System to determine pulse per second timing

Abstract

Satellites communicate with user terminals (UTs) based on accurate timing. A UT clock provides a pulse per second (PPS) signal to coordinate operation of the UT, such as transmitting data on an uplink at specified times. The clock may be disciplined by an external source that provides accurate and precise true time, such as a global navigation satellite system. The external source may sometimes be unavailable. The UT uses information about its location, satellite location, the ephemeris of the satellite, and timing data transmitted by the satellite, to calculate an estimated delay due to propagation, scintillation, and so forth. The timing data and estimated delay are used to determine a time correction. The time correction is applied to the timing data and used to determine estimated true time, that is then used to generate an alternate PPS signal. The estimated true time is used until the external source is available.