Enhancing navigation integrity for Urban Air Mobility with redundant inertial sensors

Abstract

Urban Air Mobility (UAM) uses highly automated air vehicles to offer safe and efficient low-altitude urban air transportation services, for which ensuring navigation safety (measured by integrity) is an essential precondition. UAM vehicles can navigate themselves using Global Navigation Satellite Systems (GNSS)/Inertial Measurement Unit (IMU) tightly coupled systems. However, these systems are vulnerable to IMU failures aside from GNSS faults, given that UAM vehicles will use low-cost IMUs. IMU faults can severely degrade navigation integrity, thereby threatening UAM operational safety and increasing the difficulty of urban air traffic management. This issue can be mitigated by employing redundant IMUs. Civil aircraft use consistency checks among multiple high-performance Inertial Navigation Systems (INSs) to enhance navigation integrity. But this approach is not suitable for low-cost IMUs because of fast error accumulation. In response, this work proposes a new approach to enhance navigation integrity for UAM by integrating multiple IMUs with GNSS. In this approach, multiple IMUs and GNSS are tightly coupled by a centralized Kalman filter, and the corresponding integrity monitoring algorithm is developed to (a) detect the faults in GNSS and/or IMUs and (b) evaluate the probabilistic upper bounds on navigation errors, namely protection levels. Simulations are conducted to demonstrate the proposed method and to present sensitivity analyses, and the results suggest the effectiveness of the new approach. This method is beneficial to improving UAM operational safety and can potentially be applied to civil aircraft in the future.