Future Outlook for WAAS and LAAS

Over the past decade, two separate approaches have been developed to augment the Global Positioning System to meet the accuracy, integrity, continuity, and availability needs of civil aviation users. One utilizes a network of reference stations spread across a large area and derives a single set of differential corrections that is relayed to users via GPS-like signals from Geosynchronous (GEO) satellites. It is known as the Wide Area Augmentation System (WAAS) or, more generally, as a Space Based Augmentation System (SBAS). The other utilizes a single reference station within a given airport and provides differential corrections via VHF Data Broadcast (VDB) within a 50-km region around that airport. It is known as the Local Area Augmentation System (LAAS) or, more generally, as a Ground Based Augmentation System (GBAS). This paper summarizes the history of WAAS and LAAS and provides an overview of the key technical elements of both systems. It provides up-to-date status reports for the fielding of WAAS and LAAS by the U.S. Federal Aviation Administration (FAA) and focuses on the most challenging aspect – verification of the integrity and continuity requirements. It concludes by projecting the future for both systems based on the performance improvements that appear to be possible and the most demanding requirements that WAAS and LAAS may be asked to meet.