System parameters effect on the turbulent underwater optical wireless communications link

Abstract

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.

Statistical channel model to characterize turbulence‐induced fluctuations in the underwater wireless optical communication links

“…Generalized gamma and exponentiated Weibull distributions -Kumar et al 50 Increasing turbidity Exponential decay -Vali et al 22 Weak-to-strong and saturated turbulence regimes…”

“…In the uniform channel, the UWOC link parameters such as beam divergence angle, transmission span, receiver aperture diameter, and field of view (FOV) are studied in the turbulent environment. Additionally, the characteristics of the turbulent channel based upon the received intensity are estimated through an MC simulation, which provides a Lognormal channel model for weak‐to‐strong turbulent scenarios and negative exponential distribution (NED) for saturated turbulent scenarios 22 . From a data transmission application point of view, the BER and the luminous efficiency are estimated in the moving water channel with a river flow simulator.…”

“…Additionally, the characteristics of the turbulent channel based upon the received intensity are estimated through an MC simulation, which provides a Lognormal channel model for weak-tostrong turbulent scenarios and negative exponential distribution (NED) for saturated turbulent scenarios. 22 From a data transmission application point of view, the BER and the luminous efficiency are estimated in the moving water channel with a river flow simulator. Further, by considering the lognormal turbulence channel model, the BER of the UWOC system is evaluated under different water types namely, clear, coastal, and harbor water channels.…”

Time Jitter, Turbulence and Chromatic Dispersion in Underwater Optical Wireless Links

“…The turbulence effect plays a very significant role in the terrestrial optical wireless links [39][40][41][42]. However, in the corresponding underwater systems, turbulence is still a significant mitigation factor for their performance [18,43,44]. More specifically, by assuming weak water turbulence, the irradiance fluctuations at the receiver of the UOWC link can be studied through the log-normal (LN) distribution.…”

“…More specifically, by assuming weak water turbulence, the irradiance fluctuations at the receiver of the UOWC link can be studied through the log-normal (LN) distribution. The probability distribution function (PDF) of the LN model as a function of the instantaneous normalized irradiance at the receiver, I t , is given as [18,44,45]:…”