A hybrid carrier tracking algorithm based on FQFD and EKF

Carrier tracking is one of the key technologies of software GPS receiver, whose performance mainly depends on the carrier tracking algorithm According to a typical structure of carrier tracking loop, this paper introduces the principles of the commonly used devices in carrier tracking, such as four-quadrant frequency discriminator (FQFD) algorithm and the principle of expanded Kalman Filter (EKF) algorithm, then analyses the tracking performances of these two algorithms with the input signals by setting the frequency as a constant value, or a step equation, or a simple equation or a quadratic equation of time. Based on these two algorithms, a new hybrid carrier tracking algorithm is designed. The performance of newly hybrid tracking algorithm is simulated and the result demonstrates that it is able to track carriers with different sorts of frequency changing laws, with small tracking errors.