Direct Acquisition Of Long Code In Satellite Navigation System

The global positioning system(GPS) is a space-based satellite navigation system that provides location and time information in all weather conditions. At present, the GPS satellite signal uses two kinds of pseudo-random spreading sequence, namely, C/A code for coarse positioning and P code for precise positioning. Compared to C/A code, the use of P code can provide has not only higher positioning accuracy, but also the stronger ability of anti-jamming and anti-spoof. The traditional acquisition of P code needs the assistance of the acquisition of C/A code. When C/A code is attacked, however, direct acquisition of P code becomes the only way to complete the navigation and positioning services. Because P code has a very rate and a long cycle, it is difficult to acquire P code directly. Therefore, the direct acquisition of P code has become a technical difficulty in the field of GPS navigation and positioning. In addition, the research of direct acquisition of P code to enhance our own satellite navigation and positioning system has its own significant value. This thesis focuses on the study of FFT-based algorithms for direct acquisition of P code.Firstly, the basics of GPS are introduced, mainly including GPS signal and acquisition principles. Based on the traditional FFT-based acquisition, several algorithms to realize the acquisition of aperiodic code are studied to solve the acquisition of P code in parallel. Detailed analysis and simulation of ZP(Zero-Padding)、XFAST(Extended Replica Folding Acquisition Search Technique) and DA(Direct Average) algorithm are performed. Then, a modified version of ZP algorithm, which has lower mean acquisition time, is put forward. Finally, consider that the conventional acquisition algorithm of P code realize search of code phase in parallel and Doppler frequency in serial, the technology of folding in frequency bin is applied to complement the acquisition of Doppler frequency in parallel and the feasibility of folding in frequency bin is verified, which realizes the search of code phase and Doppler frequency in parallel and accelerates the acquisition process of P code.