We are investigating the use of directional antennas and beam steering techniques to improve performance of 802.11 links in the context of communication between a moving vehicle and roadside APs. We have developed a framework called MobiSteer that provides practical approaches to perform beam steering. MobiSteer can operate in two modes – cached mode – where it uses prior radio survey data collected during “idle” drives, and online mode, where it uses probing. The goal is to select the best AP and beam combination at each point along the drive given the available information, so that the throughput can be maximized. For the cached mode, an optimal algorithm for AP and beam selection has been developed that factors in all overheads. We have extensive experimental results using a commercially available eight element phased-array antenna. We performed experiments in controlled scenarios as well as in situ scenarios. In the controlled scenarios experiments, we use our own APs, in two different multipath environments and in situ scenarios we use APs already deployed in an urban region – to demonstrate the performance advantage of using MobiSteer over using an equivalent omni-directional antenna. We show that MobiSteer improves the connectivity duration as well as PHY-layer data rate due to better SNR provisioning.
A simple and useful application of our Mobisteer architecture is to localize WiFi networks (Neighborhood APs, Mesh Routers in city wide networks etc.. ) with a steerable beam directional antenna mounted on a car and drive by the locality slowly to recieve beacons from the APs passively.
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.
"Steerable Net access Aiming directional antennas the right way gives moving vehicles faster,longer-lasting wireless Internet access. In addition to better Net surfing in moving cars, the technique is a means for vehicles to communicate with each other and with roadside devices to improve traffic safety. (MobiSteer: Using Steerable Beam Directional Antenna for Vehicular Network Access, 5th International Conference on Mobile Systems, Applications, and Services (MobiSys 2007), San Juan, Peurto Rico, June 11-14, 2007)"
Some of the interesting things people thought and said when they saw the antenna on top of the car while we were doing experiments
* Why do you carry a cooler box on top of a car?? !!!
* Is it a satellite?
* Is it a weather station!!!??
* It looks very funny!