A Clock and Ephemeris Algorithm for Dual Frequency SBAS

Juan Blanch, Todd Walter, Per Enge

Abstract:	In the next years, the new GPS and Galileo signals (L1, L5) will allow civil users to remove the ionospheric delay in the pseudoranges. This will have a large impact on the Satellite Based Augmentation Systems (SBAS), as the ionospheric delay is currently the largest error. Once this source of error is removed, the Vertical Protection Levels will decrease substantially, and other error sources will dominate. The remaining terms in the error bound were much less critical than the ionospheric delay error bound, so they have received less attention. It is therefore likely that they can still be optimized. This is true in particular for the User Differential Range Error (UDRE) algorithm which computes the clock and ephemeris error bounds. In addition, new SBAS messages will be broadcast in the L5 channel, and their content is still not fixed. Therefore, it is a good opportunity to determine whether changes can be made both in the UDRE and Message Type 28 (MT28) computation and transmission to increase overall SBAS performance. In this work, we propose an algorithm to compute the error bounds on the clock and ephemeris in SBAS. As opposed to the current Wide Area Augmentation System (WAAS) UDRE algorithm, this algorithm computes the UDRE and MT28 simultaneously and takes into account receiver failures explicitly. We will evaluate the performance of the algorithm and compare it to the current UDRE and MT28 algorithm to determine whether its implementation for dual frequency SBAS would be worthwhile.
Published in:	Proceedings of the 24th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2011) September 20 - 23, 2011 Oregon Convention Center, Portland, Oregon Portland, OR
Pages:	2513 - 2519
Cite this article:	Blanch, Juan, Walter, Todd, Enge, Per, "A Clock and Ephemeris Algorithm for Dual Frequency SBAS," Proceedings of the 24th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2011), Portland, OR, September 2011, pp. 2513-2519.
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