The EGNOS System Test Bed (ESTB) has demonstrated a 95% positioning accuracy of 1-2 meters in the horizontal components and 2-4 meters in the vertical component. However, in order to access the EGNOS service, the end user needs to have a direct line-of-sight to at least one of the EGNOS geostationary satellites that broadcast the augmentation messages.

The line-of-sight requirement is critical for users in environments such as urban canyons, valleys and fjords, since high buildings or geographical features in the vicinity of the end user can easily block the line-of-sight to the geostationary satellites. The situation becomes worse at high latitudes because of the low elevation angles of the geostationary satellites - even a small obstacle can block the signal. The satellite visibility problem can be addressed by transmission of additional augmentation signals from ground-based "pseudo-satellites" (pseudolites). The main objectives of the project are to develop a pseudolite solution to disseminate the EGNOS SIS in locations where the EGNOS GEO satellites are not visible, and to prove the concept via a demonstration in a real environment. Thus the concept will enlarge the scope of applications for the EGNOS technology. The proposed EGNOS pseudolite system will consist of:

• a number of pseudolites that transmit an EGNOS/GPS like signal
• a master control station that monitors and controls the system performance
• a user terminal to exploit the system

The pseudolite system will be connected to the EGNOS Data Access Server, which provides the system with an interface to the EGNOS service.

Key issues

The key issues to be addressed by the project are:

• provision of a basic service consisting of the broadcasting of EGNOS augmentation messages in areas where the visibility of the EGNOS geostationary satellites is limited
• improvement of the availability of ranging sources by adding a number of synchronized pseudolites
• design of a system that allows for integration of several transmitting units, and allows for the possibility of several EGNOS pseudolite systems operating in the same area with a certain degree of signal overlapping
• accomplish these goals with minimal modifications to existing SBAS capable receivers