JPH0644035B2 - Roadside beacon method - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a roadside beacon system, and more specifically, it is used for calibrating a vehicle position in a navigation system that displays the current position of the vehicle. New roadside beacon system.

<Prior Art> Conventionally, as shown in FIG. 9, a small computer and a display device (51) are mounted on a vehicle, and road map data stored in a storage device such as a compact disk is stored. While reading out and displaying it on the display device (51), using the vehicle speed data from the vehicle speed sensor and the direction data from the direction sensor as input, the position of the vehicle at each time point is calculated and the running direction is determined. Based on the determination result, a so-called navigation system has been provided in which a display (52) showing a vehicle is added to a relevant portion of a road map displayed on a display device (51). There is.

By using such a navigation system, the current position of the vehicle and the traveling direction can be easily visually identified, and the destination can be reliably reached without getting lost.

However, in the navigation system configured as described above, the errors that the vehicle speed sensor and the direction sensor inevitably have are accumulated as the traveling distance increases, and when the traveling distance becomes a predetermined distance or more (however, the predetermined distance is It is determined by the degree of error of the vehicle speed sensor and direction sensor in each vehicle, the variation of the atmospheric conditions at the position where each sensor is installed, etc., and not necessarily a fixed distance), the vehicle display position (52) on the display device (51). ) Will deviate significantly from the actual vehicle position, and it will not be able to exert its original function, resulting in a situation where you get lost.

In order to solve such a problem, the road traffic network, a roadside antenna (53) is installed for each predetermined distance shorter than the distance at which the cumulative error is a predetermined value or more, the roadside antenna (53)
Signal including position data and road direction data from
A so-called roadside beacon system that radiates only in a relatively narrow range, receives the above signal with an antenna mounted on the vehicle, captures it into a computer, and calibrates the vehicle position and traveling direction to correct data based on the received signal. The adoption of is proposed.

If such a roadside beacon system is adopted, it is possible to perform display based on accurate position data and azimuth data in a state where the accumulated error is always less than a predetermined value, so that the original performance of the navigation system is demonstrated. In particular, by installing the roadside antenna (53) near a railroad track or at a location such as a railroad crossing where a large error is likely to occur in the direction sensor, the error caused by external factors can be prevented. It has the advantage that it can be effectively calibrated.

In the roadside beacon system with the above configuration, the roadside antenna with a fairly high directivity always emits a signal including position data and road direction data, and the vehicle passes through the area covered by the radiation signal. The signal is received only when the signal is received, and the necessary calibration can be performed based on the received signal.Therefore, if the area covered by the transmitted signal is widened, the signal reception position of the roadside antenna The gap becomes large,
There is a problem that a sufficient calibration effect cannot be achieved.

More specifically, the basic function of the roadside beacon system is to give a signal including position data and road direction data to a vehicle equipped with a navigation system. However, adding the following functions to the roadside Required for effective use of beacon system. That is, assisting the smooth operation of the vehicle by adding traffic information such as road congestion situation, construction, and other road usage conditions around the location where the roadside antenna is installed to the navigation system, Add detailed map information including house placement and personal name around the place where the roadside antenna is installed,
The road map displayed by the display device can be displayed by facilitating the arrival at the final destination and adding road map information over a relatively wide range including the location of the roadside antenna to the navigation system. It has been considered that the service will be updated and additional services such as smooth operation to remote areas will be provided.
If such additional services are to be provided, it is essential to expand the transmission band by the signal radiated from the roadside antenna and the area covered by the transmission signal.

When the transmission area is expanded and the area covered by the transmission signal is expanded as described above, the deviation of the signal reception position with respect to the installation position of the roadside antenna becomes large, which is the original purpose of the vehicle. The problem arises that the position calibration cannot be performed accurately due to the influence of the above deviation.

In order to solve such a problem, the applicant of the present application has already proposed the roadside beacon system of Japanese Patent Application Nos. 62-154922 and 62-255569.

In the roadside beacon system according to the prior application, a roadside antenna is composed of two antenna elements having different main radiation directions, and various data components are carried by a first modulation system such as PSK, FSK or ASK modulation. Is divided into two parts, and the divided signals are subjected to amplitude modulation (second modulation method) in opposite phase to each other so that position data is added and power is supplied to each antenna element so that the first modulation component is in phase. On the vehicle side, the amplitude modulation component is extracted to detect the position, and the first modulation component is extracted to restore various data.

The present inventors, by the above-mentioned clever roadside beacon system,
It has become possible to implement the roadside beacon system.

<Problems to be Solved by the Invention> By the way, as shown in FIG. 10 and FIG. 11, the receiving device in these prior applications includes a vehicle-mounted antenna, a detection circuit (4
7), bandpass filter (42), detection circuit (36), peak hold circuit (37), level determination circuit (40), position detection gate circuit (38), comparator (41) It is configured.

In the position detecting part of the receiving device, it is necessary to set the threshold value of the comparator (41) in order to detect a sharp drop in the level of the amplitude modulation component. In the case of setting this threshold, there is a problem in that it is necessary to make adjustments according to the respective receiving devices due to variations in sensitivity among the receiving devices, and it takes time and effort to adjust the thresholds and the like.

Further, as a result of experiments and studies by the present inventors, as shown in FIG. 12A, 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. It has been discovered that, as shown in FIG. 12B, a distribution characteristic may appear in which a plurality of points at which the level of the amplitude modulation component drops appears due to the influence of radio waves scattered by a vehicle or the like. In the case of the distribution characteristics shown in FIG. 12B, there arises a problem that it is impossible to distinguish the level dip on the front surface of the roadside antenna from the dip in the vicinity thereof. In order to solve this problem, use an amplifier with a wide dynamic range in the receiver,
It becomes necessary to add an AGC circuit or the like.

Therefore, if the detection of the position of the roadside antenna is configured by analog elements as described above, the device becomes complicated. In addition, the number of parts naturally increases, resulting in a high price. In this case, it is impossible to achieve the demand for smooth operation of vehicles by providing traffic information to as many vehicles as possible by the roadside beacon method.

Further, in order to load the above-mentioned large amount of data into the vehicle, it is necessary for the vehicle to identify the traveling direction. Although an azimuth sensor is mounted on the vehicle to identify the traveling direction, the azimuth sensor is expensive, and there is a problem that an error is likely to occur due to the influence of an external magnetic field.

This invention has been made in view of the above problems,
Provides a roadside beacon system that eliminates the need to adjust thresholds, reduces the cost of on-vehicle equipment, and detects the roadside antenna position even when the level of the amplitude modulation component fluctuates. The purpose is to do.

<Means and Actions for Solving Problem> A roadside beacon system of the present invention for achieving the above object is a roadside beacon system in which various data is transmitted and received between a roadside device installed on the roadside and a vehicle. In, the roadside antenna of the roadside device has at least one pair of antenna elements having different main emission directions directed to the road near the roadside antenna, and the pair of antenna elements are fed in phase. For the signal, it is possible to have a combined radiation directivity having a main radiation direction along a plane of symmetry of the main radiation directions of the antenna elements forming the pair of antenna elements, and feeding the pair of antenna elements in reverse phase. For the received signal, in the plane of symmetry of the main radiation direction of each antenna element forming a pair of the above antenna elements. In addition, it is possible to have a split beam directivity in which the radiated electric field strength drops sharply. The first modulated wave signal modulated based on the transmission data frame is divided into two, and A second modulated wave signal obtained by performing amplitude modulation with a pair of modulated signals that are synchronized and set in opposite phases is applied to the pair of antenna elements so that the first modulated wave signal has the same phase. The receiving device, which is supplied with power and is installed in the vehicle, receives the transmission signal from the roadside antenna, extracts the amplitude modulation component, demodulates the first modulated wave signal, and restores the transmission data frame. , A modulated signal that is synchronized with the transmitted data frame based on the restored transmitted data frame and that corresponds to one of the pair of modulated signals for amplitude modulation. And the phase of the modulated signal is compared with the amplitude modulated component to detect in which direction the vehicle is located with respect to the roadside antenna, and the reproduced modulated signal and the amplitude modulated component are detected. The inversion of the phase relationship of is detected, and the point where the vehicle is passing when the phase relationship is inverted is set as the roadside antenna position (claim 1).

As described above, the roadside antenna included in the roadside device is directed toward the road near the roadside antenna and has at least one pair of antenna elements having different main radiation directions. This roadside antenna, for signals fed in-phase to a pair of antenna elements,
5 shows a synthetic radiation directivity having a main radiation direction along a plane of symmetry of a pair of antenna elements. Also,
For signals fed in anti-phase, split beam directivity is shown in which the radiated electric field strength drops sharply in the plane of symmetry of the pair of antenna elements in the main radiation direction. In this case, signals of opposite phases are radiated with the symmetrical plane in the main radiation direction of each antenna element forming a pair of antenna elements as a boundary.

According to the present invention, the first modulated wave signal that is modulated based on the transmission data frame is divided into two, and the amplitude modulation is performed by the modulated signals that are set in opposite phases to each other, whereby the second modulated wave signal is generated. A modulated wave signal is created. The modulation signal for the amplitude modulation is synchronized with the transmission data frame.

Each of the above halved signals is fed to a pair of antenna elements. At this time, the second modulated wave signal is fed to the pair of antenna elements so that the first modulated wave signal has the same phase. With this, for the first modulated wave signal, a combined radiation directivity having the main radiation direction in the plane of symmetry of each main radiation direction of the pair of antenna elements can be obtained. Therefore, the first modulated wave signal corresponding to the transmission data frame can be radiated in a relatively wide range near the position of the roadside antenna.

Further, for the second modulated wave signal, a split beam directivity that sharply drops in the plane of symmetry of the pair of antenna elements in the main radiation directions is obtained. At this time, the second modulated wave signals are radiated in opposite phases with respect to the symmetry plane.

The receiving device mounted on the vehicle demodulates the first modulated wave signal to restore the transmission data frame. Then, the modulated signal synchronized with this transmission data frame is reproduced. This modulated signal corresponds to one of the mutually opposite phase modulated signals for amplitude modulation. The receiver is
Further, the amplitude modulation component (corresponding to the second modulation wave signal) in the received signal is extracted, and the phases of the extracted amplitude modulation component and the reproduced modulation signal are compared. As a result, it is detected in which direction the vehicle is located with respect to the roadside antenna.

When the vehicle passes near the roadside antenna, the phase relationship between the reproduced modulated signal and the amplitude modulation component corresponding to the second modulated wave signal is inverted at the position of the roadside antenna. Therefore, the point where the vehicle is passing at the time when the phase relationship is reversed can be determined as the roadside antenna position.

In addition, based on whether the phase relationship between the reproduced modulation signal and the amplitude modulation component is inverted from the same phase to the opposite phase or from the opposite phase to the same phase, the approach direction of the vehicle, that is,
It is also possible to determine in which direction the vehicle is traveling.

As described above, according to the present invention, the position is detected by detecting the inversion of the phase of the amplitude modulation component, not based on the fluctuation of the level of the amplitude modulation component. In addition to the above, it is possible to omit troublesome work such as threshold value adjustment.

Further, it is preferable that the receiving device detects the inversion of the phase relationship between the reproduced modulation signal and the amplitude modulation component only in a region where the reception level of the received amplitude modulation component is equal to or more than a predetermined value ( Claim 2).

By doing so, even if there is a change in the level of the amplitude modulation component, it is possible to stably detect the inversion of the phase relationship.

Further, the receiving device detects the direction of the vehicle with respect to the roadside antenna by comparing the reproduced modulated signal with the amplitude modulated component in phase, and the reproduced modulation. It may have an arithmetic processing means for performing the processing for detecting the inversion of the phase relationship between the signal and the amplitude modulation component by software processing (claim 3).

According to this configuration, the configuration of the receiving device can be greatly simplified as compared with the case where each of the processes described above is realized by an analog element.

<Embodiment> An embodiment of the present invention will be described in detail below with reference to the drawings.

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

In FIG. 1A, the data transmitter (11) includes position, direction (road direction), road information, traffic information (in the case of a two-way communication roadside beacon system, includes data such as messages and FAX). Is a component that outputs as a serial code string.

The signal transmitted from the data transmitter (11) is intermittently repeatedly transmitted in frame units as shown in "A: Transmission data frame" in FIG. It includes normal phase correspondence data and reverse phase correspondence data. Here, the header arranged at the head of the frame is a portion provided with functions necessary for communication such as code element synchronization and frame synchronization. Further, in the case of this embodiment, the transmission rate of the transmission data frame is
It is set to 512 kbps.

The transmission data frame sent from the data transmitter (11) is given to the data modulator (12).

The data modulator (12) modulates the carrier wave fc (carrier wave whose center frequency is fc) given from the carrier wave generator (14) with a transmission data frame to produce a first modulated wave signal. The modulation method in the data modulator (12) is amplitude modulation,
Any modulation method may be used regardless of frequency modulation, phase modulation, or the like.

In the case of this embodiment, a PSK (phase shift keying) modulator or an ASK (amplitude shift keying) modulator is used. In terms of performance, the data modulator (12) is PS
A K modulator is preferable, but an ASK modulator may be used for cost reduction.

The first modulated wave signal generated by the data modulator (12) is divided into two parts, that is, the amplitude modulator (15) and the amplitude modulator (16), respectively.
Given to.

The modulation signal generator (13) generates an amplitude modulation signal fm (a signal whose center frequency is fm).
The amplitude modulation signal f is generated by the synchronization signal given from (11).
m is synchronized with the transmitted data frame.
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). Has been

As the frequency fm of the amplitude modulation signal, a frequency sufficiently lower than the above-mentioned carrier wave fc and data transmission rate is selected. Specifically, in the case of this embodiment, a frequency of about 1 kHz is adopted. The amplitude modulation signal fm synchronized with the transmission data frame output from the modulation signal generator (13) is
It is given to the amplitude modulator (15) as it is, and inverted to the opposite phase by the 180 ° phase shifter (17) and given to the amplitude modulator (16).

The amplitude modulator (15) amplitude-modulates the first modulated wave signal given from the data modulator (12) with the amplitude modulation signal fm output from the modulation signal generator (13). The modulation rate of 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) becomes a signal represented by "B: second modulated wave signal (positive phase)" in FIG. 2 and given to the split beam antenna (18).

The amplitude modulator (16) also has the same structure as the amplitude modulator (15), and the second modulation wave signal given from the data modulator (12) is converted into an opposite phase by the 180 ° phase shifter (17). Amplitude modulated signal f
Amplitude modulation with m. As a result, the output of the amplitude modulator (16) becomes a signal indicated by "C: second modulated wave signal (negative phase)" in FIG. This second modulated wave signal (anti-phase) is also given to the split beam antenna (18).

The split beam antenna (18) has a structure including antenna elements (19) and (20) having different main radiation directions, as shown in FIG. Is installed. When the signals are fed in phase, the antenna (18) produces a combined sum of radiation signals emitted from the antenna elements (19) and (20), and exhibits a radiation field intensity as shown in FIG. That is, with respect to the signals fed in phase, the combined radiation directivity having the main radiation direction in the plane of symmetry of the main radiation directions of the antenna elements (19) and (20) is exhibited.

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

In FIG. 1B, the signal received by the receiving antenna (21) is amplified to a required level by a receiving amplifier (22) and given to a data demodulator (23) and a modulated signal demodulator (24).
The data demodulator (23) is a data modulator of the roadside device (first A
(See the figure), and is for obtaining a received data frame by demodulating the first modulated wave signal. The received data frame demodulated by the data demodulator (23) is given to the synchronization detector (25).

The synchronization detector (25) detects element synchronization and frame synchronization from the received data frame, and functions to restore the received data and reproduce the modulated signal. The received data restored by the sync detector (25) is given to the data processing unit (26), and the output of the sync detector (25) is given to the modulation signal regenerator (27).

The modulation signal regenerator (27) is the modulation signal generator (13) of the roadside device.
It has the same function as in FIG. 1A, and reproduces the modulated signal fm 'by the frame synchronization signal based on the received data frame and the received data clock. The reproduced modulation signal fm 'is applied to one input terminal of the phase comparator (28).

The modulation signal demodulator (24) described above is an amplitude modulator of a roadside device.
It corresponds to (15) and (16) (see FIG. 1A) and functions to demodulate the second modulated wave signal and extract the amplitude modulated signal fm. Modulation signal fm demodulated by the modulation signal demodulator (24)
Is applied to the other input terminal of the phase comparator (28).

The phase comparator (28) compares the phase of the modulated signal fm 'reproduced by the modulated signal regenerator (27) with the modulated signal fm demodulated by the modulated signal demodulator (24), and its output is , Signal f
Depending on whether m'and the signal fm are in phase, it becomes either a positive signal or a binary signal of a reverse signal, which is given to the data processing unit (26).

The modulation signal fm demodulated by the modulation signal demodulator (24) is given to the level determiner (29). The level determiner (29) detects that the reception level of the amplitude modulation component is equal to or higher than a certain level, and its output is sent to the data processing unit (26) as an indication of the effective region of phase determination.

The data processing unit (26) restores the received data given from the synchronization detector (25), outputs the forward / backward signal given from the phase comparator (28) and the level decision output from the level decider (29). It is a component that performs various data processing and determination processing based on it. The data processing section (26) is specifically configured by a microcomputer or the like. Then, the output of the data processing unit (26) is given to the display unit (30) and is displayed so that it can be visually recognized by the driver of the vehicle.

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

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

In FIG. 5 (a), AB indicates the direction of the road, and the split beam antenna (18) of the roadside device for this road causes the second modulated wave signal It is radiated by the split beam characteristic of the main radiation beam of the opposite phase. That is, since the second modulated wave signal is fed to the pair of antenna elements (19) and (20) in antiphase, the roadside antenna (20) receives the second modulated wave signal.
The split beam directivity in which the radiation intensity sharply drops in the planes of symmetry of the antenna elements (19) and (20) in the main radiation directions is shown. A positive phase signal is radiated in one area and a reverse phase signal is radiated in the other area with the symmetry plane as a boundary.

If the vehicle is traveling on the road from A to B,
The receiving device mounted on the vehicle first enters the positive-phase beam emission region and receives the emission signal. Received at this time,
The signal (second modulated wave signal (positive phase)) output from the reception amplifier (22) is a signal having an electric field intensity distribution as shown in FIG. 5 (b). This signal is, as described above, a data demodulator (23), a sync detector (25) and a modulated signal regenerator (2).
In step 7), the modulated signal fm 'is reproduced and the modulated signal demodulator (24) demodulates the modulated signal fm. The output of the modulated signal demodulator (24) has an electric field distribution that causes a sharp drop in level at the main radiation direction boundary of the split beam antenna (18), as shown in FIG. 5 (c). Then, the reproduced modulation signal fm 'and the demodulated modulation signal fm are compared by the phase comparator (28), and if the received signal is the positive phase second modulated wave signal, the data processing unit It is determined in (26).

Next, when the vehicle continues to travel, the received signal enters the area that is the second modulated wave signal having the opposite phase. At this time, the data processing unit (26) detects, based on the output signal from the phase comparator (28), the point where the received signal changes from the positive phase to the negative phase, that is, the installation position of the roadside antenna.

When the vehicle travels from B to A on the road, 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 of FIG. 1 is that the functions of the phase comparator (28) and the level determiner (29) are the same as those of the data processor (26). This is realized by the software of).

The level judgment and phase comparison operation of the data processing device (26) are shown in FIG. 7 for explaining the relationship between the distribution chart of the reception level of the amplitude modulation component and the phase of the amplitude modulation component, and the waveform of FIG. It will be described with reference to the drawings. Incidentally, it is assumed that the vehicle is traveling in the direction of the arrow in FIG.

As shown in FIG. 7A, the reception level of the amplitude modulation component is affected by fading and has a fine pitch variation. Then, the level becomes higher as it gets closer to the roadside antenna, sharply falls in front of the roadside antenna, and sharply rises again. Then, as the distance from the roadside antenna increases, it decreases while exhibiting a mountain-shaped characteristic including a fine pitch variation. Therefore, due to the influence of the fading, there may be a case where the phase inversion of the amplitude modulation component cannot be accurately detected. Therefore, the threshold value Ec is set, and position detection is performed in the area where the reception level is equal to or higher than the threshold value Ec. By doing so, a position detection error due to the influence of fading is prevented.

FIG. 8 is a waveform diagram for explaining the detection of phase inversion. The data processing unit (26) demodulates the modulated signal fm ′ reproduced by the modulated signal reproducing unit (27) and the modulated signal demodulator (24). The modulated signal fm thus generated is supplied to convert these into digital signals. In the figure, E2 is a waveform obtained by digitizing the modulated signal fm ', and E1 is a waveform obtained by digitizing the modulated signal fm. Both signals show the same phase (in the case of the opposite phase, the LOW level and the HIGH level of E1 are switched). τ is a delay time when demodulating the amplitude modulation component. Because of the influence of this delay time τ,
If the phases of E1 and E2 are compared as they are to judge whether the phase is the normal phase or the reverse phase, there is a possibility that the phase inversion may be erroneously detected.

Therefore, in the data processing unit (26), E1 and E2 are
From the rising timing of E2, sampling is performed at an interval Δτ over one cycle 2T0, and a half cycle T of E2
During 0, the number of times they are in the same state and the number of times they are in different states are compared, and if the number of times they are in the same state is high, it is determined that they are in phase and they are in different states. If the number of times of contact is large, it is determined that the phase is reversed. By doing so, it is possible to accurately detect the phase inversion 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. The delay time τ is a value that can be obtained in advance by measurement and calculation, and Δτ is an interval obtained by dividing τ by an integer.

As described above, by determining the position detection area and performing the phase comparison by the data processing unit (26), it is possible to greatly simplify the configuration of the receiving device and reduce the cost of the receiving device. You can

<Effects of the Invention> As described above, according to the present invention, in the receiving device mounted on the vehicle, the amplitude modulation component extracted from the reception signal and the transmission data frame restored from the reception signal are synchronized. By comparing the phase with the reproduced modulation signal, it is possible to detect in which direction the vehicle is located with respect to the roadside antenna. Furthermore, the position of the roadside antenna can be detected by detecting the inversion of the phase relationship between the amplitude modulation component and the reproduced modulation signal. As described above, since position detection is performed by detecting the phase inversion of the amplitude modulation component, not based on the variation in the level of the amplitude modulation component, a circuit with a complicated configuration as in the past is not required. In addition, it is possible to omit troublesome work such as threshold adjustment.

Further, according to the second aspect of the present invention, since the inversion of the phase relationship is detected only in the region where the received level of the received amplitude modulation component is equal to or more than the predetermined value, the level of the amplitude modulation component varies. Even in this case, it is possible to stably detect the inversion of the phase relationship.

Further, according to the invention of claim 3, the arithmetic processing means compares the phase of the reproduced modulated signal with the amplitude modulation component to detect in which direction the vehicle is located with respect to the roadside antenna. Since the processing and the processing for detecting the inversion of the above-mentioned phase relation are performed by software processing, the configuration of the receiving device is greatly simplified as compared with configuring these various functions by analog elements. Can be converted.

[Brief description of drawings]

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 diagram for explaining signals of respective portions of the roadside apparatus shown in FIG. 1A, FIG. 3 is a schematic perspective view showing a configuration example of a split beam antenna included in the roadside apparatus of FIG. 1A, and FIG. FIG. 5 is a diagram showing a field intensity distribution of a radiated radio wave 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 block diagram showing another embodiment, FIG. 7 is a diagram for explaining the relationship between the distribution of the reception level of the amplitude modulation component and the phase of the amplitude modulation component, FIG. 8 is a waveform diagram for explaining the detection of phase inversion, and FIG. 9 is a description of the navigation system. Figures 10, 10 and 11 show conventional Communication apparatus, FIG. 12 is a diagram showing a distribution example of the reception level of the amplitude modulation component. (11) …… Data transmitter, (12) …… Data modulator, (13) …… Modulation signal generator, (14) …… Carrier generator, (15), (16) …… Amplitude modulator, (17) …… 180 ° phase shifter, (18) …… split beam antenna, (22) …… reception amplifier, (23) …… data demodulator, (24) …… modulated signal demodulator, (25) …… Synchronous detector, (26) …… Data processing unit, (27) …… Modulation signal regenerator, (28) …… Phase comparator, (29) …… Level judge

Claims (3)

[Claims] 1. In a roadside beacon system in which various data are transmitted and received between a roadside device installed on a roadside and a vehicle, a roadside antenna of the roadside device is directed to a road near the roadside antenna. Having at least one antenna element pair having mutually different main radiation directions, and with respect to a signal fed in phase to the antenna element pair, symmetry of the main radiation direction of each antenna element forming the antenna element pair. A main radiation direction of each antenna element forming a pair of the antenna elements, for a signal fed in antiphase to the pair of the antenna elements, which can have a synthetic radiation directivity having a main radiation direction along a plane. It is possible to have split beam directivity in which the radiated electric field strength drops sharply in the plane of symmetry of Yes, the first modulated wave signal that has been modulated based on the transmission data frame is divided into two, and amplitude modulation is performed on each by a pair of modulation signals that are synchronized with the transmission data frame and set in opposite phases. The second modulated wave signal obtained by the above is fed to the pair of antenna elements so that the first modulated wave signal is in phase with the first modulated wave signal. The transmission signal is received, the amplitude modulation component is extracted, the first modulated wave signal is demodulated to restore the transmission data frame, and the amplitude modulation component is synchronized with the transmission data frame based on the restored transmission data frame and the amplitude modulation is performed. By regenerating a modulation signal corresponding to one of the pair of modulation signals for performing the phase comparison of the modulation signal with the amplitude modulation component. In which direction the vehicle is located, the reversal of the phase relationship between the reproduced modulation signal and the amplitude modulation component is detected, and when the phase relationship is reversed, the vehicle A roadside beacon system characterized in that the passing point is the position of the roadside antenna. 2. The receiving device detects the reversal of the phase relationship between the regenerated modulation signal and the amplitude modulation component only in a region where the reception level of the received amplitude modulation component is a predetermined value or more. The roadside beacon system according to claim 1 characterized by the above. 3. A process in which the receiving device detects in which direction the vehicle is located with respect to the roadside antenna by phase-comparing the reproduced modulated signal with the amplitude modulation component, and the reproducing process. The arithmetic processing means for performing the processing for detecting the inversion of the phase relationship between the modulated signal and the amplitude modulation component by software processing is included. Roadside beacon system.