Wide Area Augmentation System (WAAS) E. Douglas Aguilar CAPT, USAF

Development Joint project between Joint project between –Federal Aviation Administration (FAA) –US Department of Transportation (DOT) Goal Goal –Provide horizontal and vertical navigation for precision approaches for everyone everywhere Continental US

Error Sources One Sigma Error (m) GPS Error SourcesNormal C/A CodeDual (P/Y) Ionosphere Satellite clock2.10 Ephemeris data2.10 Multipath1.40 Troposphere0.70 Receiver measurement0.50 UERE (rms) UERE Filtered (rms) WAASEGNOS Vertical DOP= Horizontal DOP=

Timeline Phase I ( ) Phase I ( ) –25 reference stations, 2 master stations and 2 satellites deployed –Supports category I precision approach, limited coverage area

Timeline Phase II ( ) Phase II ( ) –Full WAAS expected with additional reference and master stations –Airports begin upgrading landing systems –2 nd and 3 rd civil frequencies added to improve accuracy

Timeline Phase III ( ) Phase III ( ) –Full constellation of GPS satellites available for WAAS –Phase out all airport navigational aids and fully integrate WAAS for commercial aircraft

WAAS Elements as of Nov 2006 (EGNOS) WAAS Elements as of Nov 2006 (EGNOS) –Only in US (23 countries) –29 Wide-area reference stations (WRS) (34 RIMS) –3 Wide-area monitoring stations (WMS) (4MCC) –3 Ground earth stations (GES) (6 NLES) –2 to 4 geosynchronous satellites (3)WAAS Space Based Augmentation Systems

WAAS Components

WAAS Functions

Function 5 - Integrity INPUTS INPUTS –GPS satellite navigation data –GEO satellite navigation data –antenna phase center locations –satellite long term error corrections –IGP locations –IGP vertical ionosopheric delay estimate –IPG GIVE data –Satellite User differential range error (UDRE) data –message type 10 degradation parameters –fast correction degradation factor OUTPUTS OUTPUTS –data to generate “Don’t Use” messages –data to generate “Not Monitored” messages –list of satellites that should be in view but whose signals are not being received Function 5 shall generate data for a “Don’t Use” message for any satellite whose pseudorange errors are not correctable within the limits of the WASS message structure

Architecture

Commercial Aircraft

Benefits

Nav/Landing Equipment

s/news_story.cfm FAA Announcement FAA Announces Major Milestone for Wide Area Augmentation System (WAAS)- FAA Announces Major Milestone for Wide Area Augmentation System (WAAS)- –FAA Administrator Marion C. Blakey. “Less reliance on a ground-based infrastructure will result in improved safety, including enhanced approach and landing operations in marginal weather.” LNAV/VNAV 350’ LPV 250’ ILS 200’ 3o3o March 24, WAAS use will be extended to 200 feet above an airport’s surface

Coverage

WAAS Satellites Original two Inmarsat III Original two Inmarsat III –PRN#134 Pacific Ocean Region –PRN #122 Atlantic Ocean Region Two additional Two additional –PRN #135 Galaxy XV (as of Nov 9 th 2006) –PRN #138 ANIK F1R (under testing)

Issues Accuracy Accuracy –Geo satellites are low on horizon accuracy may degrade in Canada-Alaska –Correction will decrease in accuracy with distance from reference station Costly - Costly - –Update airports and receivers –Installation of ground stations and satellites

Future Improvements Nine new Wide-area Reference stations Nine new Wide-area Reference stations –Summer 2007  3 Mexico  2 Canada –Fall 2007  2 Mexico  2 Canada

Sources Federal Aviation Agency website ( Federal Aviation Agency website ( –Papers  “Wide-Area Augmentation System Performance Analysis Report” April 2002  “DOD and FAA Specification for the Wide Area Augmentation System” August 2001 –Presentations  “WAAS” Dan Hanlon, Program Manager, April 2003  “Satellite Navigation Program” August 2000 Free Flight Systems Free Flight Systems – WIKIPEDIA WIKIPEDIA – Research Papers Research Papers –“Performance Analysis of GPS Positioning Using WAAS and EGNOS” Dr. Abousalem, Mr. Tubalin; Ashtech Precision Products, May 2000

Questions?