Performance of free-space optical communications using SC-QAM signals over strong atmospheric turbulence and pointing errors

We theoretically analyze the performance of free-space optical (FSO) communication systems using subcarrier intensity quadrature amplitude modulation (SC-QAM) signals over strong atmospheric turbulence channels together with pointing errors. We take into account atmospheric attenuation, atmospheric turbulence and pointing errors. In order to model atmospheric turbulence, we employ a gamma-gamma distribution for strong turbulent condition. Meanwhile, we study pointing errors by using a fading model where the influence of beam width, detector size and jitter variance is considered. In addition, we use a combination of these models to analyze the combined effect of atmospheric turbulence and pointing error to SC-QAM/FSO systems. Finally, we derive a closed-form expression for evaluating the average symbol error rate (ASER) performance of such systems. Numerically evaluated results present the impact of pointing errors on the performance of SC-QAM/FSO systems over strong atmospheric turbulence. Moreover, simulation results show that the closed-form expression can provide a precision for evaluating ASER performance of such systems.