Assisted GPS is better than normal GPS and mainly helps the TTFF or Time To First Fix. Some pure GPS units that have a SiRF III chip, can take 30 seconds or more because it is dependent on your location, the amount of interference, and horizon information. It also takes a large number of satellite acquisitions because it doesn't know general location on cold start. So, in a large city, a full GPS system using SiRF III or anything like it will take longer than if you were out in the desert for example. Normal GPS also eats more power because of the constant acquisition of satellites ... and indoor use is limited.
aGPS takes information from the cell network to triangulate your general location from multiple towers. Since the phone has the GENERAL location from tower triangulation and other sources, it doesn't have to acquire as many satellites since it has most of the information it needs. It works better in doors because of an easier "fix" due to general location already determined by the cell network. And .... you also get better battery life because constant acquisition is not required.
Other than that ... aGPS and GPS are pretty much similar. Try it. Get a pure GPS unit and see how long it takes in-doors from a COLD START. Then get a known aGPS unit from a mobile phone and see how it works in the same in-door building. The aGPS will get a fix faster with few satellites ... well, if the pure GPS unit even makes it. LOL
|