Carl Milner representative of ENAC in the CLUG 2.0 project presented the activity related to “An Integrity Concept for GNSS/INS/Odometry Rail Localisation” in the session D3: GNSS Augmentation and Robustness for Autonomous Navigation (GNSS Integrity Augmentation) of  ION GNSS+ 2024 on September 19^th (Baltimore).

ION GNSS+ is the world's largest technical meeting and showcase of GNSS technology, products, and services. This year's conference brough together around 1000 participants within international leaders in GNSS and related positioning, navigation, and timing fields to present new research, introduce new technologies, discuss current policy, demonstrate products, and exchange ideas. The ION GNSS + 2024 technical program had more than 400 technical presentations in six areas on trade, policy, and research.

An Integrity Concept for GNSS/INS/Odometry Rail Localisation

One aspect of the CLUG2 project, as was the case for CLUG1 is the notion of positioning integrity, the capacity to prove within probabilistic limits the safety of the computed position and speed of the train. This is fundamental for any safety-of-life positioning application that is operating in real time. Requirements are placed on the tolerable hazard rate which may be interpreted with respect to the various engineering quantities (position along the track, speed on the track, track selection).

In spite of CLUG1/CLUG2 employing multiple localization sensors (GNSS, Intertial, Odometry, Digital Map) and an Extended Kalman Filter (EKF), proving the safety of the solution is challenging and the referenced paper [ION 2024] attempts to address this question.

 The first task in addressing the safety risk is to partition the system into possible states and allocate risk to each of these states. Since CLUG2 assumes two independent chains (one employing GNSS, another based on map shape matching) a top-level hazard rate of 10-6/hr is the starting point. The most challenging of feared events (faults) are localized GNSS failures, that is errors resulting from Non-Line-Of-Sight tracking of signals due to masking or Multipath due to reflections and scattering from the surrounding environment. The occurrence of such events on all satellites is therefore the worst case possible impact and the most challenging to protect against.

In order to protect against failures, monitors are defined which utilize the presence of multiple sensors and measurements to check for the presence of outliers. Two such monitoring strategies were presented in the paper, (1) based on the Kalman Filter Innovations and (2) based on a measurement combination called the Code-Minus-Carrier (CMC). With monitors in place, the paper addresses sensitivity of the faults