The need for EGNOS

The current capabilities of GPS constellation, although adequate for some user communities, present some shortfalls. The lack of civil international control is considered an important issue by European institutions. In addition, some user communities have a need for enhanced performance. In particular, the Civil-Aviation requirements for the precision approach phases of flight cannot be met by GPS only. Other modes of transport can also benefit from "augmentation" techniques, resulting in improved GPS performance. For example, in the maritime domain, port approaches cannot be performed solely with GPS receivers due to the insufficient performances of these systems in high traffic density environments.

EGNOS (European Geostationary Navigation Overlay Service) has been designed to broadcast a GPS-like ranging signal in Europe with embedded corrections, providing improved performances over GPS. With EGNOS, all navigation receivers will benefit from enhanced accuracy, availability and continuity over GPS. An accuracy of around 1 metre is foreseen. EGNOS will also provide integrity information about the GPS signals, giving an alarm within 6 seconds in case of faulty positioning information.