How to Backscatter Your Own Pirate Radio Station

Students at the University of Washington have devised a system where posters, billboards, etc can backscatter an audio or data signal onto an existing FM signal without using an external power source. Basically this is piggybacking a signal onto the radiating FM signal from a radio station. The backscatter signal will play on an adjacent channel as shown in the video below. Other users within 60 feet can receive the transmission thus having a device installed onto a poster at a bus stop or billboard is ideal for this technology.

A transmitter could potentially be a shirt woven with conductive materials and sensors so that as the user jogs, health information is transmitted to their smartphone. A street sign could transmit historical data to the local smartphones that are within range of it without having a powerful transmitter hooked to it. This could create a connected city using the power of existing radio stations as the power source. All of us that dreamed of running a pirate radio station can finally realize that dream!

If you live in a city, you’re constantly swimming in a thick soup of radio-frequency energy. FM radio stations put out hundreds of kilowatts each into the air. Students at the University of Washington, [Anran Wang] and [Vikram Iyer], asked themselves if they could harness this background radiation to transmit their own FM radio station, if only locally. The answer was an amazing yes.

The trailer video, embedded below, demos a couple of potential applications, but the paper (PDF) has more detail for the interested. Basically, they turn on and off an absorbing antenna at a frequency that’s picked so that it modulates a strong FM signal up to another adjacent channel. Frequency-modulating this backscatter carrier frequency adds audio (or data) to the product station.

This is interesting.

I'm always annoyed when I get close to someone with an illegal Chinese FM adapter for their iPod that doesn't pass FCC regulations and interferes with my radio signal.

Would be interesting to see how this interacts with different freqs, especially since the use of Space-division Muliplexing (MIMO) techniques is critical to current and next-gen wireless networks, and having things out there that cause those waves to behave in ways that they aren't expected to could be detrimental.

I'd also wonder how this compares to just absorbing the energy and using it for power generation, and then doing whatever is needed with that power.

I know that there are RFID tags that do this.