15 August 2013

No power source needed for new wireless communications technique

by Will Parker

A new wireless communications technique uses what researchers call "ambient backscatter" to allow devices to communicate and exchange information with each other by reflecting (or absorbing) existing radio and television signals. Impressively, the devices do not require any power source apart from the existing ambient radio and TV signals that already surround us.

"We can repurpose wireless signals that are already around us into both a source of power and a communication medium," said lead researcher Shyam Gollakota, from the University of Washington. "It's hopefully going to have applications in a number of areas including wearable computing, smart homes and self-sustaining sensor networks."

The researchers detailed the technique at the Association for Computing Machinery's conference held last week in Hong Kong. They received the conference's best-paper award for their work.

The ambient backscatter technique was demonstrated with credit card-sized prototype devices 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.

Groups of the devices were tested in a variety of settings in the Seattle area, including 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.

They found that 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 a rate of 1 kilobit per second when up to 2.5 feet apart outdoors and 1.5 feet apart indoors. This is far enough to send information such as a sensor reading, text messages and contact information.

"Our devices form a network out of thin air," explained co-researcher Joshua Smith. "You can reflect these signals slightly to create a Morse code of communication between battery-free devices."

The researchers say that such smart sensors could be built and placed permanently inside nearly any structure, then set to communicate with each other. "Sensors placed in a bridge could monitor the health of the concrete and steel, then send an alert if one of the sensors picks up a hairline crack," Smith envisions. "The technology can also be used for communication - text messages and emails, for example - in wearable devices, without requiring battery consumption."

Gollakota added that it was also feasible to build the technology into devices that do rely on batteries, such as smartphones. "They could be configured so that when the battery dies, the phone could still send text messages by leveraging power from an ambient TV signal."

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Source: University of Washington