JP2005027258A - Radio wave beacon receiver - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio wave beacon receiver for securely receiving road traffic information etc. sent from a radio wave beacon, and for outputting the information to a navigation device etc. in good timing after eliminating influences caused by disturbance in electric fields such as multipath, fading, etc. <P>SOLUTION: The device is designed to check the frame number of normally received data per unit time during the latest periods of the moment when the strength of electric fields of transmission wave from a radio wave beacon becomes greater than a predetermined value and the phase of AM modulation components within the transmission wave is reversed, and to output the received information such as road traffic information etc. which are received until then to the navigation device etc when the number exceeds a predetermined value. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention is installed along a road, and various road traffic information is divided into a plurality of data frames and phase-modulated. Receives radio waves from VICS (Vehicle Information and Communication System) and other radio beacons that radiate AM-modulated forward and reverse-phase transmitted waves separately in the front-rear direction with the road antenna directly underneath. In addition, the present invention relates to a radio beacon receiving device that outputs received information to a navigation device and other in-vehicle devices.

  In recent years, in order to improve the convenience of drivers and eliminate / relieve traffic jams, the installation of a system that provides traffic traffic information on traffic conditions, time required, construction / traffic regulations, etc. in real time to drivers of traveling vehicles has been promoted. It has been. As one of them, a road traffic information system called VICS (Vehicle information and Communication System) has already started operation.

 In addition to the VICS that uses light as an information transmission medium, there is a so-called radio beacon that uses a 2.5 GHz radio wave. This is a transmission system composed of a road antenna and a communication device installed along a road, which transmits radio waves including road traffic information, and receives and uses them by a receiver mounted on a vehicle.

  VICS radio beacons are provided along highways and some major national roads. The length of the communication area is about 35 m before and after the road antenna. The radio wave is a signal obtained by first dividing various road traffic information into a plurality of data frames, and a 2.5 GHz carrier wave is GMSK (Gaussian filtered Minimum Shift Keying) modulated. Subsequently, the modulated carrier wave is divided into two, one is AM-modulated with a 1 kHz clock pulse whose phase rises in synchronization with the rising edge of the data frame (hereinafter, this radio wave is referred to as a normal phase transmission wave), and the other is opposite in phase. (Hereinafter, this wave is referred to as an anti-phase transmission wave). The two transmitted waves are radiated from the road antennas in opposite directions along the road, with the border immediately below.

  This is shown in FIG. In the figure, a normal-phase transmission wave is received when the vehicle 100 approaches the road antenna 101, and a reverse-phase transmission wave is received when the vehicle 100 moves away. However, when the vehicle 100 approaches the road antenna 101 from the opposite side, the opposite is true. . In any case, the phase of the AM modulation component of the radio wave received by the vehicle 100 is inverted immediately below the road antenna 101.

  FIG. 7 shows an example of a radio beacon transmission circuit. Transmission data such as road traffic information is divided into a number of 128-bit data frames and sent to the data modulation circuit 110 at a transmission rate of 64 kbps. A 2.5 GHz carrier wave is input to the data modulation circuit 110, and this carrier wave is GMSK-modulated by transmission data. The GMSK-modulated modulated wave is divided into two and sent to the first and second AM modulation circuits 111 and 112.

  On the other hand, the transmission data is also input to the 1 kHz clock generation circuit 113. The 1 kHz clock generation circuit 113 generates a 1 kHz clock pulse CL1, which is a positive phase signal that rises in phase synchronization with the head of the data frame of transmission data. The clock pulse CL1 is sent to the first AM modulation circuit 111 and the 180 ° phase shift circuit 114, and the 180 ° phase shift circuit 114 outputs a clock pulse CL2 that is a reverse phase signal whose phase is inverted. The clock pulse CL2 is supplied to the second AM modulation circuit 112.

  In the first AM modulation circuit 111, one of the divided GMSK modulated waves is AM-modulated by the clock pulse CL1 which is a positive phase signal, and a positive phase transmission wave is generated. In the second AM modulation circuit 112, the other half of the GMSK modulated wave is AM-modulated by the clock pulse CL2, which is a reverse phase signal, to generate a reverse phase transmission wave. The generated normal-phase transmission wave and reverse-phase transmission wave are fed to a pair of road antennas 101 having different main radiation directions, and as shown in FIG. Radiated in the opposite direction. Therefore, the vehicle 100 can recognize the moment when it passes directly under the road antenna 101 by detecting the moment when the phase of the AM modulated wave is inverted by receiving the radio wave of the radio beacon.

  The position passing signal directly under the road antenna 101 is used as a timing signal for a receiver mounted on the vehicle to output and display the received road traffic information or the like on a navigation device or the like. Moreover, it may be used for correcting the position of the vehicle in dead reckoning navigation of the navigation device. Therefore, it is desired that the timing of passing the position immediately below is reliably detected.

  However, in an actual road environment, the multipath between the road antenna 101 and the receiving antenna 101 of the vehicle 100 is affected by the reflection of radio waves by road structures, vehicles running in parallel, vehicles traveling in the opposite lane, and the like. Or fading occurs and is disturbed by the electric field. Moreover, the reflected wave of the leaked radio wave of the radio beacon installed on the elevated or other road running in parallel may be received.

  When such a situation occurs, the phase of the AM modulated wave that determines whether it is directly under the road antenna 101 may be reversed at a place other than directly under the road antenna 101, and detection of the timing of passing directly under the road antenna 101 is erroneous. Happens. If such a timing detection error occurs, a situation may occur in which only the timing of transmitting the reception information to the navigation device or the like is incorrect, or the reception of the information is not yet completed at the time of transmission.

As a method for preventing such a detection error of the passage timing immediately below the road antenna, a method of determining the position directly under the position in association with the travel distance of the vehicle (for example, refer to Patent Documents 1 and 2), a normal phase or a reverse phase transmission wave A method of determining in consideration of the reception time (for example, see Patent Document 3) has been proposed.
Patent 3000826 Japanese Patent Laid-Open No. 05-40898 JP 2002-40119 A

  The present invention has been made to solve the above-mentioned problems of the prior art, and its purpose is to eliminate the influence of electric field disturbance due to multipath, fading, etc., and to transmit road traffic transmitted from a radio beacon. An object of the present invention is to provide a radio beacon receiving device that can receive information and the like and output it to a navigation device or the like with good timing.

In order to achieve the above object, the invention according to claim 1 is arranged along a road and divides various road traffic information into a plurality of data frames and performs phase modulation, and at the same time, the frequency is synchronized with the top of the data frame. The received information is received by receiving radio waves from radio wave beacons that radiate the normal phase transmission wave and the reverse phase transmission wave, which are AM-modulated separately by the normal phase signal and the negative phase signal, in the opposite directions to each other immediately below the road antenna. An output radio beacon receiving device,
A radio frequency beacon that receives radio waves from a radio beacon and converts the radio frequency beacon into an intermediate frequency signal; a data demodulator that demodulates the intermediate frequency signal and reproduces the data frame; and phase-synchronizes with the head of the demodulated data frame A reference signal generating unit that generates a reference AM signal having the same frequency and the same phase as the positive phase signal, an AM signal demodulating unit that generates an AM demodulated signal by AM demodulating the intermediate frequency signal, and a phase of the reference AM signal A phase determination unit that determines whether the phase of the AM demodulated signal is positive or negative, a level determination unit that determines the electric field strength of a radio beacon received from the magnitude of the intermediate frequency signal, and data processing A part.

  The data processing unit decodes a data frame reproduced by the data demodulating unit during a period in which the level determining unit determines that the electric field strength of the received radio wave is equal to or higher than a predetermined value, and temporarily receives the data frame as received information. And storing and measuring the number of normal received data frames per unit time in the period at a predetermined period, and the unit time at the moment when the phase of the AM demodulated signal is inverted. The radio beacon receiving device outputs the temporarily stored reception information when the latest value of the number of normal received data frames per frame is equal to or greater than a predetermined value.

  As described above, the radio beacon receiving device of the present invention does not determine the output timing of the received information only based on the fact that the phase of the AM modulation component is inverted, but the normal reception data frame per unit time at the time of the phase inversion. Judgment takes into account the number. When the number of normally received data frames per unit time in the latest period is equal to or greater than a predetermined value, the received road traffic information and the like temporarily stored are output to a navigation device or the like for display.

  Since the intensity of the received radio wave is weak at a position outside the road antenna, the number of normally received data frames per unit time is small, and the number is considered to increase as it is directly below the road antenna. Therefore, by adopting the above criteria, the received information received when the radio wave is close to the road antenna is output to the navigation device or the like at a timing directly below or near the road antenna. Thus, the reliability of received information and the optimization of the output timing are achieved.

  An embodiment of the present invention will be described with reference to FIGS. FIG. 1 is a block diagram of a radio beacon receiver according to the present embodiment. The radio wave beacon receiver 1 includes a high frequency receiving unit 2, a data demodulating unit 3, a reference signal generating unit 4, an AM signal demodulating unit 5, a phase determining unit 6, a level determining unit 7, and a data processing unit 8. .

  The high frequency receiving unit 2 includes a receiving antenna 21, a high frequency unit 22, and an intermediate frequency unit 23. The 2.5 GHz radio wave radiated from the road antenna 101 of the radio beacon is received by the receiving antenna 21 and the high frequency unit 22 and converted into an intermediate frequency signal by the intermediate frequency unit 23. The intermediate frequency signal is commonly supplied to the data demodulating unit 3, the AM signal demodulating unit 5, and the level determining unit 7.

  The data demodulator 3 demodulates the GMSK modulated wave. The demodulated transmission data has a configuration as shown in FIG. A set (1 cycle) of road traffic information is divided into 38 to 76 (variable length) data frames. One frame is composed of 128 bytes, and is in the order of synchronization code, header part, actual data part, and CRC from the top. The synchronization code is a code for synchronizing communication, and the header portion is a data header including a radio beacon number and the like. The actual data part includes actual data such as road traffic information and current position information. The CRC is a data error detection code, and the CRC value determines whether the received data frame is normal or not. Some idle is taken between frames. The data transmission speed is 64 kbps, and the data for one cycle is repeatedly sent from the road antenna 101.

  The data frame demodulated by the data demodulator 3 is sent to the data processor 8 and also sent to the synchronization detector 41 in the reference signal generator 4. The data frame sent to the data processing unit 8 is decoded internally and temporarily stored in the internal memory as reception information.

  The synchronization detector 41 detects the head of each data frame, and sends a signal synchronized with the head to the reference signal generator 42. On the basis of the synchronization signal, the reference signal generation unit 42 generates a 1 kHz reference AM signal that is phase-synchronized with the head of the data frame as shown in FIG. 3B and supplies it to the phase determination unit 6. The reference AM signal of 1 kHz is generated because the transmission wave transmitted from the road antenna 101 is AM-modulated with a 1 kHz signal that is phase-synchronized with the head of the data frame, and the reference AM signal detects its phase. This is because it is a reference signal.

  The AM signal demodulator 5 performs AM demodulation on the intermediate frequency signal to generate an AM demodulated signal, and supplies the AM demodulated signal to the phase determination unit 6. As described in the description of the transmission circuit of FIG. 7 in the prior art, the transmission wave transmitted from the road antenna 101 is AM-modulated by a 1 kHz clock pulse phase-synchronized with the head of the data frame. The phase of the 1 kHz AM modulation component is, for example, as shown in FIG. 6, the normal phase in the front area and the reverse phase in the opposite area toward the traveling direction of the vehicle 100 immediately below the road antenna 101. ing.

  FIG. 3 shows the phase relationship of these AM signals supplied to the phase determination unit 6. The reference AM signal supplied from the reference signal generator 42 is a positive phase signal that is phase-synchronized with the head of the data frame (FIG. 3A) as shown in FIG. On the other hand, the AM demodulated signal supplied from the AM signal demodulator 5 differs depending on the reception position. That is, in the case as shown in FIG. 6, when the vehicle 100 is positioned on the near side in the traveling direction with the boundary just below the road antenna 101, the positive phase signal shown in FIG. When doing so, the reverse phase signal shown in FIG. 3 (d) is received. Therefore, by comparing the phase of the AM demodulated signal with the phase of the reference AM signal, it is possible to detect whether the vehicle 100 is positioned immediately before the road antenna 101 or on the opposite side. The phase determination unit 6 determines the phase state of the AM demodulated signal based on the phase of the reference AM signal, and notifies the data processing unit 8 of the result.

  Based on the signal level of the intermediate frequency signal, the level determination unit 7 determines whether or not the electric field strength of the radio wave received by the receiving antenna 21 (hereinafter referred to as the received signal level) is equal to or higher than a predetermined value La. Is notified to the data processing unit 8.

  The data processing unit 8 is based on the phase state of the AM demodulated signal determined by the phase determining unit 6, the determination result of the received signal level from the level determining unit 7, and the information of the data frame sent from the data demodulating unit 3. Then, a process of detecting the moment when the vehicle 100 passes immediately below the road antenna 101 or the moment when the vehicle 100 is located immediately below is performed. The detection process is performed by software processing using a microcomputer.

  Next, the detection processing logic will be described with reference to the flow of FIG. In the VICS radio beacon, road traffic information for the up lane and the down lane may be transmitted from one road antenna 101 at the same time. Therefore, on the radio beacon receiver side, the content of information to be output to the navigation device or the like can be selected according to the detected order of phase change. In the following description, as shown in FIG. 6, when the vehicle 101 is positioned closer to the road antenna 101, the positive phase transmission wave is received, and the phase of the AM demodulated signal is inverted from the positive phase to the negative phase. A case will be described in which this is detected and only the received information corresponding to this is output to the navigation device 9.

  The data processing unit 8 performs the three processes of task (A) from step S1 to step S5, task (B) from step S6 to step S9, and task (C) from step S10 to step S18 in parallel. And execute. In task (A), when the received signal level is equal to or higher than the predetermined value La, the phase of the AM demodulated signal is positive, that is, the data frame normally received while the receiving antenna 21 is receiving the positive phase transmission wave The process of counting the number of Whether or not the reception is normal is determined by CRC as described above.

  In step S1 after the start of the start, a temporary memory “counter N” is provided, and the count value is cleared to zero. [Counter N] in the flow means a count value which is the contents of the memory “Counter N”. In step S2, it is checked whether or not the received signal level is equal to or higher than a predetermined value La based on the output signal of the level determining unit 7. If the received signal level is equal to or lower than the predetermined value La, that is, if the received radio wave is too weak, the process returns to step S1 without doing anything, and the memory “counter N” is cleared. If the received signal level is greater than or equal to the predetermined value La, the process moves to step S3, and data for one frame is received.

  In a succeeding step S4, it is determined whether or not the received data for one frame is normally received. If not normally received, the process returns to step S2, and if normally received, the process proceeds to step S5.

  In step S5, the content of the memory “counter N” is incremented by 1, and the process returns to step S2. By such processing, the memory “counter N” accumulates and holds the number of data frames normally received during the period in which the received signal level is the predetermined value La.

  Next, the flow of task (B) will be described. The task (B) calculates the number of normal received data frames per unit time during the latest ΔT time from the contents of the memory “counter N” at a predetermined period ΔT and stores it in the memory “number of normal frames per unit time”. The process to do is performed. “Number of normal frames per unit time” in the flow means a numerical value that is the content of the “number of normal frames per unit time”.

First, in step S6, the memory “timer” is cleared. In step S7, the elapsed time is measured by the memory "timer" in response to the internal clock pulse. In step S8, it is determined whether or not a predetermined period ΔT has elapsed since clearing in step S6.
If it has not elapsed, the process returns to step S7 to continue timing. If ΔT time has elapsed, the process proceeds to step S9. In step S9, the content of [Counter N], which is the number of normal reception data frames accumulated in task (A), is divided by ΔT time to calculate the number of normal reception data frames per unit time, Stored in “Normal Frame Count”. And it returns to step S6 and repeats the same process.

  Next, the flow of task (C) will be described. The task (C) detects the moment when the phase of the AM demodulated signal is inverted, and the value of [unit time normal frame number], which is the content of the memory “unit time normal frame number”, is equal to or greater than a predetermined value Na It is determined whether or not. And when it is more than predetermined value Na, the process which outputs received information, such as road traffic information temporarily stored in the memory inside the data processing part 8 to the navigation apparatus 9, is performed.

  In step S10 after the start of the start, a temporary memory “AM phase” is provided and its contents are cleared. In step S11, as in step S2, it is checked whether or not the received signal level is equal to or higher than a predetermined value La. If it is equal to or lower than the predetermined value La, the process returns to step S10. If it is greater than or equal to the predetermined value La, the process moves to step S12, where it is checked whether or not the phase of the AM demodulated signal determined by the phase determination unit 6 is positive. If the phase is normal, the process proceeds to step S13.

  In step S13, it is determined whether or not the content of the memory “AM phase” is “reverse phase”. If the phase is reversed, the phase is reversed, and the process proceeds to step S17. If not, the contents of the memory “AM phase” are rewritten to “normal phase” in step S14, and the process returns to step S11.

  If the phase is not normal in step S12, that is, if the phase is reverse, the process proceeds to step S15 to determine whether or not the content of the memory “AM phase” is “normal phase”. If the phase is normal, the phase is inverted, and the process proceeds to step S17. If it is not the normal phase, the content of the memory “AM phase” is rewritten to “reverse phase” in step S16, and the process returns to step S11.

  In step S17, it is determined whether or not the content of the memory “number of normal unit time frames” provided in task (B) is equal to or greater than a predetermined value Na. The value Na is preferably set to about 1/5 to 1/10 of the theoretical value. Here, in the case of VICS, the theoretical value is about 55 per second since the data transmission rate is 64 kbps, one frame is 128 bytes, and the idle between frames is 2 ms. Accordingly, the predetermined value N is 6 to 11.

  If [the number of normal frame per unit time] is equal to or greater than the predetermined value Na, the process proceeds to step S18 to perform a process of outputting the reception information temporarily stored in the memory inside the data processing unit 8 to the navigation device 9. . If it is less than the predetermined value Na, nothing is done and the process returns to step S11.

  Next, the effect of determining the timing for outputting the received information to the navigation device 9 by the three processes of task (A), task (B), and task (C) will be described with reference to FIG. . In FIG. 4A, the horizontal axis represents the distance from directly below the road antenna 101, and the vertical direction represents the received signal level (the electric field strength of the received radio wave) at those positions. .

  The GMSK-modulated carrier component is a mountain-shaped curve having a peak immediately below the road antenna 101 as shown in the figure. In addition, as shown in the figure, the component that is AM-modulated at 1 kHz in the received signal has a positive phase on the near side just below the road antenna 101 and a reverse phase on the opposite side, and the amplitude thereof is the road antenna 101. Directly below, the normal phase wave and the reverse phase wave cancel each other, so the level is low.

  In vehicle 100 that has approached road antenna 101, the received signal level exceeds predetermined value La at point a. Therefore, after point a, the determinations in steps S2 and S11 in the flow of FIG. 5 are YES, and reception of the data frame and check of the phase state of the AM modulation component are started.

  First, consider a case where there is no disturbance in the electric field of the received radio wave due to multipath or the like. The phase determination result of the AM modulation component by the phase determination unit 6 is initially in the positive phase as shown in FIG. 4B, and is inverted in the opposite phase immediately below the road antenna 101. When the phase is reversed, it is determined in step S17 in FIG. 5 whether or not the latest [number of normal frames per unit time] is equal to or greater than a predetermined value Na. In this case, since there is no disturbance of the received radio wave, the latest [number of normal frames per unit time] is equal to or greater than the predetermined value Na. Accordingly, the received information is output to the navigation device 9 in step S18. That is, when there is no disturbance of radio waves, road traffic information received at the moment of passing directly under the road antenna 101 is sent to the navigation device 9 and displayed.

  Next, consider the case where the electric field of the received radio wave is disturbed by multipath or the like. For example, as shown in FIG. 4C due to the disturbance of the electric field of the radio wave, the phase of the AM modulation component is the original phase between c1 and c2 and between d1 and d2, which are positions deviated from directly below the road antenna 101. Assume that the phase determination unit 6 determines that the phase is opposite. In the conventional method in which the phase of the AM modulation component is inverted from the normal phase to the reverse phase and it is determined that the signal passes through the road antenna 101 and the received information is output to the navigation device 9, the received information is also received at points c1 and d2. Output is performed.

  The phenomenon that the phase of the AM modulation component is reversed to the opposite phase to the original phase due to the disturbance of the electric field of the received radio wave due to multipath or the like is generally a region where the received radio wave is weak, that is, the vehicle 100 moves away from directly below the road antenna 11. Occurs when in a zone. When the vehicle 100 is in such an area, the original road traffic information or the like is not normally received. Therefore, the number of data frames determined as abnormal frames by the determination based on CRC increases.

  Therefore, at points c1 and d2, reception of a set of normal road traffic information or the like may not be completed due to an abnormal frame. If incomplete information for which reception of data necessary for display has not been completed is output to the navigation device 9, there is a problem that nothing is displayed on the navigation device 9 as a result. In addition, even if displayed, the road traffic information includes the position information of the road antenna 101, but the position information is displayed at a position greatly deviated from directly below the road antenna 101. Arise.

  In the present embodiment, in step S17, the latest [number of normal frame per unit time] value is checked. At the points c1 and d2, since there are many abnormal frames as described above, the value of [number of normal unit normal frames] rarely exceeds the predetermined value Na. Therefore, the above-mentioned problem that occurs because reception information is output at points c1 and d2 does not occur.

  In the case of the present embodiment, when the phase is reversed from the original phase to the original phase, that is, at the points c2 and d1 in FIG. However, in this case as well, since the points c2 and d1 are in a region far from the antenna 101, that is, in a region where radio waves are weak, [the number of normal frames per unit time] is rarely greater than or equal to the predetermined value Na. Accordingly, there is no problem that reception information is output at points c2 and d1.

  In the case of the present embodiment, the value of [number of normal frames per unit time] is equal to or greater than the predetermined value Na is in a region where the electric field strength of the received radio wave is strong. When the phase of the AM modulation component is inverted while in such a region, the reception information is output to the navigation device 9.

  The point where the intensity of the received radio wave is strong and the phase inversion is most likely to occur is directly under the road antenna 101. Other than that, there is a possibility that the phase is abnormally reversed in the vicinity of the road antenna 101 although the possibility is low. Although it is most preferable to output the signal directly under the road antenna 101, there is no practical problem even if the reception information is output with the phase reversed in the vicinity of the pole.

  In the case of these points d 1 and d 2, the reception information is already normally output to the navigation device 9 at the moment of passing directly under the road antenna 101. Therefore, once the reception information has been output, the reception information may not be output again until a predetermined time has elapsed or until the vehicle has traveled a predetermined distance. If such a condition is added, it is possible to eliminate the possibility that the reception information is output again at the points d1 and d2.

  In the above-described embodiment, the radio beacon receiving device 1 is provided as a device different from the navigation device 9, but both may be configured integrally.

  As described above, the radio beacon receiving device according to the present embodiment does not set the timing to output the reception information to the navigation device 9 only because the phase of the AM modulation component is inverted from the original phase, but the phase is inverted. At the moment, the output timing is determined in consideration of the value of [number of normal frames per unit time]. Therefore, when an abnormal phase reversal is detected at a position off from directly below the road antenna 101, the probability of erroneously determining that point in time as the timing for outputting received information to the navigation device 9 is greatly reduced. And only the reception information received when the vehicle 100 is in the area | region where a received signal level is strong produces the effect that it is output to the navigation apparatus 9 with sufficient timing at the moment of phase inversion.

It is a block diagram which shows the structural example of the electromagnetic wave beacon receiver of this invention. It is a block diagram of the data frame transmitted from a radio beacon. It is explanatory drawing of the phase relationship of AM signal input into a phase determination part. It is a figure explaining the relationship between the signal level of the transmission wave from a radio beacon, a phase, and a vehicle position. It is a processing flow which a data processing part performs. It is a figure explaining the relationship between the phase of AM modulation component of the transmission wave from a radio wave beacon, and a vehicle position. It is a structural example of the transmission apparatus of a radio beacon.

Explanation of symbols

In the drawings, 1 is a radio beacon receiver, 2 is a high frequency receiver, 3 is a data demodulator, 4 is a reference signal generator, 5 is an AM signal demodulator, 6 is a phase determiner, 7 is a level determiner, and 8 is A data processing unit, 9 is a navigation device, 21 is a receiving antenna, 22 is a high frequency unit, 23 is an intermediate frequency unit, 41 is a synchronization detecting unit, 42 is a reference signal generating unit, 100 is a vehicle, and 101 is a road antenna.

Claims (1)

Various road traffic information installed along the road is divided into a plurality of data frames and phase-modulated, and at the same time, each phase is phase-locked to the beginning of the data frame and the same phase and opposite-phase signals are AM-modulated separately. A radio wave beacon receiver that receives radio waves from radio beacons that radiate transmission waves and reverse-phase transmission waves in opposite directions from each other immediately below the road antenna, and outputs reception information,
A radio frequency beacon that receives radio waves from a radio beacon and converts the radio frequency beacon into an intermediate frequency signal; a data demodulator that demodulates the intermediate frequency signal and reproduces the data frame; and phase-synchronizes with the head of the demodulated data frame A reference signal generating unit that generates a reference AM signal having the same frequency and the same phase as the positive phase signal, an AM signal demodulating unit that generates an AM demodulated signal by AM demodulating the intermediate frequency signal, and a phase of the reference AM signal A phase determination unit that determines whether the phase of the AM demodulated signal is positive or negative, a level determination unit that determines the electric field strength of a radio beacon received from the magnitude of the intermediate frequency signal, and data processing With
The data processing unit decodes a data frame reproduced by the data demodulating unit during a period in which the level determining unit determines that the electric field strength of the received radio wave is equal to or higher than a predetermined value, and temporarily receives the data frame as received information. And storing the number of normally received data frames per unit time in the period at a predetermined period and storing the unit reception time at the moment when the phase of the AM demodulated signal is inverted. A radio beacon receiving device, wherein the temporarily stored reception information is output when the most recent value of the number of normally received data frames per frame is equal to or greater than a predetermined value.

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