Instability of differential time between GPS receivers

Instability of the differential time between Global Positioning System (GPS) receivers considerably limits the present accuracy of the time transfer via GPS in common view. The differential-time process was assumed to have a character of white phase noise but recent experience with state-of-the-art GPS receivers indicates that the process is more complex. Of particular significance are temperature effects on the antenna unit, which may cause variations of several nanoseconds on a day-to-day basis. In addition, some drifts have been observed. These additional perturbations cannot be filtered out by averaging and therefore they must be taken into account in receiver calibrations.