Analyses of GPS Satellite Clocks at Sub-second Time Intervals

Global Positioning System (GPS) carrier phase data collected from the radio telescope in Green Bank, West Virginia in 2005 and 2006 were analyzed to determine the sub-second onboard oscillator behavior of a subset of the GPS satellites. Stability characterization of the GPS satellites' clocks was conducted through Allan analysis. The gain of the large antenna allowed for collection of signals with sufficient signal-to-noise ratio (SNR) for evaluation of the carrier phase variance at sub-second averaging intervals. A lower stability limit was found for an isolated satellite clock that no longer depended on the signal's incoming SNR. The GPS satellite clock noise contribution to the overall phase noise stability is shown to be lower than published GPS specifications for this subset of navigation satellites. Although the satellite data from this study is somewhat dated, the technique used to obtain sub-second noise characterization can be extended to the current generations of Global Navigation Satellite System (GNSS) satellites.