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.