RIS Assisted RF Communication Systems with H-ARQ Protocols and Imperfect CSI

In this paper, we propose to compensate the effects of imperfect channel state information (CSI) through the use of a reconfigurable intelligent surface (RIS)-assisted radio frequency (RF) communication system with hybrid automatic repeat request (H-ARQ) protocols thereby enhancing coverage and improving link reliability of the RF system. We derive novel series-based expressions of the probability density function (PDF) and cumulative distribution function (CDF) for the signal-to-interference-plus-noise ratio (SINR) at the destination (D) node, which is valid for an arbitrary number of RIS reflecting plates and various transmission rounds of H-ARQ protocols. Capitalizing on the derived CDF of SINR, we compute the outage probability (OP) and throughput for at least once (ALO), chase combining (CC), and incremental redundancy (INR) H-ARQ protocols. We analyze the impact of various H-ARQ rounds, number of RIS reflecting elements, and channel correlation coefficient on the performance of the considered system. The numerical results demonstrate that the proposed communication system shows remarkable performance improvement compared to the traditional RF communication systems.