  This paper presents a literature review on recent applications and design
aspects of the intelligent reflecting surface (IRS) in the future wireless
networks. Conventionally, the network optimization has been limited to
transmission control at two endpoints, i.e., end users and network controller.
The fading wireless channel is uncontrollable and becomes one of the main
limiting factors for performance improvement. The IRS is composed of a large
array of scattering elements, which can be individually configured to generate
additional phase shifts to the signal reflections. Hence, it can actively
control the signal propagation properties in favor of signal reception, and
thus realize the notion of a smart radio environment. As such, the IRS's phase
control, combined with the conventional transmission control, can potentially
bring performance gain compared to wireless networks without IRS. In this
survey, we first introduce basic concepts of the IRS and the realizations of
its reconfigurability. Then, we focus on applications of the IRS in wireless
communications. We overview different performance metrics and analytical
approaches to characterize the performance improvement of IRS-assisted wireless
networks. To exploit the performance gain, we discuss the joint optimization of
the IRS's phase control and the transceivers' transmission control in different
network design problems, e.g.,~rate maximization and power minimization
problems. Furthermore, we extend the discussion of IRS-assisted wireless
networks to some emerging use cases. Finally, we highlight important practical
challenges and future research directions for realizing IRS-assisted wireless
networks in beyond 5G communications.
