All iPads Why is GPS and Cellular combined and not seperate?

Discussion in 'iPad' started by PracticalMac, Dec 12, 2012.

  1. PracticalMac, Dec 12, 2012
    Last edited: Dec 12, 2012

    macrumors 68020

    Joined:
    Jan 22, 2009
    #1
    A number of Android tablets have GPS without Cellular.
    So why is Apple forcing you to get Cellular if you just want GPS?

    Some guesses I have is:
    Shared antennas.
    Cellular (Qualcomm?) chip includes both functions.
    A-GPS (using cellular to quickly download updated satellite data)

    or all of the above?


    Also a ? about A-GPS,
    does one get the satellite data even if you do not subscribe to cellular service???


    EDIT:Wiki says "For billing purposes, network providers often count this as a data access", so this suggest it does require subscription, but not conclusive.
     
  2. macrumors 65816

    WhiteIphone5

    Joined:
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    Location:
    Lima, Peru
    #2
    Or it's just marketing. You want GPS pay the extra $100
     
  3. macrumors G3

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    Location:
    Atlanta, GA
    #3
    It's combined because its the same SOC; System-On-A-Chip is a sigle component.

    A-GPS is just like regular GPS but it is assisted by cell towers and wifi networks to find your location quicker. The A doesn't mean they are downloading data, it just means the cell-towers triangulate your position quicker.
     
  4. PracticalMac, Dec 12, 2012
    Last edited: Dec 12, 2012

    thread starter macrumors 68020

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    #4
    That is incorrect.

    AGPS does not use Cell Towers for location.

    AGPS might use the signal quality measurements off *a* single tower, but it does not triangulate.
     
  5. macrumors 601

    Joined:
    Feb 9, 2011
    #5
    You're not really getting "satellite data". The signal from the GPS satellites is just used to determine location. If it's not using the GPS satellites to determine your location then it's not GPS whether it's standalone or aGPS. Most aGPS receivers can fall back on standalone mode if the Ephemeris data isn't available from the assistance servers for whatever reason.

    That's not entirely correct. It doesn't use cell tower triangulation but GPS is basically triangulation.
     
  6. thread starter macrumors 68020

    Joined:
    Jan 22, 2009
    #6
    According to Wiki on ephemeris, it does actually download data from satellites.
    And yes to be accurate, triangulation is done by satellites, not cell towers.
     
  7. macrumors 6502a

    Joined:
    Mar 31, 2012
    #7
    I've read some data from the cell towers is downloaded to more quickly establish location of satellites, so it can use some data. I need a reference though.
     
  8. thread starter macrumors 68020

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    Jan 22, 2009
  9. thread starter macrumors 68020

    Joined:
    Jan 22, 2009
    #9
    Found some answers:

    iPad 3 (and iPhone 5) use Qualcomm's RTR8600 multi-band/mode RF transceiver for 3G and 4GLTE bands which includes GPS services.

    I think it is because of the SoC in the RTR8600 one gets "aGPS" (AGPS)

    I do think the antenna is separate, however.

    Likely cheaper to used a combined system then separate chips.

    Any other opinions?
     
  10. macrumors 601

    Anonymous Freak

    Joined:
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    Location:
    Cascadia
    #10
    That's certainly the reason it's true in the iPad - no dedicated GPS chip. Any other answers are Apple business decision speculation.
     
  11. macrumors 6502

    Joined:
    Jun 13, 2008
    #11
    The wireless module is neither part of the SoC nor is it what you would generally classify as a system on a chip. The module does not function on its own. You might get away with 'ASIC' if you need a label.
    It listens for, receives, and inteprets data from satellites, but to call that a "download" in the sense it is usually understood isn't really common usage, just like you don't generally say that your TV "downloads" broadcast transmissions.
    The triangulation is actually done in the receiver, to be accurate. Neither the cell tower nor the satellite actually interacts with the phone for location purposes.

    It's not the SoC; it's the fact that the package is part of the integrated logic. Almost every device with GPS and cellular data connectivity uses aGPS in some capacity--it would be foolish not to take advantage of that.
    Cheaper, less redundant, more space-efficient, more power-efficient, and better integrated into a mobile device.

    The standalone GPS chips that you might find in a TomTom or Magellan GPS are not really suitable for a mobile device.
     
  12. macrumors 601

    ActionableMango

    Joined:
    Sep 21, 2010
    #12
    Simple, concise, and accurate.

    Clearly you do not belong on the Internet.
     
  13. thread starter macrumors 68020

    Joined:
    Jan 22, 2009
    #13
    Excellent details, thanks!

    one items puzzles me.
    It sounds like the GPS will "build" a library of data listening to the satellites.

    But for Assisted, does it instead receive a file of like data?

    I also assume if in with Wi-Fi connection to internet it will also download the data (as in Cell is turned off).
     
  14. macrumors 6502

    Joined:
    Jun 13, 2008
    #14
    No problem!
    Not a persistent library. GPS satellites constantly broadcast a bunch of information, but it's only one way. The satellites constantly tell you where they are and what time it is, with an extreme amount of precision. It doesn't do any good for the GPS receiver to log data into a historical library--all of the satellite data is basically useless once it's transmitted, except for certain details that only change every few hours or days.

    The receiver listens to that data and compares the timestamp of the satellite to the time when the message is received. Knowing the location of the satellite and how long it took to receive the signal tells you where you are on the planet.

    It takes a comparatively long time to listen for long enough to get all the location information from the satellite, because it is a fairly low bandwidth transmission. That's where assisted GPS comes in.
    Radio transmissions from the satellites are slow. Terrestrial radio transmissions, even on relatively bandwidth-constrained 2G/3G networks, is much faster. In a nutshell, assisted GPS gets data on the location of GPS satellites from cell towers or other sources, rather than waiting for the complete set of data on the slow satellite signal.

    That's what makes it faster to find your location with aGPS.
    That depends on the specific GPS hardware and software in your device. Some get their data over the Internet and some get it only from the cell towers.
     
  15. macrumors 601

    Anonymous Freak

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    Cascadia
    #15
    That's the first time that has been said about me.

    Uh......

    Thanks?

    :D
     

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