Secrecy Performance Analysis for Water-to-Air Visible Light Communication

This paper investigates the physical-layer security for water-to-air (W2A) visible light communication (VLC). The impacts of surface fluctuation and underwater scattering on the channel gain are theoretically analyzed, which is verified in a laboratory W2A-VLC link. The statistical properties of wave slope under experimental conditions are measured by image processing and the probability density function of the slope can be approximated by a logistic distribution. We observe that dynamic waves can cause information leakage and experimental results indicate that the probability of secure communication increases from 90.39% to 96.18% as the eavesdropper's elevation increases from 1.15 m to 1.42 m, which are approximately consistent with the numerical results. To investigate the parameters affecting the secrecy performance, several secrecy performance metrics are numerically calculated under different wave intensities, eavesdropper's locations, divergence angles of LED, underwater scattering coefficients and wavelengths of transmitted beam. It is seen that the secrecy performance is degraded as the wave intensity increases, while random scattering can mitigate the water surface fluctuations and reduce the probability of information leakage.