A new technique developed by University of Washington engineers will allow “smart” objects to communicate directly with your car or smartphone.
A bus stop billboard could do much more than just advertise local attractions — why not enable it to send your smartphone a link with directions to the venue, maybe even a discount for your ticket? A t-shirt could do more than just clothe you while you run — why not have it monitor your vital signs, keeping an eye out for any emergency? Well, that’s exactly what one team from the University of Washington wants to do.
The problem is that up until now we didn’t have any viable way to power these devices for any meaningful period of time. So the team decided to swap out internal power sources for a ubiquitous form of energy in modern cities — ambient radio signals.
“The challenge is that radio technologies like WiFi, Bluetooth and conventional FM radios would last less than half a day with a coin cell battery when transmitting,” explains co-author and UW electrical engineering doctoral student Vikram Iyer. “So we developed a new way of communication where we send information by reflecting ambient FM radio signals that are already in the air, which consumes close to zero power.”
“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,” adds 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.”
They’re the first research team to ever prove this method of harnessing existing radio signals — called “backscattering” — actually works. Their system transmits messages by encoding data into these waves and then reflecting them without affecting the original transmissions.
Singing posters
To prove that their technology works, they created a “singing poster” for band Simply Three and placed it at a bus stop. The poster could transmit an ad and sample of the band’s music to a smartphone up to 12 feet away (3.6 meters) or to a car up to 60 feet (9 meters) away. The audio and image data were transmitted an ambient signal — a news broadcast from a local NPR radio station.
The poster uses a low-power reflector that can tap into the radio broadcast and manipulate the signal in such a way as to piggy-back the desired data on top of the signal. This data is distinct enough from the original wave to be picked up by a smartphone receiver on an unoccupied frequency in the FM radio band, not interfering with any other technology.
“Our system doesn’t disturb existing FM radio frequencies,” said co-author Joshua Smith, UW associate professor of computer science and engineering and of electrical engineering. “We send our messages on an adjacent band that no one is using — so we can piggyback on your favorite news or music channel without disturbing the original transmission.”
“Because of the unique structure of FM radio signals, multiplying the original signal with the backscattered signal actually produces an additive frequency change,” adds co-author Vamsi Talla, a UW postdoctoral researcher in computer science and engineering. “These frequency changes can be decoded as audio on the normal FM receivers built into cars and smartphones.”
Beyond this method of adding data to an unused frequency, the team demonstrated two more methods for transferring data using FM backscatter: one which simply overlays the new information on top of the existing signals, and one that relies on cooperation between two smartphones to decode the message.
In the team’s demonstrations, the total power consumption of the backscatter system was 11 microwatts, which could be easily supplied by a tiny coin-cell battery for a couple of years or powered using tiny solar cells. Connectivity requiring such a low level of power can also be used to create smart fabrics and clothes. The researchers from the UW Networks & Mobile Systems Lab used a conductive thread to sew an antenna into a T-shirt which was able to similarly backscatter data at rates of up to 3.2 kilobits per second.
The end game isn’t to make smart posters of clothes alone — but entire smart cities which can talk to you for almost no power requirement.
“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,” concludes lead faculty and UW assistant professor of computer science and engineering Shyam Gollakota.
The full paper “FM Backscatter: Enabling Connected Cities and Smart Fabrics” will be presented in Boston at the 14th USENIX Symposium on Networked Systems Design and Implementation this month.
