A Beamforming Scheme for MIMO and MISO FSO Links over Atmospheric Turbulence Channels with Imperfect Feedback

Atmospheric turbulence is one of the major chal- lenges in free space optical (FSO) communication systems. The channel state information (CSI) can be estimated at the receiver and fed back to the transmitter. However, in practical FSO systems, the feedback bits cannot be received error-free. Here, we propose an imperfect feedback-based beamforming technique for MIMO-FSO systems over K −distributed fading channels which employs equal gain combining (EGC) at the receiver. More precisely, we propose a weighting scheme (WS) that reduces the effect of selecting wrong aperture due to erroneous feedback where the optimal beamforming vector is obtained by minimizing the upper bound of the average bit error rate (BER) of the proposed scheme. For performance comparison, we consider two competitive schemes referred to as error-free feedback (EF) and repetition coding (RC). Comparative simulation results confirm the superiority of the proposed WS scheme over EF and RC beamforming schemes.