On BER of Fixed-Scale MIMO Underwater Wireless Optical Communication Systems

Underwater wireless optical communication (UWOC) has huge potential for its high speed, low latency and reliable security. However, besides the channel impairments such as absorption and scattering, dynamic ocean environments can also degrade the system performance and even incur link interruptions. In this paper, we propose a 4 × 4 fixed-scale multiple-input multiple-output UWOC system to remove the impediment of link misalignment. The system employs two collimated lens to perform a mapping from each source to associated photodetector. The bit-error rate expression is also derived to evaluate the system performance. Numerical simulations illustrate that the absorption and scattering induced path loss can be alleviated by this system when the scattering angles are relatively small and the communication range is moderate. Furthermore, the system diminishes the sensitivity of underwater vehicles to dynamic ocean environments. By taking the window truncation effect into consideration, we quantify the enhancement of system robustness to link misalignment.