CN110007294B - Time domain interference cancellation method based on energy compensation - Google Patents

Time domain interference cancellation method based on energy compensation Download PDF

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CN110007294B
CN110007294B CN201810008728.7A CN201810008728A CN110007294B CN 110007294 B CN110007294 B CN 110007294B CN 201810008728 A CN201810008728 A CN 201810008728A CN 110007294 B CN110007294 B CN 110007294B
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interference cancellation
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郑恩明
陈新华
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Institute of Acoustics CAS
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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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    • G01S7/52—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00
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Abstract

The invention discloses a time domain interference cancellation method based on energy compensation, which comprises the following steps: first, according to the data processing bandwidth [ wl,wh]Scan angle theta and interference azimuth angle theta0Constructing an energy compensation factor; then, preprocessing the line array pickup data by utilizing a time domain interference cancellation method to obtain data after interference cancellation; and finally, compensating the wave beam after the interference cancellation by using the energy compensation factors of the output signals before and after the interference cancellation to obtain the output wave beam. Compared with the original time domain interference cancellation method, the method corrects the formed wide concave or convex beam, reduces the energy difference of the output signal formed by the linear array beam, 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 the detection performance of the time domain interference cancellation method, and provides a feasible scheme for improving the performance of the time domain interference cancellation method.

Description

Time domain interference cancellation method based on energy compensation
Technical Field
The invention relates to the field of sonar signal processing, in particular to a time domain interference cancellation method based on energy compensation.
Background
In the linear array receiving data, the real target signal is often covered by strong interference, so that the target detection and tracking are very difficult. It is important to study how to suppress strong interference and improve the detection capability of weak targets, especially when there is broadband interference.
In the field of canceling broadband interference, the blocking matrix method is often applied in engineering due to small computation amount, is used for solving the problem of signal mixing in covariance matrix estimation in beamforming at the earliest time, and is then used for research in interference suppression, which is hereinafter referred to as an interference blocking method (processing interference in the time domain, which is also referred to as a "time domain interference cancellation method"). The interference blocking method realizes the interference suppression of the predicted azimuth through the blocking matrix, can cause certain degree of freedom loss on the linear array receiving data, changes the original form of the linear array receiving signals and reduces the detection performance of the target in partial intervals. The time domain interference blocking method may cause beam distortion and detection blind spot problems.
Disclosure of Invention
The invention aims to solve the problems of beam distortion and detection blind areas caused by a time domain interference blocking method, and provides a time domain interference cancellation method based on energy compensation according to the fact that a 'wide concave' or 'convex' shaped beam formed by the interference blocking method is irrelevant to the interference cancellation form of the beam and is only relevant to a data processing frequency band and an interference angle under the condition of knowing a linear array. And the numerical simulation and sea test data processing results verify that the method reduces the energy difference of output signals formed by linear array wave beams when the interference is counteracted, reduces the original attenuation interval, realizes wave beam correction, realizes detection of weak targets in the original attenuation interval and improves the detection performance.
In order to achieve the above object, the present invention provides a time domain interference cancellation method based on energy compensation, the method comprising:
first, according to the data processing bandwidth [ wl,wh]Scan angle theta and interference azimuth angle theta0Constructing an energy compensation factor; then, preprocessing the line array pickup data by utilizing a time domain interference cancellation method to obtain data after interference cancellation; and finally, compensating the wave beam after the interference cancellation by using the energy compensation factors of the output signals before and after the interference cancellation to obtain the output wave beam.
As an improvement of the above method, the method specifically comprises:
step 1) processing a frequency band [ w ] according to datal,wh]Scan angle theta and disturberAngle of orientation theta0And calculating an energy compensation factor alpha (theta) of the output signals before and after the interference cancellation according to the following formula:
Figure BDA0001539546170000021
Figure BDA0001539546170000022
in the formula, d is the array element interval, and c is the sound velocity;
step 2) preprocessing the picked data of the linear array according to the following formula to obtain data y after interference cancellationk(t),1≤k≤K-1：
Figure BDA0001539546170000023
In the formula, K is the number of linear array elements, and K is the total number of linear array elements; tau isk+1,kDelay time, n, for the k +1 th array pick-up data relative to the k array element pick-up datak(t) additive white Gaussian noise picked up for the kth array element, nk+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, xk(t) is the data picked up by the k-th array element of the linear array, and is expressed as:
Figure BDA0001539546170000024
xk+1(t) is the data picked up by the k +1 th array element at time t, and is expressed as
Figure BDA0001539546170000025
Step 3) compensating the wave beam after the interference cancellation by using the energy compensation factor alpha (theta) of the output signals before and after the interference cancellation obtained in the step 1), and obtaining an output wave beam:
Figure BDA0001539546170000031
wherein T is the cumulative length of the beamforming time,
Figure BDA0001539546170000032
2 Δ θ is the uncompensated interference cancellation width.
The invention has the advantages that:
1. compared with the original time domain interference cancellation method, the method corrects the formed wide concave or convex beam, reduces the energy difference of the output signal formed by the linear array beam, 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 the detection performance of the time domain interference cancellation method, and provides a feasible scheme for improving the performance of the time domain interference cancellation method;
2. the numerical simulation and sea test data processing result verify that the method reduces the energy difference of output signals formed by linear array wave beams when the interference is counteracted, reduces the original attenuation interval, realizes wave beam correction, realizes detection of weak targets in the original attenuation interval and improves the detection performance.
Drawings
Fig. 1 is a schematic view of a towed-line sonar structure according to the present invention;
FIG. 2 is a diagram of azimuth history before interference cancellation;
FIG. 3 is a diagram of an azimuth history of a prior art time-domain interference cancellation method;
FIG. 4 is an azimuth history chart of the time domain interference cancellation method of the present invention;
fig. 5 is a beam pattern with t ═ 1 s;
FIG. 6 is a diagram of azimuth history before interference cancellation;
FIG. 7 is a diagram of an azimuth history of a prior art time-domain interference cancellation method;
FIG. 8 is an azimuth history chart of the time domain interference cancellation method of the present invention;
fig. 9 shows a beam pattern with t equal to 15 s.
Detailed Description
The invention will now be further described with reference to the accompanying drawings.
Before describing the method of the present invention in detail, a description will be given of a receiving array to which the method of the present invention is applied. Fig. 1 is a schematic structural diagram of a towed array sonar, which comprises 6 parts, a display control and signal processor 1, a deck cable 2, a winch 3, a cable guide frame 4, a towing cable 5 and a receiving linear array 6. The linear receiver array 6 is connected with a deck cable 2 on a winch 3 through a towing cable 5, and the towing cable 5 is also arranged on a cable guide frame 4; the signal received by the receiving linear array 6 is transmitted to the display control and signal processor 1.
The process of the present invention is further illustrated below.
Time domain interference cancellation method
Next, an interference and a target situation are taken as an example and analyzed and discussed, and other situations can be traversed by the situation. At time t, relative to the head end direction of the equidistant linear array, a weak target s (t) is arranged from the direction theta1Incident, disturbance i (t) from azimuth θ0Incident, then the data x picked up by the k-th array element of the linear arrayk(t) can be expressed as:
Figure BDA0001539546170000041
in the formula, K is the number of linear array elements, and K is the total number of linear array elements; d is array element spacing, c is sound velocity, nkAnd (t) is additive white Gaussian noise picked by the kth array element. The (k + 1) th array element picks up data x at time tk+1(t) is:
Figure BDA0001539546170000042
delaying the (k + 1) th array pick-up data relative to the (k) th array element pick-up data by a time tauk+1,kThen subtracting the picked data of the kth array element to obtain new data yk(t) is:
Figure BDA0001539546170000043
from the above equation it can be seen that: when the time is delayed byk+1,kWhen the method is right, the interference can be completely cancelled. When tau isk+1,k＝dcosθ0C, new data available:
Figure BDA0001539546170000044
make each array element of the linear array pick up the background noise power equal, will yk(t) is expressed in the frequency domain as:
Figure BDA0001539546170000051
where w is 2 pi f is the data angular frequency, Nk(w) is the background noise power spectrum.
From the above formula, although in the ideal case ykThe interference in (t) is cancelled, but ykThe target signal in (t) is also distorted with respect to the true target signal s (t). The variation of the target signal in s (t) will be discussed further below.
Target signal energy change analysis
Theoretical analysis
It can be known from the analysis of the above theory that after the time domain interference is cancelled, the target signal is generated relative to the real target signal s (w)
Figure BDA0001539546170000052
A change in (c). In order to more intuitively analyze the effect of the time domain interference cancellation method on the beamformed output beam, the following analysis is made from the variation of the linear array beamformed output signals to obtain an improved time domain interference cancellation method.
The correlation between interference, signal and background noise picked up by each array element of linear array and between background noise and background noise is 0, and can be obtained by beam forming process, before interference is counteracted, the beam is formed on scanning angle theta, theta is formed into [0 deg. and 180 deg. ], and the energy of output signal is
Figure BDA0001539546170000053
In the formula, τkThe beam forming is performed by (k-1) d cos θ/c, where T is the length of one processed data sample, and the delay of the kth array element relative to the reference array element (the 1 st array element is selected as the reference array element in the present invention).
For better illustration, equation (6) may be expressed in a frequency domain form as
Figure BDA0001539546170000054
In the formula, wlLower limit of filter used for data processing, whUpper limit of filter for data processing, (-)*For the conjugate function, M is the fast Fourier transform length, S (w) is the power spectrum of the target radiation signal
Similarly, after interference cancellation, the beam forming outputs a signal energy of
Figure BDA0001539546170000061
Also, equation (8) can be expressed in the frequency domain form as
Figure BDA0001539546170000062
In the formula (I), the compound is shown in the specification,
Figure BDA0001539546170000063
comparing the equations (7) and (9), it can be seen that the energy of the output signal of the beam forming varies with γ before and after the interference cancellation2(w) are related. When the scanning angle theta is equal to theta1When the formula (7) and the formula (9) can be further represented by
Figure BDA0001539546170000064
Figure BDA0001539546170000065
Comparing equation (10) and equation (11), it can be seen that the beam is formed in the target direction θ before and after the interference cancellation1The energy variation of the upper output signal can be expressed as
Figure BDA0001539546170000066
The equation (12) gives the function of varying the energy of the output signal of the beam forming by the time-domain interference cancellation method to different degrees; from the function, the time domain interference cancellation method mainly changes the energy of the output signal of the beam forming and the gamma2(w) are related. For establishing linear arrays, γ2(w) Primary and data processing bands [ w ]l,wh]Target azimuth angle θ1And the interference azimuth angle theta0It is related.
Time domain interference cancellation method based on energy compensation
Theoretical analysis
Due to the orientation theta of the target signal in the actual data processing1Unknown, the effect of interference cancellation on the energy of the beamformed output signal cannot be compensated for by the analog target signal. The impact of interference cancellation on the energy of the beamformed output signal can be compensated for by the post-interference cancellation signal energy attenuation curve. The method comprises the following specific steps:
step 1) processing a frequency band [ w ] according to datal,wh]Scan angle theta and interference azimuth angle theta0According to formula (13), the energy variation factor of the output signal before and after the interference cancellation is obtained
Figure BDA0001539546170000071
Step 2) preprocessing the picked data of the linear array according to the formula (4) to obtain data y after interference cancellationk(t),1≤k≤K-1。
Step 3) at the scanning angle theta, obtaining the output beam formed by the beam after interference cancellation according to the formula (14)
Figure BDA0001539546170000072
In the case where the correlation between the signal and the noise, the noise and the noise is 0. Formula (14) can be further represented as
Figure BDA0001539546170000073
In the formula, NkAnd (w) is the power spectrum of the background noise picked up by the kth array element.
In the same context, let N (w) be Nk(w) for the background noise power spectrum picked up by each array element, further processing equation (15) can be obtained
Figure BDA0001539546170000081
And 4) compensating the beam after the interference cancellation according to the formula (17) by using the energy change factor alpha (theta) of the output signal before and after the interference cancellation obtained by the formula (13) to form an output beam
Figure BDA0001539546170000082
Compensating the output beam of the interference cancellation method by using alpha (theta) as an energy compensation factor, and when the scanning angle theta is equal to theta1When, the formula (18) can be changed to
Figure BDA0001539546170000083
In the formula, theta0For the interference cancellation angle, 2 Δ θ is the uncompensated interference cancellation width.
As shown in the equation (18), the output beam of the interference cancellation method is compensated by the energy compensation factor, and the energy of the compensated beam forming output signal is only related to the signal itself and already related to gamma2And (w) is irrelevant, so that the influence of the time domain interference cancellation method on the energy of the output signal formed by the linear array beam is effectively improved.
At this time, after the interference cancellation is obtained by equation (18), the system space gain at the target position is:
Figure BDA0001539546170000091
the method (referred to as the method herein for short) of the present invention has obvious advantages compared with the method (referred to as the time domain interference cancellation method for short) in the prior art.
The effect of the method of the present invention and the related method of the prior art are compared with each other by way of example.
In order to further verify that the method can effectively reduce the influence of the time domain interference cancellation method on the linear array beam forming output signals, the following numerical simulation analysis is carried out.
Make the frequency bands of interference and target signal both [1000Hz,2000Hz]The interference and the target azimuth are respectively theta030 ° and θ136 ° and background noise bandwidth [1000Hz,2000Hz °]The sound velocity of white gaussian noise is 1500m/s, the array element distance d is 0.5m, and the number of array elements K is 32. The target to interference spectral level ratio is-10 dB and the target to background noise spectral level ratio is-15 dB. FIGS. 2 to 5 are performed by different methods in the frequency bands [1000Hz,2000Hz ]]And (4) obtaining.
As can be seen from fig. 2 to 5, when the interference is cancelled, because the time-domain interference cancellation method forms a "convex" shaped beam, the signal energy output by the linear array beam formation is attenuated to different degrees, and the weak target after the interference cancellation cannot be effectively detected; the energy compensation factor variation trend is consistent with the beam variation trend after time domain interference cancellation, the time domain interference cancellation method is compensated by the energy compensation factor, the influence of the time domain interference cancellation method on the energy of the output signal formed by linear array beam formation is reduced, and weak targets in the original attenuation interval can be effectively detected when the interference is cancelled. The numerical simulation result verifies that the method can effectively reduce the time domain interference cancellation attenuation interval through energy compensation, and realizes beam correction. When strong interference is counteracted, effective detection can be realized on weak targets in the original attenuation interval.
Sea test data processing
The test data is 2016. the target detection test is carried out in south China sea. The test uses 32-element horizontal line array receiving signals, the array interval is 0.5m, and the tail end direction of the horizontal line array is set to be 180 degrees.
The length of the processed measured data is 200s, and the sampling rate is fs20 kHz. The filter has a frequency band of 1000Hz,2000Hz]The filter order is 256, the number of interference cancellations is 1, and fig. 6 to 9 are obtained by different methods.
As can be seen from fig. 6 to 9, θ is offset0When the interference moves within 100-120 degrees, because the time domain interference cancellation method can form a wide concave beam, the target signal energy output by the linear array beam forming is attenuated to different degrees, and theta in the attenuation region1The target at 100-120 degrees can not be effectively detected; the energy compensation factor has the same variation trend with the beam variation trend after time domain interference cancellation, the time domain interference cancellation method is compensated by the energy compensation factor, the influence of the time domain interference cancellation method on the energy of the output signal formed by the linear array beam is reduced, and the theta in the original attenuation region is positioned when the interference is cancelled1Weak targets at 100-120 deg. are effectively detected. The experimental data processing result verifies that the method reduces the time domain interference cancellation attenuation interval through energy compensation and realizes beam correction. When the interference is counteracted, the weak target in the original attenuation area can be effectively detected.

Claims (1)

1. A method of time-domain interference cancellation based on energy compensation, the method comprising:
first, according to the data processing bandwidth [ wl,wh]Scan angle theta and interference azimuth angle theta0Constructing an energy compensation factor; then, preprocessing the line array pickup data by utilizing a time domain interference cancellation method to obtain data after interference cancellation; finally, compensating the wave beam after the interference cancellation by using energy compensation factors of output signals before and after the interference cancellation to obtain an output wave beam;
the method specifically comprises the following steps:
step 1) processing a frequency band [ w ] according to datal,wh]Scan angle theta and interference azimuth angle theta0Is represented by the following formulaCalculating an output signal energy compensation factor alpha (theta) before and after interference cancellation:
Figure FDA0002569052010000011
Figure FDA0002569052010000012
in the formula, d is the array element interval, and c is the sound velocity;
step 2) preprocessing the picked data of the linear array according to the following formula to obtain data y after interference cancellationk(t),1≤k≤K-1：
Figure FDA0002569052010000013
In the formula, K is the number of linear array elements, and K is the total number of linear array elements; tau isk+1,kDelay time, n, for the k +1 th array pick-up data relative to the k array element pick-up datak(t) additive white Gaussian noise picked up for the kth array element, nk+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, xk(t) is the data picked up by the k-th array element of the linear array, and is expressed as:
Figure FDA0002569052010000014
xk+1(t) is the data picked up by the k +1 th array element at time t, and is expressed as
Figure FDA0002569052010000015
Step 3) compensating the wave beam after the interference cancellation by using the energy compensation factor alpha (theta) of the output signals before and after the interference cancellation obtained in the step 1), and obtaining an output wave beam:
Figure FDA0002569052010000021
wherein T is the cumulative length of the beamforming time,
Figure FDA0002569052010000022
2 Δ θ is the uncompensated interference cancellation width.
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