Design and Testing of an Intelligent GPS Tracking Loop for Noise Reduction and High Dynamics Applications

Autonomous Navigation Systems (ANS) used in ballistic or cruise missiles are mostly dependent on Global Positioning System (GPS) as a primary mean of navigation. GPS usage has limitations in terms of missile high dynamics and signal interference. The GPS receiver requirements to avoid these problems are conflicting. The Phase Lock Loops (PLLs), used to track GPS signals, are required to have a bandwidth as narrow as possible to reduce the impact of signal interference. On the contrary, the loop bandwidth has to be as wide as possible to accommodate high signal dynamics. The approach usually adopted in such cases is to use a Frequency Lock Loop (FLL) to reduce frequency acquisition/reacquisition times before switching back to PLL or FLL-assisted-PLL. This approach does not prevent frequent loss of lock, compromising the receiver performance. In this paper, a novel FLL-assisted-PLL is proposed for very high dynamic conditions with reduced measurement noise. The design is based on fuzzy control systems, and is used to directly generate the required Numerical Control Oscillator (NCO) tuning frequency using phase and frequency discriminators information. The designed system is compared against 3(rd) order PLLs, with narrow and wide bandwidths, in addition to a standard FLL-assisted-PLL. Simulation results show the enhanced performance of the proposed system where better tracking continuity and less noisy measurements are achieved.