Research on broadcast ephemeris direct fitting algorithm of BeiDou GEO satellite

The classic global positioning system (GPS) broadcast ephemeris fitting algorithm cannot be directly applied to BeiDou geostationary earth orbit (GEO) satellite because of its small inclination angle. Aim at this limitation, a broadcast ephemeris direct fitting algorithm of BeiDou GEO satellite was presented based on non-singular transformation. In this method, the classical orbit elements were replaced by a non-singular orbit elements, making all the broadcast ephemeris parameters definitely defined, and then the problem that coefficient matrix was non-positive was solved. Since this approach avoided the coordinate rotation process in the ephemeris algorithm of BeiDou GEO satellite for user, then the calculating steps were decreased and the GEO ephemeris algorithmic efficiency was enhanced. The simulation results show that this algorithm with high accuracy is well fit for broadcast ephemeris fitting algorithm of BeiDou GEO satellite, which can meet the requirement of the users fully. As for the BeiDou medial earth orbit (MEO) and inclined geosynchronous orbit (IGSO) satellite, the adaptability and utilization of this algorithm are poor, and it need further discussion and to be improved.