A fault-tolerant, integrated navigation system architecture for UAVs

The core sub-system in the integrated navigation system presented in this paper was the GPS-aided Inertial Navigation System (INS) which provided estimates for aircraft position, velocity and attitude. In parallel, a cascaded system consisting of an Attitude Heading Reference System (AHR.S) and airspeed-based dead reckoner (DR.) provided redundant estimates of the position, velocity and attitude. Limitations in the AHRS-DR system typically lead to the GPS-aided INS providing better performance when GPS measurements are available. Conversely, the AHRS-DR system typically outperforms the GPS-aided INS during unaided operations. In view of this, it may be beneficial to design a fault tolerant filter that can "softly" switch between the parallel systems to create an optimally blended solution of both. The integrated navigation system developed in this work was implemented on a small UAV flight control system, and three flight environments were tested to characterize the performance. Flight data analysis illustrated that this system is capable providing accurate state estimation even in environments that would compromise a traditional UAV navigation system.