Optimization of GPS Satellite Selection for High Precision Differential Positioning

des Instituts für Geodäsie

Heft 19/1986

Optimization of GPS Satellite Selection
for High Precision Differential Positioning


In: LANDAU, Herbert / EISSFELLER, Bernd / HEIN, Günter W. [1986]:
GPS Research 1985 at the Institute of Astronomical and Physical Geodesy
Schriftenreihe Universitärer Studiengang Vermessungswesen, Universität der Bundeswehr München, Heft 19, Neubiberg, S. 65-105.


When reaching the full operational capability of the NAVSTAR/GPS system with 18 satellites in 6 orbital planes an optimal selection of satellites becomes more and more of importance. GPS then provides 4 to 8 visible satellites above the horizon to any user in the world at any time, however, most of the receivers are able to track only four satellites. Therefore it will be necessary to select 4 satellites at any time of the tracking intervall. This selection has a great influence on accuracy of the processing results and is usually based on so so-called geometric dilution of precision (GDOP). Up to now selection algorithms are implemented in the receivers, which try to appoximate the mallest GDOP with smallest computational requirements.

Since geodesists are interested in the highest possible accuracy, the applied selection method should be based on the special geodetic observation and computation techniques using phase differences, which have a quite different error behaviour than pseudo-range measurements. The paper discusses an optimum selection method for different observation types and visibility. Various error sources like atmospheric propagation delays and ephemris errors are considered in the discussion.

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