Coherent processing method of random variable T radar

Abstract

The invention provides a coherent processing method of a random variable T radar, and provides a coherent processing algorithm of an inter-pulse time agility radar by researching residual phase information of inter-pulse time agility radar echoes, analyzing characteristics of signal subspaces of the inter-pulse time agility radar echoes, and providing a method for estimating target speed and phase deviation by using echoes of only one group of pulses. The method optimizes and improves a signal processing algorithm, compensates accumulated loss caused by phase discontinuity, improves the detection probability of a target and provides support for stable tracking of the target while the radar performs inter-pulse time parameter agility and exerts the anti-interference advantage of the radar.

Description

Technical Field

[0001] The present invention relates to the field of radar detection and signal processing. Aiming at the radar anti-interference demand, a radar coherent processing method based on spectrum peak search is proposed based on a non-stationary signal with inter-pulse time agility (randomly variable T) system to counter interference when the radar adopts an inter-pulse time agility (randomly variable T) system. Background Art

[0002] Modern jammers mostly target coherent radars to achieve suppression, deception or composite jamming. In the face of composite coherent jamming, the most effective way for radar is to make it impossible for the jammer to predict the form of the radar transmission signal (for example, frequency, repetition frequency, bandwidth, etc.), that is, to take radar parameter agility measures to counter the jammer's reconnaissance and interception of radar signal parameters, making it difficult for the jammer to effectively implement accurate jamming of the radar.

[0003] At present, there are many studies on frequency agility in radar parameter agility, especially the performance analysis and improvement methods of frequency agile radar, including frequency agility between pulse groups and frequency agility between pulses. However, due to the large fluctuation of the amplitude of the target echo at different frequencies caused by frequency agility, there is a problem that weak targets cannot be detected. Therefore, time agility between pulses has begun to attract attention. In some cases, this variable T parameter agility system can effectively improve the radar's performance against composite related interference on the basis of maintaining a certain level of clutter suppression. For jammers, the general transmission and reception work in time-sharing mode. After the radar changes T randomly between pulses, it will be difficult to accurately estimate the variable T parameters, so it cannot form effective distance Doppler or track deception interference, and can only play the role of random interference pulses. For random interference pulses entering from the sidelobe, the radar can suppress them by using the sidelobe blanking method; for random pulse interference entering from the main lobe, the radar can capture the front edge of the interference pulse through parameter agility, or filter it out based on the distance, time and amplitude distribution characteristics of the random pulse.

[0004] For pulse-to-pulse time-agile radar, clutter suppression can be performed through the MTI method, but under variable T conditions, MTD coherent accumulation cannot be performed after pulse MTI processing. To solve this problem, a dual threshold detection method of CFAR detection + sliding window detection was proposed. However, compared with radar full coherent accumulation detection, this detection method has a certain signal-to-noise ratio and detection loss. Therefore, although it can cope with the threat brought by interference, there is processing loss, and this detection method has defects. Summary of the invention

[0005] In order to overcome the shortcomings of the prior art, the present invention provides a coherent processing method for a random variable T radar. By studying the residual phase information of the inter-pulse time-agile radar echo, the characteristics of its signal subspace are analyzed, and a method of estimating the target speed and phase offset using only a group of pulse echoes is proposed, and a coherent processing algorithm for the inter-pulse time-agile radar is obtained. This method does not require priori speed information, the number of pulses required is the same as that of a normal pulse group, and the number of pulses is independent of the variable T, so it has extremely strong practicality. Simulation experiments have proved the effectiveness of this method in coherent accumulation and target detection.

[0006] The inter-pulse time-agile radar signal is a non-stationary signal. The initial phase of its echo is related to time and does not change linearly. Therefore, the traditional linear coherent processing method based on Fourier transform cannot be used. The method proposed in the present invention realizes coherent processing by estimating the initial phase change caused by time change.

[0007] The specific steps of the technical solution adopted by the present invention to solve its technical problem are:

[0008] Step 1: Receive the echo signal of each pulse, sample, and compress the pulse to form the echo data matrix Y1;

[0009] Step 2: Perform MTI processing on three-pulse cancellation to obtain the data matrix Y2 after clutter suppression;

[0010] Step 3: Calculate the data matrix R of the echo data y ;

[0011] Step 4: Phase parameter estimation, by solving the optimization problem to calculate the optimal filter coefficient w for coherent processing * = r(R0 * ,v0 * ).

[0012] Step 5: Calculate and multiply the echo data matrix by the filter coefficient to obtain the coherent processing result y * =w *H Y2.

[0013] In the first step, the coherent frequency-agile radar waveform is recorded as a(t). For a CPI containing N pulses, the transmitted signal s(t) is:

[0014]

[0015] Where: N is the number of pulses; f c is the radio frequency; T r is the basic pulse period; △T is the time interval between pulses; M n is the period number of the nth pulse;

[0016] Therefore, the echo signal is:

[0017]

[0018] Among them, β = 2v / c is the Doppler caused by speed; τ = 2R / c is the delay caused by distance; c is the speed of light;

[0019] The target echo signal at the nth pulse is:

[0020]

[0021] Where X is the coefficient sequence about R and v, and the noise sequence is defined as w n , the distance to the target scattering point is R0, the speed is v0, and the scattering intensity is ρ, then the echo signal received by the radar is:

[0022]

[0023] remember is the constraint vector;

[0024] For a CPI containing N pulses, the received data matrix is:

[0025] Y=[y1,y2,…,y N ] (5)

[0026] Clutter suppression is performed through MTI processing to obtain Y1;

[0027] In the fourth step, the target speed search range is determined, and the optimization problem is solved by searching:

[0028] max(Y1*w) (6)

[0029] Solving for R0 * and v0 * , and get the optimal filter coefficients:

[0030] w * = r(R0 * ,v0 * ) (7)

[0031] Complete the coherent processing of pulse-to-pulse time-agile radar * =Y1*w * After coherent accumulation, the real distance R and speed v of the target are obtained, that is, the target detection is completed when the phase of the target echo signal is discontinuous, and the target tracking process is continued according to the target distance and speed.

[0032] The beneficial effect of the present invention is that the coherent accumulation method proposed by the present invention can effectively solve the coherent processing problem of pulse-to-pulse time-agile radar. While the radar performs pulse-to-pulse time parameter agility and exerts its anti-interference advantage, it optimizes and improves the signal processing algorithm, compensates for the accumulation loss caused by phase discontinuity, improves the detection probability of the target, and provides support for stable target tracking.

[0033] Inter-pulse time period agility is an effective means for radar to counter active forwarding interference. However, for a long time, due to the lack of an ideal coherent accumulation algorithm, inter-pulse time agile radar has not been widely used. The present invention proposes a coherent processing method for inter-pulse time agile radar based on spectral peak search. First, the phase offset caused by the speed and time change of the target is estimated according to the echo data, and then compensation is performed to complete the coherent accumulation. At the same time, the MTI method can be used for clutter suppression. The present invention successfully overcomes the difficult problem of coherent processing of inter-pulse time agile frequency radar signals. This method does not require prior knowledge or increase the number of pulses. It has good practicality, strong robustness, and is easy to implement in engineering. It can also be combined with frequency agility to counter deceptive interference, providing important technical support for radar anti-interference. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is the pulse-to-pulse time agility signal waveform.

[0035] Figure 2 It is the coherent accumulation process of pulse-to-pulse time-agile signals.

[0036] Figure 3 This is the comparison before and after clutter suppression. Figure 3 (a) indicates that clutter suppression is not performed. Figure 3 (b) To perform clutter suppression.

[0037] Figure 4 It is the comparison before and after the coherent processing. Figure 4 (a) is the traditional method, Figure 4 (b) Optimal weights method. DETAILED DESCRIPTION

[0038] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0039] Coherent processing workflow:

[0040] Step 1: Receive the echo signal of each pulse, sample, and compress the pulse to form the echo data matrix Y1;

[0041] Step 2: Perform MTI processing (three-pulse cancellation) to obtain the data matrix Y2 after clutter suppression;

[0042] Step 3: Calculate the data matrix R of the echo data y ;

[0043] Step 4: Phase parameter estimation, by solving the optimization problem to calculate the optimal filter coefficient w for coherent processing * = r(R0 * ,v0 * ).

[0044] Step 5: Calculate and multiply the echo data matrix by the filter coefficient to obtain the coherent processing result y * =w *H Y2.

[0045] like Figure 2 As shown, assuming radar parameters:

[0046] The scene contains two targets and adopts the pulse-to-pulse time agility working mode. The time interval is randomly generated and the transmitted pulse is a linear frequency modulation signal with a time width of 20us, a bandwidth of 5MHz and 64 pulses.

[0047] Two targets are set in the simulation, and the target parameters are as follows:

[0048] Table 1 Target parameters

[0049]

[0050] By using the coherent accumulation method proposed in the present invention, the optimal filter coefficients are obtained by solving the optimization problem through phase compensation after MTI processing, thereby completing the coherent accumulation. Figure 3 It can be seen that the use of MTI pulse cancellation can suppress ground clutter. Figure 3 Figure (a) shows the image without clutter suppression. It can be seen that the target and clutter are mixed together. Since the clutter is very strong, the target cannot be detected. Figure 3 As can be seen from Figure (b), clutter is effectively suppressed, the target is fully revealed, and the ideal effect is achieved. Figure 4 It can be seen that the coherent accumulation method proposed in the present invention can avoid signal-to-noise ratio loss and achieve complete coherence. Figure 4 The result of (a) is processed by the traditional FFT method. Due to the time agility between pulses, the phase is discontinuous, and thus the method cannot be phase-coherent. Figure 4 Figure (b) fills the phase difference caused by time agility and optimizes the optimal filter coefficient to complete the coherent processing, and finally obtains the target speed and distance information.

[0051] The above implementation is only a specific example of the present invention and does not constitute any limitation to the present invention. Obviously, according to the concept of the present invention, different implementation methods can be improved, but these are all protected by the present invention.

Claims

1. A coherent processing method for a randomly variable T radar, comprising: Step 1: Receive the echo signal of each pulse, sample, and compress the pulse to form the echo data matrix Y1; Step 2: Perform MTI processing on three-pulse cancellation to obtain the data matrix Y2 after clutter suppression; Step 3: Calculate the data matrix R of the echo data y ; Step 4: Phase parameter estimation, by solving the optimization problem to calculate the optimal filter coefficient w for coherent processing * = r(R0 * ,v0 * ). Step 5: Calculate and multiply the echo data matrix by the filter coefficient to obtain the coherent processing result y * =w *H Y2.

2. The coherent processing method of the random variable T radar according to claim 1, characterized in that: In the first step, the coherent frequency-agile radar waveform is recorded as a(t). For a CPI containing N pulses, the transmitted signal s(t) is: Where: N is the number of pulses; f c is the radio frequency; T r is the basic pulse period; △T is the time interval between pulses; M n is the period number of the nth pulse; Therefore, the echo signal is: Among them, β = 2v / c is the Doppler caused by speed; τ = 2R / c is the delay caused by distance; c is the speed of light; The target echo signal at the nth pulse is: Where X is the coefficient sequence about R and v, and the noise sequence is defined as w n , the distance to the target scattering point is R0, the speed is v0, and the scattering intensity is ρ, then the echo signal received by the radar is: remember is the constraint vector; For a CPI containing N pulses, the received data matrix is: Y=[y1,y2,…,y N ] (5) Clutter suppression is performed through MTI processing to obtain Y1.

3. The coherent processing method of the random variable T radar according to claim 1, characterized in that: In the fourth step, the target speed search range is determined, and the optimization problem is solved by searching: max(Y1*w)(6) solves for R0 * and v0 * , and get the optimal filter coefficients: In * =r(R0 * ,v0 * ) (7) Complete the coherent processing of pulse-to-pulse time-agile radar * =Y1*w * After coherent accumulation, the real distance R and speed v of the target are obtained, that is, the target detection is completed when the phase of the target echo signal is discontinuous, and the target tracking process is continued according to the target distance and speed.

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