This letter presents an experimental study comparing the relative impact of turbulence induced scattering on coherent and non-coherent light propagating through water. It is shown that the scintillation index increases with increasing temperature inhomogeneity in the underwater channel. Our results indicate that a light beam from a non-coherent source has a greater resilience to temperature inhomogeneity induced turbulence effect in an underwater channel. These results will help researchers in simulating realistic channel conditions when modelling a light emitting diode (LED) based underwater optical wireless communication (UOWC) link.
This paper presents an empirical comparison of different modulation schemes in still and turbulent water conditions. Using an underwater channel emulator, it is shown that pulse position modulation (PPM) and subcarrier intensity modulation (SIM) have an inherent resilience to turbulence induced fading with SIM achieving higher data rates under all conditions. Finally, the signal processing technique termed pairwise coding (PWC) is applied to SIM in underwater optical wireless communications for the first time. The performance of PWC is compared with the, state-of-the-art, bit and power loading optimisation algorithm. Using PWC, a maximum data rate of 5.2 Gbps is achieved in still water conditions.
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