Performance enhancement of 112 Gbps UWOC link by mitigating the air bubbles induced turbulence with coherent detection MIMO DP-16QAM and advanced digital signal processing

Underwater applications like real-time marine observations, video streaming, communication between underwater sensor nodes require spectrally efficient, high-speed (>100 Gbps) and reliable wireless links. In this paper, a coherently detected dual-polarization (DP)-16 quadrature amplitude modulation (QAM) based system is proposed for turbulent underwater wireless optical communication (UWOC) which can transmit a data rate of 112 Gbps. The integration of digital signal processing (DSP) with a coherent system enables error-free transmission at longer distances. The proposed single-input single-output (SISO) system achieves reliable link ranges of 150 m, 55 m, 24 m, 10 m, and 5.5 m under the pure sea, clear ocean, coastal ocean, harbor I, and harbor II water conditions. Furthermore, spatial diversity with multiple-input multiple-output (MIMO) techniques is utilized to mitigate turbulence-induced losses and path losses. At the receiver, the multiple received MIMO branches are combined with the equal gain combining (EGC) method. The transmission range improvements have been observed with 2 × 2 MIMO and 3 × 3 MIMO techniques over the SISO UWOC system. The power budget enhancement of 6 dBm is observed by utilizing a 3 × 3 MIMO configuration over 1 × 1 SISO configuration, and 3 dBm power budget enhancement has been observed in the case of a 2 × 2 MIMO configuration over 1 × 1 SISO configuration. The proposed system can further be utilized in real ocean scenarios to transmit time-sensitive information among diverse underwater sensor nodes.