Abstract – Wi-Fi has traditionally been considered
a power-consuming communication system and has not
been widely adopting in the sensor network and IoT
space. 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 offthe-
shelf smartphones and Wi-Fi chipsets over distances
of 30–100 feet in various line-of-sight and through-thewall
scenarios. Finally, we design a passive Wi-Fi IC
that shows that 1 and 11 Mbps transmissions consume
14.5 and 59.2 mWrespectively. This translates to 10000x
lower power than existing Wi-Fi chipsets and 1000x
lower power than Bluetooth LE and ZigBee.