Performance of EGNOS in North-East European Latitudes

Abstract

The performance of Europe’s SBAS (Satellite Based Augmentation System), the European Geostationary Navigation Overlay Service (EGNOS), is being monitored at the RIMS (Ranging and Integrity Monitoring Stations) stations coupled to the system and the results are publicly available at European Satellite Services Provider’s (ESSP’s) web pages [1]. However, the EGNOS performance analysis at RIMS stations is very optimistic, mainly for two reasons: i) the same stations’ GNSS pseudorange data are being utilized to compute the EGNOS corrections, and ii) the stations are stationary and are located in sites with very good sky visibility. For these reasons, the EGNOS accuracy reported by ESSP may not always reflect the real picture of the expected accuracy within its area of coverage. In recent years, researchers in Norway have been monitoring EGNOS performance [2] with the PEGASUS performance analysis software developed by Eurocontrol [3]. It was reported in [2] that the EGNOS performance can be affected adversely by ionospheric disturbances at high latitudes. In addition, the lower availability of GPS satellites coupled with the lower number of RIMS stations at north-eastern latitudes may contribute to poorer than expected positioning performance in the north-eastern coverage area of EGNOS. A project entitled ‘Finland’s EGNOS Monitoring and Performance Evaluation (FEGNOS)’ has recently been carried out at Finnish Geospatial Research Institute in order to monitor the actual performance of EGNOS in Finland [4]. In this paper, results of the FEGNOS project will be presented by utilizing the raw GNSS data obtained from the Finnish national GNSS network of 20 permanent reference stations. The EGNOS performance will be analyzed in all these stations between the receiver’s own decoded SBAS messages and the online EDAS (EGNOS Data Access Service) provided SBAS messages for a year-long time frame. In addition, EGNOS performance will also be compared with respect to GPS stand-alone solution. The results show that the use of EGNOS significantly improves the positioning performance as compared to GPS stand-alone. But, then between the two ways how EGNOS messages are decoded by the receiver, it is observed that the receiver’s own decoded EGNOS performance is not as good as the performance obtained through EDAS server and is currently not reliable enough for the most safety critical users due to continuity challenges.