A Diversity Combining Approach for MIMO FSO Nodes with Misaligned Receivers

The performance of Free Space Optical (FSO) links is severely influenced by misalignment of optical nodes. Pointing errors and misalignment can be caused as a result of unintentional optical heads sway induced by external sources. Misalignment can be also considered intentionally under some cases, e.g. mobile FSO, to establish optical connections while maintaining node mobility. In this paper, the authors utilize an angular diversity model to characterize the performance of multiple-in multiple-out (MIMO) FSO receivers with misalignment and atmospheric turbulence. The transmitted beam is assumed as a uniform plane wave. Channel turbulence fading is modeled as a spatially correlated lognormal distribution. Diversity scheme called switch-and-examine combining (SEC) is proposed by this study. When compared with a conventional selection-combining scheme, SEC provides a reduction in processing load. The corresponding bit error rate performance, however, degrades slightly.