A software implemented receiver for satellite based
augmentation systems: an enhancement to global navigation
satellite systems

Abstract: The global navigation satellite system GPS (Global Positioning System)
offers a position accuracy of about 10-15 meters today. However, this is
not enough for some applications such as navigating ships through narrow
channels. Furthermore, GPS does not provide any integrity of the system (a
maximum error bound of the position). Integrity is critical for safety-of-
life applications, such as in the aviation industry.

EGNOS (European Geostationary Navigation Overlay System) is a satellite
based augmentation system in development, that together with GPS provides
integrity and improved accuracy of the user position. EGNOS works by closely
monitor the GPS satellites at monitoring stations scattered around Europe.
Corrections and integrity bounds of the GPS signals are computed and encoded
into messages. These messages are transferred to the users via geostationary
satellites on the same frequency as GPS.

This thesis describes a receiver implementation for decoding the EGNOS
signal-in-space into messages and applying those messages to GPS
measurements. Those steps are done in real-time. The EGNOS receiver is built
as an extension to an existing GPS receiver.

The EGNOS receiver decodes the signal-in-space into messages using a Viterbi
decoder. These messages are then processed to compute local corrections and
integrity information which are applied to the position solution. The
position accuracy is found to be improved by the use of EGNOS.