Using fuzzy logic control for the robust carrier tracking loop in a Global Positioning System/Inertial Navigation System tightly integrated system

The noise bandwidth is an important parameter on the Global Positioning System (GPS) tracking loop; the larger the bandwidth the better the high dynamic performance, but the thermal noise suppression capability is reduced. In a GPS/Inertial Navigation System (INS) tightly integration system, the GPS receiver's carrier phase lock loops (PLLs) are aided by the Doppler shift from the INS, which can reduce user most dynamics. So the noise bandwidth can be narrowed to decrease the thermal noise tracking errors. However, due to the inertial sensor errors, the external INS-derived Doppler shift information are not completely accurate, therefore a Doppler-aiding error-induced phase error source must exist. The part of tracking error is derived in this paper. Other error sources are still present, so the bandwidth of PLLs cannot be set arbitrarily. This paper applies one artificial intelligence technique, the fuzzy logic controller (FLC), to calculate the PLL noise bandwidth on-line. Simulation results prove that the proposed FLC-based software receiver does achieve a superior tracking ability over conventional tracking loops in complicated conditions. In addition, the proposed algorithm works in the real-time mode and can be used in many practical applications.