Fault-Free Integrity Analysis of Mega-Constellation-Augmented GNSS

Abstract

The ultimate in Global Navigation Satellite System (GNSS) performance is obtained using carrier phase measurements. Receiver tracking error for the carrier is lower than that for the code by two to three orders of magnitude, but achieving high accuracy carrier positioning requires that the unknown constant cycle ambiguities be determined. A costless yet efficient solution to this problem is to exploit the bias observability provided by satellite motion. Unfortunately, the large amount of time required for GNSS spacecraft to achieve significant changes in line of sight hinders its use in most real-time applications. In contrast, angular variations from low-Earth orbiting (LEO) satellites quickly become substantial. Therefore, the combination of LEO mega-constellations and GNSS observations makes quick and unambiguous carrier phase positioning possible. In this thesis, we evaluate the potential of mega-constellation-augmented GNSS (GNSS-MC) to provide fault-free high-integrity positioning in both open-sky and urban areas. We derive a method to integrate dual-frequency carrier-phase ranging measurements from GNSS at medium Earth orbit (MEO), and mega-constellations at LEO to achieve global carrier-phase positioning. From the perspective of users on earth, LEO satellites are moving much faster than GNSS at MEO. The large angular variations generated by these fast-moving LEO satellites are exploited for rapid estimation of cycle ambiguities. The addition of mega-constellations to GNSS also improves the spatial diversity of ranging sources which enables improved navigation performance in areas where visible GNSS satellites are too few to obtain a position fix, such as in dense cities and urban canyons. This research helps identify sensitive ground, space, and user segment components that are key to leveraging future communication mega-constellations in safety-critical land navigation applications.