Passive Wi-Fi

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Passive Wi-Fi

A Wi-Fi technology developed by the University of Washington for low-power sensors and mobile devices. Passive Wi-Fi is said to use 10,000 times less power than regular Wi-Fi and 1,000 times less than Bluetooth LE (Low Energy) and ZigBee.

A Shared RF Signal
When a device transmits a Wi-Fi signal, its digital baseband processor modulates the carrier frequency using tens of microwatts of power. However, the analog RF chip that generates the carrier frequency consumes hundreds of milliwatts of power, an order of magnitude more than the baseband processor.

In a Passive Wi-Fi environment, a hub plugged into an AC outlet continuously transmits the analog carrier frequency. The Passive Wi-Fi device reflects this signal modulated with its own data packets to the receiving device up to 100 feet away at 802.11b speeds (11 Mbps). Because the device does not generate the RF, it uses dramatically less power. To use this technology, wireless routers and access points must also have Passive Wi-Fi built in. See carrier frequency, baseband processor, Wi-Fi, Bluetooth LE and ZigBee.
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References in periodicals archive ?
What Passive Wi-Fi proposes to do is to have the analog RF component present along with the digital baseband in just a single plugged-in device - like a wireless router or laptop - in any wireless network.
How do these Passive Wi-Fi clients communicate back and forth?
In a comment published in Wired, Vamsi Talla, who's working on the Passive Wi-Fi project, explained: "The low power passive device isn't transmitting anything at all.
Experimental evaluation of Passive Wi-Fi so far claim that "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," according to the University of Washington's website.
Technically, the principle that Passive Wi-Fi uses to create a Wi-Fi network across several devices at such low power consumption levels is called backscattering, which is different from a more traditional mesh network (deployed in ZigBee, Bluetooth LE, etc).
While Passive Wi-Fi is exciting and promises to revolutionize wireless communications technology, we mustn't get too ahead of ourselves just yet.
Right now, Passive Wi-Fi isn't really a viable alternative to conventional Wi-Fi simply because of its operating bandwidth - right now, Passive Wi-Fi can only support speeds of up to 11 Mbps, which is roughly the same as Wi-Fi 802.11b speeds - what was fashionable way back in the mid-2000s.
The researchers believe that tiny passive Wi-Fi devices could be extremely cheap to make, perhaps less than a dollar.

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