JP2010139417A - Radio beacon - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio beacon that facilitates maintenance than before. <P>SOLUTION: The radio beacon is capable of providing information by itself for vehicles in two traveling directions although it has been so far necessary to install a radio beacon in each of the traveling directions. With two directional antennas installed thereon, electric wave signals including data on the same matter are sent out to each of two domains juxtaposed in the traveling directions so that their phases are reversed by 180 degrees from each other. The data includes data for the two traveling directions. In this instance, when the transmission of data for one traveling direction is finished, data for the other traveling direction are transmitted with their phases reversed by 180 degrees. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a radio wave beacon that is a road communication device that provides traffic information to an in-vehicle device such as a car navigation device.

As shown in FIG. 1 (a), a conventional radio wave beacon is attached at a predetermined height to a roadside pillar according to the traveling direction, and transmits a radio wave including traffic information to a predetermined area on the road. It has a function.
The radio wave transmission antenna of each radio beacon can transmit radio waves in two directions as shown in FIG. 1A, and the phase of amplitude modulation of each transmission radio wave is reversed by 180 degrees (upstream region). The radio wave transmitted to is “reverse phase” and the downstream side is “normal phase”).
When a vehicle passes in the vicinity of a radio beacon, it first enters an area where a reverse phase radio wave can be received, and then enters an area where a normal phase radio wave can be received. Then, when the phase is reversed from the reverse phase to the normal phase, the data transmitted by the radio wave is recognized as the data addressed to itself, and the operation of taking in the data is performed ( Patent Document 1).

Japanese Patent Publication No. 6-44035

Patent Document 1 describes that in-vehicle devices can capture data not only when the phase is reversed to the positive phase but also when the phase is reversed from the normal phase to the reverse phase. The in-vehicle device is designed to discard the data when it is reversed from the normal phase to the reverse phase as it is not addressed to itself, and only when it detects that the reverse phase is reversed to the normal phase. Is recognized as data addressed to itself.
Therefore, as shown in FIG. 1, it is necessary to install a radio beacon for each traveling direction of the vehicle, and there is a problem that maintenance and maintenance of the radio beacon takes time and cost. It is desirable to develop a new type of radio beacon for efficient maintenance on more roads.

  The present invention has been made in view of these points, and an object thereof is to provide a radio beacon that is easier to maintain than in the past.

  The radio beacon according to the present invention has a function of transmitting radio signals including traffic information to two areas set side by side in the traveling direction on the road, and the traveling direction of the vehicle traveling on the road Including a radio wave transmission circuit for transmitting a radio signal in a receivable manner regardless of whether the signal is in the up direction or the down direction, and a radio signal transmitted to one of the two areas and another area The amplitude modulation component of the radio wave signal transmitted to the area is inverted by 180 degrees, and the amplitude modulation component of the radio wave signal transmitted to each area is simultaneously inverted by 180 degrees for each predetermined time. (Claim 1).

  In the radio beacon according to the present invention, the normal phase and the reverse phase radio waves can be alternately transmitted to each of the two areas. Any of the vehicles traveling in the (upward direction and downward direction) can receive data. Therefore, installation work and maintenance of the radio beacon are facilitated, and maintenance of the radio beacon is facilitated, which is very convenient.

  The radio wave transmission circuit stores vehicle data including uplink data prepared for a vehicle traveling in the upward direction and downlink data prepared for a vehicle traveling in the downward direction. A data transmission unit that reads all or part of the vehicle data from the storage unit and outputs it as transmission data, a carrier wave transmission unit that generates a carrier wave signal for transmitting the transmission data, and the carrier wave transmission unit A data modulating unit that modulates and outputs an output carrier signal with transmission data output from the data transmitting unit, and a modulation signal generating unit that generates a modulation signal for amplitude modulation in synchronization with data transmission of the data transmitting unit And 180 degree phase shifter that inverts the phase of the amplitude modulation signal by 180 degrees and the amplitude modulation signal generated by the modulation signal generator. The phase of the first amplitude modulation unit that modulates the amplitude of the data and generates a radio wave signal to be transmitted to the region 1 and the amplitude modulation signal generated by the modulation signal generation unit are shifted by the 180-degree phase shifter. A second amplitude modulation unit that modulates the transmission data using a signal inverted by 180 degrees and generates a radio wave signal to be transmitted to the other region, and the modulation signal generation unit includes the predetermined signal It is preferable that the amplitude modulation signal to be generated is inverted by 180 degrees in a cycle of (Claim 2).

This circuit configuration is a configuration that can be designed relatively easily by improving the circuit of the conventional radio wave beacon, so the development period can be shortened by utilizing the design information of the conventional radio wave beacon. It becomes.
In this circuit, the predetermined period may be a period of approximately every 100 milliseconds, for example, or may be a period from the start to the end of transmission of data for a certain direction. Note that the contents of the uplink data and the downlink data may be exactly the same.

  In the radio wave transmission circuit, the data transmission unit alternately reads out uplink data and downlink data and outputs the data as transmission data to the data modulation unit. The modulation signal for amplitude modulation to be generated may be inverted 180 degrees at the time when the data contents are switched.

  As described above, by alternately sending the data for the upward direction and the data for the downward direction and inverting the modulation signal for amplitude modulation by 180 degrees each time the data is exchanged, it is possible for a vehicle traveling in any direction. It is possible to provide an equal opportunity to receive data for the traveling direction of the user.

More preferably, the modulation signal generator generates a pulse signal having a period shorter than the period of the modulation signal at a time immediately before the time when the amplitude modulation modulation signal to be generated is inverted by 180 degrees. .
By adding a pulse signal with a short period to the amplitude-modulated signal at the timing immediately before the contents of the transmission data are switched from upstream to downstream or vice versa, the vehicle side that receives this data receives the received radio wave. When performing the process of demodulating the amplitude modulation signal, if the signal has a function to monitor when the signal rises or falls, the inversion of the phase is detected by the monitoring function. Therefore, it is very advantageous in that the detection of phase inversion on the vehicle side can be made more reliable.

  As described above, the radio wave beacon according to the present invention realizes the function that cannot be realized unless two conventional radio wave beacons are installed, so that the maintenance becomes easier than the conventional radio wave beacon.

(First embodiment)
Hereinafter, a first embodiment of the present invention will be described in detail with reference to the drawings.
FIG. 1A is an installation diagram of a conventional radio beacon, and FIG. 1B is an installation diagram of the radio beacon according to the present invention.

[Overall system configuration]
As shown in (a) and (b) of FIG. 1, the conventional configuration is that two radio beacons are installed for each traveling direction of the vehicle. It is the structure which can respond to the vehicle of direction.
As shown in FIG. 1B, the radio beacon of the present invention has a function of transmitting radio waves to two areas A and B arranged in the road traveling direction. In general, these areas are set to partially overlap.

In this area A and area B, a radio wave signal amplitude-modulated with a 1 KHz modulation signal synchronized with data transmission after data modulation by a method such as GMSK is transmitted.
The radio waves transmitted to the area A and the area B are amplitude-modulated based on the modulation signals that are inverted by 180 degrees, and the amplitude modulation components of the two radio waves cancel each other in a portion where these two areas overlap. It is like that.
In Patent Document 1, the time when the phenomenon of canceling out the amplitude modulation component is confirmed is the time when the vehicle has passed through the overlapping portion (near the installation point of the radio beacon), so It also introduces a technology related to positioning that can accurately identify the position.

[Operation of conventional radio beacons]
First, the operation when a vehicle receives data from a conventional radio beacon will be described with reference to FIG.
When the vehicle-mounted device mounted on the vehicle enters the radio wave beacon transmission area, when the data is received from the radio beacon, it detects a synchronization signal from the data and reproduces the modulation signal fm2 based on the synchronization signal.
When data is received from the radio beacon, the modulation signal fm1 is extracted by demodulating the amplitude modulation component of the radio wave transmitted from the radio beacon.
Then, by comparing the modulated signal fm2 reproduced based on the received data with the amplitude modulated signal fm1 of the radio beacon, the in-vehicle device can determine whether the radio wave from the radio beacon is normal phase or reverse phase. It has a function.
In the case of a conventional radio wave beacon, since a radio wave having a reverse phase is transmitted to a reverse phase region upstream in the vehicle traveling direction, the in-vehicle device first recognizes that a radio wave having a reverse phase has been received.
Then, after exiting the reverse-phase area, it enters the normal-phase area and recognizes that it has received a normal-phase radio wave.

When the in-vehicle device recognizes that the phase has been reversed 180 degrees from the reverse phase to the normal phase, the information received up to that point and the information received thereafter are information transmitted to itself. It has a function to recognize and capture.
In this way, the radio wave beacon can provide necessary traffic information and the like to the in-vehicle device by sending the reverse phase radio wave to the upstream side in the vehicle traveling direction and the normal phase radio wave to the downstream side. It has become.

In this case, the contents of data sent to the reverse phase area and the normal phase area are exactly the same. That is, the data modulation component is always the same signal in the two areas.
On the other hand, the amplitude modulation component is inverted 180 degrees between the negative phase region and the normal phase region. Therefore, as described above, in the immediate vicinity of the radio beacon installation point where the reverse phase area and the normal phase area overlap, the amplitude modulation components of the radio waves transmitted to both areas cancel each other and become weak, and the amplitude modulation that can be received by the in-vehicle device The reception level of the component will drop sharply.
Many in-vehicle devices determine that they have passed the radio beacon installation point stored in advance by the in-vehicle device at the time of detecting a drop in the level of this amplitude modulation component. It has a function to correct.
As described above, the function of setting a region where the reception level of the amplitude modulation component suddenly drops near the installation point of the radio beacon is one of important functions that the radio beacon should have.

[Operation of the radio beacon of the present invention]
Next, an outline of the operation of the radio beacon of the present invention will be described with reference to FIG.
Conventionally, as shown in FIG. 1A, two radio beacons for each traveling direction are installed at both ends of a two-way road, and data corresponding to the traveling direction is transmitted from each radio beacon. However, according to the present invention, it is possible to provide a radio beacon that can be installed only on a two-way road and can transmit information to a two-way vehicle.

The radio wave beacon according to the present invention is provided on an installation pillar beside a road as in the prior art, and has a function of transmitting radio waves to two areas A and B along the road traveling direction. Then, one unit transmits radio waves to the lanes in both traveling directions. The two areas A and B are set so as to overlap each other in the vicinity of the installation point of the radio beacon.
The radio waves transmitted to the areas A and B are as shown in FIG.

First, the radio wave transmitted to the region A is transmitted by repeating this cycle with the radio wave shown in FIG. 3A as one cycle.
In the first half of one cycle in area A, a signal obtained by data-modulating application data 1 that is data for vehicle C1 that travels mainly from left to right on the road, and transmits radio waves having an amplitude-modulated component in reverse phase. To do. Then, when the application data 1 has been transmitted, this time, a signal obtained by performing data modulation on the application data 2, which is data for the vehicle C2 that travels mainly from the right to the left, the radio wave having the amplitude modulation component in the positive phase. Send it out.

On the other hand, the radio wave transmitted to the region B is transmitted by repeating the cycle with the radio wave shown in FIG. 3B as one cycle.
In the first half of one cycle in area B, a signal obtained by data-modulating application data 1, which is data for vehicle C1 that travels mainly from left to right on the road, transmits a radio wave whose amplitude modulation component is a positive phase. To do. When the application data 1 has been transmitted, this time, a signal obtained by performing data modulation on the application data 2 that is data for the vehicle C2 that travels mainly from the right to the left. Send it out.

The head of one cycle of each area is controlled to be synchronized, and when a reverse-phase radio wave is sent to area A, a normal-phase radio wave is sent to area B, and the contents of the data are Both are application data 1.
When a normal phase radio wave is transmitted to the area A, a reverse phase radio wave is transmitted to the area B, and the contents of the data are both application data 2.
Therefore, in the overlapping part of regions A and B, the data modulation components are always the same, and the signals are transmitted as radio waves having amplitude modulation components inverted by 180 degrees, the amplitude modulation components cancel each other, and reception in the vicinity of the radio beacon installation point The function that the level drops suddenly is realized.

It should be noted that the region lengths of the region A and the region B in the vehicle traveling direction are at least one cycle of radio wave beacon in the vehicle even when the assumed vehicle traveling speed is maximum (for example, 180 km / h). It is preferable that the length is set so as to remain in the region during the transmission period. That is, it is desirable that the total length of the area A and the area B is set so as to remain within that area within the total two-cycle radio wave transmission period.
For example, if the time required for data transmission in one cycle is 100 ms and the maximum traveling speed of the vehicle is 180 km / h, the vehicle travels a maximum of 5 m in 100 ms. Each is set to 5 m or more. Then, it is desirable to set the total length of the region A and the region B including the portion where both the regions overlap to be 10 m or more in total.

[Circuit Configuration of Radio Beacon of the Present Invention]
In order to realize the operation as described above, the radio beacon of the present invention has a circuit configuration as shown in FIG.
The data transmission unit 11 sequentially reads the application data 1 and the application data 2 that are application data for the vehicle stored in the storage unit, and outputs the application data to the data modulation unit 12. The data modulation unit 12 has a function of modulating the carrier wave generated by the carrier wave transmission unit 14 with application data and outputting it to the first amplitude modulation unit 15 and the second amplitude modulation unit 16.
An amplitude modulation signal fm (usually a signal having a frequency of 1 KHz) generated by the modulation signal generation unit 13 is generated in the first amplitude modulation unit 15, and the modulation signal generation unit 13 is generated in one second amplitude modulation unit 16. The amplitude modulation signals obtained by inverting the amplitude modulation signal fm by 180 degrees by the 180 degree phase shifter 17 are respectively supplied.

The first amplitude modulation unit 15 and the second amplitude modulation unit 16 have a function of amplitude-modulating and outputting the data modulation signal of the input application data based on these supplied amplitude modulation signals. .
In this way, application data having the same contents are subjected to amplitude modulation different from each other by 180 degrees and transmitted to the areas A and B.
The amplitude modulation signal fm generated by the modulation signal generation unit 13 is controlled so as to be synchronized with the timing at which the data transmission unit 11 outputs the head of the application data.

Here, in the present invention, the modulation signal generation unit 13 that generates the amplitude modulation signal further includes a function of inverting the amplitude modulation signal fm generated according to the transmission timing of the application data as needed.
Specifically, the amplitude modulation signal of the modulation signal generation unit 13 at a time point (time indicated by a broken line in the drawing) before sending the header of the next application data 2 after sending the footer of the application data 1 in FIG. Invert fm 180 degrees. Then, as shown in FIG. 3, the phase of the amplitude modulation component of the radio waves transmitted to the areas A and B is inverted by 180 degrees, and the radio waves of the opposite phase are transmitted to the areas where the normal-phase radio waves have been transmitted until then. However, normal-phase radio waves are transmitted to areas where reverse-phase radio waves are transmitted.
Similarly, the amplitude modulation signal fm of the modulation signal generation unit 13 is inverted 180 degrees again at the time before the transmission of the footer of the application data 2 is finished and the header of the next application data 1 is transmitted. Then, the radio waves in each area are reversed again, and the radio waves are transmitted with the same phase as when the application data 1 was transmitted last time.
As described above, by controlling the modulation signal generating unit 13 so as to invert the amplitude modulation signal fm by 180 degrees every time application data is transmitted, the operation of the radio beacon of the present invention can be realized.

[Operation of vehicle receiving radio waves from radio beacon of the present invention]
Next, the operation of the vehicle that receives radio waves from the radio beacon of the present invention will be described.
In addition, since the radio beacon of the present invention is assumed to be sequentially installed in a period of at least several years to several tens of years, it is usually installed in a mixed manner with conventional radio beacons. Therefore, it is possible to receive necessary information from both the conventional radio wave beacon and the radio wave beacon of the present invention with the same onboard machine as the conventional onboard machine that has been able to normally receive the radio wave from the conventional radio beacon. It is desirable to be able to do so.
Therefore, an in-vehicle device that can receive radio waves from a conventional radio beacon can normally receive radio waves from the radio beacon of the present invention, and can realize the same function as that of a conventional radio beacon. Explain that.

The vehicle-mounted device mounted on the vehicle C1 traveling from left to right in FIG. 1B detects the carrier wave from the radio beacon when entering the area A that is the radio wave beacon transmission area while traveling on the road. To do. When a carrier wave is detected, the carrier wave data is demodulated to read application data, and an amplitude modulation component synchronized with the data is extracted by the method described above.
Here, if it is assumed that the vehicle C1 enters the area A at the timing when the application data 1 is transmitted, the vehicle-mounted device of the vehicle C1 recognizes that it has received a reverse-phase radio wave. In the area A, when the transmission of the application data 1 is completed, the transmission of the normal-phase application data 2 is started, so the vehicle C1 receives the normal-phase application data 2 in the area A.
Since the vehicle-mounted device of the vehicle C1 detects that the phase is reversed by 180 degrees from the reverse phase to the normal phase, the vehicle C1 determines that the radio wave is being transmitted to itself at this time and is transmitted. Both the application data 1 and the application data 2 can be taken in.

On the other hand, if it is assumed that the vehicle C1 enters the area A at the timing of sending the application data 2, the vehicle-mounted device of the vehicle C1 recognizes that a positive-phase radio wave has been received. In the area A, when the transmission of the application data 2 is completed, the transmission of the reversed-phase application data 1 is started, so that the vehicle C1 receives the reversed-phase application data 1 in the area A.
Since the vehicle-mounted device of the vehicle C1 only detects that the phase has been reversed 180 degrees from the normal phase to the reverse phase, the vehicle C1 does not determine that radio waves are being transmitted to itself at this time, and data Is not captured.
In this case, if the traveling speed of the vehicle C1 is smaller than the assumed maximum traveling speed (for example, 180 km / h), the vehicle C1 finishes sending out the reverse phase application data 1, and further, the next normal phase application data. 2 is still within the region A even when the transmission of 2 is started, the vehicle-mounted device of the vehicle C1 detects that the phase is reversed 180 degrees from the reverse phase to the normal phase at this time, and takes in the data. be able to.

If the vehicle C1 is traveling at or near the assumed maximum traveling speed, the vehicle C1 exits the area A by the time the transmission of the reverse-phase application data 1 is completed, You will enter B.
In the area B, the application data 2 is transmitted in the opposite phase, contrary to the area A, and therefore the vehicle-mounted device of the vehicle C1 receives the application data 2 having the opposite phase after the application data 1 having the opposite phase. become. Therefore, at this timing, the vehicle C1 does not capture data.
However, in the region B, when transmission of the reverse-phase application data 2 is completed and transmission of the normal-phase application data 1 is started, the vehicle-mounted device of the vehicle C1 finally shifts from the reverse phase to the normal phase at this point. It is possible to capture data by detecting that the angle is reversed 180 degrees.
In this case, since the vehicle C1 has already received both the application data 1 and the application data 2, both data can be captured.

As described above, the vehicle C1 can detect the timing at which the phase reverses from the reverse phase to the normal phase regardless of the speed at which the vehicle C enters the region A. Application data 1 that is data for use can be reliably received.
Similarly, with respect to the vehicle C2 traveling from right to left on the road in FIG. 1 (b), the application data 2 that is mainly data for its own traveling direction can be reliably received as with the vehicle C1. .

  In addition, as described above, the radio beacon of the present invention can realize a function in which the amplitude modulation components cancel each other and the reception level drops sharply in the overlapping portion of the two areas near the installation point. The position location function by the machine can also be realized as before.

[Modification of Operation of Radio Beacon of the Present Invention]
When performing the operation as described above, the amplitude modulation signal fm before and after changing from the reverse phase to the normal phase is constant as shown in the figure at the time when the phase of FIG. The period is kept high. Similarly, the amplitude modulation signal fm before and after changing from the positive phase to the negative phase is kept at a low level for a certain period.
In order for the vehicle to reliably detect that the phase has been reversed, a mechanism is provided to detect the edge when the level of the amplitude modulation signal changes and the vehicle extracts the signal when the phase inversion occurs. By doing so, it is considered that the detection of phase inversion on the vehicle side can be completed.

Therefore, at the timing immediately before the phase is inverted by 180 degrees, specifically, at the time of transmitting the footer portion of the data to be transmitted immediately before the phase inversion, the edge detection pulses as shown in FIGS. For a short period (for example, the transmission period of the footer portion).
In this way, immediately before the phase is inverted, the reliability of the reception process in the amplitude modulation component detection process on the vehicle side can be improved, and the detection of the phase inversion can be made complete.

Note that the radio beacon of the present invention can be operated other than the method shown in the above embodiment.
For example, if it is not necessary to realize the location function of the vehicle-mounted device (the need for the vehicle-mounted device is scarce), the radio wave beacon radio wave signal transmission area is limited to one large area and is opposite to the normal phase. You may use the method of sending application data alternately with a phase.

Also, the application data transmission method is not a method in which application data 1 and application data 2 are transmitted alternately, but a method in which application data 2 is transmitted a plurality of times after application data 1 is transmitted a plurality of times and this is repeated. But it ’s okay. In this case, if there is a difference in the traffic volume and the average travel speed in the up and down directions, for example, the number of transmissions of application data for a vehicle traveling in a direction with a large traffic volume may be increased. A method of increasing the number of times of transmission of application data for a vehicle traveling in a higher speed direction may be used. This traffic volume and average travel speed may be obtained with reference to sensor information obtained from a vehicle sensor or the like installed in the vicinity of the radio beacon.
Note that the same application data may be sent to the vehicle traveling in either direction. That is, the contents of the application data 1 and the application data 2 may be exactly the same.

  Also, the timing at which the modulation signal generating unit 13 switches the phase of the amplitude modulation signal by 180 degrees does not have to be switched every time one application data for a traveling direction is sent, and both the application data 1 and the application data 2 are sent. It may be switched at the timing after finishing, or after sending several times. This timing may be switched at such a period as to recognize that the amplitude-modulated signal has switched from the reverse phase to the normal phase regardless of the direction of the vehicle traveling in the radio wave beacon transmission area.

  Note that the radio beacon according to the present invention may be realized by a single casing or a combination of a plurality of casings. In addition, these may be realized by any circuit configuration, and each may be realized by one computer, or may be realized by combining a plurality of computers.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

It is a schematic diagram which shows the outline | summary of installation of the conventional radio beacon and the radio beacon according to the present invention. It is a figure which shows an example of the circuit structure of the electric wave beacon which concerns on this invention. It is a figure explaining the principle which sends out an electromagnetic wave from the electric wave beacon concerning a 1st embodiment. It is a figure explaining the other method of sending out an electromagnetic wave from the electric wave beacon of this invention.

Explanation of symbols

1 radio wave beacon 10 storage unit 11 data transmission unit 12 data modulation unit 13 modulation signal generation unit 14 carrier wave transmission unit 15 first amplitude modulation unit 16 second amplitude modulation unit 17 180 degree phase shifter

Claims (4)

It has a function to send radio signals including traffic information to two areas set side by side in the direction of travel on the road, and if the vehicle travels on this road, whether the direction of travel is up or down A radio beacon including a radio wave transmission circuit for transmitting the radio signal in a receivable manner regardless of
The amplitude modulation components of the radio signal transmitted to one of the two areas and the radio signal transmitted to the other area are inverted by 180 degrees,
Furthermore, the radio wave beacon is characterized in that the amplitude modulation component of the radio wave signal transmitted to each region is simultaneously inverted by 180 degrees with a predetermined period. The radio wave transmission circuit includes:
A storage unit for storing vehicle data including data for an upward direction prepared for a vehicle traveling in an upward direction and data for a downward direction prepared for a vehicle traveling in a downward direction;
A data transmission unit that reads all or part of the vehicle data from the storage unit and outputs the data as transmission data;
A carrier wave generator for generating a carrier wave signal for transmitting the transmission data;
A data modulation unit that modulates a carrier wave signal output from the carrier wave transmission unit with transmission data output from the data transmission unit; and
A modulation signal generator for generating a modulation signal for amplitude modulation in synchronization with data transmission of the data transmitter;
A 180 degree phase shifter that inverts the phase of the amplitude modulation signal by 180 degrees;
The first amplitude modulation unit that modulates the transmission data using the modulation signal for amplitude modulation generated by the modulation signal generation unit, and generates a radio wave signal to be transmitted to the one region;
A radio wave signal that amplitude-modulates the transmission data using a signal obtained by inverting the phase of the modulation signal for amplitude modulation generated by the modulation signal generation unit by 180 degrees by the 180-degree phase shifter, and that is transmitted to the other area. The second amplitude modulation unit for generating
The radio wave beacon according to claim 1, wherein the modulation signal generation unit inverts the modulation signal for amplitude modulation to be generated by 180 degrees in the predetermined cycle. The data transmission unit alternately reads out uplink data and downlink data and outputs the data as transmission data to the data modulation unit,
The radio wave beacon according to claim 2, wherein the modulation signal generation unit inverts the modulation signal for amplitude modulation to be generated by 180 degrees when the content of the transmission data is switched. 4. The modulation signal generation unit generates a pulse signal having a cycle shorter than the cycle of the modulation signal at a time immediately before a time when the amplitude modulation modulation signal to be generated is inverted by 180 degrees. Radio beacon as described in.

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