Satellite Anomaly Detection with PPP Corrections: A Case Study with Galileo’s High Accuracy Service

Abstract

Autonomous transportation requires high accuracy positioning and, when the receiver is in safety critical operations, the solution needs to be robust to external threats and reliable from an integrity point of view (i.e. robust to internal threats). Precise Point Positioning (PPP) services may not only satisfy demanding high accuracy needs but be beneficial also for safety critical applications: using fast corrections to increase the accuracy may also help to detect or mitigate the effects of satellite faults. Even if the PPP message does not include integrity information, a receiver developing an autonomous integrity service based on PPP corrections and techniques can enhance the receiver performance. The Galileo High Accuracy Service (HAS) is transmitting satellite orbit, clock and bias corrections to support PPP freely worldwide. In order to illustrate the possible advantages of PPP services for integrity applications, this paper analyses the HAS behavior during a real satellite event. The analysis uses live HAS signals, under intermittent transmission since May 2021, and shows the behavior of the HAS corrections when a growing ranging error was affecting a Galileo satellite before it was notified to the user through the signal health status flag in the broadcast I/NAV Open Service (OS) navigation message. Thanks to the short latency and the high update rate of the HAS corrections, a HAS user could partly mitigate the event, reducing its effect over time and quickly excluding the affected satellite from the position calculation.