Wednesday, September 19, 2012

Does your iPhone Really Know Where you are?


It may seem as though your phone can pinpoint your exact location, but the real answer is no, your “phone” does not know where you are. However your iPhone does use a combination of three different programs (A-GPS, WiFI Positioning, and Cellular Network Positioning) that all work together to roughly estimate your phones location at the time the GPS or Navigation application (Ap) is being used. 

When the first iPhone had been released there was only one complaint, no GPS feature. The technology for a device that used GPS was already in existence but the integration between phone and GPS had not yet been introduced. A year later the iPhone 3G was released which included a GPS application. 

After an article was released by Paul A Zandbergen on how the iPhone 3G uses A-GPS, WiFI Positioning, and Cellular Network Positioning to determine your location it was better understood that the phone itself does not know your location; it is the opening of the GPS Ap that configures the three programs to find your location. Once the configuration between the three had become available more applications began to integrate it for their own purposes. Some of these are “Restaurant Finder”, “Facebook”, “Weather Now”, etc.  

The three programs used for the configuration process overlap to get a more accurate reading on your location. A – GPS or Assisted GPS uses “many of the functions of a full GPS receiver, [but mostly] are performed by a remote GPS location server. This remote server provides the A-GPS mobile device with satellite orbit and clock information” (Zandberbergen, 2009). Just using A – GPS still provides a bit of inaccuracy compared to a GPS only device.
 “WiFi positioning uses terrestrial based WiFi access points (APs) to determine location” (Zandberbergen, 2009). These “terrestrial access points” are signals that your phone emits when using certain Ap’s. Because of the vast amount of people always on their phones using these applications it often causes an overlap in signals “creating a natural reference system for determining location.” 
Cellular positioning uses cells and towers to estimate your location. “When a user connects to the network, the mobile device is allocated to the base station transmitting with the strongest field strength. The most basic form of cellular positioning is to use the (known) location of this base station” (Zandberbergen, 2009). Because it only allocates your position to the closest tower or base your actual location is often off by a couple of miles.

So individually each program is slightly flawed which makes it undesirable to the user. In order to get a product that is accurate Apple merged the three programs together to give you the GPS system your phone currently uses to give the best accuracy. 
 Zandberbergen, P. A. (2009). Accuracy of iPhone Locations: A Comparison of Assisted GPS, WiFI, and Cellular Positioning. Transactions in GIS, 13, 5-25.

1 comment:

  1. Being one who does not use these nifty, high-tech, internet friendly touch phone-a-migigers, I am very interested in investigating their usefulness and reliability as the means for such popularity. I consider their GPS function a largely useful application of the iPhone, second only to their ability to allow for instant communication (the basic function of a cellular phone). It is very interesting to learn about the "overlapping signal fingerprints" that results from wide range use of this GPS application which helps to create a natural reference database of location. It is also very interesting to me that their GPS functions are not a sound as one would believe at first. I see friends using this function on the iPhone often and it seems to work decently well for them, though I have seen error before. It seems like this current merger of the three basic programs for GPS positioning is the best answer to creating a decently reliable GPS function for the iPhone. As we move into the future, I will be very interested to see how companies, such as Apple, will improve the accuracy and reliability of this iPhone application.

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