ABSTRACT
All these augmentation systems operate on the
principle of numerous ground stations in known
geographical positions receiving GPS signals.
Correction signals are then sent to users in a
variety of ways. The wide area augmentation
system (WAAS) was developed specifically for
aviation users and is intended to enable GPS to be
used in airspace that requires high integrity,
availability and accuracy. WAAS improves a
GPS signal accuracy of 20 metres to
approximately 1.5 metres (typical) in both the
horizontal and vertical dimensions. WAAS is
based on a network of reference stations around
the world that monitors GPS signals and
compares them against the known position of the
reference stations. These reference stations
collect, process and transmit this data to a master
station. Updated data is then sent from the master
station via an uplink transmitter to one of two
geostationary satellites; the aircraft receiver
compares this with GPS data and messages are
sent to the crew if the GPS signal is unreliable.
