Comparisons of Two Kinds of GPS Broadcast Ephemeris Parameter Algorithms

The precision, efficiency and reliability of GPS broadcast ephemeris parameter algorithms are remarkably important in the real-time kinematic GPS navigation and positioning. Two kinds of GPS broadcast ephemeris parameters and their user algorithms are introduced in the last GPS interface specification. In this paper, the two algorithms are compared to provide some reference for the broadcast ephemeris parameter research or design. Firstly the new GPS broadcast ephemeris parameters and their user algorithms are briefly introduced, and the differences between the new and old algorithms are analyzed and it is found that the distinctness of the two user algorithms is consistent with those of the broadcast ephemeris parameters. Then the partial derivatives of the satellite position vector to the new GPS broadcast ephemeris parameters are presented based on the calculated expression of the satellite position, which is compared with those of the old GPS broadcast ephemeris parameters. Finally a set of simulation data is used to test and compare the new and old GPS broadcast ephemeris parameter algorithms. Calculation results show that the orbit characters of the MEO satellite can be accurately described by the two kinds of GPS broadcast ephemeris parameters, and the precision losses of the two fitting algorithms are almost several centimeters.