Development of a Robust Carrier Synchronizer for High Dynamic and Low Signal to Noise Ratio Signals in GPS Receivers

In this paper, a robust carrier recovery loop for high dynamic and weak signals in GPS receivers is proposed. To achieve optimal tracking performance at synchronization loops, different methods are investigated. Since phase jitter sources are identified at the receiver, suitable controller coefficients are calculated and used in carrier and timing recovery loops. This improvement induces higher speed and lower variance of jitter in acquisition and tracking modes, respectively. Furthermore, this simple design can obviate the need of large digital filters or complex circuits such as wavelet de-noising filters in the loop. To extend the linear range of the phase estimator, phase unwrapper unit is used which can improve loop tracking ability and resolve Kalman filter difficulties. To compensate the cycle-slip phenomenon, a novel recursive algorithm is introduced which causes better performance for low CNR signals and high dynamic environments. Simulation results show the effectiveness of the proposed architecture for different Doppler rates and CNRs. Moreover, the results indicate good matching between fixed-point FPGA implementation and floating-point simulation.