BER analysis of MIMO/FSO systems using rectangular QAM over gamma-gamma channels

In this paper, we theoretically analyze the performance of multiple-input multiple-output free-space optical (MIMO/FSO) communication systems employing rectangular quadrature-amplitude modulation (QAM) scheme. The gamma-gamma distribution is used to model the atmospheric turbulence channels and the equal-gain combining (EGC) receiver is employed. We analytically derive the closed-form expression of BER in term of average signal-to-noise ratio per bit. The numerical results quantitatively discuss the improvement of MIMO systems compared to the one using single-input single-output (SISO) scheme.