Analysis on GNSS space clocks performances

In Global Navigation Satellite Systems (GNSS) the role of atomic clocks is essential for the determination of the user position. Nowadays, several satellite navigation systems are operating and different clock technologies have been employed on board satellites, taking benefit of the improvements reached during the last tens of years. The analysis of GNSS clock performance is thus crucial for ensuring the GNSS positioning and timing capabilities. We performed an analysis on the clock estimates generated by the Information-Analytical Centre [1] (IAC) of the Russian Federal Space Agency, which provides a service similar to the one of the International GNSS Service (IGS). Therefore, we collected and processed the RINEX for clock files containing satellite clock estimates for GPS and GLONASS constellations, from 2008 to 2013: with our statistical tools [2] we performed an analysis of the performances of the different space clock technologies employed on board different GNSSs. In particular, we focused the attention on the frequency behaviour and the frequency stability, evaluating also the stationarity of these characteristics, with the aim of classifying and analysing the clock anomalies. In this paper, the attention is mostly focused on the change in clock noise variance.