Abstract
Underwater optical wireless communication (UOWC) has been widely advocated as a viable way to satisfy these high-speed links constraints in the marine medium through the use of the visible spectrum. Nevertheless, UOWC faces several limitations, such as the path-loss due to the absorption and scattering phenomena, caused by underwater particles. Thus, quantifying this path-loss is of paramount importance in the design of futuristic UOWC systems. To this end, several approaches have been used in this regard, namely the Beer–Lambert’s law, Monte Carlo simulation, as well as radiative transfer equation (RTE). This last mentioned evaluates the optical path-loss of the light wave in an underwater channel in terms of the absorption and scattering coefficients as well as the scattering phase function (SPF). In this paper, an improved numerical solver to evaluate the time-dependent RTE for UOWC is proposed. The proposed numerical algorithm was improved based on the previously proposed ones, by making use of an improved finite difference scheme, a modified scattering angular discretization, as well as an enhancement of the quadrature method by involving a more accurate seven-point quadrature scheme in order to calculate the weight coefficients corresponding to the RTE integral term. Importantly, we applied the RTE solver to three different volume scattering functions, namely the single-term Henyey–Greenstein (HG) phase function, the two-term HG phase function, and the Fournier–Forand phase function, over both Harbor-I and Harbor-II water types. Based on the normalized received power evaluated through the proposed algorithm, the bit error rate performance of the UOWC system is investigated in terms of system and channel parameters. The enhanced algorithm gives a tightly close performance to its Monte Carlo counterpart by adjusting the numerical cumulative distribution function computation method as well as optimizing the number of scattering angles.
Highlights
With the prospering of the wireless communication industry over the last decades, human exploration in the underwater environment increased significantly
It is noteworthy that the above equation depicts the recursive numerical solution of the proposed TD-radiative transfer equation (RTE) solver for the instantaneous light radiance, in terms of the system and channel parameters, namely the source radiance, the discretization steps in space and time coordinates, the number of directions, scattering and absorption coefficient, and light celerity in the medium as well
The proposed RTE solver was applied for three types of scattering phase functions namely, the single-term Henyey-Greenstein (STHG), two-terms Henyey-Greenstein (TTHG), and FF SPFs
Summary
With the prospering of the wireless communication industry over the last decades, human exploration in the underwater environment increased significantly. Within the past few years, the use of radiative transfer equation (RTE) has attracted significant attention in the fields of optics for biomedical imaging [13] It is considered as a deterministic solution for describing light propagation in multiple absorbing and scattering medium (e.g., fluids, underwater environment), in terms of the medium IOP, such as absorption and scattering coefficients as well as the scattering phase function (SPF). This last-mentioned defines the scattering power distribution over the various directions in the propagation medium. In [14], a numerical approach to solve the time-dependent (TD) RTE using the finite difference equation and the discrete ordinate method (DOM) was proposed.
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