Advanced techniques for the design of MIMO free space optical communication systems

Abstract

Free space optical (FSO) communication is an effective alternative to radio frequency (RF) communication in terms of potential high data rates, cost efficiency and wide bandwidth on unregulated spectrum. However, FSO systems are susceptible to severe atmospheric turbulence conditions causing random fluctuations in the intensity and phase of the optical signal. These turbulence induced fading effects may severely degrade the FSO system performance, limiting its use to only short-range applications and clear weather conditions. In this dissertaion, with the motivation to overcome these limitations, analysis and design of FSO communication systems are considered. First a unified framework for determining the inter-aperture separations in multiple-input-multiple-output (MIMO) FSO systems such that the transmitterreceiver paths are resolvable is presented. Second a novel non-coherent MIMO optical modulation method combining optical spatial modulation (OSM) with joint pulse position and amplitude modulations, which offers better power and spectral efficiencies than conventional MIMO optical modulation methods, is proposed. Then two novel FSO communication approaches based on polarization shift keying (POLSK) are considered. The first non-coherent 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, while the second employs POLSK in an OSM based MIMO architecture and introduces a spectrally efficient coherent FSO communication scheme that also offers better error performance gains than other spectrally efficient modulation techniques. Finally error ratios belonging to separate signalling dimensions of these POLSK schemes are evaluated and unequal error protection (UEP) is offered to optimize the error control coding gains attained.