  Intelligent reflecting surfaces (IRSs) are a promising technology for
enhancing coverage and spectral efficiency, both in the sub-6 GHz and the
millimeter wave (mmWave) bands. Existing approaches to leverage the benefits of
IRS involve the use of a resource-intensive channel estimation step followed by
a computationally expensive algorithm to optimize the reflection coefficients
at the IRS. In this work, focusing on the sub-6 GHz band of communications, we
present and analyze several alternative schemes, where the phase configuration
of the IRS is randomized and multi-user diversity is exploited to
opportunistically select the best user at each point in time for data
transmission. We show that the throughput of an IRS assisted opportunistic
communication (OC) system asymptotically converges to the optimal
beamforming-based throughput under fair allocation of resources, as the number
of users gets large. We also introduce schemes that enhance the rate of
convergence of the OC rate to the beamforming rate with the number of users.
For all the proposed schemes, we derive the scaling law of the throughput in
terms of the system parameters, as the number of users gets large. Following
this, we extend the setup to wideband channels via an orthogonal frequency
division multiplexing (OFDM) system and discuss two OC schemes in an IRS
assisted setting that clearly elucidate the superior performance that IRS aided
OC systems can offer over conventional systems, at very low implementation cost
and complexity.
