An Investigation of GPS Satellite Clock Offsets Prediction with Different Update Intervals and Application to Real-Time PPP

Abstract

The high precision real-time satellite clock offset and orbit products are very important for real-time PPP users. Although, the International GNSS Service provides both IGU products and real-time corrections with two different schemes, both products have obvious limitations. For the IGU scheme, the clock offset is updated with a fixed interval of 6 hours and its accuracy can only achieve the level of 3ns (RMS) and 1.5ns (STD), which cannot meet the requirements of some high precision applications. For the real-time corrections scheme, a very high update rate, typically 1-10 seconds for satellite clock, is required for users to receive precise corrections, which therefore requires continuous wireless connections between the correction suppliers and the users. For satellite clock products, most work to date focus on the old types of satellite clocks and the prediction model for up-to-date GPS IIF satellite clock offsets has not been much explored. In this paper, the GPS satellite clock offset prediction will be investigated and applied to a real-time PPP system. Firstly, the current situation of GPS satellite clocks is introduced and analyzed with respect to their stability. Then the satellite clock prediction with different update intervals will be presented, in which the satellite clock day boundary jump will be addressed. Afterwards, the investigation of the satellite clock prediction model for GPS satellite IIF clocks will be carried out in which the effect of periodic terms will be discussed. After that, the verification of the satellite clock offset prediction will be carried out. Finally, the performance of the predicted satellite clock offset in a real-time PPP system is presented.