The University of New South Wales
Galileo: A New Global Navigation System
by James Gould
Supervised by Jingling Wang
Global Navigational Satellite Systems are primarily concerned with positioning on the earth’s surface. By being able to define a location on the surface of the earth, this position on the earth enables many applications and can have direct meaning to a specific subject. Positioning on the earth’s surface has many applications from war to personal navigation, whether being in a car or on foot.
Galileo is a new GNSS currently in development jointly with the European Union and the European Space Agency. Galileo is an infrastructure which, comprises of a constellation of satellites in orbital planes that circle the earth. The Galileo Project will develop the equipment, services and applications for the navigation system. The design of Galileo makes it interoperable with other existing global navigation systems such as GPS.
On the 26th of March 2002, the European Commission (EC) and the ESA were proud to announce the go ahead for the new GNSS project Galileo. The Galileo project would have two phases. The first phase GNSS-1 named European Geostationary Navigation Overlay Service (EGNOS) and the second phase GNSS-2 named Galileo. It is planned that Galileo will be fully operational for commercial activities by 2008.
Galileo consists of 30 medium earth orbit satellites (27 active and 3 spares), orbiting at an inclination of 56 degrees. The system's main difference between previous GNSS's such as GPS and the Russian GLONASS is that Galileo will be civilian controlled rather than being run by the various military organisations. Galileo will use 10 navigational signals on 3 different frequencies. (E5a & E5b, E6, L1).
A set of simulations have been carried out to gain an understanding of the availability of satellites and dilution of precision values for the vertical and horizontal components in both GPS/Galileo integration and GPS stand alone modes.
The parameters that were set in the software were using a masking angle of 15 degrees, a date of 8th of August 2004 at 00:00hrs with a height of 50 metres. A map of points 10 degree by 10 degree longitude and latitude spacing was used for the points of calculation in the simulation. These points are where the receivers are placed across the world map, to calculate the desired information at that point on the map. This creates a map having 18 by 36 control points making the simulation calculating 648 different points on the earth’s surface.
Shown below are the combined GPS/Galileo results from the simulation.
Figure 1: Availability of GPS/Galileo
Figure 2: Horizontal Dilution of Precision for Galileo/GPS
Figure 3: Vertical Dilution of Precision for Galileo/GPS
From the results obtained for the availability of satellites in the Galileo/GPS simulation was almost double in some places on the earths surface compared to GPS alone (as shown in Figure 1). The fact that Galileo provides more satellites being available gives a richer geometry for calculations of positioning on the earth enabling better dilution of precision values which, is illustrated in the simulations. The results have clearly shown that as expected, the addition of satellites in the GNSS network will provide lower dilution of precision values with increased satellite coverage of the surface of the earth.
The Horizontal Dilution of Precision with Galileo (as shown in Figure 2) shows that its a slight improvement on what GPS already has to offer.
The Vertical Dilution of Precision with Galileo (as shown in Figure 3) shows an impressive improvement in achievable accuracy over stand alone GPS. For applications which are in need of a good vertical accuracy then, Galileo will provide the applications with a great coverage of the earth’s surface at a stage which has not been achieved in the past at a basic level as the simulation shows.
Galileo provides the world with a powerful GNSS when it’s integrated with GPS. The question still remains as to whether Galileo is actually worth it, considering the capabilities of GPS, and also the fact that GPS will be upgraded throughout the future. One thing for sure is that GPS will not be a monopoly while Galileo is going to be around providing an alternative in the market place hopefully making it more cost effective to the user.
Cederholm, Peter (2004), “PDOP Values for simulated GPS/Galileo positioning”. Department of Development and Planning, Aalborg University, Denmark.
European Space Agency (ESA), September 23rd 2002, “Mission High Level Definition” Published by the European Space Agency.
Lachapelle, G & Canon, M.E (March 2001). “Technical Benefit Analysis of Galileo for Canada”, University of Calgary, California.
Farah, Ashraf (2002), “A light on: GPS/Galileo Data Simulation”, Institute of Engineering Surveying and Space Geodesy, Nottingham University, Nottingham. p.395
Useful Galileo Links
European Space Agency Website, http://www.esa.int/export/esaNA/index.html
Directorate- General Energy and Transport Website, http://europa.eu.int/comm/dgs/energy_transport/galileo/index_en.htm
GPS World Website, http://www.gpsworld.com/gpsworld/
For more information, please contact:
Dr. J. Wang
School of Surveying and Spatial Information Systems
University of New South Wales
UNSW SYDNEY NSW 2052