A Survey on Passive Beamforming using Statistical State Information in Intelligent Reflecting Surface Assisted Networks

Intelligent reflecting surface (IRS) is one of the promising technologies for next-generation communication networks, which is capable of customizing propagation environment and provides significant improvements in terms of energy and spectral efficiency. To realize these potential benefits of the IRS, an efficient IRS passive beamforming design should be considered. However, most recent studies have relied on instantaneous channel state information (I-CSI), which changes very fast and is not practical. Alternatively, using slow-varying statistical CSI (S-CSI) or their combination (hybrid CSI) is more attractive. This paper reviews some recent studies on S-CSI and hybrid CSI for IRS passive beamforming design.