Rotational Misalignment Compensation for Underwater Optical Wireless Communication Employing Quaternary Polarization Shift Keying Modulation

In an underwater optical wireless communication (UOWC) system employing quaternary polarization shift keying (QPolSK) modulation, the rotational misalignment due to relative rotation of a transmitter and a receiver leads to drastic performance degradation. This work first presents an algorithm for estimating the deviation angle by leveraging the rotational invariance of circular polarization modulation. Then two rotational misalignment compensation methods employing digital signal processing and mechanical rotation respectively are introduced. Their feasibility is experimentally verified, and their respective features are discussed. The results indicate that their joint deployment can potentially deal with a large range of rotational misalignment.