GPS timing performance

GPS signals provide the world with Coordinated Universal Time (UTC) as realized through UTC(USNO), which is UTC's realization by the U.S. Naval Observatory (USNO) [1]. Interoperability with Galileo, and perhaps someday with other Global Navigation Satellite Systems (GNSS), is to be established through transmission of the differences between the GNSS system times. This paper describes the performance of the GPS system, which is constantly being improved.