Abstract:

The traditional carrier loop should be improved to track weak signals in shadow or in the buildings. An improved algorithm of frequency lock loop (FLL) based on Kalman filtering is proposed for tracking weak signals. In this algorithm, Kalman filter is inserted between the discriminator and the loop filter and there is a crucial feedback circuit from the loop filter to Kalman filtering in the improved FLL. The simulation experiments are carried out in traditional FLL and in improved FLL with the same paremeters. Simulation results show that the improved FLL can not only successfully track signals when SNR is as low as -30 dB, but also increase the tracking accuracy.