JP3394941B2 - FM-CW radar device - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an FM-CW radar device that outputs a continuous wave that is FM-modulated based on a triangular-wave-shaped modulation signal to obtain the distance to an obstacle located in front.

[0002]

2. Description of the Related Art An FM-CW radar device transmits a continuous wave, which is FM-modulated based on a triangular-wave-shaped modulation signal, as a transmission wave toward an obstacle such as an automobile located in front and is reflected by the obstacle. A beat signal can be obtained by mixing the received wave and the previously separated transmission wave.

A peak frequency and a peak level of this beat signal are calculated by using a frequency analysis method such as FFT, and then recognition processing such as peak pairing and grouping is performed to detect the distance and relative speed to an obstacle. Can be calculated.

[0004]

At this time, since the time required for the A / D conversion processing for sampling the beat signal and the FFT calculation processing occupies a large ratio with respect to the processing time of the entire system, it is possible to analyze. However, there is a problem in that the maximum detection frequency must be narrowed to the limit, or the number of points used for FFT calculation must be processed to the minimum that does not affect the system, and the target must be detected within the remaining processing time.

In addition, since the maximum detectable frequency that can be analyzed cannot be widened, the reflected wave from an elevated guide plate on a highway, which should not be detected in the past, the side wall and a sign in a curve, and the reflection of a median strip. There is a problem that the waves appear in the high frequency band in a form of folding back around the Nyquist frequency, and the target is erroneously detected.

The present invention has been made in view of the above points, and provides a highly accurate FM-CW radar device capable of efficiently processing A / D sampling and FFT calculation of a beat signal at high speed. .

[0007]

According to the present invention, a continuous wave that is FM-modulated based on a triangular-wave-shaped modulation signal is transmitted as a transmission wave toward an obstacle located in front, and a reception wave reflected by the obstacle is transmitted. The beat signal obtained by mixing the separated transmission wave with the pre-separated transmission wave is sampled by the A / D converter, the peak frequency and the peak level are calculated using the FFT calculation process, and then the peak pairing and the grouping are performed. In the FM-CW radar device that calculates the distance and relative speed to an obstacle by performing the recognition process of
The A / D converted value obtained by sampling the beat signal by the A / D converter is transferred by DMA to FF.
When the T arithmetic processing is performed and the distance of the obstacle detected at the shortest distance is compared with a preset threshold value and it is determined that the obstacle is ahead, the detected direction is obtained without re-taking the A / D conversion value. It is characterized in that the FFT calculation processing is performed again by changing the interval for thinning out the A / D converted values sampled only in the vicinity.

[0008]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing a basic configuration of an FM-CW radar device, and FIG. 2 is a block diagram showing an embodiment of a radar device to which the present invention is applied.

First, referring to FIG. 1, there is shown a basic configuration diagram of an FM-CW radar device. The FM-CW radar device includes a modulation signal generator 1 that generates a triangular-wave modulation signal, a voltage-controlled oscillator 2 that performs frequency modulation based on the modulation signal, and a transmission antenna 3 that transmits a continuous transmission wave.
A receiving antenna 4 for receiving a received wave reflected by an obstacle in front, and a directional coupler 5 for separating the transmitted wave in advance,
Mixer 6 for mixing the separated transmission wave and reception wave
And a beat signal is generated from the mixer 6.

This beat signal is sent to the frequency analysis processing 11 via the LPF 7, the amplifier 8, the A / D converter 9 and the DMA 10 of the radar apparatus to which the present invention shown in FIG. 2 is applied.

In the frequency analysis processing 11, the discrete value data of the beat signal of the A / D converter 9 transferred by the DMA 10 is converted into FFT (Fast Fourier Trans).
The spectrum is extracted by processing using a frequency analysis method such as form). Then, in the target recognition process 12, peak pairing and grouping of the spectrum are performed to calculate the distance and relative speed to the obstacle.

The erroneous detection discrimination processing 13 compares the distance to the obstacle closest to the radar device with a preset threshold value,
Instantaneous discrimination processing is performed so that a spectrum that appears to be higher than the maximum detectable frequency can not be determined as an obstacle.

The danger discriminator 14 discriminates the degree of danger to the obstacle from the distance and the relative speed with respect to the obstacle, and the alarm 15 displays an alarm to the driver according to the discriminated degree of danger. A warning sound is emitted to warn.

First, the operation of the A / D converter 9 shown in FIG. 2 will be described. When the beat signal that has passed through the LPF 7 and the amplifier 8 is sampled by the A / D converter 9 at a certain constant period τ, even a minute change included in the original signal is not extracted. In other words, the components above the upper limit frequency determined by the sampling period τ are not included in the sampled data. This upper limit frequency is called the Nyquist frequency, which is half the sampling frequency.

If the continuous signal contains a component having a frequency higher than the Nyquist frequency, the sample value data of the higher harmonic component cannot be distinguished from the data of the low frequency component. In other words, in order to correctly obtain the frequency component contained in the continuous signal as sample value data, two sample value data of the upper limit and the lower limit are required for the waveform of at least one cycle. Therefore, in the FM-CW radar device, by changing the sampling frequency used for A / D conversion, the maximum detectable frequency for analyzing the beat signal is also changed.

Here, the formula for calculating the beat signal fb will be described. The beat signal fb is obtained by the difference between the transmitted wave and the received wave, but when there is a relative velocity, the received wave shifts with respect to the transmitted wave due to the Doppler effect. At this time, the beat signal fb is given by the sum or difference of the distance component fr included in the reflected wave and the velocity component fd due to the Doppler shift as in the following equation.

[0018]

[Equation 1]

[Delta] F: Frequency modulation width [Hz] fm: Modulation frequency [Hz] R: Distance from FM-CW radar device to obstacle [m] C: Speed of light [m / sec] V: FM-CW radar Relative velocity of the obstacle with respect to the device [m / sec] fo: Carrier frequency [Hz] Here, when the peak frequency of the rising section is fdpkup and the peak frequency of the falling section is fdpkdn

[0020]

[Equation 2]

The distance R to the obstacle and the relative speed V are determined by the following equations.

[0022]

[Equation 3]

In other words, it is possible to give more processing time to the obstacle recognition processing after the FFT calculation processing by setting the modulation frequency to a high frequency, but from the relationship of the maximum detection distance R of the equation (1), A The / D sampling frequency also inevitably becomes a high frequency.

Therefore, after all, the A / D conversion processing and the FFT operation processing can hardly be processed in parallel, and the processing time is not different from that before the modulation frequency and the A / D sampling frequency are changed. It was

Therefore, in the first embodiment of the present invention,
As shown in FIG. 3, the result of the A / D conversion is transferred by DMA, and the load required for the A / D conversion processing on the CPU is eliminated, so that the FFT operation processing and the recognition processing are utilized more effectively than ever. It is possible.

Since the load required for the A / D conversion processing is eliminated at the same time, the beat signal is sampled at a sampling limit value that the A / D converter can perform, and this A / D conversion value is processed in the subsequent processing. It is possible to perform the FFT operation processing by thinning out the optimum value without affecting the processing time of the entire system.

Next, the DMA 10 according to the first embodiment.
The operation of will be described in detail. FIG. 3 is a block diagram illustrating transfer of A / D sampling data using the DMA according to the first embodiment.

Conventionally, since the FFT operation processing and the A / D conversion processing cannot be processed in parallel, the entire processing time is inevitably lengthened, which has a great influence on the entire system.
Therefore, in the present invention, as shown in FIG. 3, while the DMA uses the external bus to automatically transfer the A / D converted value to the external SRAM, the CPU can use the internal bus to perform parallel processing. I am trying. Of course, the CPU uses an external bus and can also use an external SRAM. Therefore, the entire processing time is significantly shortened, and real-time processing with a faster update cycle becomes possible.

Next, the erroneous discrimination processing 13 according to the second embodiment of the present invention will be described in detail. 4 and 5 show
A spectrum that is considered to have a higher frequency than the maximum analyzable detection frequency according to the second embodiment is discriminated, and based on the result, the maximum analyzable detection distance is increased, and it is instantly discriminated whether or not it is decided as a target. It is a flow chart and an explanatory view of erroneous detection discrimination processing.

In FIG. 4, first, when it is determined that the obstacle detected at the shortest distance is in front of the specified threshold value (S101), the A / D conversion value sampled only in the vicinity of the detected direction is calculated. The thinning interval is changed to perform the FFT calculation process (S102). It is again determined whether or not the target has been detected at the same frequency position (S103), and if the target has been detected at the same position, the target is determined (S105). When the target is not detected at the same position, the target detected at the next short distance is set as the closest distance target (S104).

In the second embodiment, when it is determined that the spectrum detected at the shortest distance is ahead of the preset threshold value, the thinning-out different from the previous sampling frequency is performed only near the direction detected again. A / D of rate
By performing the FFT operation using the converted value from the A / D converted values sampled at the same time, it is possible to instantly determine whether the target is a true obstacle lower than the maximum detectable frequency that can be analyzed. it can.

At this time, the characteristic is that the beat signal is again A /
Since the FFT calculation process is performed by changing only the sampling frequency without re-D-sampling, it is determined whether the target is detected again at the same frequency position as shown in S103 in the flowchart of the erroneous detection determination process in FIG. Need only be performed once, and it is not necessary to make multiple determinations in succession to avoid erroneous detection.

Further, as described above, since the A / D conversion process is performed by the DMA, it is possible to determine the virtual image of the obstacle more quickly and instantly than the conventional processes.

FIG. 5 is a diagrammatic representation of the flowchart of FIG. It is assumed that, as a result of the FFT operation processing of the A / D conversion value DMA-transferred in advance at a high sampling frequency, the spectrum is temporarily detected at around 30 kHz in FIG. 5 and further the spectrum is detected at the shortest distance.

At this time, the sampling frequency is temporarily set to 200.
If the frequency is kHz, the Nyquist frequency is 100 kHz, so if the spectrum is a virtual image, 170 kHz
The virtual image of z is detected at the position of 30 kHz shown in FIG. Therefore, even if the obstacle detected at the shortest distance is a virtual image, it will be judged as an obstacle.

Conventionally, it has been possible to determine whether or not the spectrum is a virtual image by changing the sampling frequency and changing the position where the virtual image is detected. However, by re-taking the A / D conversion value again, it is delicate. Since errors and variations occur, it is necessary to perform time-series processing such as whether or not it is established for several consecutive cycles.

However, in the present invention, since the A / D conversion value is obtained in advance by the high sampling frequency, the same data is processed by the different sampling frequency by the thinning rate different from the previous time, so that the virtual image can be instantly and accurately obtained. Can be determined.

Comparing the above, the thinning rate is 100.
This is because by changing the sampling frequency of kHz to 150 kHz, if the obstacle detected at the shortest distance is a virtual image, it will always be detected at the position of 130 kHz. At this time, naturally, if it is not a virtual image, it is detected at the position of 30 kHz as in the previous time.

[0039]

As described above, according to the present invention, the processing time required for the A / D sampling processing and the FFT calculation processing of the beat signal in the related art is processed based on the DMA transfer, so that the FFT calculation processing and the obstacle are prevented. It is possible to concentrate on the recognition processing for fixing the object, and it is possible to more effectively utilize the processing time of the entire system than ever before.

At the same time, by using DMA transfer, A / D
Since the A / D conversion can be performed by the sampling limit value, it is possible to obtain arbitrary sampling data without appropriately affecting the processing time of the entire system by thinning out the A / D conversion value afterwards.

Further, the reflected wave of the elevated guide plate on the highway, the side wall and the sign of the curve, and the central separator, which should not be detected in the past, appears in the high frequency band in the form of folding back around the Nyquist frequency to detect the target. There was a problem of false detection at this time, but if it is determined that the obstacle distance detected at the shortest distance is in front of a threshold value set in advance, the A / D conversion value is By performing FFT operation processing again using sampling data different from the previous time without retaking, it is possible to determine whether or not the target is a true obstacle lower than the maximum detectable frequency that can be analyzed at a higher speed than conventional processing. It is possible to make an instant determination.

[Brief description of drawings]

FIG. 1 is a diagram showing a basic configuration of an FM-CW radar device.

FIG. 2 is a block diagram showing an embodiment of an FM-CW radar device to which the present invention has been applied.

FIG. 3 A / D using DMA according to the first embodiment
It is a block diagram explaining transfer of sampling data.

FIG. 4 is a flowchart illustrating erroneous detection determination processing according to the second embodiment.

FIG. 5 is a diagram illustrating erroneous detection determination processing according to the second embodiment.

[Explanation of symbols]

1 Modulation signal generator 2 Voltage controlled oscillator 3 transmitting antenna 4 receiving antenna 5 directional coupler 6 mixer 7 LPF 8 amplifier 9 A / D converter 10 DMA 11 Frequency analysis processing 12 Target recognition processing 13 False detection discrimination processing 14 Risk classifier 15 alarm

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-9-43343 (JP, A) JP-A-7-151852 (JP, A) JP-A-6-160512 (JP, A) JP-A-6- 167565 (JP, A) JP 9-133765 (JP, A) JP 11-281735 (JP, A) JP 6-51055 (JP, A) JP 7-77574 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) G01S ⁷ /00-7/42 G01S 13/00-13/95

Claims (5)

(57) [Claims] 1. A continuous wave FM-modulated based on a triangular wave modulation signal is transmitted as a transmission wave toward an obstacle located in front, and a reception wave reflected by the obstacle and a transmission wave separated in advance are transmitted. The beat signal obtained by mixing
FM- which calculates the distance and relative speed to an obstacle by sampling with a D / D converter, calculating peak frequency and peak level using FFT calculation processing, and then performing recognition processing such as peak pairing and grouping.
In the CW radar device, the distance of the obstacle detected at the shortest distance is compared with a preset threshold value, and when it is determined to be in front, the beat signal is sampled by the A / D converter and obtained. The FM is characterized in that the AFT conversion processing is performed again by changing the thinning interval of the A / D conversion values sampled only in the vicinity of the detected direction without re-taking the A / D conversion values.
-CW radar device. 2. A continuous wave FM-modulated based on a triangular wave modulation signal is transmitted as a transmission wave toward an obstacle located in front, and a reception wave reflected by the obstacle and a transmission wave separated in advance are transmitted. The beat signal obtained by mixing
FM- which calculates the distance and relative speed to an obstacle by sampling with a D / D converter, calculating peak frequency and peak level using FFT calculation processing, and then performing recognition processing such as peak pairing and grouping.
In a CW radar device, an A / D converted value obtained by sampling the beat signal by the A / D converter is transferred by a DMA to an FF.
When the T arithmetic processing is performed and the distance of the obstacle detected at the shortest distance is compared with a preset threshold value and it is determined that the obstacle is ahead, the detected direction is obtained without re-taking the A / D conversion value. An FM-CW radar device, characterized in that an FFT calculation process is performed again by changing an interval for thinning out A / D converted values sampled only in the vicinity. 3. The FM-CW radar device according to claim 1, wherein the beat signal is sampled at a sampling limit value that the A / D converter can perform. 4. A continuous wave FM-modulated based on a triangular wave modulation signal is transmitted as a transmission wave toward an obstacle located in front, and a reception wave reflected by the obstacle and a transmission wave separated in advance are transmitted. The beat signal obtained by mixing
FM- which detects an obstacle by calculating the peak frequency and peak level using FFT calculation processing and performing recognition processing.
In the obstacle detection method of the CW radar device, the distance of the obstacle detected at the shortest distance is compared with a preset threshold value, and when it is determined to be ahead, the beat signal is A / D converted and sampled. Without re-acquiring the A / D converted value obtained as above, the interval for thinning out the A / D converted value sampled only in the vicinity of the detected direction was changed, the FFT calculation process was performed again, and the obstacle was detected again at the same position. FM-CW characterized by being determined as an obstacle in some cases
Obstacle detection method for radar device. 5. The obstacle detection method for an FM-CW radar device according to claim 4, wherein the beat signal is sampled at a sampling limit value that can be converted by A / D conversion.