We systematically investigate the bubble-induced performance degradation for underwater optical wireless communication (UOWC) with different bubble sizes and positions. By using different transmit and receive diversities, we investigate the effectiveness of spatial diversity on the mitigation of the bubble-induced impairment to the UOWC link. With the help of a 2 × 2 multiple input multiple output using repetition coding and maximum ratio combining, a robust 780 Mbit/s UOWC transmission is achieved. The corresponding outage probability can be significantly reduced from 34.6% for the system without diversity to less than 1%.

This Letter investigates the performance of the two-way multi-hop system for underwater optical wireless communications. With the decode-and-forward (DF) relaying, the two-way multi-hop system is modeled, where the effects of absorption, scattering, and oceanic turbulence are all taken into account. An exact closed-form expression for outage probability is derived under the assumption that the oceanic turbulence obeys a log-normal distribution. Numerical results demonstrate the impacts of various parameters on the outage performance and indicate that the two-way multi-hop system significantly improves the performance in comparison to both the one-way multi-hop system and the two-way two-hop system.

Average transmittance of multi-Gaussian (flat-topped and annular) optical beams in an anisotropic turbulent ocean is examined analytically based on the extended Huygens–Fresnel principle. Transmittance variations depending on the link length, anisotropy factor, salinity and temperature contribution factor, source size, beam flatness order of flat-topped beam, Kolmogorov microscale length, rate of dissipation of turbulent kinetic energy, rate of dissipation of the mean squared temperature, and thickness of annular beam are examined. Results show that all these parameters have effects in various forms on the average transmittance in an anisotropic turbulent ocean. Hence, the performance of optical wireless communication systems can be improved by taking into account the variation of average transmittance versus the above parameters.

In underwater optical wireless communication (UOWC), a channel is characterized by abundant scattering/absorption effects and optical turbulence. Most previous studies on UOWC have been limited to scattering/absorption effects. However, experiments in the literature indicate that underwater optical turbulence (UOT) can cause severe degradation of UOWC performance. In this paper, we characterize an UOWC channel with both scattering/absorption and UOT taken into consideration, and a spatial diversity receiver scheme, say a single-input–multiple-output (SIMO) scheme, based on a light-emitting-diode (LED) source and multiple detectors is proposed to mitigate deep fading. The Monte Carlo based statistical simulation method is introduced to evaluate the bit-error-rate performance of the system. It is shown that spatial diversity can effectively reduce channel fading and remarkably extend communication range.