Performance analysis for multi-hop UOWC system over mixture Exponential–Gamma with two IM-DD fading channels

Abstract

This paper provides the end-to-end performance of a multi-hop underwater optical wireless communication (UOWC) system using channel-state-information assisted (CSI) or fixed-gain amplify-and-forward (AF) relays, in which the intensity modulation-direct detection (IM-DD) is taken into account for detection. Particularly, not only the IM-DD input-independent but also the IM-DD cost-dependent additive white Gaussian noise (AWGN) channel is considered in such system analyses. In order to focus on multi-hop performance improvement and simplify calculation, the pointing error is not considered in this paper. In our study, the channel irradiance fluctuations are characterized by the mixture Exponential–Gamma (EG) distribution. With Fox H-function, exact analytical expressions for the probability density function (PDF) and the cumulative distribution function (CDF) are derived, respectively. Based on these formulas, with different hop numbers N, the outage probability (OP) and the average bit-error rate (ABER) of various modulation schemes are presented. Furthermore, numerical analyses are provided and to further investigate the effects of the turbulence severity on the performance of multi-hop UOWC system. And simulation results verifies the accuracy of the obtained analytical and asymptotic expressions. The obtained results indicate that the overall system performance enhances with an increase of the number of hops.