Method and system for optimizing photo-generated multipath quadrature phase coding chirp signal based on non-dominated sorting genetic algorithm

Abstract

The invention relates to the field of radar signal processing and waveform design, and relates to a photo-generated multipath quadrature phase coding chirp signal optimization method and system based on a non-dominated sorting genetic algorithm. The method comprises the following steps: firstly, generating a multi-channel phase coding sequence population through initialization; then constructing a multi-target fitness function taking minimization of a signal set autocorrelation peak side lobe and a cross-correlation peak as a target; thirdly, performing iterative optimization on the population by using a non-dominated sorting genetic algorithm (NSGA-II), and finally obtaining a Pareto optimal solution set representing different performance tradeoff; and finally, selecting an optimal coding sequence from the solution set according to system requirements, and driving a photon signal generation system to generate physical multi-path orthogonal phase coding frequency chirp radar signals. According to the invention, the advanced multi-target optimization algorithm is combined with the microwave photon technology, and higher radar detection performance is obtained while the anti-interference capability between channels and the correlation of signals are improved.

Description

Technical Field

[0001] This invention relates to the field of radar signal processing and waveform design, and in particular to a method and system for generating and optimizing multi-channel orthogonal radar signals by combining an improved genetic algorithm with microwave photonics technology. Background Technology

[0002] Multiple-input multiple-output (MIMO) radar systems represent a significant development direction in modern radar technology, with performance largely dependent on the orthogonality of the transmitted multi-channel signals. An ideal transmitted signal set should simultaneously possess extremely low autocorrelation sidelobes to improve range resolution, detection accuracy, and extremely low cross-correlation to suppress inter-channel interference. Chirped signals are widely used due to their excellent Doppler tolerance. By phase-coding the chirped signal, phase-coded chirped signals can be constructed, achieving orthogonality between signal sets while maintaining Doppler tolerance. Designing the optimal phase-coded sequence to simultaneously optimize the autocorrelation and cross-correlation characteristics of the phase-coded chirped signal set is a complex multi-objective optimization problem. Traditional genetic algorithms typically use weighted summation to transform the multi-objective problem into a single-objective problem, but this not only makes it difficult to determine the weighting factors but also fails to truly reveal the inherent balance between different objectives. On the other hand, microwave photonics technology, by combining the advantages of photonics and electronics, provides a novel solution for generating broadband, complex radar signals.

[0003] Therefore, there is an urgent need for a complete technical solution, from algorithm to physical implementation, that can efficiently solve the multi-objective optimization problem of phase-coded frequency chirped signals and seamlessly interface with advanced photon generation systems. Summary of the Invention

[0004] To address the aforementioned technical problems, this invention provides a method and system for optimizing photonic multipath orthogonal phase-coded chirped signals based on the Non-Dominated Sorting Genetic Algorithm-II (NSGA-II). This approach applies the advanced NSGA-II multi-objective optimization algorithm to the phase coding design of photonic phase-coded frequency chirped signal systems, aiming to obtain a Pareto-optimal solution set with excellent performance and flexible trade-offs, and to guide the generation of physical signals.

[0005] The technical solution of this invention is as follows:

[0006] The first aspect of this invention is to provide a method for optimizing photogenerated multipath orthogonal phase-coded chirped signals based on a non-dominated sorting genetic algorithm, comprising the following steps:

[0007] Step 1: Initialize the population, which consists of multiple sets of multi-channel phase-coded sequences. Each set of coded sequences represents a set of multi-channel orthogonal phase-coded chirped signals to be evaluated; based on the requirements of the MIMO radar system (e.g., number of channels). The encoding length corresponding to the detection range resolution (etc.), randomly generate an initial population. Each "individual" in the population is a set of... A length of The discrete phase coding sequence. The number of channels, coding length, and number of phase states of the phase coding sequence can all be preset according to the requirements of the radar system.

[0008] Step 2: Construct a multi-objective fitness function with the common minimization of the peak sidelobe level (PSL) and peak cross-correlation (PCC) of the signal set as the optimization objective;

[0009] To simultaneously optimize both autocorrelation and cross-correlation properties, this invention defines the problem as a bi-objective optimization problem, seeking to minimize the common objective functions of the following:

[0010] Objective 1 (Autocorrelation):

[0011]

[0012] Objective 2 (Cross-correlation):

[0013]

[0014] in, For the number of channels, For the first The autocorrelation function of the channel signal. For the first and the The cross-correlation function of the channel signals, This is a time delay.

[0015] These two goals are in conflict; optimizing one goal may lead to the deterioration of the other.

[0016] Step 3: Perform NSGA-II iterative optimization. Use the Non-dominated Sorting Genetic Algorithm II (NSGA-II) to perform multi-objective optimization on the population. Through non-dominated sorting, crowding calculation, elite selection, crossover and mutation operations, obtain a Pareto optimal solution set containing multiple optimal solutions.

[0017] This is the core algorithmic step of the present invention. The algorithm iteratively evolves the current population, and the operations for each generation include:

[0018] Non-dominated ranking: Ranking all individuals in a population according to their... and The values ​​are stratified. Individuals in the first stratum (Pareto front) are currently optimal and are not dominated by any other individuals.

[0019] Crowding calculation: For individuals within the same layer, calculate their crowding degree in the objective function space to maintain the diversity of solutions.

[0020] Elite selection, crossover, and mutation: Parents are selected through tournament selection (considering both non-dominant rank and crowding). Offspring are generated using operations such as simulated binary crossover (SBX) and polynomial mutation (PM), forming a new population for the next iteration.

[0021] Step 4: Determine the termination condition. If it is met, proceed to step S5; otherwise, return to step S3 to continue iterating. The termination condition can be set to the maximum number of iterations or the Pareto front showing no significant change for several consecutive generations.

[0022] Step 5: Select a set of optimal phase coding sequences from the Pareto optimal solution set according to design requirements. After the algorithm finishes, the output is a set of Pareto optimal solutions, not a single solution. Each solution represents a different trade-off between autocorrelation and cross-correlation characteristics. The most suitable set of phase coding sequences can be selected from these solutions based on specific requirements (e.g., whether detection accuracy or anti-interference capability is more important).

[0023] Step 6: Based on the optimal phase coding sequence, control the photonic signal generation system to generate physically multi-channel orthogonal phase-coded frequency chirped radar signals. The optimal phase coding sequence selected in Step 5 is used as a digital control signal and input into the photonic phase-coded frequency chirped signal generation system. In this system, the coding sequence is loaded onto a polarization modulator to perform phase difference modulation on the orthogonally polarized chirped light signals. Finally, by beat frequency modulation using a photodetector, multi-channel phase-coded frequency chirped radar signals with optimal orthogonal characteristics can be generated in the microwave frequency band.

[0024] Specifically, the selected multi-channel optimal phase-coded sequence is loaded onto the RF ports of multiple parallel polarization modulators (PolMs); the polarization modulators are used to perform phase difference modulation on the two orthogonal polarization components of the generated frequency-chirped optical signal, thereby loading the phase-coded information onto the optical signal; and the chirped optical signal carrying the phase-coded information is converted into multiple orthogonal phase-coded frequency-chirped microwave signals by a photoelectric detector (PD).

[0025] The second aspect of this invention provides a photogenerated multipath orthogonal phase-coded chirped signal optimization system based on a non-dominated sorting genetic algorithm, comprising:

[0026] The parameter initialization module is used to set and generate an initial population of multiple sets of multi-channel phase-coded sequences;

[0027] The fitness evaluation module is used to perform multi-objective fitness evaluation on each individual in the population based on the autocorrelation peak sidelobes and cross-correlation peaks of the signal set.

[0028] The iterative optimization module incorporates the Non-Dominated Sorting Genetic Algorithm (NSGA-II) to perform selection, crossover, and mutation operations on the population and generate a Pareto optimal solution set.

[0029] The optimal solution selection module is used to select a set of optimal phase coding sequences from the Pareto optimal solution set after the iteration terminates;

[0030] The photon signal generation module is connected to the optimal solution selection module and receives the optimal phase coding sequence as a control command to generate physical multi-channel orthogonal phase-coded frequency chirped radar signals.

[0031] Furthermore, the photonic signal generation module includes: a laser source, a frequency-chirped optical signal generation unit, at least one polarization modulator, and a photoelectric converter; the optimal phase encoding sequence is used to drive the polarization modulator.

[0032] Advantages and beneficial effects of the present invention:

[0033] This invention effectively solves the problem of simultaneously optimizing autocorrelation peak sidelobes and cross-correlation peaks in traditional phase coding sequence optimization methods. It can significantly improve the orthogonality and sidelobe characteristics of signals, and enhance the target detection and anti-interference performance of MIMO radar and distributed radar systems by leveraging the advantages of microwave photonics technology, such as high frequency, wide bandwidth, low power consumption, and anti-electromagnetic interference. Attached Figure Description

[0034] Figure 1A flowchart illustrating the generation of phase-encoded sequences using the method of this invention;

[0035] Figure 2 This is a schematic diagram of the photonic phase-encoded signal generation system of the present invention;

[0036] Figure 3 The diagram shows the autocorrelation and cross-correlation characteristics of different channels of the Zadoff-Chu sequence.

[0037] Figure 4 The graphs show the autocorrelation and cross-correlation characteristics of different channels of the Gold / Kasami sequence.

[0038] Figure 5 This is a characteristic diagram of the autocorrelation and cross-correlation between different channels of the phase-coded sequence generated by the method of this invention. Detailed Implementation

[0039] To further illustrate the technical means employed by the present invention to achieve the intended objectives and the final effects of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0040] The present invention will be further described below with reference to a preferred embodiment.

[0041] Suppose we need to design a 6-channel ( The encoding length is 1024 ( ), phase state is 6 ( That is, the phase value is , , , , , The phase-coded frequency chirp signal set.

[0042] Step 1: Randomly generate a population containing, for example, 100 individuals. Each individual contains 4 sequences of length 1024, with sequence elements being... Integers between [a certain range].

[0043] Step 2: For each individual, calculate the autocorrelation and cross-correlation functions of its corresponding 6-channel phase-coded frequency chirped signal, and based on... and The formula calculates the values ​​of the two objective functions.

[0044]

[0045]

[0046] Step 3: Perform NSGA-II optimization. Set the maximum number of iterations to 500. In each generation, perform non-dominated ranking and crowding calculations on 100 individuals. For example, individual A... , If the values ​​are (0.1, 0.2), individual B is (0.2, 0.1), and individual C is (0.3, 0.3), then A and B may be located in the first layer (Pareto front), while C, dominated by them, is located in the second layer. The algorithm will prioritize retaining A and B. New 100 individuals are generated by simulating binary crossover and polynomial mutation to enter the next generation.

[0047] Step 4: After 500 iterations, the algorithm terminates. At this point, a Pareto optimal front is obtained, which may contain dozens of different optimal solutions. For example, one solution A has extremely low autocorrelation sidelobes but slightly high cross-correlation, while another solution B has extremely low cross-correlation but slightly high autocorrelation sidelobes. If the current task has extremely stringent anti-interference requirements, then the phase coding sequence corresponding to solution B is selected.

[0048] Step 5: Load the six coded sequences of length 1024 from solution B obtained in Step 4 into the photonic phase-coded signal generation system. This system is as follows: Figure 1 As shown, it includes: a coherent chirped light and local oscillator light signal generation module and a multi-channel orthogonal encoding module.

[0049] The narrow-linewidth laser in the coherent chirped light and local oscillator light signal generation module provides the light source, and the two coherent frequency chirped light signals and one local oscillator light signal are generated by combining a dual-polarization dual-parallel Mach-Zehnder modulator, a Fourier mode-locked photoelectric oscillator, and a single-tone photoelectric oscillator.

[0050] The multi-path orthogonal coding module loads the six 1024-bit coded sequences obtained in step 4 into the polarization modulator array via a code loader. The polarization modulator modulates the phase difference between the two orthogonally polarized beams in real time according to the input coded sequences. The two modulated optical signals are then controlled by a polarization controller to regulate their polarization state, a polarizer to combine the beams, and a photodetector to achieve frequency matching between the signal light and the local oscillator light. The output electrical signal carries a chirped radar signal with phase coding. This process is repeated for each path to obtain multiple orthogonal phase-coded chirped radar signals, which are then radiated into free space via an antenna to complete the radar detection task.

[0051] Figures 3-5 Experimental comparison of autocorrelation and cross-correlation characteristics between traditional encoding formats and encoding formats generated by the encoding method proposed in this invention, under the same number of channels (6 channels) and code length (1024).

[0052] in, Figure 3 The encoding format used is the Zadoff-Chu sequence. Figure 4The encoding format used is the Gold / Kasami sequence. Figure 5 The encoding format used is the phase-encoded sequence generated by the method of this invention. The images along the main diagonal (top left to bottom right) show the autocorrelation characteristics of each channel signal, while the images together show the cross-correlation characteristics between different channel signals. Figures 3-5 It can be seen that, whether it is autocorrelation or crosscorrelation, the phase-coded sequence generated by the method of this invention is superior to the traditional phase-coded signal format.

[0053] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several modifications and improvements can be made without departing from the inventive concept, and these all fall within the protection scope of the present invention.

Claims

1. A method for optimizing photogenerated multipath orthogonal phase-coded chirped signals based on a non-dominated sorting genetic algorithm, characterized in that, Includes the following steps: Step 1: Initialize the population, which consists of multiple sets of multi-channel phase-coded sequences. Each set of coded sequences represents a set of multi-channel orthogonal phase-coded chirped signals to be evaluated. Step 2: Construct a multi-objective fitness function with the common minimization of the autocorrelation peak sidelobes and cross-correlation peaks of the signal set as the optimization objective; Step 3: Perform iterative optimization. Use a non-dominated sorting genetic algorithm to perform multi-objective optimization on the population. Through non-dominated sorting, crowding calculation, elite selection, crossover and mutation operations, obtain a Pareto optimal solution set containing multiple optimal solutions. Step 4: Determine whether the iteration meets the preset termination condition. If it does, proceed to step S5; otherwise, return to step S3 to continue the iteration. Step 5: Select a set of optimal phase coding sequences from the Pareto optimal solution set according to design requirements; Step 6: Based on the optimal phase coding sequence, control the photon signal generation system to generate physical multi-channel orthogonal phase-coded frequency chirped radar signals.

2. The method according to claim 1, characterized in that, The multi-objective fitness function in step S2 is specifically defined as minimizing the following two objective functions: Objective 1: Minimize the average autocorrelation peak sidelobes of all channel signals. ; Objective 2: Minimize the peak value of the maximum cross-correlation between all channel pairs: ; in, For the number of channels, For the first The autocorrelation function of the channel signal. For the first and the The cross-correlation function of the channel signals, This is a time delay.

3. The method according to claim 1, characterized in that, The non-dominated sorting genetic algorithm in step S3 includes: Perform non-dominated hierarchical sorting of the current population and calculate the crowding degree of each individual in each layer; Selection is based on non-dominance level and crowding degree, prioritizing individuals with lower levels and higher crowding degree to enter the next generation; New offspring populations are generated using simulated binary crossover and polynomial mutation.

4. The method according to claim 1, characterized in that, The number of channels, coding length, and number of phase states of the phase coding sequence can all be preset according to the requirements of the radar system.

5. The method according to claim 1, characterized in that, In step S6, controlling the photon signal generation system specifically includes: The selected multi-channel optimal phase coding sequence is loaded onto the RF ports of multiple parallel polarization modulators respectively; The polarization modulator is used to perform phase difference modulation on the two orthogonal polarization components of the generated frequency chirped optical signal, thereby loading phase encoding information onto the optical signal; The chirped optical signal carrying phase-coded information is converted into multiple orthogonal phase-coded frequency chirped microwave signals by a photoelectric converter.

6. A photogenerated multiplexed orthogonal phase-coded chirped signal optimization system based on a non-dominated sorting genetic algorithm, characterized in that, include: The parameter initialization module is used to set and generate an initial population of multiple sets of multi-channel phase-coded sequences; The fitness evaluation module is used to perform multi-objective fitness evaluation on each individual in the population based on the autocorrelation peak sidelobes and cross-correlation peaks of the signal set. The iterative optimization module has a built-in non-dominated sorting genetic algorithm for performing selection, crossover, and mutation operations on the population and generating a Pareto optimal solution set. The optimal solution selection module is used to select a set of optimal phase coding sequences from the Pareto optimal solution set after the iteration terminates; The photon signal generation module is connected to the optimal solution selection module and receives the optimal phase coding sequence as a control command to generate physical multi-channel orthogonal phase-coded frequency chirped radar signals.

7. The system according to claim 6, characterized in that, The photonic signal generation module includes: a laser source, a frequency-chirped optical signal generation unit, at least one polarization modulator, and a photoelectric converter; the optimal phase encoding sequence is used to drive the polarization modulator.

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