Capturing radio signals that are already in the air, then adding data and reflecting the combination back to passersby’s smartphones is how marketing and smart city communications should take place in the future, say researchers.
By doing so, one can use everyday objects as radio stations, say scientists from University of Washington. A kind of smart-poster would be one use for the technology, they say.
Bus stop billboards, for example, would be able to broadcast a message to be picked up by a transit customer’s FM radio already built into their smartphone. The “singing poster,” as they call it, wouldn’t need to be powered with any great oomph—the radio signal reflective technology consumes “close to zero power,” the researchers claim in an article on the university’s website.
How the broadcasting system works
A form of backscattering radio is behind the system. That’s a way of encoding data in existing radio signals, then mirroring them back at a receiver. The existing signal’s data isn’t affected because an adjacent, unused frequency is used for the re-broadcast. The already-on radio wave provides much of the power.
I’ve written about backscattering before. Late last year, Stanford scientists said they’d developed a way to harvest energy from air to power Internet of Things (IoT) devices. That technique uses the same radio energy-grabbing concept and is geared towards getting Wi-Fi chips to run 10 years on one battery—a holy grail of IoT. The Harvard system, called HitchHike, consumes 10,000-times less power than existing Wi-Fi, the researchers say.
As with HitchHike, the Washington broadcasting tool—called FM Backscatter—doesn’t need any special or bulky equipment. FM Backscatter simply makes everyday objects into reflective, tiny FM radios by embedding antennas into them.
It could be well suited to close-in communications—something currently performed by hardware-intensive beaconing. Another advantage is that short ranges mitigate interference.
Long-range broadcasting is not suitable, though, because it would require too much power.
A coin battery augments the 11 microwatts needed. Power use could be further reduced by incorporating motion sensors in the poster antennas, the scientists speculate. The message is broadcast only when someone is in front of the poster—further reducing power use.
The Washington researchers say in their paper, FM Backscatter: Enabling Connected Cities and Smart Fabrics (PDF), that it isn’t just transit passengers who could benefit. Conductive clothing could be used to send vital sign signals to close-by smartphones (MAC addresses can be used to target the data to particular smartphones), or street signs could read-out the name of an intersection to a disabled person’s phone.
“What we want to do is enable smart cities and fabrics where everyday objects in outdoor environments, whether it’s posters or street signs or even the shirt you’re wearing, can ‘talk’ to you by sending information to your phone or car,” says Shyamnath Gollakota, lead faculty and University of Washington assistant professor of computer science and engineering.
Urban environments, where there are copious radio signals bouncing around ready for plucking will be best for the application, the researchers say. Ubiquitous car radios and FM-enabled smartphones are the most suitable receivers.
Interestingly, digital data, as well as audio, can be inserted into the analog signals. That data rate could be 3.2 kbps at ranges of 5-60 feet, the scientists say.
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