Navigation Safety of GNSS/IMU Integrated System for Autonomous Vehicles

In a development from Prof. Lee’s team, a novel methodology has been developed to enhance the safety and reliability of autonomous vehicle (AV) navigation systems by addressing the critical vulnerability of Inertial Measurement Unit (IMU) sensor failures. The integration of the Global Navigation Satellite System (GNSS) and IMU in navigation is required to provide a promising navigation system for AVs. Unlike most navigation safety research that focuses on protecting against GNSS faults, this research highlights the overlooked aspect of IMU sensor failures, which can cause a cascading impact on navigation accuracy and safety. This study was published in the December 2023 issue of NAVIGATION: Journal of the Institute of Navigation, titled “Navigation Safety Assurance of a KF-Based GNSS/IMU System: Protection Levels Against IMU Failure.”

The uniqueness of this technology lies in its comprehensive approach to safeguard navigation systems by incorporating safe bound (i.e., protection levels) specifically designed to counter IMU faults. The team investigated the impact of sequential IMU sensor faults on user state estimates within the navigation filter. This investigation revealed notable differences in fault propagation characteristics during the state prediction (i.e., IMU) versus the measurement update (i.e., GNSS) steps. Building on these insights, they conducted a fault-tree analysis and designed a fault monitor specifically to address IMU failures. The integrity and continuity risks posed by this system are defined based on fault-trees that incorporate the new fault hypothesis and help set the detection requirements for fault monitors. Moreover, they derived two types of protection levels (PL) — a real-time PL and a predictive PL — to protect users against undetected faults. The researchers employed a sophisticated simulation involving an unmanned aerial vehicle (UAV) to demonstrate the effectiveness of their integrity and continuity algorithm. The simulation results validated the practical applicability of the proposed solution in enhancing navigational integrity and continuity.

This research is particularly significant to Positioning, Navigation, and Timing (PNT) as it offers a proactive and predictive mechanism to ensure navigation safety in the face of IMU sensor faults. This outcome is valuable, as the enhanced navigation safety is crucial for the widespread adoption of autonomous vehicles, promising a future of more reliable and safe autonomous transportation options. Although the methodology has not yet been used in the navigation market, its introduction has marked a pivotal step forward in addressing safety assurance challenges within multi-sensor navigation systems. The potential applications of this methodology are vast, ranging from guiding navigation safety assessments in emerging mobility technologies to establishing the foundations for universally accepted safety standards for autonomous navigation systems.

Looking to the future, Prof. Lee’s team envisions their methodology playing a crucial role in both commercial and military applications. By offering a universally applicable framework to quantify navigation safety against sensor faults, this technology paves the way for a new era in autonomous navigation, ensuring the safety and reliability of navigation systems across various domains. This innovation is poised to become a cornerstone in the development of future mobility systems, driving the continuous advancement of global navigation standards and practices.