Beyond 10 Gbps in Hostile Underwater Optical Wireless Communication Channel Conditions using Polarisation Division Multiplexing

This paper describes the empirical evaluation of polarisation division multiplexing (PDM) as a means to increase the spectral efficiency of subcarrier intensity modulation (SIM) in underwater optical wireless communications (UOWC). The UOWC channel is first characterised in order to gain an understanding of the effect of the water conditions under consideration on the propagating optical signal. Then the performance of SIM-PDM is investigated under turbulent and turbid channel conditions in terms of bit error rate (BER) and maximum data rate. Using SIM-PDM along with quadrature amplitude modulation (QAM) and the bit and power loading (BPL) technique, a maximum data rate of 12.1 Gbps is achieved in a still water channel whilst rates of 10 Gbps are maintained in turbid and turbulent water conditions.