Laboratory implementation of an adaptive thresholding system for free-space optical communication receivers with signal dependent noise

Abstract

The optimum detection threshold for optical communication receivers with large signal-dependant noise components can be derived from a Bayes' Likelihood Ratio Test; however, the bit level statistics must be known a priori. In free-space communication systems, atmospheric conditions cause variations in optical transmission and subsequently in the bit level means and variances. These bit parameters must be tracked, estimated, and predicted, in order to update the detection threshold at a rate greater than the frequency of atmospheric changes. A laboratory implementation of an adaptive thresholding system is being implemented at the U.S. Naval Research Laboratory's Chesapeake Bay Free-space Lasercom Testbed. Early results of experiments underway and initial design of the system will be presented.