Improved m-QAM-OFDM transmission for underwater wireless optical communications

In this paper, a novel OFDM symbol frame structure was proposed to improve the performance of underwater wireless optical communication (UWOC) systems with m-QAM-OFDM modulation. In the frame, the data-carrying OFDM symbol and corresponding phase-conjugated symbol was interleaved. At the receiver end, by simple superposition of received symbols, the noise suppression can be achieved. The feasibility was experimentally demonstrated by transmitting m-QAM-OFDM signal over a 12.5-m tap water channel and a 1.25-m highly scattering medium which composed of tap water and skimmed milk. The results show that BER performance can be significantly improved in both clear water channel and turbid water channel. Moreover, the proposed frame structure can provide a robust and simple path to compromise between transmission capacity and distance.