Fade statistics and aperture averaging for Gaussian beam waves in moderate-to-strong turbulence

Abstract

The performance of lasercom systems operating in the atmosphere is reduced by optical turbulence, which causes irradiance fluctuations in the received signal. The result is a randomly fading signal. Fade statistics obtained from experimental data were compared to theoretical predictions based on the lognormal and gamma-gamma distributions. The probability of fade, the expected number of fades per second, and the mean fade time were calculated from the irradiance fluctuations of a Gaussian beam wave propagating through the atmosphere along a horizontal path, near ground, in the moderate-to-strong optical turbulence regime. Irradiance data were collected simultaneously at three receiving apertures, each with a different size. Atmospheric propagation parameters were inferred from the measurements and were used in calculations for the theoretical distributions. It was found that fade predictions made by the gamma-gamma and lognormal distributions provide an upper and lower bound, respectively, for the probability of fade and the number of fades per second for the irradiance data collected in the moderate-to-strong fluctuation regime. What is believed to be a new integral expression for the expected number of fades based on the gamma-gamma distribution was developed. This new expression tracked the gamma-gamma distributed data more closely than the existing approximation and resulted in a higher number of fades.

Exponentiated Weibull distribution family under aperture averaging for Gaussian beam waves

“…Experimental studies support the fact that the LN model is valid in weak turbulence regime for a point receiver and works well in all regimes of turbulence for aperture averaged data [7,8]. On the other hand, the GG model is accepted to be valid in all turbulence regimes for a point receiver, nevertheless, this does not hold when aperture averaging takes place [2,7,9].…”

“…On the other hand, the GG model is accepted to be valid in all turbulence regimes for a point receiver, nevertheless, this does not hold when aperture averaging takes place [2,7,9].…”

Wireless Optical Communications Through the Turbulent Atmosphere: A Review

“…Experimental studies support the fact that the LN model is valid in weak turbulence regime for a point receiver and in all regimes of turbulence for aperture averaged data (Perlot & Fritzsche, 2004;Vetelino et al, 2007). On the other hand, the GG model is accepted to be valid in all turbulence regimes for a point receiver, nevertheless, this does not hold when aperture averaging takes place Vetelino et al, 2007).…”

“…The most widely accepted distributions are the Log-Normal (LN) and the Gamma-Gamma (GG) models, although, many others have been subject of studies, namely, the K, Gamma, exponential, I-K and Lognormal-Rician distributions (Churnside & Frehlich, 1989;Epple, 2010;Vetelino et al, 2007).…”

An Overview of the Physical Insight and the Various Performance Metrics of Fading Channels in Wireless Communication Systems

“…It is worth mentioning here, that the ergodic capacity is a very significant metric for the study of the wireless optical communication links, due to the strong influence of the atmospheric conditions in their performance, see e.g. (Andrews et al, 1999;Gappmair et al, 2010;Garcia-Zambrana, Castillo-Vasquez & Castillo-Vasquez, 2010;Garcia-Zambrana, Castillo-Vazquez & Castillo-Vazquez, 2010;Li & Uysal, 2003;Liu et al, 2010;Peppas & Datsikas, 2010;Popoola et al, 2008;Sandalidis & Tsiftsis, 2008;Tsiftsis, 2008;Vetelino et al, 2007;Zhu & Kahn, 2002). More specifically, the fast changes of the atmospheric turbulence conditions fades fast the transmitted signal and as a result, the estimation of the instantaneous channel capacity is nearly meaningless in this area of wireless communications.…”