JPH10153654A - Radar device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable correlated detection of a reception signal with a low S/N ratio which has been difficult to detect. SOLUTION: In a radar device for transmitting an electric wave whose bandwidth is diffused by a pseudo noise signal, receiving a reflection wave from an object based on the electric wave, inversely diffusing a received signal by the pseudo noise signal, converting the frequency of the inversely diffused reception signal to a specific frequency signal, and measuring the speed of an object based on the frequency-converted signal, and measuring distance to the object, an amplitude measurement circuit 11e of a signal processing part measures a noise floor on non-correlation, a processing circuit 11f estimates the degree of saturation of a received power based on the noise floor on non- correlation, and lowers the gain of the amplifier of a reception part according to the degree of saturation and compensates for an autocorrelation peak.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radar apparatus for detecting an object, measuring a relative speed to the object, and measuring a distance to the object by using a spread spectrum technique, and more particularly, to a synchronous detection using an amplitude measuring circuit. The present invention relates to a radar device that performs reception power measurement and relative speed measurement.

[0002]

[Related Background Art] Conventionally, in this type of radar device,
For example, Japanese Patent Application No. 8-1350065 discloses a method for detecting a correlation without using an IQ method or a surface acoustic wave element as a detection method. According to the present invention, the correlation detection is determined by determining the periodicity of the beat signal applied to the received wave that has been pulse-shaped by the waveform shaping circuit including the Schmitt trigger circuit.

Conventionally, as an azimuth estimation method in a radar apparatus, as represented by a multi-beam method,
In some cases, the azimuth is estimated from the ratio of the received power reflected from the detected object over a plurality of beams.

[0004]

However, in the radar device of the above application, when the S / N ratio of the received wave deteriorates,
Due to the characteristics of the Schmitt trigger circuit, a pulse having a period other than the original period is generated, and the probability of correlation detection is reduced, and there is a problem that the relative speed is erroneously measured.

When the azimuth estimating method is used in the radar apparatus of the above-mentioned application, an amplifier having a fixed gain sufficient for the minimum received signal to exceed the threshold of the Schmitt trigger is used. If the level exceeds the level, saturation occurs, so that there is a problem that accurate measurement of received power cannot be performed and a direction cannot be estimated. Therefore, in general, a method is conceivable in which an automatic gain adjustment circuit is used so as not to saturate the received signal, and a spectrum analysis of the received signal by fast Fourier transform is performed to measure the received power. There has been a problem that it is complicated and large-scale, and the production cost is high.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-described problems, and measures an amplitude value of a beat signal applied to a reflected reception signal by an amplitude measurement circuit for each delay of a pseudo-noise signal for reception. It is an object of the present invention to provide a radar apparatus which can detect a correlation and detect a correlation even with a received signal having a low S / N ratio, which has conventionally been difficult to detect. Another object of the present invention is to estimate a degree of saturation by measuring an autocorrelation peak at the time of correlation detection and a noise floor at the time of non-correlation,
The object of the present invention is to make it possible to measure the reflected received power even when the output signal is saturated when the reflected received power exceeds a predetermined level.

Another object of the present invention is to improve the measurement accuracy in measuring the relative speed with respect to an object.

[0008]

In order to achieve the above object, the present invention transmits a radio wave whose band is spread by a pseudo-noise signal from a transmitting unit, and transmits a reflected wave from an object based on the radio wave to a receiving unit. Receiving, despreading the received signal with the pseudo-noise signal, converting the frequency of the despread received signal by a down converter into a signal of a predetermined frequency, and an arithmetic processing unit based on the frequency-converted signal. In the radar device for measuring the speed of the object, measuring the distance to the object,
The arithmetic processing unit is a radar including: a measuring unit including an amplitude measuring circuit for measuring an amplitude of the frequency-converted signal; and a determining unit including a processing circuit for determining an autocorrelation peak based on the measured amplitude. An apparatus is provided.

That is, by comparing the amplitude value of the signal measured by the amplitude measurement circuit with a predetermined threshold value by the processing circuit,
An autocorrelation peak is determined, and correlation detection is possible even for a received signal having a low S / N ratio. According to claim 2, the amplitude measurement circuit measures the noise floor at the time of non-correlation, and the processing circuit determines the degree of saturation of the received power based on the noise floor at the time of the non-correlation and the autocorrelation peak at the time of correlation detection. It estimates and corrects the autocorrelation peak according to the degree of the saturation.

That is, when the received power exceeds a predetermined level, the peak of the autocorrelation saturates, but the noise floor becomes lower. Therefore, the received power can be measured from the noise floor and the autocorrelation peak, and the noise floor becomes smaller. Although it does not change in a state where it has decreased to finally become zero, in this case, the gain of the amplifier of the receiving unit is reduced to correct the autocorrelation peak.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A radar apparatus according to the present invention will be described with reference to FIGS. FIG. 1 is a block diagram showing a schematic configuration of an embodiment of a radar apparatus according to the present invention.
In the figure, a radar device of the present embodiment includes an arithmetic processing unit 11 for performing various controls and arithmetic processing on input signals,
A PN generator 12 connected to the arithmetic processing unit 11 for generating a pseudo-noise signal (hereinafter referred to as a "PN code") composed of a pseudo-noise code sequence, and a transmission unit 13 for transmitting radio waves band-spread by the direct spreading method A transmitting antenna 14, a delay circuit 15 connected to the arithmetic processing unit 11 and the PN generator 12 for delaying the PN code by a predetermined time and outputting the same, a receiving antenna 16, and receiving a reflected wave from the object 10. It comprises a receiving unit 17 for despreading and a down converter 18 for down converting a received signal. The transmitting antenna 14 and the receiving antenna 1
6 can be shared for transmission and reception by a circulator or other means.

The PN generator 12 includes an arithmetic processing unit 11
, A random PN code having a predetermined length (period) is output to the transmission unit 13 and the delay circuit 15. The transmitting unit 13 generates a high-frequency signal spread over a wide band by the input PN code, and the high-frequency signal is transmitted as a radio wave via the transmitting antenna 14. For example, when the radar apparatus of the present embodiment is used for a general automobile, the signal generated by the transmitting unit 13 is a signal in a millimeter wave band having an optimal frequency as a radar, for example, a signal of 60 mm.
It is a high frequency signal of GHz.

On the other hand, under the control of the arithmetic processing section 11, the delay circuit 15 delays the input PN signal by a predetermined time and outputs it to the receiving section 17. The transmitted radio wave above
For example, when the object 10 reaches a predetermined distance and is
And is received by the receiver 17 as a reception signal via the reception antenna 16. The receiving unit 17 despreads the received signal with the PN signal from the delay circuit 15 and takes a correlation. Here, when the correlation is obtained, the receiving unit 17 outputs a signal having a sharp peak in the intermediate frequency band.

The down-converter 18 converts the signal of the intermediate frequency band input from the receiving unit 17 into a plurality of stages by a plurality of mixers (not shown) and converts the signal into a low frequency of, for example, 3 kHz to 47 kHz. Output.
The arithmetic processing unit 11 confirms that the correlation has been obtained by the input of the signal from the down converter 18 and detects the presence of the object. That is, as shown in FIG. 2, the arithmetic processing unit 11 includes amplifier circuits 11a and 11b, a waveform shaping circuit 11c including a Schmitt trigger circuit, a cycle measuring circuit 11d, an amplitude measuring circuit 11e, and a processing circuit 11f. And calculates the length of one cycle of the signal after down-conversion.

In the arithmetic processing unit 11 having such a configuration, the amplifier circuit 11a is connected to the down converter 18 and is set so as to provide the maximum gain within a range that does not saturate the maximum input from the down converter 18.
When the amplitude is measured by the amplitude measuring circuit, the signal after down-conversion is amplified so as not to be saturated. That is,
When the correlation is obtained, the amplifier circuit 11a operates as shown in FIG.
The signal shown in FIG. 3A is output, and when there is no correlation, the noise floor shown in FIG. 3C is output.

The total gain of the amplifier circuits 11a and 11b is set to a gain sufficient for the minimum input from the down converter 18 to exceed the threshold of the waveform shaping circuit 11c. Thus, the amplifier circuits 11a and 11b
Since the waveform shaping circuit 11b has a gain sufficient to generate a pulse-shaped signal (hereinafter, “pulse signal”), the waveform shaping circuit 1 connected to the amplifier circuit 11b
1c can convert the amplified signal into a pulse signal as shown in FIG.

The processing circuit 11f operates so as to take in the output of the amplitude measuring circuit 11e every time the PN code for reception is delayed, and calculates an autocorrelation value having a peak value as shown in FIG. Detected. That is, when the processing circuit 11f recognizes that a peak exists by comparing / determining the output of the amplitude measurement circuit 11e and the predetermined threshold, the processing circuit 11f operates to detect the maximum value of the peak. Record the delay time when appears. By this operation, the processing circuit 11f performs the detection of the presence of the object, the distance measurement, and the measurement of the received power.

Next, the processing circuit 11f enters a period measurement mode. In the cycle measurement mode, the processing circuit 11f
One of the rising or falling edge of the pulse
The period measuring circuit 11d is controlled so as to measure the period of the section. This operation is averaged repeatedly N times to measure the period, that is, the relative speed. Here, if the S / N ratio of the received wave deteriorates, the pulse signal output from the waveform shaping circuit 11c may be missing (dropped or added) as shown in FIG. 4B. . Originally, for one period of the pulse signal, for example, as shown in FIG. 5, the measured value distributed around the count value C1 has twice the distribution around C1.
Further, depending on the state of the pulse signal missing due to the deterioration of the S / N ratio, the time corresponding to one cycle of the pulse signal is C
It can be three times, four times, and more than one, but the probability is fairly low.

Therefore, in this embodiment, the period measuring circuit 11
d is provided with a counter circuit (not shown) so as to compensate for a double distribution when measuring the pulse period.
f executes the period measurement algorithm. Next, a correction operation for obtaining an average value of one cycle of the pulse signal will be described with reference to a flowchart of FIG. In FIG. 6, the processing circuit 11f firstly calculates the sum CSUM = 0 of the count values from the counter circuit (not shown) of the cycle measuring circuit 11d,
Initial setting for i = 2 is performed (step 101). Here, i is an arbitrary number of times when the cycle measurement is performed N times. Then, it is determined whether or not | C1−Ci | <TH1 (step 102).

If the absolute value of the difference between C1 and Ci is larger than a predetermined threshold value TH1, it is determined that one of the count values has become twice as large due to the influence of the missing pulse. It is determined whether or not the magnitude relation C1> Ci of Ci (Step 103). In the magnitude relationship between C1 and Ci, if Ci is greater than C1, it is determined that Ci is in the distribution area of FIG. 5, and CSUM = CSUM + (1 /
2) Calculate Ci (step 104). In addition, the above Ci
Is smaller than C1, it is determined that C1 is in the distribution area of FIG. 5, CSUM = CSUM + 2Ci is calculated (step 105), and the processing circuit 11f in the processing circuit 11f indicating that C1 is in the distribution area is determined. The flag is set to "1" (step 106). Also, in step 102,
If the absolute value of the difference between C1 and Ci is smaller than the predetermined threshold TH1, CSUM = CSUM + Ci is calculated (step 10).
7).

Next, the processing circuit 11f adds "1" to i in order to perform the next measurement (step 108), and determines whether i has reached the number of measurements N (step 109).
Here, if i is not N, the next count value Ci is measured (step 110), and step 10 is executed.
2 and repeat the above measurement operation. When i becomes N, CSUM = CSUM + C1 is calculated by adding the first count value C1 to the total CSUM of the count values (step 111), and it is determined whether or not "1" is set in the flag. (Step 112).

If "1" is set in the flag, (CSUM / 2) / N is calculated (step 11).
3) If "1" is not set in the flag, CSUM / N is calculated (step 114), and the average value of the count value in the number of measurements N is obtained (step 11).
5), the measurement operation ends. The problem here is that the measurement value is included in the distribution of the double cycle in all the N measurements. For example, the occurrence probability of one cycle of the pulse signal in the distribution and the distribution area is “0.5. "
Assuming that “0.5” and the number of measurements N = 10, the occurrence probability is 1/2 ¹⁰ , which is a very small occurrence probability.
In an actual receivable S / N state, distribution> distribution, and it is considered that no problem occurs if the number of measurements N is increased. Note that the setting of N is determined by the false detection probability required for the system.

When the amplitude is measured every time the PN code is delayed, an autocorrelation having a peak value is detected as shown in FIG. The peak value of the autocorrelation saturates when the received power exceeds a predetermined level A as shown by the solid line in FIG. 8, but the peak value of the noise floor becomes low as shown by the broken line in FIG. Therefore, the amplitude measuring circuit 11e determines the amplitude peak of the beat signal when the correlation is obtained (FIG. 3).
The amplitude d1 of FIG. 3B and the amplitude peak of the noise floor at the time of non-correlation (the amplitude d2 of FIG. 3D) are measured, and the processing circuit 1
1f detects the received power from these peak values.

However, when the reflected received power exceeds a compression point (a limit point at which the amplifier operates linearly) of the amplifier circuit (not shown) inside the receiving unit 17, the input is limited, and in the amplifier circuit, The output is determined in such a manner as to maintain the S / N at the time of input of the received signal. For this reason,
Focusing on noise, when the input as viewed from the amplifier circuit is equal to or less than the compression, the signal is amplified by a predetermined amount. Operate.

The processing circuit 11f reads the autocorrelation value (peak of the beat signal and noise floor) measured by the amplitude measuring circuit 11e by an internal A / D converter (not shown). When the amplitude of the noise floor falls below the minimum resolution of the A / D converter, the measured value of the noise floor by the amplitude measurement circuit 11e becomes "0". That is, as shown at the position of the received power value B in FIG. 8, the amplitude of the peak of the autocorrelation value is saturated and shows a constant value, and the measured value of the noise floor becomes "0". Becomes impossible to detect the received power, and cannot be corrected.

Therefore, when the received power approaches the predetermined level B, the processing circuit 11f sends the signal to the receiving unit 1 via the gain control line.
By lowering the gain of the amplifier 7 by a predetermined amount, for example, G (dB), the auto-correlation peak value (the two-dot chain line in FIG. 8) and the noise floor (the one-dot chain line in FIG. 8) measured by the amplitude measuring circuit 11e. Also decreases by an amount corresponding to it, and the saturation point also shifts. As a result, the measured value of the noise floor is no longer “0”, and the correction operation of correcting the peak of the autocorrelation value by the processing circuit 11f can always be performed.

Since the measured value of the noise floor is actually smaller than the amplitude level of the autocorrelation value, in this embodiment, the magnification of the noise floor level is set to be larger than the autocorrelation value in FIG. It is displayed. As described above, in the arithmetic processing unit of the present embodiment, the amplitude value of the frequency-converted signal is measured by the amplitude measurement circuit, and the measured amplitude value is compared with the predetermined threshold by the processing circuit to obtain the autocorrelation peak. Is determined, correlation can be detected even with a received signal having a low S / N ratio, which has been difficult to detect conventionally.

The arithmetic processing section estimates the degree of saturation of the received power from the noise floor at the time of non-correlation measured by the amplitude measuring circuit and the peak of the auto-correlation value at the time of correlation detection, and amplifies the signal at the receiving section. By controlling the gain of the circuit, the peak of the measured autocorrelation value is corrected, so that even if the reflected reception power exceeds a predetermined level and the output signal is saturated, the reflection reception power can be measured.

[0029]

As described above, according to the present invention, a radio wave whose band is spread by a pseudo noise signal is transmitted, a reflected wave from an object based on the radio wave is received, and the received signal is converted to the pseudo noise signal. In the radar apparatus that performs despreading, converts the frequency of the despread received signal into a signal of a predetermined frequency, and measures the speed of the object based on the frequency-converted signal, and measures the distance to the object. A measuring unit for measuring the amplitude of the frequency-converted signal; and a determining unit for determining an autocorrelation peak based on the measured amplitude. The circuit detects the auto-correlation peak by measuring each delay of the pseudo-noise signal for reception, and enables correlation detection even with a received signal having a low S / N ratio, which has been difficult to detect in the past. It can improve the measurement accuracy in the measurement.

The measuring means measures the noise floor at the time of decorrelation, and the judging means estimates the degree of saturation of the received power based on the noise floor at the time of decorrelation and the autocorrelation peak at the time of correlation detection. Since the autocorrelation peak is corrected according to the degree of the saturation, the degree of saturation is estimated by measuring the autocorrelation peak at the time of correlation detection and the noise floor at the time of non-correlation, and the reflected reception power becomes a predetermined level. Even if the output signal exceeds the saturation, the measurement of the reflected reception power can be performed, and the measurement accuracy in the measurement of the relative speed with respect to the object can be improved.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of an embodiment of a radar apparatus according to the present invention.

FIG. 2 is a block diagram illustrating a configuration of an arithmetic processing unit illustrated in FIG. 1;

FIG. 3 is a waveform diagram showing outputs of an amplifier circuit and an amplitude measurement circuit when correlation is obtained and when correlation is not obtained.

4 is a waveform chart showing an output state of the waveform shaping circuit shown in FIG.

FIG. 5 is a distribution diagram showing a time distribution of one cycle of a pulse signal output from the waveform shaping circuit.

FIG. 6 is a flowchart for explaining an operation of correcting a peak of an autocorrelation value.

FIG. 7 is a characteristic diagram showing a correlation characteristic between the amplitude and the delay amount of the phase of the PN code.

FIG. 8 is a relationship diagram showing a relationship between a peak of an autocorrelation value, a peak of a noise floor, and reception power.

[Explanation of symbols]

 REFERENCE SIGNS LIST 10 object 11 arithmetic processing unit 11 a, 11 b amplifying circuit 11 c waveform shaping circuit 11 d period measuring circuit 11 e amplitude measuring circuit 11 f processing circuit 12 PN generator 13 transmitting unit 14, 16 antenna 15 delay circuit 17 receiving unit 18 down converter

Claims (2)

[Claims] 1. A radio wave whose band is spread by a pseudo noise signal is transmitted, a reflected wave from an object based on the radio wave is received, the received signal is despread by the pseudo noise signal, and the despread signal is despread. A radar device that converts a frequency of a received signal into a signal of a predetermined frequency, measures a speed of the object based on the frequency-converted signal, and measures a distance to the object, wherein an amplitude of the frequency-converted signal is measured. And a determining means for determining an autocorrelation peak based on the measured amplitude. 2. The measuring unit measures a noise floor at the time of decorrelation, and the determining unit determines a degree of saturation of received power based on the noise floor at the time of decorrelation and an autocorrelation peak at the time of correlation detection. The radar apparatus according to claim 1, wherein the autocorrelation peak is corrected according to the degree of the saturation.