Why A-GPS and Wi-Fi are the top mobile location data sources for accuracy
In a post last week, we mentioned that mobile location data provided by A-GPS and Wi-Fi has been proven to be the most accurate and reliable. So, what’s the basis for this claim? Let’s dive in a little further.
Under optimal conditions, Assisted Global Positioning System (A-GPS) technology provides the highest accuracy among location sources available on most mobile devices. A study of A-GPS accuracy on mobile phones found that the median error ranges from 5 to 8.5 meters, depending on the device type1.
Because of the space and power constraints, the GPS antenna and chipsets aren’t as effective on a phone as in a standalone GPS device, which has a median accuracy between 2 and 3 meters1.
On the other hand, because of the “assist” that A-GPS receives from its cellular network connection, it has greatly reduced “time to first fix” compared to standalone devices.
However, while A-GPS works well in open spaces with direct line-of-sight to the sky, its accuracy suffers in “urban canyons.” It’s usually either impossible or very difficult to get a location fix indoors and in crowded urban areas.
Bluetooth and Indoor Positioning Systems can provide highly accurate indoor positioning, but very few places are setup with these technologies.
With the increase in Wi-Fi access, Wi-Fi positioning has become quite effective. In an independent study of Wi-Fi position accuracy, the median position accuracies ranged from 43 to 92 meters, depending on the area of the study2.
This approach is based on a Wi-Fi “fingerprint” — a list of all the Wi-Fi access points visible to a device and their corresponding signal strengths. In a calibration phase, Wi-Fi fingerprints and their corresponding GPS locations are recorded around locations planned for Wi-Fi positioning. Over time, the library of these fingerprints grows.
When a Wi-Fi device needs to be geographically located, the new Wi-Fi fingerprint is aligned with the closest matching fingerprints in the library to get an estimated location. In practice, Android devices send their Wi-Fi fingerprints to a Google server, which sends back a predicted location, while iOS devices send their requests to an Apple server.
Accurate location data influences audience targeting, which greatly impacts mobile campaign results. While there are many potential sources of data, they’re not all equal.
1. Positional Accuracy of Assisted GPS Data from High-Sensitivity GPS-enabled Mobile Phones | Paul A. Zandbergen and Sean J. Barbeau | The Journal of Navigation, Vol. 64, No. 3 | July 2011 2. Comparison of WiFi Positioning on Two Mobile Devices | Paul A. Zandbergen | Journal of Location Based Services, Vol. 6, No. 1 | March 2012
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