User Range Error Evolution and Projected Performance

Yuan K. Chen, Jya-Syin Chien, Kamran Ghassemi, Tom Simundich, Jack Taylor, Nicholas Nyema

Abstract:	The GPS User Equivalent Range Error (UERE) is the fundamental performance parameter of GPS. Its performance combined with the geometrical factor of dilution of precision (DOP) which is a function of constellation architecture determine the statistics of user positioning accuracy and availability. UERE brings together the contribution of Space, Control and User Segments to positioning accuracy. The Signal in Space (SIS) User Range Error (URE), defined as the contribution of the space and control segments to UERE, is therefore of key significance in space and control segment design and operation. SIS URE has seen tremendous improvements since the initial estimates and specifications were drawn. Today, the constellation performance boasts a SIS URE of ~1.5 meters RMS compared to the initial allocation of 6.0 meters. Much of this improvement has been accomplished as a result of improvements in performance of satellite atomic frequency standards, hand in hand with improved operational capability in estimation and prediction of the satellite clock and ephemeris through tuning of the control segment Kalman filter and other operational considerations. This performance will be extended in the modernization era to the new signals and navigation services offered. These new services bring about new challenges as well as opportunities for further improvements. Some of the impediments inherent to the legacy signal and message structure can now be removed in the new civil and military dual frequency and single frequency services. This paper begins with an overview of the error budgets, examines the recent improvements in URE and summarizes the current on-orbit performance of each block of satellites. It then provides analytical projections of SIS URE performance as the constellation is populated with newer generation of satellites: block IIR and IIF. We examine Age-of-Data reduction techniques to be brought into operation in the IIF era. We then provide simulation results of constellation dual frequency P(Y) performance for a IIF-type constellation and discuss the expectations for the URE of the new signals.
Published in:	Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002) September 24 - 27, 2002 Oregon Convention Center Portland, OR
Pages:	1575 - 1584
Cite this article:	Chen, Yuan K., Chien, Jya-Syin, Ghassemi, Kamran, Simundich, Tom, Taylor, Jack, Nyema, Nicholas, "User Range Error Evolution and Projected Performance," Proceedings of the 15th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GPS 2002), Portland, OR, September 2002, pp. 1575-1584.
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