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Variance in FadeTime of a GammaGamma Distributed Irradiance Signal
 Date Issued:
 2012
 Abstract/Description:
 Freespace optical communications are predominantly hindered by optical turbulence, an effect caused by temperature and pressure variations within the atmosphere. The result is an optical wave interfering with itself due to multipath propagation via tiny refractiveindex fluctuations across the wavefront. Optical communication systems are affected when the channel conditions induce fading in the irradiance signal that is received at the detector. The nature of optical interference imparted by the atmosphere is a random process and therefore the received irradiance signal is often characterized by an appropriate probability density function (PDF). Data collected during past freespace optical experiments in the atmosphere support the gammagamma distribution as a practical PDF model for received irradiance fluctuations, although the irradiance fluctuations do occasionally tend towards a lognormal distribution.Utilization of the gammagamma irradiance PDF allows for calculation of statistical moments of the irradiance threshold levelcrossing distribution. Presented analysis focuses on the results of the gammagamma irradiance PDF. Previously, expressions were developed for the expected number of gammagamma distributed irradiance threshold levelcrossings. Expressions for the mean square number of gammagamma distributed irradiance threshold levelcrossings are derived and presented. The derived expressions lead to the mean and variance of signal fade time. Outcomes of the derived expressions are presented in relation to freespace optical communication system performance.Comparisons are made between the theoretical analysis and experimental data taken at the Innovative Science and Technology Facility (ISTEF) located at the Kennedy Space Center in Cape Canaveral, Florida. The strength of the atmospheric turbulence is often characterized by three measurable parameters: the refractive index structure constant Cn2, the inner scale l0, and the outer scale L0. The optical path (L~1km) was instrumented such that direct comparisons could be drawn between the measured atmospheric turbulence parameters and the parameters of the gammagamma irradiance model. Variance of fade time data were found to agree well for smaller apertures where effects of aperture averaging are not present and in cases where scintillation is weak to moderate. It is suggested that a more appropriate PDF, with a heavier focus on aperture averaging, may be applied in future studies of these fade statistics.
Title:  Variance in FadeTime of a GammaGamma Distributed Irradiance Signal. 
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Name(s): 
Leclerc, Troy, Author Phillips, Ronald, Committee Chair Weeks, Arthur, Committee Member Richardson, Martin, Committee Member Marinescu, Dan, Committee Member Andrews, Larry, Committee Member University of Central Florida, Degree Grantor 

Type of Resource:  text  
Date Issued:  2012  
Publisher:  University of Central Florida  
Language(s):  English  
Abstract/Description:  Freespace optical communications are predominantly hindered by optical turbulence, an effect caused by temperature and pressure variations within the atmosphere. The result is an optical wave interfering with itself due to multipath propagation via tiny refractiveindex fluctuations across the wavefront. Optical communication systems are affected when the channel conditions induce fading in the irradiance signal that is received at the detector. The nature of optical interference imparted by the atmosphere is a random process and therefore the received irradiance signal is often characterized by an appropriate probability density function (PDF). Data collected during past freespace optical experiments in the atmosphere support the gammagamma distribution as a practical PDF model for received irradiance fluctuations, although the irradiance fluctuations do occasionally tend towards a lognormal distribution.Utilization of the gammagamma irradiance PDF allows for calculation of statistical moments of the irradiance threshold levelcrossing distribution. Presented analysis focuses on the results of the gammagamma irradiance PDF. Previously, expressions were developed for the expected number of gammagamma distributed irradiance threshold levelcrossings. Expressions for the mean square number of gammagamma distributed irradiance threshold levelcrossings are derived and presented. The derived expressions lead to the mean and variance of signal fade time. Outcomes of the derived expressions are presented in relation to freespace optical communication system performance.Comparisons are made between the theoretical analysis and experimental data taken at the Innovative Science and Technology Facility (ISTEF) located at the Kennedy Space Center in Cape Canaveral, Florida. The strength of the atmospheric turbulence is often characterized by three measurable parameters: the refractive index structure constant Cn2, the inner scale l0, and the outer scale L0. The optical path (L~1km) was instrumented such that direct comparisons could be drawn between the measured atmospheric turbulence parameters and the parameters of the gammagamma irradiance model. Variance of fade time data were found to agree well for smaller apertures where effects of aperture averaging are not present and in cases where scintillation is weak to moderate. It is suggested that a more appropriate PDF, with a heavier focus on aperture averaging, may be applied in future studies of these fade statistics.  
Identifier:  CFE0004397 (IID), ucf:53153 (fedora)  
Note(s): 
20120801 Ph.D. Engineering and Computer Science, Electrical Engineering and Computer Science Doctoral This record was generated from author submitted information. 

Persistent Link to This Record:  http://purl.flvc.org/ucf/fd/CFE0004397  
Restrictions on Access:  campus 20150815  
Host Institution:  UCF 