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'Passive Wi-Fi' achieves 10,000 times power reduction

24 February 2016

A University of Washington team has demonstrated that it's possible to generate Wi-Fi transmissions using 10,000 times less power than conventional methods.

Passive Wi-Fi architecture (image montage courtesy of University of Washington, with stock images courtesy of

The new 'Passive Wi-Fi' system also consumes 1,000 times less power than existing energy-efficient wireless communication platforms, such as Bluetooth Low Energy and Zigbee. The technology has been named one of the ten breakthrough technologies of 2016 by MIT Technology Review.

"We wanted to see if we could achieve Wi-Fi transmissions using almost no power at all," says Shyam Gollakota, a UW assistant professor of computer science and engineering. "That's basically what Passive Wi-Fi delivers. We can get Wi-Fi for 10,000 times less power than the best thing that's out there."

Passive Wi-Fi can for the first time transmit Wi-Fi signals at bit rates of up to 11Mbit/s that can be decoded on any of the billions of devices with Wi-Fi connectivity. These speeds are lower than the maximum Wi-Fi speeds but eleven times higher than Bluetooth.

As well as saving mobile device battery life, wireless communication that uses almost no power will help enable the Internet of Things, where household devices and wearable sensors can communicate using Wi-Fi without power concerns.

To achieve such low-power Wi-Fi transmissions, the team essentially decoupled the digital and analogue operations involved in radio transmissions. In the last 20 years, the digital side of that equation has become extremely energy efficient, but the analogue components still consume a lot of power.

The Passive Wi-Fi architecture assigns the analogue power-intensive functions - like producing a signal at a specific frequency - to a single device in the network that is plugged into the wall.

An array of sensors produces Wi-Fi packets of information using very little power by simply reflecting and absorbing that signal using a digital switch. In real-world conditions on the University of Washington campus, the team found the passive Wi-Fi sensors and a smartphone can communicate even at distances of 30m between them.

"All the networking, heavy-lifting and power-consuming pieces are done by the one plugged-in device," says Vamsi Talla, an electrical engineering doctoral student. "The passive devices are only reflecting to generate the Wi-Fi packets, which is a really energy-efficient way to communicate."

Because the sensors are creating actual Wi-Fi packets, they can communicate with any Wi-Fi enabled device, 'out-of-the-box'.

"Our sensors can talk to any router, smartphone, tablet or other electronic device with a Wi-Fi chipset," says electrical engineering doctoral student Bryce Kellogg. "The cool thing is that all these devices can decode the Wi-Fi packets we created using reflections so you don't need specialised equipment."

The researchers believe the technology could enable entirely new types of communication that haven't been possible because energy demands have outstripped available power supplies.

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