JPH05264729A - Range finder - Google Patents

Abstract

PURPOSE:To prevent an influence due to multipath by raising a level of a reference signal when a counting part which is reset for each interval length of a PN code counts a plurality of correlation peak detection pulses. CONSTITUTION:A counting part counts correlation peak detection pulses and is reset by a timing interval of an interval length t2 of a PN code. When a correlation output signal S12 including a reflected wave of a reference signal level or higher is input from a correlation part to the counting part, two correlation peak detection pulses containing the reflected wave and a direct wave are counted within the interval length t2, so that a multipath detection signal is output to a reference signal control part to have a reference signal St level raised. Thus a level L2 of the reference signal St is higher than a reflected wave level, so that a correlation peak detection pulse S13 corresponding only to the direct wave is output. That is, a reflected wave due to the multipath is not detected but a true propagation delay is detected to allow a correct distance to be measured.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a distance measuring device which eliminates the influence of multipath which occurs when distance measuring is performed using a spread spectrum communication system.

[0002]

2. Description of the Related Art Distance measurement is known as an application field of spread spectrum (SS) communication system. FIG. 5 is a block diagram showing a conventional configuration of such a distance measuring device, where A is the distance measuring side,
B shows the configuration on the measured side. This range finder is SS
The signal (PN code) is returned and transmitted between the distance measuring side A and the distance measured side B to measure the distance between the two.

First, on the distance measuring side A in FIG. 5, the clock oscillator 1 outputs a PN clock signal S1 having a period length t1 as shown in FIG. 7, and a PN code is generated based on the rising edge of the PN clock signal S1. The section 2 outputs the PN code S2 having the cycle length t2 and the start pulse S3 of the PN code S2. The multiplication unit 3 is output from the PN code generation unit 2.
Baseband P with power spectrum as shown in Fig. 8
N code S4 and carrier f output from local oscillator 4
The PN code S is obtained by performing multiplication with the local signal of 1.
The high frequency modulation 4 is performed, and the PN code S5 having the center frequency f1 is transmitted from the transmitting antenna 5 to the distance-measured side B.

On the distance measuring side B, after receiving the PN code S5 shown in FIG.
The (band pass filter) 7 removes unnecessary frequency components other than the main lobe of the spectrum. After amplifying the PN code S5 by the amplifier 8, the PN code S5 is converted into the PN code S6 having the center frequency f2 as shown in FIG. Send it back. The conversion of the center frequency from f1 to f2 is performed by dividing the PN code in the frequency domain into a PN code transmitted from the ranging side A and a PN code transmitted back from the ranging side B. This is to prevent mutual interference.

On the distance measuring side A, the PN code S6 transmitted back from the distance measured side B is received by the receiving antenna 11, and the BPF 12 removes unnecessary frequency components other than the main lobe of the spectrum, and then the amplifier. The signal is amplified by 13 and then input to the correlator 14. Here, the correlation unit 14 is, for example, the analog matched filter 14A.
, The reference PN code pattern of the matched filter 14A and the received PN code S as shown in FIG.
When the correlation with the pattern 7 is obtained and the two patterns match, a triangular wave-shaped correlation output signal S8 having a sharp peak is obtained as a waveform after envelope detection.

As shown in FIG. 6, for example, the peak detection unit 15 is composed of a comparator (comparator) 15A, and the correlation output signal S8 is input to the + side which is one of the input units, and the other input unit. A reference signal St having a preset level L1 is input to the − side. Then, the peak detection unit 15 outputs the correlation peak detection pulse S9 as shown in FIG. 9 only when the correlation output signal S8 is larger than the reference signal St. This correlation peak detection pulse S9 has a cycle length t2.
have.

As shown in FIG. 10, the distance measuring section 16 has a P
The time difference between the rising edge of the start pulse S3 output from the N code generator 2 and the rising edge of the correlation peak detection pulse S9 is measured. Here, assuming that the time difference (propagation delay) measured by the distance measuring unit 16 is τ1, the distance L between the distance measurement side A and the distance measurement side B is expressed by As shown. L = C · τ 1/2 (C: speed of light)

[0008]

By the way, in the conventional distance measuring device, if multipath occurs in the radio wave propagation path from the distance measuring side A to the distance measured side B, accurate distance measurement becomes impossible. There's a problem. FIG. 11 illustrates this situation. In addition to the direct wave of the cycle length t2, the correlation output signal S10 in which the reflected wave by the multipath of the level L1 or more of the reference signal St is present in the cycle length t2 is the peak detection unit. 1
5, the peak detector 15 outputs the correlation peak detection pulse S11 corresponding to each of the direct wave and the reflected wave, so that the rising edge of the start pulse S3 of the PN code and the rising of each waveform of the pulse S11. When measuring the time difference from the edge, in addition to the true propagation delay τ1, the false propagation delay τ2
Will be measured. Therefore, it is not possible to determine which is the correct propagation delay, and it becomes impossible to measure the distance accurately.

The present invention has been made in consideration of the above problems, and an object of the present invention is to provide a distance measuring device that enables accurate distance measurement by detecting a true propagation delay. Is.

[0010]

To achieve the above object, the present invention provides a PN which outputs a PN code and a start signal.
A code generator, a transmitting means for high-frequency modulating the PN code and transmitting it to an object to be measured, a receiving means for receiving the PN code transmitted back from the object to be measured, and a receiving P
A correlation unit that outputs a correlation between the N code and the predetermined code;
A peak detection unit that outputs a correlation peak signal by comparing a correlation output signal and a reference signal, and at least a measuring unit that measures a generation time difference between the start signal and the correlation peak signal, are provided. In the distance measuring device that measures the distance to the object to be measured based on the above, the peak detection unit is a comparison unit in which the correlation output signal is input to one input unit and a reference signal is input to the other input unit. And a reference signal control unit that raises the level of the reference signal when a multipath detection signal is input, and a counting unit that counts the correlation peak signal, and a counting unit that controls the cycle length of the PN code. And a reference signal when a plurality of correlation peak signals are counted by the counting unit. It is characterized in that it comprises a peak count unit for outputting a multipath detection signal to the control unit.

[0011]

When the counting unit, which is reset by the timing signal generating unit of the peak counting unit according to the timing period of the period length of the PN code, counts a plurality of correlation peak signals (correlation peak detection pulses), the peak is output from this counting unit. The multipath detection signal is output to the reference signal control unit of the detection unit. As a result, the reference signal control unit controls to raise the level of the reference signal for comparing the magnitude relationship with the correlation output signal. As a result, the reflected wave due to the multipath having a smaller signal level than the direct wave is not detected as the correlation peak detection pulse, so that the influence due to the multipath is prevented.

[0012]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing an embodiment of a distance measuring device according to the present invention, in which A indicates the distance measuring side and B indicates the distance measured side. 1
Is a clock oscillator that outputs a PN clock signal S1 having a cycle t1, 2 is a PN code generator that outputs a PN code S2 having a cycle length t2 and a start pulse S3 based on the rising edge of the PN clock signal S1, and 3 is a PN code The PN code S4 is obtained by multiplying S4 and the local signal from the local oscillator 4.
Is a transmitting antenna for transmitting the PN code S5 of the center frequency f1 that has been subjected to high frequency modulation to the distance-measured side B.

Reference numeral 6 is a receiving antenna for receiving the PN code S5, 7 is a BPF for removing unnecessary frequency components other than the main lobe of the spectrum, 8 is an amplifying section for amplifying the PN code S5, and 9 is a PN having a center frequency f1. A frequency conversion unit 10 for converting the code S5 into a PN code S6 having a center frequency f2 is a transmission / reception antenna for transmitting the PN code S6 back to the distance measuring side A.

Reference numeral 11 is a receiving antenna for receiving the PN code S6, 12 is a BPF for removing unnecessary frequency components other than the main lobe of the spectrum, 13 is an amplifying section for amplifying the PN code S6, and 14 is a reference of the matched filter 14A. P
It is a correlating unit that correlates the N code pattern and the received PN code pattern and outputs a correlation output signal S8. The above is the same as the conventional configuration.

Reference numeral 18 denotes a peak detecting section, for example, as shown in FIG. 2, the correlation output signal S8 is inputted to the + side which is one of the input sections and the reference signal St whose level is variable to the negative side which is the other input section. Is input to the comparator (comparator) 19
And a reference signal controller 20 that raises the level of the reference signal St when a multipath detection signal is input.

Reference numeral 17 denotes a peak counting section, for example, as shown in FIG. 2, a counting section 21 for counting the correlation peak detection pulse S11, and a timing signal generation for resetting the counting section 21 by the timing cycle of the cycle length t2 of the PN code. The counting unit 21 outputs a multipath detection signal to the reference signal control unit 20 when the counting unit 21 counts two or more correlation peak detection pulses.

Next, the operation of this embodiment will be described with reference to FIG. As shown in FIG. 11, the correlation output signal S10 including the reflected wave having the level L1 or more of the reference signal St from the correlation unit 14 is
When input to the counting unit 21 of the peak counting unit 17 via the comparator 19 of the peak detecting unit 18, the counting unit 21 outputs two correlation peak detection pulses of the reflected wave and the direct wave within the cycle length t2. Since the counting is performed, the multipath detection signal is output to the reference signal control unit 20 of the peak detection unit 18 based on the above operation principle. As a result, the reference signal control unit 20 raises the level of the reference signal St input to the-side of the comparator 19 from L1 up to now to L2 as in S12 of FIG. 3 based on the above-mentioned operation principle.

As a result, the level L2 of the reference signal St becomes higher than the level of the reflected wave, so that the correlation peak detection pulse S13 corresponding to only the direct wave is output. That is,
The reflected wave due to multipath is no longer detected as a correlation peak detection pulse. Subsequently, the distance measuring unit 16 measures the time difference between the rising edge of the start pulse S3 output from the PN code generating unit 2 and the rising edge of the correlation peak detection pulse S13. Since the reflected wave is not included,
A propagation delay similar to the true propagation delay τ1 in FIG. 11 is detected, and the accurate distance L can be measured based on the above equation.

As another embodiment of the present invention, the counting unit 2
The multipath detection signal output from 1 can be used as an antenna switching signal for space diversity and frequency diversity. For example, as shown in FIG. 4, the changeover switch 24 can be controlled by the multipath detection signal for the reception signal input from the reception antenna 22 or the reception antenna 23 in the space diversity. This also makes it possible to select an antenna without being affected by multipath, as in the embodiment of the present text.

[0020]

As is apparent from the above description, according to the present invention, when the count unit of the peak count unit counts a plurality of correlation peak detection pulses, the multipath detection signal is sent to the reference signal control unit of the peak detection unit. Since the level of the reference signal is increased by outputting, the reflected wave due to the multipath is not detected as a correlation peak detection pulse, and the influence of the multipath can be prevented, so that accurate distance measurement can be performed.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a distance measuring device according to the present invention.

FIG. 2 is a block diagram showing a configuration of a main part of the distance measuring apparatus according to the present embodiment.

FIG. 3 is a timing chart between main signals for explaining the operation of the distance measuring apparatus according to the present embodiment.

FIG. 4 is a block diagram showing another embodiment of the present invention.

FIG. 5 is a block diagram showing a conventional distance measuring device.

FIG. 6 is a block diagram showing a configuration of a main part of a conventional distance measuring device.

FIG. 7 is a timing chart between main signals for explaining the operation of the distance measuring device.

FIG. 8 is a power spectrum between main signals for explaining the operation of the distance measuring device.

FIG. 9 is a timing chart between main signals for explaining the operation of the distance measuring device.

FIG. 10 is a timing chart between main signals for explaining the operation of the distance measuring device.

FIG. 11 is a timing chart between main signals illustrating a drawback of the conventional distance measuring device.

[Explanation of symbols]

 A Distance measuring side B Distance measured side 2 PN code generating section 9 Frequency conversion section 14 Correlation section 16 Distance measuring section 17 Peak counting section 18 Peak detecting section 19 Comparator 20 Reference signal control section 21 Counting section 22 Timing signal Generation part

Claims (1)

[Claims] 1. A P that outputs a PN code and a start signal
An N code generator, a transmitting means for high-frequency modulating the PN code and transmitting the modulated PN code to an object to be measured, a receiving means for receiving the PN code sent back from the object to be measured, a received PN code and a predetermined value. Correlation unit that outputs a correlation with a code, a peak detection unit that outputs a correlation peak signal by comparing a correlation output signal and a reference signal, and a measurement that measures the time difference between the start signal and the correlation peak signal. A distance measuring device for measuring the distance to the object to be measured on the basis of the generation time difference between the both signals, wherein the peak detecting section receives the correlation output signal at one input section and The reference signal is input to the other input unit, and the reference signal control unit increases the level of the reference signal when a multipath detection signal is input. And a timing signal generation unit for resetting the counting unit according to the timing cycle of the cycle length of the PN code. When the counting unit counts a plurality of correlation peak signals, the reference signal control unit A distance measuring device comprising a peak count unit for outputting a multipath detection signal.