Cambridge to host wireless sensor network

Researchers at Harvard University and BBN Technologies have designed a wireless network capable of reporting real-time sensor data across an entire city, they said Friday.

Scientists will initially use the CitySense network to monitor urban weather and pollution, and the network could eventually be adopted to provider better public wireless Internet access.

The researchers plan to install 100 sensors by 2011 on streetlamps throughout the city of Cambridge, Massachusetts, using a grant from the U.S. National Science Foundation. Each node will include an embedded PC, an 802.11a/b/g Wi-Fi interface and a collection of weather sensors, said Matt Welsh, assistant professor of computer science at Harvard's School of Engineering and Applied Sciences.

The system solves a constraint on previous wireless networks -- battery life -- by mounting each node on a municipal streetlamp where it draws power from city electricity. That approach opens up a new range of uses for the sensors, performing long-term experiments like real-time environmental monitoring, correlating micro-climates with population health, or tracking the spread of bio-chemical agents, according to BBN.

A larger challenge was how to design a network that allows remote nodes to communicate with the central servers at Harvard and BBN. CitySense will do that by allowing each node to form a mesh with its neighbors, exchanging data through multiple-hop links. That strategy allows a node to download software or upload sensor data to a distant server hub using a small radio with only a one-kilometer range, Welsh said. A prototype of the network is already running on five CitySense nodes installed in Welsh's second-floor laboratory on the Harvard campus.

Each CitySense node includes an embedded single-board computer running the Linux OS with 64M bytes of RAM and 1G-byte of flash memory, loaded on a motherboard made by Soekris Engineering Inc. of Santa Cruz, California, and packaged by Metrix Communication LLC of Seattle, Washington.

People have built such networks on smaller scales before, but have used them for private purposes or to provide wireless Internet links in towns such as Madison, Wisconsin, and Champaign, Illinois, Welsh said. In contrast, CitySense will allow academic researchers from around the world to log onto the project Web site and submit their own research programs to run on the nodes.

"Think of it like a virus infecting all the nodes. Every node can talk to its neighbor and pass along the data, and eventually you get your program up and running on all of them," Welsh said.

In turn, the servers post the database information online. In a separate announcement Thursday, Microsoft Corp. said it would overlay that data onto maps using its Virtual Earth and SensorMap technologies. That will allow scientists to track pollution spread by weather and wind on the city block level -- offering them sharper resolution and a longer time span for monitoring than they have had before. The only way researchers can collect such data today is to carry backpacks loaded with sensors, batteries and global positioning system (GPS) trackers as they trudge around the city, Welsh said.

The CitySense network will initially track environmental variables like temperature, wind speed, rainfall, barometric pressure and air quality. Future applications could use virtually any type of sensor, from those that count airborne contaminants to microphones that measure noise pollution. The network could even grow to include mobile sensors attached to cars and buses.

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