Engineers achieve WiFi at 10,000 times lower power

The new Passive WiFi 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 WiFi 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 WiFi delivers. We can get WiFi for 10,000 times less power than the best thing that’s out there.”

Passive WiFi can for the first time transmit WiFi signals at bit rates of up to 11 megabits per second that can be decoded on any of the billions of devices with WiFi connectivity. These speeds are lower than the maximum WiFi 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 WiFi without worrying about power.

To achieve such low-power WiFi 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 WiFi 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 WiFi 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 WiFi sensors and a smartphone can communicate even at distances of 100 feet between them.

In Passive WiFi, 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.

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. Courtesy of vector.me

“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 WiFi packets, which is a really energy-efficient way to communicate.”

Because the sensors are creating actual WiFi packets, they can communicate with any WiFi enabled device right out of the box.

“Our sensors can talk to any router, smartphone, tablet or other electronic device with a WiFi chipset,” said co-author and electrical engineering doctoral student Bryce Kellogg. “The cool thing is that all these devices can decode the WiFi packets we created using reflections so you don’t need specialised 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 WiFi is so power-hungry.

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

The research was funded by the National Science Foundation, the University of Washington and Qualcomm.