Accuracy and Consistency of Broadcast GPS Ephemeris Data

摘要

A detailed statistical analysis of the performance of thernGPS broadcast ephemerides is presented, spanning 1992rnto date. Broadcast ephemerides are extracted from arnsubset of International GPS Service (IGS) groundrnstations, and their quality is assessed by comparing themrnto the precise GPS orbit solutions produced by the JPLrnIGS Analysis Center (also known as FLINN orbits). Thernlatter are arguably at least an order of magnitude morernaccurate than the broadcast ephemerides and, hence, canrnserve as a truth model.rnTypical 3-D, 24-hour agreement between recent broadcastrnand FLINN orbits is at the several-meter level. However,rnwe have discovered some inconsistencies amongst thernbroadcast messages reported by different groundrnreceivers, which result in orbit differences as large as 300rnmeters. We examine these inconsistencies and search forrntheir cause. It is hoped that this study will give somerninsight into the level of confidence a user can place in thernbroadcast GPS navigation data, which can be important inrnreal-time, near-real-time, and post-processingrnapplications.