  Reconfigurable intelligent surfaces (RISs) empowered high-frequency (HF)
wireless systems are expected to become the supporting pillar for several
reliability and data rate hungry applications. Such systems are, however,
sensitive to misalignment and atmospheric phenomena including turbulence. Most
of the existing studies on the performance assessment of RIS-empowered wireless
systems ignore the impact of the aforementioned phenomena. Motivated by this,
the current contribution presents a theoretical framework for analyzing the
performance of multi-RIS empowered HF wireless systems. More specifically, we
statistically characterize the cascaded composite turbulence and misalignment
channels in terms of probability density and cumulative distribution functions.
Building upon the derived analytical expressions, we present novel closed-form
formulas that quantify the joint impact of turbulence and misalignment on the
outage performance for two scenarios of high interest namely cascaded
multi-RIS-empowered free space optics (FSO) and terahertz (THz) wireless
systems. In addition, we provide an insightful outage probability upper-bound
for a third scenario that considers parallel multi-RIS-empowered FSO systems.
Our results highlight the importance of accurately modeling both turbulence and
misalignment when assessing the performance of such systems.
