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Free-space optical communication employing polarization shift keying coherent modulation in atmospheric turbulence channel

A binary polarization shift keying (2PolSK) scheme with a coherent heterodyne receiver for a free space optical (FSO) link through atmospheric turbulence channel is proposed and discussed. The maximum ratio combining (MRC) and equal gain combining (EGC) spatial diversity techniques have been applied to mitigate the turbulence induced irradiance fluctuation with bit error rate (BER) expressions derived for each. The communication channel is modelled as a gamma-gamma channel. The analysis of the 2PolSK characteristics is based on the error performance in turbulence regimes from weak to strong. Simulation results show that using the proposed system with MRC offers the best performance but at the cost of high system complexity.