JPH0464080A - Analysis of doppler shift frequency - Google Patents

Abstract

PURPOSE:To enable analysis of a frequency at a high accuracy in a short time by setting a sampling frequency for a maximum accuracy area to determine a Doppler shift frequency with the detection of a peak of a frequency spectrum by a linear prediction coefficient obtained. CONSTITUTION:A down sampling device 31 converts a sampling frequency so that the center of a frequency distribution of a received signal Si approaches near the center of an analysis as a maximum analysis accuracy area and the results are inputted into a prediction analyzer 32, which performs a linear prediction analysis based on an analysis parameter from an initial value setting device 30 to output a prediction coefficient ai obtained. A peak frequency detector 33 determines a spectrum from a prediction coefficient ai to output a peak frequency thereof. Then, a moving speed detector 34 determines a Doppler shift frequency fd from a difference between the peak frequency fp and a transmitting frequency fc to estimate a moving speed. Thus, even when a noise and a reverberation sound are contained in the received Si, the results of a frequency analysis ares obtained at a high accuracy in a short time thereby enabling highly accurate estimation of the moving speed.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention analyzes the Doppler shift frequency received when a signal wave such as a sound wave or radio wave is reflected by a moving object,
The present invention relates to a Doppler shift frequency analysis method in a method for estimating the moving speed of an object, which estimates the moving speed of the object from the analysis result.

(Prior art) Conventionally, as a technology in this field, "Radar Holography" edited by Institute of Electronics, Communication and Information Engineers, first edition (February 10, 1980)
There was one described in P, 44-45.

FIGS. 2(a) and 2(b) are explanatory diagrams of the principle of a range Doppler radar for explaining the conventional method for estimating the moving speed of an object described in the above-mentioned literature.

As described in the above literature, range Doppler radar is a combination of a pulse radar that measures the distance to a moving object based on the round trip time of a pulse signal, and a Doppler radar that measures the speed of a moving object using the Doppler effect. It is something.

As shown in FIG. 2(a), the radar system includes a radar transceiver 1 having an antenna 1a, a processor 2, etc.
Consider the case where two objects 01 (velocity V1) and 02 (velocity V2) are separated and a distance r/velocity valve distribution map is obtained as shown in FIG. 2(b).

Now, from the antenna 1a of the radar transceiver 1, a transmission wave (
Angular frequency ω0. Amplitude a(t), phase φ(t)) u (t> =a(t)exp(jωo↑+jφ(t))...(1
), then the reflected wave from a stationary object at a distance r is g(t) r r =ru(t - )-4a(t- r r where: ": The received amount C determined by the radar equation ; Can be expressed as the speed of light.

Next, assuming that the object is moving in the distance direction at a speed v1, the distance r is expressed as rtengthr1+V1i...(3>.a and exp (jφ> is the high frequency carrier component e
If it is a function that changes more slowly than xp(jω01), it can be approximated as follows (4). Therefore, the reflected wave becomes...(5). Here, the exponential term in equation (5) represents the so-called Doppler effect, and is given by the Doppler shift frequency.

Also, it can be seen that the transmitted waveform u (t) returns with a time delay td= (7). Therefore, by measuring the Doppler shift frequency fd and the time delay ↑d, it is possible to know the distance r1 and velocity V1 to the moving object.

In this way, when a sound wave is emitted to a moving object, the moving speed v1 of the object can be estimated from the Doppler shift frequency fd of the reflected wave. Therefore, performing highly accurate frequency analysis on the Doppler shift frequency fd leads to accurate estimation of the moving speed. An example of the configuration of a conventional Doppler shift frequency analysis method is shown in FIGS. 3 and 4.

FIG. 3 is a block diagram of the configuration of an object moving speed estimating device using the conventional Doppler shift frequency analysis method based on the phase differential method.

This frequency analysis method uses a multiplier 10.11, a reference signal generator 12, a π/2 phase shifter 13, bandpass filters 14, 15, a phase differential value calculator 16, and a moving speed calculator 17. I am trying to find the moving speed of a moving object.

That is, the received signal 3i=ac from the moving object.

S (ω = 10b) is input to the multiplier 10.11, and the reference signal generator 12 generates a carrier signal 512 = C−C0S (ω.t〉) for orthogonalizing the received signal 3i. The signal is applied to the multiplier 10 and the π/2 phase shifter 13.

The π/2 phase shifter 13 converts the carrier signal 312 into −π/
By shifting the phase by 2, the orthogonal component 513=C-5i n
(ω.t) is generated and given to the multiplier 11.

In one multiplier 10, the received signal 3i and the carrier signal S
The value x(t) obtained by multiplying the received signal 3i by the orthogonal component 313 is obtained as shown in equation (8), and the value y(t) obtained by multiplying the received signal 3i and the orthogonal component 313 by 9) Calculate as shown in the formula.

×(↑) =a・cos(ωt+b)−C conflict cos(ωct)=a
-c/2- (cos((ω.+ω) 10b)+C
05((ω −ω) t−b) ) ...(8
)y(t) = a −cos(ωt+b)−c φsimouth(ωc
t)=a −c/2 ・(sin((ω.+ω)t+b
) 10s+n((ω.-ω)↑-b)) ...(9) The values X(t) and V(t) of equations (8) and (9) are set when the central angular frequency is (ω. 10Ω) bandpass filter 14
．． By passing through 15, (8) and (9
) are removed, resulting in equations (10) and (11).

[X(t) co BPF = a fist G/2 conflict cos ((ωC 10 ω) to 1 b)...(
10) [y(t)]BpF -a -C/2'' 5in ((ω.+ω) is 10b)
(11) When the outputs of the bandpass filters 14 and 15 are given to the phase differential value calculator 16, the following equations (12) to (15) are calculated by the phase differential value calculator 16. That is, if we set [x(t) coBPF, cos((ω. 10 ω) to 10 b) ...(12) From this, jan' (Z (↑)) = (ω. + ω) t+b...
(13) becomes. Therefore, if we take the difference from the value after the time Δ has elapsed, we get the following equation (14), and the angular frequency ω can be obtained from the following equation.

ω=1/Δt・((jan' (z (t+Δ1))−
tan” (z (t)))−ω.

(15) Then, the moving speed calculator 17 estimates the moving speed V of the observed object from the difference between the angular frequency of the transmitted signal wave and the angular frequency ω obtained from equation (15).

FIG. 4 is a block diagram of a Doppler shift frequency analyzer for explaining a conventional Doppler shift frequency analysis method using Fourier transform called LOFAR.

This frequency analysis method is used in ships and the like, and the received signal 3i is input to the Fourier transformer 20. The Fourier transformer 20 obtains the spectrum of the received signal S1 using fast Fourier transform (hereinafter referred to as FFT), and provides the spectrum to the spectrum display 21. The spectral display 21 marks a dot on the recording paper when the spectral power exceeds a certain threshold. An observer uses a ruler to measure changes in the peak frequency and calculates the object's moving speed.

(Problems to be Solved by the Invention) However, the above Doppler shift frequency analysis method has the following problems.

(a> In the frequency analysis method using the phase differential method shown in Fig. 3, it is assumed that the received signal 3i is a single cosine wave (or sine wave). However, when underwater or in the air, the actual received signal contains noise, reverberation, etc.
If frequency analysis is performed using the phase differential method, the estimated frequency value will have many errors.

(b) In the LOFAR shown in FIG. 4, frequency analysis is performed using Fourier transform. However, since the frequency resolution of Fourier transform depends on the number of data, highly accurate frequency analysis cannot be performed from short-time data. Furthermore, the observer must use a ruler to find the Doppler frequency diameter on the recording paper and roughly calculate the moving speed of the object from that value, which requires a large amount of manual work.

The present invention provides a Doppler shift frequency analysis method that solves the problems of the prior art, such as low frequency analysis accuracy and difficulty in short-time analysis processing.

(Means for Solving the Problems) In order to solve the above problems, the present invention analyzes the Doppler shift frequency received by a signal wave (for example, a transmitted sound wave or a reflected wave of a radio wave) by a moving object, and In the method for estimating the moving speed of an object, which estimates the moving speed of the object from the analysis result, the following measures are taken.

That is, for the input signal wave from the object, the sampling frequency is set in the maximum precision region (for example, approximately four times the average frequency of the signal wave), and linear prediction analysis is performed to obtain prediction coefficients. Next, a peak frequency of the frequency spectrum is detected from the prediction coefficient, and the Doppler shift frequency is determined from a change in the peak frequency.

(Function) According to the present invention, since the Doppler shift frequency analysis method is configured as described above, the sampling frequency of the input signal wave from the moving object is adjusted to the maximum precision region. Next, a prediction coefficient is obtained by linear prediction analysis, and a peak frequency of the frequency spectrum is detected from the prediction coefficient. The Doppler shift frequency is then determined from the difference between the peak frequency and, for example, the transmission frequency. This allows for improved frequency analysis accuracy and short-time analysis processing.

Therefore, the above problem can be solved.

(Embodiment) FIG. 1 is a functional block diagram of an object moving speed estimating device using a Doppler frequency analysis method showing an embodiment of the present invention.

This device for estimating the moving speed of an object has an initial value setter 30, to which a downsampler 31 and a prediction analyzer 32 are connected. The initial value setter 30 inputs values such as the downsampling frequency given by the observer and parameters necessary for linear predictive analysis to the downsampler 3.
1 and the predictive analyzer 32.

The downsampler 31 converts the sampling frequency so that the center of the frequency distribution of the received signal 3i approaches the maximum analysis accuracy region, and uses the conversion result as a prediction analyzer 32.
This is the circuit that feeds the The prediction analyzer 32 has a function of performing linear predictive analysis on input data based on analysis parameters and outputting the prediction coefficient a.

A peak frequency detector 33 is connected to this predictive analyzer 32, and a moving speed calculator 34 is connected roughly to its output side. The peak frequency detector 33 calculates the prediction coefficient a.
This is a circuit that obtains a spectrum from and outputs its peak frequency fp. The moving speed calculator 34 calculates the peak frequency f
From the difference between p and transmission frequency fc, Doppler shift frequency f
It has the function of determining d, estimating the moving speed V of the object, and displaying it to the observer.

Next, a Doppler shift frequency analysis method using the object moving speed estimating device as described above and an object moving speed estimating method will be described.

First, the linear prediction method will be explained.

Now, p pieces of past value data (Xt-'l, t-2, .
..., X. ) to predict the value Xt at time t is expressed as the following equation.

Intersection t=-, naHXt i ·-(16) In other words, the predicted linkage is described as a linear combination of p past values (analytical orders). At this time, the prediction error et
is e↑=XI Xt=XQatX1- 1=1 (17).

Here, consider the case where the prediction coefficient a. is determined so as to minimize . If we differentiate q with respect to J and set it to zero, we obtain (19) from θJ ak =O. (Xt) is a stationary time series, so Rk=E(
xt xt-k), Rk-t = E(xt, x
tk) is an autocorrelation function. Therefore (19)
The formula is: = 1.2. ..., p ...(20). This is a normal equation in the least squares method.

If the correlation function Rk (k=o, 1...p) is known, the prediction coefficient a is determined by solving equation (20), and the value Xt at the time can be predicted.

When performing Doppler frequency analysis using such a linear prediction method, an observer must detect a signal wave consisting of a sound wave (transmission frequency f
. ) to a moving object, and the reflected wave from the object is sent to a downsampler 31 in the form of a received signal 3i.
Enter. The initial value setter 30 sends values such as the downsampling frequency given by the observer and parameters necessary for linear predictive analysis (analysis time, analysis order p) to the downsampler 31 and the prediction analyzer 32.

The frequency analysis range by predictive analysis is from 0 to 1/2 of the sampling frequency. Among these, the frequency analysis accuracy is highest near the center of the analysis range (1/4 (=4 times) of the sampling frequency).Therefore, in the downsampler 31, the received signal is The sampling frequency is converted so that the center of the frequency distribution of S. approaches the above condition, and the conversion result is provided to the predictive analyzer 32.

The predictive analyzer 32 performs linear predictive analysis of the data from the downsampler 31 using equation (20) based on the analysis parameters given from the initial value setter 30.
The prediction coefficient a. is output to the peak frequency detector 33.

The peak frequency detector 33 uses the following equation to calculate the prediction coefficient a
・Obtain the estimated value of the spectral density, that is, the spectral frequency 5(f).

However, σ. ;Constant Δ;Sampling interval Then, the maximum value of the spectral frequency 5(f) is determined, and the frequency at that time, that is, the peak frequency fp, is output to the moving speed calculator 34.

Next, in order to estimate the movement and speed of the object, the moving speed calculator 34 calculates the peak frequency fp and the transmission frequency f according to the following equation. From which difference, the Doppler shift frequency fd is determined.

fd=fp-f.

(22) Then, based on equation (6), the moving speed v1 of the object is estimated and displayed to the observer.

This embodiment has the following advantages.

FIGS. 5(a) to 5(C) are waveform diagrams showing comparison results of frequency analysis results of the conventional method and this embodiment.

Figure 5(a) shows the reflected wave when the test acoustic signal is radiated to a moving object, and at approximately the center of the reflected wave,
The Doppler effect appears.

Figure (b) shows the frequency analysis results using the conventional phase differential method.
(C) of the same figure shows the frequency analysis results of the method of this embodiment.

Both are waveform diagrams of peak frequencies before calculating the moving speed of the object.

As shown in Figure 5(b), in the conventional phase differential method that assumes a single cosine wave (or sine wave), Figure 5(a)
) When using an actual acoustic signal with noise and reverberation as shown in Figure 2, frequency analysis reveals that the phase becomes discontinuous and the frequency becomes unstable. In contrast, in this example, frequency analysis is performed using a spectrum analysis method based on linear prediction, so as shown in Figure 5 (C), stable frequency tracking is possible and highly accurate frequency tracking is possible. Analysis results are obtained.

Roughly speaking, in this embodiment, it is also possible to obtain a more stable peak frequency % by taking a longer analysis time for predictive analysis. Also, by increasing the prediction order p,
It can be used even when the signal-to-noise ratio (S/N ratio) is poor, and highly accurate analysis results can be obtained.

Note that the present invention is not limited to the illustrated embodiment, and various modifications are possible. Examples of such modifications include the following.

(a) Although the sampling frequency was set to approximately 1/4 (approximately 4 times) the average frequency of the analysis sound waves, the present invention is not limited to this, and as long as it is around that frequency, more accurate analysis results than conventional ones can be obtained.

(b) An observer transmits a transmitted wave and analyzes the Doppler shift frequency received by the reflected wave from an object, but if there is a sound source for the transmitted wave in another location, that sound source can be used to detect the object. Frequency analysis may be performed using the reflected waves from the

(C) Even if frequency analysis is performed using a signal wave such as a radio wave other than a sound wave, almost the same operation and effect as in the above embodiment can be obtained.

(Effects of the Invention) As explained in detail above, according to the present invention, the sampling frequency is set in the maximum precision region, linear predictive analysis is performed, the peak of the frequency spectrum is detected, and the change in frequency is determined and the Doppler Since the shift frequency is analyzed, even if the received signal contains noise, reverberation, etc., highly accurate frequency analysis results can be obtained in a short time. Therefore, if the moving speed of the object is determined using the frequency analysis results, it becomes possible to estimate the moving speed with high accuracy.

Further, if the sampling frequency is set to about four times the average frequency of the analysis signal wave, high frequency analysis accuracy can be obtained.

[Brief explanation of the drawing]

FIG. 1 is a functional block diagram of an object moving speed estimating device using the Doppler frequency analysis method showing an embodiment of the present invention;
Figures 2 (a) and (b) are explanatory diagrams of the principle of range Doppler radar, and Figure 3 is a block diagram of the configuration of an object moving speed estimation device using a Doppler shift frequency analysis method based on the conventional phase differential method. , FIG. 4 is a block diagram of the configuration of a Doppler shift frequency analyzer for explaining the Doppler shift frequency analysis method used in the conventional LOFAR.
Figures (a) to (C> are waveform diagrams of frequency analysis results of the conventional method and the present embodiment. 30...Initial value setter, 31...Downsampler, 32...-Predictive analyzer, 33 ...Peak frequency detector, 34...Moving speed calculator, a...Prediction coefficient, f,...Peak frequency.

Claims (1)

[Claims] 1. A method for estimating the moving speed of an object, which analyzes the Doppler shift frequency that a signal wave receives from a moving object, and estimates the moving speed of the object from the analysis result, comprising: For the input signal wave, set the sampling frequency to the maximum accuracy region, perform linear prediction analysis to obtain a prediction coefficient, detect the peak frequency of the frequency spectrum from the prediction coefficient, and calculate the Doppler shift from the change in the peak frequency. A Doppler shift frequency analysis method characterized by determining the frequency. 2. The Doppler shift frequency analysis method according to claim 1, wherein the signal wave is a sound wave or a radio wave, and the sampling frequency is about four times the average frequency of the signal wave. 3. The Doppler shift frequency analysis method according to claim 1, wherein a transmitted wave is radiated to the object and a Doppler shift frequency received by a reflected wave from the object is analyzed.