NLOS Underwater Optical Wireless Communications With Wavy Surface Using Relay Coordination Based on Incremental Hybrid Decode-Amplify-Forward Scheme

Channel fading caused by environmental factors such as sea waves is one of the key issues that highly impedes the practical implementation and deployment of non-line-of-sight (NLOS) underwater optical wireless communication (UOWC) systems. To alleviate the channel fading and further improve the system performance, in this paper, we propose a relay coordination scheme based on incremental hybrid decode-amplify-forward (IHDAF) for NLOS UOWC system with the Pierson wave model. The proof-of-concept of the proposed scheme for NLOS UOWC system is verified via Monte Carlo (MC) simulation. The numerical results show that the transmission distance of the NLOS UOWC system to achieve the bit-error-rate (BER) below 7% hard-decision forward error correction (HD-FEC) limit of 3.8 × 10⁻³ can be improved significantly and enhanced robustness to the channel fading caused by the sea waves can be obtained with the help of the proposed IHDAF scheme as compared to conventional decode-forward (DF) or amplify-forward (AF) scheme. In addition, the optimal performance of the NLOS UOWC system employing IHDAF scheme can be achieved when the normalized distance between the transmitter and relay node and the power distribution factor are set as 0.8 and 0.9 respectively. Our research enables more accurate analysis and design of practical NLOS UOWC systems with wavy surfaces employing cooperative relaying protocols.