Broadcast vs. precise GPS ephemerides: a historical perspective

Abstract

The Navstar Global Positioning System (GPS) Operational Control Segment (OCS) generates predicted satellite ephemerides and clock corrections that are broadcast in the navigation message and used by receivers to estimate real-time satellite position and clock corrections for use in navigation solutions. Any errors in these ephemerides will directly impact the accuracy of GPS based positioning. This paper compares the satellite position computed using broadcast ephemeredes with the precise position provided by the International GPS Service for Geodynamics (IGS) Final Orbit solution. Similar comparisons have been undertaken in the past, but for only short periods of time. This paper presents an analysis of the GPS broadcast ephemeris position error on a daily basis over the entire operational lifetime of the GPS system. The comparison was undertaken from 14 November 1993 through to 31 December 2002. The statistics of these errors were also analyzed.