Wavelength diversity/or Free Space Optical Systems: Performance evaluation over log normal turbulence channels

The scientific area of Free Space Optical (FSO) communication systems have attracted significant research and commercial attention in recent years. This is due to their cost-effective and license-free high bandwidth access characteristics. On the other hand, this technology is using the atmosphere as transmission media and thus the performance of an FSO system depends strongly on the atmospheric conditions in the area of the link. One phenomenon which may significantly degrade the performance of the associated communication system is the atmospheric turbulence. Many techniques have been used in order to overcome this degradation and particular attention has been given to diversity methods. In this work, we consider the use of wavelength diversity in FSO systems that operate under weak to moderate atmospheric turbulence conditions modeled by the log normal distribution. We derive mathematical expressions for the estimation of the outage probability and the average bit error rate of the system and using these expressions we present numerical results referred to common practical FSO cases, showing that the use of wavelength diversity results in considerable performance improvement at a moderate increase of the overall system's complexity and cost.