SNUPI rhymes with snoopy – you’ll see why in just a moment. Perhaps you’re already familiar with the idea that electrical wiring can be used for a computer network. The technology has never ‘caught on,’ a few people use it though it’s never sold well, however, it works. SNUPI (Sensor Nodes Utilizing Powerline Infrastructure) is a clever variation of the idea. In addition to providing a network, the electrical power lines in a house, or anywhere for that matter, can also act as an antenna.
The two co-inventors-researchers, Shwetak Patel (University of Washington, USA) and Erich Stuntebeck (Georgia Institute of Technology, USA) discovered that home wiring is a very efficient antenna at 27 megahertz frequency. The efficiency and the fact that wiring is ubiquitous in almost every location within housing led them to believe that sensors using very low power transmissions could work in this environment. Such sensors would be small, inexpensive, and should be made so that a tiny battery could power them for a long time (as in years).
This approach solves one of the biggest problems for home automation – sensors that monitor various aspects of the home (temperature, humidity, air quality, light levels…) needed to transmit their signals far enough to be collected by a central device. This meant relatively large sensors with relatively large batteries, and they still don’t get much battery life.
To test their idea, Patel and Stuntebeck rigged each room of a 3000 square foot house (about 280 square meters) with five sensors. They found that only 5% of the house was out of range (compared to 23% for standard sensors). Their system also works to grounded pipes, that is, if the electrical system is grounded on the house’s pipes – the pipes also become part of the antenna. Most importantly, the SNUPI system used less than 1% of the power for data transmission than the next best standard model. The SNUPI sensors use less than 1 milliwatt of power for transmission. With standard watch batteries this could mean around a decade of use. Expensive medical grade batteries could last much longer.
No surprise that Patel and Stuntebeck are already commercializing the basic technology (read: selling the rights to make products from it).
When you look at home sensing, and home automation in general, it hasn’t really taken off,” said principal investigator Shwetak Patel, a UW assistant professor of computer science and and of electrical engineering. “Existing technology is still power hungry, and not as easy to deploy as you would want it to be.” That’s largely because today’s wireless devices either transmit a signal only several feet, Patel said, or consume so much energy they need frequent battery replacements. “Here, we can imagine this having an out-of-the-box experience where the device already has a battery in it, and it’s ready to go and run for many years,” Patel said. Users could easily sprinkle dozens of sensors throughout the home, even behind walls or in hard-to-reach places like attics or crawl spaces.
[Note for the paranoid: Almost every advance in sensor technology can be put to use for nefarious purposes. This one, using plain old electrical wiring and very small, long lasting low-power sensors seems like a natural for espionage. The low power might make it difficult to detect, especially if hidden among the signals of a house full of such sensors.]