I Am the Antenna: Accurate Outdoor AP Location using Smartphones
Zengbin Zhang
Xia Zhou
Weile Zhang
Yuanyang Zhang
Gang Wang
Ben Y. Zhao
Haitao Zheng
Proceedings of The 17th Annual International Conference on Mobile Computing and Networking (MobiCom 2011)
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Paper Abstract
Today's WiFi access points (APs) are ubiquitous, and provide critical
connectivity for a wide range of mobile networking devices. Many
management tasks, e.g. optimizing AP placement and detecting rogue
APs, require a user to efficiently determine the location of wireless APs.
Unlike prior localization techniques that require either specialized
equipment or extensive outdoor measurements, we propose a way to locate APs
in real-time using commodity smartphones. Our insight is that by rotating
a wireless receiver (smartphone) around a signal-blocking obstacle (the
user's body), we can effectively emulate the sensitivity and
functionality of a directional antenna. Our measurements show
that we can detect these signal strength artifacts on multiple smartphone
platforms for a variety of outdoor environments. We develop a model for
detecting signal dips caused by blocking obstacles, and use it to produce a
directional analysis technique that accurately predicts the direction
of the AP, along with an associated confidence value. The result is Borealis,
a system that provides accurate directional guidance and leads users
to a desired AP after a
few measurements. Detailed measurements show that Borealis is significantly
more accurate than other real-time localization systems, and is nearly as
accurate as offline approaches using extensive wireless measurements.