CN103197317B - Synthetic aperture radar (SAR) imaging method based on field programmable gate array (FPGA) - Google Patents
Synthetic aperture radar (SAR) imaging method based on field programmable gate array (FPGA) Download PDFInfo
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Abstract
The invention discloses a synthetic aperture radar (SAR) imaging method based on field programmable gate array (FPGA). The SAR imaging method based on the FPGA mainly solves the problems that an existing system is complex in structure and slow in data processing speed. The SAR imaging method based on the FPGA comprises the following steps: calling a multiplying unit in the FPGA, conducting fast Fourier transform (FFT) operation after multiplying each array of distance direction data and hamming window data after quantification, finishing distance pulse pressure; calculating a scene central location of the distance direction by inertia parameters, intercepting the distance direction data; transposing acquired data by interception, realizing to store aperture data based on direction; estimating a Doppler central value and a Doppler frequency modulation rate based on inertia navigation parameters; constructing a Doppler frequency shift function, a Doppler frequency modulation function and a direction hamming window function based on the estimated Doppler central value and the Doppler frequency modulation rate; conducting FFT operation by multiplying each array of the direction data after finishing the distance impulse pressure with the Doppler frequency shift function, the Doppler frequency modulation function and the direction hamming window function, and acquiring final imaging data. The SAR imaging method based on the FPGA has the advantages of simplifying an SAR imaging system structure, improving processing speed, and capable of being used in the SAR imaging under a missile-borne module.
Description
Technical field
The invention belongs to digital signal processing technique field, relate to radar imaging method, can be applicable to the fields such as the design of radar system for real-time signal processing and remote sensing, guided missile.
Background technology
Synthetic-aperture radar SAR has two-dimensional distance and orientation high resolving power, can make high-resolution two-dimensional imaging to scene.Can be round-the-clock, round-the-clock, target detected and locate at a distance, play an important role at military and many civil areas.Common SAR imaging algorithm has distance-Doppler R-D algorithm, line frequency modulation to become mark CS algorithm etc.Range-Doppler imaging algorithm, as a kind of main algorithm of synthetic aperture radar image-forming, occupies vital role in synthetic aperture radar image-forming field.
At present conventional radar imagery platform adopts FPGA+DSP form more, utilizes the high and strong feature of DSP dirigibility of FPGA degree of parallelism, two kinds of developing instruments radar imagery task that cooperated.FPGA is as primary processor, and DSP both can meet as the method for designing from processor the signal processing tasks that operand is huge, can alleviate to a certain extent again heat dissipation problem.In this form, although DSP has had the ability of complex calculation, it is realized based on serial, and its degree of parallelism is lower, the low utilization of resources, and arithmetic speed is slow.And many boards of complexity form of FPGA+DSP is high to system space and radiating condition requirement, and missile-borne SAR system environments space and radiating condition are limited, can not meet the requirement of many boards of FPGA+DSP imaging platform.
Summary of the invention
The object of the invention is to the deficiency for above-mentioned prior art, a kind of SAR formation method based on on-site programmable gate array FPGA is provided, with simplied system structure, reduce power consumption, improve the conversion speed of radar imagery.
For achieving the above object, the present invention includes following steps:
(1) produce the hamming window of 16384 with Matlab software, and be quantized into 9bit signed fixed-point number and deposit in ROM, radar return distance is multiplied each other to the hamming window in data and ROM, to realize the windowing of adjusting the distance to data;
(2) distance after windowing is carried out to FFT computing to data, complete apart from pulse pressure;
(3) according to the oblique distance of radar front end inertial navigation, angle of squint, flying speed, be calculated to be picture scene center position, and as about mid point each intercept 1024 totally 2048 data as imaging data, in the time producing address out of range, start to intercept from particular point 0 or 14337;
(4) radar return data are upwards pressed to 512 pulses of repetition accumulation of radar transmitted pulse in orientation, obtain 512 column datas as sub-aperture data, will after the data transposition of sub-aperture, store;
(5) respectively every row Data in Azimuth Direction of step (4) neutron aperture data is calculated, obtain 2048 Doppler's central values, using 2048 orientation that obtain to Doppler's central value, summation is averaged the Doppler center as this sub-aperture;
(6) calculate doppler frequency rate according to the carrier aircraft speed of radar front end inertial navigation, angle of squint and oblique distance;
(7) the Doppler center obtaining according to step (5), obtains Doppler shift function, and the doppler frequency rate obtaining according to step (6), obtains doppler frequency rate function; And produced the hamming window of 512 with Matlab software, and be quantized into 16bit signed fixed-point number and deposited in ROM;
(8) by every row Data in Azimuth Direction of step (4) neutron aperture data respectively with step (7) in Doppler shift function, doppler frequency rate function, hamming window data multiply each other, complete and orientation Dechirp in earlier stage process;
(9) to through step (8) sub-aperture after treatment data by its orientation to doing FFT computing, obtain the orientation frequency domain of sub-aperture data, each data of orientation frequency domain are asked to mould value, obtain final imaging data.
Tool of the present invention has the following advantages:
The first, the present invention adopts FPGA as kernel processor chip, the function such as because FPGA has abundant internal resource, the IP kernel that can call FPGA inside in data handling procedure is realized the reading in of data, taken advantage of again, phase calculation, fast operation; And FPGA parallel processing degree is high, and processing speed is fast, improve the conversion speed of radar imagery.
Second, tradition imaging algorithm is realized and is adopted the complicated many boards formal layout of FPGA+DSP data, wherein, realizes radar return distance to the windowing of data and apart from pulse pressure with FPGA, realize windowing and the orientation Dechirp to radar return Data in Azimuth Direction with DSP, and in the present invention, FPGA is not only used for processing distance to data, and process Data in Azimuth Direction, in whole system, signal is processed and has only been used FPGA chip like this, system architecture is simplified, power-dissipation-reduced, reliability increases.
Brief description of the drawings
Fig. 1 is process flow diagram of the present invention;
Fig. 2 is the result figure that the present invention processes radar return data imaging.
Specific embodiments
Below in conjunction with accompanying drawing, the present invention will be further described.
With reference to Fig. 1, specific embodiment of the invention step is as follows:
The compression of step 1. range pulse
1.1) windowing process: I, Q two paths of data are the real imaginary parts of radar return data, call the multiplication IP kernel of two FPGA inside, respectively the I of radar return data, Q two paths of data are multiplied by window function.Wherein, window function is the hamming window of 16384 producing with Matlab software, deposits in the ROM of FPGA after its normalizing is quantized into 9bit signed number; I, Q two paths of data are the echo datas that radar AD collects, be 12bit, after front end zero padding, be spliced into 16bit data, multiplier Output rusults is 25bit, 2 power side because follow-up FFT requires data bits, so 25bit data cutout is become to 16bit, gets the 24th sign bit as the data after intercepting of multiplier output data when intercepting, the 6th to the 20th data bit as these data;
1.2) call the inner FFT core of FPGA, process being FFT through the data of cut position after the output of previous step multiplier, FFT core input data width and phase place bit wide are set and are 16bit, adopt Scaled pattern, making to export data is also 16bit.
Step 2. intercepts distance to data
Oblique distance, angle of squint, flying speed that according to radar, inertial navigation provides are calculated scene center position x, using x as mid point left and right each intercept 1024 totally 2048 data as distance to effective contextual data, when x is less than 1023 or while being greater than 15360, just can not, at each 1023 points that intercept of x the right and left, in the time that being less than 1023, x start to intercept with the first point of scene; In the time that x is greater than 15360 taking 14337 as starting point start intercept.
Step 3. data accumulation and transposition.
The DDRII of the plug-in 2 groups of 1GB of FPGA, step 2 completes distance after data cutout, 2048 data of every row are deposited in DDRII, after accumulation 512 row as the data in a sub-aperture, realize data transposition according to the quick transposition algorithm of DDRII, make sub-aperture data by orientation to 512 arrangements, to carry out follow-up Data in Azimuth Direction processing.
Doppler center, step 4. estimator aperture and doppler frequency rate.
4.1) estimating Doppler central value:
4.1.1) call the complex multiplication IP kernel of FPGA inside, by a line Data in Azimuth Direction dislocation conjugation dot product, obtain auto-correlation vector, complex multiplication IP kernel is input as the real imaginary part of two-way and is respectively the plural number of 16bit, is output as the real imaginary part in a road and is respectively the plural number of 16bit;
4.1.2) to auto-correlation vector, summation is averaged and is obtained autocorrelation value, the CORDIC IP kernel that calls FPGA inside calculates the phase angle [alpha] of autocorrelation value, here the real imaginary part that is input as autocorrelation value of CORDIC IP kernel, output is the phasing degree of this autocorrelation value;
4.1.3), according to autocorrelation value phase angle [alpha] obtained in the previous step, calculate Doppler center f by following formula
dc:
f
dc＝α×PRF/2/π，
Wherein, PRF is the repetition of radar emission signal.
Here the calculating at Doppler center is to call the multiplier of FPGA inside to realize, multiplier Yi road is input as autocorrelation value phase angle [alpha], another road is PRF/2/ π, here need first in Matlab software, to be quantized into the signed fixed-point number with autocorrelation value R phase angle with same bit-width, be re-used as the input of multiplier.
4.1.4) repeating step 4.1.1) to step 4.1.3) three steps, until obtain all orientation to Doppler's central value, using 2048 orientation that obtain to Doppler's central value, summation is averaged the Doppler center as this sub-aperture;
4.2) call the multiplier of FPGA inside, according to the carrier aircraft speed v of radar front end inertial navigation, angle of squint θ and oblique distance Rs, calculate doppler frequency rate ka by following formula:
ka＝-2v
2cos
2θ/λ/Rs，
Wherein, λ is the wavelength of radar emission signal.
Step 5. orientation operates to Dechirp.
5.1) windowing process
I, the Q two paths of data of data after processing to step 3 through step 1 are multiplied by respectively to window function.Wherein, I, Q two paths of data refer to respectively real part and the imaginary part of data; Window function is the hamming window of 512 producing with Matlab software, deposits in the ROM of FPGA after its normalizing is quantized into 16bit signed number; Call the multiplication IP kernel of two FPGA inside, from ROM, reading the hamming window data of 16bit inputs as multiplication IP kernel Yi road, orientation is inputted as another road of two multiplication IP kernels respectively to real part, the imaginary part of 512 16bit data, after multiplying each other, obtain 32bit data, completed windowing operation;
5.2) structure Doppler shift function
Doppler shift function is according to step 4.1) in Doppler's central configuration of estimating, concrete steps are as follows:
5.2.1) produce from-255 to 256 by the always module of FPGA inside and be spaced apart 1, the vector that length is 512, wherein the bit wide of each data is set to 10bit;
5.2.2) use Matlab software by 2 × π × f
dc/ PRF is quantized into 10bit signed fixed-point number, deposits in the ROM of FPGA wherein f in
dcstep 4.1) in the Doppler center that estimates;
5.2.3) call the inner multiplication IP kernel of FPGA, using step 5.2.1) the vector sum step 5.2.2 that obtains) fixed-point number that obtains is as two groups of inputs of multiplication IP kernel, is output as length and is 512 vector;
5.2.4) call the CORDIC IP kernel of FPGA, using step 5.2.3) in the vector quantity that obtains change into 10bit signed number according to the input as CORDIC IP kernel, be output as one complex vector located, the trigonometric function cos that wherein real part of output vector is input vector, imaginary part is the trigonometric function sin of CORDIC IP kernel input vector, and output vector is Doppler shift function.
5.3) structure doppler frequency rate function
Doppler frequency rate function is to utilize step 4.2) in estimate the doppler frequency rate structure that obtains, concrete steps are as follows:
5.3.1) with Matlab software produce from-255 to 256 be spaced apart 1, length is 512 vector, each element in vector all, divided by asking after radar emission signal repetition PRF square, then changes into 16bit signed number by this data volume, stores in the ROM of FPGA;
5.3.2) call FPGA multiplication IP kernel, using step 5.3.1) vector that obtains inputs as multiplication IP kernel Yi road, by step 4.2) in estimate that the ka that obtains intercepts into after the data that bit wide is 16bit, as another road input of multiplication IP kernel, multiplication IP kernel is output as the new vector that one group of bit wide is 32bit;
5.3.3) call the CORDIC IP kernel of FPGA, using step 5.3.2) in the vector that obtains as the input of CORDIC IP kernel, be output as one complex vector located, the trigonometric function cos that wherein real part of output vector is input vector, imaginary part is the trigonometric function sin of CORDIC IP kernel input vector, and output vector is doppler frequency rate function;
5.4) Data in Azimuth Direction configuration
Call FPGA complex multiplication IP kernel twice, complex multiplication IP kernel is by Data in Azimuth Direction and the step 5.2 of radar return for the first time) the Doppler shift function that obtains multiplies each other, and is output as 48bit plural number; The output of complex multiplication is for the first time inputted as second complex multiplication IP kernel Yi road, and another road is input as step 5.3) in estimate the doppler frequency rate function that obtains, be output as the data of 64bit, become real imaginary part to be the data of 32bit through data cut position.
5.5) Data in Azimuth Direction FFT
Calling the FFT IP kernel of FPGA inside, using step 4.4) result vector that produces is as the input of FFT IP kernel, and the data that FFT IP kernel output bit wide is 32bit are final imaging data, and so far, the processing of radar return data all completes.
Effect of the present invention can further illustrate by following actual measurement:
Emulation content, one group of echo data that airborne radar is irradiated to somewhere is as the pending radar return data of the present invention, processes this data by the inventive method, draws gray-scale map by data after treatment, as shown in Figure 2.In Fig. 2, can find out clearly bridge, river, highway and farmland, imaging effect is good, the visible SAR formation method reasonable based on FPGA provided by the invention.
Claims (1)
1. the SAR formation method based on FPGA, comprises the steps:
(1) produce the hamming window of 16384 with Matlab software, and be quantized into 9bit signed fixed-point number and deposit in ROM, radar return distance is multiplied each other to the hamming window in data and ROM, to realize the windowing of adjusting the distance to data;
(2) distance after windowing is carried out to FFT computing to data, complete apart from pulse pressure;
(3), according to the oblique distance of radar front end inertial navigation, angle of squint, flying speed, be calculated to be picture scene center position, x=2 × N × γ × R/c/f
s, wherein, x is scene center, N be radar return distance to number of data points, γ is the frequency modulation rate of radar emission linear FM signal, R is radar range-to-go, c is the light velocity, f
sit is sample frequency; Using this position as mid point left and right each intercept 1024 totally 2048 data as imaging data, in the time producing address out of range, start to intercept from particular point 0 or 14337;
(4) radar return data are upwards pressed to 512 pulses of repetition accumulation of radar transmitted pulse in orientation, obtain 512 column datas as sub-aperture data, will after the data transposition of sub-aperture, store;
(5) respectively every row Data in Azimuth Direction of step (4) neutron aperture data is calculated, obtain 2048 Doppler's central values, using 2048 orientation that obtain to Doppler's central value, summation is averaged the Doppler center as this sub-aperture,
Wherein, the calculation procedure of every row Data in Azimuth Direction is as follows:
First, call the complex multiplication IP kernel of FPGA inside, by a line Data in Azimuth Direction dislocation conjugation dot product, obtain auto-correlation vector;
Then, to auto-correlation vector, summation is averaged and is obtained autocorrelation value, and the CORDIC IP kernel that calls FPGA inside calculates the phase angle [alpha] of autocorrelation value;
Finally, according to the autocorrelation value phase angle [alpha] obtaining, calculate Doppler center by following formula:
f
dc＝α×PRF/2/π，
In formula, f
dcbe Doppler center, PRF is the repetition of radar emission signal;
(6) calculate doppler frequency rate according to the carrier aircraft speed of radar front end inertial navigation, angle of squint and oblique distance:
ka＝-2v
2cos
2θ/λ/Rs，
Wherein, ka is doppler frequency rate, and v is carrier aircraft speed, and θ is angle of squint, and Rs is oblique distance, and λ is the wavelength of radar emission signal;
(7) the Doppler center obtaining according to step (5), obtains Doppler shift function, and the doppler frequency rate obtaining according to step (6), obtains doppler frequency rate function; Produce the hamming window of 512 with Matlab software, and be quantized into 16bit signed fixed-point number and deposit in ROM;
(8) by every row Data in Azimuth Direction of step (4) neutron aperture data respectively with step (7) in Doppler shift function, doppler frequency rate function, hamming window data multiply each other, complete and orientation Dechirp in earlier stage process;
(9) to through step (8) sub-aperture after treatment data by its orientation to doing FFT computing, obtain sub-aperture data orientation frequency domain, each data of orientation frequency domain are asked to mould value, obtain final imaging data.
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| CN103616681B (en) * | 2013-12-04 | 2015-07-15 | 西安电子科技大学 | Radar imaging method based on Zynq-series FPGA |
| CN104597447B (en) * | 2015-01-30 | 2017-03-08 | 西安电子科技大学 | A kind of big stravismus of sub-aperture SAR improves Omega K imaging method |
| CN104820648B (en) * | 2015-04-16 | 2018-04-06 | 中国电子科技集团公司第三十八研究所 | A kind of synthetic aperture radar inertial guidance data input method and input agency plant |
| CN105044718B (en) * | 2015-06-03 | 2017-06-20 | 西安电子科技大学 | Big stravismus radar imagery device and imaging method based on FPGA and DSP |
| CN105137428B (en) * | 2015-07-28 | 2018-09-04 | 南京航空航天大学 | Go the FPGA implementation method of the polar coordinates format image-forming algorithm of slope signal |
| US10078131B2 (en) * | 2015-09-15 | 2018-09-18 | Texas Instruments Incorporated | Method and apparatus for FMCW radar processing |
| CN106842196B (en) * | 2015-12-03 | 2019-12-17 | 中国航空工业集团公司雷华电子技术研究所 | azimuth fuzzy suppression method for SAR sub-aperture imaging |
| CN106772372B (en) * | 2016-11-29 | 2019-05-17 | 北京无线电测量研究所 | A kind of real time imagery method and system of Ka wave band carried SAR system |
| CN108872983A (en) * | 2017-05-11 | 2018-11-23 | 北京遥感设备研究所 | A kind of Missile-borne SAR imaging self-focusing method |
| CN108120980A (en) * | 2017-12-13 | 2018-06-05 | 南京航空航天大学 | A kind of implementation method of the FPGA of satellite-borne SAR multi-modal imaging signal processing algorithm |
| CN111381217B (en) * | 2020-04-01 | 2022-10-18 | 上海无线电设备研究所 | Missile-borne SAR motion compensation method based on low-precision inertial navigation system |
| CN112130145B (en) * | 2020-08-10 | 2022-02-22 | 西安电子科技大学 | Azimuth frequency modulation rate estimation method based on heterogeneous parallel computing |
| CN112014819A (en) * | 2020-08-27 | 2020-12-01 | 南京矽典微***有限公司 | Digital signal processing method, digital signal processing system and radar chip |
| CN112217574B (en) * | 2020-10-09 | 2022-02-11 | 西安石油大学 | Method for calculating aperture average function of optical receiver with arbitrary complex shape and implementation device |
| CN114626006B (en) * | 2022-03-21 | 2023-03-14 | 电子科技大学 | FPGA (field programmable Gate array) realization method for real-time generation of CS (Circuit switched) algorithm compensation factor in radar imaging |
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