Heterodyne receivers for atmospheric optical communications

The performance of an optical heterodyne receiver for communication through the clear-air turbulent atmosphere is considered. Optimum and certain suboptimum adaptive processors are developed for receivers that synchronously demodulate the IF signal and those that use envelope demodulation. Error probabilities are presented demonstrating the effects of turbulence level, signal strength, and spatial diversity on binary orthogonal communication systems. In addition, a simple expression is developed for the optimum aperture size of an optical heterodyne receiver.