The Role of Time and Frequency in Egnos (european Geostationary Navigation Overlay System)

The European Geostationary Navigation Overlay System (EGNOS) is being developed in Europe to provide GPS and GLONASS regional augmentation services to aviation, marifirne, and land users. EGNOS will provide the following services: i) GEO-based GPS-like Ranging signals to improve the availablity and continuity of GPS and GLONASS navigation services. ii) Ground Integrity Channel (GZC) to improve the integrity of GPSand GLONASS-based navigation and position determination for safefy-critical applications. And iii) Wide-Arm DiBerential corrections WAD) to improve the accuracy of GPS-SPS and GLONASS. Additionally, EGNOS will disseminate accurate time to users, synchronized to GPS, GLONASS, and UTC time scales. The paper provides an overview of EGNOS ground-segment architecture, gives requirements related to time aspects, and describes ,preliminary analysis and performances through test trials. It also covers initial results achieved in the frame of the EURlDlS program, conducted by CNES, after several months of measurements.