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GPS
HOW GPS WORKS
Currently, the GPS constellation consists of 26 orbiting satellites (including 3 spares), but this nu
mber will increase in the future.
The GPS receiver computes an accurate position by calculating the distance to the GPS satellit
es that orbit the earth. Signals are required from 3 satellites for two dimensional (2D) position
calculation whilst 4 satellites are required for three dimensional (3D) position calculation.
As mentioned earlier, GPS satellites are not geostationary, but they are orbiting the earth as illu
strated on the following figure:
[The GPS constellation]
Note that position is repeatedly fixed through the following three steps while any 3 satellites are
in line of sight.
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