JP3471392B2 - Frequency modulation radar equipment - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a frequency modulation radar device, and more particularly to a frequency modulation radar device mounted on a vehicle for measuring a relative distance and a relative speed to a target object.

[0002]

2. Description of the Related Art As a conventional frequency modulation radar device, an electromagnetic wave such as a millimeter wave is frequency-modulated and continuously transmitted, a transmission signal thereof is reflected by a reflector, and the reflected signal is received and transmitted / received. It is known to calculate the relative distance and relative speed to a reflector from the frequency difference of signals. As a method of frequency modulation, there is a technique for performing so-called triangular wave modulation, in which the frequency is modulated to an increasing side for a predetermined time and then to a decreasing side for a predetermined time thereafter.
It is disclosed in Japanese Patent Publication No. 084.

In such a triangular wave modulation type frequency modulation radar, the frequency difference between the frequency rising part of the transmitted wave and the frequency rising part of the received wave (hereinafter referred to as the beat signal of the frequency rising part) and the frequency falling part of the transmitted wave are detected. Frequency difference with the frequency falling part of the received wave (hereinafter, the beat signal of the frequency falling part)
The relative speed and relative distance can be calculated from.

When there are a plurality of reflectors in the radar detection area, peaks corresponding to the number of reflectors appear in the power spectrum of each beat signal in both the frequency rising portion and the frequency falling portion. It is important how to correlate multiple peaks. Therefore, in Japanese Unexamined Patent Application Publication No. 5-142337, the peak level of the power spectrum of the beat signal in the frequency rising portion is compared with the peak level of the power spectrum of the beat signal in the frequency falling portion. The relative distance and relative velocity of each target object are measured.

[0005]

However, when the distance between a plurality of target objects is small and the velocity difference between the target objects is large, the frequency order of the peaks of the frequency rising portion corresponding to the target object and the frequency There may be a case where the frequency order of peaks in the descending portion is different, and in such a case, there is a problem that the relative distance and relative velocity of each target object are erroneously measured.

The present invention has been made in view of the above points,
By determining the correlation amount of each peak pair and preventing the calculation of the relative distance and the relative velocity when the correlation is low, or by finding a new peak pair by the correlation for the peak pair with a low correlation, an incorrect combination is prevented. It is an object of the present invention to provide a frequency-modulated radar device in which the reliability of the peak pair is improved and the relative distance and relative velocity of the target object are accurately obtained.

[0007]

FIGS. 1A and 1B show the principle of the present invention.

In FIG. 1A, the radar apparatus main body M1
Transmits and receives a frequency-modulated carrier wave, and measures the relative distance and relative velocity to the target object from the frequencies of the peak pairs of the power spectrum of the frequency rising part and the frequency falling part of the beat signal.

The first pairing means M2 combines the peak of the power spectrum of the frequency rising portion and the peak of the power spectrum of the frequency falling portion in order of frequency.

Correlation calculating means M3 calculates the power of each peak pair combined by the first pairing means.
The correlation amount is calculated from the difference between the spectrum waveforms .

When there is a peak pair whose correlation is lower than a predetermined value, the calculation blocking means M4 blocks the calculation of the relative distance and the relative velocity based on the peak pair whose correlation is low.

Further, in FIG. 1B, the second pairing means M5 has a pair of peaks whose correlation is lower than the first predetermined value.
With respect to the above, the correlation amount is calculated from the peak of the power spectrum of one of the frequency rising part and the frequency falling part to the peak of the other power spectrum, and the peaks having high correlation are set as a new peak pair.

[0013]

In the present invention shown in FIG. 1 (A), the calculation of the relative distance and the relative velocity is prevented for the peak pairs having low correlation because the possibility of pairing error is high, and the reliability of all the peak pairs is reduced. Accurate relative distances and relative velocities are required only when the Further, in the present invention shown in FIG. 1B, a correlation amount is calculated for a peak pair having a low correlation and peaks having a high correlation are set as a new peak pair,
Determine the exact relative distance and relative velocity of the target object for what is possible.

[0014]

FIG. 2 shows a block diagram of the device of the present invention. In the figure, the transmission side circuit includes a carrier wave generator 10 and a frequency modulator 1.
2, a modulation voltage generator 14, a circulator 16, and a transmission antenna 18. A carrier wave is output from the carrier wave generator 10 and supplied to the frequency modulator 12.
On the other hand, the modulation voltage generator 14 outputs a triangular wave whose amplitude changes in a triangular shape, and the frequency modulator 12 outputs a modulated wave.
Is supplied to. As a result, the carrier wave from the carrier wave generator 10 is frequency-modulated, and a transmission signal whose frequency changes in a triangular shape over time is output. This transmission signal is supplied to the transmission antenna 18 via the circulator 16 and radiated toward the object to be detected. On the other hand, a part of the transmission signal is supplied to the mixer 22 of the receiving side circuit described later via the circulator 16.

The receiving side circuit includes a receiving antenna 20, a mixer 22, an amplifier 24, a filter 26, a fast Fourier transform processor (FFT signal processor) 28, and a target recognizer 3.
0, a risk determiner 32, and an alarm 34.
The reflected wave from the detected object is received by the receiving antenna 20 and supplied to the mixer 22. In the mixer 22, the reception signal and a part of the transmission signal from the circulator 16 are combined by a difference calculation to generate a beat signal. Mixer 22
The beat signal from is amplified by the amplifier 24 and supplied to the FFT signal processor 28 via the anti-aliasing filter 26. The FFT signal processor 28 obtains the power spectrum of each of the frequency rising portion and the frequency falling portion and supplies them to the target recognizer 30.

FIG. 3 shows a flowchart of the first embodiment of the target recognition processing executed by the target recognizer 30. This process is executed every several tens of msec. In the figure, in steps S30 and S31, all peaks of the power spectrum of the frequency rising portion and the frequency rising portion are detected.
Here, for example, as shown in FIG.
When three objects (vehicles) b and c exist, three peaks corresponding to the reflection signals from these three objects exist. FIG. 5 (A) is the power spectrum of the frequency rising portion, and FIG. 5 (B) is the power spectrum of the frequency falling portion. The peaks of the objects a, b, and c are represented by fa, fb, and fc (subscripts up and duwn indicate the frequency rising portion and the frequency falling portion, respectively). In steps S30 and S31, a portion having a predetermined first threshold power value or more is searched to detect a peak.

After that, in step S32 which is the first pairing means M2, the plurality of peaks in the frequency rising portion and the plurality of peaks in the frequency falling portion are made one to one in descending order of frequency.
Perform pairing according to.

In step S33, a predetermined frequency range (window) centered on one peak of the peak pair is cut out on the power spectrum of the frequency rising portion, and in the next step S34, the other of the pair of peaks is cut on the power spectrum of the frequency falling portion. A predetermined frequency range (window) centered on the peak is cut out. Then, in step S35, which is the correlation calculating means M3, the windows of the frequency rising portion and the frequency falling portion are divided for each predetermined frequency Δf, and the sum of differences (correlation amount) between the rising portion and the falling portion is calculated. The higher the correlation, the smaller the correlation amount.

Next, step S36 which is a calculation preventing means.
It is determined whether or not the correlation amount is less than a predetermined threshold value. If the correlation amount is less than the threshold value and the correlation of this peak pair is high, the process proceeds to step S37, and the calculation of the correlation amount of all peak pairs is completed. It is determined whether or not, and if not completed, step S
In step 33, the correlation amount of the next peak pair is calculated.

When the correlation amounts of all the peak pairs are less than the threshold value and the correlations of the peak pairs are high and there is no error in the combination, the process proceeds to step S38, and in steps S38 and S39, the relative velocity frequency and distance frequency fd = (fdown-fup) / 2 fr = (fdown + fup) / 2 and fd = 2v / c · f0 fr = 4fm Δf / c · R where v: relative speed, c: speed of light, f0: center frequency, fm:
Modulation frequency, Δf: distance and relative speed are calculated based on the frequency deviation width, and the process ends.

Further, when the correlation amount is equal to or more than the threshold value in step S36 and the correlation of the peak pair is low, as shown in FIG.
As shown in (B), it is highly likely that the frequency order of the peaks in the frequency rising part and the frequency order of the peaks in the frequency falling part are different, and there is a pairing error in the other peak pairs. The process ends without performing any calculation.

The calculated distance data and relative velocity data are supplied to the danger determiner 32. The risk determiner 32 compares the safety distance that is predetermined or calculated according to the running state of the vehicle and the calculated distance data, and if the safety distance is less than or equal to the safety distance, it is determined as dangerous. The driver is notified by the alarm device 34.

As described above, for a pair of peaks having a low correlation, the calculation of the relative distance and the relative velocity is blocked because the possibility of a pairing error is high, and the accurate relative value is calculated only when the reliability of all the peak pairs is high. Distance and relative velocity are determined.

FIG. 7 shows a flowchart of the second embodiment of the target recognition processing. In the figure, those parts which are the same as those corresponding parts in FIG. 3 are designated by the same reference numerals, and a description thereof will be omitted. In FIG. 7, when the correlation amount is equal to or more than the threshold value and the correlation of the peak pair is low in step S36, the process proceeds to step S41.

In step S41, it is determined whether or not the levels of the two peaks of the pair of peaks are equal to or higher than the second threshold value. The second threshold value is higher than the first threshold value in steps S30 and S31. Here, if the levels of the two peaks of the pair of peaks are both less than the second threshold value, the calculation of the relative distance and the velocity is performed in S4.
In step 2, the pairing of the peak pair is removed and the process proceeds to step S37.

If there is a peak having a level equal to or higher than the second threshold value in step S41, the process proceeds to step S43.

In step S43, the range of the correlation calculation of one peak of the peak pair is designated. When performing the correlation calculation of the peak of the frequency rising portion or the falling portion, which frequency range (window) of the power spectrum is cut off. Specify whether or not to perform correlation calculation by shifting.

In step S44, the power spectrum near the cut peak is shifted by a predetermined frequency Δf on the frequency axis, and the sum of differences (correlation amount) between the rising portion and the falling portion is calculated. FIG. 8 and FIG. 9 are schematic explanatory views when the correlation calculation of fupa is performed. Cut fupa
The power spectrum in the vicinity of is shifted by Δf on the power spectrum of the frequency falling portion, and the sum of the differences is calculated. In the case of reflected signals from the same object, the power spectra of the rising part and the falling part are similar, so f
At the peak fdowna that forms a pair with upa, the sum of the differences is the smallest. FIG. 8 shows the change in the correlation amount when the frequency is plotted on the horizontal axis and the correlation amount is plotted on the vertical axis. Generally, as the frequency is shifted, the correlation amount decreases and eventually becomes the minimum value. Shows increasing changes.

Here, the frequency peaks fupa and fdowna
(Or the frequency difference between fupb and fdownb and fupc and fdownc) is doubled because of the Doppler frequency fd = (fdown-fup) / 2 due to the relative speed. In the present embodiment, since the target object in the traveling direction of the own vehicle and the target object in the same direction are targeted,
The maximum relative speed is the vehicle speed V when a stationary object is detected.
It becomes 0. Therefore, in the case of fupa, the range to be frequency-shifted when performing the correlation calculation is fupa to fupa + 2fd0 where fd0 = 2f0.V0 / cf0: center frequency C: speed of light. It should be noted that when the target object is moving away from the own vehicle, fdown <fup is satisfied. However, since the moving away object is not dangerous to the own vehicle, it is not necessary to detect it and the correlation calculation is not performed. Therefore, in step S45, the shift amount is 2fd0.
It is determined whether it is within the range, and if it is within the range, the process returns to step S44. When the shift amount exceeds 2fd0, the process proceeds to step S46, and the peak of the frequency falling portion located at the frequency where the correlation amount is minimized is paired with the peak fup as the peak fdown.

The above steps S43 to S46 correspond to the second pairing means M5.

Thereafter, in step S47, it is determined whether the other peak of the pair of peaks is greater than or equal to the second threshold value. If it is greater than or equal to the second threshold value, the process proceeds to step S43, and the other peak is also paired. Do. If it is less than the second threshold value, the process proceeds to step S37.

In this way, for a pair of peaks having a low correlation, a correlation amount is calculated, peaks having a high correlation are used as a new peak pair, and accurate relative distances and relative velocities of the target object are calculated for possible peaks. It is possible to eliminate a state where the relative distance and the relative speed cannot be calculated.

[0033]

As described above, according to the frequency modulation radar device of the present invention, the correlation amount of each peak pair is obtained, and when the correlation is low, the calculation of the relative distance and the relative velocity is blocked, or the peaks having a high correlation are processed. By setting the peak pair as, it is possible to prevent an incorrect combination, improve the reliability of the peak pair, and obtain an accurate relative distance and relative velocity of the target object.
It is extremely useful in practice.

[Brief description of drawings]

FIG. 1 is a principle diagram of the present invention.

FIG. 2 is a block diagram of the device of the present invention.

FIG. 3 is a flowchart of a first example of target recognition processing.

FIG. 4 is an explanatory diagram of a radar beam and a detected object.

FIG. 5 is an explanatory diagram of a power spectrum.

FIG. 6 is an explanatory diagram of a power spectrum.

FIG. 7 is a flowchart of a second embodiment of target recognition processing.

FIG. 8 is an explanatory diagram of a correlation calculation.

FIG. 9 is an explanatory diagram of a correlation calculation.

[Explanation of symbols]

M1 radar device body M2 First pairing means M3 correlation calculation means M4 calculation prevention means M5 second pairing means 10 Carrier generator 12 Frequency modulator 14 Modulation voltage generator 16 Circulator 18 transmitting antenna 20 receiving antenna 22 mixer 24 amplifier 26 filters 28 FFT signal processor 30 Target recognizer 32 Danger judgment device 34 Alarm

   ─────────────────────────────────────────────────── ─── Continued front page       (56) Reference JP-A-5-142337 (JP, A)                 Actual Kaihei 2-131679 (JP, U)

Claims (2)

(57) [Claims] 1. A frequency-modulation radar device that transmits and receives a frequency-modulated carrier wave, and measures the relative distance and relative velocity to a target object from the frequencies of the peak pairs of the power spectrum of the frequency rising part and the frequency falling part of the beat signal. In the above, the first pairing means for combining the peak of the power spectrum of the frequency rising portion and the peak of the power spectrum of the frequency falling portion in the order of frequency, and each power for each peak pair combined by the first pairing means Correlation calculating means for calculating the correlation amount from the difference between the spectrum waveforms and calculation preventing means for preventing the calculation of the relative distance and the relative speed based on the peak pair with low correlation when the correlation has a peak pair lower than a predetermined value. A frequency modulation radar device having. 2. A frequency modulation radar device that transmits and receives a frequency-modulated carrier wave and measures the relative distance and relative velocity to a target object from the frequency of the peak pair of the power spectrum of each of the frequency rising portion and the frequency falling portion of the beat signal. In the above, the first pairing means for combining the peak of the power spectrum of the frequency rising portion and the peak of the power spectrum of the frequency falling portion in the order of frequency, and each power for each peak pair combined by the first pairing means Correlation calculating means for calculating a correlation amount from the difference between spectrum waveforms, and for a pair of peaks having a correlation lower than a first predetermined value , one of the power spectrum peaks of the frequency rising portion and the frequency falling portion to the other power spectrum. By calculating the correlation amount for the peak of And a second pairing means for setting the peaks of the peaks as new peak pairs.