Experimental Demonstration of Non-Hermitian Symmetry for DC-SC-FDM in UOWC Systems

Abstract

This study demonstrates the high spectrum efficiency of DC offset single-carrier frequency division multiplexing (DC-SC-FDM) for underwater optical wireless communications (UOWC). I and Q components were separately transmitted using dual lasers. As a result, the requirement of Hermitian symmetry is alleviated, and the computation time latency is reduced. The Gram–Schmidt orthogonalization procedure was adopted to address the I and Q orthogonality. The system comprises a 1024-point inverse fast Fourier transform (IFFT), a cyclic prefix of 32 samples, and a digital-to-analog converter (DAC) of 400 Msps, and laser diodes possess a wavelength of 553 nm with a power of 150 mW. The study includes real transmissions in a freshwater communication channel and reports experimental results. In addition, the bit error rate has been evaluated. The results show that at the forward error correction (FEC) limit, a communication distance of 10 m can be achieved. A peak-to-average power ratio reduction of 4.96 dB is reached.