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Passive Wi-Fi Promises Simpler, Lower-Power Sensor Networks

Gareth Halfacree

University of Washington Passive Wi-Fi Prototypes

One of the biggest barriers to the growth of the Internet of Things (IoT) is the difficulty in building a wireless network of devices. In the consumer space Wi-Fi is the dominant standard, but its high power draw makes it unsuitable for long-running battery-powered remote sensor nodes. Alternatives like Bluetooth Low Energy and ZigBee draw less power, but bring their own problems to the table. Researchers at the University of Washington, though, believe they may have cracked the problem with a new Wi-Fi variant which draws as little as a ten-thousandth the power of today's equivalent.

Dubbed Passive Wi-Fi, the team's creation is built specifically with sensor networks in mind. Using the same back-scatter technology as entirely passive systems like radio frequency identification (RFID) and near-field communications (NFC) tags, the Passive Wi-Fi system is able to harvest power when it needs to drive its radio - dropping the power draw into the micro-watt range, lower even than Bluetooth Low Energy.

While it would be easy to dismiss the technology as Yet Another Competing Wireless Standard, Passive Wi-Fi has one major advantage over its rivals: the radio packets the system creates are entirely compatible with existing 802.11b Wi-Fi networks. In prototype experimentation, the team was able to successfully communicate data between remote Passive Wi-Fi nodes and an entirely unmodified smartphone at a range of 100 feet using the device's built-in 802.11b-compatible Wi-Fi radio. In other words: Passive Wi-Fi devices should be entirely plug-and-play - or, rather, battery-and-play - with any full-power Wi-Fi equipment.

The team's paper describes the details of Passive Wi-Fi, its advantages over rival standards, and how it has been tested, and will be presented in March at the USENIX Symposium on Networked Systems Design and Implementation. Sadly, the team has not yet indicated when - or if - the technology will reach the hands of consumers and makers.

We wanted to see if we could achieve Wi-Fi transmissions using almost no power at all. 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.
Shyam Gollakota, University of Washington.

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