Passive Wi-Fi more energy efficient than conventional Wi-Fi, ZigBee and Bluetooth LE
While it's become a necessity of modern life, Wi-Fi is also an energy hog, draining the batteries of all those connected devices surrounding us. That may change with the recent demonstration by University of Washington (UW) researchers of Wi-Fi transmissions generated using 10,000 times less power than conventional methods. Known as Passive Wi-Fi, the system also uses 1,000 times less power than current energy-efficient wireless communication platforms, like ZigBee and Bluetooth LE.
According to study co-author Shyam Gollakota, a professor of computer science and engineering at UW, the team wanted to see whether Wi-Fi transmissions that used almost no power were possible. The Passive Wi-Fi system uses just tens of microwatts of power, and is able to transmit at up to 11 megabits per second – that's much less than the highest Wi-Fi speeds, but 11 times faster than Bluetooth.
The discovery also has positive implications for the "Internet of Things," which would better enable connected devices and sensors in homes and on wearables without having to worry about a continual power drain.
Wi-Fi transmissions have both a digital and analog component. The digital side has become very energy efficient over the years, scaling along with Moore's law, but the analog component continues to consume hundreds of milliwatts of power. To achieve their low-power results, the researchers assigned the power-hungry analog portion to a single device plugged into an outlet. The signal sent out is then reflected by the remote device with its own data added to it. It works something like Radio Frequency Identification (RFID) chips using backscatter communication, and can communicate at a distance of up to 100 feet (30 m) in real-world conditions.
Essentially, the networking and power-consuming parts of the process are handled by the device plugged into the wall, while the passive Wi-Fi devices only have digital base band (no analog) and are reflecting and absorbing the signal from the plugged in device to generate the Wi-Fi packets of info.
According to co-author Bryce Kellogg, an electrical engineering doctoral student at UW, the sensors can talk to any device with a Wi-Fi chipset, including routers, smartphones and tablets. "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," he said.
The research, which was funded by the National Science Foundation, UW and Qualcomm, will be presented in a paper next month at the USENIX Symposium on Networked Systems Design and Implementation.
The technology is demonstrated in the video below.