Selective relay decode-and-forward QAM/FSO systems over atmospheric turbulence channels

In this paper, we analytically investigate the performance of selective relay free-space optical (FSO) systems employing decode-and-forward scheme (DF) and sub-carrier quadrature amplitude modulation (SC-QAM) taking into account of the fading effect caused by the atmospheric turbulence. The log-normal distribution is used to model the fading channel. The closed-form of system symbol-error rate (SER) is analytically derived, and the numerical results quantitatively highlight the impact of the number of relays, turbulence strengths and QAM signaling on the average SER improvement of the selective relay FSO systems. We also verify the theoretical analysis by Monte-Carlo simulation and a good agreement between the analytical and simulation results is confirmed.