  Reconfigurable Intelligent Surfaces (RIS) will play a pivotal role in
next-generation wireless systems. Despite efforts to minimize pilot overhead
associated with channel estimation, the necessity of configuring the RIS
multiple times before obtaining reliable Channel State Information (CSI) may
significantly diminish their benefits. Therefore, we propose a CSI-free
approach that explores the feasibility of optimizing the RIS for the uplink of
a communication system in the presence of interfering users without relying on
CSI estimation but leveraging solely some a priori statistical knowledge of the
channel. In this context, we consider a multiport network model that accounts
for several aspects overlooked by traditional RIS models used in Communication
Theory, such as mutual coupling among scattering elements and the presence of
structural scattering. The proposed approach targets the maximization of the
average achievable rate and is shown to achieve performance that, in some
cases, can be very close to the case where the RIS is optimized leveraging
perfect CSI.
