Wide Area System Increase

WAAS ( Wide Area Increase System ) corresponds to a request of Federal Aviation Administration of the USA: it aims to reach a precision of 3m in horizontal and vertical absolute positioning. This system comprising 3 geostationary satellites will be fully operational in 2003 and will ensure a free permanent service whatever the weather conditions: the phase of test (26/01 - 3/31/2003) makes it possible to currently carry out the last adjustments.

It comprises 25 stations on ground (WRS: Wide area Refers Stations) collecting and transmitting their data to two principal stations (WMS: Wide area Master Stations, located on the west coasts and Is). Corrections of clock, orbits of the satellites GPS, ionospheric and tropospheric are calculated, then transmitted at the same time as of information of integrity relating to the health of the satellites GPS to the geostationary satellites via stations of transmission (GUS: Group Uplink Stations). A message is transmitted by the three satellites on the frequency L1 (1575,42 MHz) compatible with the structure of the signal GPS; it can be read by all receiving GPS without complementary equipment of reception WAAS.

Objectives of WAAS for the FAA:

To support takeoffs, approaches, landings, operations by all times,
Guidance of the planes in particular in the vertical component
To reduce the distance between planes, air lanes…: densifier and to improve traffic circulation.

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