CN108490411B - Method for inhibiting color clutter in target detection - Google Patents
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- 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
The invention discloses a method for inhibiting color clutter in target detection, which adds a waveform design of code modulation in a multi-cycle target detection signal according to cycles, designs a phase code with sharp autocorrelation characteristic, can adopt a spread spectrum pseudo-random code or a non-pseudo-random code, and is beneficial to separating target echoes and inhibiting clutter by decoding during target detection. The decoding method on the column item of the echo pulse pressure matrix can inhibit the interference of the noise on the slow time dimension of the MTD. The step of spread spectrum code modulation and decoding in Moving Target Detection (MTD) can be before the pulse pressure step, and can also be after the pulse pressure step and before the FFT step. The method can inhibit the interference of narrow-band, low-frequency, stable or non-stable color clutter on target detection, and can obtain better clutter inhibition effect without estimating a clutter map and a clutter model of a known environment and a complex filter bank.
Description
Technical Field
The invention relates to a method for suppressing color clutter in target detection, in particular to a method for suppressing the color clutter in the target detection by adopting a spread spectrum code modulation Frequency Modulation Continuous Wave (FMCW) radio signal and a decoding process.
The method can effectively improve the color clutter resistance in target detection without priori knowing a color clutter model or performing clutter map accumulation estimation, and is suitable for the complex environments such as slow target detection or through-wall target detection in a clutter environment.
Background
Although the clutter originates from the transmitted signal itself, due to the terrain and environmental factors, part of the signals are overlapped at the receiver end after a large amount of scattering processes, forming clutter which has poor correlation with the original signal and even is independent, but the clutter itself has time correlation, namely color clutter.
Due to the low moving speed of the ground or sea surface target and the complex clutter scene caused by environmental reflection, the target detection is difficult. Moving Target Indication (MTI) and Moving Target Detection (MTD) algorithms are two major radar clutter suppression techniques. MTI suppresses static or slowly varying clutter by subtracting pulses of subsequent cycles, but the MTI approach implicitly does not take into account the bandwidth of the clutter spectrum, resulting in slow target signals also being subtracted. The MTD makes up the defects of the MTI in signal detection, is a moving target detection technology designed according to the optimal filter theory, and is considered to consist of the MTI and a pulse coherent accumulation Doppler filter. The pulse Doppler detection (PD) method is also used for ground target detection, but the clutter rejection principle is similar to the former two, and the filtering processing is still carried out by utilizing the Doppler frequency difference between the target and the clutter, thereby achieving the purposes of clutter suppression and moving target display.
In the aspect of anti-clutter technology in recent years, the clutter map detection method obtains the estimation of the clutter intensity by iterating the echo of the previous multiple scanning of the detection unit, utilizes the relative stationarity of the clutter environment time domain, and is not easily influenced by the nonstationary clutter at the ground clutter or the land-sea boundary; by the clutter Doppler model, the clutter covariance matrix and the clutter suppression projection matrix can be constructed, ground clutter and sea clutter which accord with the model can be effectively suppressed, and the influence of a specific clutter environment and non-stationarity can be still achieved.
CN101089653B "short-range frequency modulation continuous wave FMCW radar anti-interference method", in which pseudo-random code modulation is performed based on FMCW waveform to solve the mutual interference problem when multiple radars are working simultaneously, the method has similarity to the present application in terms of wave pattern, but the radar processing method and process are different from the solved problem, and do not play a role in suppressing color clutter by MTD.
Using linear frequency modulationNumber (LFM) is taken as an example, and the detection signal is in the form of
As shown in (r) of fig. 1, where N is the number of repeated pulses, μ is the LFM chirp rate, and T is the pulse repetition period. The distance between pulses is omitted from the signal formula, since the output representation is not affected.
The conventional MTD method is:
firstly, pulse pressure in a pulse period is carried out on the signal to obtain N periods of range gate pulse, and the nth period of range unit signal is set as xi，n＝pi，n+Ci，nI-0, …, L-1, N-0, …, N-1, wherein Ci，nIs the clutter and noise component, pi，nIs an echo signal component;
secondly, all the N periods of the distance unit signal xi，nArranged in an NxL matrix
FFT transformation of the column terms (also referred to as slow time dimension sample signals):
after the FFT, an N × L "range-doppler frequency" matrix is obtained.
When a moving or stationary object is present, a higher amplitude pulse y is obtained at the corresponding range i and velocity (doppler frequency) k positionsi，k. In the environment of color clutter, color clutter Ci，nFrequency interference can be generated on a distance-Doppler frequency plane, and particularly, a low-speed moving target echo y is generated in a low-frequency clutter environment such as ground clutter or sea clutteri，kThe signal is easily swamped by clutter and cannot be resolved.
Disclosure of Invention
The invention provides a method for suppressing color clutter in target detection by adding a waveform design of code modulation to multi-cycle pulse of target detection and adding a decoding process in an echo MTD (maximum transmission digital) detection process aiming at ground or sea surface low-speed target detection with color clutter. The method is characterized in that the uncorrelated of clutter signals and target echo signals is utilized, an MTD method based on Frequency Modulated Continuous Wave (FMCW) pulse pressure is mainly used, slow time dimension spread spectrum codes are added into the MTD signals, color clutter is suppressed through decoding or 'de-spreading' processing in detection, and clutter suppression is not influenced by clutter characteristics and clutter non-stationarity.
The invention relates to a method for inhibiting color clutter in target detection, which aims to inhibit the interference of the color clutter on a distance-Doppler frequency plane, and phase coding is carried out on a slow time dimension signal through waveform design, so that the slow time dimension signal is separated from a clutter signal through decoding or de-spreading.
The invention relates to a method for inhibiting color clutter in target detection, which comprises the following concrete steps:
(1) the waveform design of code modulation is added to a multicycle target detection signal according to periods, and a phase code c with sharp autocorrelation characteristics is designed2(N), N is 0, 1, … N-1, the phase code is spread spectrum pseudo random code or non pseudo random code, similar to LFM code c2(n)＝exp(jπηn2) Eta 1/NT, and c2(n)·c2(n)*1, ", denotes conjugation;
(2) taking the chirp signal LFM as an example, the detection signal is set as:
wherein N is the number of the repetitive pulses, mu is the LFM frequency modulation slope, T is the pulse repetition period, and the phase coding is carried out in the slow time dimension of the original detection signal;
(3) assuming that echo signals r (T) (s (T) + c (T)), c (T) are clutter and noise, consistent with the conventional MTD method, the echo is firstly subjected to pulse pressure and sampling in a period T, and a distance unit signal of the nth period is obtained as xi，n＝c2(n)pi，n+Ci，nI-0, …, L-1, N-0, …, N-1, wherein Ci，nIs a clutter and noise component;
(4) all will beN periods of range bin signal xi，nArranged in an NxL matrix
As will be shown below, in the following,
column item xi，n(N-0, 1, …, N-1) decoding: c. C2(n)*·xi，nOr may be called despreading, such that xi，nSignal part of
Is restored to pi，n，pi，nIs an echo signal component;
and the noise part of the clutter is c2(n)*·Ci，nThe method is equivalent to spreading the spectrum of the clutter, inhibits the interference of the color clutter, and can inhibit low-frequency clutter and non-stationary clutter as long as the spectrum width of the clutter is less than 1/T, and particularly can effectively inhibit the influence of the low-frequency clutter such as ground or sea clutter and the like on slow-moving targets such as walking, sailing and the like;
in addition, this step may be performed before step (3), and the echo signal may be decoded in a pulse cycle:
wherein N is the number of repetitive pulses, mu is the LFM frequency modulation slope, and T is the pulse repetition period;
(5) FFT is carried out on the decoded column item signals, and the decoded column item signals are consistent with MTD processing, two-dimensional output of range-Doppler frequency (speed) can be obtained, and the color clutter is expanded in the Doppler frequency dimension, so that the interference of the color clutter on Doppler frequency signals is reduced.
In the method of the present invention, steps (2) and (4) are the core of the present invention, and are distinguished from the conventional MTD target detection method.
The method for inhibiting the color clutter in the target detection is characterized in that a waveform design of code modulation is added into a multi-period target detection signal according to periods, a phase code with a sharp autocorrelation characteristic is designed, and a spread spectrum pseudo-random code or a non-pseudo-random code can be adopted, so that the target echo can be separated and the clutter can be inhibited through decoding during the target detection. The decoding method on the column item of the echo pulse pressure matrix can inhibit the interference of the noise on the slow time dimension of the MTD. The step of spread spectrum code modulation and decoding in Moving Target Detection (MTD) can be before the pulse pressure step, and can also be after the pulse pressure step and before the FFT step.
The invention relates to a method for inhibiting color clutter in target detection, which is used for inhibiting the color clutter in the target detection by a Frequency Modulation Continuous Wave (FMCW) signal modulated by spread spectrum codes and adding a decoding process into MTD processing of an echo, thereby inhibiting the interference of narrow-band, low-frequency, stable or non-stable color clutter on the target detection. The method can obtain better clutter suppression effect without estimating clutter maps and clutter models of known environments and without complex filter banks.
Drawings
FIG. 1 is a schematic diagram of a periodic FMCW pulse encoding;
in the figure, a Frequency Modulated Continuous Wave (FMCW) signal having a period T is shown;
spread spectrum coding c with sharp autocorrelation2(n)·N；
Coded FMCW modulated signal after coding.
Detailed Description
The present invention will be described in further detail with reference to the following examples and drawings, but the present invention is not limited thereto.
Examples
A method for suppressing color clutter in target detection specifically comprises the following steps:
(1) the waveform design of code modulation is added to a multicycle target detection signal according to periods, and a phase code c with sharp autocorrelation characteristics is designed2(N), N is 0, 1, … N-1, the phase code is spread spectrum pseudo random code or non pseudo random code, similar to LFM code c2(n)＝exp(jπηn2) Eta 1/NT, and c2(n)·c2(n)*1, "+" indicates conjugation, as shown in fig. 1;
(2) taking the chirp signal LFM as an example, the detection signal is set as:
wherein N is the number of repetitive pulses, mu is the LFM frequency modulation slope, T is the pulse repetition period, and phase encoding is carried out in the slow time dimension of the original detection signal, as shown in the third in FIG. 1;
(3) assuming that echo signals r (T) (s (T) + c (T)), c (T) are clutter and noise, consistent with the conventional MTD method, the echo is firstly subjected to pulse pressure and sampling in a period T, and a distance unit signal of the nth period is obtained as xi，n＝c2(n)pi，n+Ci，nI-0, …, L-1, N-0, …, N-1, wherein Ci，nIs a clutter and noise component;
(4) all N periods of range bin signal xi，nArranged in an NxL matrix
As will be shown below, in the following,
column item xi，n(N-0, 1, …, N-1) decoding: c. C2(n)*·xi，nAnd thus xi，nSignal part of
Is restored to pi，n，pi，nIs an echo signal component;
and the noise part of the clutter is c2(n)*·Ci，nIt is equivalent to spread spectrum and suppress clutter spectrumThe interference effect of the color clutter is achieved, and as long as the clutter spectrum width is less than 1/T, the interference effect of the color clutter on low-frequency clutter and non-stationary clutter can be suppressed, and especially the influence of the low-frequency clutter such as ground or sea clutter and the like on slow-moving targets such as walking, boat-going and the like can be effectively suppressed;
in addition, this step may be performed before step (3), and the echo signal may be decoded in a pulse cycle:
wherein N is the number of repetitive pulses, mu is the LFM frequency modulation slope, and T is the pulse repetition period;
(5) FFT is carried out on the decoded column item signals, and the decoded column item signals are consistent with MTD processing, two-dimensional output of range-Doppler frequency (speed) can be obtained, and the color clutter is expanded in the Doppler frequency dimension, so that the interference of the color clutter on Doppler frequency signals is reduced.
By adopting the method, a clutter map and a clutter model of a known environment do not need to be estimated, and a good clutter suppression effect can be obtained without a complex filter bank.
Claims (2)
1. A method for suppressing color clutter in target detection is characterized by comprising the following steps:
(1) the waveform design of code modulation is added to a multicycle target detection signal according to periods, and a phase code c with sharp autocorrelation characteristics is designed2(N), N is 0, 1, … N-1, the phase code is spread spectrum pseudo random code or non pseudo random code, similar to LFM code c2(n)＝exp(jπηn2) Eta 1/NT, and c2(n)·c2(n)*1, ", denotes conjugation;
(2) taking the chirp signal LFM as an example, the detection signal is set as:
in which N is a repetitive pulseThe number, mu is LFM frequency modulation slope, T is pulse repetition period, and phase coding is carried out in the original detection signal slow time dimension;
(3) assuming that echo signals r (T) (s (T) + c (T)), c (T) are clutter and noise, consistent with the conventional MTD method, the echo is firstly subjected to pulse pressure and sampling in a period T, and a distance unit signal of the nth period is obtained as xi，n＝c2(n)pi，n+Ci，nI-0, …, L-1, N-0, …, N-1, wherein Ci，nIs a clutter and noise component;
(4) all N periods of range bin signal xi，nArranged in an NxL matrix
As will be shown below, in the following,
column item xi，n(N-0, 1, …, N-1) decoding: c. C2(n)*·xi，nAnd thus xi，nSignal part of
Is restored to pi，n，pi，nIs an echo signal component;
and the noise part of the clutter is c2(n)*·Ci，nThe method is equivalent to spreading the clutter spectrum, inhibits the interference of the color clutter, and can inhibit low-frequency clutter and non-stationary clutter as long as the clutter spectrum width is less than 1/T;
(5) and performing FFT on the decoded column item signals, wherein the FFT is consistent with MTD processing, two-dimensional output of range-Doppler frequency can be obtained, and the color clutter is expanded in the Doppler frequency dimension, so that the interference of the color clutter on Doppler frequency signals is reduced.
2. The method of suppressing color clutter in target detection according to claim 1, wherein: the step (4) may be performed before the step (3), and the echo signal is decoded according to the pulse period:
where N is the number of repetitive pulses, μ is the LFM chirp rate, and T is the pulse repetition period.
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| CN1224503A (en) * | 1996-05-08 | 1999-07-28 | 小格雷里A·安德鲁斯 | Radar/sonar system concept for extended range-doppler coverage |
| CN101017203A (en) * | 2006-09-26 | 2007-08-15 | 南京大桥机器有限公司 | Portable X wave range Doppler weather radar signal processing method and device thereof |
| CN101231339A (en) * | 2008-02-22 | 2008-07-30 | 东南大学 | Method for implementing uniform period repetition phase encoding continuous-wave radar diversity impulse |
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