How does GPS work?

[Inukami]

it doesn't use any internet right? is it by satelite or the ATT towers?

[sr5878]

gps uses global positioning satellites in space.

a-gps uses gps satellites in space, but also local AT&T towers to triangulate your position.

google maps requires an active edge, 3g, or wifi connection to access map data.

[skiesforme]

it doesn't use any internet right? is it by satelite or the ATT towers?

It's through satellites
Conventional GPS's work like this? (http://www.google.com/search?q=how+does+GPS+work&ie=utf-8&oe=utf-8&aq=t&rls=org.mozilla:en-US:official&client=firefox-a)

I guess iPhone GPS is A-GPS based on triangulation from Base Stations.

[Hawkeye411]

I believe that it uses both.

[Inukami]

gps uses global positioning satellites in space.

a-gps uses gps satellites in space, but also local AT&T towers to triangulate your position.

google maps requires an active edge, 3g, or wifi connection to access map data.

so an unlocked 3G iphone using prepaid ATT sim card would be able to use this or not? It would use Edge/3G if available in the area but what kind of Edge/3G are we talking about. Just normal frequency or internet.

[kdarling]

Stop.

A-GPS does NOT use cell towers for triangulation. GPS uses satellites. Period.

The only difference with A-GPS is that the phone can get assistance (the "A") obtaining information about the satellites in view and their orbits. This is normally received over many minutes from the satellites themselves. Assistance cuts that time to mere seconds. Cell id can also help with a vague starting location, but is not necessary for GPS to work.

The satellite info assistance can come from the carrier over signaling channels, or over the internet via a data channel. Depends on the implementation.

After the initial assistance, most smartphones go into standalone GPS mode until they need updated sat info again (a few hours).

If GPS or A-GPS cannot get a lock on enough satellite signals, then the phone could resort to cell id or wifi locating... or the carrier in some cases will use towers for locating (especially for E911)... none of which are A-GPS.

In the case of Google maps, data access is needed to download the images.