GPS: Primary tool for time transfer

Global Positioning System (GPS) is not only a navigation system, it is also a time-transfer system. As a time-transfer system it provides stability ve ry close to one part in ten to the fourteenth over one day (1 ns/day). Afte r a brief introduction to timekeeping terms, this paper reviews the role of GPS in time distribution and clock synchronization over the last few years . GPS coarse acquisition (C/A)-code single-frequency single-channel (one sa tellite) common-view (CV) time transfer will then be discussed Special cons ideration will be given to recent progress in GPS C/A-code CV time and freq uency transfer through the use of "all-in-view" multichannel receivers. Thi s technique increases the number of daily observations by a factor of ten r elative to conventional single-channel receivers and results in an improvem ent in time and frequency transfer stability by a factor of about three. Ot her important improvements that will be discussed are the use of GPS carrie r phase measurements and temperature-stabilized antennas. The latter reduce the daily and seasonal delay variations of GPS time-receiving equipment. T he use of GLONASS as a complementary tool to GPS time transfer will also be reported. These improvements indicate that GPS, as a time-transfer system, should provide the capability to reach a stability of one part in ten to t he fifteenth over one day (100 ps/day) during the next few years and subseq uently reach one part in ten to the sixteenth over one day (10 ps/day).