Towards Sub-10 -16 Transcontinental GPS Carrier-Phase Frequency Transfer: a Simulation Study

A simulation study is performed using GIPSY software in order to determine the impact of site-based and satellite-based systematic errors on the accuracy of between-site GPS carrier-phase frequency comparisons. The data are analyzed using both the precise point positioning (ppp) and network methods: in the former, the time differences between the satellite clocks and system time are fixed to predetermined values. In the latter, the time differences of both the satellite clocks and the receiver clocks are estimated relative to some reference clock (usually a ground-based receiver clock). We also analyze data both with and without the added constraint of double-difference ambiguity fixing. We find that between-site frequency comparisons are largely unaffected by site-based and satellite-based systematic errors when 100% of the double-difference ambiguities are fixed. We also find that in the ppp method, although fixing ambiguities removes between-site frequency errors, it can cause errors in the values of the individual receiver clocks relative to system time. Finally, we find that when a network solution is performed and ambiguities are not fixed, an error made at site A may adversely affect frequency comparisons between sites B and C