Satellite selection for multi-constellation

There will be 70~90 navigation satellites operating at the same time when Glonass and Galileo reach full operation capability. As a result, the number of visible satellites can reach 30. Thus the positioning accuracy will be improved greatly. However, so many satellite measurements may burden the receiverpsilas processing element when to use them to find a solution and to do integrity monitoring. Satellite selection can decrease the number of measurements and as a result can shorten the computing time. ldquoDoes satellite selection be still needed for multi-constellation?rdquo At first, this paper analyses the amount of calculation of least square estimation techniques to calculate user position with different number of measurements. The results show that reducing the number of measurements can cut the amount of calculation greatly. Then the relationship between GDOP and the volume of polyhedron formed by the ends of unit user-to-satellite vectors is analyzed. We found that the relationship when the number of satellites is more than 4 is different with that when the number of satellites equals 4. Therefore the relationship when the number of satellites is more than 4 is researched in detail and a fast satellite selection method is proposed. The main idea is selecting a subset whose geometry is most similar to the optimal subset among all the visible satellites. The simulation tests prove that the fast satellite selection method can reduce the number of required subsets to look up the optimal geometry greatly and the increased GDOP is relatively small. Meanwhile, this method can not only be applicable for multi-constellation, but also for single constellation.