P Code Directly Capture The Gps Satellite Positioning System Technology Research

This thesis investigates the structure of digitalized GPS receiver, especially the methods of P code fast acquisition in low SNR and high-dynamic environment, and presents a new P-Code acquisition method - local resident bidirectional fast search method based on FFT. Some quantized IF data is stored in RAM and is reused during the search until code phase and carrier frequency are acquired. The AntiP code generation is designed and validated for the reverse search, which generates a series reverse to the stand P code series. Farther more, this method discards the traditional acquisition structure that is the parallel of code tracking loop and carrier tracking loop. Instead of that, it enhances the dynamic performance by search the code and carrier serially.The simulation result shows that, the operand decline to about 1/10 or less of before by using FFT arithmetic. The AntiP code generation is designed to implement the reverse search of code phase, which increases the clock of acquisition system 5 to 10 times or more than traditional structure. Serial search of Doppler frequency and code phase can evidently reduce the attenuation of SNR caused by Doppler. Different search speed, dynamic and noise performance could be easily achieved in order to adapt the environment just by use different Doppler search step and range, the point and effective point of FFT.