WAAS performance in the 2001 Alaska Flight Trials of the high speed Loran data channel

Abstract

The wide area augmentation system (WAAS) enables the Global Positioning System (GPS) to provide the performance and integrity necessary for en route flight and many landing procedures. Currently, WAAS employs two geostationary satellites to provide coverage to the United States. However, operational WAAS will require a redundant broadcast of WAAS throughout the US. Additional geostationary satellites will be used to provide some redundancy. Loran can serve as a cost-effective additional broadcast channel for WAAS. While additional geostationary satellites are still necessary, Loran can further augment broadcast of the WAAS message particularly in terrain, urban canyons or high latitudes. Using Loran has some appealing features. First, Loran can be modified to attain the capacity to support the WAAS message. Second, it could also provide a reversionary positioning capability in case the GPS/WAAS signal is lost due to radio frequency interference (RFI). Loran can be particularly helpful in Alaska, where terrain combined with high latitudes could block the signal from the geostationary satellite that appears low in the Alaskan sky. This paper describes the flight and ground tests of the reception of WAAS from Loran and the geostationary satellite.