JP2765773B2 - Millimeter wave radar distance / velocity measurement system - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a millimeter-wave radar distance / velocity measuring device for frequency-modulating a transmission signal of a continuous wave radar and simultaneously receiving a reflected signal from a target to measure a distance and a speed. In particular, an object of the present invention is to prevent the peak frequency of a beat signal measured due to noise or the like from fluctuating, thereby preventing distance and speed from becoming unstable.

[0002]

2. Description of the Related Art Conventionally, as a technique relating to a millimeter wave radar distance / velocity measuring apparatus in such a field, "Radar technology" is known.
(Institute of Electronics, Information and Communication Engineers). When the frequency of the transmission signal of the continuous wave radar is modulated and appropriately repeated, and the beat is taken with the reception signal, the beat frequency f can be expressed as f = 4R · fm · Δf / c (1). Here, R is the distance to the target, fm is the repetition frequency of frequency modulation, Δf is the frequency shift width, and c is the speed of light. Therefore, when the beat frequency f is obtained, the distance to the target is obtained.

[0003] Next, when the target is moving, the beat signal frequency f is superimposed on the beat signal frequency f in the case of a fixed target in the relationship between the transmission signal and the reception signal due to the Doppler effect. The direction alternates between rising (up) and falling (down) for each modulation cycle, and changes the Doppler frequency fp to fp = 2 · f0 · V / c (2) where f0 is the transmission center frequency. f0 = N / fs, N: F
The number of points of an FT (Fast Fourier Transformer), fs: sampling frequency, V: relative speed with respect to the target, that is, the frequency of the rising and falling edges of the beat signal with respect to the target are as follows: Can be expressed.

Fu (up) = f−fp (3) fd (down) = f + fp (4) Accordingly, fu (up) and f (fp) are set every half cycle of modulation.
If d (down) is measured separately, f = {fu (up) + fd (down)} / 2 (5) fp = {fu (up) -fd (down)} / 2 (6) , That is, the target distance and the speed can be separately obtained from the f and fp.

[0005]

In the conventional millimeter-wave radar distance / velocity measuring apparatus, when the target is a single target, the beat signal has a sine wave, so that the beat signal is pulse-counted. Distance and the like were measured every tens of msec. However, when a conventional millimeter-wave radar distance / velocity measuring device is used, for example, mounted on an automobile to produce a measurement result, the sine wave due to the number of moving targets can be distorted when calculating only the actual data at the moment. There is a problem in that the measurement result of the beat signal varies due to the reflection state at the, and the speed and distance display become unstable.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a millimeter-wave radar distance / velocity measuring apparatus capable of stably displaying a distance and a speed while preventing a variation in counting of a beat signal.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention applies frequency modulation to a transmission signal of a transmission signal of a continuous wave radar and repeats the frequency modulation appropriately so that a beat between the reception signal and the transmission signal is obtained. In a millimeter-wave radar distance / velocity measuring device for obtaining a distance and a speed from a signal, the beat signal is subjected to frequency analysis using a fast Fourier transformer (FFT), and peak frequencies are respectively calculated on an ascending side and a descending side of the frequency modulation frequency. Ask. This peak frequency analysis is performed continuously for each modulation cycle. When this peak frequency is in the range of a predetermined width around the peak number of frequency last time,
The current peak frequency is used to derive the distance and the speed, and when the current peak frequency is not within the range of the predetermined width, the previous peak frequency is used to derive the distance and the speed. Similarly, the peak frequency at the rising side and the falling side for a plurality of targets, when the current peak frequency is in the range of a predetermined width around the peak number of frequency the last time, the the current peak frequency It is used to derive a distance and a speed. When the current peak frequency is not within the range of the predetermined width, the previous peak frequency is used to derive the distance and the speed. further,
A constant speed while measuring the number of peak frequencies the current peak frequency and the last, to predict the current frequency,
And comparing the current frequency and the predicted value, when the current peak frequency is in the range of said predetermined fixed width around the peak number of frequency the last time, derives the distance and speed the current peak frequency When the current peak frequency is not in the range of the predetermined width, the previous peak frequency is used to derive the distance and the speed. Conversely, the present distance and speed may be obtained by linear prediction from a plurality of past distances and velocities, respectively, and the present ascending and descending peak frequencies may be predicted from these distances and velocities.

[0008]

According to the millimeter-wave radar range rate measurement apparatus of the present invention, when the current peak frequency is in the range of a predetermined width around the peak number of frequency last time, it derives the distance and speed the current peak frequency When the current peak frequency is not in the range of the predetermined width, the previous peak frequency is used to derive the distance and the speed, so that the result of the FFT of the beat signal is affected by noise or the like. Once the target also captures the target, the peak frequency is determined based on the target, so that a stable distance and speed can be obtained. Also, information that the same target is being captured can be obtained. By doing the same for the peak frequencies on the ascending and descending sides for a plurality of targets, stable distances and velocities can be derived for all the peak frequencies captured by the FFT. Further, the constant velocity between which measures the number of peak frequencies the current peak frequency and the last, to predict the current frequency. Thus comparing the current frequency and the predicted value, the last The peak frequency of the noise is continuous due to noise etc., and the variation is also stabilized by the predicted value, and after that, even if noise etc. disappears, the peak frequency during that time is predicted, so capture the current peak frequency within the above specified width range Thereafter, the distance and the speed can be stably provided. Further , the prediction accuracy is improved by predicting the current peak frequencies on the ascending side and the descending side from a plurality of past distances and velocities.

[0009]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing an overall configuration of a millimeter wave radar distance / velocity measuring apparatus according to an embodiment of the present invention. The millimeter-wave radar distance / velocity measuring apparatus shown in FIG. 1 includes a sensor 1 that transmits a continuous wave signal of triangular wave modulation and mixes the signal with a received signal reflected by a target to form a beat signal. A low-pass filter 2 for removing a high-pass signal so that the signal 1 does not return, and an A / D (Analog to Digital Converter) converter for converting an analog signal from the low-pass filter 2 into a digital signal. 3
A signal processing unit 4 comprising a DSP (Digital Signal Processor) for frequency-analyzing the beat signal converted into a digital signal from the A / D converter 3 and processing it into a signal of distance and speed; It includes a controller 5 for performing control for displaying the distance and speed data obtained by the signal processing unit 4, and a display unit 6 for displaying data controlled by the controller 5.

FIG. 2 shows the formation of the output signal of the sensor of FIG. As shown by the solid line in FIG.
, A continuous transmission signal of triangular wave modulation is transmitted, and the signal reflected by the target is received by the sensor 1 as shown by the dotted line. Further, as shown in FIG. 2B, a beat signal fu on the rising side of the triangular wave modulation and a beat signal fd on the falling side are formed by a mixer (not shown). The symbols and reference numerals used in this figure are the same as those described in the related art.

FIG. 3 is a diagram showing a configuration of the signal processing unit shown in FIG. As shown in the figure, the signal processing unit 4 has a unit time 1 / fm with respect to the repetition frequency fm of frequency modulation.
A frequency analyzer 41 for analyzing the frequency of the beat signal from the A / D converter 3 at an interval defined by an FFT (Fast Fourier Transformer), and an analysis of the beat signal obtained by the analysis by the frequency analyzer 41 A storage unit 42 that stores the resulting rising and falling peak frequencies Au and Ad, a comparison unit 43 that compares the peak frequency from the frequency analysis unit 41 with the previous peak frequency from the storage unit 42, Normally, it includes a switch section 44 which outputs a signal from the frequency analysis section 41 and outputs an output signal from the storage section 42 when there is a control signal from the comparison section 43.

FIG. 4 is a flowchart of signal processing by the signal processing unit shown in FIG. As shown in the figure, the peak frequency is obtained by the frequency analysis unit 41 (step 1), and the storage unit 42 stores and updates the peak frequency (step 2). In the comparison unit 43, the frequency analysis unit 4
1 and the previously input Au (T-1) and Ad from the storage unit 42.
By comparing with (T-1), it is determined whether or not the following expression is satisfied.

Au (T−1) −Δ ≦ Au (T) ≦ Au (T−1) + Δ (7) Ad (T−1) −Δ ≦ Ad (T) ≦ Ad (T−1) + Δ. (8) Here, T is a time measured by the unit time 1 / fm. Further, Δ is determined in consideration of the amount of change in the Au (T) and Ad (T) and the noise that can change due to the relative movement of the target during the unit time 1 / fm. If converted, it may be set to about 2 m (step 3). This means that the relative speed between cars can be, for example, 100
Assuming that Km /, 1 / fm = 50 msec, this corresponds to the distance that the target moves during this period being about 1.4 m.
If the above equation is satisfied, the Au input this time
(T) and Ad (T) are transmitted (step 4). Conversely, if the above expression is not satisfied, the Au (T) input this time,
Au (T-1), A previously input instead of Ad (T)
d (T-1) is transmitted to the subsequent stage by the switch unit 44 (step 5). In this case, the storage unit 42 replaces the Au (T) and Ad (T) with Au (T-1),
Ad (T-1) is stored and becomes a reference for the next comparison.

FIG. 5 is a diagram showing the states of signals processed in the flowchart of FIG. This figure explains only the rising side to make the above signal processing easier to understand.In summary with reference to this figure, if the current signal has a predetermined width compared to the previous signal, the current Is determined to be correct, and this is used, but if the current signal is not within the predetermined width, it is excluded because it is affected by noise. Therefore,
Once the target is captured, the result can be captured stably because the frequency peak is corresponded based on the target, and information that the same target is captured can also be obtained.

In the above description, the case where there is a single target is used, but the present invention can be applied to a case where there are a plurality of targets. The description is given below. When t = T, targets A and B are captured, and their peak frequencies are (Au, Ad), (Bu, B
Suppose d). FIG. 6 is a diagram showing a state of a signal processed in the case of a plurality of targets. This figure shows the peak frequency on the rising side, and the peak frequency a at t = T + 1.
1, b1 are obtained, and Au (T) −Δ ≦ a1 ≦ Au
Since (T) + Δ is satisfied, the peak frequency a1 corresponds to the target A. Similarly, b1 also corresponds to target B. Below t = T
+2, T + 3, a2 is target A, c2 is target B, a
3 corresponds to the target A, and c3 corresponds to the target B. The same processing is performed on the descending side, and those corresponding to the target A are sequentially x
1, x2, y3 and those corresponding to the target B are y1, z2,
If it is z3, it will be as follows.

T: T T + 1 T + 2 T + 3 Target A: (Au, Ad) (a1, x1) (a2, x2) (a3, y3) Target B: (Bu, Bd) (b1, y1) (c2, z2) (C3, z3) According to the above equations (5) and (6), f and fp are obtained for each combination, and the distance and speed can be obtained stably from this. In FIG. 6, b2 and b3 on the ascending side are targets A and B
It is also considered a new target, but it is determined to be noise because there is no peak frequency corresponding to the descending side. Thus, in the related art, when there are a plurality of measured peak frequencies, it was difficult to determine to which target the target frequency belongs. However, according to this embodiment, it is now possible to stably recognize that the target is the same target. .

In the above description, the present peak frequency is directly compared with the previous peak frequency. However, it is determined that the current peak frequency is continuously caused by noise, and the previous peak frequency is not updated. Even if the peak frequency is not due to noise but is true, the peak frequency may not fall within the range of Δ. Therefore, the present peak frequency is predicted from the previous peak frequency as described below, and the predicted value is compared with the current peak frequency.

From the above equations (5) and (6), the direct distance and speed are obtained as follows. R = (c / (4 · Δf)) · (N / fs) · (fu + fd) (9) V = (c · fs) / (4 · f0 · N) · (N / fs) · (fu− fd) (10) The underlined portion is normalized by the FFT frequency resolution.

Therefore, the distance R and the speed V can be abbreviated as follows. R = a · (fu + fd) (11) V = b · (fu−fd) (12) where a and b are constants obtained from equations (9) and (10). a = (c / (4 · Δf)) · (N / fs) (13) b = (c · fs) / (4 · f0 · N) (N / fs) (14) Assuming that the measurement time from the previous time to the current time is Δt, the distance R0 can be expressed by the following equation.

R0 = V · Δt + R (15) Assuming that the rising and falling peak frequencies obtained this time are fu1 and fd1, respectively, R0 and V are given by the following equations. R0 = a ・ (fu1 + fd1) (16) V = b ・ (fu1-fd1) (17) From this, (fu1 + fd1) = R0 / a (18) (fu1-fd1) = V / b (19) Here, R0 = a · (fu + fd) + Δt · b · (fu−fd) (20) Therefore, from equations (18) and (19), fd1 = 1/2 · (R0 / a−V / b) ) = １ ／ · (fu + fd + (b / a) · Δt · (fu−fd) − (fu−fd)) = fu + (b / 2a) · Δt · (fu−fd) (21) fu1 = 1 /(R0/a+V/b)=1/2.(fu+fd+(b/a)..DELTA.t.(fu-fd)+(fu-fd))=fd+(b/2a)..DELTA.t.(fu- fd) (22) The predicted values fu1 and fd1 are compared with, for example, the comparison unit 43 in FIG.
, And this may be used as the previous peak frequency and compared with the current peak frequency. The stability of the measurement of the peak frequency with respect to the target is thus increased.

Next, means for improving the accuracy of the predicted values fu1 and fd1 will be described. The result of the FFT of the beat signal varies due to the influence of noise and the like, while the result that should be actually obtained has a small change. Therefore, a means for stabilizing the measurement by filtering past data or results for several blocks and combining the resulting data will be described below.

FIG. 7 shows a circuit for estimating the predicted speed signal V0 from the speed signal V obtained from the equations (11) and (12). The circuit shown in FIG. 2A is composed of an FIR filter, and is connected to, for example, four delay units connected in series to delay signals by a unit time of 1 / fm, and to the output of each of the delay units. It comprises a multiplier having a count of 1/4 and an adder for adding the output of each of the multipliers, thereby, as shown in FIG.
From the speed signals of T-2 and T-1, the speed signal V at T
0 can be predicted.

FIG. 8 shows a circuit for estimating the predicted distance signal R00 from the distance signal R0 obtained from the equations (11) and (12). The circuit shown in this figure (a) is composed of an FIR filter, for example, four delay units connected in series to delay signals by unit time 1 / fm, respectively, and a first stage delay unit from the input side. A multiplier connected to the output and the output of the last stage delay device and having respective counts-／ and 4/3;
An adder for adding the output of each of the multipliers is used. As shown in FIG. 3B, the data based on the past distance signal is assumed to have linearity in a short time, and the past time T-4 , T-3, T-2, and T-1, the distance signal R00 at T can be predicted. With respect to the speed signal V0 and the distance signal R00 thus obtained, (1
By obtaining fu1 and fd1 from 6) and (17), the accuracy of the predicted value is further improved.

[0024]

According to the present invention described above, according to the present invention, when the current peak frequency is in the range of a predetermined width around the peak number of frequency previous derives the distance and speed the current peak frequency When the current peak frequency is not within the range of the predetermined width, the previous peak frequency is used to derive the distance and the speed, so that a stable distance and speed can be obtained. The same applies to the peak frequencies on the ascending and descending sides for a plurality of targets, and the same effect can be obtained for each target. Further, the constant velocity between which measures the number of peak frequencies the current peak frequency and the last, to predict the current frequency, similar to the so as to compare the current frequency and the predicted value As the distance and speed are obtained, the stability is increased.

[Brief description of the drawings]

FIG. 1 is a diagram showing an overall configuration of a millimeter wave radar distance / velocity measuring apparatus according to an embodiment of the present invention.

2 shows the formation of the output signal of the sensor of FIG. 1;

FIG. 3 is a diagram illustrating a configuration of a signal processing unit illustrated in FIG. 1;

FIG. 4 is a flowchart of signal processing by a signal processing unit shown in FIG. 3;

FIG. 5 is a diagram showing states of signals processed in the flowchart of FIG. 4;

FIG. 6 is a diagram illustrating a state of a signal processed in a case of a plurality of targets.

FIG. 7 shows a circuit for obtaining a speed signal V used in equations (18) and (19).

FIG. 8 shows a circuit for obtaining a distance signal R0 used in equations (18) and (19).

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Sensor 2 ... Low-pass filter 3 ... A / D converter 4 ... Signal processing part 5 ... Controller 6 ... Display 41 ... Frequency analysis part 42 ... Storage part 43 ... Comparison part 44 ... Switch part

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-3-191890 (JP, A) JP-A-2-212793 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G01S 13/34

Claims (4)

(57) [Claims] 1. A millimeter-wave radar distance / velocity measuring apparatus for performing frequency modulation on a transmission signal of a transmission signal of a continuous wave radar and appropriately repeating the transmission signal to obtain a distance and a speed from a beat signal between the reception signal and the transmission signal. each Ru the peak frequency in ascending side and descending side of the frequency of said frequency modulating the beat signal frequency analysis
A frequency analysis unit, and a peak frequency obtained by the frequency analysis unit are stored.
When the current peak frequency is within a predetermined range around the previous peak frequency based on the peak frequency stored in the storage unit, the current peak frequency is determined by the distance and speed. A millimeter wave radar distance / velocity measuring apparatus, wherein when the current peak frequency is not within the range of the predetermined width, the previous peak frequency is used to derive a distance and a speed. The peak frequency of at 2. A rising side and the falling side for a plurality of targets, when the current peak frequency is in the range of a predetermined width around the peak number of frequency the last time, the the current peak frequency 2. The millimeter wave radar distance velocity according to claim 1, wherein the distance and velocity are used to derive a distance and a velocity, and when the current peak frequency is not within the range of the predetermined width, the previous peak frequency is used to derive the distance and the velocity. measuring device. 3. The system according to claim 2, wherein said current peak frequency is within a range of said predetermined width.
If not, measure the peak frequencies of the current and previous times.
From the previous peak frequency with the speed during
Predict the peak frequency this time,
The current peak frequency derives the next distance and speed.
Is used as the previous peak frequency when
The millimeter-wave radar distance / velocity measuring apparatus according to claim 1, which is a feature . 4. The system according to claim 1, wherein said current peak frequency is within a range of said predetermined width.
If not, a line is derived from the distance and speed derived in the past.
The current distance and speed are obtained by type prediction, and the current
Predict the current peak frequency from the distance and speed
The peak frequency predicted this time is
When deriving the distance and speed, use the previous peak frequency.
Characterized in that it is used Te, millimeter wave radar range rate measurement apparatus according to claim 1.