Integrity Monitoring of GNSS with LEO Satellites to Reduce the Time to Alarm

Leveraged by LEO (Low Earth Orbit) mega constellations deployed in recent times for communications, LEO PNT (Positioning, Navigation and Timing) has raised a high interest worldwide. Current integrity augmentations such as Space Based Augmentation Systems cannot provide time to alarms (TTAs) shorter than 6 seconds and rely on complex dedicated ground segments. The usage of the planned LEO mega constellations is investigated to implement an Integrity Monitor for a future Integrity Concept for the European Global Navigation Satellite System (EGNSS) high accuracy focused on automotive users with no intervention of a ground segment and with minimal capabilities on board of the satellite. The selected solution for the Integrity Monitor relies solely on a GNSS receiver on board of each LEO for collecting MEO-LEO observables and a communications link to the user for relaying this data, potentially in the same L-band. The user combines this information from the different LEOs in view and implements locally an Integrity Monitor. The Integrity Monitor checks individually each MEO against the Failure Modes allocated according to the Fault Tree Analysis (FTA) of the Integrity Concept. This study addresses generic failure modes such as satellite clock events or pseudorange errors. Service Volume Simulations are presented to demonstrate the feasibility of the proposed solution based on existing on-board GNSS receivers’ features and the future LEO mega constellations.