Design of High Performance and Cost Efficient Constellations for a Future Global Navigation Satellite System

M.M. Romay-Merino, J. A. Pulido Cobo, E. Herraiz-Monseco

Abstract:	GPS and GLONASS, are not able to satisfy the requirements of most of the civil users. To improve the situation several augmentation systems are currently being developed (EGNOS, MTSAT, and WAAS). Those new GNSS systems will improve the situation by satisfying some of the requirements of some specific users, mainly aeronautical users. But there are still some needs that will not be covered by those systems. USA is actually working in an advanced GPS system, while Europe is aiming to develop a new navigation system, the GNSS-2 system. Future satellite navigation systems shall improve significantly the performances of any other available system. In addition to that the new system shall be cost efficient, this means not only that the system shall be low-cost, but also that it would be possible to recover the invested money by providing some new, or significantly improved, services. An improvement in performances means that the new system shall be able to satisfy most of the requirements of very demanding users without augmentations. Performances can be improved by improving either the signal in space or the geometrical conditions. Studies going on in USA and Europe are mainly focused in trying to improve the signal in space, and not so much effort is devoted to the constellation refinement. While USA considers a GPS constellation, Europe is discussing within LEO, MEO, IGSO, GEO and hybrid constellations. Preliminary analysis are showing that a significant improvement coming from the signal in space shall not be expected. This is mainly due to the lack of available frequencies, and also from the fact that a maximum compatibility with current systems shall be maintained. The major improvements may came from the resistance to interference or jamming and by mitigating multipath effects. At this stage it seems that it would not be possible to obtain an UERE (considering all the effects) significantly below one meter, so the major improvement has to come from the geometry, by optimising the constellation design. While a better signal in space will allow to improve the performance in differential mode, allowing to use for instance Three Carrier Ambiguity Resolution (TCAR) techniques. The clear need for optimising the future GNSS constellation has encouraged to GMV to start with the development of a software tool specifically designed to improve performances by minimising the total cost of the system. The space segment contributes to about an 80% of the total cost, so a significant effort has been devoted to reduce the number of satellites, but also considering: spare satellites policy, launch cost (about a 50% of the total space segment cost), constellation degradation and maintenance, etc. This paper describes the developed tool and some results and conclusions obtained using this tool.
Published in:	Proceedings of the 11th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1998) September 15 - 18, 1998 Nashville, TN
Pages:	1085 - 1096
Cite this article:	Romay-Merino, M.M., Cobo, J. A. Pulido, Herraiz-Monseco, E., "Design of High Performance and Cost Efficient Constellations for a Future Global Navigation Satellite System," Proceedings of the 11th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 1998), Nashville, TN, September 1998, pp. 1085-1096.
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