Abstract—Free Space Optical (FSO) has emerged as a commercially viable standalone wireless technology as well as complementary technology to Radio Frequency (RF) and millimeter wave wireless systems for reliable and rapid deployment for high-speed data, voice and video within the access networks. However, the atmospheric channel is affected by thick fog, smoke, and turbulence as well as the challenge to the attainment of 99.999% availability. These factors pose challenges to long-range terrestrial and Space FSO communication links. In this research, the performance of Orthogonal Frequency Division Multiplexing (OFDM) - Free Space Optical (FSO) communication system over Gamma-Gamma Turbulence channel is investigated. The performance of the system is impeded by various fluctuations of irradiance and atmospheric turbulence. The OFDM-FSO channel is adapted to alleviate the effect of channel impairments by employing two traditional modulation schemes namely: Binary Phase Shift Keying (BPSK) and M-ary Quadrature Amplitude Modulation (QAM). A comprehensive analysis of Average Bit Error Rate (ABER) versus Carrier to Noise plus Distortion Ratio (CNDR) have been carried out for the above modulation schemes. In addition, Forward Error Correction (FEC) has been added to the system to enhance the robustness of the chosen modulations to further reduce the effect of turbulence and scintillation on the FSO channel. The results obtained illustrates that the coded BPSK has a better error performance when compared to other modulation scheme used at all the considered turbulence thresholds.

Index Terms—Atmospheric turbulence, free space optical communication, Orthogonal Frequency Division Multiplexing (OFDM), Gamma-Gamma turbulence model, Binary Phase Shifting Keying (BPSK) modulation, Quadrature Amplitude Modulation (QAM).

Cite: Bukola D. Ajewole, Kehinde O. Odeyemi, Pius A. Owolawi, and Viranjay M. Srivastava, "Performance of OFDM-FSO Communication System with Different Modulation Schemes over Gamma-Gamma Turbulence Channel," Journal of Communications, vol. 14, no. 6, pp. 490-497, 2019. Doi: 10.12720/jcm.14.6.490-497.