A Fast Monte Carlo Simulation Method for Underwater Wireless Optical Channels with Large Attenuation Length.

In this work, a fast Monte Carlo (MC) simulation method is proposed to deal with the common problem of lengthy simulation time in underwater wireless optical channels with large attenuation lengths. By conducting plenty of simulations and experiments, the linear relationship between the received optical power (ROP) and reception area under large attenuation length has been observed, analyzed, and experimentally verified. Specifically, when using laser diodes (LDs) as light sources, the ROPs exhibited a linearly increasing trend as the detector diameter varied from 10 cm to 200 cm for a transmission distance of 12 m in harbor water. When using light-emitting diodes (LEDs) as light sources, a similar linear relationship held for transmission distances longer than 20 m, 10 m, and 5 m in clear water, coastal water, and harbor water, respectively. After that, our experiment also confirmed that as the water became increasingly turbid, even through only a 20-cm water body, the LD beam spot tended to homogenize. By adding 3-gram Mg(OH) 2 powder and within a measured radial displacement of ±5 cm, the normalized ROP difference would not exceed 5%. In summary, such a linear relationship can be applied to shorten the MC simulation time by simply increasing the reception area of detectors. It is greatly beneficial to the rapid design of underwater wireless optical communication systems that can support a long transmission distance or work in relatively turbid waters.