Thursday, August 7, 2008

Reason for "online" need of GPS found?

iPhoneatlas reports that there is a function to "call home" hidden somewhere in core location. Obviously, this is used to revoke "bad" applications distributed trough App Store.

So, might this be the reason for GPS to work only when connected to a cellular network? I don't think so, because you just have to have reception of a cellular network for the GPS to work but there is no need to have working connection to the internet.

By the way, I've got no response yet to my inquiry to Infineon and I somehow doubt there will be one at all... With further information on the chipset, I could determine whether you need cellular network in order to have working GPS and if this could be changed to standalone or not.


  1. You don't need the "reception of a cellular network" for the GPS to work. It works also fine, if there is "No Service" for the iPhone.

  2. You sure do need reception of a cellular network!

    Please, don't mix up reception of a network and actually being logged onto a certain network. That isn't the same thing.
    The iPhone needs to "see" a cellular tower (which can be "seen" by receiving cell phone tower radio signals, which is actually the reception of a cellular network) in order to provide a GPS position.

    So, if you turn your phone into flight mode, you won't be able to get a GPS position.

    This could only be cross checked if you were able to go somewhere without reception of any cell tower. I still have to figure out where this might be ;-)

  3. Well, isn't there a difference between an accurate GPS position with A-GPS and a GPS position without assistance, which takes longer to capture and is not that accurate. But the latter should still work without an cell towers.

  4. Well, as the name denotes, A-GPS is an assisted GPS. A GPS with an assistance.

    With A-GPS, you definedly will get a fix faster than using a standard GPS receiver. Also, the positional information may be more accurate than using a GPS receiver without A-GPS, but the emphasis is on "may" (for example, my Garmin will easily aquire a position that is accurate up to 2 meters and doesn't even know of A-GPS).

    Sure, GPS works without any cell towers, but you are missing the point here. What if the iPhones GPS wasn't meant to work without cellular reception at all?

    At this time, I think the implementation of Core Location does this: it infinitely tries to acquire a cell tower based location and not till this is acquired a GPS based evaluation is tried. So still, no cellular network means no location information.

    Once again: this is a software issue, not a hardware or (A-)GPS one.
    I hope this is subject to change with iPhone OS 2.1, because I find it a bit stupid (yeah, wouldn't it be nice to use GPS in an airplane?).

    Unfortunately, Infineon still doesn't respond to my inqiry, so I can't have a look at the protocols their chipset actually "talks".
    Maybe, some day I will find the time to have a closer look to all this hardware stuff...