The data bits and spread spectrum codes of the spaceborne spread-spectrum transponder are asynchronous. Due to the influence of transmission system noise and Doppler frequency shift,it can cause attenuation of peak values related to receiving and transmitting spread spectrum codes,leading to a decrease in capture performance. Traditional capture techniques often have problems such as high algorithm complexity,slow capture speed,and difficulty adapting to the requirements of large frequency offsets of hundreds of kilohertz. This article proposes a spread spectrum sequence search method that truncates the spread spectrum sequence into two segments for correlation operations,and combines the signal squared sum FFT loop for a large frequency offset locking,effectively suppressing the attenuation of correlation peaks and improving pseudocode capture performance. MATLAB simulation and FPGA board level testing show that the proposed spread spectrum signal capture scheme can resist Doppler frequency shifts of up to±300 kHz,with an average capture time of about 95 ms. In addition,the FPGA implementation of this algorithm saves about 47％ of LUT,43％ of Register,and more than half of DSP and BRAM resources compared to traditional structures,making it of great application value in resource limited real-time communication systems.
关键词
多普勒频移/伪码捕获/FPGA
Key words
Doppler frequency shift/PN code synchronization/FPGA
维普
万方数据