A General Orthogonal Transform Aided MIMO Design for Reliable Maritime Visible Light Communications

In maritime visible light communication (VLC) systems, user information is delivered among different terminals distributed in the atmosphere, and the underwater environment. To combat the complex and variant marine channel conditions induced by the absorption, scattering, and turbulence influence, in this article, we propose a general orthogonal transform (OT) aided multiple input multiple output (MIMO) transmission scheme to enhance the transmission reliability performances. In our design, we propose to construct the orthogonal transform matrix recursively with the Hadamard matrix. Thus we could exploit the repetitive property of the elements in the orthogonal matrix to enlarge the Euclidean distances among the signals. Moreover, the value of the elements could be adjusted dynamically to adapt to time-changing channel conditions. Thanks to the orthogonality of the matrix, and the singular value decomposition (SVD), the interferences among signals could be effectively suppressed. Accordingly, the reliability performances can be improved. Furthermore, we derive the theoretical symbol error rate (SER) expressions for the proposed design. Numerical simulations are performed to validate the theoretical analysis. Furthermore, the SER performances with different water types, and wind speeds in various scenarios of the atmosphere, underwater, and air-water interface channels are investigated, and compared with the counterpart systems.