Date Added: Oct 2012
Free space optical communication has widespread use because of its advantages such as high modulation bandwidth, enhanced security and low power. In free space optical communication, laser beam signals are transmitted through air. Due to atmospheric turbulence, signals are affected. This atmospheric turbulence leads to fading of the channel. The variations in the temperature and pressure of the atmosphere cause variations in the refractive index. The beam distortions have been analyzed using various models. Particularly K-distributed models have been widely used for km-scale FSO links. In order to mitigate the effect of turbulence, error control codes and spatial diversity schemes are used. Atmospheric turbulence causes fluctuations in the intensity (scintillation) and phase of the received laser beam signal.