Performance Analysis of Distributed Alamouti based UWOC System

Abstract

Underwater wireless optical communication (UWOC) system serves as an efficient transmission solution in comparison to the RF and acoustic counterparts for a variety of underwater applications like surveillance, explorations and climate monitoring as it offers higher data rates, lower latency and reduced energy consumption. However, the performance of an UWOC system degrades with an increase in temperature and pressure gradients, air bubble levels and salinity variations, which collectively contribute to underwater optical turbulence (UOT). In this paper, UOT is characterized by the Exponential-Generalized Gamma (EGG) distribution. Moreover, to improve the reliability and performance of UWOC links, a 2 $\times$ 1 Alamouti based space-time block code (STBC) employing Intensity Modulation/Direct Detection (IM/DD) with subcarrier intensity modulation (SIM) technique using M-PSK is considered, which significantly improves the error rate of the UWOC system. An MGF based approach is used to derive the average SER and the diversity order of the considered UWOC system. The performance of the UWOC system is analysed under different underwater channel conditions, for both salty as well as fresh waters and it is observed that water salinity affects the system performance in a greater degree than air bubbles. Furthermore, the diversity analysis demonstrates that the diversity gain is upper bound to 1.