  Reconfigurable intelligent surface (RIS)-empowered communication is one of
the promising 6G technologies that allows the conversion of the wireless
channel into an intelligent transmit entity by manipulating the impinging waves
using man-made surfaces. In this paper, the potential benefits of using RISs
are investigated for indoor/outdoor setups and various frequency bands (from
sub 6 GHz to millimeter-waves). First, a general system model with a single RIS
is considered and the effect of the total number of reflecting elements on the
probabilistic distribution of the received signal-to-noise ratio and error
performance is investigated under Rician fading. Also for this case, the path
loss exponent is analyzed by considering empirical path loss models.
Furthermore, transmission models with multiple RISs are developed and analyzed
for indoor and outdoor non line-of-sight (NLOS) scenarios. The conventional RIS
selection strategies are also integrated for systems equipped with multiple
RISs for the first time. Through extensive simulations, it is demonstrated that
the RIS-assisted systems provide promising solutions for indoor/outdoor
scenarios at various operating frequencies and exhibit significant results in
error performance and achievable data rates even in the presence of system
imperfections such as limited range phase adjustment and imperfect channel
phase estimation at RISs.
