Signal Intensity Estimators for Free-Space Optical Communications Through Turbulent Atmosphere

Estimators which are motivated by the minimum mean-square error estimation criterion are proposed for the estimation of optical signal intensity in free-space optical communication systems impaired by atmospheric-induced scintillation. It is assumed that the received signal is detected using a p-i-n photodiode and that the receiver operates under a shot-noise-limited condition. The optical channel is modeled using a log-normal distribution for the received signal intensity for low (<0.75) scintillation indexes, whereas for the fully developed speckle case, a negative exponential probability density function is used to model the received signal intensity. With the aid of simulation, it is shown that the proposed estimators outperform maximum likelihood estimators for small scintillation indexes.