Accuracy and Consistency of Broadcast GPS Ephemeris Data

摘要

A detailed statistical analysis of the performance of the GPS broadcast ephemerides is presented, spanning 1992 to date. Broadcast ephemerides are extracted from a subset of International GPS Service (IGS) ground stations, and their quality is assessed by comparing them to the precise GPS orbit solutions produced by the JPL IGS Analysis Center (also known as FLINN orbits). The latter are arguably at least an order of magnitude more accurate than the broadcast ephemerides and, hence, can serve as a truth model. Typical 3-D, 24-hour agreement between recent broadcast and FLINN orbits is at the several-meter level. However, we have discovered some inconsistencies amongst the broadcast messages reported by different ground receivers, which result in orbit differences as large as 300 meters. We examine these inconsistencies and search for their cause. It is hoped that this study will give some insight into the level of confidence a user can place in the broadcast GPS navigation data, which can be important in real-time, near-real-time, and post-processing applications.