Precision and accuracy of GPS time transfer

The precision of time transfer over intercontinental distances by the Global Positioning System (GPS) common-view method reaches 3-4 ns for a single 13-min measurement, and decreases to 2 ns when averaging several measurements over a period of one day. Such precision can only be achieved by using measured ionospheric delays, precise ephemerides, and a consistent set of station coordinates. The accuracy of GPS time transfer is estimated by using three intercontinental links encircling the Earth to establish a closure condition. It is found that the accuracy is also at the level of a few nanoseconds, and mainly depends on the set of ephemerides which is used for the satellites