City to host Harvard wireless sensor network

Researchers in Massachusetts plan to build an urban network using 100 street-lamp sensors by 2011

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

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

The researchers plan to install 100 sensors on street-lamps throughout the city of Cambridge, Massachusetts by 2011, using a grant from the US National Science Foundation. Each node will include an embedded PC, an 802.11a/b/g wi-fi interface and a collection of weather sensors, says 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 street-lamp 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 bigger challenge is 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 neighbours, 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-kilometre range, Welsh says. 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 64Mb of RAM and 1Gb of flash memory, loaded on a motherboard made by Soekris Engineering of California and packaged by Metrix Communication of Washington.

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

“Think of it like a virus infecting all the nodes. Every node can talk to its neighbour and pass along the data and, eventually, you get your programme up and running on all of them,” Welsh says.

In turn, the servers post the database information online. In a separate announcement, Microsoft said it would overlay the data on to maps using its Virtual Earth and SensorMap technologies. This 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 says.

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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