  The employment of intelligent reflecting surfaces (IRSs) is a potential and
promising solution to increase the spectral and energy efficiency of wireless
communication networks. Despite their many advantages, IRS-aided communications
have limitations as they are subject to high propagation losses. To overcome
this, the phase rotation (shift) at each element needs to be designed in such a
way as to increase the channel gain at the destination. However, this increases
the system's complexity as well as its power consumption. In this paper, we
present an analytical framework for the performance of random rotation-based
IRS-aided communications. Under this framework, we propose four low-complexity
and energy efficient schemes, based on a coding or a selection approach. Both
of these approaches employ random phase rotations and require limited knowledge
of channel state information. Specifically, the coding-based schemes use
time-varying random phase rotations to produce an equivalent time-varying
channel. On the other hand, the selection-based schemes select a partition of
the IRS elements based on the received signal power at the destination.
Analytical expressions for the achieved outage probability and energy
efficiency of each scheme are derived. It is demonstrated that all schemes can
provide significant performance gains as well as full diversity order.
