Abstract: Methods and apparatus for receiving an estimate of L1 iono delay and L1 iono delay rate, receiving GEO slant ionospheric delay, receiving user iono vertical error information for a GEO satellite, and computing a L1/L5 bias estimate from the estimate of L1 iono delay and L1 iono delay rate and GEO slant ionosperic delay. A wide area augmentation system (WAAS) includes L1/L5 bias estimation. The L1/L5 bias is the differential bias between the WAAS GEO satellite L1 and L5 signals. The data used in the L1/L5 bias estimation include the GEO L1 ionospheric delay estimated from a Kalman filter, and the GEO slant ionospheric delay calculated from the Ionospheric Grid Point (IGP) information in a WAAS message. The Sigma User Ionospheric Vertical Error (UIVE) is used as one of the conditions for performing the L1/L5 bias estimation.

Abstract: A system to provide navigation signals to a space vehicle includes an uplink system for a geostationary earth satellite having clock steering derived from smoothed receiver clock error, long term clock error average, and long term clock offset average information. A proportional-integral-differential controller can be used to generate clock adjustment commands to a frequency standard clock.