Wavefront distortion of data-carrying laser beam propagating through the atmosphere has been reported to have detrimental effects on the performance of Free-Space Optical (FSO) communication systems. Optical intensity fluctuation models generally assume clear air optical turbulence where atmospheric aerosols warming effects are neglected. This variation of the refractive index structure parameter (Cn2) of the atmosphere due to the aerosol induced warming and its influence on Bit Error Rate (BER) performance of FSO systems are studied in this paper using high-resolution radiosonde and multi-satellite observations of aerosols and atmospheric thermodynamics. Based on an approximate mathematical expression built on Gauss-Laguerre quadrature rule, and a radiative transfer model-based analysis, the BER of a Differential Phase Shift Keying (DPSK) FSO communication link through Exponentiated Weibull modelled turbulence with aperture averaging has been investigated. Our results show significant signal deterioration with the aerosol-induced turbulence taking a toll on the signal to noise ratio (SNR) over more than 15 dB. BER analysis under different receiver aperture dimensions is performed with the selected intensity fluctuation model. We show that aperture averaging does not have significant influence on the performance enhancement under aerosol perturbed atmospheric conditions.
Free space optical (FSO) communication is a line of sight technology capable of carrying large volume of data using laser signals through the atmosphere. This unguided propagation of laser beams through the atmosphere confronts with turbulent fluctuations and suspended aerosol particles on its en route to the receiver. Random fluctuations in the atmospheric refractive index causes variations in the propagation constant and thereby affects the optical pulse propagation. We examine the local atmospheric warming effects of absorbing aerosols on the atmospheric refractive index fluctuation statistics and its influence on the group velocity dispersion (GVD) parameter. Black Carbon (BC) aerosols increase local temperature through solar absorption, which will be amplified when they reside in the upper atmosphere for longer duration, owing to the reduced atmospheric density prevailing at higher altitudes. To elucidate the implications of elevated BC layer heating on FSO links, vertical BC mass concentration was measured using an Aethalometer (Model AE-42, of Magee Scientific, USA) mounted on a hydrogen filled balloon. Long term analysis of multi-satellite observations along with in-situ measurements of aerosol parameters show dependence of GVD on aerosol induced local atmospheric warming. Effect of warming on outage probability of FSO systems employing chirped Gaussian pulses are also presented.
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