38), and a comparator (41).

In the portion of the receiving device that performs position detection, it is necessary to set a threshold value for the comparator (41) in order to detect a sudden drop in the level of the amplitude modulation component. When setting this threshold value, since there are variations in sensitivity among each receiving device, it is necessary to adjust it according to each receiving device, and there is a problem that adjusting the threshold value etc. takes time and effort.

Additionally, as a result of experiments and research by the present inventors, it has been found that there are cases where the amplitude modulation component has a distribution characteristic in which the level of the amplitude modulation component sharply drops in front of the roadside antenna as shown in FIG. 12A, and other cases. It has been discovered that, as shown in FIG. 12B, due to the influence of radio wave scattering by vehicles and the like, a distribution characteristic may occur in which multiple points at which the level of the amplitude modulation component drops appear. If the distribution shown in FIG. 12B is characteristic, a problem arises in that it is not possible to distinguish between a drop in level in front of the roadside antenna and a drop in the vicinity thereof. In order to solve this problem, it becomes necessary to use an amplifier with a wide dynamic range or add an AGC circuit or the like to the receiving device.

Therefore, if detection of the position of the roadside antenna and the like are configured with analog elements as described above, the apparatus becomes complicated. Furthermore, since the number of parts is naturally increased, the price is high. This makes it impossible to achieve the goal of providing traffic information to as many vehicles as possible using the road and vehicle beacon system, thereby ensuring smooth vehicle operation.

Furthermore, in order to have the vehicle take in the aforementioned large amount of data, it is necessary to have the vehicle identify the direction of travel. A vehicle is equipped with a direction sensor to identify the traveling direction, but the direction sensor is expensive and has a high probability of causing errors due to the influence of external magnetic fields.

This invention was made in view of the above problems,
Provides a roadside beacon method that eliminates the need to adjust thresholds, etc., reduces the cost of on-vehicle devices, and enables detection of the roadside antenna position even when the level of the amplitude modulation component fluctuates. It is intended to.

Means for Solving the Problems> In order to achieve the above object, the present invention provides a roadside antenna of a roadside device having at least one pair of antenna elements having main radiation directions different from each other. A first modulated wave signal obtained by dividing the first modulated wave signal modulated based on the data frame into two, and applying amplitude modulation to each half using modulating signals that are synchronized with the transmitted data frame and set to have opposite phases to each other. The second modulated wave signal is fed to the pair of antenna elements such that the first modulated wave signal is in phase with the first modulated wave signal, and the receiving device mounted on the vehicle receives the transmitted signal from the roadside antenna. extracts the amplitude modulation component, demodulates the first modulated wave signal to restore the transmission data frame, reproduces a modulation signal synchronized with the transmission data frame from the restored transmission data frame, and converts the modulation signal into the above-described modulation signal. By comparing the phase with the amplitude modulation component, it is possible to detect which area in the main radiation direction of the roadside antenna the vehicle is located in, detect the phase change point of the amplitude modulation component, and identify the phase change point as the roadside antenna position. It is characterized by

Further, the receiving device is characterized in that the receiving device detects the phase change point only in a region where the reception level of the received amplitude modulation component is equal to or higher than a predetermined value.

Furthermore, by comparing the phase of the reproduced modulation signal with the amplitude modulation component, it is possible to detect which region of the main radiation direction of the roadside antenna the vehicle is located in, and arithmetic processing is performed to detect a change point in the phase of the amplitude modulation component. It is characterized by having means.

According to the invention with the above configuration, by synchronizing the transmission data frame to which the first modulation is applied and the amplitude modulation signal to which the second modulation is applied, the transmission data frame is radiated from antennas having different main radiation directions. Based on the received signal, the receiving device can determine in which main radiation direction the main radiation beam is directed. Then, the phase change point of the amplitude modulation component is detected, and the roadside antenna position can be detected based on this change point.

Therefore, when the receiving device receives a signal from a roadside device while traveling on a road, it is possible to determine the intrusion side of the vehicle, that is, which direction on the road the vehicle is traveling toward. In addition, since position detection is not performed based on fluctuations in the level of the amplitude modulation component, there is no need for a circuit with a complicated configuration as in the past.
Further, the time-consuming adjustment of threshold values and the like can be omitted.

can become.

Furthermore, the receiving device detects the phase change point only within a region where the reception level of the received amplitude modulation component is equal to or higher than a predetermined value, so that even if there is a fluctuation in the level of the amplitude modulation component,
Phase change points can be detected stably.

Furthermore, the arithmetic processing means compares the phase of the reproduced modulation signal with the amplitude modulation component to detect which region of the main radiation direction of the roadside antenna the vehicle is located in, and further detects the point of change in the phase of the amplitude modulation component. By detecting this, the configuration of the receiving device can be greatly simplified compared to configuring these functions using analog elements.

<Embodiment> Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1A is a configuration block diagram of a roadside device according to an embodiment of the present invention, and FIG. 2 is a waveform diagram schematically representing the signals in FIG. 1A.

In FIG. 1A, the data transmitter (11) is located at a location.

This is a component that outputs the direction (direction of the road), road information, traffic information (in the case of a two-way communication roadside beacon system, this includes data such as messages and faxes), etc., in a serial code string.

The signal sent from this data transmitter (11) is
As shown in "A: Transmission data frame" in the figure, the frame is intermittently and repeatedly transmitted in frame units, and this frame includes a header, common data, normal phase corresponding data, and negative phase corresponding data. Here, the header arranged at the beginning of the frame is a part provided with functions necessary for communication such as code element synchronization and frame synchronization. Further, the transmission route of the transmission data frame is set to 512 kbps in this embodiment.

A transmission data frame sent out from a data transmitter (11) is provided to a data modulator (12).

The data modulator (12) modulates the carrier wave fc (carrier wave with center frequency fc) given from the carrier wave generator (14) with the transmission data frame to generate a first modulated wave signal. The modulation method in the data modulator (12) may be any modulation method, including amplitude modulation, one frequency modulation, and one phase modulation.

In this example, P S K (phase sh
lftkeying) modulator or ASK (al
IpHtude 5h11'tkeying) modulator is used. In terms of performance, it is preferable that the data modulator (12) be a PSK modulator, but if cost reduction is desired, an ASK modulator may be used.

The first modulated wave signal created by the data modulator (12) is
The signal is divided into two and applied to the amplitude modulator (15) and amplitude modulator (1B), respectively.

The modulation signal generator (13) generates an amplitude modulation signal fm (a signal whose center frequency is fm), and the amplitude modulation signal fm is generated into a transmission data frame by a synchronization signal given from the data transmitter (11). It has been synchronized to . Specifically, in the case of this embodiment, the same clock signal used in the data transmitter (11) is counted down, and the operation is started in accordance with the synchronization signal from the data transmitter (11). It is being done.

The frequency fm of the amplitude modulation signal is selected to be sufficiently lower than the carrier wave fc and the data transmission rate described above. Specifically, in this embodiment, a frequency of about 1 kHz is employed. Amplitude modulation signal f synchronized with the transmission data frame output from the modulation signal generator (13)
m is given to the amplitude modulator (15) as is, and
The signal is inverted in phase by a 180° phase shifter (17) and is applied to an amplitude modulator (1B).

The amplitude modulator (15) amplitude modulates the first modulated wave signal given from the data modulator (12) with the amplitude modulated signal fm which is the output of the modulated signal generator (13). The modulation rate is selected to be 0.5 or less so that the first modulated wave signal does not become too small. The signal modulated by the amplitude modulator (15) is
The modulated wave signal (positive phase) is a signal expressed by "modulated wave signal (positive phase)" and is given to the split beam antenna (18).

The amplitude modulator (16) also has the same configuration as the amplitude modulator (15), and has a second
The modulated wave signal is amplitude-modulated by an amplitude modulation signal fm whose phase is reversed by a 180° phase shifter (17). As a result, the output of the amplitude modulator (16) becomes a signal indicated by "C: second modulated wave signal (reverse phase)" in FIG.

This second modulated wave signal (reverse phase) is also given to the split beam antenna (18).

The split beam antenna (18), an example of which is shown in FIG. 3, includes antenna elements (19) and (20) having different main radiation directions. When the antenna (18) is fed with in-phase signals, the radiated signals radiated from each antenna element (19) and (20) become a composite sum, and exhibit a radiated electric field strength as shown in FIG. 4A. Furthermore, when the signal is fed in reverse phase, as shown in Fig. 4B, the radiation electric field strength at the boundary line between different main radiation directions rapidly decreases in level.
Shows split beam directivity.

A signal radiated from the split beam antenna (18) of the roadside device is received by a receiving device mounted on a vehicle having the configuration shown in FIG. 1B.

In FIG. 1B, a signal received by a receiving antenna (21) is amplified to a required level by a receiving amplifier (22), and is then amplified by a data demodulator (23) and a modulated signal demodulator (24).
) is given to The data demodulator (23) corresponds to the data modulator (see Figure 1A) of the roadside device, and
This is to demodulate the modulated wave signal of 1 to obtain a received data frame. The received data frame demodulated by the data demodulator (23) is provided to the synchronization detector (25).

The synchronization detector (25) detects element synchronization and frame synchronization from the received data frame, and functions for restoring received data and reproducing modulated signals. The received data restored by the synchronization detector (25) is given to the data processing section (2B), and the output of the synchronization detector (25) is given to the modulated signal regenerator (27).

The modulated signal regenerator (27) has the same function as the modulated signal generator (13) (Fig. 1A) of the roadside device, and generates a modulated signal using a frame synchronization signal based on the received data frame and the received data clock. fm'. The reproduced modulated signal fm' is sent to a phase comparator (28)
is applied to one input terminal of

The above-mentioned modulated signal demodulator (24) corresponds to the amplitude modulator (15), (1B) (see Fig. 1A) of the roadside device, and demodulates the second modulated wave signal to generate the amplitude modulated signal f.
It works to extract m. The modulated signal fm demodulated by the modulated signal demodulator (24) is applied to the other input terminal of the phase comparator (28).

The phase comparator (28) performs a phase comparison between the modulated signal fm' regenerated by the modulated signal regenerator (27) and the modulated signal fm demodulated by the modulated signal demodulator (24), and its output is , depending on whether the signal fm' and the signal fm are in phase, it becomes either a positive signal or an inverse binary signal,
It is given to the data processing section (26).

The modulated signal fm demodulated by the modulated signal demodulator (24) is
The signal is applied to the level determiner (29). Level determiner (2
9) detects that the received level of the amplitude modulation component is above a certain level, and its output is sent to the data processing section (2B) as an indication of the effective region for phase determination.

The data processing section (26) restores the received data given from the synchronization detector (25), the forward/reverse signal given from the phase comparator (28), and the level judgment output from the level judgment device (29). This is a component that performs various data processing and judgment processing based on.

Specifically, the data processing section (2B) is constituted by a microcomputer or the like. The output of the data processing section (26) is then given to the display section (30) and displayed so as to be visible to the driver of the vehicle or the like.

FIG. 5 is a diagram for explaining the receiving operation of the receiving device shown in FIG. 1B while the vehicle is running.

Next, the operation of the receiving apparatus shown in FIG. 1B will be explained with reference to FIG. 5.

In FIG. 5(a), A-B represents the direction of the road, and the second modulated wave signal is in phase with the main radiation beam and It is radiated with a split beam characteristic of the main radiation beam having an opposite phase.

Suppose a vehicle is traveling along the road towards A-B.
The receiving device mounted on the vehicle first enters the beam radiation area in positive phase and receives the radiation signal.

The signal (second modulated wave signal (normal phase)) received at this time and output from the reception amplifier (22) is a signal with an electric field strength distribution as shown in FIG. 5(b). As described above, this signal is processed in the data demodulator (23), the synchronization detector (25), and the modulated signal regenerator (27) to regenerate the modulated signal fm' and the modulated signal demodulator (24). ) demodulates the modulated signal fm. As shown in FIG. 5(C), the output of the modulated signal demodulator (24) has an electric field distribution that causes a rapid level drop at the boundary line of the main radiation direction of the split beam antenna (18).

The reproduced modulated signal fm' and the demodulated modulated signal fm are compared by the phase comparator (28), and the data processing unit determines that the received signal is the second modulated wave signal in phase. It is determined in (26).

Next, as the vehicle continues to travel, it enters a region where the received signal is a second modulated wave signal with an opposite phase. At this time, the data processing unit (2B) detects the point where the received signal changes from normal phase to negative phase, that is, the installation position of the roadside antenna, based on the output signal from the phase comparator (28).

When the vehicle is traveling toward road 84A, the operation of the receiving device is opposite to that described above, and first, the second modulated wave signal having the opposite phase is received.

FIG. 6 is a block diagram showing another embodiment. The difference from the embodiment shown in FIG. 1 is that the functions of the phase comparator (28) and level judger (29) are ) software.

The level determination and phase comparison operations of the data processing device (26) are explained in FIG.
The explanation will be based on the waveform diagram shown in the figure.

In FIG. 7, it is assumed that the vehicle is moving in the direction of the arrow.

As shown in FIG. 7A, the reception level of the amplitude modulation component is affected by fading and has small pitch fluctuations. Then, the level increases as it approaches the roadside antenna, drops sharply in front of the roadside antenna, and then rises again sharply. Then, as it moves away from the roadside antenna, it decreases while exhibiting a chevron-shaped characteristic including fine pitch fluctuations. Therefore, due to the influence of fading, it may not be possible to accurately detect the phase inversion of the amplitude modulation component. Therefore, a threshold value Ec step is set, and position detection is performed in an area where the reception level is equal to or higher than the threshold value Ec.

By doing this, position detection errors due to the influence of fading can be prevented.

FIG. 8 is a waveform diagram illustrating detection of phase inversion, in which the data processing section (2B) demodulates the modulated signal fm' regenerated by the modulated signal regenerator (27) and the modulated signal fm' by the modulated signal demodulator (24). modulated signal fm, and converts these into digital signals. In the figure, El is a waveform obtained by digitizing the modulation signal fm', and E2 is a waveform obtained by digitizing the modulation signal fm. Both signals are in the same phase (in the case of opposite phases, the LOW level of El and the old OH level are interchanged). τ is a delay time when demodulating the amplitude modulation component. This delay time τ
Therefore, if the phases of El and E2 are directly compared to determine whether they are in positive phase or negative phase, there is a risk that phase reversal will be detected incorrectly.

Therefore, in the data processing section (2B), □El and E2
and one period 2TO from the rising timing of E2
Sampling is performed at intervals of Δτ over the period, and the number of times that both are in the same state and the number of times that they are in different states during the half cycle TO of E2 is compared, and if the number of times that they are in the same state is large. In this case, it is determined that they are in phase, and if the number of times that they are in different states is large, it is determined that they are in reverse phase. By doing so, it is possible to accurately detect the phase reversal and detect the traveling direction, regardless of the delay time τ. Then, this phase inversion detection signal is output as a roadside antenna position signal, as shown in FIG. 7B. Note that the delay time τ is a value that can be determined in advance by measurement and calculation, and Δτ is an interval obtained by dividing τ by an integer.

As described above, by having the data processing unit (2B) perform the determination of the position detection area and the phase comparison, the configuration of the receiving device can be greatly simplified and the cost of the receiving device can be reduced. Can be done.

<Effects of the Invention> As described above, according to the present invention, by performing a phase comparison between the transmission data frame of the first modulated wave signal and the amplitude modulated signal subjected to the second modulation in the receiving device, the road side The position of the antenna can be detected and the current position of the vehicle can be determined.

Therefore, when the receiving device receives a signal from a roadside device while traveling on a road, it is possible to determine the intrusion side of the vehicle, that is, which direction on the road the vehicle is traveling toward. In addition, since position detection is not performed based on fluctuations in the level of the amplitude modulation component, there is no need for a circuit with a complicated configuration as in the past.
Further, the time-consuming adjustment of threshold values and the like can be omitted.

Further, according to the invention of claim 2, since the phase change point is detected only in a region where the reception level of the received amplitude modulation component' is equal to or higher than a predetermined value, there is no fluctuation in the level of the amplitude modulation component. It is also possible to stably detect the phase change point.

Furthermore, according to the invention of claim 3, the arithmetic processing means compares the phase of the reproduced modulation signal with the amplitude modulation component to detect which region of the main radiation direction of the roadside antenna the vehicle is located in; Furthermore, since the point of change in the phase of the amplitude modulation component is detected, the configuration of the receiver can be greatly simplified compared to configuring these functions with analog elements.

[Brief explanation of the drawing]

FIG. 1A is a configuration block diagram of a roadside device according to an embodiment of the present invention, FIG. 1B is a configuration block diagram of a receiving device mounted on a vehicle according to an embodiment of the present invention, and FIG. FIG. 3 is a schematic perspective view showing a configuration example of a split beam antenna included in the roadside device shown in FIG. 1A, FIG. 4A and FIG. 4B is a diagram showing the electric field strength distribution of radiated radio waves in a split beam antenna, FIG. 5 is a diagram for explaining the operation of the receiving device shown in FIG. 1B, and FIG. 6 is a diagram showing another example. 7 is a diagram illustrating the relationship between the reception level distribution of the amplitude modulation component and the phase of the amplitude modulation component, FIG. 8 is a waveform diagram illustrating detection of phase inversion, and FIG. Explanatory diagrams of the navigation system, FIG. 10 and FIG.
The figure is a diagram showing an example of distribution of reception levels of amplitude modulation components. (11)...Data transmitter, (12)...Data modulator, (13)...Modulation signal generator, (14)...
Carrier wave generator, (15), (1B)...Amplitude modulator, (17)...180° phase shifter, (18)...Split beam antenna, (22)...Reception amplifier, (
23)...Data demodulator, (24)...Modulated signal demodulator, (25)...Synchronization detector, (26)...Data processing section, (27)...Modulated signal regenerator ,(28)・
・・Phase comparator, (29) ・・Level judger (and 1 more)
21: Receiving antenna Fig. 21: Receiving antenna Roadside antenna location diagram Fig.

Claims (3)

[Claims] 1. In a roadside beacon system that transmits and receives various data between a roadside device installed on the roadside and a vehicle, the roadside antenna of the roadside device has at least one pair of antenna elements having mutually different main radiation directions. The first modulated wave signal that has been modulated based on the transmitted data frame is divided into two, and amplitude modulation is applied to each half using modulating signals that are synchronized with the transmitted data frame and set to have opposite phases to each other. A second modulated wave signal obtained by is fed to the pair of antenna elements so that the first modulated wave signal is in phase, and the receiving device mounted on the vehicle receives the transmission from the roadside antenna. Receive the signal, extract the amplitude modulation component, demodulate the first modulated wave signal to restore the transmission data frame, and reproduce the modulation signal synchronized with the transmission data frame from the restored transmission data frame, By comparing the phase of the modulated signal with the amplitude modulation component, it is possible to detect which area in the main radiation direction of the roadside antenna the vehicle is located in, detect the phase change point of the amplitude modulation component, and detect the phase change point. A roadside beacon system characterized by a roadside antenna position. 2. The receiving device receives the received amplitude modulation signal. within an area where the reception level for minutes is higher than the specified value. The special feature is to detect only the above phase change point. What is stated in claim 1 of the above patent claim roadside beacon system. 3. The above-mentioned receiving device receives the above-mentioned regenerated modulated signal. The phase of the signal is compared with the above amplitude modulation component. Due to this, the vehicle may Detect whether you are in the area in the main radiation direction of Detect the phase change point of the amplitude modulation component characterized by having an arithmetic processing means The roadside vehicle according to claim 1 above. -Con method.