Interference suppression method for random phase modulation electromagnetic metasurface

Abstract

The invention discloses an interference suppression method for a random phase modulation electromagnetic metasurface. The interference suppression method comprises the following steps: constructing a mathematical model for a modulated radar echo signal; wherein a random phase modulation electromagnetic metasurface is installed on the surface of a target, a radar transmitting signal enters the random phase modulation electromagnetic metasurface, and after random time domain phase modulation, a radar echo signal is generated; discrete sampling processing is carried out after digital down-conversion and dechirping are carried out on radar echo signals, and then additional phase information is estimated after self-mixing processing is carried out. Phase compensation is carried out on the radar echo signal after discrete sampling processing under the condition that noise is considered, and then time domain differential transformation and discrete Fourier transformation are carried out; estimating a phase mutation moment by using a subspace algorithm, and reconstructing an interference modulation sequence based on an estimation result; and demodulating random phase interference by using the reconstructed interference modulation sequence, and performing matched filtering processing to obtain an output signal.

Description

Technical Field

[0001] The present invention relates to the field of radar signal processing and electromagnetic interference countermeasure, and in particular to a method for suppressing random phase modulation interference generated when an electromagnetic modulation metasurface is placed on a camouflaged target surface. Background Art

[0002] As an active microwave target detection device, radar has the ability to detect and perceive targets all day and all weather. It is an important means of situational awareness in the air, land, and sea battlefields, and plays an irreplaceable role in various surveillance systems. The core of modern electronic warfare lies in how to gain dominance over information in a complex electromagnetic environment. The importance of radar anti-interference capability is no less than the development of the radar system itself; the development of radar equipment with anti-interference capability is the key to obtaining information and winning in a battlefield with a complex and changeable electromagnetic environment. With the rapid development of the field of electromagnetic modulation materials, the response speed, deception and camouflage capabilities of existing new passive jamming systems have been greatly improved, and the electromagnetic battlefield combat environment has more dynamic and strong game performance. At present, the jammer has effectively achieved the integrated stealth jamming effect of camouflaged targets by installing electromagnetic modulation metasurfaces on the target surface, which has put forward higher requirements for radar detection.

[0003] Random phase modulation interference is a new type of electromagnetic interference formed by electromagnetic modulation materials modulating the phase of incident electromagnetic waves and then forwarding them. Since the electromagnetic modulation material itself does not emit electromagnetic wave signals, its interference effect is achieved by changing the phase characteristics of the incident wave, which belongs to the passive interference type. When the radar transmission signal reaches the electromagnetic modulation surface, the dynamic impedance of the electromagnetic material surface shifts the spectrum of the incident signal through phase regulation, weakening the fundamental component while generating a large number of randomly distributed coherent harmonic components. After matched filtering of the modulated echo, the radar receiver generates a large amount of distance-dimensional deceptive interference, and the target energy at the real position is greatly weakened, posing a great threat to radar detection.

[0004] Existing interference suppression methods cannot directly deal with phase modulation interference, and commonly used anti-interference methods have the following technical difficulties: 1) After the radar transmission signal is phase modulated and reflected by the electromagnetic modulation surface, the spectrum of the incident wave signal is redistributed, and the real target energy corresponding to the fundamental wave is severely weakened. At the same time, the harmonic component can produce a large number of highly realistic distance-dimensional false targets after matched filtering. The anti-interference method based on energy feature recognition cannot handle the situation where the real target energy is moved, the interference component energy is suppressed or the feature is deceived in the phase modulation interference scenario; 2) The electromagnetic modulation surface modulates the incident electromagnetic wave very quickly. Compared with the intermittent forwarding interference based on digital radio frequency storage technology, it can directly reflect the radar electromagnetic wave signal that has been phase modulated with zero delay. When using signal processing algorithms to suppress interference at the receiving end, it is impossible to judge the useful target component and the interference component based on the delay difference and time-frequency parameter information of the received echo. The anti-interference method based on time-frequency feature recognition cannot deal with the strongly coupled phase modulation interference with "parasitic" properties.

[0005] In summary, considering the technical bottlenecks of existing anti-interference methods in phase modulation interference scenarios, it is urgent to carry out research on phase modulation interference suppression technology to solve technical problems such as "real target blanking", "interference feature deception", and "strong coupling of true and false targets", so as to effectively improve the radar's interference perception and target detection capabilities in high-dynamic and strong game electronic confrontation scenarios. Summary of the invention

[0006] In view of the problem that the existing anti-interference technology is unable to detect the stealth interference integrated target installed with electromagnetic modulation materials, the purpose of the present invention is to provide an effective and accurate method for suppressing phase modulation interference after reconstruction, accurately estimate and reconstruct the time domain phase modulation sequence of random phase modulation interference, and effectively suppress the interfered echo through signal processing means.

[0007] In order to achieve the above tasks, the present invention adopts the following technical solutions:

[0008] An interference suppression method for a random phase modulation electromagnetic metasurface, comprising:

[0009] A mathematical model is constructed for the modulated radar echo signal; wherein a random phase modulated electromagnetic metasurface is installed on the target surface, and the radar transmission signal is incident on the random phase modulated electromagnetic metasurface, and the radar echo signal is generated after random time domain phase modulation;

[0010] Using the parameter information of the radar transmission signal, the radar echo signal is digitally down-converted and de-linearized for discrete sampling.

[0011] The additional phase information is estimated by performing self-mixing processing on the discretely sampled echo signal;

[0012] Using the estimation result of the additional phase information, phase compensation is performed on the radar echo signal after the discrete sampling process while taking noise into consideration;

[0013] Performing time domain differential transformation and discrete Fourier transform on the radar echo signal generated after compensation;

[0014] Based on the sequence after discrete Fourier transform, the subspace algorithm is used to estimate the phase mutation moment, and the interference modulation sequence is reconstructed based on the estimation result;

[0015] The random phase interference is demodulated using the reconstructed interference modulation sequence and matched filtering is performed to obtain the output signal.

[0016] Furthermore, the mathematical model of the radar receiving the echo signal is expressed as:

[0017]

[0018] Where t is the time parameter, Δτ is the time delay between the radar station and the target with the electromagnetic modulation metasurface attached, and T p is the pulse duration, K p is the modulation frequency, f0 is the carrier frequency, rect(·) is the rectangular window function, j is the imaginary unit, M is the number of random phase modulated code elements, m represents the mth code element, T c is the code element width, a m For the tth m The code element amplitude corresponding to the time, φ m t m The symbol phase corresponding to the time instant, u(t) is a step function, and g(·) is a step function.

[0019] Furthermore, the radar echo signal is digitally down-converted and de-linearly modulated using the parameter information of the radar transmission signal, and then discretely sampled, including:

[0020] s de (t) = s j (t)·exp(-jπK p t 2 )·exp(-jπf0t)

[0021] s de [n] = s de (nT s )

[0022] =β1·β2·p[n]·exp(j2πf r nT s )

[0023] Among them, exp(-jπf0t), exp(-jπK p t 2 ) are respectively for s j (t) Perform digital down-conversion and linear frequency modulation processing, s de [n] is for s de (t) with sampling frequency f s =1 / T s Discrete expression after discrete sampling; T s is the sampling interval of discrete sampling, n represents the nth discrete sampling point, s de (nT s ) represents the de (t) is a discrete time sequence formed after discrete sampling; s remains constant within each sampling interval, so the simplified s de (nT s )Use de [n] represents the discrete sequence after sampling, p[n] represents the discrete form of the random time-domain phase modulation sequence p(t) after sampling, β1 = exp(j2πf0Δτ), β2 = exp(jπK p Δτ 2 ) is a constant term, f r The additional phase caused by the delay.

[0024] Furthermore, the discretely sampled echo signal is subjected to self-mixing processing to estimate the additional phase information, which is expressed as:

[0025]

[0026] Where FT(·) represents discrete Fourier transform, and f is the frequency domain parameter after Fourier transform.

[0027] Furthermore, the estimation result of the additional phase information is used to perform phase compensation on the radar echo signal after the discrete sampling process while taking noise into consideration, including:

[0028]

[0029] Among them, N Noise Represents the noise sequence after discrete sampling, let s de [n] is the radar echo signal after discrete sampling processing, Indicates de [n] The new sequence generated after phase compensation.

[0030] Furthermore, the performing time domain differential transformation and discrete Fourier transformation on the radar echo signal generated after compensation includes:

[0031] For com [n] After the first-order difference, we can get:

[0032]

[0033] in, Indicates com [n] Perform first-order difference processing;

[0034] The sampling time corresponding to d[n] = 1 is defined as the phase mutation time t` m , then the discrete Fourier transform of the sequence d[n] is:

[0035]

[0036] Among them, D[k],S com [k] are the sequences d[n] and s com [n] The expression after discrete Fourier transform, k represents the kth frequency domain sampling point after discrete Fourier transform, N is the number of points of discrete Fourier transform, M` is the number of phase mutation points obtained after time domain difference, M`≤M, a m =[-1,1].

[0037] Furthermore, the method of estimating the phase mutation moment based on the sequence after discrete Fourier transformation by using a subspace algorithm and reconstructing the interference modulation sequence based on the estimation result includes:

[0038] Let d s =[D[s],D[s+1],...,D[s+K]] T ,s∈[0,S-1],S=KM`, where D[s] represents the value of the sth frequency domain sampling point, K is the order of the autocorrelation matrix, and the value needs to satisfy K>M` to construct the autocorrelation matrix:

[0039]

[0040] in(·) T ,(·) H represent transpose and conjugate transpose transformations respectively;

[0041] R d After eigendecomposition, the noise subspace G = span {μ M`+1 ,μ M`+2 ,…,μ K},μ M`+1 Represents R d The M`+1th eigenvalue is obtained after eigendecomposition. span(·) is the span of multiple vectors. The phase mutation time t` is classified by the multiple signal classification algorithm.m The estimated results are:

[0042] a(w)=[1,e -jw ,…,e -j(S-1)w ] H

[0043]

[0044] Where w = 2πf represents the signal angular frequency, f is the signal frequency, a(w) is the constructed search vector, represents the spectrum function in the peak search step in the multiple signal classification algorithm. The findpeaks(·) function is used to search for the local maximum of a set of one-dimensional data. Peaks represents the angular frequency value corresponding to the local maximum. in express The time when the mth local maximum value of appears is the phase mutation time t` m The results of the estimation;

[0045] The reconstructed interference modulation sequence is:

[0046] Furthermore, the random phase interference is demodulated by using the reconstructed interference modulation sequence, and matched filtering is performed to obtain an output signal, including:

[0047]

[0048] Among them, s j [n] is the radar echo signal s after random phase coding modulation reflection j (t) The result after discrete sampling;

[0049]

[0050] Wherein, DFT and IDFT are discrete Fourier transform and discrete inverse Fourier transform operations respectively, h[n] is the reference signal in the matched filter operation, and y[n] is the output signal.

[0051] A terminal device comprises a processor, a memory and a computer program stored in the memory; when the processor is executed by a computer, the interference suppression method for a random phase modulation electromagnetic metasurface is implemented.

[0052] A computer-readable storage medium stores a computer program; when the computer program is executed by a processor, the interference suppression method for a random phase modulation electromagnetic metasurface is implemented.

[0053] Compared with the prior art, the present invention has the following technical features:

[0054] The random phase modulation interference suppression method proposed in the present invention divides the received echo signal of the modulated interference into two paths, one of which is used to estimate the modulation parameter reconstruction of the electromagnetic modulation surface, and uses the known parameter information of the transmitted signal to eliminate the influence of the carrier frequency term and the quadratic term through digital down-conversion and demodulation frequency preprocessing. For the additional primary phase caused by the echo time delay, the additional term is estimated and compensated by self-mixing processing. According to the sparsity of the differential transformation of the compensated signal in the time domain, and the position of the sparse point, that is, the moment of the corresponding modulation sequence, the phase mutation moment is estimated by using a subspace signal estimation algorithm, and finally a random phase modulation sequence of the electromagnetic modulation surface is constructed; the other path is used to eliminate the influence of the random phase modulation interference on the received echo, and the random phase interference is demodulated by using the reconstructed interference modulation sequence and then matched filtering is performed, which effectively solves the spectrum shift, spectrum aliasing and distance-dimensional dense false target problems caused by the random phase modulation interference, and improves the robust and accurate detection performance of the radar in the electromagnetic modulation material confrontation scenario. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 is a flow chart of the method of the present invention;

[0056] Figure 2 (a) is a schematic diagram of the electromagnetic modulation material modulating the radar transmission signal in an example of the present invention;

[0057] Figure 2 (b) is a time domain envelope diagram of the modulation of the incident electromagnetic wave by the electromagnetic modulation surface in the example of the present invention;

[0058] Figure 3 It is a spectrum comparison diagram of radar receiving echo with and without interference in the example of the present invention;

[0059] Figure 4 (a) is a time-frequency analysis diagram of radar receiving echo without interference in an example of the present invention;

[0060] Figure 4 (b) is a time-frequency analysis diagram of radar receiving echo in the case of interference in the example of the present invention;

[0061] Figure 5 is the processing result of the additional phase estimation step in step 3 of the present embodiment;

[0062] Figure 6 It is the time domain diagram after additional phase compensation in step 5 of the present invention and the time domain diagram after time domain difference processing in step 6;

[0063] Figure 7 is the jump time estimation result of the subspace parameter estimation method in step 6 of the example of the present invention;

[0064] Figure 8 is the comparison result between the reconstructed random phase modulation sequence and the real modulation sequence in the example of the present invention;

[0065] Fig. 9 It is the comparison result of matched filtering processing before and after interference suppression in the example of the present invention. DETAILED DESCRIPTION

[0066] Referring to the accompanying drawings, the present invention provides an interference suppression method for a random phase modulation electromagnetic metasurface. First, according to the known parameters of the radar transmission signal, the interference echo signal after the electromagnetic modulation metasurface installed on the target is received by the radar and digitally down-converted and de-linear frequency modulation is performed to eliminate the influence of the carrier frequency and the frequency modulation rate on the subsequent processing; considering that the demodulated echo contains an additional phase caused by the target delay, the additional phase is estimated after self-mixing processing; then the additional phase of the demodulated echo is compensated by the estimation result of the previous step; after the processing result after the phase compensation is subjected to the time domain difference operation, the phase jump time domain information of the phase modulation interference is obtained. After the above processing transformation, the interference suppression problem is converted into a parameter estimation problem, and the modulation sequence of the phase modulation interference is estimated by the subspace algorithm; finally, the reconstructed modulation sequence is multiplied with the received echo to eliminate the phase regulation of the radar incident signal by the time-varying impedance of the electromagnetic modulation surface, and finally the real energy recovery and accurate target detection of the camouflaged target in the random phase modulation interference confrontation scenario are realized. The specific implementation steps of the present invention are further described in detail below.

[0067] Step 1: Since there is a propagation time for the radar transmission signal to reach the electromagnetic modulation metasurface, there is a delay between the radar transmission signal and the phase modulation sequence. The delay is equal to the distance between the radar station and the camouflaged target. To simplify the consideration, the radar receiving echo is modeled as follows:

[0068] Assuming that the camouflaged target surface is completely covered by the electromagnetic modulation metasurface, the radar received echo signal after the radar transmission signal is randomly phase modulated in the time domain by the electromagnetic modulation metasurface is expressed as: J (t):

[0069] s J (t) = s r (t)×p(t)=s t (t-Δτ)×p(t)

[0070] Among them, s r (t) is the electromagnetic wave incident along the normal direction of the electromagnetic modulation metasurface, t is the time parameter, Δτ is the time delay between the radar station and the target attached with the electromagnetic modulation metasurface, p(t) is the random time domain phase modulation sequence of the electromagnetic modulation metasurface; the radar transmission signal s tThe expression of (t) is:

[0071]

[0072] Among them, T p is the pulse duration, K p To adjust the frequency, B is the signal bandwidth, f0 is the carrier frequency, c is the speed of light, λ is the wavelength of the transmitted signal, rect(·) is the rectangular window function, and j is the imaginary unit.

[0073] The expression of random time-domain phase modulation sequence p(t) is:

[0074]

[0075] Where M is the number of random phase modulation symbols, m = 0, 1, ..., M-1 represents the mth symbol, T c is the code element width, A m =a m exp(jφ m ), a m For the tth m The code element amplitude corresponding to the time, φ m t m The symbol phase corresponding to the time, u(t) is the step function, j is the imaginary unit, g(·) is the step function, g(t-mT c )=u(tt m )-u(tt m+1 ).

[0076] Furthermore, the radar echo signal after random phase coding modulation reflection is expressed as:

[0077]

[0078] Step 2: Use the known parameters in the radar transmission signal to adjust the frequency K p and carrier frequency f0, for the radar echo signal s j (t) Perform digital down-conversion and de-linear frequency modulation to eliminate the influence of carrier frequency and frequency modulation on subsequent processing, and perform discrete sampling on the processed radar echo signal; specifically, it can be expressed as:

[0079] s de (t) = s j (t)·exp(-jπK p t 2 )·exp(-jπf0t)

[0080] s de [n] = s de (nT s )

[0081] = exp(j2πf0Δτ)·exp(jπK p Δτ 2 )·p(nT s )·exp(j2πK p nT s Δτ)

[0082] =β1·β2·p[n]·exp(j2πK p nT s Δτ)

[0083] =β1·β2·p[n]·exp(j2πf r nT s )

[0084] Among them, exp(-jπf0t), exp(-jπK p t 2 ) are respectively for s j (t) Perform digital down-conversion and linear frequency modulation processing, s de [n] is for s de (t) with sampling frequency f s =1 / T s The discrete expression after discrete sampling; Ts is the sampling interval of discrete sampling, n represents the nth discrete sampling point, s de (nT s ) represents the de (t) The time domain discrete sequence formed after discrete sampling; p(nT s ) is a fixed sampling interval T s The discrete form of the random time-domain phase modulation sequence p(t) after sampling, due to T s remains constant within each sampling interval, so the simplified s de (nT s )Use de [n] represents the discrete sequence after sampling, and p[n] represents p(nT s ); β1=exp(j2πf0Δτ), β2=exp(jπK p Δτ 2 ) is a constant term and can be ignored. r The additional phase caused by the delay.

[0085] When the discrete modulation sequence p[n] of the electromagnetic modulation metasurface is subjected to single-bit phase modulation (the phase corresponding to p[n] is only 0° and 180°, that is, the phase state is only 0 and 1), at t m Code element amplitude a m =1, symbol phase φ m=[0,π]; When the radar receiver processes the echo signal, when the phase of the single-bit phase-coded modulation sequence p[n] changes continuously between 0° and 180° in an unknown order, it is impossible to reconstruct the change of p[n] by directly observing the echo time domain; when the phase of p[n] is 0°, the corresponding amplitude is 1, and when the phase of p[n] is 180°, the corresponding amplitude is -1, so p[n] can be further regarded as a set of discrete sequences with values ​​randomly changing between 1 and -1; p 2 [n] is a discrete sequence with an amplitude of 1, and its sequence length is consistent with p[n].

[0086] Step 3: perform self-mixing processing on the discretely sampled echo signal to estimate the additional phase.

[0087] Additional phase information can be obtained by performing self-mixing processing on the discretely sampled echo signal. The specific processing is as follows:

[0088]

[0089] Where FT(·) represents discrete Fourier transform, and f is the frequency domain parameter after Fourier transform.

[0090] Step 4: After obtaining the estimated result of additional phase information After that, the signal expression after phase compensation processing of the data in step 2 is:

[0091]

[0092] In the ideal noise-free case, the last two terms in the above equation cancel out completely, and β1 and β2 are fixed constants; therefore, the sequence s obtained after phase compensation is com [n] can reflect the phase change of p[n]; but in practice, the influence of noise must be considered. Under the assumption of Gaussian white noise, the above formula can be further transformed into:

[0093]

[0094] Among them, N Noise Represents the noise sequence after discrete sampling, let and Respectively represent s de [n] and N Noise The new sequence generated after multiplying by the compensation term.

[0095] Step 5, Sequence The phase jump information in the original modulation sequence p[n] is consistent with s com[n] is the sequence contaminated by noise; in order to eliminate the influence of noise and accurately restore the modulation information of p[n], a time domain difference transform is performed on it and the estimated value of the mutation time is obtained using the subspace parameter estimation algorithm.

[0096] For com [n] After the first-order difference, we can get:

[0097]

[0098] in, Indicates com [n] Perform first-order difference processing.

[0099] Because s com [n] is a set of discrete sequences with values ​​randomly changing between -1 and 1. After the first-order difference processing, the discrete sequence d[n] formed has values ​​between 0 and 1. d[n] = 0 means s com [n] The values ​​of the discrete sampling points before and after the continuous time are consistent, d[n] = 1 means s com The values ​​of the discrete sampling points before and after [n] are opposite. The sampling time corresponding to d[n] = 1 is defined as t` m .

[0100] According to the differential property of discrete Fourier transform, the discrete Fourier transform of sequence d[n] is:

[0101]

[0102] Among them, D[k],S com [k] are the sequences d[n] and s com [n] The expression after discrete Fourier transform, j is the imaginary unit, k represents the kth frequency domain sampling point after discrete Fourier transform, N is the number of points of discrete Fourier transform, M` is the number of phase mutation points obtained after time domain difference (M`≤M), a` m =[-1,1].

[0103] It can be seen that the above formula is a classic spectrum estimation problem, and the result of the estimation is the phase mutation moment t` m Considering the influence of noise and estimation accuracy, in the subsequent steps, a subspace algorithm is used to estimate t` m Make an estimate.

[0104] Step 6: Reconstruct the interference modulation sequence using a subspace algorithm.

[0105] Let d s =[D[s],D[s+1],...,D[s+K]] T,s∈[0,S-1],S=KM`, where D[s] represents the value of the sth frequency domain sampling point, K is the order of the autocorrelation matrix, and the value needs to satisfy K>M` to construct the autocorrelation matrix:

[0106]

[0107] in(·) T ,(·) H represent transpose and conjugate transpose transformations respectively.

[0108] R d After eigendecomposition, the noise subspace G = span {μ M`+1 ,μ M`+2 ,...,μ K},μ M`+1 Represents R d The M`+1th eigenvalue is obtained after eigendecomposition. span(·) is the span of multiple vectors. The phase mutation time t` is classified by the multiple signal classification algorithm. m The estimated results are:

[0109] a(w)=[1,e -jw ,…,e -j (S-1)w] H

[0110]

[0111] Wherein, j is the imaginary unit, N is the number of Fourier transform points, w = 2πf represents the signal angular frequency, f is the signal frequency, a(w) is the constructed search vector, represents the spectrum function in the peak search step in the multiple signal classification algorithm. The findpeaks(·) function is used to search for the local maximum of a set of one-dimensional data. Peaks represents the angular frequency value corresponding to the local maximum. in express The time when the mth local maximum value of appears is the phase mutation time t` m Estimated results.

[0112] The type of electromagnetic modulation metasurface in this scheme is single-bit phase modulation, so the modulation sequence P[n] is essentially a set of sequences whose values ​​change randomly between [-1, 1]; the time parameters reconstructed in this step actually reflect the changing moments of the P[n] sequence, and these changing moments can be used to effectively reconstruct P[n].

[0113] Therefore, the reconstructed interference modulation sequence is:

[0114] Step 7: demodulate the random phase interference using the reconstructed interference modulation sequence. The specific operation is:

[0115]

[0116] Among them, s j [n] is the result of discrete sampling of sj(t).

[0117] Step 8: Perform matched filtering on the demodulated signal to obtain an output signal y[n]. The specific operation is as follows:

[0118]

[0119] Wherein, DFT and IDFT are discrete Fourier transform and discrete inverse Fourier transform operations respectively, and h[n] is the reference signal in the matched filtering operation.

[0120] Example:

[0121] Step 1, transmit signal with time width μ = 10us, bandwidth B = 2MHz, frequency modulation K p =2×10 11 , the sampling frequency is 10MHz, the carrier frequency is 10GHz, the pulse repetition time is 100us, the target distance is 975m, the corresponding delay is 6.5us, the input signal-to-noise ratio is 5dB, the time-varying impedance coefficient of the electromagnetic modulation material surface adopts a random phase modulation mode, the modulation code element width is 10us, the modulation sequence within the radar signal time width is [1110101101], and the corresponding mutation time is [9.9us, 10.9us, 11.8us, 12.8us, 14.9us, 15.9us], where the value 1 represents the phase modulation state is π, and the value 0 represents the phase modulation state is 0. The expression of the reflected echo after the radar transmit signal is modulated by the random phase modulation surface is:

[0122]

[0123] Step 2: According to the carrier frequency and modulation frequency of the radar transmission signal, the echo signal s j (t) After digital down-conversion and de-linear frequency modulation processing, we can get:

[0124] s de [n] = s de (nT s )

[0125] = exp(j2πf0Δτ)·exp(jπK p Δτ 2 )·p(nT s )·exp(j2πK p nTs Δτ)

[0126] =β1·β2·p[n]·exp(j2πK p nT s Δτ)

[0127] =β1·β2·p[n]·exp(j2πf r nT s )

[0128] Among them, f r =1.3×10 6 .

[0129] Step 3, performing self-mixing processing on the signal after the carrier removal and de-linear frequency modulation processing to estimate the additional phase.

[0130]

[0131] Calculated The estimated result is 1.2988×10 6 .

[0132] Step 4: Based on the estimated result of the primary phase After that, the signal expression after phase compensation processing of the data in step 2 is:

[0133]

[0134] Step 5, for s com [n] After differentiation, we can get:

[0135]

[0136] According to the differential property of discrete Fourier transform, the discrete Fourier transform of sequence d[n] is:

[0137]

[0138] The number of discrete Fourier transform points N=100, and the number of phase mutation points after time domain difference processing M`=6.

[0139] Step 6: Reconstruct the interference modulation sequence using a subspace-based parameter estimation method.

[0140] Let d s =[D[s],D[s+1],...,D[s+K]] T ,s∈[0,S-1],S=KM`, where the autocorrelation matrix order K is 32, the number of time domain jump points of the random phase modulation sequence is 6, and the autocorrelation matrix is ​​constructed:

[0141]

[0142] R d After eigendecomposition, the noise subspace G = span {μ M`+1 ,μ M`+2 ,...,μ K}, using the multiple signal classification algorithm to classify the phase mutation time t` m The estimated results are:

[0143] a(w)=[1,e -jw ,…,e -j (S-1 ) w] H

[0144]

[0145] The reconstructed interference modulation sequence is: [9.9us, 11us, 11.9us, 12.9us, 14.9us, 15.9us].

[0146] Step 7: demodulate the random phase interference using the reconstructed interference modulation sequence. The specific operation is:

[0147]

[0148] Step 8: Perform matched filtering on the demodulated signal to obtain the output signal y[n]. The specific operation is as follows:

[0149]

[0150] After interference suppression processing, the peak position after matched filtering is 6.5us, and the measured target distance is 975m.

[0151] The above embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present application, and should all be included in the protection scope of the present application.

Claims

1. An interference suppression method for a random phase modulated electromagnetic metasurface, characterized in that: include: A mathematical model is constructed for the modulated radar echo signal; wherein a random phase modulated electromagnetic metasurface is installed on the target surface, and the radar transmission signal is incident on the random phase modulated electromagnetic metasurface, and the radar echo signal is generated after random time domain phase modulation; Using the parameter information of the radar transmission signal, the radar echo signal is digitally down-converted and de-linearized for discrete sampling. The additional phase information is estimated by performing self-mixing processing on the discretely sampled echo signal; Using the estimation result of the additional phase information, phase compensation is performed on the radar echo signal after the discrete sampling process while taking noise into consideration; Performing time domain differential transformation and discrete Fourier transform on the radar echo signal generated after compensation; Based on the sequence after discrete Fourier transform, the subspace algorithm is used to estimate the phase mutation moment, and the interference modulation sequence is reconstructed based on the estimation result; The random phase interference is demodulated using the reconstructed interference modulation sequence and matched filtering is performed to obtain the output signal.

2. The interference suppression method for random phase modulation electromagnetic metasurface according to claim 1, characterized in that: The mathematical model of the radar receiving echo signal is expressed as: Where t is the time parameter, Δτ is the time delay between the radar station and the target with the electromagnetic modulation metasurface attached, and T p is the pulse duration, K p is the modulation frequency, f0 is the carrier frequency, rect(·) is the rectangular window function, j is the imaginary unit, M is the number of random phase modulated code elements, m represents the mth code element, T c is the code element width, a m For the tth m The code element amplitude corresponding to the time, φ m t m The symbol phase corresponding to the time instant, u(t) is a step function, and g(·) is a step function.

3. The interference suppression method for random phase modulation electromagnetic metasurface according to claim 1, characterized in that: The method of using the parameter information of the radar transmission signal to digitally down-convert and de-linearly modulate the radar echo signal and then perform discrete sampling processing includes: s de (t)=s j (t)·exp(-jπK p t 2 )·exp(-jπf0t) s de [n]=s de (nT s ) =β1·β2·p[n]·exp(j2πf r nT s ) Among them, exp(-jπf0t), exp(-jπK p t 2 ) are respectively for s j (t) Perform digital down-conversion and linear frequency modulation processing, s de [n] is for s de (t) with sampling frequency f s =1 / T s Discrete expression after discrete sampling; T s is the sampling interval of discrete sampling, n represents the nth discrete sampling point, s de (nT s ) represents the de (t) is a discrete time sequence formed after discrete sampling; s remains constant within each sampling interval, so the simplified s de (nT s )Use de [n] represents the discrete sequence after sampling, p[n] represents the discrete form of the random time-domain phase modulation sequence p(t) after sampling, β1 = exp(j2πf0Δτ), β2 = exp(jπK p Δτ 2 ) is a constant term, f r The additional phase caused by the delay.

4. The interference suppression method for random phase modulation electromagnetic metasurface according to claim 1, characterized in that: The additional phase information is estimated after the self-mixing process is performed on the discretely sampled echo signal, which is expressed as: Where FT(·) represents discrete Fourier transform, and f is the frequency domain parameter after Fourier transform.

5. The interference suppression method for random phase modulation electromagnetic metasurface according to claim 1, characterized in that: The method of using the estimation result of the additional phase information to perform phase compensation on the radar echo signal after the discrete sampling process while taking noise into consideration includes: Among them, N Noise Represents the noise sequence after discrete sampling, let s de [n] is the radar echo signal after discrete sampling processing, Indicates de [n] The new sequence generated after phase compensation.

6. The interference suppression method for random phase modulation electromagnetic metasurface according to claim 1, characterized in that: The time domain differential transformation and discrete Fourier transformation of the radar echo signal generated after compensation include: For com [n] After the first-order difference, we can get: in, Indicates com [n] Perform first-order difference processing; The sampling time corresponding to d[n] = 1 is defined as the phase mutation time t` m , then the discrete Fourier transform of the sequence d[n] is: Among them, D[k],S com [k] are the sequences d[n] and s com [n] The expression after discrete Fourier transform, k represents the kth frequency domain sampling point after discrete Fourier transform, N is the number of points of discrete Fourier transform, M` is the number of phase mutation points obtained after time domain difference, M`≤M, a` m =[-1,1].

7. The interference suppression method for random phase modulation electromagnetic metasurface according to claim 1, characterized in that: The method of estimating the phase mutation moment based on the sequence after discrete Fourier transformation by using a subspace algorithm and reconstructing the interference modulation sequence based on the estimation result includes: Let d s =[D[s],D[s+1],...,D[s+K]] T ,s∈[0,S-1],S=KM`, where D[s] represents the value of the sth frequency domain sampling point, K is the order of the autocorrelation matrix, and the value needs to satisfy K>M` to construct the autocorrelation matrix: in(·) T ,(·) H represent transpose and conjugate transpose transformations respectively; R d After eigendecomposition, the noise subspace G = span {μ M`+1 ,μ M`+2 ,…,μ K },μ M`+1 Represents R d The M`+1th eigenvalue is obtained after eigendecomposition. span(·) is the span of multiple vectors. The phase mutation time t` is classified by the multiple signal classification algorithm. m The estimated results are: a(w)=[1,e -jw ,…,have been -j(S-1)w ] H Where w = 2πf represents the signal angular frequency, f is the signal frequency, a(w) is the constructed search vector, represents the spectrum function in the peak search step in the multiple signal classification algorithm. The findpeaks(·) function is used to search for the local maximum of a set of one-dimensional data. Peaks represents the angular frequency value corresponding to the local maximum. in express The time when the mth local maximum value of appears is the phase mutation time t` m The results of the estimation; The reconstructed interference modulation sequence is:

8. The interference suppression method for random phase modulation electromagnetic metasurface according to claim 1, characterized in that: The random phase interference is demodulated by using the reconstructed interference modulation sequence, and matched filtering is performed to obtain an output signal, including: Among them, s j [n] is the radar echo signal s after random phase coding modulation reflection j (t) The result after discrete sampling; Wherein, DFT and IDFT are discrete Fourier transform and discrete inverse Fourier transform operations respectively, h[n] is the reference signal in the matched filter operation, and y[n] is the output signal.

9. A terminal device, comprising a processor, a memory, and a computer program stored in the memory; when the processor is executed by a computer, it implements the interference suppression method for random phase modulation electromagnetic metasurface according to any one of claims 1-8.

10. A computer-readable storage medium, wherein a computer program is stored in the medium; characterized in that: When the computer program is executed by a processor, the interference suppression method for a random phase modulated electromagnetic metasurface according to any one of claims 1 to 8 is implemented.

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