From the post:
They overlaid the audio and data on top of ambient news signals from a local NPR radio station. “FM radio signals are everywhere. You can listen to music or news in your car and it’s a common way for us to get our information,” said co-author and UW computer science and engineering doctoral student Anran Wang. “So what we do is basically make each of these everyday objects into a mini FM radio station at almost zero power.
”Such ubiquitous low-power connectivity can also enable smart fabric applications such as clothing integrated with sensors to monitor a runner’s gait and vital signs that transmits the information directly to a user’s phone. In a second demonstration, the researchers from the UW Networks & Mobile Systems Lab used conductive thread to sew an antenna into a cotton T-shirt, which was able to use ambient radio signals to transmit data to a smartphone at rates up to 3.2 kilobits per second.
The system works by taking an everyday FM radio signal broadcast from an urban radio tower. The “smart” poster or T-shirt uses a low-power reflector to manipulate the signal in a way that encodes the desired audio or data on top of the FM broadcast to send a “message” to the smartphone receiver on an unoccupied frequency in the FM radio band.
For the details:
The UW team has — for the first time — demonstrated how to apply a technique called “backscattering” to outdoor FM radio signals. The new system transmits messages by reflecting and encoding audio and data in these signals that are ubiquitous in urban environments, without affecting the original radio transmissions. Results are published in a paper to be presented in Boston at the 14th USENIX Symposium on Networked Systems Design and Implementation in March.
So government agents can cover cellphone frequencies with Stingray (“cell site simulators”) devices.
Wonder if they can cover the entire FM band? 😉
I’m guessing not. You?
Imagine a phone or shirt that is tuned to the frequency of a covert FM transmitter at a particular location. The information is just hanging out there but unless the “right” receiver walks by, its never known to anyone.
Ideal for messages directing public gatherings with near zero risk of interception by, shall we say, unfriendly parties?
Or other types of messages, imagine a singing dead drop as it were. You move away, the song goes away.