Abstract
The next generation of satellite-based augmentation systems (SBAS) will support aviation receivers that take advantage of the ionosphere-free dual-frequency combination. By combining signals of the L1 and L5 bands, about 99% of the ionospheric refraction effects on the GNSS (Global Navigation Satellite Systems) signals can be removed in the user receivers without additional SBAS corrections. Nevertheless, even if most of the negative impacts on GNSS signals are removed by the ionospheric-free combination, some residuals remain and have to be taken into account by overbounding models in the integrity computation conducted by safety-of-live (SoL) receivers in airplanes. Such models have to overbound residuals as well, which result from the most rare extreme ionospheric events, e.g., such as the famous “Halloween Storm”, and should thus include the tails of the error distribution. Their application shall lead to safe error bounds on the user position and allow the computation of protection levels for the horizontal and vertical position errors. Here, we propose and justify such an overbounding model for residual ionospheric delays that remain after the application of the ionospheric-free linear combination. The model takes into account second- and third-order ionospheric refraction effects, excess path due to ray bending, and increased ionospheric total electron content (TEC) along the signal path due to ray bending.
Highlights
Airplanes need to rely on ground-based radio systems such as the instrument landing systems (ILS) or satellite-based augmentation systems (SBAS) to be able to perform precise landing operations independent of the weather conditions
By combining signals of the L1 and L5 bands, about 99% of the ionospheric refraction effects on the GNSS (Global Navigation Satellite Systems) signals can be removed in the user receivers without additional SBAS corrections
We presented a model to overbound ionospheric residuals that remain after the application of the ionospheric-free linear combination
Summary
Airplanes need to rely on ground-based radio systems such as the instrument landing systems (ILS) or satellite-based augmentation systems (SBAS) to be able to perform precise landing operations independent of the weather conditions. Given the fact that SBAS, similar to the European Geostationary Overlay System (EGNOS) or the American Wide Area Augmentation System (WAAS, allow an efficient use of airspace without maintenance or calibration cost for airports, more and more airports are already taking advantage of this technology based on GNSS (Global Navigation Satellite System). The ionospheric propagation effects degrade the true range measurements, whereas the ionospheric irregularities may cause signal loss due to rapid fluctuation of the signals, which is known as ionospheric scintillation. Signal fluctuations may cause cycle slips; if these cycle slips are detected, precise navigation can be achieved under scintillation conditions [1]. Demyanov et al [3] found degradation in the single-frequency WAAS services during geomagnetic storm conditions
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