WAAS Future and Evolutions

WAAS
Title	WAAS Future and Evolutions
Author(s)	GMV.
Level	Basic
Year of Publication	2011

The Wide Area Augmentation System (WAAS) is the United States Satellite Based Augmentation System. The programme, started in 1992, is being carried out by the Federal Aviation Agency (FAA) and is specially developed for the civil aviation community. The system, which was declared operational in late 2003, currently supports thousands of aircraft instrument approaches in more than one thousand airports in USA and Canada. WAAS service area includes CONUS, Alaska, Canada and Mexico. The WAAS programme is continuously in evolution; two development phases have been already covered, a third is in progress, and there are plans to improve the capability of the system in parallel with the evolution of the SBAS standards towards a dual-frequency augmentation service.

WAAS Future and Evolutions

The WAAS Development Phases are:

• Phase I –Initial Operating Capability (IOC). Completed in 2003.
• Phase II -Full LPV Performance. Completed in 2008.
• Phase III -Full LPV-200 Performance. Planned for 2009-2013.
• Phase IV -Dual Frequency Operations. Planned for 2014-2028.

These phases imply improvements in three fields:

1. Improvement to aviation operations
   In 2007, WAAS vertical guidance was projected to be available nearly all the time (greater than 99%), and its coverage encompasses the full continental U.S., most of Alaska, northern Mexico, and southern Canada. At that time, the accuracy of WAAS would meet or exceed the requirements for Category 1 ILS approaches, namely, three-dimensional position information down to 200 feet (60 m) above touchdown zone elevation. As of Aug 26th, 2010 there have been 2209 LPV approaches serving 1174 Airports: 1350 to non-ILS Runways Ends and 859 to ILS Runways Ends. There have been LPVs at 553 Non-ILS Airports and 246 have been LPVs-200.
2. Software improvements
   Software improvements, fully implemented in September 2008, significantly improve signal availability of vertical guidance throughout the CONUS and Alaska. Area covered by the 95% available LPV solution in Alaska improves from 62% to 86%. And in the CONUS, the 100% availability LPV-200 coverage rises from 48% to 84%, with 100% coverage of the LPV solution. In phase III the new evolutions of software shall update WAAS algorithms to give full LPV-200 performance over CONUS and Alaska, and also to prepare for Dual Frequency Operations.
   

   Broadcast footprints of the WAAS GEOs in December 2010
3. Space segment upgrades
   Both Galaxy 15 (PRN #135) and Anik F1R (PRN #138) contain an L1 & L5 GPS payload. This means they will potentially be usable with the L5 modernized GPS signals when the new signals and receivers become available. With L5, avionics will be able to use a combination of signals to provide the most accurate service possible, thereby increasing availability of the service. These avionics systems will use ionospheric corrections broadcast by WAAS, or self-generated onboard dual frequency corrections, depending on which one is more accurate. In November 2010, a third GEO satellite, Inmarsat AMR (PRN #133), has started to transmitt the WAAS signal.

For Phase IV, WAAS shall begin to operate with Dual Frequency. This would imply:

• Maintain a robust, reliable, and sustainable LPV-200 capability.
• Support Single frequency WAAS users through end of Phase IV (until 2028).
• Implement WAAS Changes Needed for Dual Frequency (L1/L5) GPS Operations.