QZSS broadcast ephemeris accuracy evaluation and fitting accuracy analysis

Broadcast ephemeris is needed to calculate the satellite position in real-time navigation and positioning. The continuous iteration is used to improve the calculation accuracy in the quasi-zenitic satellite system (QZSS) built by Japan during calculating the satellite position, which can result in the real-time calculation efficiency reduction. In order to ensure the calculation accuracy and improve the calculation efficiency of QZSS broadcast ephemeris coordinates, a chebyshev polynomial is proposed to fit the satellite orbit. Firstly, the traditional methods are used to calculate satellite position, the precision ephemeris is regarded as a reference to verify that the satellite coordinate accuracy of QZSS broadcast ephemeris is meter-level. And then, a chebyshev polynomial is used to fit satellite three-dimension coordinates, and the factors affecting the fitting accuracy are discussed. When the fitting time-interval is fixed, the optimal fitting order increases with the number of nodes; Under different time-intervals, the optimal fitting order is not equal in different orbit types, and the optimal fitting order of the same orbit is equal, but the fitting error gradually increases with the increase of time-interval. The result shows that QZSS broadcast ephemeris can be fitted by using a chebyshev polynomial and choosing appropriate fitting time-interval and fitting order for different orbit types. The fitting accuracy and computational efficiency can meet the needs.