As of today, all Ground Based Augmentation Systems operate using only the navigation signals from GPS (and Glonass for a number of stations in Russia) in the L1 band. Ionospheric activity, especially in equatorial and polar regions, limits the availability of the service in those regions. Therefore, an extension to dual-frequency and multiconstellation (DFMC) techniques is currently being developed. In previous work we presented an initial concept for ionospheric monitoring and preliminary evaluations using the L1/L2 frequency combination of GPS. In this paper we present an analysis of the monitoring threshold depending on the number of satellites and constellations used. Furthermore, we discuss the potential issue of multiple satellites being affected by a gradient simultaneously which causes the monitoring to become quite sensitive in the original monitoring concept. Next, we consider the impact of ground and airborne noise and multipath on the monitoring performance using latest results of the effort of developing the respective models. Finally, we show the performance of the monitor in real-world operations using flight test data from flight trials with our Airbus A320 and our experimental dual-frequency multi-constellation GBAS ground station with the currently available Galileo satellites broadcasting signals on E1 and E5a and the GPS Block IIF satellites that broadcast signals on L1 and L5.

Keywords: GBAS, DFMC, dual-frequency, ionosphere