Robust Precise on Board Orbit Determination Exploiting T-RAIM for LEO-PNT

The rapid development of LEO-PNT constellations offers an opportunity to enhance GNSS services with additional signals from LEO satellites. These signals aim to improve performance and reliability for GNSS users. With various global initiatives, LEO-PNT systems utilize cost-effective, multi-tiered architectures that rely on GNSS spaceborne receivers for ODTS. These receivers use P2OD technology and PPP-like corrections to achieve real-time decimeter-level orbit reconstruction and unbiased nanosecond-level time synchronization. However, the interdependency between LEO and MEO layers can lead to cascading faults. This paper explores the extension of RAIM-like capabilities to spaceborne receivers, specifically T-RAIM, to mitigate these risks. The research validates the successful integration of T-RAIM with advanced HAS driven P2OD techniques in LEO scenarios, using a Hardware-in-the-Loop testing environment. The results show that an architecture with T-RAIM can preserve the nominal positioning and timing accuracy, even amidst MEO clock faults, ensuring ongoing system functionality without necessitating P2OD restarts—events that could interrupt the LEO-PNT services. The proposed loosely coupled integration seeks to handle the computational load and complexity while accommodating the limited resources of spaceborne receivers, aiming to offer a robust yet viable LEO-PNT solution.