Integrity Assurance of LIRTK Using SS-RAIM Against Sensor Faults for UAV Applications

Abstract

This study proposes an integrity assurance architecture of Loosely-Coupled Kalman Filter-based Inertial Aiding for RTK (LIRTK) using Solution Separation based Receiver Autonomous Integrity Monitor (SS-RAIM). An integrity risk allocation tree of LIRTK is developed for each sensor fault hypothesis including the nominal hypothesis, single-satellite fault hypotheses, an IMU sensor fault hypothesis, and an incorrect fix fault hypothesis. Two P(CF) requirements for integrity risk and false alarm rate were defined in order to calculate the Vertical Protection Level (VPL) of the fixed solution. In order to improve the fixed rate by lowering the P(CF) requirement for false alarm rate, an ambiguity check process is newly proposed. In the ambiguity check process, the fixed ambiguities estimated under nominal and fault hypothesis are compared. After passing the ambiguity check process, this study found a new lower bound that relaxes the P(CF) requirement for false alarm rate and validated its mathematical proof. VPL simulations were performed for different Global Navigation Satellite System (GNSS) measurement noise levels and Inertial Measurement Unit (IMU) sensor grades. The simulation results demonstrated that the ambiguity check process significantly improved the fixed rate of LIRTK and exhibited a much higher value compared to single-epoch RTK.