BER analysis and capacity evaluation of FSO system using hybrid subcarrier intensity modulation with receiver spatial diversity over log-normal and gamma–gamma channel model

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In this work, the performance of free space optical system is evaluated in terms of bit error rate (BER) and capacity using PPM–BPSK–SIM (hybrid-SIM) modulation scheme. Addition to that, we have applied spatial diversity technique for the proposed system. We have calculated the BER and the capacity at various atmospheric turbulence levels over the log-normal and gamma–gamma channel models. The analysis has been carried out at different signal-to-noise-ratio (SNR) values and link distances. The simulation results show that hybrid-SIM modulation scheme achieves better BER performance than BPSK–SIM scheme in both the channel models; furthermore, the BER performance gets improved significantly by spatial diversity technique.