Capacity analysis of underwater visible light communication systems over a lossy channel in the presence of noises.

Absorption and scattering losses due to impurities and turbidity in the water affect the transmission quality of underwater visible light communication links, restricting the channel capacity. For the first time to our knowledge, this paper analytically studies the channel capacity of a point-to-point underwater visible light communication link in the presence of input-independent and -dependent noises along with absorption and scattering losses. This way, novel lower and upper bound expressions on channel capacity are derived when average and peak-intensity constraints are imposed on the channel input. Our proposed upper and lower bounds are tight at high optical signal-to-noise ratio. The derived analytic expression of capacity also helps to evaluate the available data rate in the presence of different types of noise and water. From the results, we can say that input-dependent noise causes more system capacity degradation than input-independent noise. The results show that good water quality is crucial for high-capacity communication links. Furthermore, it is shown that the attenuation of the optical signal is more in water when compared to air as a medium, and channel capacity decreases as the link range increases. The results reported in this paper provide valuable insight into the design of underwater visible light communication systems.