Clock model for GSTB VI clock prediction performance assessment experimentation

The Galileo system test bed (GSTB) VI aims to investigate and to make early experimentation on those elements of the Galileo system, which are considered critical. The GSTB VI is then a great added value to the final Galileo, in terms of design consolidation, key technology qualification and gained confidence and experience. In the frame of GSTB VI the experimentation activities will be organised and conducted in different test cases related to the different critical areas of Galileo ground processing. One of the project area to be investigated is related to modelling of atomic clocks in the frame of orbit determination and time synchronisation and verification of clock estimation performance. In fact in navigation systems, models are used to simulate the process, to estimate the clock parameters based on the measurements and to predict the clock behaviour for the user navigation/positioning function. In the frame of clock prediction accuracy assessment test case alenia spazio is in charge to develop a clock model algorithm able to represent the different atomic clock types in order to support the experimentation. Both the systematic and stochastic errors are considered and modelled in the clock simulator tool. This paper presents the mathematical model, its implementation in a dedicated environment and the first validation results both with respect to theoretical expected behaviour in terms of clock stability evaluation and by comparison with real clock data.