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By hijacking FM radio signals, we can have singing posters, talking shirts

FM Backscatter
Imagine spotting a poster for a new band playing in your neighborhood and easily being able to tune your car to a radio station that allows you to sample their music. That is the goal of a new research project being carried out at the University of Washington as part of its ongoing investigation into smart cities.

The technology involves a technique called “backscattering,” in which outdoor FM radio signals can be used to reflect and encode audio and data. Best of all, because this communication piggybacking is done on an unoccupied frequency in the FM radio band, it doesn’t disturb the original broadcast.

“This work enables everyday objects such as posters, road signs and billboards in outdoor environments to communicate with cars and smartphones, without worrying about power,” Shyam Gollakota, assistant professor in the Department of Computer Science and Engineering at the University of Washington, told Digital Trends. “The way we do this is by transforming these objects into FM radio stations. The challenge is that a poster broadcasting music consumes a lot of power and so running an FM radio station is infeasible. Instead, what we do is reflect existing FM radio signals in the environment — say from your favorite NPR station — and embed our own information on top of these ambient signals. The information we embed, including songs and data, can be decoded using any FM radio on your car or a smartphone.”

The work is described in a new paper, set to be presented in Boston at the 14th USENIX Symposium in March. It refers to a real-life demo the team carried out using the “singing poster” scenario mentioned above. The investigators found that the sound from the poster could be picked up on a smartphone at a distance of 12 feet, or by a car considerably further away.

Some aspects of this example could also be carried out by different means using a scannable QR code, but Gollakota pointed out that the use-cases are different.

“QR codes cannot be read from a car,” he said. “Further, QR codes embed static information, while we can sense and transmit dynamic arbitrary data. Finally, QR codes require you to point your phone to capture the image. Our design can work up to distances of 60 feet away and do not require any specific phone orientation.”

Looking further down the line, the researchers are hoping the technology could have other applications, such as being used for signs in cities able to transmit information to individuals with disabilities. It could also be used as a component of smart fabrics — for example, a shirt that’s able to monitor your perspiration while running and then send this information to your phone.

In the meantime, work on the project continues. “We can achieve data rates of 3.2 kbps and ranges of five to 60 feet,” Gollakota said. “While this is sufficient for a number of connected cities and smart fabric applications, we are working on increasing the data rate and the range of this communication.”

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