The team of University of Washington computer scientists and electrical engineers has been trying to solve one of Wi-Fi’s biggest problems, its comparatively high energy usage. On a smartphone, the Wi-Fi radio often accounts for a healthy percentage of the phone’s total battery usage. When used for a prolonged period of time, such as when watching a video or gaming, even more power is drawn.
The researchers wanted to find a way to reduce this power consumption. The result is “Passive Wi-Fi,” a system which lets Wi-Fi radios operate with much less energy. Power consumption can be as much as 10,000 times less than current products and 1,000 times less than existing low-energy wireless tech such as Bluetooth Low Energy.
“We wanted to see if we could achieve Wi-Fi transmissions using almost no power at all,” said Shyam Gollakota, co-author of the study and 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.”
The system works by doing away with the power-hungry analogue components of current Wi-Fi transmitters. A Wi-Fi transmitter has analogue and digital components as it converts packets of digital data into analogue radio waves for transmission.
The digital side of the mechanism is now very efficient but the analogue components remain energy intensive. The team decided to decouple the two parts, creating a single dedicated device to hold the analogue section.
A standalone mains-powered base tower provides all the analogue functionality of the Wi-Fi transmitter so connected devices don’t need to. They can rely entirely on digital transmissions, saving battery power. An array of sensors produces packets of Wi-Fi data by reflecting and absorbing the analogue signals by means of a digital switch.
“All the networking, heavy-lifting and power-consuming pieces are done by the one plugged-in device,” said study 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.”
There are still a few issues to be sorted out, particularly around speed. A transfer rate of 11Mbps has been observed in testing, a usable connection but around 100 times slower than the best 5GHz Wi-Fi signals. Further development should lead to improvements in this area though, making it better suited for consumer network use.
The technology could prove to have major ramifications for the Internet of Things, especially for Wi-Fi devices. Currently, Bluetooth is the favoured technology for smart devices as it uses much less power than Wi-Fi.
However, power consumption 1,000 times less than Bluetooth Low Energy means Passive Wi-Fi could become an even better solution, letting products last for weeks, months or even years on a charge. Speed isn’t an issue here either as current devices are limited to the 1Mbps data rate of Bluetooth.
Unlike other break-through technologies, Passive Wi-Fi could come to the consumer market relatively soon. People won’t even need to buy new devices to take advantage of it as all existing Wi-Fi products are capable of connecting to Passive Wi-Fi, saving power in the process.
Passive Wi-Fi has now been named one of the 10 Breakthrough Technologies of 2016 by the MIT Technology Review.
