Establishing and Maintaining a Reliable Optical Wireless Communication in Underwater Environment

TL;DR

This paper develops control algorithms for an underwater optical communication system between an autonomous underwater vehicle and a surface ship, ensuring stable connectivity and high data rates despite environmental uncertainties.

Contribution

It introduces a novel NLPD control strategy with Lyapunov stability analysis for maintaining optical link stability in underwater environments.

Findings

NLPD controller improves tracking error by over 70% under nominal conditions.

Controller maintains stable optical link despite oceanic disturbances.

Numerical simulations validate the effectiveness of the proposed control algorithms.

Abstract

This paper proposes the trajectory tracking problem between an autonomous underwater vehicle (AUV) and a mobile surface ship, both equipped with optical communication transceivers. The challenging issue is to maintain stable connectivity between the two autonomous vehicles within an optical communication range. We define a directed optical line-of-sight (LoS) link between the two-vehicle systems. The transmitter is mounted on the AUV while the surface ship is equipped with an optical receiver. However, this optical communication channel needs to preserve a stable transmitter-receiver position to reinforce service quality, which typically includes a bit rate and bit error rates. A cone-shaped beam region of the optical receiver is approximated based on the channel model; then, a minimum bit rate is ensured if the AUV transmitter remains inside of this region. Additionally, we design two control algorithms for the transmitter to drive the AUV and maintain it in the cone-shaped beam region under an uncertain oceanic environment. Lyapunov function-based analysis that ensures asymptotic stability of the resulting closed-loop tracking error is used to design the proposed NLPD controller. Numerical simulations are performed using MATLAB/Simulink to show the controllers' ability to achieve favorable tracking in the presence of the solar background noise within competitive times. Finally, results demonstrate the proposed NLPD controller improves the tracking error performance more than $70\%$ under nominal conditions and $35\%$ with model uncertainties and disturbances compared to the original PD strategy.