Research On Synchronization Technology In Satellite Ranging System Based DSSS

Spread spectrum ranging technology is increasingly widely applied in the field of aerospace monitoring and controlling because of its features of non-fuzzy distance, high accuracy, strong anti-interference, security and confidentiality, and easy sharing of frequency resources.This paper presents the design of a ranging system based on DSSS (Direct Sequence Spread Spectrum) working at a large Doppler frequency offset, focusing on the pseudo-noise (PN) code synchronization and carrier synchronization. PN code Synchronization can be achieved by PN code acquisition and tracking. Carrier synchronization includes carrier frequency offset estimation and exact tracking with Phase Locked Loop (PLL). According to the system requirements, the paper proposes an anti-offset acquisition algorithm based on FFT. The system still works normally at the frequency offset of700kHz when the number of section is256, greatly improving the anti-offset performance. The larger the section number is, the better the anti-offset performance presents; and the more samples the calculation of FFT involves, the less spectral energy leaks, the bigger the normalized correlated value becomes, and the greater the probability of the PN code acquisition grows. The method of carrier frequency offset estimation and pretreatment are introduced to enable the system to possess the advantage of changing a large frequency offset into a certain range. The digital Costas loop is realized, focusing on the design of the key parameters. The smaller the equivalent noise bandwidth of loop is, the longer the acquisition time lasts, but the better the anti-noise performance presents. The energy detector, different from the ordinary PLL, is adopted when designing the phase detector of code tracking loop. Single PN code ranging system can achieve an accuracy of Ins for distance ranging. Finally, the system is implemented with FPGA and can work properly.