Diversity and Multiplexing for Near-Field Atmospheric Optical Communication

In this paper, the performance of multi-beam free-space optical (FSO) communication systems are studied through an accurate analytical approach which does not rely on far-field assumptions commonly used in the literature. A framework is presented for analytical and numerical performance analyses of multi-beam FSO systems employed in a diversity or multiplexing scheme. The performance analyses show that the far-field assumptions may not correctly estimate the system behavior in many geometrical scenarios within practical interest. The results demonstrate the degrading effects of diffraction and spatial correlation of atmospheric turbulence in the form of diversity gain reduction in diversity systems and crosstalk in multiplexing systems. These effects have been mostly neglected in the literature by applying far-field assumptions. Our results can thus be useful in the design of practical diversity or multiplexing FSO systems especially when a compact design is desired.