FPGA Implementation Of BAQ Compression Algorithm For SAR Original Data

Synthetic aperture radar(SAR)system can achieve high spatial resolution by transmitting broadband linear frequency modulation(LFM)signal and combining with synthetic aperture technology,and is widely used in military and civil fields.In recent years,semiconductor and large-scale integrated circuit have developed rapidly,FPGA,DSP,GPU and other real-time signal processing capabilities,high-speed data communication capabilities have been greatly improved,ADC sampling,resolution and other indicators have been continuously improved.With the development of electronic information technology,the performance indexes of spaceborne synthetic aperture radar,such as working bandwidth,pulse repetition frequency,observation cliw and resolution have been greatly improved.However,as a result,the amount of original data has increased dramatically,which brings severe challenges to large capacity data storage and downlink data transmission on the satellite.Data compression is an indispensable means to reduce the original data rate of spaceborne SAR system.SAR original echo data has unique probability and statistical characteristics,and cannot be compressed by conventional de-redundancy method.Since the 1980 s,the research on SAR original echo data compression algorithm has never stopped.In this paper,we analyzed the statistical characteristics of SAR original echo data,introduced the basic theoretical knowledge of SAR original data compression.At the same time,several compression algorithms tha t have been applied in spaceborne SAR system are introduced.Then we gave the implementation process and analyzed their advantages and disadvantages.Looking at the original data compression of the active satellite-borne synthetic aperture radar system in various countries,BAQ algorithm is the most widely used and has undergone the verification of multiple space flight missions.It is a stable,mature and real-time data compression algorithm.The FPGA implementation of BAQ algorithm in this paper used Xilinx 7XC7VX485 T chip.The original data was a data block of size 4(channel)256 3000 Byte obtained by an onboard Interferometric Imaging Radar Altimeter(InIRA).The results show that in addition to storage,other resources occupy less than 20% of the chip resources,and the data processing rate is 840 Mbps.In view of the shortcomings of BAQ algorithm and the characteristics of original echo data,this paper also improves the algorithm.The compressed output bit of the improved algorithm is 4.4bit,which is consistent with the elevation error when the output of traditional BAQ is 6bit.The height measurement error of 0.36 c m is exchanged for a 45% data rate reduction when the resolution is 10 km.Therefore,the compression rate is higher than the traditional BAQ algorithm,and the processing rate is also superior.In addition,the effects of different compression ratios and block modes on the performance are analyzed to provide reference for the measurement of the ocean height of the spaceborne SAR data compression system in the future.