Performance analysis of OOK and PPM modulation schemes in MIMO-FSO links under gamma-gamma atmospheric turbulence

Abstract

Free Space Optics (FSO) technologies are a promising and cost-effective solution to meet the increasing demand for bandwidth. These technologies ensure high transmission security and are compatible with OCDMA (Optical Code Division Multiple Access) systems, providing potential for an all-optical communication network in the future. However, FSO systems suffer from two major limitations that must be overcome: high dependence on atmospheric conditions and Multiple Access Interference (MAI) in FSO-MIMO (Multiple Input Multiple Output) networks. In this study, we simulated an FSO-MIMO-Direct Sequence)-OCDMA transmission link considering a Gamma-Gamma channel. The DS-OCDMA sequences were modulated using OOK (On-Off Keying) and PPM (Pulse Position Modulation), which are commonly used in FSO transmissions. The performance of the transmission link was evaluated in terms of BER (Bit Error Rate) using a Monte Carlo algorithm. Our simulations indicate that PPM modulation provides better resistance to atmospheric scintillation while allowing access to a higher number of users than OOK modulation.