BER Performance Comparison of Gamma-Gamma FSO link for Different Modulations and Diversity Techniques

Nowadays, FSO is the best choice for last-mile communication due to its high data rate and low complexity. There are many challenges in FSO, like atmospheric turbulence, scintillation, background noise, beam divergence loss, etc. However, to overcome these, we have several mitigation techniques like modulation and coding, diversity, adaptive optics, aperture averaging, and hybrid RF/FSO. The FSO link needs to be compared for different modulation and diversity schemes to check its effectiveness against atmospheric turbulence. This article compares the BER performance of different modulation schemes like BPSK, DBPSK, QPSK, 8-QAM, 8-PSK, binary and quaternary Optical Space Shift Keying (OSSK) in different strengths of atmospheric turbulence considering the Gamma-Gamma channel model. We have also compared diversity and combining schemes like Maximum Ratio Combining (MRC) and Equal Gain Combining (EGC) to overcome the effect of atmospheric turbulence in weak, strong, and moderate turbulence.