Experimental Comparison of Modulation Techniques for LED-based Underwater Optical Wireless Communications

This paper presents an experimental comparison of pulse amplitude modulation (PAM), carrierless amplitude and phase (CAP), and quadrature amplitude modulation-orthogonal frequency division multiplexing (QAM-OFDM) in a turbid underwater optical wireless communications (UOWC) channel. It is shown that the transmission rates of PAM and CAP are maintained at around 180 Mbps even as turbidity increases. However, the highest transmission rate of 472 Mbps is achieved using 16-QAM-OFDM in tap water. Finally, bit power loading (BPL) is applied to further improve the performance of QAM-OFDM, yielding an increased maximum transmission rate of 557 Mbps in tap water.