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Two Soylentils sent in news about passive Wi-Fi.

takyon writes:

Computer scientists and electrical engineers at the University of Washington have created a device that can transmit Wi-Fi packets "passively" by reflection and absorption. The system uses 0.01% of the power required by conventional Wi-Fi, transmits at bit rates up to 11 Mbps, and can communicate with existing devices at ranges up to 100 feet:

Computer scientists and electrical engineers have demonstrated that it's possible to generate Wi-Fi transmissions using 10,000 times less power than conventional methods. The new Passive Wi-Fi system also consumes 1,000 times less power than existing energy-efficient wireless communication platforms, such as Bluetooth Low Energy and Zigbee. "We wanted to see if we could achieve Wi-Fi transmissions using almost no power at all," says coauthor Shyam Gollakota, assistant professor of computer science and engineering at the University of Washington. "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."

Passive Wi-Fi can for the first time transmit Wi-Fi signals at bit rates of up to 11 megabits per second that can be decoded on any of the billions of devices with Wi-Fi connectivity. These speeds are lower than the maximum Wi-Fi speeds but 11 times higher than Bluetooth. [Note: this appears to refer to the 1 Mbps "basic rate" of Bluetooth.]

[...] The Passive Wi-Fi 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 Wi-Fi packets of information using very little power by simply reflecting and absorbing that signal using a digital switch. In real-world conditions, researchers found the passive Wi-Fi sensors and a smartphone can communicate even at distances of 100 feet between them.

[...] The researchers will present a paper (pdf) describing their results in March at the 13th USENIX Symposium on Networked Systems Design and Implementation. The National Science Foundation, the University of Washington, and Qualcomm funded the work.

University of Washington.

[Continues.]

Phoenix666 writes:

We introduce Passive Wi-Fi that demonstrates for the first time that one can generate 802.11b transmissions using backscatter communication, while consuming 3 - 4 orders of magnitude lower power than existing Wi-Fi chipsets. Passive Wi-Fi transmissions can be decoded on any Wi-Fi device including routers, mobile phones and tablets. Building on this, we also present a network stack design that enables Passive Wi-Fi transmitters to coexist with other devices in the ISM band, without incurring the power consumption of carrier sense and medium access control operations. We build prototype hardware and implement all four 802.11b bit rates on an FPGA platform. Our experimental evaluation shows that passive Wi-Fi transmissions can be decoded on off-the-shelf smartphones and Wi-Fi chipsets over distances of 30 - 100 feet in various line-of-sight and through-the-wall scenarios. Finally, we design a Passive Wi-Fi IC that shows that 1 and 11~Mbps transmissions consume 14.48 and 49.28 µW respectively. This translates to 10000x lower power than existing Wi-Fi chipsets and 1000x lower power than Bluetooth LE and ZigBee.

Link to the full paper (PDF) is here.

Original Submission #1 Original Submission #2