Aperture-averaged level-crossing probability in an atmospheric communication link.

The intensity statistics of light pulses in an atmospheric communication link are studied here for the case of a finite (nonpoint) detector aperture. The calculation of the statistics of the pulse intensities averaged over the aperture is performed by using a discrete aperture model and applying the multidimensional ognormal distribution. The results of the numerical calculations demonstrate the dependence of the level-crossing probability on aperture radius, number of pulses, and the length of a pulse sequence. The level-crossing probabilities were measured experimentally and found to be in close agreement with the theoretical values.