A sidelobe suppression method for radar inter-pulse phase coded signal

Abstract

The invention discloses a radar inter-pulse phase coding signal sidelobe suppression method, comprising: modulating a transmitting antenna signal according to a phase coding sequence and transmitting simultaneously, and receiving an echo signal reflected by a target by a receiving antenna; performing matched filtering processing on the received echo signal to obtain a range Doppler spectrum, and completing range dimension target detection to obtain an over-detection range point; for each over-detection range point, obtaining a Doppler frequency and peak information of a strong target through Doppler dimension target detection; establishing a peak point correction matrix through combining the Doppler frequency and peak information of the strong target with an orthogonal component frequency domain response based on an error model to obtain a corrected peak point of the current target; adopting a hypothesis detection method to restore the Doppler spectrum of the target with a maximum SINR as a criterion, performing residual orthogonal component elimination of the current target in the frequency domain, and finally repeatedly completing residual orthogonal component elimination of the over-detection target point until the Doppler dynamic range of the range point is greater than a threshold.

Description

Technical Field

[0001] The invention belongs to the technical field of radar signal processing, and in particular relates to a radar inter-pulse phase coding signal sidelobe suppression method. Background Art

[0002] MIMO (Multiple Input Multiple Output) technology is widely used because it can achieve higher angular resolution under given radar size and number of antennas. When applying MIMO technology, it is crucial to choose a suitable waveform. In addition to meeting the requirements of resolution and low sidelobes, the MIMO radar waveform must also achieve orthogonality in the transmitted waveform. Inter-pulse phase coding technology is one of the important ways to achieve orthogonality in MIMO transmitted waveforms.

[0003] The basic idea of ​​pulse-to-pulse phase coding technology is as follows: at the transmitting end, the linear frequency modulation continuous wave (FMCW) signal is modulated by the pulse-to-pulse phase coding sequence to modulate the initial phase of the signal and transmitted simultaneously by each antenna. At the receiving end, since the receiving antenna receives the signal echoes of different transmitting antennas at the same time, the echo signal coupling between the transmitting antennas is inevitable. Usually, the echo signal needs to be decoded to achieve echo separation. However, after the decoding process, the residual orthogonal components of each transmitting antenna still exist. After the component is weighted by the target amplitude, it will cause the overall elevation of the sidelobes on the Doppler spectrum. At this time, weak targets will be submerged in the high sidelobes of strong targets, resulting in missed detection. Therefore, how to reduce the Doppler sidelobes and improve the dynamic range of the signal to interference plus noise ratio (SINR) of Doppler-dimensional targets is an urgent problem to be solved when the pulse-to-pulse phase coding waveform is applied to MIMO radar.

[0004] In response to the Doppler sidelobe elevation problem of the above-mentioned inter-pulse phase-coded waveform, a large number of studies have started from coding design, and have alleviated the impact of residual orthogonal components by improving the orthogonality of the inter-pulse phase-coded sequence. However, the improvement of the Doppler SINR dynamic range by coding design is limited. The document "Slow time waveform design for MIMO GMTIradar using CAZAC sequences, 2018 IEEE Radar Conference" mentioned that even if a pulse phase-coded sequence with strong orthogonality is obtained through coding design, its Doppler SINR dynamic range will not exceed 10log 10(L) dB, where L is the coding sequence length, that is, the number of frequency modulated continuous wave sequences. And with the increase in the number of transmitting antennas and the number of targets, the dynamic range will continue to decrease, resulting in the fact that the pulse-to-pulse phase coded signal is still limited in practical applications.

[0005] In order to solve the problem of Doppler sidelobe rise of inter-pulse phase coded signals, it is necessary to further study the Doppler sidelobe suppression method, reduce the influence of residual orthogonal components, and improve the Doppler dynamic range. In this regard, Delphi Corporation of Germany proposed in its patent "Residue cancellation for automated vehicle MIMO radar" (patent number: US9952319) to use the target spectrum windowing and truncation method to extract target information, restore the decoded residual orthogonal components, and then eliminate the influence of residual orthogonal components. This method is a rough estimate of target information. Although the Doppler sidelobe is reduced after the residual orthogonal components are eliminated, it is easy to cause pseudo peaks on the spectrum, resulting in false alarms. General Motors of the United States proposed in its patent "Multi-target detection in CDMA radar system" (patent number: US10795013B2) to reconstruct and eliminate the decoded residual signal in the time domain through target detection information. However, this method reconstructs the signal in the time domain and does not consider factors such as parameter estimation errors, so the Doppler sidelobe suppression effect is poor in robustness. In addition, constructing time domain signals and multiple time-frequency conversions will greatly increase the amount of calculation. Summary of the invention

[0006] The invention discloses a radar inter-pulse phase coding signal sidelobe suppression method, which can quickly and effectively suppress the Doppler sidelobe of strong targets, improve the Doppler dimension SINR dynamic range, thereby improving the detection capability of weak targets and reducing the missed detection rate.

[0007] The present invention is achieved through the following technical solutions.

[0008] A radar inter-pulse phase coded signal sidelobe suppression method, comprising:

[0009] The transmitting antenna signal is modulated according to the phase coding sequence and transmitted simultaneously, and the echo signal reflected by the target is received by the receiving antenna; the received echo signal is subjected to matched filtering to obtain the range Doppler spectrum, and the range dimension target detection is completed to obtain the over-detection distance point;

[0010] For each of the detected distance points, a strong target Doppler frequency and peak information are obtained through Doppler dimension target detection; for each detected target point in turn, a peak point correction matrix is ​​established by combining the strong target Doppler frequency and peak information with the orthogonal component frequency domain response based on the error model to obtain the corrected peak point of the current target;

[0011] The hypothesis detection method is adopted to restore the Doppler spectrum of the target with the maximum SINR as the criterion, and the residual orthogonal components of the current target are eliminated in the frequency domain. Finally, the residual orthogonal components of the detected target point are eliminated repeatedly until the Doppler dynamic range of the distance point is greater than the threshold.

[0012] Beneficial effects of the present invention:

[0013] The present invention selects a coding design criterion and an inter-pulse phase coding sequence with strong orthogonality to preliminarily meet the Doppler dynamic range requirements. The residual orthogonal components of strong targets raise the Doppler sidelobes, and a method based on strong target detection information and decoded residual orthogonal component frequency domain response is proposed to quickly restore the interference residual signal spectrum, thereby directly eliminating interference in the frequency domain and completing sidelobe suppression. In addition, a parameter estimation error model is added to improve the strong target spectrum recovery accuracy and achieve robust Doppler sidelobe suppression. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a flow chart of the method for suppressing sidelobe of pulse-to-pulse phase coded signal of the present invention;

[0015] Figure 2 It is the time-frequency phase diagram of the inter-pulse phase coding signal of the present invention;

[0016] Figure 3 It is a processing flow chart of the Doppler sidelobe suppression method of the present invention;

[0017] Figure 4 This is a comparison diagram of the Doppler spectrum of the decoded signal of the present invention and the Doppler spectrum after sidelobe suppression. DETAILED DESCRIPTION

[0018] The present invention will be described in detail below in conjunction with the accompanying drawings.

[0019] like Figure 1 As shown, a radar inter-pulse phase coded signal sidelobe suppression method in this specific implementation manner specifically includes:

[0020] Step 1: The transmitting antenna signal is modulated according to the phase coding sequence and transmitted simultaneously, and the echo signal reflected by the target is received by the receiving antenna;

[0021] In this embodiment, the phase coding sequence is obtained in the following manner:

[0022] Determine the number of transmitting antennas as N, the number of frequency modulation sequences in a single frame as L, the frequency modulation sequence repetition period as T, and design N groups of phase coding sequences based on the minimum peak interference residual (PIR), denoted as a1, a2, …, a N , the length of each sequence is L;

[0023]

[0024] where a n (l) and a h (l) are sequence a n With sequence a h The lth element of represents the phase coding value of the nth transmitting antenna and the hth transmitting antenna in the lth FMCW signal; is the maximum Doppler frequency.

[0025] like Figure 2 As shown, in this embodiment, the transmitting antenna signal is modulated according to the phase coding sequence and transmitted simultaneously, specifically including: performing phase modulation on the FMCW signal between pulses according to the phase coding sequence, and transmitting simultaneously by N transmitting antennas. In specific implementation, all antennas at the transmitting end simultaneously transmit FMCW signals with completely consistent time-frequency coefficients, the initial phase of the signal of each transmitting antenna is modulated by the corresponding coding sequence, and the phase coding value switches with the transmitting pulse, that is, the initial phase φ of the signal modulation of the nth transmitting antenna in the lth transmitting cycle is the coding value a n (l).

[0026] In this embodiment, the echo signal reflected by the target is received by a receiving antenna. Specifically, M receiving antennas perform de-chirp and AD sampling processing on the echo signal at the receiving end to obtain a digital echo signal of a size of K×L×M, wherein K is the number of fast time sampling points, M is the number of receiving antennas, and L is the number of single-frame frequency modulation sequences.

[0027] Step 2: Perform matched filtering on the received echo signal to obtain the range-Doppler (RD) spectrum, complete range-dimensional target detection, and obtain the detection distance point;

[0028] In this embodiment, the following steps are specifically included:

[0029] 201. Perform data windowing and FFT processing on the received single frequency modulated continuous wave signal to complete target distance dimension focusing;

[0030] 202. Perform slow time decoding processing at each distance point along the range-slow time spectrum to complete echo signal separation and obtain range-slow time spectra of M×N virtual channels;

[0031] 203. Perform FFT processing on the distance-slow time spectra of the M×N virtual channels along the slow time dimension to complete two-dimensional focusing of the target and obtain RD spectra of M×N virtual channels;

[0032] 204. Perform non-coherent accumulation processing on the M×N virtual channel RD spectra, and perform range-dimensional target detection on the RD spectra after the non-coherent accumulation to obtain J passed-detection distance points.

[0033] Step three: for each of the above-mentioned over-detected distance points, obtain the Doppler frequency and peak information of I strong targets through Doppler-dimensional target detection; for each over-detected target point in turn, establish a peak point correction matrix through the strong target Doppler frequency and peak information combined with the orthogonal component frequency domain response based on the error model to obtain the corrected peak point of the current target; then, adopt the hypothesis detection method to quickly restore the Doppler spectrum of the target with the maximum SINR as the criterion, and complete the residual orthogonal component elimination of the current target in the frequency domain. Finally, repeat the elimination of residual orthogonal components of the over-detected target point until the Doppler dynamic range of the distance point is greater than the threshold SINR. min .

[0034] 301. Perform Doppler target detection on the jth detection distance point to obtain I detection targets. Sort the detection targets according to their peak amplitudes and record them as targets Target1, Target2, ..., Target I ; In specific implementation, the initial value of j is 1,

[0035] 302. According to the i-th target Target i The range index rangeIndex and the Doppler index dopplerIndex are used to extract multi-channel peaks p1, p2, ..., p on the RD spectra of M×N virtual channels. MN Data, retake the peak data to get the peak matrix P:

[0036]

[0037] The peak matrix is ​​compared with the peak point correction matrix B based on the error model δ Multiply them to get the corrected peak point amplitude phase P δ ';In specific implementation, the initial value of i is 1;

[0038] The frequency domain response matrix of the orthogonal components based on the error model is A δ

[0039]

[0040] A δ A is a vector matrix, each element in the matrix is ​​a complex sequence of length L. δ The element in the nth row and hth column is denoted by A n / h,δ , by sequence a n / h,δ Perform Fourier transform to obtain. n / h,δ The lth element of the sequence is represents the residual orthogonal component with the velocity measurement error δ added, where λ represents the signal wavelength; specifically, the velocity measurement error δ is set to Q cases, and the values ​​include

[0041]

[0042] By A δ The peak point correction matrix can be obtained as

[0043]

[0044] Therefore, by multiplying the peak matrix with the peak correction matrix based on the error model, the corrected peak point is

[0045] P δ '=PB δ (6)

[0046] 303. Determine the orthogonal component spectrum matrix A based on the error model according to the target Doppler index δ The displacement is dopplerIdx, and the matrix A is obtained δ | dopplerIdx , the corrected peak point P δ 'With A δ | dopplerIdx The target spectrum recovered by multiplication is recorded as Y δ,target , in the target spectrum Y δ,target After removing the peak point information, the residual orthogonal component term is Y δ,residual ;

[0047] Y δ,target =P δ 'A δ | dopplerIdx (7)

[0048] Y δ,residual =Y δ,target -P (8)

[0049] 304. Eliminate the residual term Y of the strong target signal spectrum interference on the Doppler spectrum Y δ,residual , and get the spectrum Y δ ';

[0050] Y δ '=YY δ,residual (9)

[0051] 305. Calculate the spectrum Y under different error models δ ' SINR, update Y to the spectrum corresponding to the maximum SINR;

[0052]

[0053]

[0054] 306. Calculate the ratio of the strongest point of the spectrum to the noise power to obtain the current Doppler SINR dynamic range. If the dynamic range is greater than or equal to SINR min , then the Doppler sidelobe suppression of the distance point is completed, and the process continues to step 307; otherwise, let i=i+1, and repeat steps 302 to 306 to eliminate the residual orthogonal components of the next target at the distance point;

[0055] 307 , j=j+1, repeat 301 to 307 until Doppler sidelobe suppression of all the detection range points is completed.

[0056] Embodiment 1:

[0057] In this embodiment, three targets are set, including two strong targets and one weak target, where the parameters are:

[0058] Number of transmitting antennas N = 3

[0059] Number of receiving antennas M = 4

[0060] Number of frequency modulation sequences L = 256

[0061] FM sequence repetition period T = 50us

[0062] Fast time sampling points K = 625

[0063] Minimum peak interference residual PIR = 29.67dB

[0064] Number of error models Q = 8

[0065] Doppler SINR dynamic range threshold SINR min =23dB

[0066] In this implementation case, due to the superposition of multi-target residual orthogonal components, the dynamic range of the SINR in the Doppler dimension after decoding is only 14.9 dB. Figure 4 As shown in the figure, at this time, the weak target has been submerged in the sidelobe and cannot be detected. After the residual orthogonal components of the strong target are eliminated by this method, the Doppler sidelobe is effectively suppressed, and the weak target is revealed. At this time, the SINR dynamic range of the Doppler dimension is increased to 27.8dB. It can be seen that this method can effectively reduce the Doppler sidelobe, expand the SINR dynamic range of the Doppler dimension of the inter-pulse phase coded signal, and improve the weak target detection capability. In addition, after the sidelobe elimination is completed, the method can keep the spectrum flat and avoid the formation of Doppler pseudo peaks causing false alarms.

[0067] In summary, the above are only preferred embodiments of the present invention and are not intended to limit the protection scope of the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A radar pulse-to-pulse phase coded signal sidelobe suppression method, characterized in that: include: The transmitting antenna signal is modulated according to the phase coding sequence and transmitted simultaneously, and the echo signal reflected by the target is received by the receiving antenna; the received echo signal is subjected to matched filtering to obtain the range Doppler spectrum, and the range dimension target detection is completed to obtain the over-detection distance point; For each of the detected distance points, a strong target Doppler frequency and peak information are obtained through Doppler dimension target detection; For each detected target point in turn, a peak point correction matrix is ​​established by combining the strong target Doppler frequency and peak information with the orthogonal component frequency domain response based on the error model to obtain the corrected peak point of the current target; The hypothesis detection method is adopted to restore the Doppler spectrum of the target with the maximum SINR as the criterion, and the residual orthogonal components of the current target are eliminated in the frequency domain. Finally, the residual orthogonal components of the detected target point are eliminated repeatedly until the Doppler dynamic range of the distance point is greater than the threshold. The peak point correction matrix is ​​established by combining the strong target Doppler frequency and peak information with the orthogonal component frequency domain response based on the error model, which specifically includes the following steps:

301. Perform Doppler target detection on the j-th passed-detection distance point to obtain I passed-detection targets, and sort the passed-detection targets according to peak amplitudes; 302. Extract multi-channel peak data on the RD spectra of the M×N virtual channels according to the i-th target distance index and the Doppler index, rearrange the peak data to obtain a peak matrix; multiply the peak matrix by a peak point correction matrix based on an error model to obtain a corrected peak point amplitude phase; 303. Determine the displacement of the orthogonal component spectrum matrix based on the error model according to the target Doppler index to obtain a matrix, multiply the corrected peak point by the matrix to obtain a restored target spectrum, and after removing the peak point information from the target spectrum, obtain a residual orthogonal component term; 304. Eliminate the residual interference term of the spectrum of the strong target signal on the Doppler spectrum to obtain a spectrum; 305. Calculate the SINR of the spectrum under different error models, and update the spectrum to the spectrum corresponding to the maximum SINR; 306. Calculate the ratio of the strongest point of the spectrum to the noise power to obtain the current Doppler SINR dynamic range. If the dynamic range is greater than or equal to SINR min , then the Doppler sidelobe suppression of the distance point is completed, and step 307 is continued; otherwise, steps 302 to 306 are repeated to eliminate the residual orthogonal components of the next target at the distance point; 307. Repeat the above steps until the Doppler sidelobe suppression of all the detection range points is completed.

2. A radar inter-pulse phase coded signal sidelobe suppression method as claimed in claim 1, characterized in that: The phase encoding sequence is designed in the following manner: Determine the number of transmitting antennas as N, the number of frequency modulation sequences in a single frame as L, the frequency modulation sequence repetition period as T, and design N groups of phase coding sequences based on the minimum peak interference residual (PIR), denoted as a1, a2, …, a N , the length of each sequence is L; where a n (l) and a h (l) are respectively sequence a n With sequence a h The lth element of represents the phase coding value of the nth transmitting antenna and the hth transmitting antenna in the lth FMCW signal; is the maximum Doppler frequency.

3. A radar inter-pulse phase coded signal sidelobe suppression method as claimed in claim 2, characterized in that: The transmitting antenna signal is modulated according to the phase coding sequence and transmitted simultaneously, specifically including: The FMCW signal is phase modulated between pulses according to the phase coding sequence and transmitted simultaneously by N transmitting antennas, wherein all antennas at the transmitting end simultaneously transmit FMCW signals with completely consistent time-frequency coefficients, and the initial phase of the signal of each transmitting antenna is modulated by the corresponding coding sequence, and the phase coding value switches with the transmitting pulse, that is, the initial phase φ of the signal modulation of the nth transmitting antenna in the lth transmitting cycle is the coding value a n (l).

4. A radar inter-pulse phase coded signal sidelobe suppression method as claimed in claim 1, 2 or 3, characterized in that: The echo signal reflected by the target is received by the receiving antenna. Specifically, the M receiving antennas perform de-chirp and AD sampling processing on the echo signal at the receiving end to obtain a digital echo signal of size K×L×M, wherein K is the number of fast time sampling points, M is the number of receiving antennas, and L is the number of single-frame frequency modulation sequences.

5. A radar inter-pulse phase coded signal sidelobe suppression method as claimed in claim 1, 2 or 3, characterized in that: The matched filtering process is performed on the received echo signal to obtain the range Doppler spectrum, and the range dimension target detection is completed to obtain the detection distance point, which specifically includes the following steps:

201. Perform data windowing and FFT processing on the received single frequency modulated continuous wave signal to complete target distance dimension focusing; 202. Perform slow time decoding processing on N phase coding sequences along each distance point according to the range-slow time spectrum, complete echo signal separation, and obtain range-slow time spectra of M×N virtual channels; 203. Perform FFT processing on the distance-slow time spectra of the M×N virtual channels along the slow time dimension to complete two-dimensional focusing of the target and obtain RD spectra of M×N virtual channels; 204. Perform non-coherent accumulation processing on the M×N virtual channel RD spectra, and perform range-dimensional target detection on the RD spectra after the non-coherent accumulation to obtain J passed-detection distance points.

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