WAAS G-III Reference Receiver User Manual Rev 1
15
Chapter 1
Introduction
The NovAtel G-III Reference Receiver is a high-performance receiver designed for installation as a core
component of Satellite-Based Augmentation Systems (SBAS). This chapter provides information on the
features and functionality of the G-III Reference Receiver and how it operates in the context of the SBAS
system.
1.1
SBAS Overview
A Satellite-Based Augmentation System (SBAS) is a safety-critical system designed to augment the
Department of Defense Global Positioning System (GPS) Standard Positioning Service (SPS). SBAS enhances
GPS service by providing:
• a ranging function to the SBAS satellites to improve signal availability and reliability
• GPS signal corrections to improve accuracy
• integrity monitoring to improve safety
The primary mission of the SBAS system is to provide a means for air navigation for all phases of flight in the
National Airspace System (NAS) from departure, through en route, and approach. The principal functions of
SBAS include:
• determining ionospheric corrections
• determining satellite orbits
• determining satellite clock corrections
• determining satellite integrity
• independent data verification
• SBAS message broadcast and ranging
• system operations & maintenance
As shown in
Figure 2
on
Page 16
, the SBAS system consists of a series of
Reference Stations
and
Master
Stations
, a
Ground Uplink Subsystem
, and
Geostationary Satellites
(
GEOs
). The
Reference Stations
, which are
strategically located to provide adequate coverage, record GPS satellite data and route it to the
Master Stations
.
The
Master Stations
then processes the data to determine the signal integrity, signal corrections, and residual
errors for each monitored satellite. This information is sent to the
Ground Uplink Subsystem
for transmission to
the
GEOs
, which then re-transmits the data on the L1 and L5 frequencies.
