Space time block coded spatial modulation for free space optical communication

Spatial modulation (SM) is a promising technique for improving spectral efficiency for both radio frequency (RF) and optical wireless communication (OWC) systems. Space-time block coding (STBC) scheme is another important technique to enhance the system performance of RF and OWC. Recently, STBC and SM techniques are combined for RF systems to take advantages of both systems while avoiding their drawbacks. In this paper, we propose space-time block coded spatial modulation (STBC-SM) for free space optical communication (FSO). We derived the analytical bit-error rate (BER) expression of the proposed system for log-normal and gamma-gamma atmospheric turbulence channels where the pulse amplitude modulation (PAM) is considered for Intensity Modulation (IM) with Direct Detection (DD). We confirm the accuracy of our analytical expression through computer simulations. Additionally, we compare our proposed optical STBC-SM scheme with the optical SM scheme in terms of BER performance.