Performance Analysis of Seamless Rate-Adaptive Non-Line-of-Sight Underwater Optical Wireless Communications With Wavy Surface

Non-line-of-sight (NLOS) underwater optical wireless communication (UOWC) systems can provide high-speed data transmission in the environment with channel blockages but are severely affected by channel fading caused by sea waves. In this paper, we propose a novel rate compatible modulation (RCM) scheme for NLOS UOWC system with the Pierson wave model to address the issue and further improve the system performance. We verify the proof-of-concept of the proposed scheme for NLOS UOWC system through Monte Carlo (MC) simulation. Our results show that seamless rate adaptations can be achieved regardless the channel conditions with the help of the proposed RCM scheme, which results in significant improvement of the achievable uninterrupted transmission distance and enhanced robustness to the channel fading caused by the sea waves, solar radiation, water absorption and scattering as compared to conventional adaptive modulation and coding (AMC) schemes based on LDPC codes. In addition, the maximum achievable data rate of the NLOS UOWC system employing RCM schemes with weight set of <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$W_{4}$</tex-math></inline-formula> = <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula>1, <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula>1 and <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$W_{5}$</tex-math></inline-formula> = <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$\pm$</tex-math></inline-formula>1 can be achieved when the receiver orientation angle (ROA) is 52.5°. Our work provides huge potential and fundamental frameworks for the implementation and design of practical NLOS UOWC systems and networks.