Waving Effect Characterization for Water-to-Air Optical Wireless Communication

In this paper, we establish and experimentally verify a water-to-air (W2A) visible light communication (VLC) system through dynamic air-water interface. Considering the complexity of waves in real environments, we divide waves into largescale wave and small-scale wave. Monte Carlo simulation and experimental results show that small-scale wave mainly affects the energy distribution of the light spot on the receiving plane and the variation frequency of link gain, while largescale wave mainly affects the coverage of the light spot. In the W2A-VLC system based on light-emitting diode (LED), the statistical characteristics of variation time and link gain are mainly related to the small-scale wave, and the effect of large-scale wave can be treated as slow fading. In order to design a reliable communication system, a large-divergence-angle LED array and avalanche photodiode (APD) array are used under dynamic water surface. We investigate three cases, namely single-input multiple-output (SIMO), multiple-input single-output (MISO) and multiple-input multiple-output (MIMO). In the SIMO or MISO systems, the correlation coefficient of channel gain decreases with the inter-receiver or inter-transmitter distance. A significant transmission performance enhancement can be achieved by deploying more transmitters or receivers and increasing the distance between the transmitters or receivers. A MIMO structure can effectively increase the achievable rate. We further establish a W2A-VLC link in a deep wave pool to verify our research in the real environment. The results show that more intensive small-scale wave yields higher bit error rate (BER), and the diversity scheme can improve the transmission stability and decrease BER.