How does GPS work?

Discussion in 'iPhone' started by Inukami, Aug 27, 2008.

  1. Inukami macrumors 6502

    Jul 11, 2008
    it doesn't use any internet right? is it by satelite or the ATT towers?
  2. sr5878 macrumors 6502a

    Jun 5, 2007
    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.
  3. skiesforme macrumors 6502


    Feb 4, 2008
    It's through satellites
    Conventional GPS's work like this?

    I guess iPhone GPS is A-GPS based on triangulation from Base Stations.
  4. Hawkeye411 macrumors 68000


    Jun 6, 2007
    Canada EH!!!
  5. Inukami thread starter macrumors 6502

    Jul 11, 2008
    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.
  6. kdarling macrumors demi-god


    Jun 9, 2007
    First university coding class = 47 years ago

    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.

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