14 Gbps QAM–OFDM optical wireless communication system employing pulse shaping technique in coastal water environment with optimization of cyclic prefix length

With the growing development of human activities in underwater, the demand of underwater optical wireless communication (UOWC) link with high data-rate is expanding day by day and it is widely used in security surveillance, environmental monitoring, oil pipe inspection etc. UOWC system provides high data-rate and larger bandwidth. Employing Quadrature amplitude modulation and orthogonal frequency division multiplexing (QAM OFDM), a UOWC system has been demonstrated using 520 nm green laser-diode (LD). 14 Gbps data-rate has been transmitted by applying 64, 128 and 256 QAM OFDM signals over 28.5 m, 27 m and 25 m distances. The BER values are 6.04 \(\times {10}^{-9}\) $\times {10}^{-9}$ over 28.5 m transmission for 64-QAM–OFDM, 5.26 \(\times {10}^{-9}\) $\times {10}^{-9}$ for 128-QAM–OFDM over 27 m transmission and 2.15 \(\times {10}^{-9}\) $\times {10}^{-9}$ for 256-QAM–OFDM over 25 m transmission, in coastal water environment. Clear constellation diagrams, good Q-values and smaller BER values have been obtained using our proposed architecture with optimized CP-lengths. Hence our proposed system is useful for large data-rate transmission employing this QAM–OFDM modulation technique.