GPS Receiver Tracking Loop Design based on a Kalman Filtering Approach

In this paper, we applied an eight-state Kalman filter on a software defined GPS receiver by replacing conventional tracking with the feedback solution from the navigation filter to control the local code and carrier generators. The code phase and carrier frequency outputs from the delay lock loop (DLL) and frequency lock loop (FLL) discriminators are employed as measurements to update the filter. A hardware-in-the-loop test is made using a GPS L1 signal simulator. Numerical results show that the integration of Kalman filter with tracking loops can improve the tracking robustness and bridges the short GPS outage periods (i.e., less than 4 satellites in view).