Sub-band frequency coded chip interference suppression method

Abstract

The present invention discloses a sub-band frequency coded slice interference suppression method, which mainly solves the problem that the prior art can not eliminate the interference data of intermittent sampling and forwarding by only using correlation, resulting in the inability to correctly identify the target when the interference signal energy is greater than the signal energy, and when the interference-to-signal ratio is too large, the transition band interference residue will submerge the adjacent target signal segment, resulting in the inability to correctly identify the target. The specific steps of the present invention are: 1. Estimating slice interference parameters; 2. Generating a transmission signal of the sub-pulse frequency within the pulse; 3. Encoding the sub-pulse frequency of the transmission signal according to the interference parameters; 4. Constructing an echo signal waveform containing interference and target; 5. Segmented pulse compression anti-interference. The present invention uses frequency coding to concentrate the sampled and forwarded sub-pulse and unsampled sub-pulse frequency bands respectively, thereby improving the target detection probability, target accumulation gain and target detection reliability.

Description

Technical Field

[0001] The present invention belongs to the field of radar technology, and further relates to a sub-band frequency coded slice interference suppression method in the field of radar signal processing technology. The present invention can be used to encode the sub-pulse frequency within a pulse to suppress intermittent sampling and forwarding interference and thus correctly identify the target. Background Art

[0002] The forwarding deception jammer based on digital radio frequency memory (DRFM) has great similarity with the target signal, which has a serious impact on radar target recognition and detection. In particular, the intermittent sampling forwarding jammer can quickly and accurately slice the echo signal, so that the jammer signal and the target echo signal arrive at the receiver in the same pulse repetition period, forming a multi-false target jammer band. For this kind of jammer, conventional pulse-to-pulse waveform agility methods such as phase coding and carrier frequency hopping can no longer effectively counteract it, and new anti-jamming measures are urgently needed.

[0003] Changsha University of Science and Technology has publicly proposed a radar signal design method that is resistant to intermittent sampling and forwarding interference in its patent document "A radar signal design method that is resistant to intermittent sampling and forwarding interference" (application number: CN113138370A application publication number: CN 113138370 A). From the perspective of waveform design, this method first uses a chaotic sequence with good pseudo-randomness to encode each symbol in the time domain, and then randomly arranges a part of each signal data in the time domain and adds an equal amount of redundant coding. Finally, each subcarrier is generated based on the chaotic code after adding redundant coding to obtain an anti-interference radar signal. The disadvantage of this method is that the correlation between the radar echo and the intermittent sampling interference is reduced only by reducing the intra-pulse correlation of the radar transmission signal, thereby suppressing the interference amplitude. However, this method can only achieve an improvement of 3-4dB in the interference-to-signal ratio. When the energy of the interference signal is greater than the target, the interference suppresses the real target and cannot achieve correct identification and detection of the target.

[0004] Zhang Jianzhong et al. proposed a method for resisting intermittent sampling and forwarding interference based on intra-pulse stepped linear frequency modulation waveform in their published paper "Anti-interruption sampling and forwarding interference method based on intra-pulse stepped LFM waveform" (System Engineering and Electronic Technology, 2019, 41(05): 1013-1020.). This method first outputs the echo sub-pulses in segmented pulse compression, and then eliminates the sampled interference signal segments through the orthogonality between the intra-pulse sub-pulses, and accumulates the remaining target signal segments to achieve the anti-interference effect. The shortcoming of this method is that although the intra-pulse stepped linear frequency modulation waveform proposed by it can suppress the slice interference to a certain extent, when the interference-signal ratio is too large, the transition band interference cannot be suppressed, which will submerge the target signal segment and make it impossible to identify and detect the target normally. Summary of the invention

[0005] The purpose of the present invention is to propose a sub-band frequency coded slice interference suppression method to address the deficiencies of the above-mentioned prior art, so as to solve the problem that when the interference signal energy is greater than the signal energy, the method of only relying on reducing the correlation between the echo and the intermittent sampling interference cannot distinguish between the target and the interference in the signal, and when the interference-to-signal ratio is too large, after the intra-pulse stepped linear frequency modulation waveform is sampled and forwarded by the jammer, its transition band will submerge the target signal segment, resulting in the inability to correctly identify the target.

[0006] The idea of ​​the purpose of the present invention is that the present invention estimates interference parameters through pulse compression and envelope cross-correlation method, and then designs the sub-pulse frequency within the pulse by encoding the sub-pulse, so that the unsampled pulse frequency band is concentrated, so as to achieve the effect of reducing the influence range of transition band interference on the target signal segment, thereby improving the anti-interference performance of the radar to intermittent sampling interference, and solving the problem that when the interference-to-signal ratio of the prior art is too large, the transition band submerges the signal and causes the target to be unable to be correctly identified. The present invention divides the radar transmission signal pulse into sub-pulses and encodes the sub-pulse frequency, so that the sub-pulses are orthogonal in the frequency domain and cover each other. After segmenting the pulse compression according to the carrier frequency and bandwidth of each sub-pulse, the interference data forwarded by the intermittent sampling of the jammer can be eliminated, which solves the problem that the prior art cannot eliminate the interference pulse by using correlation, resulting in the inability to identify the target when the interference signal energy is greater than the signal energy.

[0007] To achieve the above object, the technical solution of the present invention comprises the following steps:

[0008] Step 1, estimate the slice interference parameters:

[0009] (1a) The intermittent sampling forwarding interference signal S J (t) Perform pulse compression to obtain the number of interference slice forwarding times M;

[0010] (1b) Construct the transmission reference pulse S ref(t) and the intermittent sampling interference signal envelope S r (t); Envelope cross-correlation method is used to calculate the interference slice width T J and slice forwarding period T u ;

[0011] Step 2: Generate a transmission signal s with agile sub-pulse frequency within the pulse p (t);

[0012] Step 3: According to the slice interference parameter, the transmitted signal s p The sub-pulse frequency of (t) is encoded:

[0013] (3a) Calculate the position of each sub-pulse sampled by the jammer in the transmitted signal according to the following formula:

[0014]

[0015] Wherein, q(i) represents the position of the i-th sub-pulse sampled by the jammer in the transmitted signal, i represents the i-th sub-pulse sampled by the jammer, i=0,1,2...L, L represents the total number of sub-pulses sampled by the jammer, Indicates the rounding down operation, T p Represents the width of the entire transmit pulse, T p =GΔt, G represents the total number of sub-pulses in the sub-pulse frequency coded signal within the pulse, Δt represents the width of each sub-pulse in the sub-pulse frequency coded signal within the pulse, Δt=T J , T J Indicates the width of the interference slice.

[0016] The frequency of the sub-pulse at position q(i) is: f q(i) =f0+d I [q(i)]Δf, where f0 represents the carrier frequency of the transmitted signal, d I [·] represents the coefficient of Δf, d I [·]∈{0,1,2,...,L}, Δf represents the minimum sub-pulse frequency interval. To improve the frequency domain orthogonality between sub-pulses, Δf≥2B sub , B sub represents the bandwidth of the sub-pulse,

[0017] (3b) After removing q(i) from the G sub-pulses, the position of the remaining sub-pulses not sampled by the jammer is p(j), and the frequency of the sub-pulses not sampled by the jammer is: f p(j) =f0+d T [p(j)]Δf, where d T [·] represents the coefficient of Δf, d T [·]∈{L+1,L+2,...G-1};

[0018] Step 4: Construct the echo signal waveform S(t) containing interference and target:

[0019] Step 5: Segmented pulse pressure anti-interference:

[0020] The passband parameters of the corresponding bandpass filter are designed according to the bandwidth of the sub-pulse and the carrier frequency of each sub-pulse frequency band, the sub-pulses in the echo signal S(t) are sorted, and the interference data is eliminated after pulse compression.

[0021] Compared with the prior art, the present invention has the following advantages:

[0022] First, the present invention concentrates the sliced ​​interference sampled sub-pulses that need to be eliminated in the frequency domain through intra-pulse sub-pulse frequency encoding, which greatly reduces the impact of transition band interference on the target signal segment. It overcomes the defect of the prior art that when the interference-to-signal ratio is too large, the transition band interference residue will submerge the adjacent target signal segment, resulting in the inability to correctly identify the target. This makes the present invention have the advantages of improving the target detection probability and the target accumulation gain.

[0023] Secondly, the present invention uses intra-pulse sub-pulse frequency encoding to make the sub-pulses orthogonal to each other in the frequency domain and cover each other. After segmented pulse compression, the interference data of the jammer for intermittent sampling and forwarding can be eliminated, which overcomes the defect that the prior art cannot eliminate the interference data of intermittent sampling and forwarding by only using correlation, resulting in the inability to correctly identify the target when the interference signal energy is greater than the signal energy. The present invention has the advantage of being less constrained by the interference-to-signal ratio and improves the reliability of target detection. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is a flow chart of the present invention;

[0025] Figure 2 It is an amplitude diagram of the pulse pressure result of the intermittent sampling and forwarding interference of the present invention;

[0026] Figure 3 is the slice forwarding period T of the present invention u =Distribution diagram of the two-dimensional amplitude of repeated forwarding interference in the case of 6μs;

[0027] Figure 4 is the slice forwarding period T of the present invention u =Integral curve diagram for the case of 6μs;

[0028] Figure 5 It is a pulse pressure result diagram of each sub-pulse after anti-interference of the coding waveform designed in the simulation experiment of the present invention;

[0029] Figure 6 This is a graph of the pulse pressure results of each sub-pulse after the random frequency jump waveform in the pulse is anti-interference in the simulation experiment of the present invention. DETAILED DESCRIPTION

[0030] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0031] Reference Figure 1 , the sub-band frequency coded slice interference suppression method of the present invention is further described in detail.

[0032] Step 1: Estimate slice interference parameters.

[0033] Without loss of generality, the present invention takes repeated forwarding of intermittent sampling interference as an embodiment.

[0034] (1.1) The intermittent sampling forwarding interference signal S J (t) Perform pulse compression to obtain the number of interference slice forwarding times M.

[0035] The intermittent sampling forwarding interference signal S J (t) is:

[0036]

[0037] Where m represents the sequence number of the number of times the interfering slice is forwarded, M represents the total number of times the interfering slice is forwarded, and N c represents the total number of interference slices in the intermittent sampling and forwarding interference signal, n represents the sequence number of the interference slice in the intermittent sampling and forwarding interference signal, t represents the time variable, τ represents the interference delay of the intermittent sampling and forwarding interference signal, T n represents the start time of the nth interference slice, exp represents the exponential operation with the natural constant e as the base, j represents the imaginary unit symbol, π represents pi, K r Represents the frequency modulation slope of the linear frequency modulation signal of the intermittent sampling forwarding interference signal, φ d Indicates the Doppler phase.

[0038] The pulse compression is achieved by the following formula:

[0039]

[0040] Among them, S M (t) represents the compressed intermittent sampling forwarding interference signal pulse, sinc represents the Sinker function, and the pulse compression result S M The number of false target groups can be obtained from (t) as the maximum forwarding times M of the interference slice.

[0041] Figure 2 Intermittent sampling forwarding interference signal S J (t) Pulse pressure result S M The amplitude diagram of (t), Figure 2 The horizontal axis represents SM (t) is the number of sampling points, and the ordinate represents the normalized amplitude. Figure 2 Each point in represents the amplitude of the corresponding sampling point. Figure 2 The number of each peak in represents the maximum forwarding times of the interference slice, from which it can be judged that the maximum forwarding times of the interference slice is M=2.

[0042] (1.2) Construct the transmitted reference pulse S respectively ref (t) and the intermittent sampling interference signal envelope S r (t); Envelope cross-correlation method is used to calculate the interference slice width T J and slice forwarding period T u .

[0043] The reference pulse S ref (t) and the intermittent sampling interference signal envelope S r (t) is:

[0044]

[0045] Where rect(·) represents the rectangular window function, T w represents the pulse width of the transmitted reference pulse, T u,k represents the delay of the kth intermittent sampling forwarding interference pulse, T c,k Represents the pulse width of the kth intermittent sampling forwarding interference pulse.

[0046] The envelope cross-correlation method is used to calculate the interference slice width T J and slice forwarding period T u The steps are as follows:

[0047] Step 1: Transmit reference pulse S ref (t) and the intermittent sampling interference signal envelope S r (t) Perform cross-correlation processing to obtain the envelope cross-correlation function R c (T w ,t) are as follows:

[0048]

[0049] in, represents the cross-correlation operation, Tra(·) represents the isosceles trapezoidal function, which is a function with a width of T w and T c,k The output of the convolution of two impulses, <T c,k ,T w > indicates that the width of the upper base of the trapezoid is |T c,k -T w |, the bottom width is |T c,k +T w |.

[0050] In the second step, the envelope cross-correlation functions under different reference pulse widths are arranged in rows to construct a matrix and the matrix is ​​modulo-calculated to obtain a two-dimensional amplitude distribution diagram, and the distribution diagram is time-integrated to obtain an integral curve.

[0051] Step 3: Estimate the slice forwarding period T u =t0, where t0 represents the position of the first maximum point in the integral curve diagram.

[0052] Step 4: Combined with the estimated maximum number of forwarding times M of the interference slice, the estimated slice width is

[0053] Figure 3 is the slice forwarding period T of the present invention u = 6μs case repeated forwarding interference two-dimensional amplitude distribution diagram, Figure 3 The horizontal axis represents time in microseconds, and the vertical axis represents the reference pulse width in microseconds. Figure 3 Each point in represents the amplitude of the envelope cross-correlation function under the reference pulse width at the corresponding moment of the point. The brighter the color of the point, the larger the amplitude.

[0054] Figure 4 is the slice forwarding period T of the present invention u =Integral curve diagram for the case of 6μs, Figure 4 The horizontal axis represents the reference pulse width in microseconds, and the vertical axis represents the integrated value of the amplitude. Figure 4 Each point in it represents the integrated amplitude under the reference pulse width.

[0055] Step 2: Generate a transmission signal s with agile sub-pulse frequency within the pulse p (t) are as follows:

[0056]

[0057] Where g represents the sub-pulse number in the sub-pulse frequency coding signal within the pulse, and f g Represents the carrier frequency of the gth sub-pulse in the sub-pulse frequency coded signal within the pulse.

[0058] Step 3: According to the slice interference parameter, the transmitted signal s p The sub-pulse frequency of (t) is encoded.

[0059] In the echo signal, there is a transition band between the interfered sampling sub-pulse and the adjacent undisturbed target sub-pulse. When the interference energy is much greater than the target echo signal energy, the sampling sub-pulse transition band and the adjacent sub-pulse pulse pressure form interference residues. Since the interference-to-signal ratio is too large, even if the interfering sub-pulse is eliminated, the interference residues in the transition band will still submerge the adjacent target signal segment, forming an interference band, and the target cannot be correctly detected and identified. In order to reduce the impact of transition band interference on the target signal segment, the present invention proposes an intra-pulse sub-pulse frequency coding method based on interference estimation parameters. Through sub-pulse frequency coding, the sampled interference segment sub-pulses are adjacent in the frequency domain and concentrated in a certain frequency range, while the unsampled target segment sub-pulses are adjacent to each other and concentrated in another frequency range, thereby greatly reducing the impact range of transition band interference on the target signal segment. The specific coding method is as follows:

[0060] (3.1) According to the following formula, calculate the position of each sub-pulse sampled by the jammer in the transmitted signal:

[0061]

[0062] Wherein, q(i) represents the position of the i-th sub-pulse sampled by the jammer in the transmitted signal, i represents the i-th sub-pulse sampled by the jammer, i=0,1,2...L, L represents the total number of sub-pulses sampled by the jammer, Indicates the rounding down operation, T p Represents the width of the entire transmit pulse, T p =GΔt, G represents the total number of sub-pulses in the sub-pulse frequency coded signal within the pulse, Δt represents the width of each sub-pulse in the sub-pulse frequency coded signal within the pulse, Δt=T J , T J Indicates the width of the interference slice.

[0063] The frequency of the sub-pulse at position q(i) is: f q(i) =f0+d I [q(i)]Δf, where f0 represents the carrier frequency of the transmitted signal, d I [·] represents the coefficient of Δf, d I [·]∈{0,1,2,...,L}, Δf represents the minimum sub-pulse frequency interval. To improve the frequency domain orthogonality between sub-pulses, Δf≥2B sub , B sub Represents the bandwidth of the sub-pulse.

[0064] (3.2) After removing q(i) from the G sub-pulses, the position of the remaining sub-pulses not sampled by the jammer is p(j), then the frequency of the sub-pulses not sampled by the jammer is: f p(j) =f0+d T[p(j)]Δf, where d T [·] represents the coefficient of Δf, d T [·]∈{L+1,L+2,...G-1}.

[0065] After frequency encoding, the sampled interference segment sub-pulses are concentrated in the first half of the frequency domain with a smaller frequency, while the target segment sub-pulses are concentrated in the second half with a larger frequency. Only one target segment sub-pulse adjacent to the interference segment is directly affected by the transition band interference, which greatly reduces the probability of the target segment sub-pulse being interfered with.

[0066] Step 4: construct an echo signal waveform S(t) containing interference and target.

[0067] The implementation steps of constructing the echo signal model S(t) including the target and intermittent sampling interference are as follows:

[0068] The first step is that at a certain moment, the sub-pulse frequency coding signal entering the jammer is s p (t), the repeated forwarding interference sampling signal is p(t), then the intermittent sampling repeated forwarding interference s jx (t) can be expressed as:

[0069]

[0070] In the second step, the total echo signal received by the radar receiver is the sum of the target echo signal and the interference echo signal:

[0071] S(t)=s p (t-η)+s jx (t)

[0072] Wherein, η is the delay of the signal echo.

[0073] Step 5: Segmented pulse pressure anti-interference.

[0074] Since the jammer samples and forwards the intercepted radar signal in segments, forming intermittent sampling interference, the sub-pulses of the sub-pulse frequency coded signal in the pulse can cover each other. By constructing a bandpass filter group to segment the echo signal and perform pulse compression, the energy of the interference signal is much greater than the energy of the target signal, the filter output of the interfered sub-pulse can be suppressed, and the output of the target sub-pulse can be accumulated to achieve the purpose of anti-interference. The specific steps are as follows:

[0075] (5.1) A filter for the echo signal is designed according to the bandwidth of the sub-pulses and the carrier frequency of each sub-pulse frequency band, and the sub-pulses in the echo signal S(t) are sorted. The sorted sub-pulses are pulse compressed and then the interference data is removed.

[0076] The first step is to design the passband corresponding to each sub-pulse in the frequency domain according to the following formula:

[0077]

[0078] Among them, H g (f) represents the bandpass filter corresponding to the g-th sub-pulse, g∈{L+1,L+2,...G-1}, B bpf represents the bandwidth of the bandpass filter, satisfying B sub <B bpf <Δf.

[0079] The second step is to perform FFT on the echo signal S(t) to obtain the spectrum S(f) of S(t), and then combine S(f) with the g-th bandpass filter H g (f) multiply to obtain the filtered signal s g (f).

[0080] (5.2) The sorted sub-pulses are pulse compressed and then the interference data is eliminated.

[0081] The first step is to g (f) After IFFT, the time domain sub-pulse echo signal s is obtained g (t), let s g (t) Obtain the pulse compression output signal s of each sub-segment through the corresponding sub-pulse matching filter out_g (t) are as follows:

[0082]

[0083] in, represents the convolution operation, s g * (-t) means s g (t) The corresponding matching function, * indicates the conjugate operation.

[0084] In the second step, the pulse pressure variance of each sub-segment is calculated according to the following formula and the mean of the variance is taken as the basic threshold E for interference suppression:

[0085]

[0086] Among them, mean(·) represents the mean operation, and var(·) represents the variance operation.

[0087] In the third step, the variance of each sub-segment is tested according to the following formula, and the sub-segments whose variance exceeds the threshold are judged as interference segments that should be eliminated, and the sub-segments that do not exceed the threshold are judged as target segments that should be retained.

[0088]

[0089] Wherein, μ represents the scaling factor, and its value is selected according to the requirements of the interference suppression basic threshold in actual engineering.

[0090] The effect of the present invention can be further illustrated by the following simulation experiment:

[0091] 1. Simulation conditions:

[0092] The simulation experiment of the present invention uses an Intel(R) Core(TM) i5-6500 CPU@3.20GHz, a 64-bit Windows operating system, and the simulation software uses MATLAB (R 2016a).

[0093] The simulation experiment parameters of the present invention are set as follows. For generality, the intermittent sampling interference in the simulation experiment adopts repeated forwarding interference, and the sampling time width T J =2μs, sampling period T u =6μs, signal-to-interference ratio is -36dB. The simulation parameters of the sub-pulse frequency coding waveform within the pulse are as follows: sub-pulse bandwidth B sub =5MHz, sub-pulse width t sub =2μs, the minimum frequency hopping interval of the sub-pulse frequency band Δf = 2B sub =10MHz, number of sub-pulses M=8.

[0094] 2. Simulation content and result analysis:

[0095] Under the above simulation conditions, the method of the present invention is used to design the intra-pulse sub-pulse frequency coding waveform, and the waveform is used as a radar transmission signal to carry out an anti-interference simulation experiment. Figure 5 Figures (a) to (e) in the figure are the result diagrams of pulse compression of the remaining 5 sub-pulses in the target signal after bandpass filtering using the intra-pulse sub-pulse frequency coding waveform of the present invention. Figure 5 The horizontal axis represents the number of sampling points, and the vertical axis represents the normalized amplitude. Figure 5 Each point in Figures (a) to (e) represents the correlation amplitude at the sampling moment, and the number of peaks represents the number of targets.

[0096] As a comparison, Figure 6 This is the result of pulse compression of the remaining 5 sub-pulses in the target signal after bandpass filtering using the uncoded intra-pulse random frequency hopping waveform. Figure 6 The horizontal axis represents the number of sampling points, and the vertical axis represents the normalized amplitude. Figure 6 Each point in Figures (a) to (e) represents the correlation amplitude at the sampling moment, and the number of peaks represents the number of targets.

[0097] By comparison, it can be seen that Figure 6In the anti-interference simulation results of the random sub-pulse frequency coding shown in FIG, after the interference sub-pulse is eliminated, the five target segment sub-pulses that are not interfered by the slice are seriously affected by the transition band interference, resulting in the transition band interference energy being greater than the target energy, and the target cannot be correctly identified; and after the anti-interference simulation is performed using the intra-pulse sub-pulse frequency coding waveform proposed by the present invention, as shown in FIG. Figure 5 As shown, among the remaining target segment signal sub-pulses, only Figure 5 In Figure (a), the target peak is greatly affected by the transition band interference, while the pulse compression results of the other sub-pulses all show a good transition band interference suppression effect.

Claims

1. A method for suppressing slice interference of sub-band frequency coding, characterized in that: The sub-pulse frequency in the pulse is encoded so that the sampled sub-pulse frequency band and the unsampled sub-pulse frequency band in the transmitted signal are respectively concentrated in the frequency domain; the specific steps of the interference suppression method include the following: Step 1, estimate the slice interference parameters: (1a) The intermittent sampling forwarding interference signal S J (t) Perform pulse compression to obtain the number of interference slice forwarding times M; (1b) Construct the transmission reference pulse S ref (t) and the intermittent sampling interference signal envelope S r (t); Envelope cross-correlation method is used to calculate the interference slice width T J and slice forwarding period T u ; Step 2: Generate a transmission signal s with agile sub-pulse frequency within the pulse p (t); Step 3: According to the slice interference parameter, the transmitted signal s p The sub-pulse frequency of (t) is encoded: (3a) Calculate the position of each sub-pulse sampled by the jammer in the transmitted signal according to the following formula: Wherein, q(i) represents the position of the i-th sub-pulse sampled by the jammer in the transmitted signal, i represents the i-th sub-pulse sampled by the jammer, i=0,1,2...L, L represents the total number of sub-pulses sampled by the jammer, Indicates the rounding down operation, T p Represents the width of the entire transmitted pulse, T p =GΔt, G represents the total number of sub-pulses in the sub-pulse frequency coded signal within the pulse, Δt represents the width of each sub-pulse in the sub-pulse frequency coded signal within the pulse, Δt = T J , T J represents the width of the interference slice, T u It is the slice forwarding period; The frequency of the sub-pulse at position q(i) is: f q(i) =f0+d I [q(i)]Δf, where f0 represents the carrier frequency of the transmitted signal, d I [·] represents the coefficient of Δf, d I [·]∈{0,1,2,...,L}, Δf represents the minimum sub-pulse frequency interval. To improve the frequency domain orthogonality between sub-pulses, Δf≥2B sub , B sub represents the bandwidth of the sub-pulse; (3b) After removing q(i) from the G sub-pulses, the position of the remaining sub-pulses not sampled by the jammer is p(j), and the frequency of the sub-pulses not sampled by the jammer is: f p(j) =f0+d T [p(j)]Δf, where d T [·] represents the coefficient of Δf, d T [·]∈{L+1,L+2,...G-1}; Step 4, constructing an echo signal waveform S(t) including interference and target; Step 5: Segmented pulse pressure anti-interference: The filter of the echo signal is designed according to the bandwidth of the sub-pulse and the carrier frequency of each sub-pulse frequency band, the sub-pulses in the echo signal S(t) are sorted, and the sorted sub-pulses are pulse compressed to remove interference data.

2. The method for suppressing sub-band frequency coded slice interference according to claim 1, characterized in that: The intermittent sampling forwarding interference signal S described in step (1a) J (t) is: Where m represents the sequence number of the number of times the interfering slice is forwarded, M represents the total number of times the interfering slice is forwarded, and N c represents the total number of interference slices in the intermittent sampling and forwarding interference signal, n represents the sequence number of the interference slice in the intermittent sampling and forwarding interference signal, t represents the time variable, τ represents the interference delay of the intermittent sampling and forwarding interference signal, T n represents the start time of the nth interference slice, exp represents the exponential operation with the natural constant e as the base, T J represents the width of the interference slice, j represents the symbol of the imaginary unit, π represents the circumference ratio, K r Represents the frequency modulation slope of the linear frequency modulation signal of the intermittent sampling forwarding interference signal, φ d Indicates the Doppler phase.

3. The method for suppressing sub-band frequency coded slice interference according to claim 2, characterized in that: The pulse compression described in step (1a) is achieved by the following formula: Among them, S M (t) represents the compressed intermittent sampling forwarding interference signal pulse, sinc represents the Sinker function, and the pulse compression result S M The number of false target groups can be obtained from (t) as the maximum forwarding times M of the interference slice.

4. The method for suppressing sub-band frequency coded slice interference according to claim 1, characterized in that: The reference pulses S are constructed separately as described in step (1b) ref (t) and the intermittent sampling interference signal envelope S r (t) are as follows: Where rect(·) represents the rectangular window function, T w represents the pulse width of the transmitted reference pulse, T u,k represents the delay of the kth intermittent sampling forwarding interference pulse, T c,k Represents the pulse width of the kth intermittent sampling forwarding interference pulse.

5. The method for suppressing sub-band frequency coded slice interference according to claim 4, characterized in that: The interference slice width T is calculated by using the envelope cross-correlation method in step (1b). J and slice forwarding period T u The steps are as follows: The first step is to transmit the reference pulse S ref (t) and the intermittent sampling interference signal envelope S r (t) Perform cross-correlation processing to obtain the envelope cross-correlation function R c (T w ,t) are as follows: in, represents the cross-correlation operation, Tra(·) represents the isosceles trapezoidal function, which is a function with widths Tw and T c,k The output of the convolution of two impulses, <T c,k ,T w > indicates that the width of the upper base of the trapezoid is |T c,k -T w |, the bottom width is |T c,k +T w |; The second step is to construct a matrix by arranging the envelope cross-correlation functions under different reference window lengths in rows and modulo the matrix to obtain a two-dimensional amplitude distribution diagram, and then perform time integration on the distribution diagram to obtain an integral curve; Step 3: Estimate the slice forwarding period T u =t0, where t0 represents the position of the first maximum point in the integral curve diagram; Step 4: Combine the estimated maximum number of forwarding times M of the interference slice and estimate the slice width to be 6. The method for suppressing interference of sub-band frequency coded slices according to claim 1, characterized in that: The sub-pulse frequency agility signal s generated in step 2 p (t) are as follows: Where g represents the sub-pulse number in the sub-pulse frequency coding signal within the pulse, and f g Represents the carrier frequency of the gth sub-pulse in the sub-pulse frequency coded signal within the pulse.

7. The method for suppressing sub-band frequency coded slice interference according to claim 6, characterized in that: Step 4: The implementation steps of constructing the echo signal model S(t) including the target and intermittent sampling interference are as follows: The first step is that at a certain moment, the sub-pulse frequency coding signal entering the jammer is s p (t), the repeated forwarding interference sampling signal is p(t), then the intermittent sampling repeated forwarding interference s jx (t) can be expressed as: In the second step, the total echo signal received by the radar receiver is the sum of the target echo signal and the interference echo signal: S(t)=s p (t-η)+s jx (t) Wherein, η is the delay of the signal echo.

8. The method for suppressing sub-band frequency coded slice interference according to claim 7, characterized in that: The steps for sorting sub-pulses in step 5 are as follows: The first step is to design the passband corresponding to each sub-pulse in the frequency domain according to the following formula: Among them, H g (f) represents the bandpass filter corresponding to the g-th sub-pulse, g∈{L+1,L+2,...G-1}B bpf represents the bandwidth of the bandpass filter, satisfying B sub <B bpf <Δf; In the second step, the echo signal S(t) is subjected to FFT to obtain the spectrum S(f) of S(t), and then S(f) is respectively combined with the g-th bandpass filter H g (f) to obtain the filtered signal sg(f).

9. The method for suppressing sub-band frequency coded slice interference according to claim 8, characterized in that: The steps of removing interference data after pulse compression on the sorted sub-pulses in step 5 are as follows: The first step is to g (f) After IFFT, the time domain sub-pulse echo signal s is obtained g (t), let s g (t) Obtain the pulse compression output signal s of each sub-segment through the corresponding sub-pulse matching filter out_g (t): in, represents the convolution operation, s g * (-t) means s g (t) The corresponding matching function, * indicates the conjugate operation; In the second step, the pulse pressure variance of each sub-segment is calculated according to the following formula and the mean of the variance is taken as the basic threshold E for interference suppression: Among them, mean(·) represents the mean operation, and var(·) represents the variance operation; In the third step, the variance of each sub-segment is tested according to the following formula, and the sub-segments whose variance exceeds the threshold are judged as interference segments that should be eliminated, and the sub-segments that do not exceed the threshold are judged as target segments that should be retained: Wherein, μ represents the scaling factor, and its value is selected according to the requirements of the interference suppression basic threshold in actual engineering.

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