Channel Modeling for Orbital Angular Momentum Based Underwater Wireless Optical Systems

The underwater turbulence channel is modelled and a unified statistical distribution is applied for characterizing orbital angular momentum (OAM) propagation in underwater wireless optical communication (UWOC) systems. Based on Monte-Carlo simulations, the effects of turbulences are characterized by the multiple phase screens model considering both the coherence width and scintillation index. The phase screen samples are processed by the randomized spectral sampling discrete Fourier transform (DFT) technique. To validate the propagated field distribution, both the phase structure function and optical transfer function are derived and evaluated with the aid of ensemble-averaged results. The Generalized Gamma Distribution (GGD) enriched by an additional independent parameter is applied for modelling the probability density function (PDF) of both the reference-channels, fluctuating irradiance as well as the intermodal crosstalk irradiance between different OAM modes. Furthermore, based on the PDF, the performance metrics of both single input multiple output (SISO) and multiple input multiple output (MIMO) systems are analyzed, based on the average capacity, the bit-error rate and the outage probability.