Ultra-high capacity long-haul PDM-16-QAM-based WDM-FSO transmission system using coherent detection and digital signal processing

The ever-increasing demand for wide channel bandwidth, high-speed information, and spectral-efficient communication links with advanced modulation schemes has led to the evolution of the free space optics (FSO) links. This paper proposes an FSO transmission link based on eight-channel wavelength division multiplexing technique integrating spectral-efficient polarization division multiplexing with a 16-level quadrature amplitude modulation (PDM-16-QAM) scheme, with each channel carrying 160 Gbps of information. The proposed link deploys coherent detection technique and the digital signal processing unit to boost the system efficiency and to compensate for the deterioration of the information signal due to channel fading, atmospheric attenuation and atmospheric turbulence. Using numerical simulations, we demonstrate an effective transmission of 1.28 Tbps data with FSO link range varying from 84 km to 1.95 km depending on the weather conditions with reasonable bit error rate results. We also scrutinize the output of the system with published works and demonstrate a better performance for the proposed FSO system i.e. bit rate and range. The proposed system can be implemented under complex atmospheric conditions to achieve a reliable high-speed transmission of information for fronthaul and backhaul links.