A target range image false peak elimination method based on slice modulation design

Abstract

The present application relates to a kind of target range image false peak elimination methods based on slice modulation design, comprising: first, slice modulation sequence design.Second, forwarding signal and target echo segmented pulse compression.Third, forwarding signal parameter estimation.Fourth, amplitude compensation and range image false peak cancellation.The beneficial effects of the present application mainly include: first, two kinds of slice modulation signals are designed, respectively modulate linear frequency modulation signal processing, increase the complexity of signal.Second, the superposition signal model of slice modulation echo and forwarding echo is built, and segmented pulse compression processing of echo is realized.Third, the range image obtained by two segmented pulse compression processing is used to estimate the parameter of forwarding control signal.Fourth, using the characteristics of forwarding control signal and slice modulation signal, realize false peak amplitude compensation, realize false peak elimination by range image cancellation, obtain accurate target range image.

Description

Technical field

[0001] The present invention relates to a method for eliminating false peaks of a target range image based on slice modulation design, belongs to the field of radar signal processing, and specifically relates to a method for performing high-speed slice modulation design on a linear frequency modulation signal, and utilizing echo range image amplitude compensation and cancellation to eliminate false peaks of the range image and obtain target information. [Background Technology]

[0002] The linear frequency modulated pulse signal is forwarded in segments. The radar will receive the target echo and forwarded signal. After matched filtering, false peaks will appear in the target range image, affecting the radar target detection performance. In order to suppress the target false peaks, [Reference [1] Yang Xiaopeng, Han Bowen, Wu Xuchen, Long Teng. Intermittent sampling forwarding interference identification method based on short-time fractional Fourier transform [J]. Signal Processing, 2019, 35(6): 1002-1010.] By extracting the interference time-frequency domain characteristic parameters, the forwarding parameters are effectively extracted, providing a parameter basis for false peak suppression. [Reference [2] Cao F, Chen ZH, Feng XW, et al. Optimal design of anti-interrupted sampling repeater jamming waveform for missile-borne radar based on an improved genetic algorithm [J]. IET Signal Processing. 2021, 15(9): 1751-9675.] Using the chaotic sequence to initialize the population, the orthogonal phase coded waveform was designed by genetic algorithm to achieve false peak suppression in the forwarded echo range image. In general, the methods for suppressing target false peaks mainly focus on forwarding parameter estimation, transmission signal optimization design, etc., but the accuracy of parameter estimation is limited by the signal-to-noise ratio, and the convex optimization algorithm and genetic algorithm used in the transmission signal optimization design have slow convergence speed. [Summary of the invention]

[0003] To address these issues, the present invention proposes a method for eliminating false peaks in target range profiles based on slicing modulation. By slicing radar pulses, both uniform and non-uniform slicing methods can be employed to rapidly generate a large number of transmit signals with varying characteristics. Furthermore, slicing sequence design and echo processing can be used to eliminate false peaks in the target range profile, thereby obtaining an accurate target range profile and enabling target information extraction.

[0004] The present invention designs two slicing sequences with different amplitudes to modulate radar pulses respectively, and eliminates false peaks of range images caused by segmented forwarding at the receiving end through range image cancellation to obtain accurate target information.

[0005] In summary, the technical problem to be solved by the present invention is: to realize the modulation of radar pulses by two high-speed slicing sequences, eliminate the problem of false peaks in the target range image caused by segmented forwarding of radar pulses, and finally obtain an accurate target range image.

[0006] The present invention provides a method for eliminating false peaks of target range images based on slice modulation design, and the technical solution adopted is as follows:

[0007] The first step is slice modulation sequence design.

[0008] Slice modulation of the radar pulse signal can be achieved through a slice sequence with amplitude 0 and amplitude 1, and the slice modulation signal can be obtained as u1(t)

[0009]

[0010] Where δ(·) is the impulse function; n is the number of segmented samples of the entire pulse, τ is the corresponding sampling width, T s is the corresponding sampling period; * is the convolution operation, rect(·) is the rectangular function, and

[0011]

[0012] When a slice sequence with positive and negative amplitudes is used for signal modulation, the slice sequence in the formula can be amplitude-shifted to obtain a positive and negative amplitude slice modulation signal, which can be expressed as

[0013]

[0014] Where D = τ / T s is the duty cycle of the slice modulation signal in the formula, which is also the amplitude shift value, so u2(t) becomes a modulation signal with an amplitude of -D to 1-D.

[0015] The second step is segmented pulse compression of the forwarded signal and target echo.

[0016] The linear frequency modulation signal emitted by the radar can be expressed as

[0017]

[0018] Among them, T p is the linear frequency modulation signal pulse width, f c is the signal carrier frequency, μ=B / T p is the modulation slope, and B is the signal bandwidth.

[0019] Using two slice modulation methods, the radar transmission signal can be expressed as

[0020] s1(t)=u1(t)s(t) (5)

[0021] s2(t)=u2(t)s(t) (6)

[0022] When performing slice modulation, the slice frequency f corresponding to the slice modulation signals u1(t) and u2(t) s =1 / T s Should be greater than the linear frequency modulation signal bandwidth, that is, f s >B.

[0023] Segmented forwarding of radar signals can cause multiple false peaks to appear in the target range image. The segmented forwarding control signal is p(t). By segmentally forwarding equations and respectively, the radar will obtain the superposition signal of the forwarded signal and the target echo, which can be expressed as

[0024] s echo1 (t) = s1(t-Δt1)p(t-Δt1) + s r1 (t) (7)

[0025] s echo2 (t) = s2(t-Δt1)p(t-Δt1) + s r2 (t) (8)

[0026] Among them, Δt1 is the delay of forwarding signal, s r1 (t) = s1(t-Δt) is the target echo corresponding to the formula, s r2 (t)=s2(t-Δt) is the target echo corresponding to the formula, and Δt is the target echo delay.

[0027] Pulse compression of the target echo can be achieved through matched filtering. The matched filtering reference signal is s ref The two echoes of Equation 1 and Equation 2 are subjected to segmented matched filtering to obtain the pulse compression results y1(t) and y2(t), which represent the pulse compression range image of the target.

[0028] The third step is to estimate the forwarding signal parameters.

[0029] Based on the pulse compression range image y2(t) obtained in the previous step, the two points with the highest peak values ​​in the range image are found to be R1 and R2 (R2>R1).

[0030] The linear frequency modulation signal emitted by the radar is forwarded, and the false peak spacing of the range image is obtained as follows:

[0031]

[0032] Among them, f IS is the frequency of the forwarding control signal, and c is the propagation speed of electromagnetic waves.

[0033] For the distance image y2(t), it satisfies

[0034] R2-R1=2ΔR (10)

[0035] Thus, the forwarding cycle

[0036]

[0037] In the range image y1(t), find the peak at the same position as R1 and R2, and obtain the peak amplitude A0 at the position R0 = (R1 + R2) / 2, and obtain its ratio to the peak amplitude A1 at R1, satisfying

[0038]

[0039] The numerical calculation method can be used to find the D close to the result of the above calculation. IS As an estimate of the duty cycle of the forwarding control signal.

[0040] According to the period T of the forwarding control signal IS and duty cycle D IS , we can get the spectrum of the multiplication of the forwarding control signal p(t) and the slice modulation signals u1(t) and u2(t). Combined with the peak amplitudes of each order of the spectrum, we can achieve amplitude compensation in the next step.

[0041] The fourth step is amplitude compensation and distance image false peak cancellation.

[0042] According to the forwarding control signal period T calculated in the third step IS and duty cycle D IS , combined with the period T designed by slice modulation s The peak amplitude of the range profile y2(t) can be compensated by using the duty cycle D. The compensated range profile is expressed as y′2(t).

[0043] The range image y1(t) is subtracted from y′2(t) to cancel out the false peaks in the range image, which can be expressed as

[0044] y0(t)=y1(t)-y2′(t) (13)

[0045] y0(t) is the target range image after cancellation.

[0046] The beneficial effects of the present invention mainly include:

[0047] First, two slice modulation signals are designed to modulate the linear frequency modulation signal respectively, which increases the complexity of the signal.

[0048] Second, a superposition signal model of slice modulation echo and forwarding echo was constructed to realize segmented pulse compression processing of echo.

[0049] Third, the range images obtained by two segmented pulse compression processes are used to estimate the parameters of the forwarding control signal.

[0050] Fourth, the characteristics of the forwarding control signal and the slice modulation signal are utilized to achieve false peak amplitude compensation, and the false peaks are eliminated through range image cancellation to obtain an accurate target range image.

Brief Description of the Drawings

[0051] Figure 1 It is the processing flow of pulse slice modulation and range image false peak elimination.

[0052] FIG2(a) is the waveform of the first slice modulation signal, and FIG2(b) is the waveform of the second slice modulation signal.

[0053] FIG3( a ) is an LFM signal after the first slice modulation process, and FIG3( b ) is an LFM signal after the second slice modulation process.

[0054] FIG4( a ) is a range image of the target echo modulated by the first slice, and FIG4( b ) is a range image of the target echo modulated by the second slice.

[0055] FIG5(a) is a range image obtained by superimposing the target echo modulated by the first slice and the forwarding signal, and FIG5(b) is a range image obtained by superimposing the target echo modulated by the second slice and the forwarding signal.

[0056] Figure 6 It is the real target range image after amplitude compensation and false peak cancellation. [Specific implementation method]

[0057] The present invention will be further described below with reference to the accompanying drawings.

[0058] The present invention provides a target range image false peak elimination method based on slice modulation design. The method is simulated and implemented by Matlab software in a Windows 10 system with an i7-10750H CPU and 32GB of memory.

[0059] The specific steps are as follows:

[0060] The first step is slice modulation sequence design.

[0061] The slice modulation signal with an amplitude of 0 to 1 is u1(t)

[0062]

[0063] Where δ(·) is the impulse function; n is the number of segmented samples of the entire pulse, τ is the corresponding sampling width, T s is the corresponding sampling period; * is the convolution operation, rect(·) is the rectangular function, and

[0064]

[0065] The corresponding spectrum can be expressed as

[0066]

[0067] Where D = τ / T s =τf s is the duty cycle of the slicing signal, f s =1 / T s is the slicing frequency.

[0068] The slice modulation signal with -D to 1-D amplitude can be expressed as

[0069]

[0070] The corresponding spectrum can be expressed as

[0071]

[0072] The second step is segmented pulse compression of the forwarded signal and target echo.

[0073] The linear frequency modulation signal emitted by the radar can be expressed as

[0074]

[0075] Among them, T p is the linear frequency modulation signal pulse width, f c is the signal carrier frequency, μ=B / T p is the modulation slope, and B is the signal bandwidth.

[0076] Using two slice modulation methods, the radar transmission signal can be expressed as

[0077] s1(t)=u1(t)s(t) (20)

[0078] s2(t)=u2(t)s(t) (21)

[0079] The corresponding target echoes are s r1 (t) and s r2 (t), which can be expressed as

[0080] s r1 (t)=u1(t-Δt)s(t-Δt) (22)

[0081] s r2 (t)=u2(t-Δt)s(t-Δt) (23)

[0082] Pulse compression of the target echo can be achieved through matched filtering. The matched filtering reference signal is s ref (t), its spectrum can be expressed as

[0083]

[0084] The distance image after matched filtering of the formula and the formula can be expressed as

[0085]

[0086]

[0087] Among them, S r1 (f) and S r2 (f) is the echo s r1 (t) and s r2 The spectrum of (t).

[0088] When the slicing frequency f s When it is greater than the signal bandwidth B, there will be no extra peaks in the equations and . Therefore, when designing the slice, the slice frequency must satisfy f s >B.

[0089] Segmented forwarding of radar signals can cause multiple false peaks to appear in the target range image. The segmented forwarding control signal is p(t)

[0090]

[0091] The spectrum of the forwarding control signal is

[0092]

[0093] Among them, D IS =τ IS f IS =τ IS / T IS is the duty cycle of the forwarding control signal.

[0094] By forwarding Equation 1 and Equation 2 in sections, the radar will obtain the superposition signal of the forwarding signal and the target echo, which can be expressed as

[0095] s echo1 (t) = s1(t-Δt1)p(t-Δt1) + s r1 (t) (29)

[0096] s echo2 (t) = s2(t-Δt1)p(t-Δt1) + sr2 (t) (30)

[0097] Wherein, Δt1 is the delay of forwarding signal.

[0098] Perform segmented matched filtering on the two echoes of Equation and Equation, and obtain the pulse compression results y1(t) and y2(t), which can be expressed as

[0099]

[0100]

[0101] y1(t) and y2(t) are the range profiles obtained by superimposing the target echo and the forwarding signal. The second term in the above two equations causes false peaks in the range profile. To eliminate these false peaks, it is necessary to estimate the parameters of the forwarding control signal p(t).

[0102] The third step is to estimate the forwarding signal parameters.

[0103] Based on the range image y2(t) obtained in the previous step, find the two points with the highest peak values ​​in the range image, which are R1 and R2 (R2>R1).

[0104] The linear frequency modulation signal emitted by the radar is forwarded, and the false peak spacing of the range image is obtained as follows:

[0105]

[0106] Among them, f IS The frequency of forwarding control signals.

[0107] For the distance image y2(t), it satisfies

[0108] R2-R1=2ΔR (34)

[0109] Thus, the forwarding cycle

[0110]

[0111] In the range image y1(t), find the peak at the same position as R1 and R2, and obtain the peak amplitude A0 at the position R0 = (R1 + R2) / 2, and obtain its ratio to the peak amplitude A1 at R1, satisfying

[0112]

[0113] Find D that is close to the result calculated above IS As an estimate of the duty cycle of the forwarding control signal.

[0114] The fourth step is amplitude compensation and distance image false peak cancellation.

[0115] Substituting the estimated value into the formula, we can get

[0116] A com1 (f)=P(f)*U1(f) (37)

[0117] A com2 (f)=P(f)*U2(f) (38)

[0118] Since the matched filter reference signal s is used ref (t) is the same. The false peak in the formula is determined by the spectrum peak in the formula, and the false peak of the range image in the formula is determined by the spectrum peak in the formula, and the two correspond to each other. By calculating the amplitude ratio of each order spectrum, the false peak amplitude compensation coefficient in the formula can be obtained.

[0119] Multiply the amplitude compensation coefficient by the peak value of the formula to obtain the range image after amplitude compensation, which is y′2(t). Subtract the range image y1(t) from y′2(t) to cancel the false peaks in the range image, which is expressed as

[0120] y0(t)=y1(t)-y2′(t) (39)

[0121] y0(t) is the target range image after cancellation.

[0122] Simulation example:

[0123] Considering the target is located at 4km, according to Figure 1 The linear frequency modulation pulse width is T p =16μs, bandwidth is B=5MHz. The period of the two slice modulation signals is T s =0.05μs, the duty cycle is set to D=0.5, and the slice modulation signal waveforms are shown in Figures 2(a) and 2(b). The LFM signals after slice modulation are shown in Figures 3(a) and 3(b), respectively. When there is no forwarding signal but only target echo, the range images obtained by pulse compression of the two slice modulated target echoes are shown in Figures 4(a) and 4(b). The period of the forwarding signal is T IS =2μs, duty cycle is D IS = 0.5, the two range images of the forwarded signal and the target echo after segmented pulse compression are shown in Figures 5(a) and 5(b). It can be found that the false peaks in Figure 5(a) correspond to the peaks in Figure 5(b) one-to-one, but there are differences in amplitude. According to the fourth step, the amplitude compensation of the different peak distributions in Figure 5(b) is performed, and through cancellation, the false peaks in Figure 5(a) can be eliminated, thereby obtaining the true target range image, as shown in Figure 5(b). Figure 6 As shown in the figure, the target position is 4000.0559m, which is the same as the simulation setting.

Claims

1. A method for eliminating false peaks in target range images based on slice modulation design, characterized by: The first step is slice modulation sequence design; The radar pulse signal is slice modulated by a slice sequence with amplitude 0 and amplitude 1, and the obtained slice modulated signal is u1(t); Where δ(·) is the impulse function; n is the number of segmented samples of the entire pulse, τ is the corresponding sampling width, T s is the corresponding sampling period; * is the convolution operation, rect(·) is the rectangular function, and: When a slice sequence with positive and negative amplitudes is used for signal modulation, the slice sequence in equation (1) is amplitude-shifted to obtain a positive and negative amplitude slice modulation signal, which can be expressed as: Where D = τ / T s is the duty cycle of the slice modulation signal in formula (1), which is also the amplitude shift value; The second step is segmented pulse compression of the forwarded signal and target echo; The linear frequency modulation signal transmitted by the radar is expressed as: Among them, T p is the linear frequency modulation signal pulse width, f c is the signal carrier frequency, μ=B / T p is the modulation slope, B is the signal bandwidth; Using two slice modulation methods, the radar transmission signal is expressed as: s1(t)=u1(t)s(t) (5) s2(t)=u2(t)s(t) (6); The radar signal is forwarded in segments, so that multiple false peaks appear in the target range image. The segment forwarding control signal is p(t). After segment forwarding Equation (5) and Equation (6) respectively, the radar will obtain the superposition signal of the forwarded signal and the target echo, which can be expressed as: s echo1 (t)=s1(t-Δt1)p(t-Δt1)+s r1 (t) (7) s echo2 (t)=s2(t-Δt1)p(t-Δt1)+s r2 (t) (8) Among them, Δt1 is the delay of forwarding signal, s r1 (t) = s1(t-Δt), s r1 (t) is the target echo corresponding to formula (5), s r2 (t) = s2(t-Δt), s r2 (t) is the target echo corresponding to formula (6), Δt is the target echo delay; The pulse compression of the target echo is achieved by matched filtering. The matched filtering reference signal is s ref (t); perform segmented matched filtering on the two echoes of equations (7) and (8), and obtain the pulse compression results y1(t) and y2(t), which represent the pulse compression range image of the target; The third step is forwarding signal parameter estimation; According to the period T of the forwarding control signal IS and duty cycle D IS , obtain the spectrum of the multiplication of the forwarding control signal p(t) and the slice modulation signals u1(t) and u2(t), and combine the peak amplitudes of each order of the spectrum to achieve amplitude compensation in the next step; The fourth step is amplitude compensation and distance image false peak cancellation; According to the forwarding control signal period T calculated in the third step IS and duty cycle D IS , combined with the period T designed by slice modulation s and duty cycle D, to compensate the peak amplitude of the range image y2(t); the compensated range image is expressed as y′2(t); The range image y1(t) is subtracted from y′2(t) to cancel out the false peaks in the range image, which can be expressed as: y0(t)=y1(t)-y′2(t) (9) y0(t) is the target range image after cancellation.

2. The method for eliminating false peaks of target range image based on slice modulation design according to claim 1, characterized in that: In the first step, the amplitude of the positive and negative amplitude slice modulation signal u2(t) is -D to 1-D.

3. The method for eliminating false peaks of target range profile based on slice modulation design according to claim 1, characterized in that: In the second step, when performing slice modulation, the slice frequency f corresponding to the slice modulation signals u1(t) and u2(t) s =1 / T s Greater than the linear frequency modulation signal bandwidth, that is, f s >B.

4. The method for eliminating false peaks of target range profile based on slice modulation design according to claim 1, characterized in that: The forwarding control signal period T in the third step IS , obtained by the following method: According to the pulse compression range image y2(t) obtained in the second step, find the two points with the highest peak values ​​in the range image as R1 and R2, and R2>R1; The linear frequency modulation signal transmitted by the radar is forwarded, and the false peak spacing of the range image obtained is: Among them, f IS is the frequency of the forwarding control signal, c is the propagation speed of electromagnetic waves; For the distance image y2(t), it satisfies: R2-R1=2ΔR (11) Thus, the forwarding cycle is obtained:

5. The method for eliminating false peaks of target range image based on slice modulation design according to claim 1, characterized in that: The duty cycle D in the third step IS , obtained by the following method: In the range image y1(t), find the peak at the same position as R1 and R2, and obtain the peak amplitude A0 at the position R0 = (R1 + R2) / 2. The ratio of the peak amplitude A0 to the peak amplitude A1 at R1 is obtained, satisfying: Use numerical calculation method to find D close to the result of the above formula. IS As an estimate of the duty cycle of the forwarding control signal.

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