A method for simulating radar echo amplitude fluctuation characteristics based on FPGA and VGA

Abstract

The present invention discloses a method for simulating the amplitude fluctuation characteristics of radar echoes based on FPGA and VGA. First, a linear feedback shift register (LFSR) is used in the FPGA to generate a uniformly distributed random sequence, followed by Box‑Muller transformation and mathematical calculation to generate a random sequence that obeys the distribution of multiple complex functions; then the generated random sequence is processed, and the random data in it is decomposed into normalized fine amplitude modulation and coarse amplitude modulation values; then, the amplitude of the radar echo is finely modulated using fine amplitude modulation inside the FPGA, and after the modulation is completed, an analog signal is output through a DAC and connected to a VGA, so that the VGA performs coarse modulation on the amplitude of the radar echo according to the coarse amplitude modulation value, and completes the accurate simulation of the specified fluctuation characteristics of the radar echo amplitude. The present invention solves the problems of low accuracy and small dynamic range in the current simulation of the fluctuation characteristics of radar echoes, and improves the fidelity of the echoes generated by the radar echo simulator.

Description

Technical Field

[0001] The present invention relates to the field of signal generation, and in particular to a method for simulating radar echo amplitude fluctuation characteristics based on FPGA and VGA. Background Art

[0002] Radar is the core equipment in modern electronic warfare and has a decisive impact on the situation of modern warfare. With the development of radar technology, radars with more functions, stronger performance and better stability are the future development direction of radar technology. In the process of radar research and development, using radar echo simulators to generate high-precision echoes for radar performance testing is an efficient means to improve the efficiency of radar system research and development and reduce research and development costs.

[0003] When using the radar echo simulation system to model radar echoes, traditional methods rarely consider the impact of the movement of the radar target on the radar echo amplitude, so it is assumed that its amplitude is fixed. The radar echo generated by this method can meet the needs of the general function of the radar, but for some radars that are sensitive to the echo amplitude (such as SAR radar) or where the scattering characteristics of the radar target vary greatly between echoes, this echo has a large error compared to the real radar echo, so it cannot be used. In actual situations, the motion state of the real radar target is uncertain. The view angle, distance and speed of the radar target relative to the radar are in a dynamic change process, resulting in the RCS of the radar target also changing dynamically and cannot be determined by a certain moment. Therefore, it is more in line with the actual situation if the dynamic RCS characteristics of the radar target are analyzed.

[0004] In the radar echo simulation system, if the radar echo amplitude is directly multiplied by a value that conforms to the fluctuation characteristics, the input bit number of the DAC chip data will have a large range of changes, and some echo signals with smaller amplitudes may not be recognized. If a variable gain amplifier is added to the radar intermediate frequency analog output, although the simulation of the echo amplitude with a large dynamic range can be completed, considering that the target RCS characteristics generally follow a model with higher data accuracy, the simulation accuracy of this method is limited. Summary of the invention

[0005] The technical problem to be solved by the present invention is to provide a method for simulating the amplitude fluctuation characteristics of radar echo based on FPGA and VGA in order to address the defects involved in the background technology, thereby solving the technical problem of real-time and accurate simulation of the fluctuation characteristics of radar target echo.

[0006] The present invention adopts the following technical solutions to solve the above technical problems:

[0007] A method for simulating radar echo amplitude fluctuation characteristics based on FPGA and VGA, comprising the steps of:

[0008] Step 1), using two LFSRs (linear feedback shift registers) inside the FPGA to generate a non-periodic first uniformly distributed random sequence and a second uniformly distributed random sequence respectively;

[0009] Step 2), Box-Muller transformation is performed on the first uniformly distributed random sequence and the second uniformly distributed random sequence to obtain a first Gaussian distributed random sequence and a second Gaussian distributed random sequence that are independent of each other and have a mean of 0, and then mathematical operations are performed on the first Gaussian distributed random sequence and the second Gaussian distributed random sequence to obtain random sequences of uniform distribution, exponential distribution, lognormal distribution, Rayleigh distribution, and Rice distribution, and the mathematical operation method is as follows:

[0010] Step 2.1), perform a logarithmic operation on the first uniform distribution sequence and multiply it by -1 / λ to obtain an exponential distribution random sequence, where λ is an arbitrary real number;

[0011] Step 2.2), respectively adding preset constants ucos θ and usinθ to the first Gaussian distribution random sequence and the second Gaussian distribution random sequence to obtain a third Gaussian distribution random sequence and a fourth Gaussian distribution random sequence with means ucosθ and usinθ, respectively, where u and θ are arbitrary real numbers, and then square the third Gaussian distribution random sequence and the fourth Gaussian distribution random sequence and sum them, and calculate the square root of the summed result to obtain a Ricean distribution random sequence;

[0012] Step 2.3), square the first Gaussian distribution random sequence and the second Gaussian distribution random sequence respectively and then sum them, and then perform a square root operation on the summed results to obtain a Rayleigh distribution random sequence;

[0013] Step 2.4), performing exponential calculation on the first Gaussian distribution random sequence to obtain a log-normal distribution random sequence;

[0014] Step 3), according to the requirements, select a sequence from the first Gaussian distribution random sequence, exponential distribution random sequence, lognormal distribution random sequence, Rayleigh distribution random sequence, and Rice distribution random sequence as the operation data sequence for decomposition, and each random data in the operation data sequence will be decomposed into two values: the normalized value of the precision amplitude modulation value ΔRCS between (0,1] i and the normalized coarse amplitude modulation value ARCS greater than 1 i , where i is the sequence number of random data in the operation data sequence;

[0015] Step 4), for each random data in the operation data sequence:

[0016] The reference radar echo signal with a preset amplitude of 1 is multiplied by the decomposed fine amplitude modulation value in sequence inside the FPGA to obtain an amplitude-precisely modulated digital domain echo signal. The echo signal is then converted from digital to analog through a DAC to obtain a radar echo analog signal and connected to a VGA. The VGA performs a 0-40dB amplitude coarse modulation on the radar echo analog signal according to the decomposed coarse amplitude modulation value to complete the amplitude modulation of the corresponding radar echo.

[0017] As a further optimization scheme of the radar echo amplitude fluctuation characteristic simulation method based on FPGA and VGA of the present invention, the detailed steps of step 3) are as follows:

[0018] Step 3.1), set the threshold δ(RCS i ), the threshold value represents the amplitude of the radar echo when the radar echo simulation system DAC is at full scale output;

[0019] Step 3.2), when the amplitude RCS of the i-th echo i Less than δ(RCS i ), ΔRCS i =RCS i / δ(RCS i )≤1, ARCS i =0, the VGA coarse amplitude modulation module does not need to modulate the radar echo amplitude;

[0020] Step 3.3), when the amplitude RCS of the i-th echo i Greater than δ(RCS i )hour:

[0021] Step 3.3.1), set [RCS i / δ(RCS i )] and perform remainder operation to obtain the precise amplitude modulation coefficient ΔRCS i (ΔRCS i <1);

[0022] Step 3.3.2), set [RCS i / δ(RCS i )] / [ΔRCS i ×δ(RCS i )] to obtain the coarse amplitude modulation coefficient ARCS i (1 <ARCS i <100).

[0023] Compared with the prior art, the present invention adopts the above technical solution and has the following technical effects:

[0024] 1. Multiple high-precision random sequences are generated inside the radar echo simulation system, which can not only be used to simulate the fluctuation characteristics of radar echoes, but also to simulate the noise, interference, clutter and other signals received by the radar echo simulation system in a real environment, and has broad application prospects;

[0025] 2. The radar echo amplitude is first finely modulated inside the FPGA, and then coarsely modulated through a variable gain amplifier. This combination of coarse and fine modulation solves the problems of low accuracy and small dynamic range in the current simulation of radar echo fluctuation characteristics, and improves the fidelity of the echo generated by the radar echo simulator. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is a schematic diagram of the process of step 2) of the present invention;

[0027] Figure 2 (a) Figure 2 (b) Figure 2 (c) Figure 2 (d) The statistical histograms of noise signals that conform to exponential distribution, Rayleigh distribution, Gaussian distribution, and Rice distribution, respectively;

[0028] Figure 3 is a schematic diagram of the process of decomposing the operation data sequence in step 3) of the present invention;

[0029] Figure 4 It is a schematic diagram of simulating the amplitude of radar echo based on log-normal data;

[0030] Figure 5 It is a schematic diagram of simulating the amplitude of radar echo based on exponential distribution data. DETAILED DESCRIPTION

[0031] The technical solution of the present invention is further described in detail below in conjunction with the accompanying drawings:

[0032] The present invention can be implemented in many different forms and should not be considered to be limited to the embodiments described herein. On the contrary, these embodiments are provided to make this disclosure thorough and complete, and will fully express the scope of the present invention to those skilled in the art. In the accompanying drawings, components are enlarged for clarity.

[0033] The present invention discloses a method for simulating the high dynamic range fluctuation characteristics of radar echo amplitude based on FPGA (field programmable gate array) and VGA (ADRF6518 variable gain amplifier), comprising the following steps:

[0034] Step 1), using two LFSRs (linear feedback shift registers) inside the FPGA to generate a non-periodic first uniformly distributed random sequence and a second uniformly distributed random sequence respectively;

[0035] Step 2), Box-Muller transformation is performed on the first uniformly distributed random sequence and the second uniformly distributed random sequence to obtain a first Gaussian distributed random sequence and a second Gaussian distributed random sequence that are independent of each other and have a mean of 0, and then mathematical operations are performed on the first Gaussian distributed random sequence and the second Gaussian distributed random sequence to obtain random sequences of uniform distribution, exponential distribution, lognormal distribution, Rayleigh distribution, and Rice distribution, and the mathematical operation method is as follows:

[0036] Step 2.1), perform a logarithmic operation on the first uniform distribution sequence and multiply it by -1 / λ to obtain an exponential distribution random sequence, where λ is an arbitrary real number;

[0037] Step 2.2), respectively adding preset constants ucos θ and usinθ to the first Gaussian distribution random sequence and the second Gaussian distribution random sequence to obtain a third Gaussian distribution random sequence and a fourth Gaussian distribution random sequence with means ucosθ and usinθ, respectively, where u and θ are arbitrary real numbers, and then square the third Gaussian distribution random sequence and the fourth Gaussian distribution random sequence and sum them, and calculate the square root of the summed result to obtain a Ricean distribution random sequence;

[0038] Step 2.3), square the first Gaussian distribution random sequence and the second Gaussian distribution random sequence respectively and then sum them, and then perform a square root operation on the summed results to obtain a Rayleigh distribution random sequence;

[0039] Step 2.4), performing exponential calculation on the first Gaussian distribution random sequence to obtain a log-normal distribution random sequence;

[0040] Step 3), according to the requirements, select a sequence from the first Gaussian distribution random sequence, exponential distribution random sequence, lognormal distribution random sequence, Rayleigh distribution random sequence, and Rice distribution random sequence as the operation data sequence for decomposition, and each random data in the operation data sequence will be decomposed into two values: the normalized value of the precision amplitude modulation value ΔRCS between (0,1] i and the normalized coarse amplitude modulation value ARCS greater than 1 i , where i is the sequence number of random data in the operation data sequence;

[0041] Step 4), for each random data in the operation data sequence:

[0042] The reference radar echo signal with a preset amplitude of 1 is multiplied by the decomposed fine amplitude modulation value in sequence inside the FPGA to obtain an amplitude-precisely modulated digital domain echo signal. The echo signal is then converted from digital to analog through a DAC to obtain a radar echo analog signal and connected to a VGA. The VGA performs a 0-40dB amplitude coarse modulation on the radar echo analog signal according to the decomposed coarse amplitude modulation value to complete the amplitude modulation of the corresponding radar echo.

[0043] The detailed steps of step 3) are as follows:

[0044] Step 3.1), set the threshold δ(RCS i ), the threshold value represents the amplitude of the radar echo when the radar echo simulation system DAC is at full scale output;

[0045] Step 3.2), when the amplitude RCS of the i-th echo i Less than δ(RCS i ), ΔRCS i =RCS i / δ(RCS i )≤1, ARCS i =0, the VGA coarse amplitude modulation module does not need to modulate the radar echo amplitude;

[0046] Step 3.3), when the amplitude RCS of the i-th echo i Greater than δ(RCS i )hour:

[0047] Step 3.3.1), set [RCS i / δ(RCS i )] and perform remainder operation to obtain the precise amplitude modulation coefficient ΔRCS i (ΔRCS i <1);

[0048] Step 3.3.2), set [RCS i / δ(RCS i )] / [ΔRCS i ×δ(RCS i )] to obtain the coarse amplitude modulation coefficient ARCS i (1 <ARCS i <100).

[0049] The present invention first uses two 32-bit LFSRs to generate a non-periodic uniformly distributed random sequence, then performs Box-Muller transformation, and uses the CORDIC algorithm to complete the Box-Muller transformation. The ln(x) and sin(x) / cos(x) functions are calculated to generate random sequences that obey the normal distribution. Then, based on the mathematical definitions of other complex functions, random sequences that obey the distribution of other complex functions are obtained through related mathematical operations.

[0050] The random sequence generated by the complex function distribution is decomposed into two numbers according to certain rules, namely ΔRCS i and ARCS i The same random sequence can be decomposed into different ΔRCS i and ARCS i , its specific value is related to the threshold δ(RCS i ) is related to δ(RCS i ) is the echo amplitude corresponding to the full-scale output of the DAC in the echo simulation system, corresponding to the normalized amplitude of 1. When the amplitude RCS of the i-th echo i Less than δ(RCS i ), the decomposed internal precision amplitude modulation coefficient ΔRCS i =RCS i / δ(RCS i )≤1, this value is the normalized value, which converts the full-scale output echo to ΔRCS i Multiply by DAC output, VGA coarse amplitude modulation coefficient ARCS i = 0, no amplitude modulation is performed on the echo. When the amplitude RCS of the i-th echo i Greater than δ(RCS i ), first set [RCS i / δ(RCS i )] and perform remainder operation to obtain the precise amplitude modulation coefficient ΔRCS i (ΔRCS i <1), the radar echo amplitude corresponding to the precision amplitude modulation coefficient is [ΔRCS i ·δ(RCS i )], so the amplitude coefficient of coarse amplitude modulation ARCS i =[RCS i / δ(RCS i )] / [ΔRCS i ·δ(RCS i )](1 <ARCS i <100), through the comprehensive use of FPGA and VGA to complete the fine amplitude modulation and coarse amplitude modulation of the radar echo, the technical problem of real-time and accurate simulation of the fluctuation characteristics of the radar target echo was solved.

[0051] The amplitude of a single pulse echo signal is modulated using the log-normal distribution and exponential distribution random sequences generated by the noise signal as modulation data. The statistical histogram of the actual measured echo signal amplitude is consistent with the ideal probability density curve, which verifies the feasibility and correctness of the proposed method.

[0052] Figure 1 This paper describes the process of generating random signal sources in the simulation of radar echo fluctuation characteristics. First, two 32-bit LFSRs are used to generate two sets of random series that obey uniform distribution and give different seeds, so the period of the signal is 2 32 ×2 32 ×1 / f clk ≈683217 days, where f clk is the working clock of FPGA 312.5MHz. Therefore, it can be considered that the generated uniformly distributed random sequences are all non-periodic. The principle of Box-Muller algorithm is shown in the following formula:

[0053]

[0054]

[0055] The formula mainly involves ln(x), And sin(x) / cos(x) operation, after completing the above operations through the CORDIC algorithm, according to Figure 1 By performing a series of data operations, you can get a variety of random sequences that obey different complex function distributions, including: exponential distribution, normal distribution, lognormal distribution, Rayleigh distribution, and Rice distribution random sequences. All generated random sequences are saved to the 20th bit after the binary decimal.

[0056] Figure 2 Statistical histograms of four typical noise signals are generated and an ideal probability density curve is fitted in the figure. It can be seen from the figure that the probability distribution characteristics of the generated noise signal are highly consistent with the ideal probability density curve. The noise signal generation module provides a high-quality signal source for the simulation of radar echo fluctuation characteristics.

[0057] Figure 3 The schematic diagram of radar echo fine amplitude modulation and coarse amplitude modulation is described. The DAC fine amplitude control module firstly adjusts the amplitude of the radar echo according to the ΔRCS. i The value is multiplied internally to complete the echo amplitude precision adjustment, and is converted into an analog signal through the DAC chip and sent to the ADRF6518 variable gain amplifier. At this time, ADRF6518 will adjust the amplitude according to ARCS. i The radar echo amplitude is roughly adjusted by the value of , and its adjustable range is 0~40dB. The following example will illustrate the amplitude adjustment process.

[0058] Assume that the amplitude RCS of the i-th echo is i is 0.25, the threshold δ(RCS i ) is set to 0.4, then the amplitude fine modulation data ΔRCS of the first echo is i Relative to the threshold δ(RCS i ) is 0.25 / 0.4=0.625, so multiply the radar echo by 0.625. At this time, ARCS i =0, no coarse amplitude modulation is required.

[0059] Assume that the amplitude RCS of the i-th echo is i is 0.52, the threshold δ(RCS i ) is also set to 0.4, the echo amplitude RCS i The relative ratio to the threshold is [RCS i / δ(RCS i )]=0.52 / 0.4=1.3, take the remainder, then ΔRCS i =0.3, this data is the data of the amplitude fine modulation module. i = 0.3, the normalized value of the radar echo amplitude adjustment relative to the threshold is ΔRCS i ·δ(RCS i )=0.12, so the data ARCS of the coarse amplitude adjustment module i =[RCS i / δ(RCS i )] / [ΔRCS i ·δ(RCS i )]=1.3 / 0.12=10.83. The dynamic fluctuation characteristics of radar echo are simulated by the method of amplitude fine adjustment and coarse adjustment. The amplitude of radar echo is simulated by the exponential distribution and logarithmic normal data generated by the noise signal generation module. The actual test results are as follows Figure 4 , Figure 5 As shown, it can be seen that the histogram of the fluctuation characteristics of the radar echo simulated by this method can conform to the characteristics of the exponential distribution and the log-normal distribution probability density function, which verifies the effectiveness and accuracy of this method.

[0060] It will be understood by those skilled in the art that, unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as those generally understood by those skilled in the art in the art to which the present invention belongs. It should also be understood that terms such as those defined in common dictionaries should be understood to have meanings consistent with the meanings in the context of the prior art, and will not be interpreted with idealized or overly formal meanings unless defined as herein.

[0061] The specific implementation methods described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific implementation method of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for simulating radar echo amplitude fluctuation characteristics based on FPGA and VGA, characterized in that: Includes steps: Step 1), using two LFSRs (linear feedback shift registers) inside the FPGA to generate a non-periodic first uniformly distributed random sequence and a second uniformly distributed random sequence respectively; Step 2), Box-Muller transformation is performed on the first uniformly distributed random sequence and the second uniformly distributed random sequence to obtain a first Gaussian distributed random sequence and a second Gaussian distributed random sequence that are independent of each other and have a mean of 0, and then mathematical operations are performed on the first Gaussian distributed random sequence and the second Gaussian distributed random sequence to obtain random sequences of uniform distribution, exponential distribution, lognormal distribution, Rayleigh distribution, and Rice distribution, and the mathematical operation method is as follows: Step 2.1), perform a logarithmic operation on the first uniform distribution sequence and multiply it by -1 / λ to obtain an exponential distribution random sequence, where λ is an arbitrary real number; Step 2.2), respectively adding preset constants ucosθ and usinθ to the first Gaussian distribution random sequence and the second Gaussian distribution random sequence to obtain a third Gaussian distribution random sequence and a fourth Gaussian distribution random sequence with means ucosθ and usinθ, respectively, where u and θ are arbitrary real numbers, and then square the third Gaussian distribution random sequence and the fourth Gaussian distribution random sequence and sum them, and calculate the square root of the summed result to obtain a Ricean distribution random sequence; Step 2.3), square the first Gaussian distribution random sequence and the second Gaussian distribution random sequence respectively and then sum them, and then perform a square root operation on the summed results to obtain a Rayleigh distribution random sequence; Step 2.4), performing exponential calculation on the first Gaussian distribution random sequence to obtain a log-normal distribution random sequence; Step 3), according to the requirements, select a sequence from the first Gaussian distribution random sequence, exponential distribution random sequence, lognormal distribution random sequence, Rayleigh distribution random sequence, and Rice distribution random sequence as the operation data sequence for decomposition, and each random data in the operation data sequence will be decomposed into two values: the normalized value of the precision amplitude modulation value ΔRCS between (0,1] i and the normalized coarse amplitude modulation value ARCS greater than 1 i , where i is the sequence number of random data in the operation data sequence; Step 4), for each random data in the operation data sequence: The reference radar echo signal with a preset amplitude of 1 is multiplied by the decomposed fine amplitude modulation value in sequence inside the FPGA to obtain an amplitude-precisely modulated digital domain echo signal. The echo signal is then converted from digital to analog through a DAC to obtain a radar echo analog signal and connected to a VGA. The VGA performs a 0-40dB amplitude coarse modulation on the radar echo analog signal according to the decomposed coarse amplitude modulation value to complete the amplitude modulation of the corresponding radar echo.

2. The method for simulating radar echo amplitude fluctuation characteristics based on FPGA and VGA according to claim 1, characterized in that: The detailed steps of step 3) are as follows: Step 3.1), set the threshold δ(RCS i ), the threshold value represents the amplitude of the radar echo when the radar echo simulation system DAC is at full scale output; Step 3.2), when the amplitude RCS of the i-th echo i Less than δ(RCS i ), ΔRCS i =RCS i / δ(RCS i )≤1, ARCS i =0, the VGA coarse amplitude modulation module does not need to modulate the radar echo amplitude; Step 3.3), when the amplitude RCS of the i-th echo i Greater than δ(RCS i )hour: Step 3.3.1), set [RCS i / δ(RCS i )] and perform remainder operation to obtain the precise amplitude modulation coefficient ΔRCS i , where ΔRCS i <1; Step 3.3.2), set [RCS i / δ(RCS i )] / [ΔRCS i ×δ(RCS i )] to obtain the coarse amplitude modulation coefficient ARCS i , where 1 <ARCS i <100.

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