Drive-by localization of roadside WiFi networks

We use a steerable beam directional antenna mounted on a moving vehicle to localize roadside WiFi access points (APs), located outdoors or inside buildings. Localizing APs is an important step towards understanding the topologies and network characteristics of large scale WiFi networks that are deployed in a chaotic fashion in urban areas. The idea is to estimate the angle of arrival of frames transmitted from the AP using signal strength information on different directional beams of the antenna - as the beam continuously rotates while the vehicle is moving. This information together with the GPS locations of the vehicle are used in a triangulation approach to localize the APs. We show how this method must be extended using a clustering approach to account for multi-path reflections in cluttered environments. Our technique is completely passive requiring minimum effort beyond driving the vehicle around in the neighborhood where the APs need to be localized, and is able to improve the localization accuracy by an order of magnitude compared with trilateration approaches using omni-directional antennas, and by a factor of two relative to other known techniques using directional antennas.