Galileo evolution: Enhanced error correction strategies and integrity assessments

Abstract

Galileo corrections will be generated and broadcasted to the users in the navigation message using the same principle as GPS. For that reason the Galileo ground segment determines the ephemeris and satellite clock parameters for all satellites using observations from monitoring stations and estimates the extrapolation parameters to be uplinked to the satellites. By using measured GPS data, from IGS stations (International GPS Service) and post processing data, it is possible to compute the instantaneous pseudo range errors for a given period of time. Thanks to a fast Fourier transformation of these time series, an error spectrum is generated and among other characteristics, the periodicities of errors are extracted. From these GPS measurements, an error model is build taking into account these periodicities of errors and their magnitudes. Thanks to the foreseen UERE (User Equivalent Range Error) budget for Galileo, a corresponding error model for Galileo is generated. From these models, simulations using different correction rates are made and the impact of these simulations at error spectrum level will allow to draw conclusions on the relationship between error correction rates and periodicities of effects. This analysis acts as basis for identifying the best extrapolation strategy to be used in order to minimize the residual pseudo range error. The above defined work is made at pseudo range level and constitutes the first part of our study. A second part of the work deals with the impact of these corrections strategies at position level. The above defined techniques will have impact on both the accuracy and the integrity of the overall system. These performances are assessed, their applicability to Galileo is studied and recommendations for Galileo evolutions are given.