Diversity-reception UWOC system using solar panel array and maximum ratio combining.

We demonstrated a diversity-reception lens-free underwater wireless optical communication system employing a 2×2 solar panel array as detectors. The respective relationships between solar panel sizes and photocurrents, output voltages, system bandwidths were studied theoretically and experimentally. The signals output from the array were combined via maximum ratio combining in order to improve the signal quality. A 450-nm blue laser was used in the transmitter and a light spot with a size of 20mm×35mm was formed on the receiving plane after a 7-m transmission in tap water. With the solar panel array, a data rate of 84 Mbps was achieved with a bit error rate of 2.17 × 10-3 using 16-QAM OFDM signal. Meanwhile, a single solar panel with the same size as the array only achieved 60 Mbps. Solar panel array can bring about 40% data rate improvement. With the same detection area, the horizontal detection range of detectors increased from 37 mm for single solar panel to 55 mm for solar panel array thanks to the diversity reception. The results show that solar panel array using maximum ratio combining can enhance the transmission data rate as well as the detection range. The impacts of air bubbles, water fluctuation and microscopic particulates suspension on the proposed solar panel array-based system were also investigated. The results show that the received power sensitivity of solar panel array is 5.22 dB higher than single solar panel with the same detection area with a data rate of 60 Mbps and a BER of 10-3.