Free-space optical communication using subcarrier modulation in Gamma-Gamma atmospheric turbulence

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 and consequently impaired error performance. In this paper, the error performance of the FSO using a subcarrier intensity modulation (SIM) based on a binary phase shift keying scheme in clear but turbulent atmosphere is presented. To evaluate the system error performance in turbulence regimes from weak to strong, the probability density function of the received irradiance after traversing the atmosphere is modelled using the gamma-gamma distribution and the effect of turbulence induced irradiance fluctuation is mitigated using spatial diversity