Assessment of GPS carrier-phase stability for time-transfer applications

We have conducted global positioning system (GPS) carrier-phase time-transf er experiments between the master clock (MC) at the U.S. Naval Observatory (USNO) in Washington, DC and the alternate master clock (AMC) at Schriever Air Force Base near Colorado Springs, Colorado. These clocks are also monit ored on an hourly basis with two-way satellite time-transfer (TWSTT) measur ements. We compared the performance of the GPS carrier-phase and TWSTT syst ems over a 236-d period. Because of power problems and data outages during the carrier-phase experiment, the longest continuous time span is 96 d. The data from this period show agreement with TWSTT within +/-1 ns, apart from an overall constant time offset (caused by unknown delays in the GPS hardw are at both ends). For averaging times of a day, the carrier-phase and TWST T systems have a frequency uncertainty of 2.5 and 5.5 parts in 10(15), resp ectively.