JPH0229898A - Vehicle position detecting system - Google Patents

Abstract

PURPOSE:To simplify the constitution of a device by smoothing the field intensity of a radio signal in a navigation system and finding out the peak of a chevron shaped wave exceeding a fixed threshold. CONSTITUTION:A field intensity deciding part 9 compares a threshold Ec larger than a noise level with the field intensity, and at the time of Ei<Ec, the Ei is dropped as a noise level. Only when the decided result of the deciding part 9 is E>Ec, a position detecting pulse Q is generated when a position detecting pulse sending part 10 goes Ei-1>Ei. Since Ei-1>Ei is formed more than the level of the Ec, the nearby position of a point L is detected and the position detecting pulse Q is generated at Ej. At that time, the position is most close to a side antenna. Since Ek<Ec is formed on a point 0, a peak value pulse is generated, but the position detecting pulse Q is not generated and the point 0 is removed as noise. Thus, malfunction can be reduced and a correct position can be detected by the simple constitution.

Description

DETAILED DESCRIPTION OF THE INVENTION (G) Technical Field The present invention relates to a position detection method in an automobile navigation system or the like.

The navigation system has the function of detecting the current location of the vehicle and displaying this information along with a map on the display.

For this reason, it is necessary to accurately determine the current position.

This is often referred to as a location system.

In order to accurately determine the current position, it is sufficient to perform integral calculations on the traveling speed in the two axis directions, X and Y, from a certain starting point.

For this purpose, an orientation sensor and a wheel speed sensor are required. The azimuth sensor determines the running direction angle of the vehicle with respect to a certain azimuth. Multiplying the wheel speed by the sine and cosine of the direction angle gives
The wheel speed in the x and y axis directions is known. By integrating this wheel speed over time, the moving distance in the X%y direction from the starting point can be determined.

Now, we need to find the correct position of the starting point. This involves placing a sign at a fixed point on the road and determining the time when a car passes this point. The present invention relates to a vehicle position detection method for determining this.

There is not just one starting point, but many can be set up along the road. By doing so, errors in integral calculations will not be accumulated, and a correct result can be obtained each time position detection is performed.

0) Conventional technology Install the antenna on the roadside at an appropriate point on the road.

It has a transmitter that allows radio signals to be emitted from the antenna. This radio signal carries a carrier wave,
It is modulated by a data signal.

Data signals can be used to convey information about antenna location and road conditions.

This data signal is not required for wheel position detection. It is only necessary to detect the strength of the wireless signal as a whole.

Cars have antennas and receivers that receive wireless signals from roadside antennas.

FIG. 1 is a block diagram of an on-vehicle receiver installed in an automobile.

An on-vehicle antenna 1 catches radio signals. The receiving section 2 selects and amplifies only radio signals of a predetermined frequency. This is a signal in which the carrier wave is modulated by a data signal.

This is demodulated by the data demodulating section 3 to obtain a data output. Although this part carries various information, it is not related to the present invention.

The received signal enters the position detection section 4 and generates a position detection pulse Q. This is a pulse that is generated when the antenna passes closest to the roadside antenna.

Since the position of the antenna has been detected, it can also be called antenna detection or gauge point detection. However, by detecting the antenna, it is detected that the position of the car at that time is at the antenna position, so it can be said that the position of the car has been identified. Therefore, it is called a position detection pulse Q.

The fact that it is located closest to the roadside antenna should be easily understood from the fact that the strength of the radio waves generated from the antenna is at its maximum.

This is because the electric field strength should attenuate in proportion to the square of the distance from the antenna.

FIG. 2 shows an example of fluctuations in the reception level of radio signals when a car travels along a road.

As the car approaches the roadside antenna, the reception level increases as follows.

Point L is the closest position to the roadside antenna. The electric field strength is maximum.

After passing point L, the signal moves away from the antenna, and the reception level decreases in the order of M, N, and so on.

It is sufficient to detect the L point. This is the eye. There were two conventional methods.

(a) One is to detect that the electric field strength of a received wireless signal has exceeded a certain level.

The Colpel is set to a value intermediate between the level of the 1% M point and the level of the L point in FIG. If the electric field strength is greater than this level, it means that it is closest to the antenna.

(b) The other method uses two antennas to generate radio signals with opposite phases. When in the middle of the antenna, the two radio signals cancel each other out exactly. Therefore, the moment the signal becomes 0, the car passes through the midpoint between the two antennas.

←) Problem to be Solved by the Invention The method of (a) compares the fixed level and the received level, and when the latter is larger, it is detected that the car is closest to the roadside antenna.

The principle is simple. However, the transmitter and receiver equipment will be sophisticated. Since we are comparing the absolute value of the electric field,
The transmitter output must be stable. The performance of a car's receiver must be constant for all cars. Also, the performance of the receiver must not deteriorate over time.

This is because if it deteriorates, position detection becomes impossible.

Thus, a high degree of stability and accuracy is required in the performance of the transceiver. This results in an extremely expensive device.

Not only that, even if the transmitting and receiving functions are stable, the strength of the radio waves will be affected by the road conditions. If a large truck is driving in front of you, the radio waves will be blocked. In such cases, position detection may not be possible.

In the method of Can), the configuration of the transmitter is somewhat complicated.

However, it is not necessary that the absolute value of the radio field intensity is stable. Since the two antennas emit radio waves that cancel each other out, the range of the radio waves is naturally narrow.

The center of the antenna is not the only point where the electric field becomes zero. The electric field becomes zero even in a range far away from the antenna. We must distinguish between the two.

Furthermore, even if the outputs of the two antennas are equal, if there is a shield, the electric fields may not be the same, and they may not cancel each other out at the midpoint.

As a result, the device becomes complicated and there is a possibility of malfunction.

Gr-) Purpose It is an object of the present invention to provide a vehicle position detection method that has a simple configuration, has few malfunctions, and can accurately detect the position.

i) Configuration The present invention relates to the configuration of the position detection section 4 of the vehicle-mounted receiver shown in FIG.

The device of the present invention detects that a car is in the vicinity of the antenna by the following operation.

(1) The radio reception level intensity is oscillating violently as shown in Figure 2, but this is changed to a gentle mountain-shaped waveform with a single peak by applying it to a low-pass filter.

(2) Sample the strength of the received signal at every certain timing and compare the previous signal and the current signal.

(3) If the current signal is smaller than the previous signal,
This means that the peak of the electric field strength (point L) has passed, so a position detection pulse is generated.

(4) However, since the nozzle must not be picked up, the position detection pulse is not generated when the reception level is below a certain level.

This will be explained using drawings.

The device of the present invention also includes an on-vehicle receiver like the one shown in FIG. Roadside antennas are installed at predetermined locations on the road transportation network. It transmits radio signals containing various types of data. The in-vehicle antenna 1 receives this, and the receiving section 2 tunes and amplifies it.

A position detector 4 is used to determine the position of the vehicle, and a configuration diagram thereof is shown in FIG.

The receiver signal enters the filter section 5. As shown in FIG. 2, this signal is a signal with a high frequency and many peaks and valleys. The horizontal axis in FIG. 2 is the position of the car along the road, but since the car is running, the horizontal axis is the time axis.

Filter section 5 is a low-pass filter.

Since it is a low-pass filter, there are no thin irregularities (like the mountain-like waveform KJ with one peak as shown in Figure 4).
Become LMN.

The switch 6 is a switch that opens and closes in synchronization with a certain sampling signal. Every time this sampling a occurs, the electric field strength (E,) is stored in the electric field strength storage section 7.

The comparison unit 8 stores the current electric field strength Ei and the electric field strength storage unit 7.
The previous electric field strength "i-1" stored in "i-1" is compared.

Here, 1.2,...11... are sampling numbers, and the electric field strength at that time is Eo, E2,..., Ei,
...and so on.

The comparator 8 generates an output signal pulse P when the current intensity Ei is smaller than the previous intensity Ei-1. This is to find the peak of the electric field strength. This corresponds to point L and point 0 in FIG. At point L, Ej-0>Ej, and at point 0, E, -0>Ek.

However, although the L point is the closest position to the antenna, the 0 point is only the maximum point of noise. This is because the electric field is small. A position detection signal must not be generated at the 0 point.

Malfunctions due to noise peaks such as the 0 point must be avoided.

For this purpose, an electric field strength determining section 9 is provided. This compares the electric field strength with a threshold Ec that is greater than the noise level,
If Ei<Ec, Ei is reduced as a noise level.

Only when the electric field strength determination section 9 determines that E>Ec, and when the position detection pulse transmission section 10 determines that Ei-0>Ei,
A position detection pulse Q is generated.

This becomes E on the sand, so Cl-
Since 1>El, it means that the vicinity of point L in FIG. 4 was detected.

A position detection pulse Q is generated at E. In this case, it is closest to the roadside antenna.

Since Ek<Eo at point 0, the peak value pulse P is generated, but the position detection pulse Q is not generated. 0 points will be removed. Tip 9: Noise can be removed.

A wheel speed pulse from a wheel speed sensor can be used as the sampling signal. Then, the electric field strength will be sampled for each wheel speed pulse. and,
This means that the position detection pulse Q is generated when an electric field strength that is smaller than the previous value and larger than EC appears.

a) Examples The present invention will be explained in detail with reference to FIG.

The first amplifier 11 receives the signal a from the receiver through the resistor R0
, R2. The connection point between the resistors R0 and R2 and the output of the first amplifier 11 are connected by a capacitor C0. The input of the first amplifier 11 is grounded by a capacitor C2.

The voltage amplification factor of the first amplifier 11 is 1 (A=1).

This is to lower impedance.

Resistors R1 and R2 and capacitors C1 and C2 constitute a low-pass filter.

FIG. 6(a) shows the waveform of input a of the low-pass filter. Since this is a signal as received, the waveform contains vibration components with many irregularities.

FIG. 6(b) shows the waveform of the output of the low-pass filter. It has a gentle mountain-shaped waveform with one peak.

The second amplifier 12 has a voltage amplification factor of 1 (A=1) and is used to lower impedance.

The switch 6 is an analog switch that opens and closes in synchronization with the wheel speed pulse.

The third amplifier 13 is for storing the analog voltage that has passed through the switch 6, and has a capacitor C3 connected to its output.

Capacitor C3 stores the previous voltage value Ei-1 as a voltage value. The comparator 14 corresponds to the comparison section 8.

This compares the output Ei of the second amplifier and the output "i-1" of the third amplifier 13.

In reality, there is a resistor for discharging capacitor C3. This time constant may be made larger than the sampling period. To be more precise, capacitor C
3, a switch may be provided that momentarily closes just before the wheel speed pulse.

The smoothed signal is also given to the non-inverting input of the comparator 15. The comparator 15 has a certain threshold value Ec,
This is for comparison with signal E. This corresponds to the electric field strength determination section 9.

A resistor R3 and a variable resistor R4 are connected between power supply voltage Vcc and ground. An intermediate terminal of variable resistor R4 is connected to an inverting input of comparator 15.

This voltage EC corresponds to the electric field threshold.

Comparator 15 is at H level when E>EC;
A signal C that is at L level when <Eo is generated. This is shown in FIG. 6(C).

This is connected to the reset input R of the D flip-flop 16. The D flip-flop 16 outputs the value of the D input to the Q output when a clock input is input, and holds this value. The D input is connected to the power supply Vcc.

The output d of the comparator 14 is output from the D flip-flop 16
The clock is included in the human power Ck.

The reset force i is to turn off the D flip-flop when R=L.

Comparator 14 compares Ei-0 and Ei, and
-1<Ei, L level output is given, and Ei-1>"i, H level output is given. This waveform is shown in FIG. 6(d). This is the same as the peak value Ej-0 in FIG. 6(b). , and the next value Ej, Ej becomes >Ej, so Ej
0) which rises to H level at the time of .

The output Q of the D flip-flop 16 rises simultaneously with the signal d, as shown in FIG. 6(e). This is d
This is because the rising edge of Ck enters the clock input Ck, so the D input (H level) appears at the Q output.

The Q output is connected to buffer amplifier 17.1g. The amplifiers 17 and 18 have a voltage amplification factor of 1 and only amplify current.

A resistor R5 and an inverter 19 are connected in series to the output of the amplifier 1B. A capacitor C4 is connected between R5 and inverter 19.

Resistor R5 and capacitor C4 constitute a delay circuit.

The time constant is determined by C4R5.

The output of the amplifier 18 rises in the same way as the output of the amplifier 17, but the voltage of the capacitor C4 rises with a little delay.

This is inverted by an inverter 19.

FIG. 6(f) shows the output f of the inverter 19. Since this is a slightly delayed and inverted version of waveform e, it falls at point C.

The output of the amplifier 17 has a waveform e1, and the output of the inverter 19 has a waveform f. This is input to the AND gate 20. This output g is obtained by ANDing g = e f of both. From point B to point C, e = H, f =
=H, so g=H. This output becomes a short pulse as shown in FIG. 6 (ω).

In this way, the generation of the pulse Q indicates that the peaks Ej-0 and Ej have been passed.

In reality, it's later than peak hours.

However, wheel speed pulses occur every fixed distance. For example, 40 to 90 pulses are generated each time the tire rotates.・In other words, the distance traveled per pulse is determined. Then, if you know that the wheel speed pulse is delayed by two pulses, you can subtract the distance equivalent to two pulses.

The D flip-flop 16 maintains its output as it is, but when the low-pass filter output becomes equal to or less than EC, the output of the comparator 15 decreases (tick).

In response to this, it is reset and the output of the D flip-flop 16 falls (point 2). The output of the comparator 19 rises after a delay time (point E).

This completes the D flip-flop 16 and allows it to receive a signal to the next input Ck.

A peak like point O in FIG. 4 does not make the output C of the comparator 15 H level, so the D flip-flop 16
The output Q cannot be raised. In other words, such peaks are discarded.

←) Effect The electric field strength of the wireless signal is smoothed, and the peak of the mountain-shaped waveform that exceeds a certain threshold is found.

Therefore, it is not necessary to strictly control the output of the antenna, the performance of the transmitter/receiver, etc. Therefore, the configuration of the device is simplified.

It can be used to detect the starting point position of a navigation system.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of an on-vehicle receiver that forms part of a navigation system. Figure 2 shows when a car passes near a roadside antenna.
The figure which shows an example of the distance traveled and the reception level change of a radio signal. FIG. 3 is a circuit configuration diagram of a vehicle position detection circuit according to the present invention. FIG. 4 is a signal waveform diagram obtained by smoothing a received radio signal through a filter section. FIG. 5 is a circuit diagram showing an embodiment of the present invention. FIG. 6 is a waveform diagram at each point in the circuit of FIG. 5. １・・・・・・・・・・・・ ２・・・・・・・・・・・・ ３・・・・・・・・・・・・ ４・・・・・・・・・・・・・・・ 5・・・・・・・・・・・・ 6・・・・・・・・・・・・ 7・・・・・・・・・・・・ 8・・・・・・・・・・・・・・・ 9・・・・・・・・・・・・ 10 ・・・・・・・・・ 11～13・・・・・・ 14.15・・・・・・ 17.18・・・・・・・・ 19 ・・・・・・・・・ 20 ・・・・・・・・・ Inventor

Claims (1)

[Claims] A roadside antenna installed at a fixed position on the side of the road emits a radio signal of a constant strength modulated by various data, and an on-board antenna mounted on the car receives this radio signal, demodulates it, and converts the data. A position detection unit of a vehicle-mounted receiver for determining the timing when a vehicle passes closest to a roadside antenna for the purpose of calibrating the position of a navigation system configured to receive radio signals, without demodulating the radio signals received by the vehicle-mounted antenna. A filter section 5 receives the input as it is and removes high vibration components to form a chevron-shaped voltage waveform with one peak, and an analog switch 6 connected to the output of the filter section 5 which opens and closes in response to the wheel speed pulse generated by the wheel speed sensor.
, an electric field strength storage section 7 that temporarily stores the voltage value passed through the switch 6, and a current voltage output E_i of the filter section 5.
and the previous voltage value E_i stored in the electric field strength storage unit 7
_-_1 and generates a peak value signal P when E_i_-_1>E_i; and a predetermined threshold value E.
The electric field strength determination unit 9 compares __c with the current electric field strength E_i, and when the determination of the electric field strength determination unit 9 is E_i>E_c, the position detection pulse Q is generated when the peak value signal P from the comparison unit 8 is received. A vehicle position detection system characterized by comprising a position detection pulse sending unit 10 that generates a position detection pulse.