Low C/N0 Carrier Tracking Loop Based on Optimal Estimation Algorithm in GPS Software Receivers

Suppressing jitter noises in a phase locked loop (PLL) is of great importance in order to keep precise and continuous track of global positioning system (GPS) signals characterized by low carrier-to-noise ratio(C/N-0). This article proposes and analyzes an improved Kahnan-filter-based PLL to process weak carrier signal, in GPS software receivers. After reviewing the optimal-bandwith-based traditional second-order PLL,a Kahnan-filter-based estimation algorithm is implemented for the new PLL by decorrelating the model error noises and the measurement noises. Finally,the efficiency of this new Kalman-filter-based PLL is verified by experimental data. Compared to the traditional second-order PLL, this new PIA. is in position to make correct estimation of the carrier phase differences and Doppler shifts with less overshoots and noise disturbances and keeps an effective check on the disturbances out of jitter noises in PLL The results show that during processing normal signals,this improved PLL reduces the standard deviation front 0.010 69 cycle to 0.007 63 cycle,and for weak signal prouessing, the phase jitter range and the Doppler shifts can be controlled within +/- 17 degrees and +/- 5 Hz as against +/- 25 degrees and +/- 15 Hz by the traditional PLL.