Research And Realization On Synchronization Technology Of High Sensitivity GNSS Software Receiver

High sensitivity GPS technology acquires and tracks weak GPS signals through specific algorithm to achieve the navigation and positioning in indoor environment. One of the important applications of weak-signal GPS positioning technology is the personal positioning service in emergency circumstances. Along with the improvement in HSGPS, the service is believed to have a promising market acceptance. This paper first briefly describes the concept, consistence and development trend of the GNSS system. Then it focuses on the theoretical research and software realization for the weak signal acquisition and tracking of the GPS system which is the most mature and widely used currently.First we briefly describe the consistence and positioning principle of GPS system, analyze the signal processing procedure of the RF front-end, directly generate the IF digital sequence which is the output of the RF front-end ADC converter, and add WGN to construct signals with different SNR as simulation signal sources.Second we analyze the generation principle of the Doppler phenomenon, analyze the coherent cumulative algorithm (CC), non-coherent cumulative algorithm (NCC), differential coherent cumulative algorithm (DCC) which are used in GPS acquisition step and make a comparison among them.Third, we provide the definition of weak GPS signal, analyze the main factor of its origin and propose three improvements for weak signal processing. Among them, the whole bit acquisition algorithm solves the problem of searching bit edges and maximizes the processing gain of the combination of CC and NCC, which follows it. Aaveraging correlation algorithm deals with the computation burden of the 2-based FFT under 5MHZ sampling frequency, which is used to compute the C/A code correlation peak in frequency domain. We provide complete acquisition module, simulate and compare the performances of the improved algorithm and differential algorithm. The result shows the effectiveness of the improved whole bit acquisition algorithm for the acquisition of the weak signal.The acquisition step completes the in-accurate estimation of the C/A code phase and doppler frequecy and tracks the GPS signal on such bases. This paper is divided into three parts, which can be followed as the discussion of the principle and structure of DLL, FLL and PLL, procedure of signal processing and discriminator algorithm. We simulate the synchronical tracking of the C/A code and the carrier. After all, we realize the system by C under VC++ 6.0.