Researchers look to root out those annoying Wi-Fi dead zones

Researchers at Rice University and Hewlett-Packard Laboratories say they have come up with a technique to eradicate those infuriating Wi-Fi dead zones that can crop up in large scale wireless deployments.

The general idea behind the research is to make it cheaper and easier to get proper wireless coverage in a large urban area using readily available information, the researchers said. Basically that means using a small number of measurements to predict how well a wireless transmitter will cover a particular portion of a neighborhood. The only information required is basic topography, street locations and general information about land use, researchers said.

The researchers also demonstrated their new method on two high-profile networks -- Google's system in Mountain View, Calif., and an experimental network designed and built by Rice and owned and operated by Houston-based nonprofit Technology For All.

Specifically, in a paper presented at the recent MobiCom 08 show, the researchers stated:  "Assessment of deployed networks must address two key issues: Non-uniform physical-layer propagation and high spatial variance in performance. Our framework estimates a mesh node's metric region via a data-driven sectorization of the region. We find each sector's radius with a two-stage process of estimation and then measurement-driven, push-pull refinement of the estimated boundary. To address high spatial variation, our coverage estimation couples signal strength measurements with terrain information from publicly available digital maps to estimate propagation characteristics between a wireless node and the client's location.

To limit measurements and yield connected metric regions, we consider performance metrics (such as signal strength) to be [uniform] with distance from the wireless node within each sector. We show that despite measured violations in coverage, we obtain high accuracy with this assumption.

We validate our estimation and refinement framework with measurements from 30,000 client locations obtained in each of two currently operational mesh networks, Google-Wi-Fi and TFA. We study three illustrative metrics: coverage, modulation rate, and redundancy, and that to achieve a given accuracy, our framework requires two to five times fewer measurements than grid sampling strategies. Finally, we use the framework to evaluate the two deployments and study the average size and location of their coverage holes as well as the impact of client association policies on load-balancing."

"In the real world there are many things than can interfere with signals and limit coverage," said lead researcher Edward Knightly, professor in electrical and computer engineering at Rice. "Our goal was to efficiently characterize the performance of urban-scale deployments, and our techniques can be used to either guide network deployment or to assess whether a deployed network meets its performance requirements."

How all this is used in the real world remains to be seen.

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