Comparison Of Availability Of Galileo, Gps And A Combined Galileo/Gps Navigation Systems

Galileo satellites have been planned to be launched in 2006 by the European Union. Launching these satellites will double the number of positioning satellites currently accessible to users. As a consequence, accuracy and reliability will be improved dramatically. Besides accuracy and reliability, availability is also used for quantification of a Global Navigation Satellite System performance. This paper briefly describes the constellation of space segment of the proposed Galileo navigation system in comparison with the well-known Global Positioning System (GPS). Availability of GPS, Galileo and Galileo/GPS satellites are then formulated in terms of Satellite Appearance Distribution Function (SADF). Achievable accuracy in horizonal and vertical positions and timing are expressed using the respective Dilution of Precisions based on the derived mathematical formulation.