An Analysis of Heterodyne Pulse-Position Modulation Communication Systems Over Unguided, Turbulent Optical Channels

This article investigates the performance of the heterodyne detection scheme for optical pulse-position modulation (PPM) communications channels when nonideal laser transmitters are employed. Two aspects of this channel will be considered. First, the limitations of unguided, turbulent channels in accommodating coherent laser communications are addressed. This is followed by an investigation of the performance of a heterodyne optical PPM communication system. It is demonstrated here that, due to the presence of laser phase noise, noncoherent (or asynchronous) RF detection is a preferred mode of detection and that the overall performance is severely hampered in the presence of phase noise. The performance of the proposed receiver is compared with that of the avalanche photodiode detector (APD)-based direct-detection receiver. It is shown here that the APD-based detector outperforms its heterodyne counterpart across a wide range of background radiation levels.