Development of a MatLab Based Global Navigation Satellite System Orbit Model
- Paper number
IAC-06-B3.6.09
- Author
Ms. Janice Hendry, University of Southampton, United Kingdom
- Year
2006
- Abstract
Europe will enter the competition of Global Navigation Satellite Systems (GNSS) with the planned launch of the complete Galileo constellation by 2008. The first satellite, GIOVE-A, was launched on the 27 December 2005 from the Baikonur Cosmodrome in Russia. Its first navigational signals were received at 17:25 GMT on the 12th January 2006. The main advantage of Galileo is that it will be controlled by the public sector rather than the military and therefore has certain guarantees for continued maintenance and will have requirements for up-time and position accuracy. The owners of current GNSS can, at any time, cease to maintain or refuse to allow the general public, private firms or government agencies to use their constellation. It is predicted that with the guarantees given by the Galileo GNSS, the aviation industry will be able to rely more on GNSS as a means of navigation. It is therefore very important to have accurate position prediction algorithms for the Galileo GNSS receivers. This paper discusses how the orbits of the satellites in the GPS and Galileo constellations can be simulated, and how one can predict accuracy of measurements using this simulation. The model uses Keplerian orbit equations with corrections for the second zonal harmonic (J2) and the Earth being ellipsoidal. The model not only provides a visual output of the satellite positions in 2D and 3D with respect to the Earth, but also details dilution of precision (DOP) for GPS and Galileo constellations. In addition, basic GNSS positioning theory will be discussed to give a better understanding of how these calculations of accuracies are made. The model predicts that there should always be between 5 and 14 satellites in view from Romsey, UK, in comparison to between just 4 and 10 satellites for the GPS constellation at the same location. This paper details the user interface, the progress of the model to date and possibilities for further improvement, such as implementing full SGP and SDP equations to replace the corrected Keplerian equations. It will also show the output data from the model for both GPS and Galileo, including a data set for a 24 hour period. More satellite constellations can easily be integrated into this model, such as GLONASS, by the creation of an orbit data file for the satellites in that constellation. Finally this paper discusses how the model can be used in a complete GNSS system model to predict positioning accuracy in real environments, such as built up areas where “urban canyons” form. It is hoped that these models can be combined to give the user or developer details of how many satellites are in view, how many are actually in view due to buildings and Earth topology, the level of multipath and signal distortion due to the local environment, and from this an estimate of how accurate the position reading will be.
- Abstract document
- Manuscript document
IAC-06-B3.6.09.pdf (🔒 authorized access only).
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