Does Iphone 3g have actual GPS antenna? After reading arstechnica's...

Discussion in 'iPhone' started by Ride9650, Jul 15, 2008.

  1. Ride9650 macrumors 6502

    Jun 29, 2007
    review, I am mildly hesitant to purchase the phone because from what Ive heard, they're usually pretty reliable.

    Anyways they say in their review...

    "The iPhone's GPS is an Assisted GPS (A-GPS for short), which means that an Assistance Server is called over the cellular network to both offload and speed up the location acquisition process....both the old and new iPhone also can make use of cell tower triangulation, as well as a directory of WiFi hotspots provided by Skyhook Wireless for a third method of finding one's location. "

    Now I coulda swore A-GPS is the method that uses cell tower triangulation...and standard GPS uses satellites...and that the Iphone 3g is supposed to have a regular GPS radio....

    Though its not really a dealbreaker, itd be nice to know....

    Im confused...:confused:
  2. sr5878 macrumors 6502a

    Jun 5, 2007
    assisted gps is true gps. it just uses cell towers to hone in on the general area, reducing use of the power-draining gps antenna.
  3. Epix macrumors member

    Jul 10, 2008
    A-GPS simply uses cell phone towers to cut down on the time it takes to aquire a satellite signal.
  4. Pointer macrumors regular

    Jun 19, 2007
    If only we had a dollar for everytime somebody thought that A-GPS wasn't real GPS we'd be as rich as Steve Jobs.
  5. Ride9650 thread starter macrumors 6502

    Jun 29, 2007
    I currently have verizon and when I used to have a razr, I used VZ navigator, which from what I had read, used A-GPS, and used cell towers to triangulate my position, hence the confusion.

    anywho thanks for clearing that up guys !
  6. abijnk macrumors 68040


    Oct 15, 2007
    Los Angeles, CA
    That's where your confusion is coming in to play. Your undestanding is correct, but incomplete. :) It uses cell tower triangulation to get a general area, then the actual GPS antenna to get to the most accurate position.
  7. kkat69 macrumors 68020


    Aug 30, 2007
    Atlanta, Ga
    Main reasoning is just as above. Without a 'general' area the phone would need to call up to the sky, wait for a response and would need more than one sat to determine where you are, then continue to transmit/rec to get an accurate response. With A-GPS it can at least pinpoint your general location and talk to the sats easier.
  8. MBHockey macrumors 68040


    Oct 4, 2003
    New York
    Thread #680 on this exact topic. Simply stunning.
  9. kdarling macrumors demi-god


    Jun 9, 2007
    First university coding class = 47 years ago
    And still confusing. Tower triangulation is not A-GPS. Only satellite locating is.

    First, the basic precept of A-GPS is that the phone asks a server for information on which satellites are visible, and what their exact orbits and timing data are. Otherwise the phone would have to listen to each satellite for a minimum of 30 seconds to download the same data at a slow 50 bytes per second.

    Verizon's A-GPS works in two modes. The first, for 911 calls, is designed to be fast, to get help to you as quickly as possible. It does not use the data channel, but exchanges info over the phone control channels. For LBS, everything is done over data channels. If there's no GPS signal, Verizon falls back on cell tower triangulation.

    iPhone's A-GPS ... parts are unknown. For example, I'm not sure if it uses GSM control channel assistance lookup, or if it uses data channel comms. Either way, it supposedly gets satellite assistance first, and if it can't get a lock within a second or two, it falls back on the usual WiFi locator and then the cell id method. However, evidence exists that the latter methods aren't used if you're on 3G.

    As usual, Apple says nothing.
  10. kdarling macrumors demi-god


    Jun 9, 2007
    First university coding class = 47 years ago
    For many people, that's true only if it can also operate in autonomous mode.
  11. kdarling macrumors demi-god


    Jun 9, 2007
    First university coding class = 47 years ago
    Nothing transmits "up to the sky".

    GPS is receive only.

    Note to mods: I would've multi-quoted but responses came later.
  12. Michael CM1 macrumors 603

    Feb 4, 2008
    It's as if GPS doesn't stand for GLOBAL POSITIONING SATELLITE. The iPhone site says "Maps with GPS." I don't know how much clearer it could get. In fact, I would say that assisted GPS is better since you have 2 more types of points to figure out where you're at. If aliens hit the satellite, you can know where you are before Will Smith and Jeff Goldblum light their cigars.
  13. michaelmaxwell2 macrumors regular

    Jul 2, 2008
    The phone does have actual gps, its a hamerhead gps II chip,

    Attached Files:

  14. kdarling macrumors demi-god


    Jun 9, 2007
    First university coding class = 47 years ago
    That's correct... A-GPS means GPS is involved.

    See above. A-GPS = GPS. Cell id, wifi, etc ... not= GPS.

    GPS along with other forms of location = hybrid GPS, a totally different thing than regular A-GPS.
  15. Stuart in Oz macrumors 6502

    Jan 16, 2008
    Sydney, Australia
    GPS receivers don't transmit anything, as another poster pointed out. A short primer:

    Essentially the satellites emit messages specifying the exact location of the satellite, it's trajectory and speed, the time each message was sent and the rough location of all the other satellites in the constellation. By comparing this info to the time the signal was received a distance from the satellite to the receiver can be determined. When you have three or more satellites you can triangulate your location in three dimensions relative to the positions of the satellites.

    But in poor GPS reception areas (like cities) the parts of the GPS signal about location, speed and orbital trajectory tend to drop out first. A-GPS feeds that info, for every satellite in that part of the world, to the phone from a central database via the mobile network. Now the phone just has to search for the short timing signals from each satellite, which are easier to receive than the other parts of the transmission. Put the two lots of info together and bingo - location.

    A-GPS is designed to help the phone in poor GPS reception areas. Out in the open it won't be needed or used. In the city canyons it may help your phone position itself when it otherwise couldn't.

    PS - It also helps the men in dark suits to locate you. :rolleyes:
  16. robecq macrumors regular


    Jun 21, 2006
    Actually GPS stands for GLOBAL POSITIONING SYSTEM. But everything else is correct.
  17. Calmz macrumors newbie

    Jul 17, 2008

    Just wondering if the A-GPS needs the other 2 technologies(cell towers, and wifi) to be available before it can work.
    Reason asking is if I will be taking it overseas, and iPhone requires for A-GPS to work with say the cell towers, I can tell you that it won't be a cheap holiday! :p

    Calmz :D
  18. View macrumors regular

    Apr 18, 2007
    I don't think so. Cell tower/wifi locations are only used to speed up the process. But, if you're using google map, be sure you have wifi before you use the map, because data is expensive when roaming...
  19. Calmz macrumors newbie

    Jul 17, 2008

    Hey View,

    Thanks man!
    But what happened if I'm nowhere near say in the middle of small village ...the A-GPS will still work right??! I mean as long as it's not cloudy...well I hope so!.....

    Oh by the way, I kinda just realised, I think it may need the cell towers or wifi to load the maps right? So it may need wifi or cell towers after all?

  20. iVoid macrumors 65816

    Jan 9, 2007
    Exactly. A-GPS will work without any cell or WIFI service to give the iPhone your location on Earth. But Google Maps relies on a cell or wifi connect to download maps to display your location. So it knows where you are, but can't show you on a map.

    For isntance: The camera would still be able to geo-tag photos without cell/wifi connections being available.

    Other apps with built in maps will be available that would allow you to navigate without cell/wifi.

    I'm surprised there isn't a GPS app already that just allows you to get your current GPS coordinates (and maybe log where you've been for download later). That would seem to be very easy to do.
  21. Calmz macrumors newbie

    Jul 17, 2008

    Hi iVoid,

    Thanks for your reply. It kinda make sense to me since it's using googlemap.
    But I would have thought since iPhone has quite a bit of space for googlemaps to be installed or downloaded permanent into it.

    For all of those iphoneholics outhere who has the 3g version, can the googlemaps be saved permanently, so it doesn't have to keep going back to internet to load it up? or maybe any GPS software for iphone that has all the maps?

  22. Matti macrumors regular

    Nov 25, 2007

    Google doesn't own the map data. It only licenses it from TeleAtlas (stopped using Navteq data after Nokia bought Navteq).

    Google's license only includes streamed maps (the lack of turn by turn navigation is also for this reason).

    EDIT: Stored data or voice guided navigation would be more expensive. Google provides maps for free.
  23. yoman444 macrumors newbie

    Dec 25, 2010
    one more question

    can the gps work without cell phone towers or wifi? lets say geocaching in the wilderness?
  24. Rajani Isa macrumors 65816

    Rajani Isa

    Jun 8, 2010
    Rogue Valley, Oregon
    Should, as far as I know - main reason why Google Maps doesn't work off the network is it doesn't store the maps on the phone - it downloads them anew each time.

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