GPS Constellation Navigation: L-Band Measurements Only

J. Y. Cruz, M. D. Menn, W. A. Feess and V. Nuth

Abstract:	A study is in progress to determine the Signal-In-Space (SIS) User Range Error (URE) achievable by GPS III with various architectures and in the comparatively near term. This report focuses on the use of downlink L-band code and carrier measurements only. A future effort will address the use of crosslink measurements. The study initially tested several algorithm alternatives against configurations of eleven and sixteen monitor stations. Accuracy was evaluated over 30 minutes of prediction. The simplest algorithms used pseudoranges only and the most complex used carrier phase measurements. Real tracking data were used and results were compared to the National Geospatial–Intelligence Agency (NGA) precise ephemeris and clock. An automated tuning process was developed to select filter parameters corresponding to measurement and propagation error variances. The results established the feasibility of achieving a 20-cm SIS URE assuming that: (a) prediction time, including latency, can be held to a half hour or less, (b) the satellites all have rubidium clocks or better, (c) the full eleven-monitor-station set of the NGA is added to the Air Force (AF) network, and (d) the control segment estimator includes strong use of carrier phase measurements and estimation of troposphere delay parameters. The planned Legacy Accuracy Improvement Initiative (LAII) upgrade to the control segment estimator motivated the second part of the study. The upgrade will use the six core NGA and six AF stations, a fully correlated instead of partitioned estimator, and the more recent Jet Propulsion Laboratory (JPL) solar pressure models. The study examined whether the automated tuning process could improve a set of proposed filter parameter values. These values had already been the result of some tuning. The results show that retuning improves the URE modestly by 2% over 24 hours and 3% over 30 minutes of prediction, and by 8% at zero age-of-data.
Published in:	Proceedings of the 2005 National Technical Meeting of The Institute of Navigation January 24 - 26, 2005 The Catamaran Resort Hotel San Diego, CA
Pages:	792 - 798
Cite this article:	Cruz, J. Y., Menn, M. D., Feess, W. A., Nuth, V., "GPS Constellation Navigation: L-Band Measurements Only," Proceedings of the 2005 National Technical Meeting of The Institute of Navigation, San Diego, CA, January 2005, pp. 792-798.
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