Conceptualization and Implementation of a Closed-Loop Ground Based Augmentation System

Chad Davis, John Dyer, Andy Archinal, Hengqing Wen and John Fagan

Abstract:	A Ground Based Augmentation System (GBAS) uses multiple stationary references to facilitate the computation of pseudorange corrections for the local environment. The information from the Reference Stations (RS) are relayed to the GBAS Base Station where it is processed, converted to a standardized message format, and transmitted to the airborne user via VHF Data Broadcast (VDB). Current GBAS prototypes rely primarily on a probabilistic assessment of the computed pseudorange corrections to predict system integrity. This methodology requires extensive development of mathematical models and specialized algorithms to determine whether the pseudorange corrections calculated by the GBAS Base Station meet the specified FAA requirements. Failure to meet these requirements may result in Hazardous Misleading Information (HMI) and produce a safety risk to the airborne user. This paper explores the use of an integrity monitor network to reduce the probability of HMI and mitigate integrity risks. The integrity monitors provide a deterministic assessment of all broadcasted GBAS information. When these measurements are utilized as feedback to the control logic of the Base Station, the open-loop system is transformed into a closed-loop system. This research involves the conceptualization and implementation of a new and novel closed-loop GBAS (CL-GBAS) ground facility. The high-level architecture design details, primary software algorithms, and simulation results are presented. Using this research as the foundation, the pursuit of achieving certification of CL-GBAS under the FAA-2937 specification is the focal point of future work.
Published in:	Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007) September 25 - 28, 2007 Fort Worth Convention Center Fort Worth, TX
Pages:	461 - 466
Cite this article:	Davis, Chad, Dyer, John, Archinal, Andy, Wen, Hengqing, Fagan, John, "Conceptualization and Implementation of a Closed-Loop Ground Based Augmentation System," Proceedings of the 20th International Technical Meeting of the Satellite Division of The Institute of Navigation (ION GNSS 2007), Fort Worth, TX, September 2007, pp. 461-466.
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