Communication performance in the focusing and saturation regimes inherent to the turbulent channel: a tutorial

Early studies of laser beam propagating in turbulence indicated that the log-amplitude variance of the received intensity would grow without bound as the refractive index structure parameter and range increase. This was an ominous observation. It suggests that the laser communications and remote sensing systems would not be useful during the hot daytime conditions. Fortunately, it does not increase without limit. We describe the various scintillation indices that predict this type of performance. Specifically, we will develop the scintillation indices for satellite communications (SATCOM) downlink, SATCOM uplink, and atmospheric slant path and horizontal communications link geometries, which also include tracking, untracked, and aperture averaging receiver effects. The focusing and saturation regimes in the turbulent channel will be defined. An example analysis will be provided using this information. The importance of log-amplitude variance is that the scintillation indices will have peak values for some refractive index structure parameters and range values.