Narrow-beam optical communications in underwater wireless network with passive node mobility

Underwater wireless sensor networks are garnering a greater research interest as human's endeavor to investigate deeper into the depths of the ocean. However, infrastructure is currently lacking in underwater communications. Acoustic communications have been long the preferred method, however, as applications become more resource intensive, the low bit rates and high latency of acoustic communications require the use of optical or electromagnetic communications. In this research, we propose a surface-to-floor optical link capable of carrying higher bit rates and with a much improved latency. However, much research in underwater optical communications does not take into account passive node mobility. Passive node mobility is caused by water currents moving nodes in jet streams and vortices. We therefore introduced a mobility model to our research to better simulate the underwater communications channel. Passive node mobility can cause transmitter and receiver misalignment, a problem for free space optical communications. This misalignment can also introduce a greater temporal spread in received photons further degrading the links performance. It was found that when both the transmitter and receiver exhibited passive node mobility, the temporal spread increased greatly and Inter Symbol Interference which could produce higher bit error rates than previously suggested in literature.