Determination of the Ionospheric Error Using Only Ll Frequency GPS Receiver

Laurent Lestarquit

Abstract:	The determination of the ionospheric error in real time with an accuracy in the range of a few nanosecondls is necessary for new GNSS Geostationary Overlay systems. Dual frequency methods may no longer be used in the future as the Anti Spoofmg is expected to be upgraded and the permanent availability of the present L2 signal is not garanteed for civilian use. Therefore, a single frequency method, independent of the L2 frequency could be required until the second civilian frequency (L5) is made available on block IIF satellites,, A method requiring a multi-channel receiver which makes both code and carrier phase measurements was developped. This paper will show the difficulties encountered when using only Ll : measurements are both noisy and ambiguous. For these reasons measurements from every satellite in view are processed simultaneously. The code/carrier phase slipping from all-in-view GPS satellites is processed through a Kalman filter to determine a local model of the ionospheric vertical delay and the carrier ambiguity for each satellite. After an initialization period, the ionosphere can be estimated in real time. Simulated data derived from simple ionospheric model were used to check the convergence rapidity and accuracy of the filter. Results obtained from real data, collected during the CE-GPS experimentation [I] & [2], will show the robustness of the software, but also that it is affected by multi-paths. Some potential improvements are under study , automatic multipath detection and use of programable chip spacing receivers to reduce multipaths. Comparison to dual frequency datas will be required to know the accuracy of the method. This paper will conclude that this method and this IONO-GPS software is a potential candidate for ionospheric error determination.
Published in:	Proceedings of the 1997 National Technical Meeting of The Institute of Navigation January 14 - 16, 1997 Loews Santa Monica Hotel Santa Monica, CA
Pages:	313 - 321
Cite this article:	Lestarquit, Laurent, "Determination of the Ionospheric Error Using Only Ll Frequency GPS Receiver," Proceedings of the 1997 National Technical Meeting of The Institute of Navigation, Santa Monica, CA, January 1997, pp. 313-321.
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