Performance evaluation of pre-equalized UVLC links over outdated lognormal turbulence channels

Underwater visible light communication (UVLC) is important for various underwater applications, including diver-to-diver information sharing, oil field exploration, port security, underwater surveillance systems, and environmental monitoring. However, it should be remembered that UVLC links are strongly affected by underwater optical turbulence (UOT). This may necessitate frequent adjustments in transmit power based on current channel state information (CSI) to mitigate fading effects. In some applications, such as diver-to-diver links, the quasi-static variations in the channel coefficient between transmission frames—attributable to the semi-fixed positions of the transmitting and/or receiving nodes—lead to practical implementations of the transmit power selection that may rely on outdated CSI. In this paper, we investigate the degradation in error rate performance caused by the use of outdated channel information in setting transmit power. Especially, we derive a closed-form expression for the bit error rate (BER) for a pre-equalized UVLC link over outdated lognormal turbulence channels. We verify the derived expression using Monte Carlo simulations.