CSI Wireless Seres, Reference Manual

Page: 23 / 134

Seres Reference Manual
3
Note – When using a differential correction service, the resultant
position may be referenced to a local datum rather than the
WGS-84 ellipsoid. Please refer to your signal provider for more
information.
1.2.1 How it Works
DGPS involves setting up a reference GPS receiver at a point of known
coordinates. This receiver makes distance measurements, in real-time, to
each of the GPS satellites. The measured ranges include the errors present
in the system. The base station receiver calculates what the true range,
without errors, knowing its coordinates and those of each satellite. The
difference between the known and measured range for each satellite is the
range error. This error is the amount that needs to be removed from each
satellite distance measurement in order to correct for errors present in
the system.
1.2.2 Real-Time DGPS
The base station transmits the range error corrections to remote receivers
in real-time. The remote receiver corrects its satellite range measurements
using these differential corrections, yielding a much more accurate position.
This is the predominant DGPS strategy used for a majority of real-time
applications. Positioning using corrections generated by DGPS
radiobeacons will provide a horizontal accuracy of 1 to 5 meters with a
95% confidence. More sophisticated, short-range DGPS systems (10 to
15 km) can achieve centimeter-level accuracy, but are expensive and often
limited to precise survey applications due to technical constraints on their
use.
1.3 DGPS Format
For manufacturers of GPS equipment, commonality is essential to maximize
the utility and compatibility of a product. The governing standard
associated with GPS is the Interface Control Document, ICD-GPS-200,