JPH11271431A - FMCW radar equipment - Google Patents

Abstract

(57) [Summary] An FMCW radar device reliably detects a peak of a target from unnecessary reflected signals (clutter) other than the target. SOLUTION: A detector 16 detects a transmission signal frequency-modulated by a triangular wave and a reception signal reflected by a target,
Generate a beat signal. The beat signal is sent to the signal processing device 18
, And are subjected to frequency analysis to detect peaks of the upstream phase and the downstream phase. The threshold value calculation unit 18d of the signal processing device 18 sets the next peak detection threshold value based on the frequency spectrum obtained by removing the peak corresponding to the target from the past frequency analysis result, and the peak detection unit 18b is set. A peak is detected using a threshold. Since the threshold is set based on the past frequency spectrum,
Even if clutter exists, only the peak of the target can be detected.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an FMCW radar apparatus, and more particularly to a threshold setting for detecting a peak necessary for obtaining a distance and a speed of a target from a beat signal.

[0002]

2. Description of the Related Art Conventionally, a transmission wave is frequency-modulated by, for example, a triangular wave and transmitted to a target, and a reception signal is detected based on the transmission wave to generate a beat signal, and a frequency rising section (up phase). An FMCW radar device that detects a distance and a speed from a peak pair to a target in a beat signal of a frequency signal and a beat signal in a frequency falling section (down phase) is known. Specifically, the Doppler frequency fd is added to the beat frequency (frequency of the difference between the transmission frequency and the reception frequency) fb in the up phase of the beat signal, and the Doppler frequency fd is subtracted from the beat frequency in the down phase. From the peak frequency fb1 of the up phase and the peak frequency fb2 of the down phase,

R = {c / (8fmΔf)} · (fb1 + fb2) (1)

V = {(c / (4f0)}｝ (fb1−fb2) (2) The distance R and the velocity V can be detected, where
fm is the repetition frequency, Δf is the frequency shift width, c is the speed of light, and f0 is the center frequency.

[0003] As described above, in the FMCW radar device, it is necessary to detect peaks from the up phase and the down phase of the beat signal. Therefore, conventionally, a method has been used in which a certain threshold value is provided, and a frequency analysis result, such as a complex FFT, which exceeds the threshold value is determined as a peak for a target.

However, when the threshold value is fixed, the peak value from a target at a long distance or a target having a low radio wave intensity may be lower than the threshold value, and there is a problem that the sensitivity to these targets is reduced. .

Therefore, for example, as in a frequency modulation radar apparatus disclosed in Japanese Patent Application Laid-Open No. 6-214015, the threshold is changed according to the type of target (vehicle type, etc.) determined from the processing result of the image obtained by the imaging apparatus. Techniques have been proposed for preventing a decrease in sensitivity to a target having a low radio wave intensity (such as a motorcycle).

In addition, it has been proposed to lower the threshold value in accordance with the distance so as to prevent a reduction in sensitivity at a distant place.

[0007]

However, in order to detect a peak for a target (for example, a vehicle) from the result of frequency analysis of the beat signal, a peak protruding from the thermal noise level is accurately extracted, and a tree other than the target is extracted. It is necessary to accurately extract the peak of the target from unnecessary reflected signals (clutter) from roadside objects such as roads and guardrails.

The above-mentioned prior art can extract the target peak from the former, that is, the thermal noise level, but it is difficult to accurately extract the target peak from the clutter as shown in the latter. there were. That is, in the above-described conventional technology, if the threshold value is reduced in order to detect a motorcycle or the like, a peak of a roadside object other than the motorcycle can be easily extracted, and the peak of the motorcycle may be buried in clutter.

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems of the prior art, and has as its object to reliably detect a target peak from a thermal noise level and to reliably detect a target peak from clutter. It is another object of the present invention to provide an FMCW radar device that can perform the above-mentioned operations.

[0010]

In order to achieve the above object, the present invention provides a method for transmitting a frequency-modulated wave, receiving a reflected wave from a target, and detecting the received signal based on the transmission signal. An FMCW radar device for detecting a distance and a speed of the target from a peak frequency of a beat signal to be obtained, and for detecting a peak based on a frequency spectrum obtained by removing a peak corresponding to the target from a frequency analysis result of a past beat signal. It has a threshold setting means for setting a threshold.

When a past frequency analysis result includes a clutter component, a frequency spectrum obtained by removing a peak corresponding to a target from the frequency analysis result also includes a clutter component. Therefore, by setting a threshold at the present time (the next processing timing) based on this frequency spectrum, the threshold has frequency dependence, and the threshold also changes according to the clutter component. That is, if there is a clutter component, the threshold value at that frequency will also increase, and even if clutter is included in the frequency analysis result of the current beat signal, it is possible to remove the clutter and extract only the target peak. it can.

The part of the frequency spectrum other than the peak corresponding to the target may be interpolated by an appropriate method, and the method of interpolation is arbitrary.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing the configuration of this embodiment. The FMCW radar device according to the present embodiment includes a voltage controlled oscillator 10, a transmitting antenna 12, a receiving antenna 1,
4. It includes a detector 16 and a signal processing device 18.

The voltage-controlled oscillator 10 frequency-modulates a transmission wave, for example, modulates a frequency with a triangular wave, and generates an up phase and a down phase in the transmission wave. FIG. 2 shows the relationship between the output voltage of the voltage controlled oscillator 10 and time. In the figure, the horizontal axis represents time, and the vertical axis represents voltage, and the voltage increases with time (frequency increases).
The period is an up phase, and the period in which the voltage decreases with time (frequency decreases) is the down phase.

Transmission antenna 12 and reception antenna 14
Each transmits a signal modulated by a triangular wave to a target, and receives a signal reflected from the target, and can be mounted on, for example, a front part of a vehicle. A part of the transmission wave and the signal received by the receiving antenna are supplied to the detector 16.

The detector 16 detects a reception signal based on the transmission signal, generates a beat signal having a frequency component of a difference between the transmission frequency and the reception frequency, and supplies the beat signal to the signal processing device 18.

The signal processing device 18 detects a peak pair from a beat signal to detect the distance and speed to a target.
a, a peak detection unit 18b, a peak pairing unit 18c,
It comprises a threshold value calculation unit 18d and a distance / speed calculation unit 18e.

The frequency analyzer 18a analyzes the frequency of the beat signal using a complex FFT or the like, and detects a complex amplitude (voltage) at an appropriate frequency interval (frequency bin). The detection result is output to the peak detector 18b. FIG. 3 shows an example of a frequency analysis result. In the figure, the horizontal axis represents frequency and the vertical axis represents voltage, which is discretized at appropriate frequency intervals. In the drawing, as an example, the peaks of the up phase and the down phase when an object exists in addition to the target are shown.

The peak detector 18b calculates the frequency analysis result,
That is, a peak is detected from the voltage for each frequency bin. Specifically, the number of the bin indicating the peak and the complex amplitude (voltage) of the bin are detected using the threshold set by the threshold calculator 18d. The detected peak is output to the peak pairing unit 18c.

The peak pairing unit 18c determines a combination of peaks in the up phase and the down phase, and outputs the combination of peaks (peak pair) to the distance / speed calculation unit 18e. The peak pair is also output to the threshold calculator 18d.

The threshold calculator 18d is provided with a peak detector 18b.
Set the peak detection threshold for detecting the peak from the frequency analysis result of the beat signal in the past, instead of fixing or changing according to the radio wave intensity of the target as in the past, the past frequency analysis result and the past The current (next processing timing) threshold value is dynamically set based on the peak pair. Specifically, for example, the value of the frequency analysis result of a high, low, predetermined frequency width centered on the frequency indicating the peak value is replaced with a value interpolated using the values of the higher and lower frequencies than the frequency width. A predetermined value is added to the result obtained by smoothing the result on the frequency axis to obtain a threshold.
As a result, the threshold value has frequency dependency,
Even if clutter is included, the threshold value changes according to the clutter. The threshold setting method will be further described later.

The distance / speed calculating section 18e calculates and outputs the distance and the speed to the target based on the peak pair supplied from the peak pairing section 18c using the above equations (1) and (2).

In such a configuration, the present embodiment is characterized in that the threshold value is dynamically set by the threshold value calculating section 18d, whereby the peak of the target is reliably taken out even when a roadside object other than the target exists. Like that.

Hereinafter, the threshold value setting process in the threshold value calculation unit 18d will be described.

FIG. 4 shows an example of a frequency analysis result (frequency spectrum) of the beat signal. In the figure, the horizontal axis represents frequency (frequency bin), and the vertical axis represents voltage. It should be noted that, for convenience of explanation, only one phase of up and down is shown in the figure. Normally, discrete FFT processing is performed, and the result of frequency analysis is output at certain frequency intervals (frequency bins).

FIG. 5 is a partially enlarged view showing the vicinity of the peak in FIG. In the figure, the horizontal axis represents the frequency bin, and the (j) -th bin indicates the peak bi
n. The threshold value calculation unit 18d that has input such a frequency analysis result outputs the peak bin (that is, the (j) -th bi
The values of the analysis results of a predetermined number of frequencies bin including high and low including n) are replaced with values interpolated using the values on both sides thereof.

FIG. 6 shows a case where the predetermined number is 2 bins each of high and low including the peak bin.
2 bins including the (j) bin which is the peak bin
The one higher by (min) is the (j + 1) th bin,
What is lower by the amount is the (j-1) th bin. The values of the (j-1) th bin to the (j + 1) th bin are represented by the values on both sides thereof, ie, the value of the (j-2) th bin and the value of
2) Interpolate with the value of bin. Various methods can be used as the interpolation method, for example, linear interpolation can be used. In the figure, broken lines indicate interpolated values.

FIG. 7 shows a final threshold value obtained by smoothing the interpolated value shown in FIG. 6 on the frequency axis and further adding a predetermined value to the smoothed value. In the figure, the one-dot chain line indicates a value obtained by smoothing the interpolation value (broken line) on the frequency axis, and the two-dot chain line indicates a final threshold value obtained by adding a predetermined value. The predetermined value differs depending on the detection performance of the radar device and the use environment, but may be set to approximately several dB to 10 dB.

As described above, by setting the threshold based on the frequency spectrum obtained by excluding the peak of the target from the frequency analysis result detected in the past, when there is a peak (clutter) due to a roadside object other than the target, However, since the threshold is set according to the clutter (that is, if the clutter is large, the threshold is also increased at the frequency portion), it is possible to reliably detect the target peak from the clutter. .

In the present embodiment, two high and low frequency analysis values including the target peak are replaced. However, three or more values including the peak can be replaced. . Specifically, the frequency width to be replaced is preferably determined based on the peak intensity or the peak sharpness. The larger the peak intensity or the smaller the sharpness, the larger the frequency width to be replaced is set. Is preferred.

[Brief description of the drawings]

FIG. 1 is a configuration block diagram of an embodiment of the present invention.

FIG. 2 is an explanatory diagram of frequency modulation according to the embodiment.

FIG. 3 is an explanatory diagram of frequency analysis according to the embodiment;

FIG. 4 is a graph showing a frequency analysis result for explaining a method of setting a threshold.

FIG. 5 is a partially enlarged view of a peak portion in FIG. 4;

FIG. 6 is a graph for explaining interpolation of a peak portion.

FIG. 7 is a graph showing a threshold value.

[Explanation of symbols]

10 voltage controlled oscillator, 12 transmitting antenna, 14 receiving antenna, 16 detector, 18 signal processing device.

 ──────────────────────────────────────────────────続 き Continuing from the front page (72) Inventor Tomo Harada 41-Cho, Yokomichi, Nagakute-cho, Aichi-gun, Aichi Prefecture Inside Toyota Central Research Laboratory Co., Ltd. 41, Yokomichi, Toyota Central Research Institute, Inc.

Claims (1)

[Claims] 1. A frequency modulated wave is transmitted, a reflected wave from a target is received, and a distance and a speed of the target are detected from a peak frequency of a beat signal obtained by detecting a received signal based on a transmission signal. An FMCW radar apparatus, comprising: threshold setting means for setting a peak detection threshold based on a frequency spectrum obtained by removing a peak corresponding to a target from a frequency analysis result of a past beat signal. apparatus.