Finding the True Repeat Times of the GPS Constellation by using Broadcast Ephemeris

GPS positioning attained an accuracy level that the residual sources of errors are known as station effects or multipath errors. In fact there are no stations notbeing affected by multipath errors. The socalled errors are fundamental elements in precise positioning and subtle use of high rate GPS. Since the multipath errors are dependent on the GPS satellite geometry and the constellation of that system’s satellites is repeatable, the so-called errors are repeatable too. Techniques for calibration and correction of these errors are based on repeatability of the system constellation. It is assumed that the repeatability occurs based on the sidereal repeat period of satellites; however, the true repeat period of this repeatability varies even for each satellite. The real daily advance of constellation of the GPS satellites can be determined by the broadcast ephemeris. In this paper, the true repeat period and its average are computed, and the average of the periods of ground track of the recent decade is estimated as 23 hours, 55 minutes and 55 second.