Polarization Diversity in MIMO Communication Over Atmospheric Turbulence Channels

In this work we consider multiple-input multiple-output (MIMO) communication over atmospheric turbulence channels and propose two novel free space optical communication approaches based on polarization shift keying (POLSK). The first approach combines MIMO POLSK with pulse position modulation (PPM) constituting a good compromise between power and spectral efficiencies compared to standard uses of PPM and POLSK. The second approach employs POLSK in an optical spatial modulation based MIMO architecture and introduces a spectrally efficient scheme that also offers better error performance gains than other spectrally efficient modulation techniques. We also consider error protection for the proposed systems and show the importance of unequal error protection for the bits corresponding to different signalling dimensions. We provide theoretical analyses to evaluate the performance of both systems over atmospheric turbulence channels and provide average bit error probability bounds. The theoretical derivations are also corroborated via extensive simulation results and comparisons with conventional modulation approaches.