User's Manual Part 1

78 OEMV Family Installation and Operation User Manual Rev 5B
Chapter 5 Positioning Modes of Operation
and so on). However, because a receiver makes all of its
single-point pseudorange measurements using the same
common clock oscillator, all measurements are equally
offset, and this offset can generally be modeled or quite
accurately estimated to effectively cancel the receiver
clock offset bias. Thus, in single-point positioning,
receiver clock offset is not a significant problem.
• Multipath Signal Reception Multipath signal reception can potentially cause large
pseudorange and carrier phase measurement biases.
Multipath conditions are very much a function of
specific antenna site location versus local geography and
man-made structural influences. Severe multipath
conditions could skew range measurements by as much
as 100 meters or more. Refer to the Multipath section of
the GPS+ Reference Manual for more information.
5.2 Satellite-Based Augmentation System (SBAS)
A Satellite-Based Augmentation System (SBAS) is a type of geo-stationary satellite system that
improves the accuracy, integrity, and availability of the basic GPS signals. Accuracy is enhanced
through the use of wide area corrections for GPS satellite orbits and ionospheric errors. Integrity is
enhanced by the SBAS network quickly detecting satellite signal errors and sending alerts to receivers
to not use the failed satellite. Availability is improved by providing an additional ranging signal to
each SBAS geostationary satellite.
SBAS includes the Wide-Area Augmentation System (WAAS), the European Geo-Stationary
Navigation System (EGNOS), and the MTSAT Satellite-Based Augmentation System (MSAS). The
Chinese SNAS and Indian GAGAN systems are also planned. At the time of publication, there are
three WAAS satellites over the Pacific Ocean (PRN 122, PRN 134 and PRN 135), an EGNOS satellite
over the eastern Atlantic Ocean (PRN 120) and another EGNOS GEO satellite over the African mid-
continent (PRN 124). SBAS data is available from any of these satellites and more satellites will be
available in the future.
 Since July, 2003, WAAS has been certified for Class 1/ Class 2 civilian aircraft navigation.
Figure 24, SBAS and NovAtel 2006 on Page 79 shows the regions applicable to each SBAS system
mentioned in the paragraph above and how NovAtel is involved in each of them.