  Intelligent reflecting surface (IRS) is an enabling technology to engineer
the radio signal prorogation in wireless networks. By smartly tuning the signal
reflection via a large number of low-cost passive reflecting elements, IRS is
capable of dynamically altering wireless channels to enhance the communication
performance. It is thus expected that the new IRS-aided hybrid wireless network
comprising both active and passive components will be highly promising to
achieve a sustainable capacity growth cost-effectively in the future. Despite
its great potential, IRS faces new challenges to be efficiently integrated into
wireless networks, such as reflection optimization, channel estimation, and
deployment from communication design perspectives. In this paper, we provide a
tutorial overview of IRS-aided wireless communication to address the above
issues, and elaborate its reflection and channel models, hardware architecture
and practical constraints, as well as various appealing applications in
wireless networks. Moreover, we highlight important directions worthy of
further investigation in future work.
