Free-Space Optical Communication With Spatial Modulation and Coherent Detection Over H-K Atmospheric Turbulence Channels

The use of optical spatial modulation (OSM) is proposed as a simple low-complexity means of achieving spatial diversity in coherent free-space optical (FSO) communication systems. In doing so, this paper presents a generic analytical framework for obtaining the average bit error probability (ABEP) of uncoded and coded OSM with coherent detection in the presence of turbulence-induced fading. Although the framework is general enough to accommodate any type of channel models based on turbulence scattering, the focus of the analysis is on the H-K distribution as such model is very general and valid over a wide range of atmospheric propagation conditions. Using this framework, it is shown that OSM can offer comparable performance with conventional coherent FSO schemes employing spatial diversity at the transmitter or the receiver only, while outperforming the latter in terms of spectral efficiency and hardware complexity. Furthermore, various numerical performance evaluation results are also presented and compared with equivalent results obtained by Monte Carlo simulations which verify the accuracy of the derived analytical expressions.