The paper explores the usage of LEO-PNT (Positioning, Navigation, and Timing) for providing navigation integrity to GNSS (Global Navigation Satellite System) constellations. LEO mega constellations, positioned between GNSS and users, offer closer-to-the user geometry, improving performance, reducing Time To Alarm (TTA) and enabling integrity monitoring without complex ground segments of any sort. The aim is to use future LEO mega constellations as the Integrity Monitor for a forthcoming European Global Navigation Satellite System (EGNSS), specifically focused on automotive users, emphasizing minimal onboard satellite capabilities without ground involvement. This plan builds on earlier studies, anticipating performance for the upcoming LEO-PNT In-Orbit-Demonstration (IOD constellation).
The strategy focuses on using GNSS receivers onboard LEO satellites to gather MEO-LEO observables (step 1), broadcasting dedicated integrity messages through the LEO-User navigation band (step 2). It simplifies previous strategy that required high-data-rate communication channels at the cost of reducing some flexibility. Leveraging onboard Precise Point Positioning (PPP) of LEO-PNT satellites, derived PPP sub-products form a dedicated integrity navigation message broadcasted to users in step 2.

Users integrate this data from visible LEOs, locally implementing an Integrity Monitor in step 3. This monitor checks individually each GNSS MEO satellite, aligning with Integrity Concept's Fault Tree Analysis (FTA) for failure modes like satellite clock events or pseudorange errors. The accuracy of the check needs to be in the order of 20 cm to meet the EGNSS performance.

Service Volume Simulations are presented that demonstrate the feasibility of the proposed solution based on existing on-board GNSS receivers’ features and the future full LEO constellations and promising results with the upcoming 4-satellite IOD LEO constellation.