Results in GPS system time restitution with Kalman filters

The paper describes the restitution of the GPS system time by using a Kalman filter which calculates the GPS system time as well as the clock rate of the used local clock. For improving the quality of the filter results, the algorithm uses the data from all visible satellites, not just from a fixed lower limit of satellites (for example 4). For that the Kalman filter algorithm had to be modified in a manner to handle observation vectors of time variant order. The paper outlines the principle of operation of this Kalman filter and the system and observation model used. The capability of the filter is shown by tests, where the results are verified with a clock near to GPS-time as well as by comparing the results with a Kalman filter algorithm similar to that in (1992). Thus, a Common-View has been performed between our master clock, a passive H-maser (CH1-76), called H1(DLR), and the USNO H-maser, MC2(USNO), to which GPS-time is closely steered. We take into account that the long baseline Common-View (about 6800 km) decreases the accuracy of our experimental approach, but it is the only way to link our results to a clock which is very close to GPS-time