Harnessing wider spectrum of ambient radio waves for powerless IoT device communication
Most of the devices and sensors connecting to the Internet of Things (IoT) rely on transmitting radio waves to communicate, which requires power, which means batteries if mains power isn't an option. A team at Disney Research is looking at harnessing a technique called ultra-wideband (UWB) ambient backscatter, which would allow devices to piggyback their communications on the multitude of FM and cellular signals already in the air.
"As we move towards connecting the next billion wireless devices to the internet, the use of batteries to power these devices will become unworkable," explains Markus Gross, vice president at Disney Research. "UWB ambient backscatter systems, which potentially could be deployed in any metropolitan area, hold great potential for solving this dilemma."
Ambient backscatter techniques basically utilize the ever-present cloud of TV and cellular signals already in the air to either power small transistors or to piggyback data transmissions. This significantly cuts the power requirements of such sensors, by potentially allowing them to communicate without transmitting their own radio waves.
Such technology has been trialled several times in recent years, from developing advertising posters that could piggyback FM signals in the air and send ads to nearby devices, to powering small sensors without any external battery power.
The new innovation developed by the Disney Research Wireless Systems group allows a single device to backscatter a multitude of available ambient sources. Where prior devices were calibrated to feed or piggyback off a single specific FM or cellular signal, this new UWB approach leverages all broadcast signals in the 80 MHz to 900 MHz range, including digital TVs, FM radios and cellular networks, resulting in a greater signal-to-noise ratio and extending range.
The new system requires a single reader hub to receive and decode the sensor data carried on the backscatter signals, but realistically that would mean a variety of backscatter-based sensors could easily be deployed in an office or home environment that would communicate with one central powered source.
The team was able to demonstrate communication from node to reader over 22 m (72 ft) when using ambient signals from broadcast towers, and over 50 m (164 ft) with data rates of up to 1 kbps by simultaneously harnessing 17 ambient signal sources.
Future prospects for this technology could allow inert, unpowered objects to be embedded with communicative sensors, such as a bus stop pole that holds live timetable information, a t-shirt that communicates heart rate information to its wearer, or even a smartphone that could transmit text messages after its battery has died.