Researchers at the University of Washington have detailed a new Wi-Fi radio variant, dubbed Passive Wi-Fi, which can operate with a power draw some 10,000 times lower than today's equivalent.
The researchers' Passive Wi-Fi system promises to one day replace both long-range Wi-Fi networking and shorter-range low-power radio networks like Bluetooth Low Energy (BLE), boasting of a power draw some 10,000 times lower than the former and 1,000 times lower than the latter. 'We wanted to see if we could achieve Wi-Fi transmissions using almost no power at all,
' claimed paper co-author Shyam Gollakota of his team's inspiration. '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.
Naturally, Passive Wi-Fi has a few drawbacks compared to the higher power variants in use today. Chief among these is the bitrate: Passive Wi-Fi is capable of a peak speed of 11Mb/s, a fraction of that of 802.11n or 802.11ac. Compared to Bluetooth Low Energy, though, this figure is a considerable improvement - and it's in the area of smart sensors and other low-power devices that the team is hoping to see Passive Wi-Fi making an impact.
As the name suggests, Passive Wi-Fi gains its ultra-low power draw by operating largely passively: each node in a Passive Wi-Fi network harvests energy from the Wi-Fi signals it receives, using a digital switch to reflect and absorb signals as required. During real-world testing, the team claims to have successfully communicated data from Passive Wi-Fi nodes to a Wi-Fi-enabled smartphone at distances up to 100 feet. Impressively, this required no modification oto the smartphone: the Passive Wi-Fi sensors produce a signal entirely compatible with existing Wi-Fi radios capable of operation in 802.11b mode on the 2.4GHz spectrum.
More information on the technology is available in the team's paper
(PDF warning), which is due to be presented in March at the USENIX Symposium on Networked Systems Design and Implementation. A video demonstration of the technology is reproduced below.