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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This paper experimentally demonstrates the resilience of frequency-shift keying (FSK) signalling to turbulence effect in underwater optical wireless communications. The findings offer valuable insight into the design trade-off between spectral efficiency and resistance to turbulence.