Evaluating Performance of Ionospheric Anomaly Monitor for DFMC GBAS with Flight Data in Ionospheric Disturbed Conditions

Susumu Saito, Takayuki Yoshihara, Tim Murphy, Matt Harris, Glaucia Balvedi, Joel Wichgers, Linda Lavik, Morten Topland, Mutaz Tuffaha

Abstract:	Architecture of the Dual-Frequency and Multi-Constellation (DFMC) Ground-based Augmentation System (GBAS) using the GNSS signals at L1 and L5 frequencies is under development at International Civil Aviation Organization (ICAO). Two concepts have been proposed. One is the GBAS Approach Service Type F (GAST F) developed as part of the Single European Sky Air Traffic Management Research (SESAR). Another one is GAST X [2] proposed to enhance system availability, robustness to the environment, and future extensibility. In the GAST F concept, the nominal positioning mode is based on single-frequency measurement processing which is used to avoid enhanced measurement noise that occurs when using dual-frequency ionosphere-free (IFree) measurement processing. However, the single-frequency processing is susceptible to temporal and spatial ionospheric delay differences between the ground reference receivers and airborne receivers. In the GAST X concept, nominal positioning is based on dual-frequency measurements using Divergence Free (DFree) processing, which avoids the enhanced measurement noise inherent in IFree processing and has essentially the same measurement noise a SF processing. However, a primary benefit of using GAST X primary mode DFree processing over GAST F single frequency processing is that the effects of the ionospheric divergence resulting from ionospheric temporal gradients are effectively removed from smoothed pseudorange. However, neither the GAST X DFree processing mode nor the GAST F SF processing mode remove the effects of the instantaneous residual ionospheric delay caused by spatial gradients. Thus, the nominal GAST X DFree smoothing mode is more robust to ionospheric temporal gradients than the GAST F nominal SF smoothing mode, and both GAST X and GAST F nominal modes of operation are susceptible to large ionospheric spatial gradients. Therefore, a monitor to detect intolerable ionospheric delay differences between the ground and airborne receivers is needed. (Note that the levels of intolerable ionospheric delay differences for GAST F and GAST X are different, with GAST X being more robust to larger ionospheric effects).
Published in:	Proceedings of the 36th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2023) September 11 - 15, 2023 Hyatt Regency Denver Denver, Colorado
Pages:	1144 - 1155
Cite this article:	Saito, Susumu, Yoshihara, Takayuki, Murphy, Tim, Harris, Matt, Balvedi, Glaucia, Wichgers, Joel, Lavik, Linda, Topland, Morten, Tuffaha, Mutaz, "Evaluating Performance of Ionospheric Anomaly Monitor for DFMC GBAS with Flight Data in Ionospheric Disturbed Conditions," Proceedings of the 36th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS+ 2023), Denver, Colorado, September 2023, pp. 1144-1155. https://doi.org/10.33012/2023.19479
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