Intelligent Reflecting Surface Aided Multicasting With Random Passive Beamforming

In this letter, we consider a multicast system where single-antenna transmitter sends common message to multiple users, aided by an intelligent reflecting surface (IRS) equipped with N passive elements. Prior works on IRS have mostly assumed the availability of channel state information (CSI) for designing its beamforming. However, acquisition CSI requires substantial training overhead that increases N. contrast, propose in letter novel random beamforming scheme, performs independent reflection Q ? 1 times each coherence interval without need acquisition. For proposed first derive closed-form approximation outage probability, based which optimal best performance can be efficiently obtained. Then, purpose comparison, lower bound probability traditional CSI-based Numerical results show small is preferred high-outage regime (or high rate target) and becomes larger as decreases target decreases). Moreover, scheme significantly outperforms taken into consideration when and/or number users are large, thus offering promising CSI-free alternative existing schemes.