Engineers Design "Passive" Wi-Fi That Uses 10,000 Times Less Energy


Robin Andrews

Science & Policy Writer

63 Engineers Design "Passive" Wi-Fi That Uses 10,000 Times Less Energy
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Wi-Fi is everywhere these days, providing remote, wireless access to the Internet and saving us from tripping over bunches of cables. However, it does consume a lot of energy, and it drains the batteries of connected devices incredibly quickly. Fortunately, engineers at the University of Washington (UW) have come to the rescue: They’ve demonstrated a technique that allows Wi-Fi to be generated using 10,000 times less energy than normal.

This new "Passive Wi-Fi" also consumes 1,000 times less power than Bluetooth. In fact, compared to conventional methods, this novel technology uses almost no energy at all. Although it currently transmits data at rates of up to 11 megabits per second – far lower than peak Wi-Fi speeds – this data transfer rate is still 11 times higher than Bluetooth.


This proof-of-concept research builds on a technique called Wi-Fi backscattering, wherein the signal being sent between a Wi-Fi router and any wireless receiving device is manipulated. Previous research by UW has shown that low-power equipment can be used to reflect and “distort” this signal, encoding it as it’s being transmitted. The connected device would receive these new distortions as unique data.

Passive Wi-Fi represents an evolution of this technique. First, a connection to the Internet is made by a single, plugged-in router, which beams out a Wi-Fi signal as it would traditionally. An array of remote, Passive Wi-Fi sensors reflect and absorb this signal, creating multiple streams of data that can be “bounced” towards multiple receiving devices.

Traditionally, these devices would all be connected to the router, which would significantly drain their power. With Passive Wi-Fi, almost all of the power is used in generating the initial signal by the router; the sensors merely bounce this signal back and forth, which uses effectively no energy.



“Our sensors can talk to any router, smartphone, tablet or other electronic device with a Wi-Fi chipset,” said Bryce Kellogg, an electrical engineering doctoral student at UW and coauthor of the study, in a statement. “The cool thing is that all these devices can decode the Wi-Fi packets we created using reflections so you don't need specialized equipment.”

This low power Wi-Fi system means that devices of all shapes and sizes can be connected to the Internet, for long periods of time, with negligible power drainage. A future full of essentially powerless, interconnected devices is part of a concept known as the “Internet of Things.” Imagine a series of sensors that detect changes in light, heat, movement, noise, air quality, then transmit this data to other devices in the house without having their power drained by Wi-Fi.

Some of these sensors already use essentially no energy: A tiny temperature sensor invented last year is powered by the radio waves sent from the Wi-Fi network it uses to communicate its data. Combining this with Passive Wi-Fi may lead to a new generation of ultra-low power communication networks.


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