A method for slice forwarding signal detection and suppression based on coded waveforms

Abstract

The application provides a slice forwarding signal detection and suppression method based on coded waveform, which comprises the following steps: step one, coded waveform design; signal coding modulation is performed to change the frequency spectrum characteristics; step two, radar signal and coded waveform emission strategy; originally, in each pulse repetition interval (PRI) of the radar, only a linear frequency modulation signal is emitted; after the coded waveform is introduced, in each PRI, a linear frequency modulation signal and a coded waveform are emitted in sequence; step three, echo segmentation processing; for the received echo, the echo is divided into a linear frequency modulation echo s r1 (t) and a coded waveform echo s r2 (t), and segmented matched filter processing is performed; step four, slice forwarding signal range image reconstruction and suppression; according to the characteristics of the coded waveform echo range image, the range image of the slice forwarding signal is reconstructed, then the range image of the linear frequency modulation echo is subtracted to obtain the range image of the target echo, and the suppression of the slice forwarding signal is realized.

Description

Technical field

[0001] The present invention belongs to the field of radar countermeasures, and specifically relates to anti-slicing forwarding signal technology, in particular to detecting and suppressing slicing forwarding signals based on coded waveforms. [Background Technology]

[0002] The principle of slice forwarding signals is to sample a small segment of the signal and then forward it, repeating this process until the entire radar signal ends, so that the slice forwarding signal and the echo arrive at the receiving antenna almost at the same time. Due to the partial correlation between the slice forwarding signal and the transmitted signal, it will form a large number of false targets after pulse compression, which will seriously affect the radar's target detection, recognition and other functions. Existing methods to counter slice forwarding signals are mainly divided into receiving-end signal processing methods and transmitting-end waveform design methods. The receiving-end signal processing methods are mainly based on filtering, interference reconstruction and suppression, but there are problems such as over-reliance on the accuracy of interference segment detection and low interference suppression performance. The transmitting-end waveform design method has problems such as long calculation time and limited waveform design freedom.

[0003] The present invention utilizes a coding waveform to detect false targets formed by slice forwarding signals, and accurately reconstructs the range image of the slice forwarding signal based on the relationship between the coding waveform and the range image of the linear frequency modulation signal, thereby quickly suppressing the slice forwarding signal. [Summary of the invention]

[0004] The technical problem to be solved by the present invention is: for the false targets formed by the slice forwarding signal, a coding waveform is designed to realize the detection of the false targets; and the relationship between the coding waveform and the range image of the linear frequency modulation signal is used to reconstruct the range image of the slice forwarding signal, and subtract it from the original range image to realize the suppression of the slice forwarding signal.

[0005] The present invention proposes a method for detecting and suppressing slice forwarding signals based on coded waveforms, and the technical solutions adopted are as follows:

[0006] The first step is coding waveform design.

[0007] Coded modulation of a signal can alter its spectral characteristics. The coded control signal can be represented as p1(t), where each symbol has the same width and an amplitude of 1 or -1. Multiplying the coded control signal by the transmitted signal yields the corresponding coded waveform. If the linear frequency modulated signal transmitted by the radar is s(t), the coded waveform can be represented as s(t)·p1(t).

[0008] The second step is the radar signal and coded waveform transmission strategy.

[0009] Originally, radars only transmitted a linear frequency modulation signal in each pulse repetition interval (PRI). However, with the introduction of coded waveforms, the linear frequency modulation signal and the coded waveform are transmitted sequentially in each PRI.

[0010] The third step is echo segmentation processing.

[0011] For the received echo, it is divided into linear frequency modulation echo s r1 (t) and coded waveform echo s r2 (t), and perform segmented matched filtering. If the matched filter is h(t), the pulse pressure output of the linear frequency modulation echo part is y1(t) = s r1 (t)*h(t), where "*" represents the convolution operation. The pulse pressure output of the echo portion of the coded waveform is y2(t)=s r2 (t)*h(t).

[0012] The fourth step is to reconstruct and suppress the range image of the slice forwarding signal.

[0013] According to the characteristics of the coded waveform echo range image, the range image of the slice forwarding signal is reconstructed, and then subtracted from the linear frequency modulation echo range image to obtain the range image of the target echo, thereby achieving the suppression of the slice forwarding signal.

[0014] The beneficial effects of the present invention are:

[0015] First, by utilizing the characteristics of the coded waveform, it is possible to accurately detect whether the system is interfered with by the slice forwarding signal and the location of the false target, providing a basis for suppressing the slice forwarding signal.

[0016] Second, by using the relationship between the coded waveform range image and the linear frequency modulation range image, the range image of the slice forwarding signal is accurately reconstructed, and then subtracted from the linear frequency modulation range image to suppress the slice forwarding signal. The advantages of this method are fast calculation speed and high performance.

Brief Description of the Drawings

[0017] Figure 1 It is a flow chart of a specific embodiment of the technical solution provided by the present invention.

[0018] Figure 2 It is a linear frequency modulation signal and a coded waveform echo.

[0019] Figure 3 is the linear frequency modulation echo range image.

[0020] Figure 4 It is the range image of the coded waveform echo.

[0021] Figure 5It is the linear frequency modulation echo range image after suppressing the slice forwarding signal. [Specific implementation method]

[0022] The present invention will be further described below with reference to the accompanying drawings. Figure 1 As shown, the specific implementation process is:

[0023] The first step is coding waveform design.

[0024] The coded control signal p1(t) can be expressed as:

[0025]

[0026] Where δ(·) is the impulse function; t is time; n is the encoding cycle number; T s1 is the encoding period; τ1 is the length of time in each period when the amplitude is 1, so the duty cycle D1 = τ1 / T s1 , which represents the proportion of time with an amplitude of 1 in one cycle; * represents the convolution operation; rect(·) is the rectangular function:

[0027]

[0028] The spectrum corresponding to formula (1) is:

[0029]

[0030] Where f is the frequency, f s1 =1 / T s1 , sinc(x)=sin(πx) / (πx), let D1=0.5, then formula (3) can be further simplified as:

[0031]

[0032] Assume that the linear frequency modulation signal emitted by the radar is s(t), then the coded waveform is s(t)·p1(t), and its spectrum is:

[0033]

[0034] Where S(f) represents the spectrum of s(t). According to the characteristics of the linear frequency modulation signal, S(f) is not zero when -B / 2≤f≤B / 2, and is approximately zero at other times. B is the bandwidth of the linear frequency modulation signal. From formula (5), we can see that when f s1 When f > B, the spectrum of the coded waveform is 0 when -B / 2≤f≤B / 2.

[0035] The second step is the radar signal and coded waveform transmission strategy.

[0036] The strategy for using coded waveforms to counter slice forwarding signals is as follows: in each PRI, a linear frequency modulation signal is first transmitted, and then a coded waveform is transmitted after a certain guard time (at least τ2, the definition of τ2 is described later). The characteristics of the two waveforms are combined to achieve the purpose of target detection and anti-interference.

[0037] The third step is echo segmentation processing.

[0038] According to the transmission strategy in the second step, in each PRI, a linear frequency modulation echo s can be obtained. r1 (t) and coded waveform echo s r2 (t). Their echo contains the target's echo and the slice forwarding signal,

[0039] That is s r1 (t) = s rt1 (t)+s rj1 (t), s r2 (t) = s rt2 (t)+s rj2 (t), where s rti (t) represents the target echo, s rji (t) represents interference, i=1 represents a linear frequency modulation echo, and i=2 represents a coded waveform echo.

[0040] If the linear frequency modulation echo s r1 The output of matched filtering on (t) is y1(t), which can be expressed as:

[0041] y1(t)=s r1 (t)*h(t)=s rt1 (t)*h(t)+s rj1 (t)*h(t) (6)

[0042] Where h(t)=s * (-t) is a matched filter, and the superscript "*" is a conjugate operation. rt1 (t)*h(t) is the actual range image of the target, s rj1 (t)*h(t) is the distance image of the slice forwarding signal, which needs to be suppressed. The following is for s rj1 (t)*h(t) is derived.

[0043] s rj1 (t) can be expressed as:

[0044] s rj1 (t)=c0·s(t-t0)·p2(t-t0) (7)

[0045] Where t0 represents the delay caused by the target at distance R0, c0 represents the amplitude of the slice forwarding signal, and p2(t) is the control signal for generating the slice forwarding signal:

[0046]

[0047] Among them, T s2 is the sampling period; τ2 is the sampling pulse width in each period, so the duty cycle D2=τ2 / T s2 It represents the ratio of the sampling pulse width to the sampling period, and its spectrum can be expressed as:

[0048]

[0049] Among them, f s2 =1 / T s2 .

[0050] s rj1 (t)*h(t) can be expressed as:

[0051]

[0052] Wherein, IFFT{·} denotes inverse fast Fourier transform, P2(f) is the spectrum of p2(t), and H(f) is the spectrum of h(t).

[0053] Formula (10) can be further expanded to calculate:

[0054]

[0055] If the coded waveform echo s r2 The output of matched filtering on (t) is y2(t), which can be expressed as:

[0056] y2(t)=s r2 (t)*h(t)=s rt2 (t)*h(t)+s rj2 (t)*h(t) (12)

[0057] Among them, s rt2 (t)*h(t) is the actual range image of the target, s rj2 (t)*h(t) is the range image of the slice forwarding signal, and the spectrum of h(t) is H(f)=S * (f), for s rt2 Further calculation of (t)*h(t) yields:

[0058]

[0059] According to the properties of linear frequency modulation, S(f) and S *The spectrum of (f) is concentrated at -B / 2≤f≤B / 2, when f s1 When >B, formula (13) is almost equal to 0. At this time, it can be approximately considered that:

[0060]

[0061] When f s1 =Nf s2 When , simplify P1(f)*P2(f):

[0062]

[0063] Let nN+m=r, then formula (15) can be further simplified:

[0064]

[0065] Substituting formula (16) into formula (14),

[0066]

[0067] Comparing formula (14) and formula (17), it can be seen that the range image of the coded waveform echo and the range image of the slice forwarding signal part in the linear frequency modulation echo have the same false target position. Therefore, the true and false targets in the linear frequency modulation echo range image can be judged by the coded waveform range image.

[0068] The fourth step is to reconstruct and suppress the range image of the slice forwarding signal.

[0069] Formula (11) and formula (17) not only illustrate that the position of the false target in the coded waveform range image and the linear frequency modulation range image is equal, but also reveal the amplitude and phase relationship of the false target of the same order. Therefore, the false target at the corresponding position can be generated by constructing linear frequency modulation signals with different frequency shifts, and then compensated according to the amplitude and phase relationship of formula (11) and formula (17) to generate the range image of the slice forwarding signal for interference suppression.

[0070] Take the suppression of -r order false targets in the linear frequency modulation range image as an example. First, read out the position R0 and amplitude A0 of the 0 order false target in the coded waveform range image, and use t0 = 2R c / C calculates t0, where C is the propagation speed of electromagnetic waves.

[0071] Next, construct a frequency shift rf s2 Linear frequency modulation signal Its matched filter output is expressed as J r ′(t),

[0072]

[0073] When r = 0, the peak amplitude of J0′(t) is |J0′(t) max , from formula (17) and formula (18), we can know;

[0074]

[0075] The amplitude phase coefficient to be compensated is expressed as A r , according to formula (11):

[0076]

[0077] The compensated -r order false target is expressed as J r (t);

[0078] J r (t) = A r ·J r ′(t) (21)

[0079] The range image of the slice forwarding signal finally reconstructed is The slice forwarding signal can be suppressed according to the following formula:

[0080]

[0081] Among them, y T (t) is the linear frequency modulation range image after suppressing the slice forwarding signal, which is different from the actual range image s of the target obtained using the linear frequency modulation signal. rt1 (t)*h(t) are approximately equal.

[0082] The following are the results of simulation experiments using the present invention.

[0083] Linear frequency modulation signal pulse width T p = 40μs, bandwidth is B = 5MHz, there are two targets, the distances between the targets and the radar are 60km and 60.45km respectively, the target scattering intensity is the same, and the first target can interfere with the radar by slicing the forwarding signal. The sampling period of the slicing forwarding signal is T s2 =0.8μs, duty cycle is D2=0.2. Encoding waveform encoding period T s1 =0.1μs, duty cycle D1=0.5, signal-to-interference ratio is -20dB, and signal-to-noise ratio is 5dB.

[0084] Figure 2 This is a linear frequency modulation signal (left) and the echo of the coded waveform in the PRI (right), which includes the target echo and the slice forwarding signal. After matching the linear frequency modulation signal echo, we can get Figure 3As shown in the range image, it can be seen that when the signal-to-interference ratio is -20dB, the amplitude of the false target formed by the slice forwarding signal is stronger than the real target, making it difficult to distinguish between the real and false targets. Figure 4 The range image shown. The true target peak of the coded waveform is almost 0, and only the range image formed by the slice forwarding signal can be seen in its range image, which is consistent with the derivation of formula (14). In addition, compared Figure 3 and Figure 4 It can be seen that the position of the false target is the same, so it can be determined by Figure 4 Detected Figure 3 True and false targets. Figure 5 This is the result of reconstructing the range profile of the slice forwarding signal and subtracting it from the chirp echo range profile to achieve interference suppression. As can be seen, the interference in the range profile is suppressed, and two peaks of real targets appear, located at 60 km and 60.45 km, respectively, which matches the simulation parameters.

Claims

1. A method for detecting and suppressing slice forwarding signals based on coded waveforms, characterized in that: The steps are as follows: Step 1: coding waveform design; The signal is coded and modulated to change its spectral characteristics. The coded control signal is represented by p1(t), where each code element has the same width and an amplitude of 1 or -1. The coded control signal is multiplied by the signal to be transmitted to obtain the corresponding coded waveform. If the linear frequency modulation signal transmitted by the radar is s(t), the coded waveform is represented by s(t)·p1(t). Step 2: radar signal and coded waveform transmission strategy; Originally, the radar only transmitted a linear frequency modulation signal in each pulse repetition interval (PRI). After the coded waveform was introduced, the linear frequency modulation signal and the coded waveform were transmitted successively in each PRI. Step 3: echo segmentation processing; For the received echo, it is divided into linear frequency modulation echo s r1 (t) and coded waveform echo s r2 (t), and perform segmented matched filtering processing; if the matched filter is h(t), the pulse pressure output of the linear frequency modulation echo part is y1(t)=s r1 (t)*h(t), where "*" represents the convolution operation; the pulse pressure output of the echo portion of the coded waveform is y2(t)=s r2 (t)*h(t); Step 4: Slice forwarding signal range image reconstruction and suppression; Based on the characteristics of the coded waveform echo range image, the range image of the slice forwarding signal is reconstructed, and then subtracted from the linear frequency modulation echo range image to obtain the range image of the target echo, thereby suppressing the slice forwarding signal; In step 1, the coded control signal p1(t) is expressed as: Where δ(·) is the impulse function; t is time; n is the encoding cycle number; T s1 is the encoding period; τ1 is the length of time in each period when the amplitude is 1, so the duty cycle D1 = τ1 / T s1 , which represents the proportion of time with an amplitude of 1 in one cycle; * represents the convolution operation; rect(·) is the rectangular function:

2. The method for detecting and suppressing slice forwarding signals based on coded waveforms according to claim 1, wherein: The spectrum corresponding to formula (1) is: Where f is the frequency, f s1 =1 / T s1 , sinc(x)=sin(πx) / (πx), let D1=0.5, then formula (3) is simplified to:

3. The method for detecting and suppressing slice forwarding signals based on coded waveforms according to claim 2, wherein: Assume that the linear frequency modulation signal emitted by the radar is s(t), then the coded waveform is s(t)·p1(t), and its spectrum is: Where S(f) represents the spectrum of s(t). According to the characteristics of the linear frequency modulation signal, S(f) is not 0 when -B / 2≤f≤B / 2, but is 0 at other times. B is the bandwidth of the linear frequency modulation signal. According to formula (5), when f s1 When f > B, the spectrum of the coded waveform is 0 when -B / 2≤f≤B / 2.

4. The method for detecting and suppressing slice forwarding signals based on coded waveforms according to claim 1, wherein: In step 2, in each PRI, a linear frequency modulation signal is first transmitted, and then a coded waveform is transmitted after a certain guard time. The characteristics of the two waveforms are combined to achieve the purpose of target detection and anti-interference.

5. The method for detecting and suppressing slice forwarding signals based on coded waveforms according to claim 3, wherein: In step three, s r1 (t) = s rt1 (t)+s rj1 (t), s r2 (t) = s rt2 (t)+s rj2 (t), where s rti (t) represents the target echo, s rji (t) represents interference, i=1 represents a linear frequency modulation echo, and i=2 represents a coded waveform echo.

6. The method for detecting and suppressing slice forwarding signals based on coded waveforms according to claim 5, characterized in that: If the linear frequency modulation echo s r1 The output after matched filtering of (t) is y1(t), which is expressed as: y1(t)=s r1 (t)*h(t)=s rt1 (t)*h(t)+s rj1 (t)*h(t) (6) Where h(t)=s * (-t) is a matched filter, and the superscript "*" is a conjugate operation; s rt1 (t)*h(t) is the actual range image of the target, s rj1 (t)*h(t) is the range image of the slice forwarding signal, which needs to be suppressed; s rj1 (t) is expressed as: s rj1 (t)=c0·s(t-t0)·p2(t-t0) (7) Where t0 represents the delay caused by the target at distance R0, c0 represents the amplitude of the slice forwarding signal, and p2(t) is the control signal for generating the slice forwarding signal: Among them, T s2 is the sampling period; τ2 is the sampling pulse width in each period, so the duty cycle D2=τ2 / T s2 It represents the ratio of the sampling pulse width to the sampling period, and its spectrum is expressed as: Among them, f s2 =1 / T s2 ; s rj1 (t)*h(t) is expressed as: where IFFT{·} denotes inverse fast Fourier transform, P2(f) is the spectrum of p2(t), and H(f) is the spectrum of h(t); Formula (10) is further expanded to calculate:

7. The method for detecting and suppressing slice forwarding signals based on coded waveforms according to claim 6, characterized in that: If the coded waveform echo s r2 The output after matched filtering of (t) is y2(t), which is expressed as: y2(t)=s r2 (t)*h(t)=s rt2 (t)*h(t)+s rj2 (t)*h(t) (12) Among them, s rt2 (t)*h(t) is the actual range image of the target, s rj2 (t)*h(t) is the range image of the slice forwarding signal, and the spectrum of h(t) is H(f)=S * (f), for s rt2 (t)*h(t) is further calculated to obtain: According to the properties of linear frequency modulation, S(f) and S * The spectrum of (f) is concentrated in -B / 2≤f≤B / 2, When f s1 When >B, formula (13) is equal to 0, and it is considered that: When f s1 =Nf s2 When , simplify P1(f)*P2(f): Let nN+m=r, then formula (15) is further simplified: Substituting formula (16) into formula (14), 8. The method for detecting and suppressing slice forwarding signals based on coded waveforms according to claim 7, characterized in that: In step 4, the position R0 and amplitude A0 of the 0th order false target in the coded waveform range image are read out, and t0 is calculated by t0=2R0 / C, where C is the propagation speed of the electromagnetic wave; The frequency shift is rf s2 Linear frequency modulation signal Its matched filter output is expressed as J r ′(t), When r = 0, the peak amplitude of J′0(t) is |J′0(t)| max , from formula (17) and formula (18), we can get; 9. The method for detecting and suppressing slice forwarding signals based on coded waveforms according to claim 8, characterized in that: The amplitude phase coefficient to be compensated is expressed as A r , according to formula (11): The compensated -r order false target is expressed as J r (t); J r (t)=A r ·J′ r (t) (21) The range image of the slice forwarding signal finally reconstructed is Slice forwarding signal suppression: Among them, y T (t) is the chirp range image after suppressing the slice forwarding signal.

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