  Wireless communication has become a standard solution to address
ever-increasing demands for information transfer in our modern society.
Conventional systems work in an active way in the sense that an active carrier
signal is mandatorily required to transfer information from Alice to Bob.
Especially in the era of 5G6G and with the advent of the Internet of Things
(IoT), an exponential growth of users and connectivity confronts conventional
systems with important challenges including limited spectrum resources,
information security, energy consumption and cost efficiency. Here, we
introduce the fundamentally different concept of passive wireless communication
(PWC) which has the potential to resolve the above-mentioned issues. PWC
transfers digital information by modulating demodulating already existing
omnipresent ambient stray electromagnetic waves using a programmable
metasurface. We provide a theoretical framework for encoding decoding and
modulating demodulating in PWC and build a proof-of-principle prototype system
leveraging existing commodity 2.4GHz Wi-Fi signals. We demonstrate information
transfer from Alice to Bob with data rates on the order of hundreds of Kbps
using distinguishable information-carrying control coding patterns of
metasurface, neither necessitating an active carrier signal and its associated
radio-frequency chain nor affecting the background active wireless
communication. The presented strategy is particularly appealing for green IoT
connectivity. At the same time, the concept is applicable to all types of wave
phenomena and provides a fundamentally new perspective on the design of future
wireless communication architectures.
