This activity aims to develop a tool to support investigating the failure modes of GNSS systems and to characterise the tolerance of GNSS systems to failures.

The activity aims at developing a tool that can investigate the failure modes of GNSS systems. Such tool can then be used for detection of failures, and/or to characterise the tolerance of GNSS system or subsystem architectures to failures. Focus will be given primarily to failures and failure modes that may impact critical services (e.g. Safety-of-Life). The tool shall be able to model GNSS systems and subsystems (i.e. ground or space segments, elements and/or components) and its failure modes in a modular way. This modularity would then allow the user either to investigate the failure modes at subsystem level, or to create different GNSS architectures whose tolerance to various failure modes can be quantified. The failure modes shall be modelled into a 'database' and can be used as the building blocks for the more complex modules. In this way, the failure modes can be kept up to date more easily and can be updated independently of each other, while interactions between failure modes can still be modelled. An aspect to be characterised is the impact of failure modes in the achievable performance, by taking into account the constellation geometry to calculate Position, Velocity and Time.