Performance evaluation of M-ary pulse position modulation and on off keying in a direct detection optical wireless communication system in the presence of atmospheric effects

Optical wireless communication--in space and in both outdoor and indoor terrestrial applications is rapidly becoming a major feature of modern life and so it has been the subject of much research in recent years. The major sources of performance degradation have been identified as the spatial, angular, and temporal spread of the propagating beam when the propagation channel is multiscattering, resulting in reduced power reception and inter signal interference, as well as turbulence-induced scintillations and noise due to receiver circuitry and background illumination. In this paper performance analysis is carried out for an optical wireless link in the presence of atmospheric scintillation using OOK and M-ary PPM modulation schemes. Then a theoretical analysis of coherence interference in optical wireless communication through scattering channels is carried out for a fixed a scintillation variance and try to quantify the resultant performance degradation due to multiscattering channel. We conclude that for both atmospheric scintillation and multiscattering effect higher order PPM offers better performance than OOK.