Design And Implementation Of Mars SAR Original Echo Data Compression System Using FPGA

In recent years,with the continuous development of China's space technology,the desire to go deeper into the universe has become stronger and faster.Mars has become another detection hotspot after the Moon.Synthetic Aperture Radar(SAR)is an active,high spatial resolution microwave imaging device for observing targets on the ground.Because synthetic aperture radar can transmit electromagnetic waves to penetrate the surface of Mars,it can be used to search the constituent of Mars subsurface which from several meters to several kilometers.Exploration can obtain the information about the composition and structure of the Mars also.Due to the high resolution,large mapping bandwidth,multiple frequency bands,and multiple polarization channels,the number of original echo data obtained by the subsurface detection radar increases geometrically.Mars probe downlink data rate is low,but SAR raw echo data compression system available resources are less than 20% of the XQ4VSX55 chip.How to compress the data when the hardware resources are particularly scarce is a very important issue,which has important engineering value and significance.This paper improves the BAQ algorithm based on the actual requirements of the Mars SAR original echo data compression problem.Using the amplitude logarithm-phase algorithm,a complete SAR raw echo data compression system was designed on a chip model XQ4VSX55-10FF1148 M.Based on this,the compression performance of the compression system is analyzed in the thesis.The main work of this paper is as follows:(1)Phase information is the main factor that affects the compression quality.For the problem that BAQ algorithm has insufficient phase information after compression of real and imaginary data,the amplitude logarithm-phase algorithm used in this paper converts the real imaginary part of the data into amplitude and phase,and then evenly quantizes the phase and allocates more Many quantization bits.This solve the problem of insufficient retention of phase information.For BAQ algorithm unified processing of data,no attention was paid to the loss of subsurface echo signals in the process of compression and decompression,resulting in a large loss of subsurface echo signals.This paper uses the nonlinear characteristics of the logarithmic function,performs BAQ quantization on the amplitude logarithmic and improves the resolution of the subsurface echo signal.(2)The BAQ algorithm consumes more resources when compressing SAR raw echo data,but it is resource-constrained in the context of Mars exploration.In order to solve this contradiction,this paper optimizes the BAQ quantization coding table.Calculations are used instead of table lookup When the standard deviation is calculated,which uses logical resources to replace memory resources,thereby reducing memory resource consumption.After statistics,only 5% of memory resources and 17% of logic resources are consumed and controlled within the available resources.(3)To verify the compression effect of the SAR original echo data compression system,this paper compares the BAQ algorithm and the algorithm used in this paper from signal-noise ratio and data quality evaluation criterion curve.The results show that the signal to noise ratio is maximum,the data quality evaluation criterion curve can more easily distinguish the subsurface echo main lobe,and the overall compression effect is better when the phase quantization bits are two bits larger than the amplitude logarithm.By analyzing the resources and speeds,it shows that the original SAR echo data compression system designed and implemented in this paper consumes less resources and the Processing speed is higher than back-end data transmission speed,which satisfies the actual requirements of Mars exploration tasks.