CN111624561B - Filtering method for discrete multi-target signal equalization - Google Patents

Filtering method for discrete multi-target signal equalization Download PDF

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Publication number
CN111624561B
CN111624561B CN202010337759.4A CN202010337759A CN111624561B CN 111624561 B CN111624561 B CN 111624561B CN 202010337759 A CN202010337759 A CN 202010337759A CN 111624561 B CN111624561 B CN 111624561B
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frequency
target
signal
filter
echo
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CN111624561A (en
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颜卫忠
胡鹏程
孔凡伟
钱婧怡
陈栋志
白旭东
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Shanghai Scientific Instrument Factory Co ltd
Shanghai Aerospace Electronics Co ltd
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Shanghai Scientific Instrument Factory Co ltd
Shanghai Aerospace Electronics Co ltd
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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
    • G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
    • G01S7/02—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S13/00
    • G01S7/40—Means for monitoring or calibrating
    • G01S7/4052—Means for monitoring or calibrating by simulation of echoes
    • G01S7/4056—Means for monitoring or calibrating by simulation of echoes specially adapted to FMCW
    • 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
    • G01S13/00—Systems using the reflection or reradiation of radio waves, e.g. radar systems; Analogous systems using reflection or reradiation of waves whose nature or wavelength is irrelevant or unspecified
    • G01S13/02—Systems using reflection of radio waves, e.g. primary radar systems; Analogous systems
    • G01S13/50—Systems of measurement based on relative movement of target
    • G01S13/52—Discriminating between fixed and moving objects or between objects moving at different speeds
    • G01S13/536—Discriminating between fixed and moving objects or between objects moving at different speeds using transmission of continuous unmodulated waves, amplitude-, frequency-, or phase-modulated waves
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A90/00—Technologies having an indirect contribution to adaptation to climate change
    • Y02A90/10—Information and communication technologies [ICT] supporting adaptation to climate change, e.g. for weather forecasting or climate simulation

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  • Engineering & Computer Science (AREA)
  • Radar, Positioning & Navigation (AREA)
  • Remote Sensing (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Physics & Mathematics (AREA)
  • General Physics & Mathematics (AREA)
  • Radar Systems Or Details Thereof (AREA)

Abstract

The embodiment of the invention provides a filtering method for discrete multi-target signal equalization, which is characterized in that through designing some parameters of a filter, beat signal frequencies corresponding to all targets are in a transition section of the filter, and passband frequencies of the filter are selected to be near to the maximum beat signal frequency, so that near targets attenuate greatly, far targets attenuate less, and the effect that echo amplitudes of targets at different distances are nearly consistent is realized.

Description

Filtering method for discrete multi-target signal equalization
Technical Field
The invention relates to the field of radar signal processing, in particular to a filtering method for discrete multi-target signal equalization.
Background
The Linear Frequency Modulation Continuous Wave (LFMCW) system has the characteristics of small volume, low cost, extremely high resolution, no distance blind area and being particularly suitable for short-distance application, and is attracting continuous attention.
For single targets or targets with more distinct speed discrimination, conventional approaches can be well discriminated. However, as the number of targets increases, the targets no longer appear as individual peaks in the frequency spectrum but are multiple; and because of the influence of signal attenuation, noise interference and the like, the difference of the echo amplitudes of targets at different distances is larger, namely, the echo amplitude of a target at a short distance is larger, the echo amplitude of a target at a long distance is smaller, and how to avoid the annihilation of a target at a long distance by a target at a short distance is a key problem in multi-target signal processing. However, since little research is done in the literature to date on this problem, it is necessary to develop methods that allow for the equalization of discrete multi-target echo signals.
Disclosure of Invention
The invention aims to provide a filtering method for discrete multi-target signal equalization, which is characterized by comprising the following steps:
step 1: according to the characteristics of the linear frequency modulation continuous wave radar, the target distance R can be calculated i Determining the frequency of the beat signal of the target echo
Wherein f i The frequency of the beat signal is B is the frequency modulation bandwidth, T is the frequency modulation period and c is the light speed.
According to the maximum target distance R max And a minimum target distance R min Calculating maximum and minimum beat frequencies
Step 2: according to different target distances R i Determining target echo signal amplitude A r,i
Let us assume radar cross section sigma of different targets i Equal, determining that the echo signal amplitude is inversely proportional to the square of the frequency according to the relation between the target distance and the echo signal amplitude and the beat signal frequency, namely A r,i ∝1/f i 2 The method comprises the steps of carrying out a first treatment on the surface of the Let the minimum distance (R min ) The echo amplitude of the target is 1, and the echo amplitudes of other targets are
Then the echo amplitude of the different frequencies is expressed as
Step 3: determining stop band frequency f of high pass filter stop And passband frequency f pass 。
Designing the stop band frequency of the high-pass filter to be less than the minimum beat signal frequency, i.e. f stop <f min The method comprises the steps of carrying out a first treatment on the surface of the Passband frequency f of a design high pass filter pass Approximating the maximum beat frequency as much as possible, e.g. meeting |f pass -f max |/f max ≤δ；
Step 4: determining that attenuation characteristics of a filter satisfy
p is the attenuation coefficient of the dc signal (f=0), p <1. The echo signal amplitude equalization of a plurality of targets can be realized by the target echo through a designed filter.
Preferably, in the step 3, the setting of the passband frequency includes: the passband frequency is greater than the maximum beat signal frequency f max I.e. all target beat signal frequencies lie in the transition section (f stop <f min <…<f max <f pass )。
Preferably, in the step 3, the setting of the passband frequency includes: to ensure that the attenuation of the echo signal of the furthest target in the filter is as small as possible, the passband frequency is set at the maximum beat signal frequency f max And the sub-maximum beat signal frequency f N-1 Between, i.e. f stop <f min <…<f N-1 <f pass ≤f max 。
Preferably, in order to ensure the best filter effect, a cascaded filter design is employed, taking into account that the beat signal frequency range of all targets exceeds an order of magnitude.
Preferably, after the step 3, the method further includes:
step 3a: assuming that N filters are designed, the linear segments of the N filter characteristic curves are expressed as:
after cascading a plurality of filters, the total filter characteristics are respectively
Substituting (22) into (23) to obtain the total filter characteristic
Preferably, the step 3a includes a step 3b:
and (3) cascading the filters determined in the step (3 a), and performing signal processing after the target echoes pass through the filters, so that echo signal amplitude equalization of a plurality of targets with scattered distances can be realized.
In the process of processing echo signals of triangular frequency modulation continuous waves, the invention provides a filtering method for equalizing discrete multi-target signals, and by the method, the equalization of each dispersed target echo signal can be well ensured, and the measurement of a plurality of target parameters is convenient to realize.
The beneficial effects of the invention include:
(1) Low frequency signal capable of filtering leakage
Aiming at the low-frequency triangle wave frequency component with leakage in the echo signal, a high-pass filter is adopted to effectively filter the low-frequency signal, so that the subsequent useful signal amplification and target observation are facilitated.
(2) Facilitating simultaneous measurement of multiple distance discrete objects
By designing a high-pass filter, the beat signal frequencies corresponding to all targets are in the transition section of the filter, namely the near target attenuation is large and the far target attenuation is small, so that the echo amplitude of targets with different distances is nearly consistent, and the method is beneficial to measuring a plurality of discrete targets with different distances.
(3) The hardware circuit can be repeatedly configured, and can meet various target test conditions.
Drawings
FIG. 1 is a schematic diagram of echo signals of targets at different distances according to the present invention.
FIG. 2 is a schematic diagram of the attenuation characteristics of the filter and the spectrum of echo signals corresponding to targets with different distances according to the present invention.
FIG. 3 is a graph showing the amplitude-frequency characteristics of N high-pass filters according to the present invention.
FIG. 4 is a schematic diagram showing the amplitude-frequency characteristics of a cascaded high-pass filter according to the present invention.
Fig. 5 is a spectrum diagram of a pre-filter echo signal according to the present invention.
FIG. 6 is a graph showing the amplitude-frequency characteristic of a cascaded high-pass filter according to the present invention.
Fig. 7 is a spectrum diagram of the pre-and post-filter echo signal in the present invention.
Fig. 8 is a flow chart of the method of the present invention.
Detailed Description
In order that the above-recited objects, features and advantages of the present invention will become more readily apparent, a more particular description of the invention will be rendered by reference to the appended drawings and appended detailed description.
The final implementation effect of the scheme is shown in fig. 4. According to the characteristics of the linear frequency modulation continuous wave radar, the frequency of a beat signal of a target echo and the amplitude of echo signals corresponding to targets with different distances can be determined according to the target distance. Parameters of the high-pass filter are designed so that beat signal frequencies corresponding to all targets are in a transition section of the filter, and therefore the echo amplitudes of targets with different distances are nearly consistent. If the frequency range of the beat signals of all targets is wider, a cascading filter design is adopted to ensure the best filter effect. The target echo is subjected to signal processing after passing through the cascade filter, so that echo signal amplitude equalization of a plurality of targets with scattered distances can be realized.
With reference to fig. 1-8, the specific implementation scheme of the present invention is as follows:
step 1: according to the characteristics of the linear frequency modulation continuous wave radar, the frequency of the beat signal of the ith target echo can be determined by the target distance R i Determination of
Wherein f i The frequency of the beat signal is B is the frequency modulation bandwidth, T is the frequency modulation period and c is the light speed.
According to the maximum target distance R max And a minimum target distance R min Calculating maximum and minimum beat frequencies
Step 2: according to different target distances R i Determining target echo signal amplitude A r,i
Assuming that radar scattering cross sections sigma of different targets are equal, according to the relation between the target distance and the echo signal amplitude and the beat signal frequency, the inverse proportion of the echo signal amplitude and the square of the frequency, namely A, can be determined r,i ∝1/f i 2 See fig. 1. Let the minimum distance target R be assumed to be N targets min The echo amplitude is 1, then the echo amplitude of other targets is
Then the echo amplitude of the different frequencies can be expressed as
Therefore, a high-pass filter can be designed, so that the beat signal frequencies corresponding to all targets are in the transition section of the filter, and the near-uniformity of the echo amplitudes of targets with different distances is basically realized.
Step 3: determining stop band frequency f of high pass filter stop And passband frequency f pass 。
Setting the stop band frequency of the high-pass filter to be less than the minimum beat signal frequency, i.e. f stop <f min . There are 2 schemes for the setting of passband frequencies: 1) The passband frequency is greater than the maximum beat signal frequency f max I.e. all target beat signal frequencies lie in the transition section (f stop <f min <…<f max <f pass ) The method comprises the steps of carrying out a first treatment on the surface of the 2) To ensure that the attenuation of the echo signal of the furthest target in the filter is as small as possible, the passband frequency is set at the maximum beat signal frequency f max And the sub-maximum beat signal frequency f N-1 Between, i.e. f stop <f min <…<f N-1 <f pass ≤f max See fig. 2.
Step 4: in view of the fact that the beat signal frequency range of all targets may exceed an order of magnitude, a cascaded filter design is employed to ensure optimal filter effect. Suppose that N filters are designed (fig. 3). It is noted that f in the figure k Is the passband frequency of each filter, not the beat frequency corresponding to the target k, and f N ＝f pass 。
The linear segments of the N filter characteristic curves can be expressed as:
after cascading a plurality of filters, the total filter characteristics are respectively
Substituting (23) into (24) yields the overall filter characteristics (FIG. 4)
Step 5: and (3) cascading the filters determined in the step (4), and performing signal processing after the target echo passes through the filters, so that echo signal amplitude equalization of a plurality of targets with scattered distances can be realized.
The technical scheme of the invention is described in the following by specific examples.
A filtering method for discrete multi-target signal equalization realizes discrete distributed target echo signal equalization through filter design. The technical scheme of the invention is further described in detail below by taking a triangular sweep signal with a center frequency of 24.125GHz and a bandwidth of 250MHz as an example. It should be noted that the present invention is not limited to 24GHz signals, but is a general method of designing a discrete multi-objective signal equalization filter. The simulation parameters are shown in table 1.
TABLE 1
Parameters (parameters) Numerical value
Sampling frequency f s 0.6MHz
FFT points N fft 2048
Frequency modulation period T 1ms
Signal to noise ratio SNR 15dB
Target 1 distance R 1 10m
Target 2 distance R 2 20m
Target 3 distance R 3 50m
Target 4 distance R 4 100m
The implementation flow is as follows:
step 1: according to the parameters of the linear frequency modulation continuous wave radar and the target distance R i Calculating the frequency f of the target echo beat signal i . The echo beat signal frequencies of the respective targets can be obtained according to the parameters of Table 1 as [ f ] 1 ,f 2 ,f 3 ,f 4 ]＝[16.67kHz,33.33kHz,83.33kHz,166.67kHz]. Thus, the minimum and maximum beat signal frequencies f min ＝16.67kHz，f max ＝166.67kHz。
Step 2: according to the distance R of different targets i Determining echo signal amplitude A r,i . Let the minimum distance target R min The echo amplitude is 1, and the echo amplitudes of the other 3 targets are A r,2 ＝0.25，A r,3 ＝0.04，A r,4 =0.01. To no oneThe fourier transform is performed on the superimposed signal of the target echo, the spectrum of which is shown in fig. 5. As can be seen, the spectral amplitude of the target decreases with increasing frequency, and the amplitude of the near (low frequency) target is much greater than the amplitude of the far (high frequency) target (80 times different), which will cause the far target to annihilate in noise, causing missed alerts.
Step 3: here we set f stop =10khz, for convenience, using scheme 1) set passband frequency, f pass =180 kHz. From the calculation, the maximum target echo amplitude differs from the minimum by 40dB, so the other parameters of the filter are as follows: the stop band amplitude is-50 dB, and the passband amplitude is 0dB.
Step 4: because the frequency range of the beat signal exceeds an order of magnitude, a segmented filter design is adopted to ensure the best filter effect. Here, we design 5 filters with parameters: (1) P is p 1 ＝0.1,f 1 ＝20kHz；(2)p 2 ＝0.1,f 2 ＝40kHz；(3)p 2 ＝0.12,f 2 ＝80kHz；(4)p 2 ＝0.15,f 2 ＝120kHz；(5)p 2 ＝0.15,f 2 =180 kHz. The amplitude-frequency characteristic of the cascaded high-pass filter is shown in fig. 6.
Step 5: and (3) carrying out signal processing on the target echo after passing through the filter, so as to realize the amplitude equalization of echo signals of a plurality of targets with scattered distances. Fourier transforming the filtered echo signal is performed, see fig. 7. Compared with the spectrum before filtering, the spectrum amplitude of 4 targets after filtering is relatively close, which is beneficial to the differentiation of different targets and the calculation of target information.
It will be apparent to those skilled in the art that various modifications and variations can be made to the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention also include such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.

Claims (6)

1. A method of filtering for discrete multi-target signal equalization, comprising the steps of:
step 1:according to the characteristics of the linear frequency modulation continuous wave radar, the target distance R can be calculated i Determining the frequency of the beat signal of the target echo
Wherein f i The frequency of the beat signal is B is the frequency modulation bandwidth, T is the frequency modulation period and c is the light speed;
according to the maximum target distance R max And a minimum target distance R min Calculating maximum and minimum beat frequencies
Step 2: according to different target distances R i Determining target echo signal amplitude A r,i
Let us assume radar cross section sigma of different targets i Equal, determining that the echo signal amplitude is inversely proportional to the square of the frequency according to the relation between the target distance and the echo signal amplitude and the beat signal frequency, namely A r,i ∝1/f i 2 The method comprises the steps of carrying out a first treatment on the surface of the Let the minimum distance R assuming N targets min The echo amplitude of the target is 1, and the echo amplitudes of other targets are
The echo amplitude of the different frequencies is expressed as
Step 3: determining stop band frequency f of high pass filter stop And passband frequency f pass ；
Designing the stop band frequency of the high-pass filter to be less than the minimum beat signal frequency, i.e. f stop <f min The method comprises the steps of carrying out a first treatment on the surface of the Passband frequency f of a design high pass filter pass As close as possible to the maximum beat frequency f max Satisfy |f pass -f max |/f max ≤δ；
Step 4: determining that attenuation characteristics of a filter satisfy
p is the attenuation coefficient of the direct current signal, and p is less than 1; the echo signal amplitude equalization of a plurality of targets can be realized by the target echo through a designed filter.
2. The filtering method for equalizing a discrete multi-target signal according to claim 1, wherein in said step 3, the setting of the passband frequency comprises: the passband frequency is greater than the maximum beat signal frequency f max I.e. all target beat signal frequencies are located in the transition section f of the filter stop <f min <…<f max <f pass 。
3. The filtering method for equalizing a discrete multi-target signal according to claim 1, wherein in said step 3, the setting of the passband frequency comprises: to ensure that the attenuation of the echo signal of the furthest target in the filter is as small as possible, the passband frequency is set at the maximum beat signal frequency f max And the sub-maximum beat signal frequency f N-1 Between, i.e. f stop <f min <…<f N-1 <f pass ≤f max 。
4. A method of filtering a discrete multi-target signal equalization as claimed in claim 1, wherein a cascaded filter design is employed to ensure optimum filter performance taking into account that the beat signal frequency range of all targets exceeds an order of magnitude.
5. The method of filtering discrete multi-target signal equalization as claimed in claim 4, further comprising, after said step 3:
step 3a: assuming N filters, the linear segments of the N filter characteristic curves are expressed as:
after cascading a plurality of filters, the total filter characteristics are respectively
Substituting (7) into (8) to obtain the total filtering characteristic;
6. the method of filtering discrete multi-target signal equalization as claimed in claim 5, wherein said step 3a is followed by step 3b:
and (3) cascading the filters determined in the step (3 a), and performing signal processing on the target echoes after passing through the filter bank, so that echo signal amplitude equalization of a plurality of targets with scattered distances can be realized.
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CN110118957A (en) * 2019-05-06 2019-08-13 上海航天电子有限公司 A kind of target matching method of the upper and lower frequency sweep of triangle CW with frequency modulation

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CN109270511A (en) * 2018-11-28 2019-01-25 深圳大学 Radar Signal Processing System and method based on FPGA and DSP
CN110118957A (en) * 2019-05-06 2019-08-13 上海航天电子有限公司 A kind of target matching method of the upper and lower frequency sweep of triangle CW with frequency modulation

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