Angle of arrival of underwater wireless optical communications

Underwater wireless optical communication (UWOC) has been regarded as one of the promising solutions to underwater wireless communication systems due to its advantages of high bandwidth, fast transmission and good confidentiality. In UWOC systems, after emitting from light source, photons will be scattered with random deviated angles before propagating to the receiver plane. Hence, the light beam suffers a spatial angle spread at the receiver side. In order to improve the system performance with an appropriate receiver design, it is of significance to figure out the angle of arrival (AOA) distribution of the received light beam. In addition, the UWOC channel is susceptible to other effects such as absorption, turbulence and bubbles, especially when it is exposed to the complex ocean environment. Therefore, analyzing the impacts of these factors on AOA distribution is also essential to evaluate UWOC system performance. The existing studies of AOA distribution only considered single scattering component, which is not practical for turbid water. Furthermore, there are few studies focusing on multi-source scenarios. In this paper, we first present a simple expression for AOA distribution with single light source, taking both single and multiple scattering components into account. Then we extend the work to multi-source scenarios and derive the corresponding closed-form expression of AOA distribution. Compared to the traditional single scattering case, numerical results show that the proposed AOA distribution can fit well with Monte Carlo simulation results with various water types, link distances, and the characteristics of actual light sources.