  Integrating reconfigurable intelligent surfaces (RISs) in emerging
communication systems is a fast-growing research field that has recently earned
much attention. While implementing RISs near the base station (BS), i.e.,
BS-side RIS, or user equipment (UE), i.e., UE-side RIS, exhibits optimum
performance, understanding the differences between these two deployments in
terms of the system design perspective needs to be clarified. Critical design
parameters, such as RIS size, phase shift adjustment, control link, and element
type (passive/active), require greater clarity across these scenarios.
Overlooking the intricacies of such critical design parameters in light of 6G
demands endangers practical implementation, widening the gap between
theoretical insights and practical applications. In this regard, our study
investigates the impact of each RIS deployment strategy on the anticipated 6G
requirements and offers tailored RIS design recommendations to fulfill these
forward-looking requirements. Through this, we clarify the practical
distinctions and propose a comprehensive framework for differentiating between
BS-side and UE-side RIS scenarios in terms of their design parameters.
Highlighting the unique needs of each and the potential challenges ahead, we
aim to fuse the theoretical underpinnings of RIS with tangible implementation
considerations, propelling progress in both the academic sphere and the
industry.
