Bouncing Off TV Signals for Local Power, Communications

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Really local wireless networks that can power “Internet-of-Everything” devices by piggybacking onto existing TV and mobile transmissions are viable and inexpensive, according to a technical paper unveiled this week.  University of Washington researchers outlined the system in their presentation “Ambient Backscatter: Wireless Communication Out of Thin Air”, which won the “best paper” at an Association for Computing Machinery communications conference in Hong Kong.

As one wag jokingly observed, “ambient backscatter” could also give broadcasters a new retransmission-consent opportunity – seeking payments for devices that use TV signals to bounce the ambient backscatter data.  

“Ambient backscatter” would enable devices, such as thermostats, appliances, implantable medical devices and even books and furniture to interact and communicate with each other without relying on batteries or wires for power. Smart cards and other commercial applications are also envisioned. The technology, still some years away from implantation, could offer a breakthrough in home networking services, especially ones involving “smart” devices.

At the core of the system is the multipath reflection that accompanies wireless transmissions.  This capability offers the potential to create local networking delivery that would avoid the current spectrum allocation battles and concerns about unregulated wireless devices. 

“We can repurpose wireless signals that are already around us into both a source of power and a communication medium,” said lead researcher Shyamnath Gollakota, a UW assistant professor of computer science and engineering.  He envisions applications including “wearable computing, smart homes and self-sustaining sensor networks.”

The ambient backscatter system allows devices to exchange information by reflecting or absorbing existing radio waves, including television and mobile phone transmissions.  Devices communicate with each other by reflecting the existing signals to exchange information. For field tests described in their paper, the researchers built credit-card sized, battery-free devices with antennas that could detect, harness and reflect a TV signal, which then is picked up by other similar devices.

“Our system adds an additional reflection to the mix,” Gollakota told me in an email response to my query. “TV receivers are designed to track and account for these reflections. So the interference (to TV signals) is minimal.”

The researchers conclude that ambient backscatter holds an advantage over traditional backscatter technologies because it enables devices to decode each other’s transmissions. Energy detection is especially important, they emphasize.  

Devices “can potentially perform carrier sense: detect the beginning of other packet transmissions (preamble correlation), and detect energy in the middle of a packet transmission,” according to the experiments conducted as part of the University of Washington research.

The paper notes that ambient backscatter “avoids the power barriers of other forms of low-power communication” (such as Radio Frequency Identification and Near-Field Communications: RFID and NFC). In field tests, the system worked over distances ranging from a few meters to more than six miles.

“We believe that ambient backscatter provides a key building block that enables ubiquitous communication (with no restrictions except the existence of ambient RF signals) among pervasive devices which are cheap and have near-zero maintenance,” the academics conclude.

The technical paper does not delve into regulatory or marketplace factors.  But its findings suggest a range of applications for residential and commercial services that could figure significantly into emerging Internet of Things.

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