Selection decode-and-forward cooperative FSO systems with adaptive rate strategy over Gamma-Gamma fading channels

This paper analytically studies the performance of selection decode-and-forward (DF) cooperative free-space optical communication (FSO) systems, employing adaptive subcarrier quadrature amplitude modulation (SC-QAM) and taking into account the fading effect caused by atmospheric turbulence. Closed-form expressions of outage probability, spectral efficiency and bit-error rate (BER) are derived, using a novel accurate series approximation method. Numerical results highlight the improvement of the proposed system compared with all-active relaying and non-adaptive FSO systems. The validity of the analytical method is also confirmed by Monte-Carlo simulations.