This paper presents the results of a research project that investigated the potential benefits
of a combined Galileo/GPS navigation system. The research addressed in detail the two key
required navigation performance (RNP) parameters of accuracy and integrity. The project
was supported by Alcatel Space and was a contribution to the Galileo definition studies
(supported by the European Community under the GALA project). The results show
significant improvements in both accuracy and integrity (achievable through RAIM) when
a combined constellation is used rather than Galileo alone.
