Performance analysis of OSTBC in gamma-gamma fading channels

The multi-input multi-output (MIMO) system with a subcarrier intensity modulation (SIM) scheme in free-space optics (FSO) has a huge merit for ultra wide band communications mainly due to its diversity gain to be able to mitigate the signal scintillation caused by the atmospheric turbulence. In this study, we have analyzed the performance of the orthogonal space-time block codes (OSTBCs) in FSO links. In particular, the power series expressions of the outage probability and average bit error rate (BER) of the OSTBC for any number of antennas are derived in gamma-gamma fading channels using the SIM scheme. According to the analysis, the 3×2 OSTBC scheme could achieve a significantly high signal-to-noise ratio (SNR) gain of 62.5 dB in a strong turbulence regime, and also a moderately high SNR gain of 48 dB in a moderate turbulence regime over the no diversity at the BER of 10^-6. Monte Carlo simulation results verify the accuracy of our analysis.