Aperture averaging is a technique used to mitigate the effect of atmospheric turbulence by increasing the size of the receiver aperture. Increasing the aperture naturally increases the irradiance since more light reaches the sensor. This increase acts as an averaging function by providing an overall boost in signal strength, decreasing noise, and eliminating scintillation caused by small atmospheric eddies. There is some suggestion that aperture averaging may be advantageous only for satellite downlink, not uplink. 
The decrease in scintillation with increasing light-collecting area was recognized in early astronomical measurements made in the 1950s. These measurements revealed that aperture averaging causes a frequency downshift in the irradiance power spectrum. In essence, this downshift averages out the fastest (highest order/highest frequency) fluctuations from scintillation. More recently, aperture averaging effects have been studied in the context of laser beam propagation through atmospheric turbulence.