The United States Federal Aviation Administration’s (FAA) Wide Area Augmentation System (WAAS) uses Hexagon | NovAtel technologies, including reference receivers and signal generators, to provide the accuracy and integrity necessary to safely operate civil aircraft. Here’s a look at the updated technologies and how they enable GPS as a safety of life service for aviation.
GPS alone is not enough to safely navigate civil aircraft. It simply doesn’t provide sufficient accuracy or the integrity necessary for all aviation operations, which is why the FAA developed the Wide Area Augmentation System (WAAS) back in the mid-1990s.
As a safety-of-life augmentation of GPS, WAAS improves position accuracy and integrity for aviation, said Brian Jackson, the FAA’s systems engineer lead for satellite navigation, space-based augmentation systems (SBAS). The service offers an extra layer of safety that allows aircraft to make use of GPS, providing warnings when errors are detected in the GPS or WAAS network.
Thousands of airport runways in North America rely on WAAS because it provides Instrument Landing System (ILS) level of service performance without the need to install additional radio equipment at the runways. Jackson described the system as an “integral component” of the FAA’s National Airspace System (NAS).
“WAAS augments GPS by improving accuracy, integrity and availability,” said Neil Paskiw, chief engineer, aerospace at Hexagon | NovAtel. “WAAS was developed so aircraft could use GPS during all phases of flight including precision
approaches. WAAS provides vertical navigation information during approach, similar to existing
instrumentation and systems, but at a much lower cost.”
NovAtel’s Critical Role
NovAtel has delivered key technology into WAAS from the beginning, providing three generations of reference receivers. The most recent WAAS G-III Ground Reference Receiver and two generations of GUS Signal Generators were placed into operational service in 2015, with fielding at all sites completed in 2016.
Late last year, NovAtel delivered the next-generation of Ground Uplink Station (GUS) Signal Generators to the FAA in support of WAAS modernization. The new GUS Signal Generator, or SIGGEN, replaces the legacy signal generator, which has operated successfully for more than 15 years. The original SIGGENs offered “very good performance,” Jackson said.
“The new Signal Generators carry forward the same functionality as the current unit’s, but with expanded capability to allow for a wider range of frequency offsets and output power levels,” Jackson said. “The GUS Signal Generator is separate from the G-III receiver. Ultimately, the G-III receives the WAAS waveform generated after transmission from the GEO (geostationary) satellite.”
How WAAS Works
WAAS provides navigation services across the entire NAS to improve accuracy and position integrity estimates. Through the service, 38 precisely surveyed reference stations, or Wide Area Reference Stations (WRS), spaced out across North America receive GPS signals, Jackson said. The receivers then process these signals and transmit them to WAAS Master Stations (WMS).
Once received, the WMS processes the GPS signals and formulates correction messages. These messages are sent to uplink stations and then transmitted to navigation payloads on GEO communications satellites. The navigation payloads broadcast the messages via a GPS-like signal across the NAS.
The WMS generates a message every second, enabling the receivers to remove errors in the GPS signal for
improved location accuracy and integrity. Users are notified within six seconds of any information that could lead to an error in the position estimate.
“The WAAS message,” Jackson said, “improves the accuracy, availability and integrity of GPS-derived position information.”
