CN105738878B - A kind of precision instrumentation radar frequency measuring method based on frequency deviation classification - Google Patents
A kind of precision instrumentation radar frequency measuring method based on frequency deviation classification Download PDFInfo
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- G—PHYSICS
- G01—MEASURING; TESTING
- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
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Abstract
A kind of precision instrumentation radar frequency measuring method based on frequency deviation classification of the disclosure of the invention, is related to precision instrumentation radar frequency measurement field.This method obtains the frequency shift amount of radar signal based on frequency deviation sorting technique, and by the frequency shift amount compared with reference threshold, the size of the reference threshold is relevant with the second largest value of radar signal amplitude and the size of maximum, is not fixed value；The method that the frequency at center is calculated according to how much judgements of frequency shift amount；Using frequency spectrum translation to improve measurement accuracy away from main lobe center；In the case of frequency deviation is less, FFT measurement frequencies are directly used.This method is mutually obviously improved in measurement accuracy, in stability than existing methods.
Description
Technical Field
The invention relates to the field of precision measurement radar frequency measurement.
Background
At present, the frequency measurement method of the precision measurement radar is mature, and comprises an RIFE (radio over Ethernet), an energy center of gravity method and an FFT (fast Fourier transform) refining method. The traditional ratio method has the advantages of higher frequency measurement precision, less calculation amount and easy realization, so the traditional ratio method becomes the most precise measurement radar frequency measurement method used in engineering. The traditional ratio method comprises the following steps: step 1, mixing and filtering the echo and the transmitted wave to obtain a difference frequency signal; step 2, performing FFT on the difference frequency signal to obtain an amplitude maximum value X (k) and a secondary maximum value X (k + r), wherein r is +/-1; and 3, obtaining the estimated frequency through the position of the maximum FFT value and the relation between the times X (k) and X (k + r). From step 3, it can be seen that if the frequency deviation is measured in a noise environment, a signal sequence with a small frequency deviation may have a second largest value judgment error, which may cause a frequency estimation error.
Disclosure of Invention
The invention improves and designs a precision measurement radar frequency measurement method based on frequency deviation classification aiming at the defects of the background technology, the method obtains the frequency shift quantity of radar signals based on the frequency deviation classification method, compares the frequency shift quantity with a reference threshold value, and the size of the reference threshold value is related to the magnitude of the second maximum value and the maximum value of the amplitude of the radar signals and is not a fixed value; judging a method for calculating the frequency of the center according to the frequency shift amount; improving measurement accuracy by using spectral translation to move away from the center of the main lobe; in the case of small frequency offset, the frequency is measured directly by the FFT.
The technical scheme of the invention is a frequency deviation classification-based precision measurement radar frequency measurement method, which comprises the following steps:
step 1: mixing the echo and the transmitted wave, and then passing through a filter to obtain a difference frequency signal;
step 2: FFT is carried out on the difference frequency signal to obtain the maximum value X (k) of the amplitude 0 ) And a second largest value X (k) 0 +r)；
When X (k) 0 +1)>X(k 0 -1), r =1; when X (k) 0 +1)≤X(k 0 -1)，r＝-1；
And 3, step 3: using the formula:
acquiring a frequency spectrum shifting value delta k; using the formula:
obtaining an estimated frequency f 1 (ii) a Wherein: f. of s Representing the sampling frequency, and N representing the number of FFT points;
and 4, step 4: obtaining a contrast frequency f 0 ：f 0 ＝f s .k/N(k∈[1,N])；
And 5: if f 1 -f 0 |<, 0.02 delta f, then the center frequency is assumed to be f e ＝f 0 Wherein Δ f = f s /N；
If f 1 -f 0 |>, 0.2 Deltaf, the central frequency f is determined e ＝f 1 ；
If 0.2. Delta. F ≧ f 1 -f 0 | ≧ 0.02 Δ f, multiplying the difference frequency signal obtained in step 1 by exp [ j2 π nr (1/2- Δ k)/N]Wherein n represents a serial number representing a discrete sequence, and FFT-transforming the translated signal to find a frequency corresponding to the maximum amplitude value, and identifying the frequency as a center frequency f e 。
Further, the method for acquiring the contrast frequency in step 4 is to acquire the maximum value X (k) of the amplitude in step 1 0 ) Corresponding frequency, which is the contrast frequency f 0 。
Compared with the existing method, the method for precisely measuring the radar frequency measurement based on frequency deviation classification obviously improves the measurement precision and the stability.
Drawings
The simulation condition for 1,2,3 is that the FFT point number is N =512 and the sampling frequency is set to fs =512khz. Beat signal frequency set to f IF ∈[30000,31000]Two by two with a difference of 10hz. 1000 Monte Carlo experiments were performed.
FIG. 1 shows the frequency measurement performance of the conventional RIFE method and frequency offset factor method when SNR is 5dB
FIG. 2 shows the frequency measurement performance of the conventional RIFE method and frequency offset factor method when SNR is-3 dB
FIG. 3 is a diagram showing the frequency measurement performance of the conventional M-RIFE method and frequency offset factor method when the SNR is 5dB
Detailed Description
A frequency deviation classification-based precision measurement radar frequency measurement method comprises the following steps:
step 1: mixing the echo and the transmitted wave, and then passing through a filter to obtain a difference frequency signal;
and 2, step: FFT is carried out on the difference frequency signal to obtain the maximum value X (k) of the amplitude 0 ) And a second largest value X (k) 0 +r)；
When X (k) 0 +1)>X(k 0 -1), r =1; when X (k) 0 +1)≤X(k 0 -1)，r＝-1；
And step 3: using the formula:
acquiring a frequency spectrum shifting value delta k; using the formula:
obtaining the estimated frequency f 1 (ii) a Wherein: f. of s Representing the sampling frequency, and N representing the number of FFT points;
and 4, step 4: obtaining a contrast frequency f 0 ：f 0 ＝f s .k/N(k∈[1,N])；
Step 5, if | f 1 -f 0 |<0.02Δf，f e ＝kΔf；
If f 1 -f 0 |>0.2Δf，f e ＝f IF ，
If 0.2. Delta. F ≧ f 1 -f 0 | ≧ 0.02 Δ f, mixing y (N) = x (N) · exp [ j2 π nr (1/2- Δ k)/N]FFT to obtain the maximum value Y (k) 1 ) And a second largest value Y (k) 1 +r 1 ) (ii) a Wherein r is 1 K is = + -1, the determination method is consistent with r 1 ∈[1,N](ii) a Obtaining the frequency f after the frequency spectrum shifting 2 ＝(k 1 +r 1 c 1 ) Δ f where c 1 ＝Y(k 1 +r 1 )/[Y(k 1 +r 1 )+Y(k 1 )](ii) a By f 2 Subtracting the shifting frequency and r (1/2-delta k) delta f to obtain the final frequency f e ＝[k 1 +r 1 c 1 -r(1/2-Δk)].Δf。
The invention is illustrated with reference to the accompanying drawings:
the method for precisely measuring radar frequency measurement based on the frequency deviation classification factor can ensure that the frequency deviation factor is between 0.2 delta f and 0.5 delta f after frequency shift, ensure that the amplitude of the maximum value after FFT is very close to the amplitude of the second maximum value, namely the amplitude difference between the second maximum value and the third maximum value is obvious, and under the condition of a certain signal-to-noise ratio, the condition of very large frequency estimation error caused by r positive and negative judgment error can not occur. In fig. 1,2, the quotient of the frequency error and the frequency error obtained by the conventional RIFE (conventional ratio method) and frequency offset factor method respectively under the condition of 5db snr is obtained, and when the frequency offset Δ k ∈ 0.5, -0.2 ∈ u [0.2,0.5], the two methods are essentially the same, and the measured results are the same. When the frequency deviation delta k belongs to (-0.2,0.2), the precision measurement radar frequency measurement algorithm based on frequency deviation factor classification is obviously improved in measurement precision and stability compared with the RIFE method. The frequency measurement precision of the frequency offset in delta k epsilon (-0.2,0.2) is 1.35 times to 13.23 times of that of the traditional interpolation frequency measurement algorithm, and the stability is 1.2 times to 6.3 times of that of the traditional interpolation frequency measurement algorithm. And noise immunity is good.
Fig. 3 is an absolute value of mean error of conventional M-RIFE and frequency offset factor method under the condition of SNR =5 dB. In the conventional frequency offset method, since the frequency offset factor is constant, the measurement accuracy of the corresponding signal for some frequencies is still very low in a certain noise environment. The frequency offset factor threshold is more accurate and fine, and the most suitable signal processing method is adopted for a specific region, so the measurement precision is high.
Claims (2)
1. A frequency deviation classification-based precision measurement radar frequency measurement method comprises the following steps:
step 1: mixing the echo and the transmitted wave, and then passing through a filter to obtain a difference frequency signal;
step 2: FFT is carried out on the difference frequency signal to obtain the maximum value X (k) of the amplitude 0 ) And a second largest value X (k) 0 +r)；
When X (k) 0 +1)＞X(k 0 -1), r =1; when X (k) 0 +1)≤X(k 0 -1)，r＝-1；
And step 3: using the formula:
acquiring a frequency spectrum shift value delta k; using the formula:
obtaining the estimated frequency f 1 (ii) a Wherein: f. of s Representing the sampling frequency, and N representing the number of FFT points;
and 4, step 4: obtaining a contrast frequency f 0 ：f 0 ＝f s .k/N，k∈[1,N]；
And 5: if f 1 -f 0 If | < 0.02 Δ f, the center frequency is determined to be f e ＝f 0 Wherein Δ f = f s /N；
If f 1 -f 0 If | > 0.2 Δ f, the center frequency f is determined e ＝f 1 ；
If 0.2. Delta. F ≧ f 1 -f 0 | ≧ 0.02 Δ f, multiplying the difference frequency signal obtained in step 1 by exp [ j2 π nr (1/2- Δ k)/N]Wherein n represents a serial number representing a discrete sequence, and FFT-transforming the translated signal to find a frequency corresponding to the maximum amplitude value, and identifying the frequency as a center frequency f e 。
2. The method of claim 1, wherein the step 4 of obtaining the contrast frequency is to obtain the maximum value of amplitude X (k) in step 1 0 ) Corresponding frequency, which is the contrast frequency f 0 。
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| US5497160A (en) * | 1993-09-17 | 1996-03-05 | Motorola, Inc. | Method and apparatus for improved auto-correlation and range correlation in pseudo-random noise coded systems |
| CN102353838A (en) * | 2011-06-30 | 2012-02-15 | 南京航空航天大学 | Rapid high precision frequency measuring realization method by applying FPGA chip |
| CN105158740A (en) * | 2015-08-24 | 2015-12-16 | 西安电子科技大学 | High-precision frequency estimation-based noise amplitude-modulation interference suppression method |
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| WO2006079181A1 (en) * | 2005-01-31 | 2006-08-03 | Genesys Design Pty Ltd | Frequency estimation |
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| US5497160A (en) * | 1993-09-17 | 1996-03-05 | Motorola, Inc. | Method and apparatus for improved auto-correlation and range correlation in pseudo-random noise coded systems |
| CN102353838A (en) * | 2011-06-30 | 2012-02-15 | 南京航空航天大学 | Rapid high precision frequency measuring realization method by applying FPGA chip |
| CN105158740A (en) * | 2015-08-24 | 2015-12-16 | 西安电子科技大学 | High-precision frequency estimation-based noise amplitude-modulation interference suppression method |
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