Satellite Positioning P Code Directly Capture Technology Research

The Global Positioning System (GPS) P-code has a higher chipping rate, better accuracy and anti-jamming property than C/A code. When C/A code is not available, direct P-code acquisition is useful.This thesis investigates the synchronization of digitalized DSSS receiver in high-dynamic and low SNR environment, presents and realizes the methods of fast P-code acquisition in GPS. Firstly, the background of this thesis and fundamental theory of GPS are introduced, and the significance of direct P-code acquisition in GPS receiver is displayed. Secondly, this thesis introduces several conventional code acquisition methods and the reason why they are not fit for direct P-code acquisition. In order to realize direct P-code acquisition, this thesis also introduces the way to generate the P-code which can set the P-code at any specific time during a week, and simulates the cross correlation and partial autocorrelation of P-code for different GPS satellites. In the precondition of good cross correlation and partial autocorrelation of P-code, fast P-code acquisition scheme based on FFT is proposed and realized in FPGA and DSP.Compared to conventional slipping correlation method, the time of fast P-code acquisition scheme based on FFT is reduced more than ten times and the calculation is reduced rapidly. It's useful for other direct long PRN codesacquisition.