Transmittance, scintillation and BER analysis in underwater optical wireless communication systems

Underwater Wireless Optical Communication (UWOC) has been more popular in recent years due to the need for high data rate transmission in underwater communication. In this thesis, UWOC system is considered to improve its performance by analyzing the effects of different beam types on the system in turbulent underwater medium. More specifically, the influences of oceanic turbulence on the link performance of UWOC such as the transmittance, beam spread, scintillation and BER are examined thoroughly for different optical sources beams. PCFT, cosine Gaussian, partially coherent cosine-Gaussian, cosine-hyperbolic Gaussian and partially coherent cosine-hyperbolic Gaussian beams are used as the source to benchmark the performance of the system. To investigate the oceanic turbulence effect on the UWOC system, the power spectrum of the ocean is assumed to be homogeneous and isotropic. Additionally, the extended Huygens Fresnel principle is employed to analyze the average transmittance. In particular, on-axis and off-axis average transmittance is examined for the PCFT, cosine-Gaussian, cosine-hyperbolic Gaussian, and their partially coherent cases as well. With the help of Carter's definition, beam spread is observed for the PCFT beam. The scintillation calculation is also benefited from the extended Huygens Fresnel principle. Apart from these, oceanic turbulence effects on BER, which is another performance criterion, in the UWOC link was also studied. Calculations were carried out by using the MATLAB program. All the system performance phenomena are examined against the important parameters of oceanic turbulence, such as the rate of dissipation of mean square temperature, ratio of the temperature and salinity contributions to the refractive index spectrum and the rate of dissipation of kinetic energy for the unit mass of fluid. Moreover, with these analyses, the degree of coherence and off-axis parameters are also studied. With this thesis, we aim at selecting suitable beams for the underwater turbulent environment and to examine the performance of UWOC links in different aspects under various excitations.