CN110007296B - A Time Domain Interference Cancellation Method Based on Pilot Signal Correction - Google Patents

Abstract

The invention discloses a time-domain interference cancellation method based on pilot signal correction. The method comprises: using ocean noise n′ _k (t) actually recorded by a linear array as a pilot signal to obtain data after interference cancellation; The pilot signal outputs energy P _y′,n (θ) at the scanning angle θ; and uses P _y′,n (θ) as a correction factor to correct the output energy after the linear array interference cancellation. Compared with the original time domain interference cancellation method, the method of the present invention corrects it to form a "wide concave" or "convex" beam, and reduces the size of the linear array The difference of beamforming output signal energy reduces the influence of the original time-domain interference cancellation method on the target detection performance in the attenuation azimuth interval, improves the anti-interference performance and detection performance of the time-domain interference cancellation method, and provides a method for improving the performance of the time-domain interference cancellation method. a feasible solution.

Description

A Time Domain Interference Cancellation Method Based on Pilot Signal Correction

technical field

The invention relates to the field of sonar signal processing, in particular to a time-domain interference cancellation method based on pilot signal correction.

Background technique

In the data received by the line array, the real target signal is often masked by strong interference, which makes target detection and tracking very difficult. It is particularly important to study how to suppress strong interference and improve the detection ability of weak targets, especially when there is broadband interference.

In offsetting broadband interference, the blocking matrix method is often applied in engineering due to its small computational complexity. The method of the present invention was first used to solve the problem of signal mixing in the estimation of covariance matrix in beamforming, and then used for research on interference suppression. Also known as the interference blocking method (the present invention processes the interference in the time domain, also known as the "interference cancellation method in the time domain"). The interference blocking method is to suppress the interference of the predicted azimuth through the blocking matrix, which will cause a certain degree of freedom loss to the received data of the linear array, change the original shape of the received signal of the linear array, and reduce the detection performance of the target in some areas.

For the problem of beam distortion and detection blind area caused by the time-domain interference blocking method, the "wide concave" or "convex" beam formed by the interference blocking method in the present invention has nothing to do with its interference cancellation form. The data processing frequency band and the interference angle are related, and since the target signal azimuth θ ₁ is unknown in the actual data processing, it is impossible to correct the interference and cancel the influence on the beamforming output signal energy by simulating the target pilot signal. Therefore, a method based on simulated background noise as the pilot signal is proposed The modified time domain interference cancellation method realizes the correction of the output beam of the interference blocking method in the time domain, reducing the influence of the "wide concave" or "convex" beam on the target detection results, and the weak target in the original attenuation range. Implement detection. And through the numerical simulation and sea trial data processing results, it is verified that the method of the present invention reduces the energy difference of the output signal of the linear array beamforming when canceling the interference, reduces the original attenuation interval, and realizes beam correction. The inner weak target is detected and its detection performance is improved.

SUMMARY OF THE INVENTION

The purpose of the present invention is to solve the problems of beam distortion and detection blind area caused by the time-domain interference blocking method, and propose a time-domain interference cancellation method based on pilot signal correction.

In order to achieve the above purpose, the present invention proposes a time-domain interference cancellation method based on pilot signal _correction . Calculate the output energy P _y ′, _n (θ) of the pilot signal at the scanning angle θ from this; use P _y ′, _n (θ) as the correction factor to correct the output energy after the linear array interference cancellation.

As an improvement of the above method, the method specifically includes:

Step 1) The ocean noise n _k ′(t) actually recorded by the linear array is used as the pilot signal. At this time, the noise data x _k ′(t) picked up by the kth element of the linear array is expressed as:

x _k '(t)=n _k '(t),k=1,2,...,K

In the formula, K is the number of array elements of the linear array;

Step 2) Process the pilot signal as follows, and obtain the data y' _k (t) after interference cancellation, 1≤k≤K-1:

In the formula, θ ₀ is the interference angle, d is the spacing of the array elements, and c is the speed of sound;

Step 3) After the interference cancellation is obtained according to the beamforming process, the output energy of the pilot signal at the scanning angle θ is:

In the formula, τ _k =(k-1)d cosθ/c is the delay performed by the kth array element relative to the reference array element, and the reference array element is the first array element; T is the beamforming processing data sampling length;

Step 4) Using P _y′ , _n (θ) as the correction factor, the output energy after the linear array interference cancellation is corrected as follows:

The data x _k (t) picked up by the k-th element of the linear array is expressed as:

In the formula, n _k (t) is the additive white Gaussian noise picked up by the kth array element, n _k+1 (t) is the additive white Gaussian noise picked up by the k+1th array element, and s(t) is The signal is incident from the azimuth θ ₁ , and i(t) is the incident interference from the azimuth θ ₀ .

The advantages of the present invention are:

Compared with the original time domain interference cancellation method, the method of the present invention corrects it to form a "wide concave" or "convex" beam, and reduces the size of the linear array The difference of beamforming output signal energy reduces the influence of the original time-domain interference cancellation method on the target detection performance in the attenuation azimuth interval, improves the anti-interference performance and detection performance of the time-domain interference cancellation method, and provides a method for improving the performance of the time-domain interference cancellation method. a feasible solution.

Description of drawings

Fig. 1 is the structure schematic diagram of the tow line array sonar of the present invention;

Fig. 2 is the azimuth history diagram before interference cancellation;

Fig. 3 is the azimuth history diagram of the existing time domain interference cancellation method;

Fig. 4 is the orientation history diagram of the method of the present invention;

Figure 5 is a beam pattern (t=1s);

Fig. 6 is the azimuth history diagram before interference cancellation;

Fig. 7 is the azimuth history diagram of the existing time domain interference cancellation method;

Fig. 8 is the orientation history diagram of the method of the present invention;

Figure 9 is a beam pattern (t=160s).

Detailed ways

The present invention will now be further described with reference to the accompanying drawings.

Before the method of the present invention is described in detail, the receiving array to which the method of the present invention is applicable is described first. Figure 1 is a schematic diagram of the structure of a towed array sonar. The towed array sonar includes 6 parts, a display control and signal processor 1, a deck cable 2, a winch 3, a fairlead 4, a tow cable 5, and a receiving line array. 6. The receiving line array 6 is connected with the deck cable 2 located on the winch 3 through the towing cable 5, and the towing cable 5 is also installed on the fairlead 4; the signal received by the receiving line array 6 is transmitted to the display control and signal processing machine 1.

The method of the present invention will be further described below.

Time Domain Interference Cancellation Method

Next, take an interference and a target situation as an example to analyze and discuss them, and other situations can be traversed by this situation. At time t, relative to the direction of the head end of the equidistant linear array, there is a weak target s(t) incident from azimuth θ ₁ , and interference i(t) incident from azimuth θ ₀ , then the data picked up by the kth element of the linear array x _k (t) can be expressed as:

In the formula, 1≤k≤K is the number of linear array elements, d is the distance between the array elements, c is the speed of sound, and n _k (t) is the additive white Gaussian noise picked up by the kth element. Then the data x _k+1 (t) picked up by the k+1th array element at time t is

The delay time τ _k+1,k of the data picked up by the k+1th array relative to the data picked up by the kth array element, and then subtracted from the data picked up by the kth array element, the new data y _k (t) can be obtained as

It can be seen from the above formula that when the delay time τ _k+1,k is properly obtained, this method can completely cancel out the interference. When τ _k+1,k =dcosθ ₀ /c, the new data that can be obtained

Let each element of the line array pick up the same background noise power, and express y _k (t) in the frequency domain form as follows:

In the formula, w=2πf is the data angular frequency, and N _k (w) is the background noise power spectrum picked up by the kth array element.

It can be seen from the above formula that although the interference in y _k (t) is canceled in the ideal case, the target signal in y _k (t) is also distorted relative to the real target signal s(t). The variation of the target signal in s(t) will be discussed further below.

Analysis of target signal energy change

theoretical analysis

的变化。为了更直观分析时域干扰低消方法对波束形成输出波束影响，下面从线列阵波束形成输出信号和噪声变化上进行分析说明，以便得到改善时域干扰抵消方法。It can be seen from the previous analysis that after the time-domain interference is cancelled, the target signal is relatively different from the real target signal S(w).

The change. In order to more intuitively analyze the influence of the time-domain interference reduction method on the beamforming output beam, the following analysis is performed from the line array beamforming output signal and noise changes, so as to obtain an improved time-domain interference cancellation method.

Let the correlation between the interference, signal and background noise, and background noise and background noise picked up by each array element of the linear array be 0, which can be obtained from the beamforming process. Before the interference is canceled, the beam is formed at the scanning angle θ, θ∈[0° , 180°], the output signal and noise energy are respectively

In the formula, τ _k =(k-1)d cosθ/c is the beamforming, the delay performed by the kth array element relative to the reference array element (the first array element is selected as the reference array element in the present invention), and T is the primary processing Data sample length.

For better description, Equation (7) can be expressed in frequency domain as

In the formula, w _l is the lower limit of the filter used in data processing, w _h is the upper limit of the filter used in data processing, ( ) ^* is the conjugate function, and M is the length of the fast Fourier transform. Under the same background, N(w )=N _k (w) is the background noise power spectrum picked up by each array element.

In the same way, after the interference is cancelled, the beamforming output signal and noise energy at the scanning angle θ are respectively

Similarly, Equation (8) can be expressed in frequency domain as

当θ＝θ₁时，γ(w)＝β(w)。In the formula,

When θ= _θ1 , γ(w)=β(w).

Comparing Equation (7) and Equation (9), it can be seen that before and after interference cancellation, the change of beamforming output signal energy is related to γ ² (w), and the change of noise energy is related to β ² (w).

When the scanning angle θ=θ ₁ , equations (7) and (9) can be further expressed as

Comparing Equation (10) and Equation (11), it can be seen that before and after the interference cancellation, the beamforming output signal and noise energy change in the target direction θ ₁ can be expressed as

Equation (12) gives the function of varying degrees of variation of the beamforming output signal energy and noise energy caused by the time domain interference cancellation method; from this function, it can be known that the time domain interference cancellation method causes the beamforming output signal energy and noise energy. It is mainly related to γ ² (w), and its change trend is consistent. For established line arrays, γ ² (w) is mainly related to the data processing frequency band (wl , _wh ), the target azimuth θ ₁ and the interference azimuth _{θ 0 .}

A Time Domain Interference Cancellation Method Based on Pilot Signal Correction

theoretical analysis

Since the target signal azimuth θ ₁ is unknown in the actual data processing, it is impossible to correct the interference by simulating the target pilot signal to cancel the influence on the beamforming output signal energy. However, from the above theoretical analysis results, it can be seen that the change trends of the output signal energy and noise energy of the linear array beamforming before and after the interference cancellation are consistent. In this regard, the influence of the interference cancellation on the beamforming output signal energy can be corrected by simulating the background noise as the pilot signal, and then the interference cancellation method is used to cancel the pilot signal to obtain the variation trend of the output energy after interference cancellation, and then according to the variation trend of the output energy. Correct the effect of interference cancellation on the actual data after processing.

In order to truly simulate the influence law of interference cancellation on the output noise energy of the linear array beamforming, the present invention adopts the ocean noise n _k ′(t) actually recorded by the linear array as the pilot signal. At this time, the noise data x _k '(t) picked up by the k-th element of the linear array can be expressed as:

x _k ′(t)=n _k ′(t) (13)

According to the interference cancellation method shown above, the new data after interference cancellation can be obtained as

It can be obtained from the beamforming process. After the interference is cancelled, the beamforming output energy at the scanning angle θ is

Using P _y ′, _n (θ) as the correction factor, the output energy of equation (12) is corrected according to equation (20), so that the energy ratio of the output signal of the line array beamforming before and after cancellation of the time domain interference is approximately 1, That is, the correction method can effectively reduce the influence of the time-domain interference cancellation method on the output signal energy of the linear array beamforming.

The method of the present invention (referred to as the method of the present invention) has obvious advantages compared with the method in the prior art (referred to as the time-domain interference cancellation method).

Below in conjunction with examples, the effect of the method of the present invention and the related methods in the prior art are compared.

In order to further verify that the correction method can effectively reduce the influence of the time-domain interference cancellation method on the output signal of the linear array beamforming, the following numerical simulation analysis is carried out.

Let the frequency bands of the interference and target signals be [100Hz, 200Hz], the azimuth angles of the interference and the target are θ ₀ =60° and θ ₁ =63°, the background noise is Gaussian white noise with a bandwidth of [100Hz, 200Hz], and the speed of sound is c =1500m/s, the array element spacing d=4m, and the array element number is K=64. The target-to-interference spectral level ratio is -20dB, and the target-to-background noise spectral level ratio is -15dB. Figures 2 to 5 are obtained in the frequency band [100Hz, 200Hz] by different methods.

As can be seen from Figure 2 to Figure 5, when canceling the interference, the time-domain interference cancellation method will form a "convex" beam, which will cause varying degrees of attenuation to the signal energy output by the linear array beamforming, and weak targets cannot be effectively detected after interference cancellation. And the simulation background noise of the present invention as a pilot signal change trend is consistent with the change trend of the beam after the time domain interference cancellation, using the simulated background noise as a pilot signal to correct the time domain interference cancellation method, reducing the time domain interference cancellation method. Due to the influence of the output signal energy of the linear array beamforming, when the interference is canceled, the weak targets in the original attenuation range can be effectively detected. Numerical simulation results verify that the method of the present invention can effectively reduce the time domain interference cancellation attenuation interval by using simulated noise as a pilot signal, and realize beam correction. When canceling strong interference, it can effectively detect weak targets in the original attenuation range.

Sea trial data processing

The length of the processed measured data is 160s, and the sampling rate used is f _s =5kHz. The filter frequency band is [80Hz, 250Hz], and the filter order is 256. Figures 6 to 9 are obtained by different methods.

It can be seen from Fig. 6 to Fig. 9 that when the interference is canceled, since the time-domain interference cancellation method will cause different degrees of attenuation to the energy of the output target signal from the linear array beamforming, the weak target after cancellation cannot be effectively detected; and the method of the present invention The simulated background noise is used as the pilot signal to correct the time-domain interference cancellation method, which reduces the influence of the time-domain interference cancellation method on the output target signal energy of the linear array beamforming. , 140 ° ~ 100 ° weak moving targets are well detected. The processing results of the experimental data 2 verify that the method of the present invention reduces the time-domain interference cancellation attenuation interval through the pilot signal, and realizes the beam correction. When the interference is canceled, the weak target in the original attenuation range can be effectively detected.

Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the embodiments, those of ordinary skill in the art should understand that any modification or equivalent replacement of the technical solutions of the present invention will not depart from the spirit and scope of the technical solutions of the present invention, and should be included in the present invention. within the scope of the claims.

Claims (1)

1. A method for time domain interference cancellation based on pilot signal modification, the method comprising:

marine noise n 'actually recorded by adopting linear array'_k(t) as a pilot signal to obtain interference-cancelled data; thereby calculating the output energy P of the pilot signal at the scanning angle theta_y′,_n(θ); with P_y′,_n(theta) as a correction factor to correct the output energy after the interference cancellation of the linear array;

the method specifically comprises the following steps:

step 1) actually recorded marine noise n 'by adopting linear array'_k(t) as a pilot signal, at this time, noise data x 'picked up by the k-th array element of the linear array'_k(t) is expressed as:

x′_k(t)＝n′_k(t),k＝1,2,…,K

in the formula, K is the array element number of the linear array;

step 2) processing the pilot signal according to the following formula to obtain data y 'after interference cancellation'_k(t),1≤k≤K-1：

In the formula, theta₀D is the array element interval, and c is the sound velocity;

and 3) after interference cancellation is obtained according to the beam forming process, the output energy of the guide signal on the scanning angle theta is as follows:

in the formula, τ_kD cos theta/c is the time delay of the kth array element relative to a reference array element, wherein the reference array element is the first array element; t is the sampling length of the beam forming processing data;

step 4) Using P_y′,_n(θ) as a correction factor, correcting the output energy after the line array interference cancellation according to the following formula:

θ∈[0°,180°]

data x picked up by k-th array element of linear array_k(t) is expressed as:

in the formula, n_k(t) additive white Gaussian noise picked up for the kth array element, n_k+1(t) additive white Gaussian noise picked up by the (k + 1) th array element, and s (t) from the orientation theta₁Incident signal, i (t) being from the azimuth θ₀Incident interference.

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