Paper Summary:

Satellite-to-underwater communication over FSO can potentially be applied to a variety of naval applications via a passive optical network (PON) using non-orthogonal multiple access visible light communication (NOMA-VLC). The proposed system delivers a channel rate of 10/2.5 Gbps and  support for 290 underwater devices. Receiver sensitivities of of 23 dB for downlink and 10dB for uplink under clear environmental conditions. A high 10 dBM signal-to-noise ratio is maintained over 10km of SO, 100 km of fiber and 5 m of VLC range. This is demonstrated with a low 10^−9 bit error rate (BER).

As 5G networks and traffic demands have advanced, satellite systems have been incorporated into underwater communications systems, particularly FSO based systems. In the underwater domain FSO is referred to as Underwater Optical Wireless Communications (UWOC) and is used for applications such as environmental and pollution monitoring, offshore exploration, port security and oceanography. In order to meet these demands a hybrid PON-FSO system using VLC and wave division multiplexing and optical code multiple access. OCDMA works by encoding each bit of data with a unique code that can be recognized and correlated to the intended recipient at the receiving end, allowing for multiple users to transmit at the same time. specifically, a modified zero cross-correlation MNZCC OCDMA code is used.

Source:

https://www.mdpi.com/2073-8994/15/3/739