User's Manual

Table Of Contents
Chapter 5: Configuration
AGPS (Assisted Global Positioning System)
Psion Teklogix Omnii Hand-Held Computer User Manual 151
5.9.4 AGPS (Assisted Global Positioning System)
To determine your location, a GPS module receives data from three or more GPS satellites
in fixed orbit around the Earth. The GPS module triangulates your location based on the
time it takes for signals to get to and from the satellites. This works well in fairly clear areas,
outdoors for example. However, if you’re attempting to triangulate your location in city
centres where signals bounce off tall concrete buildings or from within a building, the GPS
module will have greater difficulty calculating a fix.
AGPS reduces Time To First Fix (TTFF) and increases the likelihood of finding and keeping
a fix in poor coverage areas such as indoor sites. AGPS downloads satellite ephemeris (or-
bital) data to Omnii periodically through Wi-Fi or WWAN. The downloaded data is used by
the GPS module to speed the process of getting a fix.