System Parameters Effect on the Turbulent Underwater Optical Wireless Communications Link

In underwater optical wireless communications (UOWC) the link performance is greatly affected by the turbulence. Turbulence is due to the random variations of the refractive index of water, which leads to both intensity (i.e., fading) and phase fluctuation of the optical beam. The effects of turbulence on link performance depend on the choice of system parameters. In this paper, the effects of the transmission link span, divergence angle of the transmitted Gaussian beam, receiver’s (Rx) aperture diameter and field of view (FOV) on the UOWC link performance under the turbulence condition is investigated. The results show that, lognormal and negative exponential distributions fit well with the probability density function of the received light intensity under weak-to-strong and saturated turbulence regimes or for a link span longer than 120 m. The goodness of fit test is performed to validate the conformity of the two distributions with the simulation results. The scintillation index (SI) variation as a function of the four mentioned parameters under different turbulence regimes is investigated. It is shown that, for a 100 m link span and under weak turbulence, while the effect of transmitter’s FOV on SI is negligible, increasing the transmitter’s divergence angle by 1.72º and decreasing the Rx's aperture diameter by 9.2 cm, increases the SI by 53 times and 77 times, respectively.