In the currently standardized Ground-based augmentation system (GBAS), a Ground Station (GS) calculates differential corrections and associated integrity data for the GNSS satellite signals received by the ground subsystem and broadcasts this information to GBAS -equipped aircraft in the vicinity of an airport. GBAS enables for GNSS based precision landing capabilities in all-weather conditions. The GBAS approach services are differentiated into several types, namely GBAS Approach Service Types (GAST), which are available when the GBAS airborne equipment and ground station match their performance and functional requirements to enable those service types. Currently GAST C is deployed in several airports supporting CAT I operations (and CAT II using ionospheric monitoring on ground from SBAS), and GAST D has been designed and standardized to support landing operations in lower visibility conditions including CAT III operations. The currently standardized GASTs are based on augmenting GNSS satellite SF (Single Frequency) signals.
The EDGAR (EGNSS DFMC for GBAS bAsed opeRations) project aims to support the development of an improved GBAS solution based on Dual-Frequency Multi-Constellation (DFMC) GBAS, focused on GPS and Galileo.
Hence, the main objectives of this proposal are: to further develop and validate the GBAS DFMC solution so as to modernize and improve air operations, with emphasis on providing safety, availability, and robustness in all situations, including during challenging ionospheric conditions; to analyze the distinguishing features of Single-Frequency Multi- Constellation, or SFMC, GBAS brought by the addition of Galileo; and to facilitate CAT II service to GAST C airborne users based on a GAST D ground station with European Global Navigation Satellite System (EGNSS) integration (from Galileo or EGNOS).
Two concepts were still competing for the DFMC GBAS when the project was proposed, the so-called GAST F (based on transmitting corrections for the signals) and the GAST X (based on the transmission of raw ground station pseudorange and carrier phase measurements for the differential corrections to be computed onboard by the avionics). However, during grant preparation, a convergence between both concepts at ICAO level led to the selection of a different approach, known as GAST E. Consequently, the project activities have been adapted to take into account this decision.
