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How IoT sensors could connect via ambient radio waves

System was demonstrated in an indoor office environment, using ambient signals from 14 radio towers as well as two mobile phones

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Could ambient radio waves from TV, radio and cell phones be the future for the IoT?
Could ambient radio waves from TV, radio and cell phones be the future for the IoT?

Most Internet of things (IoT) systems link networks of sensors via radio, but radios demand battery power thus limiting usability. A group of researchers from Disney Research, however, has proposed using the ambient radio waves from TV, radio and cell phones and to get rid of the radios all together.


The process known as “backscatter communication” requires an ultra-low-power system of sensors that transmit data to a central receiver by reflecting the ambient radio waves from commercial broadcasting systems that already bathe most office environments.


“Our idea is to reuse all the radio signals that are around us as a medium for transmitting data, much like sending ripples across a pond,” said Alanson Sample, associate lab director and leader of Disney Research’s wireless systems group.


This approach radically reduces the power requirements of the sensor nodes because it is the generation of radio waves that consumes most of their battery power. In a demonstration in a Disney Research lab, the researchers were able to meet the tiny bit of power demand that remained by using solar cells optimised for low-light conditions.


Backscatter communication already is used in passive RFID tags. In that case, an RFID reader transmits radiofrequency power to the battery-free RFID tag; the tag sends data to the reader by reflecting, or backscattering, the carrier wave back to the reader. These systems have limited range, which makes them impractical for IoT systems.


According to Sample, the ultra-wideband (UWB) approach -- which backscatters all ambient sources -- offers key advantages. Using multiple backscatter channels boosts the signal-to-noise ratio, substantially improving the sensitivity of the backscatter reader and decreasing dead zones. That, in turn, enables the system to operate on real-world ambient sources and substantially extends the range to 22 metres when using ambient signals from broadcast towers and 50 metres when using ambient signals generated by mobile phone up-link traffic.


The ultra-low-power sensor nodes are necessarily simple, Sample said, which requires the backscatter reader to do the heavy lifting for the system. The reader must receive the backscatter signals, decode and combine multiple backscatter carriers to recover the data from each sensor. The reader uses four software-defined radio receivers -- one for the FM radio band, another to cover most of the cellular uplink and downlink bands and two for digital TV bands.


Because the hardware doesn’t have to be tuned to any particular frequency band, the UWB system can be deployed in almost any metropolitan area, he added. Unlike other experimental systems that leverage ambient radio waves, the Disney system doesn’t focus on a single signal source, but uses all available ambient radio sources, from FM radio broadcasts to digital TV signals to the transmissions to and from cellular phones.


“The promise of the Internet of Things is that wireless sensors will be ubiquitous, allowing devices to sense their environments and talk to each other,” said Markus Gross, vice president, Disney Research. “As we move towards connecting the next billion wireless devices to the internet, however, the use of batteries to power these devices will become unworkable. UWB ambient backscatter systems, which potentially could be deployed in any metropolitan area, hold great potential for solving this dilemma.”



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