Session B4: GNSS Integrity and Augmentation

Development and Evaluation of a Multi-Constellation Multi-frequency GBAS Prototype for Air Navigation
Felipe Tintino Linhares de Souza, Weverton da Costa Silva, Crislaine Menezes da Silva, Italo Tsuchiya and João Francisco Galera Monico, São Paulo State University (UNESP), School of Technology and Sciences
Location: Beacon B

GBAS (Ground Based Augmentation System) is an augmentation system designed to ensure the maintenance of essential quality parameters (integrity, continuity, accuracy, and availability) related to GNSS (Global Navigation Satellite System) positioning in aviation. It uses the DGNSS (Differential GNSS) positioning method, where ground reference stations generate pseudorange corrections that are transmitted to aircraft, improving positional accuracy to support approach procedures. According to the International Civil Aviation Organization (ICAO), GBAS is currently authorized to use the GPS and GLONASS L1 frequencies, while the L2 frequency is not permitted, as it falls outside the aviation-protected spectrum. In the future, the L5 frequency and additional constellations, such as Galileo and BeiDou, are expected to be incorporated, making GBAS more robust, especially in mitigating ionospheric effects. The integration of new GNSS signals and constellations in aviation depends on ongoing research and investigation to support upcoming changes and implementations. This work aimed to develop a GBAS Prototype, called GBAS UNESP Experimental, which is capable of operating with Multiconstellation and Multifrequency GNSS, enabling its use in air navigation. This prototype functions as a GBAS performance monitoring station that can indicate the condition of precision approach categories using GNSS, indicating which type of GBAS service can be used based on the ionospheric gradient monitor. For this study, GNSS data was collected from 5 reference stations of the INCT GNSS NavAer network, with 4 stations representing the ground system (PRU2, PRU4, DMC1, and MOR3) and one station simulating an aircraft (STAV). The selected day was DOY 227/2024 (August 14, 2024), during which no ionospheric scintillation was observed. The GBAS UNESP Experimental was implemented in Matlab using pseudorange and phase observables, collected at a 0.5 second interval, with a 10° elevation mask for the L1/E1 and L5/E5a frequencies of the GPS and Galileo systems, respectively. Using the GNSS data, the performance of each GBAS subsystem (Ground and Aircraft) was evaluated, initially focusing only on the L1/E1 frequencies (GPS and Galileo) and with 100 seconds for smoothing constant. In the experiment, the ground subsystem produced results aligned with the literature and the characteristics of the data used. The aircraft subsystem demonstrated that the system's horizontal component met integrity requirements in nearly all processed epochs (99.999%). However, the vertical component exceeded operational limits in 2.466% of epochs. Further analysis revealed undetected errors that bypassed quality controls, potentially affecting results. Implementing statistical tests in DGNSS positioning could enhance error detection and improve GBAS availability. Future evaluations will consider ionospheric scintillation occurring.