Link range optimisation for detection methods under scintillation effects on FSO system

Free-space optical (FSO) communication is a promising technology that aims to solve the problem of limited bandwidth in modern cellular communication systems. This work investigates the FSO communication systems under varying atmospheric conditions using direct, Mach-Zehnder interferometer (MZI), and coherent detection methods. A detailed analysis evaluates their trade-offs in cost, complexity, and performance. Results indicate that coherent detection achieves the highest link range with an optimal bit error rate (BER) across all turbulence regimes, with maximum feasible ranges of 7.4 km, 6.6 km, and 6.5 km under weak, moderate, and strong scintillation, respectively. Further, optimising local oscillator (LO) power significantly improves system reliability under strong turbulence, enabling robust communication. This study highlights the advantages of coherent detection for FSO systems, particularly in strong scintillation regimes, which provide better receiver sensitivity and link range coverage.