Average Bit-Error Rate of the Alamouti Scheme in Gamma-Gamma Fading Channels

Multi-input multi-output (MIMO) in free-space optics communications with subcarrier intensity modulation has been a big research issue due to the diversity gain of MIMO to mitigate the signal scintillation caused by the atmospheric turbulence. In this work, we have analyzed the performance of the Alamouti scheme in FSO links. Particularly, a power series expression of the average bit-error rate (BER) of the Alamouti scheme is derived in gamma-gamma fading channels. As a result, the Alamouti scheme could achieve a high signal-to-noise ratio (SNR) gain of 37 dB in a strong turbulence regime, and also a high SNR gain of 27 dB in a moderate turbulence regime over the no diversity at the BER of 10^-6.