Primer: Wireless Sensor Networks

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What are they? Groups of devices that send data from sensors, like temperature gauges, to a central application using wireless protocols. They can also send commands to devices based on current conditions; for example, if a hotel room is unoccupied, the air conditioning unit could be instructed to shut off, to reduce electricity costs.

Haven't electronic sensors been around for decades? Yes. What's new are relatively low-cost, low-power wireless radios that make it possible to collect information from sensors without having to string power or data wiring to each sensor. Wireless sensor nodes can operate on ordinary batteries and configured to send data intermittently (say, every 5 minutes) to conserve power. Companies selling such products claim a node with two AA batteries can last up to five years. In addition, wireless sensor nodes can relay data to each other, creating a mesh network that eliminates the need for multiple transmitters, which higher-speed wireless networks typically require.

Who are the vendors? They fall into three categories. First are startups such as Crossbow Technology, Dust Networks, Millennial Net and Sensicast Systems, which provide the devices and software to build and manage wireless sensor networks. Next are companies that manufacture low-powered wireless networking chips for those systems, including Chipcon, Ember and Freescale Semiconductor (formerly part of Motorola). Finally, companies like General Electric and Honeywell International deliver wireless sensor networks that work with their industrial and commercial equipment.

Where are they being used? Initially, where wired sensors have been used: in building automation (i.e., to turn on lights when someone walks into a room) and industrial automation (i.e., to shut off a machine if it starts to overheat). But there are other applications. For example, grocery chain Supervalu is using devices from Dust Networks in one of its Minneapolis stores to measure the energy consumption of its equipment to see where it could conserve power.

Are there standards? A few. The Institute of Electrical and Electronics Engineers (IEEE) has defined a standard for low-power, low-data-rate wireless data transmission called 802.15.4. It provides a way to send up to 250 kilobits of data per second, which is only 2% of the bandwidth provided by a typical Wi-Fi wireless network but is ample for sending something like a temperature reading every few minutes. Meanwhile, the ZigBee Alliance (www.zigbee.org), a consortium of technology companies, has created a specification for sending control and status information over low-data-rate wireless networks.

What's not standardized? Vendors including Dust Networks, Millennial Net and Sensicast have created their own proprietary protocols for routing data among wireless sensor networking nodes and minimizing the power a node consumes. In fact, for now it's one of their key points of differentiation.

So how much does this cost? It's not exactly dirt cheap. Individual wireless nodes can sell for $30 to $50 apiece. However, the more sophisticated your setup, the pricier it becomes: Deploying a wireless network with industrial sensors (such as flowmeters, which measure the volume of delivery of a liquid or gas) in a manufacturing facility can run about $300 to $500 per sensor, according to Sensicast. Suppliers expect costs to come down eventually, as the technology becomes more widely adopted and unit volumes increase.

This article was originally published on 2005-10-01
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