  Reconfigurable intelligent surface (RIS)-empowered communications is on the
rise and is a promising technology envisioned to aid in 6G and beyond wireless
communication networks. RISs can manipulate impinging waves through their
electromagnetic elements enabling some sort of control over the wireless
channel. In this paper, the potential of RIS technology is explored to perform
a sort of virtual equalization over-the-air for frequency-selective channels
whereas, equalization is generally conducted at either the transmitter or
receiver in conventional communication systems. Specifically, with the aid of
an RIS, the frequency-selective channel from the transmitter to the RIS is
transformed to a frequency-flat channel through elimination of inter-symbol
interference (ISI) components at the receiver. ISI is eliminated by adjusting
the phases of impinging signals particularly to maximize the incoming signal of
the strongest tap. First, a general end-to-end system model is provided and a
continuous to discrete-time signal model is presented. Subsequently, a
probabilistic analysis for the elimination of ISI terms is conducted and
reinforced with computer simulations. Furthermore, a theoretical error
probability analysis is performed along with computer simulations. It is
analyzed and demonstrated that conventional RIS phase alignment methods, can
successfully eliminate ISI and the RIS-aided communication channel can be
converted from frequency-selective to frequency-flat.
