Towards a Trustworthy Position Solution; OSNMA Authentication and the use of Multi-Constellations

Autonomously operating vehicles rely on precise and trustworthy position velocity time (PVT) solutions, which can be compromised by distortions in Global Navigation Satellite Systems (GNSS) signals. The Galileo Open Service Navigation Message Authentication (OSNMA) provides an additional protection layer by authenticating Galileo signals. However, this authentication does not extend to signals of other constellations and does not provide an integrity layer in the position domain. This paper proposes a consistency check as a safety measure to enhance the robustness of a loose OSNMA implementation against spoofing of non-authenticated navigation messages. In addition, this provides for improved performance in positioning and a system level integrity monitor. The Advanced Receiver Autonomous Integrity Monitor (ARAIM) based consistency check involves wide fault subset exclusion by comparing PVT solutions from subsets of measurements containing only OSNMA-authenticated signals, signals from unauthenticated constellations, and combined datasets. The results show that the proposed check can effectively exclude spoofed GPS signals from a dataset with authenticated Galileo signals. However, exclusion of GPS signals may still lead to a solution categorized as unavailable due to degraded observability of signals. The study demonstrates that a loose OSNMA implementation with a consistency check can provide a higher number of available solutions compared to a strict OSNMA implementation, this is particularly of relevance in urban environments. While preliminary, these findings suggest that the proposed method can enhance the trustworthiness of PVT solutions. Further research is needed to extend and implement this method to its full potential.