Researchers are calling it ambient backscatter, since the new system takes advantage of TV and cellular transmissions already surrounding us. By reflecting the existing signals to exchange information, two devices can communicate with each other. The engineers built small, battery-free devices with antennas that can identify, exploit and reflect a TV signal, which then is picked up by other similar devices.
“We can repurpose wireless signals that are already around us into both a source of power and a communication medium,” said Shyam Gollakota, lead researcher. “It’s hopefully going to have applications in a number of areas including wearable computing, smart homes and self-sustaining sensor networks.”
Smart Sensors and Wearable Messaging
“Our devices form a network out of thin air,” co-author Joshua Smith said. “You can reflect these signals slightly to create a Morse code of communication between battery-free devices.”
Smart sensors could be made and located permanently within almost any structure, then set to communicate with each other. For instance, sensors placed in a bridge span could monitor the health of the concrete and steel, then send an alert if one of the sensors detects a hairline stress crack.
The technology could also be used for communication; text messages and emails, for example could be sent from wearable devices, without needing a battery.
Ambient Backscatter Testing
The ambient backscatter technique was tested using credit card-sized prototypes placed within several feet of each other. For each device the researchers built antennas into ordinary circuit boards that flash an LED light when receiving a communication signal from another device.
Clusters of the devices were tested various settings around the Seattle area; this included inside an apartment building, on a street corner and on the top level of a parking garage. These locations ranged from less than half a mile away from a TV tower to about 6.5 miles away.
The researchers demonstrated the devices were able to communicate with each other, even the ones farthest from a TV tower. The receiving devices picked up a signal from their transmitting counterparts at 1 kilobit per second when up to 2.5 feet apart outdoors and 1.5 feet apart indoors. This is sufficient to send information such as a sensor reading, text messages and contact information.
It would also be possible to embed this technology in devices that rely on batteries, such as smartphones. It could be designed so that when the battery dies, the phone could still send text messages by leveraging power from an ambient TV signal.
Ambient Backscatter: Wireless Communication Out of Thin Air (pdf) Vincent Liu, Aaron Parks, Vamsi Talla, Shyamnath Gollakota, David Wetherall, Joshua R. Smith University of Washington
_ photo courtesy University of Washington _
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