  The Reconfigurable Intelligent Surface (RIS) constitutes one of the prominent
technologies for the next 6-th Generation (6G) of wireless communications. It
is envisioned to enhance signal coverage in cases where obstacles block the
direct communication from Base Stations (BSs), and when high carrier
frequencies are used that are sensitive to attenuation losses. In the
literature, the exploitation of RISs is exclusively based on traditional
coherent demodulation, which necessitates the availability of Channel State
Information (CSI). Given the CSI, a multi-antenna BS or a dedicated controller
computes the pre/post spatial coders and the RIS configuration. The latter
tasks require significant amount of time and resources, which may not be
affordable when the channel is time-varying or the CSI is not accurate enough.
In this paper, we consider the uplink between a single-antenna user and a
multi-antenna BS and present a novel RIS-empowered Orthogonal Frequency
Division Multiplexing (OFDM) communication system based on the differential
phase shift keying, which is suitable for high noise and/or mobility scenarios.
Considering both an idealistic and a realistic channel model, analytical
expressions for the Signal-to-Interference and Noise Ratio (SINR) and the
Symbol Error Probability (SEP) of the proposed non-coherent RIS-empowered
system are presented. Our extensive computer simulation results verify the
accuracy of the presented analysis and showcase the proposed system's
performance and superiority over coherent demodulation in different mobility
and spatial correlation scenarios.
