Friday March 10, 2017

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.