Targeted Parameter Inflation Within Ground-Based Augmentation Systems to Minimize Anomalous Ionospheric Impact

Abstract

Anomalous ionospheric conditions can cause large variations in propagation delays of transionospheric radio waves, such as global navigation satellite system (GNSS) signals. Although very rare, extremely large spatial variations pose potential threats to ground-based augmentation system (GBAS) users. Because GBAS provide safety-of-life services, namely precision approach and landing aircraft guidance, system safety must be guaranteed under these unusual conditions. Position-domain geometry-screening algorithms have been previously developed to mitigate anomalous ionospheric threats. These algorithms prevent aircraft from using potentially unsafe GNSS geometries if anomalous ionospheric conditions are present. The simplest ground-based geometry-screening algorithm inflates the broadcast sigma(vig), parameter in GBAS to signal whose geometries should not be used. However, the sigma(vig) parameter is not satellite-specific, and its inflation affects all satellites in view. Hence, it causes a higher than necessary availability penalty. A new targeted parameter inflation algorithm is proposed that minimizes the availability penalty by inflating the satellite-specific broadcast parameters: sigma(prgnd) and P values. In this new algorithm, sigma(prgnd) and P values are inflated by solving optimization problems. The broadcast parameters obtained from this algorithm provide significantly higher availability than optimal sigma(vig) inflation at Newark Liberty International Airport and Memphis International Airport without compromising system safety. It is also demonstrated that the computational burden of this algorithm is low enough for real-time GBAS operations.