Bit error rate and outage analysis of MIMO-FSO communications over K-distributed atmospheric channels with imperfect feedback

In this paper, we propose a weighting scheme (WS) for an imperfect feedback-based multiple-input multiple-output free-space optical (MIMO-FSO) system over K-distributed fading channels which employs equal gain combining (EGC) at the receiver. More precisely, the optimal beam-forming vector is obtained so as to minimize the upper bound of the average bit error rate (BER) of the proposed scheme. For performance comparison, we consider three competitive schemes referred to as error-free feedback (EF), erroneous feedback (FWE) and repetition coding (RC). Moreover, the performance of the proposed method is analyzed in terms of outage probability. To this aim, we first derive the expression of the outage probability for the WS (proposed), FWE, RC and EF schemes and then, the performance of these methods is compared through different numerical simulations. We show that the proposed beamforming scheme outperforms the FWE and RC schemes in terms of BER and outage probability, even under an imperfect feedback link. Moreover, we show that the performance of the proposed scheme approaches that with ideal feedback by decreasing the error probability of the feedback link.