JP2001325698A - On-vehicle beacon receiver - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an on-vehicle beacon receiver which can decide more accurately the position right under a road beacon transmitter and also the running direction of a vehicle. SOLUTION: A reference signal generation part 21 generates a reference signal A0 having its frequency of 1 kHz and a sampling clock generation part 22 generates a sampling clock having its frequency of 2 kHz. An AM demodulation signal A1 that is produced by performing AM demodulation of a radio wave beacon and the signal A0 are inputted to an EXOR gate 23. The outputs of the gate 23 are sampled by the sampling clock and these sampling results are counted by an up-down counter 25. When a single frame is over, a phase decision part 26 decides this frame as an in-phase, anti-phase or undefined frame in accordance with the value of the counter 25.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an in-vehicle beacon receiver for receiving traffic information transmitted from outside a vehicle via a radio beacon.

[0002]

2. Description of the Related Art In recent years, a system for providing traffic information such as accident information, traffic congestion information, and parking lot availability information to vehicles running on a road using an optical beacon or a radio beacon has been put to practical use. In order to use such a system, for example, a vehicle is equipped with a beacon receiver and a navigation device. The beacon transmitter is installed on the road, and when the vehicle approaches the installation position of the beacon transmitter, the beacon receiver mounted on the vehicle receives the beacon information. The beacon receiver extracts traffic information from the received beacon information and sends it to the navigation device. The navigation device displays the traffic information sent from the beacon receiver on a display device. For example, when the navigation device receives the traffic jam information, the navigation device displays a red arrow indicating the traffic jam along the corresponding road on the map displayed on the display device.

In a radio beacon, one packet is 128 bytes and data is GMSK (Gaussian Filtered MSK).
) And AM modulation at 1 kHz. FIG. 6 is a diagram showing a frame configuration of a radio beacon. This figure 6
As shown in the figure, one frame of the radio wave beacon has a 4-byte synchronization code, a data portion of 122 bytes, and a CR of 2 bytes.
It is composed of C codes. Also, the data part is 19
It is composed of a header part of bytes and a real data part of 103 bytes. The header includes a code for identifying whether the data is data for the main direction, data for the slave direction, or data for both the master and slave, and provides the user with traffic information according to the traveling direction of the vehicle. It is supposed to.

FIGS. 7A and 7B show A of radio wave beacon.
FIG. 3 is a diagram illustrating a relationship between an M demodulated signal and a data packet.
The radio beacon receiver demodulates the received radio beacon and performs AM detection to obtain a data packet and an AM demodulated signal having a frequency of 1 kHz. When the AM demodulation signal rises in synchronization with the reception of the first bit of the data packet for one frame, the phase is the same (see FIG. 7A), and when the AM demodulation signal falls, the phase is reversed (see FIG. 7B).
That. In addition, the region where the in-phase signal is received is the in-phase region,
A region where a signal of the opposite phase is received is called an opposite phase region.

As shown in FIG. 8, an in-phase signal and an out-of-phase signal are transmitted from a radio beacon transmitter to a vehicle traveling on an up lane and a vehicle traveling on a down lane. The case where the vehicle travels in the direction from the in-phase region to the opposite phase region is called a main direction, and the case where the vehicle travels in the direction from the opposite phase region to the in-phase region is called a slave direction. The radio beacon receiver determines that the vehicle is traveling in the main direction when the radio beacon changes from the same phase to the opposite phase, and determines that the radio beacon is traveling in the secondary direction when the radio beacon changes from the opposite phase to the same phase. The navigation device extracts data corresponding to the traveling direction from the received data and displays the data on a display device.

[0006] In a conventional radio beacon receiver, the phase is determined by the following method. That is, in the conventional in-vehicle radio beacon receiver, a 1 kHz reference signal is generated in synchronization with the reception of the first bit of the data packet, and an AM demodulated signal having a frequency of 1 kHz is sampled with this reference signal, for example, four times. The same phase is defined as the same phase, and the phase reversed four or more times is defined as the opposite phase. And
After identifying the point that changed from in-phase to the opposite phase, or the point that changed from in-phase to in-phase, and the position directly below the radio beacon transmitter, and the position immediately below the radio beacon transmitter is determined,
It is determined whether the vehicle is traveling in the main direction or in the sub direction.

[0007]

However, the conventional beacon receiver described above does not have sufficient reliability in determining the position immediately below the beacon transmitter and the traveling direction of the vehicle.
FIG. 9 shows the distance from the radio beacon transmitter on the horizontal axis,
It is a figure which shows electric field intensity distribution near a radio beacon transmitter, taking electric field intensity on a vertical axis. As shown in FIG.
The electric field strength is low just below the radio beacon transmitter,
The phase of the AM demodulated signal is disturbed by the influence of the mixture of the in-phase component and the phase component, the multipath, and the like. For this reason, in the conventional beacon receiver, there is a possibility that the determination of the position immediately below the beacon transmitter and the traveling direction of the vehicle may be erroneous.

Japanese Unexamined Patent Application Publication No. 11-296792 aims to improve the reliability of the determination of the position immediately below the radio beacon transmitter. It has been proposed to change the number of times the AM modulation component is sampled in some cases. However, in this method, it is necessary to appropriately set the threshold value of the electric field level, and the reliability is not sufficient.

Accordingly, an object of the present invention is to provide an in-vehicle beacon receiver that can more accurately determine the position immediately below a road beacon transmitter and the traveling direction of a vehicle.

[0010]

An object of the present invention is to provide a radio beacon receiver for receiving a radio beacon, an AM demodulator for demodulating an output of the radio beacon to extract an AM demodulated signal, A data demodulation unit that demodulates the output of the beacon reception unit and outputs bit data; a synchronization detection unit that detects a synchronization code from the bit data and outputs a synchronization signal; and a reference signal that generates a reference signal having a constant frequency. A generation unit, a sampling clock generation unit that generates a sampling clock having a frequency higher than the reference signal, a comparison unit that compares the AM demodulated signal with the reference signal, and synchronizes an output of the comparison unit with the sampling clock. A sampling unit that performs sampling at the specified timing, and counts the output of the sampling unit, which is initialized by the synchronization signal. A counter that is solved by a vehicle-mounted beacon receiver; and a determining phase determination unit phase in accordance with the output of the counter.

The operation of the present invention will be described below. In the present invention, the comparison unit compares the AM demodulated signal with the reference signal, and samples the output of the comparison unit with a sampling clock having a higher frequency than the reference signal. Then, the result is counted by a counter, and the phase is determined based on the count value from the synchronization signal to the next synchronization signal (that is, for one frame). Thus, in the present invention, the phase is determined for each frame. For example, by monitoring the phase determination for each frame over a plurality of frames, the boundary between the in-phase region and the opposite-phase region, that is, the position immediately below the road beacon transmitter and the traveling direction of the vehicle can be determined with high accuracy. .

[0012]

Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 1 is a block diagram illustrating a configuration of a beacon receiver according to an embodiment of the present invention, and FIG. 2 is a block diagram illustrating a configuration of a phase comparison determination unit. The beacon receiver 10 includes a beacon receiver 11, a data demodulator 12, a 1 kHz AM demodulator 13, an electric field level detector 1,
4, a synchronization detection unit 15, a phase comparison determination unit 16 and a data processing unit 17, which are connected to the navigation device 30.

The beacon receiving section 11 converts a high-frequency signal (radio wave beacon) of a predetermined frequency received by the antenna 18 into an intermediate frequency signal (IF signal) and outputs it. The data demodulation unit 12 performs GMSK modulation on the intermediate frequency signal output from the beacon reception unit 11 and extracts bit data. A
The M demodulator 13 performs AM detection on the intermediate frequency signal output from the beacon receiver 11, and extracts an AM demodulated signal A1 having a frequency of 1 kHz. The electric field level detector 14 detects an intermediate frequency signal to detect a received electric field level, and outputs a signal corresponding to the received electric field level.

The synchronization detector 15 monitors the bit data output from the data demodulator 12 and, when a synchronization code is detected, outputs a synchronization signal in synchronization with the detection timing of the synchronization code. As shown in FIG. 2, the phase comparison determination unit 16
Reference signal generator 21, sampling clock generator 2
2. EXOR gate (exclusive OR gate) 2
3, a sampling unit 24, an up / down counter 25, and a phase determination unit 26.

The reference signal generator 21 generates and outputs a reference signal A0 having a frequency of 1 kHz at a timing synchronized with the synchronization signal. The sampling clock generator 22 generates and outputs a sampling clock having a frequency of 2 kHz at a timing synchronized with the synchronization signal. The EXOR gate 23 outputs the AM demodulated signal A output from the AM demodulator 13.
1 and the reference signal A0 output from the reference signal generation unit 21, and as shown in FIG.
"L" when the logical values of the reference signal A0 and the reference signal A0 match.
And outputs the AM demodulated signal A1 as shown in FIG.
"H" when the logic values of the reference signal A0 and the reference signal A0 are different from each other.
Is output.

The sampling section 24 samples the output of the EXOR gate 23 at the frequency of the sampling clock output from the sampling clock generating section 22. The up / down counter 25 is initialized by a synchronization signal. When the output of the sampling section 24 is "H", 1 is added to the counter value (+1), and when it is "L", 1 is subtracted from the counter value. (-1). In this example, the up / down counter 25 can count from 0 to 63, and the counter value a is assumed to be 32 when initialized by a synchronization signal. The phase determination unit 26 controls the up / down counter 2 at a timing synchronized with the synchronization signal.
5, and outputs a phase determination signal indicating in-phase, out-of-phase or indefinite according to the count value.

The data processing unit 17 receives bit data from the data demodulation unit 12 and responds to the phase determination signal output from the phase comparison determination unit 16 and the electric field level signal output from the electric field level detection unit 14. The bit data is processed to determine the position immediately below the on-road beacon transmitter, determine the traveling direction of the vehicle, and extract traffic information. These data are sent to the navigation device 30, and traffic information according to the traveling direction of the vehicle is displayed on the display device of the navigation device 30.

FIG. 4 is a timing chart showing the operation of the phase comparison / determination section 16. As shown in FIG.
The M demodulated signal A1 has a jitter due to the influence of noise, a filter, and the like, particularly at the rising and falling portions of the signal. In addition, immediately below the beacon transmitter, A
The M demodulated signal may become unstable. FIG. 5 is a flowchart showing the operation of the beacon receiver according to the present embodiment when determining the phase. First, in step S11, when a synchronization code is detected by the synchronization detection unit 15 and a synchronization signal is output, the process proceeds to step S12. Then, the up / down counter 25 is initialized, and 32 (a = 32) is set in the up / down counter 25 as an initial value of the count value a.

Thereafter, the flow shifts to step S13, where a reference signal A0 having a frequency of 1 kHz is generated at a timing synchronized with the synchronizing signal.
0 is compared with the AM demodulated signal A1. Further, a sampling clock having a frequency of 2 kHz is generated at a timing synchronized with the synchronization signal, and the sampling unit 24 outputs the EXOR gate 2 at a timing synchronized with the sampling clock.
3 is sampled. Up / down counter 2
5 indicates that the signal output from the sampling unit 24 is “L”
In the case of, 1 is added to the count value a, and in the case of "H", 1 is subtracted from the count value a. Then, the count value a is output to the phase determination unit 26 at a timing synchronized with the next synchronization signal.

Next, in step S14, the value of the count value a is checked. That is, when the count value a is equal to or greater than 37 (a ≧ 37), the phase determination unit 26 determines in step S
When the count value a is 27 or less (a ≦ 27), the process proceeds to step S14a, where it is determined that the phase is reversed. When the count value a is larger than 27 and smaller than 37, the process proceeds to step S14a. (27 <a <37) corresponds to step S14b.
And the phase is determined to be indefinite, and the result is output to the data processing unit 17.

In the data processing unit 17, for example, when the output of the phase comparison / determination unit 16 continues in phase (or in phase) over several frames and then continues in phase (or in phase) over several frames, the road beacon The position immediately below the transmitter is determined, and the direction is determined whether the vehicle is traveling in the main direction or in the sub direction, and the result is transmitted to the navigation device 30 together with the traffic information extracted from the beat data. introduce. In the navigation device 30,
Based on the direction determination sent from the beacon receiver, traffic information corresponding to the traveling direction is displayed on the display device.

In this embodiment, as described above, it is determined for each frame whether the phase is in-phase, opposite-phase, or indefinite. Then, the data processing unit 17 monitors the state of the phase for several frames, and when the state changes from a state where the in-phase is continuous to a state where the anti-phase is continuous (or a state where the anti-phase is continuous and the state where the in-phase is continuous). Is determined to be a position immediately below the on-road beacon transmitter. As a result, an effect is obtained that the reliability of the determination result of the position immediately below the beacon transmitter and the traveling direction of the vehicle is improved.

[0023]

As described above, according to the present invention,
The comparison section compares the AM demodulated signal with the reference signal, samples the output of the comparison section with a sampling clock having a higher frequency than the reference signal, counts it with a counter, and determines the phase based on the count value. The reliability of the determination result of the position immediately below the transmitter and the traveling direction of the vehicle is improved.

[Brief description of the drawings]

FIG. 1 is a block diagram illustrating a configuration of a beacon receiver according to an embodiment of the present invention.

FIG. 2 is a block diagram showing a configuration of a phase comparison determination unit of the beacon receiver.

FIG. 3A is a diagram showing the output of an EXOR gate and the count of an up-down counter when the AM demodulated signal and the reference signal are in phase, and FIG. 3B is a diagram showing the relationship between the AM demodulated signal and the reference signal. FIG. 9 is a diagram illustrating the output of the EXOR gate and the count of the up / down counter when the phase is reversed.

FIG. 4 is a timing chart illustrating an operation of a phase comparison determination unit.

FIG. 5 is a flowchart illustrating an operation of the beacon receiver according to the embodiment at the time of phase determination.

FIG. 6 is a diagram illustrating a frame configuration of a radio wave beacon.

FIGS. 7A and 7B are diagrams showing a relationship between an AM demodulated signal of a radio wave beacon and a data packet.

FIG. 8 is a schematic diagram illustrating a phase of an AM modulation signal transmitted from a beacon transmitter.

FIG. 9 is a diagram showing an electric field strength distribution near a radio wave beacon transmitter.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 ... Radio beacon receiver, 11 ... Beacon receiving part, 12 ... Data demodulation part, 13 ... AM demodulation part, 14 ... Electric field level detection part, 15 ... Synchronization detection part, 16 ... Phase comparison judgment part, 17 ... Data processing part Reference numeral 18: antenna, 21: reference signal generator, 22: sampling clock generator, 23: EXOR gate, 24: sampling unit, 25: up / down counter, 26: phase determination unit, 30: navigation device.

Claims (5)

[Claims] A radio beacon receiving section for receiving a radio beacon; an AM demodulation section for demodulating an output of the radio beacon receiving section to extract an AM demodulated signal; A data demodulation unit that outputs bit data, a synchronization detection unit that detects a synchronization code from the bit data and outputs a synchronization signal, a reference signal generation unit that generates a reference signal having a constant frequency, A sampling clock generation unit that generates a sampling clock having a high frequency; a comparison unit that compares the AM demodulated signal with the reference signal; a sampling unit that samples an output of the comparison unit at a timing synchronized with the sampling clock; A counter initialized by the synchronization signal and counting an output of the sampling unit; A beacon receiver for a vehicle, comprising: a phase determination unit configured to determine a phase according to an output of the beacon. 2. The in-vehicle beacon receiver according to claim 1, wherein the counter is an up / down counter that goes up and down according to a logical value of an output of the sampling unit. 3. The in-vehicle beacon receiver according to claim 1, wherein the reference signal has the same frequency as the AM demodulated signal. 4. The in-vehicle beacon receiver according to claim 1, wherein the comparison unit is configured by a logic circuit that calculates an exclusive OR of the AM demodulated signal and the reference signal. 5. The in-vehicle beacon receiver according to claim 1, wherein the reference signal is generated at a timing synchronized with the synchronization signal.