Autonomous Single-frequency Ionospheric Correction Model for Safety-of-life Applications

Denis Bouvet

Abstract:	Unlike the current generation of GPS/SBAS equipment used in civil aviation, the next generation of multi-constellation receivers should benefit from dual-frequency measurements to compensate for ionosphere effects. However, in fallback mode where the equipment can only use one frequency, ionospheric correction models are still necessary. GPS and SBAS L1 already broadcast data for this use, but for other constellations, either the correction model is missing (e.g. GLONASS) or it has not been validated yet for safety-of-life applications (e.g. NeQuick G for Galileo). This paper proposes a correction model that could be applied to such measurements, with the associated error model for computing accuracy and integrity bounds. In a first time, we analyze the ionospheric parameters broadcast from 1991 to 2016, to reconstruct almost 95% of the 2960 entries used by the GPS ground segment to correct ionosphere in single-frequency mode. From this database, we derive a correction model that uses 37 sets of ionospheric parameters (one per 10-day period) selected to minimize the discrepancies with the broadcast set corresponding to the actual solar activity. The model variances defined in the GPS/SBAS MOPS DO-229 are then inflated to guarantee that the horizontal 95%-accuracy indicator (HFOM) includes not only the Klobuchar model residual error, but also the additional error introduced by the use of a default set of ionospheric parameters. Finally, we check RAIM/FDE availability performance with the proposed model, which shows minor degradation for phases of flight with HAL down to 0.3 nautical miles.
Published in:	Proceedings of the 30th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2017) September 25 - 29, 2017 Oregon Convention Center Portland, Oregon
Pages:	1735 - 1746
Cite this article:	Bouvet, Denis, "Autonomous Single-frequency Ionospheric Correction Model for Safety-of-life Applications," Proceedings of the 30th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2017), Portland, Oregon, September 2017, pp. 1735-1746. https://doi.org/10.33012/2017.15188
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