Temporal spectrum of atmospheric scintillation and the effects of aperture averaging and time averaging

Historical perspective of free space optical communications: from the early dates to today's developments

“…the regular motion of air cells due to thermal turbulence fluctuation can be determined. More variations of the refractive index results in random optical beam fluctuations at a frequency range of ∼10 Hz to about 800 Hz, typically for the PSD of scintillation for horizontal propagation path with a point Rx [9][10][11]27]. The optical beam interaction with the atmosphere along the optical path is not the same throughout due to the random fluctuations and power loss of the air mass along the FSO path.…”

“…Since the atmospheric conditions play a vital role in determining the FSO system performance it needs to be accounted for while calculating the LM for any FSO system design. Existing LM models that include atmospheric channel and transmit-receive station parameters can be found in [9,10,15,27,31,32]. These models support the designers to have an optimum transmit-receive station parameter to initiate a data link with the maximum possible data rate for all weather conditions at a given location.…”

“…PDF is difficult. The C n 2 and received power PDF prediction models designed based on the open-atmosphere and indoor man-made atmospheric chamber can be found in the literature [9,10,15,27]. Some of the main factors, corresponding to the optical channel that needs to be considered to install the FSO system are beam divergence loss, background noise, sky radiance, miss-alignment or pointing loss, cloud blockage, atmospheric seeing, and angle of arrival (AOA) fluctuations.…”

“…3. Water droplets and aerosol particles formed by vapours of size of a few hundred microns and they can alter the characteristics of propagating optical wave, completely hamper it, degrade the wave front quality, which may result in the signal loss and/or fluctuations of the signal intensity/phase caused by their combined interactions of absorption, scattering, and reflection [9,10,[26][27][28], thereby limiting the link availability with increased system BER [19,26,27,36]. Fog substantially attenuates visible and near-IR radiations.…”

“…The main factor for the scintillation of the optical field at the Rx optics is the fluctuation of atmospheric turbulence strength along the optical path due to the solar inhomogeneous heating of channel air pockets. The scintillation ultimately creates intensity/phase fluctuations over time at the Rx optics [9-12, 36, 38], which has to be treated as a random variable [9,10,27,38]. In the short-range (<1 km) optical propagation, the effects due to scintillation are smaller than the effects in long-range (>1 km).…”