Research And Implementation On Baseband Signal Processing Technology Of Beidou Satellite Navigation Receivers

BeiDou Navigation Satellite System(BDS)is a global navigation satellite system,being implemented in China's independent development and operation.BDS has been applied in many fields and brought remarkable economic and social benefits,especially to the homeland security defense playing the key role.As one of the satellite navigation receivers' main functional units,baseband signal processing effect has close relation with navigation signal's rapid acquisition and stable tracking,directly impacts the performance of satellite navigation receivers,baseband signal processing technology of BeiDou satellite navigation receivers has important research significance.Based on the spread spectrum communication theory,BDS B1 frequency point of civil navigation signal for the research object,this paper focused in studying satellite navigation signal acquisition and tracking.Verified on FPGA+DSP hardware platform,the FPGA processes with digital IF signal from RF front-end for despread and demodulation;the DSP resolves location,speed and time(PVT),outputs navigation and location results.This paper analyzed the basic acquisition methods of BDS navigation signal: time domain search method and parallel search method based on FFT,determined the acquisition method of parallel code phase search based on FFT as BDS signal acquisition method,designed the main function modules' implementation and simulation.BDS navigation signal tracking includes carrier tracking and code tracking: Frequency-locked loop has good dynamic performance,strong anti-jamming capability,tracks low SNR signal,but the tracking of signal is not tight,the output of carrier phase measurement owes accuracy.Phase-locked loop tracks navigation signal closely,outputs accurate carrier phase measurement,but its tolerance of dynamic stress is poor.Comprehensively analyzed,for the carrier tracking,selected second-order frequency-locked loop assisting third-order phase-locked loop as the tracking loop;For the code tracking,selected delayed lock loop(DLL)as the tracking loop.Results show that acquisition method of parallel code phase search based on FFT achieves the purpose of fast acquisition with high efficiency;Delayed lock code tracking method and second-order frequency-locked assisting third-order phase-locked carrier tracking method track signal stably,meet the design requirements.