GBAS ionospheric threat analysis using DLRs hardware signal simulator

Ionospheric fronts pose a significant threat to single frequency ground based augmentation systems (GBAS) for airplane precision approach. Here, we show our implementation of two ionospheric threat models in the DLR MASTER GNSS Simulator, a modified Spirent GSS7780/779. These threat models include the standard GBAS ”front” threat model as required for CAT-1 certification and a simplified plasma bubble model intended to represent equatorial conditions. These models can now easily be simulated at the German Aerospace Center's facilities. As an example, we simulate a GBAS ground facility (with a code carrier divergence monitor) affected by both a plasma bubble with a constant differential delay of -2 m and fronts of various gradients and speeds. Results confirm that a plasma bubble can lead to worst case position biases that may cause misleading and hazardously misleading information to be used by an approaching aircraft. Moreover, we confirm that ionospheric fronts at a speeds close to the airplane approach speed and propagating into the approach direction cause the most severe range biases. These, mapped to the position domain, can also cause hazardously misleading information.