from: arstechnica, Sean Gallagher
Passive Wi-Fi consumes 1/10,000th the power of conventional wireless networks.
A team of computer scientists and electrical engineers from the University of Washington has developed an extremely power-efficient version of Wi-Fi wireless networking technology that consumes 10,000 times less power than the current Wi-Fi components, allowing Wi-Fi networking to be built into a much wider range of devices. The team will present a paper (PDF) with the results of their research into what they have dubbed Passive Wi-Fi at the upcoming USENIX Symposium on Networked Systems Design and Implementation in March.
Passive Wi-Fi is, as the name suggests, partially passive—it takes in radio wave energy from an outside source and reflects that signal with its data added to it. Vamsi Talla, a UW electrical engineering doctoral student and co-author of the research, explained, “All the networking, heavy-lifting and power-consuming pieces are done by the one plugged-in device. The passive devices are only reflecting to generate the Wi-Fi packets, which is a really energy-efficient way to communicate.”
The technology works much in the way Radio Frequency Identification (RFID) chips (and, more infamously, retroreflector bugs like the ones used by the Soviet Union to bug the US Embassy in Moscow) do—using a technique called backscatter communication.
Backscatter of normal Wi-Fi signals has been used in the past in experiments to create separate narrowband channels for “Internet of Things” (IoT) communications, such as with BackFi, a similar technology developed by a team at Stanford University unveiled last year. BackFi, which used existing Wi-Fi networks’ signals to generate a reflected signal, was capable of transmitting 5 megabits per second of data back to the network.
Passive Wi-Fi is compatible with normal Wi-Fi, but it uses a separate base station to generate the radio signal for its backscatter-based devices. It’s capable of handling data at speeds up to 11 megabits per second and has been tested to work at distances of over 100 feet.
Because backscatter communication only requires devices to use a tiny amount of power to modulate the reflected radio signal, Passive Wi-Fi could be used in devices that would typically use Bluetooth or another low-power wireless networking technology, with the added benefit of Wi-Fi security. It can also easily be integrated into IoT sensors and other devices, allowing them to talk directly to the cloud rather than depend on another device (such as a smartphone or PC) to act as an intermediary.