Backscattering, a passive broadcasting method, has an increasingly clear future as public agencies move aggressively to deliver services more cheaply and serve residents more effectively.
A team of researchers has found that a venerable audio transmitting technique could hold promise for smart cities, as well as private companies looking to inexpensively reach large numbers of people.
The technology described in a white paper titled FM Backscatter: Enabling Connected Cities and Smart Fabrics — written by three student researchers and two faculty advisers from the University of Washington (UW) — is a new approach to what’s known as backscattering, or ambient backscattering; it’s a relative of today’s RFID technology, and a passive broadcasting method that figured in one of the Cold War’s most notorious spy scandals.
The team will deliver a presentation based on the white paper on Monday, March 27 at the 14th USENIX Symposium on Networked Systems Design and Implementation in Boston — a presentation that signals the group is confident the technology has an increasingly clear future as public agencies move aggressively to deliver services more cheaply and serve residents more effectively.
According to one expert, the system has concrete potential for cities, including in autonomous vehicle deployments where the device might one day replace traffic signals and stop signs now recognized by human drivers.
In the presentation’s abstract, group members spell out their discovery — using ambient FM radio signals as a source for backscatter for the first time — and what that means.
“This paper enables connectivity on everyday objects by transforming them into FM radio stations,” the abstract reads. “Our design creates backscatter transmissions that can be decoded on any FM receiver including those in cars and smartphones. This enables us to achieve a previously infeasible capability: backscattering information to cars and smartphones in outdoor environments.”
Their backscatter technique uses a device they built to find an existing FM radio signal, then reflecting it, jumping on-board and riding a very short distance to deliver audio or even data. The device is ultra low-powered, small and doesn’t passively transmit very far — 100 feet or less — ensuring multiples could be installed in relatively close proximity without competing.
Researchers achieved the breakthrough by using a new modulation technique, making backscatter follow existing FM transmissions in the Seattle area to successfully send sound and data short distances to a Moto G1 smartphone and a 2010 Honda CR-V.
“This enables us to embed both digital data as well as arbitrary audio into ambient analog FM radio signals,” the group wrote.
To test their work, members embedded the FM antenna devices they designed into posters and billboards, then showed they could communicate with receivers in the car and the smartphone.
They also sewed conductive thread into a T-shirt to create a “smart” fabric that could send data to a smartphone.
The results convinced them the technique shows promise for public agencies, even if we may be more likely to see it in reruns of the science fiction TV series Extant in the immediate future than along a local highway.
“The concept of backscatter itself is not a new thing, but what we’re showing here is we can leverage these FM signals that are all around major cities and communicate to off-the-shelf receivers as well as cars,” said Vikram Iyer, a UW doctoral student in electrical engineering and an author of the paper.
Cities, Iyer told Government Technology, could set aside a particular FM radio frequency on which to transmit — then reflect on it to “broadcast public information on those or pretty much anything you wanted at a particular location.”
The advantage, he said, “is you’d really be using infrastructure that already exists. All we really need to add is these devices that backscatter.”
The team built its device to backscatter on an FM signal from readily available components and cheaply, Iyer said. But on the receiving end, while our cell phones and cars may have the capability to receive FM radio broadcasts, Iyer notes that they would need additional equipment or apps to refine it.
Because backscatter audio and data “travels” on an existing signal, it arrives with that signal as well — meaning receiver designers would have to create noise-cancelling equipment or apps to mute the FM signal and let listeners hear just the backscattered information.
Bhaskar Krishnamachari, professor of Electrical Engineering and Computer Science and director of the Center for Cyber-Physical Systems and the Internet of Things at the USC Viterbi School of Engineering, praised the device’s low power usage, noting that “backscatter transmitters don’t do anything if there’s no signal.”
But he pointed out that “in terms of how far out we may be from seeing it in smart cities, the question in purely technical terms, the one bottleneck would be, 'What kind of receiver do you need and how widely available is it?'”
That said, Krishnamachari acknowledged the system’s potential for cities as a universal docent in self-guided walking tours, delivering a pre-recorded message through a smartphone app about an historic building or area; and in autonomous vehicle deployments, where the small device might one day replace traffic signals and stop signs now recognized by human drivers.
“From a city’s perspective, I think backscatter technology will be cheap as far as the transmitters are concerned or even potentially the receivers," he said. "It allows you to deploy these things more widely."
Backscattering has the potential to be “more or less as useful as other ‘smart cities’ initiatives,” says Cincinnati Chief Performance Officer Leigh Tami, who pointed out that smart cities and “smart” technologies are only as smart as the city using or implementing them.
Tami told Government Technology via email that two things, can give so-called smart initiatives the ability to implement and scale: ensuring backscattering, like any other new technology, is fully integrated with existing infrastructure — and here, its relatively low cost would be an advantage; and making sure, like any other tech piece, it meets a specific need.
“There's a lot of cool stuff out there, but not all of it necessarily meets a need in the realm of government service delivery, efficiency, or citizen engagement,” said Tami, who added that she’d be interested to hear more about proposed use cases.