阅读说明：本技术 一种可变分段lfm波形生成及优化方法 (Variable segmentation LFM waveform generation and optimization method ) 是由 陶海红 瞿建 时亮 王海锐 廖桂生 曾操 于 2020-04-28 设计创作，主要内容包括：本发明公开了一种可变分段LFM波形生成及优化方法,其中,生成方法包括：获取M个发射波形；其中,每个所述发射波形包括N个波形子脉冲；对每个所述波形子脉冲进行分段,得到每个所述波形子脉冲分段的子时宽；根据每个所述波形子脉冲分段的子时宽得到矩形窗函数和每个所述波形子脉冲分段的调频斜率；根据所述矩形窗函数和所述波形子脉冲分段的调频斜率建立可变分段LFM波形的信号模型,以得到M组不同子时宽向量组成的正交波形。本发明提供的可变分段LFM波形同时采用调频时宽分集和分段数分集,且子时宽长度和分段数都可变,具更大的设计自由度和灵活性,且调制简单,易于生成,更加适用于MIMO雷达系统的多发射体制。(The invention discloses a variable segmentation LFM waveform generation and optimization method, wherein the generation method comprises the following steps: acquiring M emission waveforms; wherein each of the transmit waveforms comprises N waveform sub-pulses; segmenting each waveform sub-pulse to obtain the sub-time width of each waveform sub-pulse segment; obtaining a rectangular window function and a frequency modulation slope of each waveform sub-pulse segment according to the sub-time width of each waveform sub-pulse segment; and establishing a signal model of the variable segmented LFM waveform according to the rectangular window function and the frequency modulation slope of the waveform sub-pulse segment so as to obtain an orthogonal waveform consisting of M groups of different sub-time-width vectors. The variable segmented LFM waveform provided by the invention simultaneously adopts frequency modulation time width diversity and segment number diversity, and the sub time width length and the segment number are variable, so that the variable segmented LFM waveform has higher design freedom and flexibility, is simple to modulate and easy to generate, and is more suitable for a multi-transmitting system of an MIMO radar system.)

1. A method for generating a variable-segment LFM waveform, comprising:

acquiring M emission waveforms; wherein each of the transmit waveforms comprises N waveform sub-pulses;

segmenting each waveform sub-pulse to obtain the sub-time width of each waveform sub-pulse segment;

obtaining a rectangular window function and a frequency modulation slope of each waveform sub-pulse segment according to the sub-time width of each waveform sub-pulse segment;

and establishing a signal model of the variable segmented LFM waveform according to the rectangular window function and the frequency modulation slope of the waveform sub-pulse segment so as to obtain an orthogonal waveform consisting of M groups of different sub-time-width vectors.

2. The method of claim 1, wherein the sub-time width of the waveform sub-pulse segment is expressed as:

wherein, T_mniThe sub-time width of the ith segment of the nth sub-pulse of the mth transmitting waveform is represented, M is 1,2, …, M and M represent the number of transmitting waveforms, N is 1,2, …, N and N represent the pulse number of the waveform sub-pulse, I is 1,2, …, I and I represent the maximum number of sub-time width segments, T represents the width of the sub-pulse, P represents the number of discrete pulse width codes, c represents the number of discrete pulse width codes, and_mnia code vector representing an ith piecewise sub-temporal width of an nth sub-pulse of an mth transmit waveform, and satisfying:

3. the method of generating a variably segmented LFM waveform according to claim 2, wherein said rectangular window function is:

the frequency modulation slope of the waveform sub-pulse segment is as follows:

wherein, T_mniA sub-time width, mu, of an i-th segment representing an n-th sub-pulse of an m-th transmit waveform_mniIndicates the chirp rate of the ith segment of the nth sub-pulse of the mth transmit waveform, and B indicates the bandwidth.

4. The method of generating a variably segmented LFM waveform according to claim 3, wherein said signal model of said variably segmented LFM waveform is:

wherein, T_mniA sub-time width, mu, of an i-th segment representing an n-th sub-pulse of an m-th transmit waveform_mniShowing the chirp rate of the ith segment of the nth sub-pulse of the mth transmit waveform, f₀Represents the center frequency of the signal, rect (-) represents a rectangular window function.

5. A method for optimizing a variable-segment LFM waveform, comprising:

acquiring a signal model of the variable segmented LFM waveform to obtain M groups of orthogonal waveforms; wherein the M sets of orthogonal waveforms are generated by the variable segment LFM waveform generation method of any one of claims 1 to 4.

Calculating the self-correlation sequence and the cross-correlation sequence of each group of orthogonal waveforms to obtain the optimization index of each group of orthogonal waveforms; wherein the optimization index comprises an autocorrelation sidelobe peak level and a cross-correlation peak level;

determining the weight of the optimization index;

and optimizing each group of orthogonal waveforms by adopting a genetic algorithm according to the weight of the optimization index to obtain optimized waveform parameters.

6. The method of claim 5, wherein calculating the auto-correlation sequence and the cross-correlation sequence of each set of orthogonal waveforms to obtain the optimization index of each set of orthogonal waveforms comprises:

obtaining an autocorrelation function of the nth sub-pulse of the mth waveform;

processing the autocorrelation function to obtain an autocorrelation sequence of the mth waveform;

obtaining the autocorrelation sidelobe peak level according to the autocorrelation sequence;

correspondingly, acquiring a cross-correlation function between the nth pulse of the mth waveform and the ith waveform;

processing the cross-correlation function to obtain a cross-correlation sequence of the mth waveform and the l waveform;

and obtaining the cross-correlation peak value level according to the cross-correlation sequence.

7. The method of claim 6, wherein the autocorrelation sidelobe peak level is expressed as:

wherein the content of the first and second substances,

8. The method of claim 7, wherein the cross-correlation peak level is expressed as:

wherein the content of the first and second substances,represents the cross-correlation sequence of the mth waveform and the lth waveform, K2 { -K +1, -K +2, …, -1,0, …, K-1},representing the peak point of the autocorrelation sequence of the ith waveform.

9. The method of claim 8, wherein the optimizing each set of orthogonal waveforms by using a genetic algorithm according to the weight of the optimization index to obtain optimized waveform parameters comprises:

initializing genetic algorithm parameters; the genetic algorithm parameters comprise a maximum evolutionary algebra, a population scale, a cross probability and a variation probability;

determining a fitness function of the genetic algorithm according to the weight of the optimization index;

and carrying out cross and variation operation on each group of orthogonal waveforms according to the genetic algorithm parameters and the fitness function until the evolution algebra reaches the maximum evolution algebra to obtain optimized waveform parameters.

10. The method for optimizing a variable-segment LFM waveform of claim 9, wherein the fitness function is:

wherein, w_mWeighting factor, ASPL, representing the peak level of the m-th waveform autocorrelation sidelobe^(m)Showing the autocorrelation sidelobe peak level, CPL, of the mth waveform^(ml)Represents the cross-correlation peak level, w, of the mth waveform and the l waveform_mlA weighting coefficient representing a cross-correlation peak level of the mth waveform and the lth waveform.

Technical Field

The invention belongs to the technical field of radar waveform design, and particularly relates to a variable segmented LFM waveform generation and optimization method.

Background

In recent years, Multiple Input Multiple Output (MIMO) radars have attracted a lot of interest and attention in the field of array signal processing. The MIMO radar adopts a waveform diversity technology, and has more degrees of freedom on transmitting waveforms. MIMO radars generally emit mutually orthogonal waveforms that add up incoherently in space. Because an ideal orthogonal waveform with good autocorrelation performance and zero cross correlation does not exist, it is very important to design an orthogonal waveform with good autocorrelation performance and minimum cross correlation for the MIMO radar system.

At present, several orthogonal waveforms and optimization methods thereof are proposed in the prior art, one of which is that orthogonal phase encoding signals are used to achieve orthogonality between waveforms by optimizing encoding sequences, and the orthogonality of up-down Linear Frequency Modulation (LFM) signals and Non-Linear Frequency Modulation (NLFM) signals is good. Secondly, orthogonal waveforms are designed through a frequency diversity method, such as Discrete Frequency Coding Waveform (DFCW), and the LFM signal is used for replacing a constant frequency signal as a sub-pulse to obtain a DFCW-LFM signal; and meanwhile, the continuous sub-pulse is changed into a discontinuous sub-pulse to obtain an MDFCW-LFM signal, and the autocorrelation side lobe and the cross correlation of the waveform are reduced to optimize the waveform. Thirdly, a Piecewise Linear Frequency Modulation (PLFM) signal is adopted, the waveform uses three LFM signals with different polarities, the polarities of a first section and a third section are opposite to the polarity of a second section, the duration of the second section of each sub-pulse is different from the sub-time widths of the first section and the third section, the sub-time widths of the first section and the third section are the same, and the purpose of optimizing the waveform is achieved by optimizing the duration sequence of the second section to reduce cross-correlation.

However, the first method has the disadvantage that only two sets of orthogonal waveforms are available, and the first method is only suitable for the MIMO radar of two-generator system; the frequency diversity method provided by the second method has low utilization rate of bandwidth, and the modulation method is complex and not easy to generate; the PLFM signal provided by the third method is not enough in design freedom and flexibility, and cannot be well suitable for an MIMO radar system.

Disclosure of Invention

In order to solve the above problems in the prior art, the present invention provides a variable segment LFM waveform generation and optimization method. The technical problem to be solved by the invention is realized by the following technical scheme:

a method of variable segment LFM waveform generation, comprising:

acquiring M emission waveforms; wherein each of the transmit waveforms comprises N waveform sub-pulses;

segmenting each waveform sub-pulse to obtain the sub-time width of each waveform sub-pulse segment;

obtaining a rectangular window function and a frequency modulation slope of each waveform sub-pulse segment according to the sub-time width of each waveform sub-pulse segment;

and establishing a signal model of the variable segmented LFM waveform according to the rectangular window function and the frequency modulation slope of the waveform sub-pulse segment so as to obtain an orthogonal waveform consisting of M groups of different sub-time-width vectors.

In one embodiment of the present invention, the sub-time width of the waveform sub-pulse segment is expressed as:

wherein, T_mniThe sub-time width of the ith segment of the nth sub-pulse of the mth transmitting waveform is represented, M is 1,2, …, M and M represent the number of transmitting waveforms, N is 1,2, …, N and N represent the pulse number of the waveform sub-pulse, I is 1,2, …, I and I represent the maximum number of sub-time width segments, T represents the width of the sub-pulse, P represents the number of discrete pulse width codes, c represents the number of discrete pulse width codes, and_mnia code vector representing an ith piecewise sub-temporal width of an nth sub-pulse of an mth transmit waveform, and satisfying:

in one embodiment of the present invention, the rectangular window function is:

the frequency modulation slope of the waveform sub-pulse segment is as follows:

wherein, T_mniA sub-time width, mu, of an i-th segment representing an n-th sub-pulse of an m-th transmit waveform_mniIndicates the chirp rate of the ith segment of the nth sub-pulse of the mth transmit waveform, and B indicates the bandwidth.

In one embodiment of the present invention, the signal model of the variable segmented LFM waveform is:

wherein, T_mniA sub-time width, mu, of an i-th segment representing an n-th sub-pulse of an m-th transmit waveform_mniShowing the chirp rate of the ith segment of the nth sub-pulse of the mth transmit waveform, f₀Represents the center frequency of the signal, rect (-) represents a rectangular window function.

A variable segment LFM waveform optimization method comprises the following steps:

acquiring a signal model of the variable segmented LFM waveform to obtain M groups of orthogonal waveforms; wherein, the M groups of orthogonal waveforms are generated by the variable segment LFM waveform generation method described in the above embodiment.

Calculating the self-correlation sequence and the cross-correlation sequence of each group of orthogonal waveforms to obtain the optimization index of each group of orthogonal waveforms; wherein the optimization index comprises an autocorrelation sidelobe peak level and a cross-correlation peak level;

determining the weight of the optimization index;

and optimizing each group of orthogonal waveforms by adopting a genetic algorithm according to the weight of the optimization index to obtain optimized waveform parameters.

In an embodiment of the present invention, calculating an autocorrelation sequence and a cross-correlation sequence of each group of orthogonal waveforms to obtain an optimization index of each group of orthogonal waveforms includes:

obtaining an autocorrelation function of the nth sub-pulse of the mth waveform;

processing the autocorrelation function to obtain an autocorrelation sequence of the mth waveform;

obtaining the autocorrelation sidelobe peak level according to the autocorrelation sequence;

correspondingly, acquiring a cross-correlation function between the nth pulse of the mth waveform and the ith waveform;

processing the cross-correlation function to obtain a cross-correlation sequence of the mth waveform and the l waveform;

and obtaining the cross-correlation peak value level according to the cross-correlation sequence.

In one embodiment of the invention, the autocorrelation sidelobe peak level is expressed as:

wherein the content of the first and second substances,denotes the autocorrelation sequence of the mth waveform, K1 ═ {0,1, …, K-1}, K denotes the number of sub-pulse discrete sample points, and

f_srepresents the sampling frequency; Ω denotes a set of main lobe indices, and Ω ═ 0, …, L denotes oversampling multiples,representing the peak point of the autocorrelation sequence of the mth waveform.

In one embodiment of the invention, the cross-correlation peak level is expressed as:

wherein the content of the first and second substances,represents the cross-correlation sequence of the mth waveform and the lth waveform, K2 { -K +1, -K +2, …, -1,0, … K-1},

representing the peak point of the autocorrelation sequence of the ith waveform.

In an embodiment of the present invention, optimizing each group of orthogonal waveforms by using a genetic algorithm according to the weight of the optimization index to obtain optimized waveform parameters includes:

initializing genetic algorithm parameters; the genetic algorithm parameters comprise a maximum evolutionary algebra, a population scale, a cross probability and a variation probability;

determining a fitness function of the genetic algorithm according to the weight of the optimization index;

and carrying out cross and variation operation on each group of orthogonal waveforms according to the genetic algorithm parameters and the fitness function until the evolution algebra reaches the maximum evolution algebra to obtain optimized waveform parameters.

In one embodiment of the present invention, the fitness function is:

wherein, w_mWeighting factor, ASPL, representing the peak level of the m-th waveform autocorrelation sidelobe^(m)Showing the autocorrelation sidelobe peak level, CPL, of the mth waveform^(ml)Represents the cross-correlation peak level, w, of the mth waveform and the l waveform_mlA weighting coefficient representing a cross-correlation peak level of the mth waveform and the lth waveform.

The invention has the beneficial effects that:

1. the variable segmented LFM waveform provided by the invention simultaneously adopts frequency modulation time width diversity and segment number diversity, and the length of the sub-time width and the number of the segments are variable, so that the variable segmented LFM waveform has higher design freedom and flexibility than the conventional PLFM waveform;

2. each sub-time width of the variable-segment LFM waveform provided by the invention is a linear frequency modulation signal with the same central frequency, and different segments adopt positive and negative alternation of frequency modulation rate, the central frequency is unchanged, the frequency change is continuous, the modulation is simple, and the generation is easy;

3. the variable segmentation LFM waveform optimization method provided by the invention obtains a plurality of orthogonal waveforms with better orthogonality and optimized comprehensive performance by setting the weighted value of each index and searching by using a genetic algorithm, and is more suitable for a multi-emitter system of an MIMO radar system.

The present invention will be described in further detail with reference to the accompanying drawings and examples.

Drawings

Fig. 1 is a schematic diagram of a variable segment LFM waveform generation method according to an embodiment of the present invention;

FIG. 2 is a schematic diagram of a variable segment LFM waveform provided by an embodiment of the present invention;

FIG. 3 is a detailed schematic diagram of a single pulse of a waveform provided by an embodiment of the present invention;

fig. 4 is a schematic diagram of a method for optimizing a variable-segment LFM waveform according to an embodiment of the present invention;

FIG. 5 is a graph of the optimal fitness value and the average fitness value according to the evolution algebra variation provided by the embodiment of the present invention;

FIG. 6 is a schematic diagram of the autocorrelation of 4 sets of waveforms provided by an embodiment of the present invention;

fig. 7 is a cross-correlation diagram of 4 sets of waveforms provided by an embodiment of the present invention.

Detailed Description

The present invention will be described in further detail with reference to specific examples, but the embodiments of the present invention are not limited thereto.