Friday, February 09, 2007

Wireless Sensor Networks in Practice – Discussion with Bob King

I recently had a discussion with Robert King of the Colorado School of Mines. Bob is an avid LabVIEW user and is currently performing work in the machine condition monitoring and the environmental monitoring area. In our discussion about wireless sensor networks, it appears that most of the available systems on the market are difficult to program. Text-based programming is a challenge for those not experienced with the chipsets used in wireless sensor network nodes. Also, setting up a network with different topologies to find the most optimal one for an application is not easily done. Most sensor networks on the market provide a star configuration and little more. The mesh network seems to be found primarily in basic research.

Wireless sensor networks do provide benefits even at the twenty to fifty node level. The first is wireline replacement. Wiring an application can cost anywhere from $20 to $2000 a foot depending on the wire and the environment. Also, wires come with connectors which require maintenance.

Construction sites are becoming an interesting application area for WSNs. To monitor for structural damage on adjacent buildings, engineers place sensors on the building and monitor vibrations and movements. Running wires on an existing building is an expensive proposition and a difficult one to do if the wires need to come out through the construction area.

A second advantage of a wireless sensor network over a wired network is its ability to change the network topology. Topologies range from star, to tree, to mesh. Each has its own advantages. The star is the easiest to implement but in long-range applications (carrying a signal over several miles), it is not practical – a mesh network is better suited for such an application. By placing the coordinator closer to the source of information, one can eliminate sending coordination information throughout the network and preserve node resources (memory, battery power, etc) for transmitting data.

Some users complain about the lost data that comes from using battery-powered nodes in an area crowded with other wireless signals. One way to mitigate lost data is to build redundancy into the system by adding additional nodes to the network for backup. As nodes fall in price, deploying additional nodes may solve the problem of nodes dropping out due to a run-down battery or an interfering EMI signal.

Best regards,
Hall T.