Performance of free-space optical MIMO systems using SC-QAM over atmospheric turbulence channels

We theoretically analyze the performance of free-space optical (FSO) multiple-input multiple-output (MIMO) systems using rectangular sub-carrier quadrature modulation (SC-QAM) signaling. The systems's average symbol-error rate (ASER) is derived taking into account the atmospheric turbulence effects on the FSO MIMO channel, which is modeled by lognormal and the gamma-gamma processes for the cases of weak-to-strong turbulence conditions. We quantitatively discuss the influence of turbulence strength, link distance and different MIMO configurations on the ASER. We also derive and discuss the FSO MIMO average (ergodic) channel capacity (ACC), which is expressed in terms of average spectral efficiency (ASE), under the impact of various channel conditions.