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TV, Cellular Signals Harnessed for Power, Communications

Prototype ambient backscatter devices

Prototype ambient backscatter devices (University of Washington)

Computer scientists and engineers at University of Washington in Seattle developed a wireless process that harnesses existing television and cell phone signals as sources of power and a way of communicating. The team led by computer science professors Shyam Gollakota and Joshua Smith describes the process in a paper at ACM’s Special Interest Group on Data Communication 2013 conference that starts today in Hong Kong, and where it won the event’s award for best paper.

Gollakota, Smith, and colleagues call their process ambient backscatter that takes advantage of the TV and cellular transmissions already in circulation. Devices built for ambient backscatter exchange information by reflecting these existing signals without generating their own radio waves, nor the need for external power.

The researchers tested ambient backscatter with prototype circuit-board devices (pictured at top) about the size of credit cards, with antennas attached, and LED lights that lit up when receiving a signal. The tests took place in and around Seattle at three venues: in an apartment house, on a street corner, and on the top level of a parking garage. The tests ranged from 0.5 to 6.5 miles from a television transmission tower.

Gollakota, Smith, and colleagues discovered the devices could send and receive messages at all three locations, even those furthest from the television tower. The devices, say the researchers, could receive a signal transmitted at 1 kilobit per second when separated by a distance of 1.5 feet indoors and 2.5 feet outside. That rate is sufficient for short messages, but still those with value, such as sensor readings, text messages, and business card/contact data.

The researchers say ambient backscatter technology could be useful with sensors implanted in buildings or bridges to monitor their structural integrity, without the need for external power. Communication devices enabled with the ambient backscatter could also be part of wearable systems, such as health monitors. They could likewise be integrated with battery-powered systems, such as smartphones, to send and receive emergency text messages when their installed batteries lose power.

Gollakota and Smith plan to continue enhancing and refining the ambient backscatter process to extend its range and network capacity. The researchers tell more about and demonstrate the process in the following video.

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