A method for designing complementary waveform transmission sequence with flat sidelobe distribution

Abstract

The present invention belongs to the field of radar sonar target detection, and specifically relates to a complementary waveform transmission sequence design method with a flat sidelobe distribution. The method designs a new complementary waveform transmission sequence scheme, which counts the number of symbol changes in each row of the Walsh matrix and arranges the Walsh matrix in ascending order to reorganize and transform it into a new vector, then cuts the vector to a length equal to the number of transmitted pulses, and then uses the cut vector as the complementary waveform transmission sequence scheme to obtain a time delay-Doppler image with flattened sidelobes. The beneficial results of the present invention are as follows: 1. The method proposed in the present invention has a flatter sidelobe distribution than existing methods, thereby reducing false alarms that may be caused by strong sidelobes; 2. The method proposed in the present invention has a higher Doppler resolution than existing methods; 3. The method proposed in the present invention does not require nonlinear processing, is applicable to complementary waveforms with any number of pulses, and has a simple principle and is easy to implement in engineering.

Description

Technical Field

[0001] The invention belongs to the field of radar sonar target detection, and in particular relates to a complementary waveform emission sequence design method with flat sidelobe distribution. Background Art

[0002] As a coded waveform with a high degree of design freedom, the complementary waveform can theoretically achieve zero sidelobes in the range direction after matched filtering, significantly improving the range resolution and sidelobe suppression capabilities of target detection in radar and sonar missions. According to the inventor's previously filed invention patents ZL201710037908.3, "A Multi-Target Detection Method Based on Gray Complementary Waveforms," and ZL201811184076.9, "A Method for Improving Doppler Resolution of Gray Complementary Waveforms," the sidelobe distribution in the delay-Doppler image can be modified by designing the complementary waveform transmission sequence and matched filtering weights, thereby achieving better sidelobe suppression performance near the target Doppler.

[0003] On the other hand, the two aforementioned patents also have the following issues that may affect target detection performance: For invention patent ZL201710037908.3, this method requires prior knowledge of the target's Doppler information before use, otherwise its effectiveness will be greatly reduced; and the patent uses nonlinear processing that minimizes the value point by point, which may eliminate target information when the target is jittering. As for invention patent ZL201811184076.9, although this method does not use nonlinear processing and obtains a larger sidelobe suppression area, it also significantly reduces the target Doppler resolution, and this method also limits the number of transmitted pulses to an even number.

[0004] In addition, there is a common problem for the above two patents, that is, the maximum sidelobe energy in the delay-Doppler image obtained by these two methods is too high, and this problem will directly lead to it being easily misjudged as a false target during the target detection process, affecting the target detection performance. Summary of the Invention

[0005] In order to reduce false alarms in the target detection process and solve the problems existing in the above two patents, the present invention proposes a complementary waveform transmission sequence design method with flat sidelobe distribution.

[0006] The technical solution of the present invention comprises the following steps:

[0007] The first step is to set the number of complementary waveform emission pulses to N, where N is a positive integer, and find the power of 2 that is greater than or equal to N and closest to N, which is recorded as 2 M , M is a positive integer;

[0008] The second step is to generate a 2 if M is an odd number.M+1 ×2 M+1 Walsh matrix; otherwise, a 2 M ×2 M Walsh matrix;

[0009] The third step is to count the number of sign changes of each row in the Walsh matrix generated in the second step (i.e., the number of times +1 becomes -1 or -1 becomes +1);

[0010] The fourth step is to rearrange all rows in ascending order of the number of times the sign changes to form a new matrix;

[0011] Step 5: Starting from the second row, the new matrix is sequentially spliced onto the back of the previous row to form a vector;

[0012] Step 6: intercept the 1st to Nth values of the recombined vector obtained in step 5 as the transmission order of the complementary waveform;

[0013] In the seventh step, the delay-Doppler image of the complementary waveform is calculated using the transmission sequence obtained in the sixth step.

[0014] The beneficial result of the present invention is that the time delay-Doppler image obtained by the method proposed in the present invention has flatter sidelobes (i.e., smaller maximum sidelobe energy) and higher Doppler resolution than the methods in the aforementioned two patents under the same number of transmitted pulses, does not require nonlinear processing, and is applicable to complementary waveforms of any number of pulses (the number of pulses does not need to be limited to an even number), which is convenient for engineering implementation. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 It is an implementation flow chart of the present invention;

[0016] Figure 2 The delay-Doppler image comparison results obtained by simulation experiments using three methods are as follows:

[0017] (a) is the time delay-Doppler image obtained using the method of patent ZL201710037908.3;

[0018] (b) is the time delay-Doppler image obtained using the method of patent ZL201811184076.9;

[0019] (c) is a time delay-Doppler image obtained using the method of the present invention;

[0020] Figure 3 yes Figure 2 Comparison results of the target main lobe cross section at time delay equal to 0. DETAILED DESCRIPTION

[0021] Figure 1This is a flow chart of the implementation of the present invention. The specific implementation method includes the following steps:

[0022] The first step is to set the number of complementary waveform emission pulses to N, where N is a positive integer, and find the power of 2 that is greater than or equal to N and closest to N, which is recorded as 2 M , M is a positive integer;

[0023] The second step is to generate a 2 if M is an odd number. M+1 ×2 M+1 Walsh matrix; otherwise, a 2 M ×2 M Walsh matrix;

[0024] The Walsh matrix is a special binary column orthogonal matrix that can be composed of a 2 M-1 The Walsh matrix of order is generated by the following iteration:

[0025]

[0026] in

[0027] The iterated Walsh matrix All -1 values in are replaced by 0, then each row (or each column, because the matrix is a symmetric matrix) in the matrix can represent the emission order of a set of Gray complementary waveforms.

[0028] The third step is to count the number of sign changes of each row in the Walsh matrix generated in the second step (i.e., the number of times +1 becomes -1 or -1 becomes +1);

[0029] Assuming the Walsh matrix dimension is P×P, the number of sign changes in each row can be recorded as a value between 0 and P-1, and the number of sign changes in each row will not be the same.

[0030] The fourth step is to rearrange all rows in ascending order of the number of times the sign changes to form a new matrix;

[0031] Place the row with the sign changing times 0 in the first row of the new matrix, the row with the sign changing times 1 in the second row of the new matrix, and so on, and place the row with the sign changing times P-1 in the last row of the new matrix.

[0032] Step 5: Starting from the second row, the new matrix is sequentially spliced onto the back of the previous row to form a vector;

[0033] In the sixth step, the first to Nth values of the recombined vector obtained in the fifth step are intercepted as the transmission order of the complementary waveform.

[0034] In the seventh step, the delay-Doppler image of the complementary waveform is calculated using the transmission sequence obtained in the sixth step.

[0035] Figure 2 It is the comparison result of time delay-Doppler images obtained by simulation experiments using three methods. Figure 2 In all sub-graphs, the horizontal axis represents Doppler in radians (rad), the vertical axis represents delay in seconds (s), and the color of the color bar represents the energy of the pixel in the graph in dB. The number of transmitted pulses for the complementary waveform is N = 64. Figure 3 The horizontal axis represents Doppler, and the unit is "radian (rad)", and the vertical axis represents normalized amplitude, and the unit is "dB". Figure 2 (a) represents the time delay-Doppler image obtained by the method proposed in patent ZL201710037908.3, Figure 2 (b) represents the time delay-Doppler image obtained by the method proposed in patent ZL201811184076.9, Figure 2 (c) shows the delay-Doppler image obtained by the method of the present invention. It can be found that the sidelobe distribution of the method proposed by the present invention is flatter than that of the two aforementioned patents: Figure 2 The maximum sidelobe energy of (a) is about -23.54dB. Figure 2 The maximum sidelobe energy of (b) is about -13.84dB. Figure 2 The maximum sidelobe energy of (c) is about -28.93dB, indicating that the maximum sidelobe energy of the method proposed in the present invention is 5.39dB and 15.09dB lower than that of the method proposed in Patent ZL201710037908.3 and the method proposed in Patent ZL201811184076.9, respectively; and it has a higher target Doppler resolution with the same number of transmitted pulses.

[0036] Figure 3 yes Figure 2 Comparison results of target main lobe cross section at time delay equal to 0. Further through Figure 3 It can be seen that the Doppler resolution of the method proposed in the present invention is about 0.10 rad, while the Doppler resolutions of the methods proposed in patent ZL201710037908.3 and patent ZL201811184076.9 are 0.20 rad and 0.62 rad, respectively, which are 1 times and 6 times lower than those of the method proposed in the present invention, respectively.

Claims

1. A method for designing a complementary waveform transmission sequence with a flat sidelobe distribution, characterized in that: The method is divided into the following steps: The first step is to set the number of complementary waveform emission pulses to N, where N is a positive integer, and find the power of 2 that is greater than or equal to N and closest to N, which is recorded as 2 M , M is a positive integer; The second step is to generate a 2 if M is an odd number. M+1 ×2 M+1 Walsh matrix; otherwise, a 2 M ×2 M Walsh matrix; The third step is to count the number of sign changes in each row of the Walsh matrix generated in the second step; The fourth step is to rearrange all rows in ascending order of the number of times the sign changes to form a new matrix; Step 5: Starting from the second row, the new matrix is sequentially spliced onto the back of the previous row to form a vector; Step 6: intercept the 1st to Nth values of the recombined vector obtained in step 5 as the transmission order of the complementary waveform; In the seventh step, the delay-Doppler image of the complementary waveform is calculated using the transmission sequence obtained in the sixth step.

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