Engineers achieve Wi-Fi at 10,000 times lower power

February 23, 2016 by Jennifer Langston, University of Washington
University of Washington computer scientists and electrical engineers have generated "passive" Wi-Fi transmissions that use 10,000 times less power than current methods. Credit: University of Washington

The upside of Wi-Fi is that it's everywhere - invisibly connecting laptops to printers, allowing smartphones to make calls or stream movies without cell service, and letting online gamers battle it out.

The downside is that using Wi-Fi consumes a significant amount of energy, draining the batteries on all those connected devices.

Now, a team of University of Washington computer scientists and electrical engineers has demonstrated that it's possible to generate Wi-Fi transmissions using 10,000 times less power than conventional methods.

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. A paper describing those results will be presented in March at the 13th USENIX Symposium on Networked Systems Design and Implementation.

The technology has also been named one of the 10 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," said co-author 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."

In Passive Wi-Fi, power-intensive functions are handled by a single device plugged into the wall. Passive sensors use almost no energy to communicate with routers, phones and other devices. Credit: University of Washington

Passive Wi-Fi can for the first time transmit Wi-Fi signals at bit rates of up to 11 megabits per second 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 11 times higher than Bluetooth.

Aside from saving battery life on today's devices, wireless communication that uses almost no power will help enable an "Internet of Things" reality where household devices and wearable sensors can communicate using Wi-Fi without worrying about power.

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

The Passive Wi-Fi architecture assigns the analog, 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 UW campus, the team found the passive Wi-Fi sensors and a smartphone can communicate even at distances of 100 feet between them.

"All the networking, heavy-lifting and power-consuming pieces are done by the one plugged-in device," said co-author 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 right out of the box.

"Our sensors can talk to any router, smartphone, tablet or other electronic device with a Wi-Fi chipset," said co-author and 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 specialized equipment."

The technology could enable entirely new types of communication that haven't been possible because energy demands have outstripped available power supplies. It could also simplify our data-intensive worlds.

For instance, smart home applications that use sensors to track everything from which doors are open to whether kids have gotten home from school have typically used their own communication platforms because Wi-Fi is so power-hungry.

"Even though so many homes already have Wi-Fi, it hasn't been the best choice for that," said co-author Joshua Smith, UW associate professor of computer science and engineering and of . "Now that we can achieve Wi-Fi for tens of microwatts of and can do much better than both Bluetooth and ZigBee, you could now imagine using Wi-Fi for everything."

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1 / 5 (2) Feb 23, 2016
That's the same idea how passive NFC works.

5 / 5 (4) Feb 23, 2016
In the late 1970s, there were ham radio enthusiasts playing with 10 GHz retro-reflection modulation. The signal would hit a reflector and then get modulated with a 30 MHz carrier. With small dish antennas, this system worked over distances measured in kilometers. Yes, the retro-reflector carrier could have been modulated with all sorts of information. I had thought it might be neat to develop cheap telemetry sensors with this, but I never followed up on it.

So a resonant retro-reflector for, say, 122.5 GHz could be modulated with data speeds greater than what we're doing with 802.11n and it would work quite well. The downside is that the transmitter from the base would have to be remain just as powerful as before, and it would have to poll for new members because they wouldn't be able to transmit by themselves. Oh, and it might not go through walls as well as current WiFi standards.

Nevertheless, this is quite creative. I'm impressed.
not rated yet Feb 26, 2016
Aside from saving battery life on today's devices, wireless communication that uses almost no power will help enable an "Internet of Things" reality where household devices and wearable sensors can communicate using Wi-Fi without worrying about power.

As I see it, what is going to enable the "Internet of Things" is companies making such products that actually implement reasonable security measures. Right now, there is a complete lack of security in the "Internet of Things" devices. Even if I were interested in the "Internet of Things" devices, I would not purchase any if it did not have decent security. Right now, the "Internet of Things" seems to be a buzzword for journalists trying to attract reads.

Just the other day, I was at my car dealer getting my car serviced. There were two devices on their Wi-Fi network advertising themselves as "Thermostats." Both of them advertised themselves as unsecured for a Wi-Fi connection. Go figure!!
Whydening Gyre
5 / 5 (1) Feb 26, 2016
BTW, a long time ago, around 1970, I worked in Thailand on Space diversity microwave communications link, where they used two 5 GHz antennas side by side separated by about 30 feet and both fed a 1000 watt signal, communicated with another unit just like it but 150 Km apart.

Was logistics management for S korea MW communications backbone in 1974,75 Mountaintop to mountain top, Busan to Seoul and all points in between. Max I remember was about 40 miles... Did a lot of helicopter rides...;-)

Feb 26, 2016
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