Investigation of Different Modulation Techniques Under Strong FSO Turbulance Channel in South Africa

Free-space optical communication provides an alternative to radio frequency (RF) communication over the last two decades. Besides this advantages of the FSO, the major limitation is the strong atmospheric turbulence, which severely reduce the performance of the signal transmitted in the channel. Poor FSO communication performance is the direct effect of scintillation which resulted in deep signal fading and thus increasing the bit error rate. This research paper aims to find the most suitable modulation schemes for FSO system under strong weather challenged channel with a focus on the South African climatic conditions. The performance of power efficiencies, bandwidth efficiency, BER (Bit Error Rate) and SNR (Signal-to-noise ratio) for the four modulation schemes (On-Off keying (OOK), Binary Phase Shift Keying (BPSK), Differential Phase Shift Keying (DPSK) and Quadrature Phase Shift Keying (QPSK) have been studied and compared. The simulated results for BER, channel capacity and outage probability of various modulation techniques are plotted and analyzed for different values of α and β (where α = 4.0, β = 1.2 and α = 4.2, β = 1.0 for large scale and small scale). Observed that the BPSK BER performs better when compared with the other modulation schemes, as PAM scheme is the bandwidth efficient scheme while PPM scheme is the power efficient with lower dB.