Real-time global GNSS signal monitoring for prompt detection of anomalous events

Abstract

High integrity is a key requirement for safety-critical applications, such as autonomous car driving, maritime navigation, railway signaling and unmanned aerial vehicles (UAV). Over the last few years, particularly in view of the changing geopolitical situation, the requirement of high security has acquired a major relevance for such applications due to the increasing number of jamming events occurring worldwide. In this context, signal monitoring systems play a fundamental role. For integrity assessments, signal threat analysis is an important contribution of such systems to improve the knowledge of system faults, including their detection and frequency of occurrence. The addition of high-security requirements for safety-critical applications calls for the implementation of additional layers to monitoring systems to detect events, such as jamming or radio-frequency interference (RFI), that hinder the continuity of navigation services. Other than typical interference events that occur and have influence at the local level, in recent years, sources of interference having an impact over much larger geographical areas have also been detected. In particular, recent analyses have identified jamming sources that are originated in space. As the interference events caused by this type of sources may extend to a global scale, detection of such events should be considered as an extension of traditional signal threat analysis. This contribution presents a unified monitoring scheme for multi-frequency GNSS signal power and code biases for the detection of anomalous events at a global scale. It leverages observations from the publicly-available, continuously-operated and globally-distributed network of the International GNSS Service (IGS). The presented monitoring scheme is based on the computation and analysis of a set of monitoring metrics using C/N0 observations and pseudorange geometry-free combinations that are tailored to detect satellite- and station-specific events. Given its characteristics, the proposed scheme is flexible enough to be implemented in real time (e.g. with observation data rates of 1 Hz). The performance of the proposed metrics has been tested using recent known anomalous signal deformation event occurred to GPS IIF SVN73 and the space-based transient interference events, mostly affecting the Baltic region.