Impact Of Scintillation On Laser Communication Systems: Recent Advances In Modeling

Laser communication systems offer several advantages over conventional radio frequency (RF) systems but, because of shorter wavelength, are subject to various atmospheric effects. Particularly significant in this regard is the signal fading below a prescribed threshold value owing primarily to optical scintillations associated with the received signal. Over terrestrial paths of 1-3 km, or at large zenith angles between the transmitter and receiver in an uplink/downlink channel, the intensity fluctuations can easily exceed the limitations imposed by weak fluctuation theory. Under strong conditions the intensity fluctuations can no longer be modeled by a lognormal distribution - instead, we find the gamma-gama distribution to be an excellent model over virtually all conditions of irradiance fluctuations. In this paper we discuss some recent advances in the modeling of optical scintillation under weak-to-strong fluctuations associated with both terrestrial links and satellite/ground links. The analysis presented here specifically addresses scintillation effects on detector signal-to-noise ratio (SNR) and on related fading probability and error probability or bit error rate (BER). We also discuss the use of multiple aperture receivers to mitigate the effects of optical turbulence