An optical signal suffers from irradiance and phase fluctuations when propagating through the free space optical (FSO) turbulence channel, thus resulting in the degradation of the bit error rate (BER) performance. The BER performance can be improved by adopting the multiple-input multiple-output (MIMO) scheme. In this paper, we propose a coherent binary polarization shift keying (BPOLSK) modulation scheme with MIMO employing maximum ratio combining and equal gain combining diversity techniques to mitigate the turbulence effect. The gamma–gamma statistical channel model is adopted for all the turbulence regimes. The BER performance for the proposed BPOLSK-MIMO FSO link is compared with the single-input single-output and ON–OFF-keying systems by means of computer simulation. The optical power gain is investigated and demonstrated under different turbulence regimes for a number of transmitters/receivers.
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