Date Added: Apr 2009
Free-Space Optical communications (FSO) propagated over a clear atmosphere suffers from irradiance fluctuation caused by small but random atmospheric temperature fluctuations. This results in decreased Signal-to-Noise Ratio (SNR) and consequently impaired performance. In this paper, the error performance of the FSO using a Subcarrier Intensity Modulation (SIM) based on a Binary Phase Shift Keying (BPSK) scheme in a clear but turbulent atmosphere is presented. To evaluate the system error performance in turbulence regimes from weak to strong, the Probability Density Function (PDF) of the received irradiance after traversing the atmosphere is modeled using the gamma-gamma distribution while the negative exponential distribution is used to model turbulence in the saturation region and beyond.