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Underwater visible light communication emerges as a promising technique to enhance the capacity of underwater wireless communication networks for upcoming generation. Major technical problem with underwater visible light communication systems in motion is the pointing, acquisition, and tracking. To ease pointing, acquisition, and tracking, hence it is important to navigate optical information beam over broad range and adjust the transmitter beam divergence angle according to the link condition, which is adjusted by the Optisystem software. In this paper, performance comparison among wide range of transmittance optical beams in underwater visible light communications system for high-speed communication is presented for PIN as well as for Avalanche photodiode. The effect of using variable transmittance beam-divergence angle on the bit-error rate, signal-to-noise ratio, communication link distance is also investigated. OptiSystem and MATLAB software is used to implement the underwater visible light communication transceiver system. Finally, it is shown in the paper that in the presence of pointing errors, adaptive beam control techniques improve the performance of high-speed Underwater visible light communication system. [ABSTRACT FROM AUTHOR]

To balance the output stability and maximum efficiency of a system, an efficiency optimization method based on adaptive frequency control is proposed. In this paper, load transmission is carried out using a DC–DC converter at the receiving end. When the load changes, controlling the rectified output voltage is carried out to realize the maximum efficiency point tracking. Meanwhile, the duty cycle of the rear stage DC–DC converter is changed to keep the output voltage constant. The sampled rectified voltage is compared with the estimated value and the resulting error data are sent to the system transmitter through ASK modulation wireless communication. Then the transmitter demodulation communication information through PID algorithm control is used to achieve the frequency of the adaptive adjustment. The feasibility of the proposed method has been verified by the simulation and experimental results. When the output voltage is 5 V, the constant voltage accuracy is within ± 1%, the maximum efficiency is up to 79.2%, and the dynamic response time is only 160 ms. [ABSTRACT FROM AUTHOR]