JPH0540168A - Fw-cw radar device - Google Patents

Abstract

PURPOSE:To enable an accurate speed and distance of each target to be detected in the case of multiples targets when performing Discrete Fourier transform to a reception beat wave for two times. CONSTITUTION:An RF signal generation circuit 1A performs frequency modulation to a transmission signal with a repetition frequency from a frequency modulation wave generation circuit 1 and then sends it to a target 4 (-1 to M) via a directivity coupler 2 and a transmission antenna 3. A distance to the target 4 and a relative speed between the target 4 and an observer are detected with the frequency of beat wave by a mixer 6 from the reflection wave and a local oscillation wave of the connector 2. At this time, a signal from the mixer 6 is A/D converted 17 and is subjected to window processing 8 and then is subjected to Discrete Fourier transform for two times by a two- time Discrete Fourier circuit 9. In this manner, a distance frequency is obtained by the first Fourier transform and a speed frequency is obtained by the second Fourier transform, thus enabling a distance to a plurality of targets 4 and the relative speed between a plurality of target 4 and an observer to be detected.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention sends out a signal frequency-modulated (FM-modulated) with a modulation wave having a predetermined repetition frequency, and determines the target from the frequencies of the beat waves of the reflected wave from the target and the local oscillation wave. The present invention relates to an FM-CW radar device (frequency modulation continuous wave radar device) that detects a distance to a vehicle and a relative velocity between a target and an observer, and is particularly suitable for use in avoiding a collision of an automobile with an obstacle on a road. The present invention relates to an FM-CW radar device.

[0002]

2. Description of the Related Art An FM-CW radar device is a radar device used for detecting the position and relative velocity of a target (obstacle) and avoiding a collision with the target. It is relatively small and can be realized at a low price.

The principle of such an FM-CW radar device is as follows. That is, a carrier wave is FM-modulated by an output from an oscillator and transmitted, this FM-modulated wave is used as a local oscillation wave, a beat wave of a reflected wave from a target and a local oscillation wave is taken, and the frequency of the beat wave is processed. The position and velocity of the target are detected by measuring with a measuring instrument.

In this case, since the reflected wave from the target is subject to the delay due to the distance to the target and the Doppler shift due to the relative velocity with the target, the position and velocity are beat by applying FM modulation to the transmitted wave. It can be detected from the frequency of the wave.

Since the frequency of the beat wave observed is equal to the absolute value of the sum and difference of the distance frequency and velocity frequency to be detected, addition or subtraction is performed on the frequency of the beat wave to determine the distance frequency and velocity frequency. Seeking

[0006]

However, in such a conventional FM-CW radar device, since the range frequency and the velocity frequency are obtained by adding or subtracting to the frequency of the beat wave, a plurality of targets can be obtained. In the case of, there is a problem that the accurate speed and distance of each target can be detected only in a limited number of cases.

The present invention was devised in view of the above problems, and by an inexpensive method, even when there are a plurality of targets,
An object of the present invention is to provide an FM-CW radar device capable of detecting the accurate velocity and range of each target.

[0008]

FIG. 1 is a block diagram of the principle of the present invention. In FIG. 1, reference numeral 1 is a frequency modulated wave generating circuit, 1A is an RF signal generating circuit, and the frequency modulated wave generating circuit 1 is repeatedly used. The frequency modulated wave of
The signal generation circuit 1A is for subjecting a transmission signal to frequency modulation.

In this case, it is preferable to use a triangular wave as the repetitive frequency modulated wave. Further, in this frequency modulation, it is preferable to perform frequency modulation at a repetition frequency that is at least twice as high as a speed frequency that depends on the speed in the frequency of the beat wave described later.

Further, the distance frequency dependent on the distance in the frequency of the beat wave is higher than twice the repetition frequency of the frequency modulated wave, and the speed frequency dependent on the speed in the frequency of the beat wave is the repetition frequency of the frequency modulated wave. It is advisable to set the repetition frequency of the frequency-modulated wave so that it is lower than 1/2 times.

Reference numeral 2 is a directional coupler.
Is a signal modulated by the repeated frequency modulation wave from the frequency modulation wave generation circuit 1 in addition to the transmission antenna 3
The local oscillation wave is extracted to the mixer 6 side.

Reference numeral 3 denotes a plurality of targets 4 which are signals modulated by repeated frequency modulation waves from the frequency modulation wave generation circuit 1.
-1 to 4-M (M is an integer of 2 or more) is a transmitting antenna, and 5 is a receiving antenna that receives reflected waves from each target 4-i (i = 1 to M).

Reference numeral 6 denotes a mixer which mixes the reflected wave from the receiving antenna 5 and the locally oscillated wave from the directional coupler 2 to generate a reflected wave from each target 4-i and a local oscillation. It outputs a beat wave with a wave.

Reference numeral 7 is an A / D converter, and this A / D converter 7
Is for digitally converting the analog beat wave signal from the mixer 6. Reference numeral 8 denotes a window processing circuit, which performs digitized window processing on the received beat wave.

Reference numeral 9 denotes a two-time discrete Fourier transform circuit,
The discrete Fourier transform circuit 9 includes a window processing circuit 8
Then, the distance to each target 4-i and the relative velocity between each target 4-i and the observer are detected by performing the discrete Fourier transform twice on the received beat wave subjected to the digitized window processing. To do.

The distance frequency depending on the distance in the frequency of the beat wave is 1/2 of the repetition frequency of the frequency modulated wave.
If the repetition frequency of the frequency modulated wave is set so that the speed frequency that is higher than the double frequency and that depends on the speed in the frequency of the beat wave is lower than twice the repetition frequency of the frequency modulated wave, The distance frequency is obtained by the discrete Fourier transform of the above and the velocity frequency is obtained by the second discrete Fourier transform, whereby the distances to the plurality of targets and the relative velocities between the plurality of targets and the observer are detected. ..

It is also possible to take in the data to be subjected to the discrete Fourier transform in the first half of the repetition cycle of the frequency modulated wave and to perform the discrete Fourier transform in the latter half of the repetition cycle of the frequency modulated wave.

[0018]

In the above-described FM-CW radar device of the present invention, the signal modulated by the repetitive frequency modulation wave (preferably triangular wave) from the frequency modulation wave generation circuit 1 to the RF signal generation circuit 1R is transmitted from the transmission antenna 3. Then, a beat wave of the reflected wave from each target 4-i received by the receiving antenna 5 and the local oscillation wave from the directional coupler 2 is obtained by the mixer 6, and this beat wave is obtained by the A / D converter 7 And digitized by the window processing circuit 8 and then twice discrete Fourier transform by the twice discrete Fourier transform circuit 9 to obtain the distance to the plurality of targets 4-i and the plurality of targets 4-i. The relative velocity between 4-i and the observer is detected.

At this time, the distance frequency depending on the distance in the frequency of the beat wave is 2 times the repetition frequency of the frequency modulated wave.
The repetition frequency of the frequency-modulated wave is set so that the speed frequency that is higher than double and that depends on the speed in the frequency of the beat wave is lower than 1/2 times the repetition frequency of the frequency-modulated wave. In this case, the distance frequency is obtained by the first discrete Fourier transform, and the velocity frequency is obtained by the second discrete Fourier transform to detect the distances to the plurality of targets and the relative velocities between the plurality of targets and the observer.

Data to be subjected to the discrete Fourier transform is taken in the first half of the repetition period of the frequency modulated wave, and the discrete Fourier transform is performed in the latter half of the repetition period of the frequency modulated wave.

[0021]

Embodiments of the present invention will be described below with reference to the drawings. 2 is a block diagram showing an embodiment of the present invention. The FM-CW radar device shown in FIG. 2 has a triangular wave generator (triangular wave oscillator) 10, an RF signal generating circuit 11, a directional coupler 12, and a transmitting antenna. 13, receiving antenna 15, mixer 16, A / D converter 17, window processing circuit 1
It is configured by including an 8 and 2 times discrete Fourier transform circuit 19 and a synchronizing signal generating circuit 20.

Here, the triangular wave generator 10 generates a triangular wave, and the RF signal generating circuit 11 generates a signal frequency-modulated (FM-modulated) by the triangular wave. In this case, a triangular wave is used as the repeating FM modulated wave. That is, in this case, the triangular wave is used to increase the frequency with respect to the time axis (upward slope).
The FM modulation in two directions of decreasing direction (downward gradient) is repeatedly performed.

Further, in this FM modulation, rather than the velocity frequency depending on the velocity in the frequency of the beat wave described later,
Frequency modulation is performed at a repetition frequency that is at least 1/2 times higher.

Further, the distance frequency fr depending on the distance in the frequency fb of the beat wave is 2 times the repetition frequency of the triangular wave.
The repetition frequency of the triangular wave is set so that the frequency frequency fd, which is higher than double and is dependent on the speed in the frequency of the beat wave, is lower than 1/2 times the repetition frequency of the triangular wave.

The directional coupler 12 extracts the RF signal frequency-modulated by the triangular wave to the transmitting antenna 13 and the mixer 16 side as a local oscillation wave. The transmission antenna 13 outputs the repeated FM modulated waves from the RF signal generation circuit 11 to a plurality of targets (obstacles) 14-1 to 14-.
Since the signal is transmitted to M (M is an integer of 2 or more), the receiving antenna 15 receives the reflected wave from each target 14-i (i = 1 to M).

The mixer 16 mixes the reflected wave from the receiving antenna 15 and the locally oscillated wave from the directional coupler 12 to generate beat waves of the reflected wave from each target 14-i and the locally transmitted wave. It is output. The A / D converter 17 converts the analog beat wave signal from the mixer 16 into a digital signal.

The window processing circuit 18 performs window processing digitized on the received beat wave (for this window processing, the Hanning window shown in FIG. 5 and the triangular window shown in FIG. 7 are used).

The twice-discrete Fourier transform circuit 19 performs the discrete Fourier transform twice on the received beat wave subjected to the window processing by the window processing circuit 18 to obtain the distance to the target 14-i. And the relative speed between the target 14-i and the observer is detected.
Is a Fourier transform processing circuit (FFT processing circuit) 19-
1, a memory 19-2, and a data control circuit 19-3.

Here, the FFT processing circuit 19-1 performs a Fourier transform process, and a dedicated DSP is used. The memory 19-2 stores processed data (for example, the result of the first discrete Fourier transform). The data control circuit 19-3 controls data exchange between the FFT processing circuit 19-1 and the memory 19-2.

In this case, the frequency fb of the beat wave
The distance frequency fr that depends on the middle distance is higher than twice the repetition frequency of the FM modulated wave, and the velocity frequency fd that depends on the velocity in the frequency fb of the beat wave is higher than 1/2 times the repetition frequency of the FM modulated wave. Since the repetition frequency of the FM modulated wave is set so as to be low, the distance frequency fr is obtained by the first discrete Fourier transform, and the velocity frequency fd is obtained by the second discrete Fourier transform. The distance to -i and the relative velocities of the targets 14-i and the observer are detected.

Further, in the first half of the repetition period of the FM modulated wave, the data to be subjected to the discrete Fourier transform is fetched, and F
Discrete Fourier transform is performed in the latter half of the repetition cycle of the M-modulated wave (see FIG. 12).

The synchronizing signal generating circuit 20 includes an RF signal generating circuit 11, an A / D converter 17, a window processing circuit 18,
The synchronizing signal is generated for the two-time discrete Fourier transform circuit 19.

Next, the principle of the FM-CW radar device when the triangular wave is used as the modulation wave will be described with reference to FIGS. First, the transmission wave subjected to FM modulation is reflected by the target and then received by the receiving antenna 15 to become a reception wave. The frequency of the received wave deviates from that of the transmitted wave by the delay due to the distance to the target and the Doppler shift due to the relative velocity between the target and the observer. The mixer 1 receives the received wave and the local wave.
When mixing with 6, the shifted frequency component (beat wave)
Is detected.

Further, from this frequency component, the distance frequency f
A method of separating r from the velocity frequency fd will be described. In the case of FM modulation with a triangular wave, the distance frequency fr and the velocity frequency fd are expressed by the following equations. The distance frequency fr depends on the period T of the modulated wave and the modulation width ΔΩ, but the velocity frequency fd is the period of the modulated wave. T, does not depend on the modulation width ΔΩ. fr = (4ΔΩT / c) R fd = (2f ₀ / c) v where c is the speed of light, R is the distance to an obstacle (target), and f
₀ is the transmission center frequency, and v is the relative velocity with the obstacle (target).

Now, the distance frequency f corresponding to the distance resolution
The modulation width ΔΩ and the modulation wave period T (1 / T = repetition frequency) are set so that r is higher than ½ times the repetition frequency and the velocity frequency fd is lower than twice the repetition frequency. That is, fr> 2 / T, (1/2
Since T)> fd, the received wave Sr when there is one target is as follows. Sr = Acos [2π (fr-fd) t] This received wave has a section [(n-1) T, (n-1) T + T /
When the discrete Fourier transform is performed in 2], the range of the velocity frequency fd is lower than 1/2 of the reciprocal of the section to be sampled, so only the distance frequency fr is detected. The velocity frequency fd is detected as a phase component.

That is, DFT {Acos [2π (fr
−fd) t] −2πfdnT} is ex when f = fr
p (j2πfdnT), and when f = −fr, exp
(J2πfdnT), and becomes 0 when f ≠ ± fr.

Further, the discrete Fourier transform is performed for each n =
0 ,. ． ． , Nd−1, the time series of the phase component is obtained for each distance frequency fr, which is equal to the sample value sequence obtained by sampling the signal having the velocity frequency fd as the frequency at the sampling interval T. ..

Further, since the data for f = -fr is unnecessary, as shown in FIG. 11, half of the data in the region of fr <0 can be discarded, and each remaining data has f = fr ( When the discrete Fourier transform is applied to fr> 0), the velocity frequency fd is detected.

That is, DFT (DFT {Acos [2
π (fr-fd) t] -2πfdnT}) is the DFT
{Exp (j2πfdnT)}, and this DFT
{Exp (j2πfdnT)} is f = (fr, fd)
Is 1 when, and 0 when f ≠ (fr, fd).

Similarly, the received wave when there are a plurality of targets 14-i as in the present embodiment is as follows. Sr = ΣA _k cos [2π (fr _k −fd _k ) t] Note that the above equation is calculated for k = 1 to M.

Therefore, when the same operation is performed on this signal, the range frequency and the velocity frequency can be obtained for each target 14-i. By the way, if the FFT is applied to the data sampled in the finite section, the signal is distorted. This is because a rectangular window (see FIG. 9) is implicitly applied. The rectangular window thus Fourier-transformed has a large side lobe, as shown in FIG.
Applying FFT to the data sampled in the finite section is equivalent to taking a convolution of the true spectrum and the spectrum of the rectangular window, so that side lobes are generated around each spectrum component and the signal is distorted.

However, by performing the window processing, the side lobe when FFT is applied is reduced, and more accurate distance and relative velocity can be detected.
For example, in the rectangular window, the level of the largest side lobe with respect to the peak level is −13 dB, but in the triangular window shown in FIG. 7, it is −26 dB, and in the Hanning window shown in FIG. 5, it is as small as −31 dB (see FIG. 6, FIG. 8). Therefore, if you perform window processing using a triangular window or Hanning window,
The side lobes of the signal are greatly reduced as compared with the case where window processing is not performed (corresponding to the case where a rectangular window is used).

With the above configuration, the transmitting antenna 1 receives the signal from the RF signal generating circuit 11 frequency-modulated by the triangular wave.
Target 14-
The beat wave of the reflected wave from i and the local oscillation wave from the directional coupler 12 is obtained by the mixer 16, and this beat wave is A /
The D converter 17 digitizes it, and the window processing circuit 18 tunes it to the modulated wave and performs window processing for each T / 2. By performing the window processing in this way and then performing the discrete Fourier transform twice in the discrete Fourier transform circuit 19, the distances to the plurality of targets 14-i and the relative distance between the plurality of targets 14-i and the observer. Detecting the speed is performed.

At this time, the distance frequency fr is obtained by the first discrete Fourier transform, and the velocity frequency fd is obtained by the second discrete Fourier transform, whereby the distance to the plurality of targets 14-i and the plurality of targets 14-i are obtained. The relative velocity with the observer is detected.

That is, as shown in FIG. 13, with respect to the beat waves from the plurality of targets 14-i, the first discrete Fourier transform shows the distance frequencies fr (f1, f2, f3 in the figure) as shown in FIG. Then, in the second discrete Fourier transform, as shown in FIG. 15, the velocity frequency fd (F
1, F2, F3).

The two-time discrete Fourier transform circuit 1
In 9, the digital data that has entered the section of the up (or down) gradient of the modulated triangular wave is sent to the FFT processing device and FFT processing is performed in the section of the down (or up) gradient. No data is sent to the FFT processor in the section of the down (or up) gradient (see FIG. 12). Also, once FFT
The processed data is sequentially stored in the memory 19-2. After performing Fd processing Nd times, the data stored in the memory 19-2 is extracted for each distance frequency,
The FFT process is performed to obtain the range frequency and velocity frequency of each target. And finally, the distance and relative velocity of each target are obtained from the range frequency and velocity frequency.

In this way, each distance and relative velocity can be accurately detected even when a plurality of targets 14-i are present. In addition, since this apparatus uses a digital circuit, the circuit configuration is simple and the cost can be reduced, which makes it suitable for a vehicle-mounted radar.

By using the method of the present invention, a plurality of (10
FIG. 16 shows the simulation result of obtaining the distance and the relative velocity for each target. here,
The reason why a plurality of calculation results (a plurality of lines) appear in one target portion is that the frequency is roughly discretized with respect to the data.

[0049]

As described in detail above, the FM-C of the present invention
According to the W radar device, for example, frequency modulation is performed at a repetition frequency that is at least ½ or more times higher than the velocity frequency depending on the velocity in the frequency of the beat wave, that is, the distance frequency depending on the distance in the frequency of the beat wave. Is higher than twice the repetition frequency of the frequency-modulated wave, and the speed frequency depending on the speed in the frequency of the beat wave is lower than 1/2 times the repetition frequency of the frequency-modulated wave. By setting the wave repetition frequency and applying the discrete Fourier transform twice to the received beat wave,
An advantage that the distance to a plurality of targets and the relative speed between the plurality of targets and an observer can be accurately detected by obtaining the distance frequency by the first discrete Fourier transform and obtaining the velocity frequency by the second discrete Fourier transform There is.

Further, since it is possible to use a triangular wave as the repetitive frequency-modulated wave or to subject the received beat wave to digital window processing and then to perform the discrete Fourier transform twice, it is possible to easily and accurately measure the distance and relative distance. It becomes possible to detect the distance.

Further, in the first half of the repetition period of the frequency modulated wave, the data to be subjected to the discrete Fourier transform is fetched,
Discrete Fourier transform can be performed in the latter half of the repetition period of the frequency-modulated wave, and this has the advantage that the processing time can be shortened.

[Brief description of drawings]

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

FIG. 2 is a block diagram showing an embodiment of the present invention.

FIG. 3 is a diagram illustrating the principle of an FM-CW radar device.

FIG. 4 is a diagram illustrating the principle of an FM-CW radar device.

FIG. 5 is a Hanning window characteristic diagram.

FIG. 6 is a side lobe characteristic diagram based on a Hanning window.

FIG. 7 is a characteristic diagram of a triangular window.

FIG. 8 is a side lobe characteristic diagram based on a triangular window.

FIG. 9 is a rectangular window characteristic diagram.

FIG. 10 is a side lobe characteristic diagram of a rectangular window.

FIG. 11 is a diagram for explaining the frequency domain after the two-time discrete Fourier transform.

FIG. 12 is a diagram illustrating a relationship between FFT data acquisition and FFT processing.

FIG. 13 is a diagram showing how the phase is changed by Doppler shift in order to explain the principle of multiple target identification.

FIG. 14 is a diagram illustrating a first Fourier transform for explaining the principle of multiple target identification.

FIG. 15 is a diagram illustrating a second Fourier transform to explain the principle of multiple target identification.

FIG. 16 is a diagram showing simulation results for obtaining distances and relative velocities for a plurality of targets.

[Explanation of symbols]

 1 Frequency Modulation Wave Generation Circuit 1A RF Signal Generation Circuit 2 Directional Coupler 3 Transmission Antenna 4-i Target 5 Reception Antenna 6 Mixer 7 A / D Converter 8 Window Processing Circuit 9 2 Times Discrete Fourier Transform Circuit 10 Triangular Wave Generator ( Triangle wave oscillator) 11 RF signal generation circuit 12 Directional coupler 13 Transmission antenna 14-i Target 15 Reception antenna 16 Mixer 17 A / D converter 18 Window processing circuit 19 2 times discrete Fourier transform circuit 19-1 Fourier transform processing circuit ( FFT processing circuit) 19-2 memory 19-3 data control circuit 20 synchronization signal generation circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Tamio Saito 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited (72) Inventor Yoji Ohashi 1015, Kamedotachu, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited ( 72) Inventor Kawasaki Yoshihiro 1015 Kamiodanaka, Nakahara-ku, Kawasaki City, Kanagawa Prefecture, Fujitsu Limited (72) Inventor, Osamu Isaji 1-22, Goshodori, Hyogo-ku, Kobe, Hyogo Prefecture, Fujitsu Ten Limited

Claims (6)

[Claims] 1. A signal frequency-modulated by a modulation wave having a predetermined repetition frequency is transmitted, and the target wave (1) is detected from the frequencies of beat waves of a reflected wave from a target (14-i) and a local oscillation wave.
In an FM-CW radar device that detects the distance to 4-i) and the relative velocity between the target (14-i) and the observer, a plurality of targets ( An FM-CW radar device characterized by detecting a distance to 14-i) and a relative velocity between a plurality of targets (14-i) and an observer. 2. The frequency modulation is performed by a modulation wave having a repetition frequency which is at least twice as high as a speed frequency depending on the speed in the frequency of the beat wave.
The FM-CW radar device according to claim 1. 3. The distance frequency dependent on the distance in the frequency of the beat wave is higher than twice the repetition frequency of the frequency modulated wave, and the speed frequency dependent on the speed in the frequency of the beat wave is the frequency modulated wave. The repetition frequency of the frequency-modulated wave is set so as to be lower than half the repetition frequency, and the distance frequency is obtained by the first discrete Fourier transform, and the velocity is calculated by the second discrete Fourier transform. The FM-CW according to claim 1, wherein the distance to the plurality of targets (14-i) and the relative velocity between the plurality of targets (14-i) and the observer are detected by obtaining the frequency. Radar equipment. 4. The FM-CW radar device according to claim 1, wherein a triangular wave is used as the repetitive frequency modulated wave. 5. The FM-CW radar device according to claim 1, wherein the received beat wave is subjected to digital window processing and then subjected to twice discrete Fourier transform. 6. The data is to be subjected to discrete Fourier transform in the first half of the repetition cycle of the frequency modulated wave, and the discrete Fourier transform is applied in the latter half of the repetition cycle of the frequency modulated wave. FM-CW described in 1.
Radar equipment.