Performance enhancement of RIS-assisted MRR-UOWC systems using the spectral-power-efficient [formula omitted]QAM-MPPM

Abstract

Reconfigurable Intelligent Surfaces (RISs), proposed as innovative units, possess the potential to establish reliable connections in Underwater Optical Wireless Communication (UOWC) systems, where direct transmission (DT) experiences significant weakening due to dynamic channel conditions. In this paper, we examine the performance of a UOWC system consisting of an RIS and a modulating retroreflector (MRR), referred to as the RIS-assisted MRR-UOWC system. The channel is affected by a combination of path loss, gamma–gamma (G–G) turbulence, and pointing error (PE). The considered system employs the spectral-power-efficient L-ary Quadrature Amplitude Modulation Multi-Pulse Pulse-Position Modulation (LQAM-MPPM) technique. For our system performance measures, we present upper-bound (UB) and approximate UB expressions for the average bit-error rate (BER) of LQAM-MPPM signals. These expressions are used to analyze the system’s performance. Performance metrics are established by deriving the Probability Density Function (PDF), Cumulative Distribution Function (CDF), and Moment-Generating Function (MGF) for the end-to-end signal-to-noise ratio (SNR), resulting from the sum of products of independent but not identically distributed (i.ni.d) channel coefficients. The results of our study indicate that the LQAM-MPPM scheme surpasses traditional schemes.