Influence of Phase States of Binary Unit Cell on Ris Characteristics

Reconfigurable Intelligent Surfaces are devices capable of enhancing signal strength at the receiver by manipulating reflected waves. They are particularly useful in complex environments, where they can redirect signals to the receiver while bypassing obstacles. To achieve directional reflection, reconfigurable intelligent surfaces employ phaseshifting techniques at each unit cell. Various methods exist for phase modulation, with the simplest and most cost-effective using a binary phase shift. This raises an important question: can a reconfigurable intelligent surface with binary unit cells provide sufficient directional radiation? In this study, numerical simulations were conducted to analyze the dependence of received signal power on the number of available phase states in a reconfigurable intelligent surface. The obtained characteristics were compared with those of a perfect reconfigurable intelligent surface, in which each unit cell generates a continuous phase shift. Simulation results indicate that the power difference between a reconfigurable intelligent surface with binary unit cells and a perfect reconfigurable intelligent surface is approximately 6.88 dB. Additionally, the attenuation coefficient in the reconfigurable intelligent surfacesassisted link was analyzed as a function of the number of reconfigurable intelligent surfaces elements. The results show that the power deficiency of binary unit cells can be compensated by increasing the reconfigurable intelligent surfaces array size. Specifically, a <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$12 \times 12$</tex> reconfigurable intelligent surface with binary unit cells achieves higher received power than an <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$8 \times 8$</tex> reconfigurable intelligent surface with four-phase unit cells. Furthermore, simulations were extended to configurations with unit cells providing three, four, and five discrete phase states.