Raymarine RAYSTAR 120, Owner'S Handbook Manual, Page: 8 / 26

1-2 Raystar 120 GPS Receiver
The combination of the WAAS, EGNOS and MSAS systems will
provide global satellite based differential GPS augmentation into the
future.
How it Works
The following description is based on WAAS, but the principles
apply equally to the EGNOS and MSAS systems.
WAAS comprises the following components:
• Ground Reference Stations across the USA
• Master Stations located at East Coast and West Coast
• Geostationary Satellites located above the equator
The Ground Reference Stations are located at known positions and
receive data continuously from GPS. The Ground Reference Stations
send their data to the Master Stations which calculate the error of the
GPS-received positions and generate correctional data.
The corrected ‘differential’ signals are then sent to the two
Geostationary Satellites which broadcast the corrected data on the
standard GPS frequency, making it available to the user’s
Raystar 120 GPS Receiver.
The Raystar 120 GPS Receiver uses the correctional data transmitted
by the Geostationary Satellites to refine the GPS positional data for
greater accuracy.
WAAS is shown diagramatically in Figure 1-2 .
81170_2.BOOK Page 2 Thursday, July 19, 2001 2:36 PM