The Global Positioning System !

taki.tsikhist

Hi everybody, i am new here and reeeally looking for the help:)
in about 3 days, i have a junior project in physics about Global Positioning System. I have already sent the written part, where i only covered Trilateration and talked a little about satellites and how they help to locate.. Can somebody tell me what else is essential to cover? I would add it during the presentation..
Thanks!