We introduce the concept of on-demand (OnD) reconfigurable intelligent surfaces (RISs), which can provide cost and spectrum resource advantages. In a case study, we demonstrate how the OnD RIS technology can be implemented. In addition, we discuss its impacts on the channel capacity and average received power. Finally, we discuss future research directions. Â

This paper derives symbolic models for end-to-end RIS-assisted FSO systems built on the fading model’s probability density functions (PDFs) characterizing the sub-channels. We study some of the most popular models and derive closed-form expressions of PDFs, cumulative distributions, and moment-generating functions that are further exploited to analyze systems’ performance. By comparing scenarios in which the sub-channels are similar and different, we provide a clear understanding of how the overall RIS-assisted FSO channel behaves, along with comparative results based on commonly used models.