Performance of M -ary Pulse Position Modulated Underwater OWC Links With Turbulence and Path Loss Effects

Recent years have seen a surge in the usage of optical signals for real-time wireless data transfer in a wide range of underwater applications because of their large bandwidth, higher data rates, low latency, security, power, and cost efficiency. However, underwater optical wireless communication (UOWC) is substantially impaired by absorption, scattering, and turbulence effects that induce scintillations during optical signal propagation. A potential modulation scheme can be a promising solution to overcome such scintillations. The pulse position modulation (PPM) may address the fading and optical irradiance across the underwater channels while providing the power efficiency to the wireless sensor networks (WSNs). To access the link performance under the proposed modulation scheme, the closed-form expressions for outage probability and BER metrics are typically required. Unlike horizontal and single-layered models, this work evaluates the performance of vertical cascaded links in the North and Baltic oceans affected by the combined effects of absorption, scattering, and turbulence by utilizing anM-ary PPM scheme. The unified expressions for the probability density function (PDF) and cumulative distribution function (CDF) are obtained by integrating depth-dependent layered Gamma-Gamma (GG) turbulence with absorption- and scattering-based path-loss (PL) attenuations. The closed-form expressions for the outage probability (OP) and the average bit error rate (ABER) are derived by following the derived PDF and CDF to evaluate the end-to-end (E2E) performance underM-ary PPM. The analytical results are validated using experimentally extracted channel parameters and rigorous Monte-Carlo (MC) simulations.