Comparison of Two-Way Satellite Time and Frequency Transfer and GPS Common-View time transfer during the INTELSTAT field trial

For a decade and a half GPS Common-View time transfer has greatly served the needs of primary timing laboratories for regular inter-comparisons of remote atomic clocks. However, GPS as a one-way technique has natural limits and may not meet all challenges of the comparison of the coming new generations of atomic clocks. Two-Way Satellite Time and Frequency Transfer (TWSTFT) is a promising technique which may successfully complement GPS. For two years, regular TWSTFTs have been performed between eight laboratories situated in both Europe and North America, using INTELSAT satellites. This has enabled an extensive direct comparison to be made between these two high performance time transfer methods. The performance of the TWSTFT and GPS Common-View methods are compared over a number of time transfer links. These links use a variety of time transfer hardware and atomic clocks and have baselines of substantially different lengths. The relative merits of the two time transfer systems are discussed.