Performance evaluation of 6.4 Tbps WDM-MIMO FSO system employing QAM-FSK dual modulation in diverse atmospheric conditions

Free-space optics (FSO) is a promising technology for meeting the high bandwidth and data rate requirements of modern wireless communications. However, atmospheric instability, such as turbulence, significantly degrades the quality of the received signal. This challenge can be effectively mitigated by integrating wavelength-division multiplexing (WDM) and multiple-input multiple-output (MIMO) techniques. This research presents a simulation-based performance analysis of a quadrature amplitude modulation frequency-shift keying (QAM-FSK) dual-modulated, linearly polarised WDM-MIMO-FSO system under various atmospheric conditions, including haze, rain, and fog. The proposed system uses eight individual wavelength channels, each carrying 200 Gbps of QAM-FSK-modulated data, which are then transmitted via four FSO-MIMO links. This configuration achieves a high net data transmission rate of 6.4 Tbps. The simulation results show that under clear weather conditions, the system can achieve a remarkable link range of up to 113 km. Furthermore, across all eight wavelength channels and under various adverse atmospheric conditions, the proposed system demonstrates a superior Q-factor, high signal-to-noise ratio (SNR), and low bit error rate (BER) when compared to prior works in the literature.