Vetelino Frida Strömqvist, Young Cynthia, Andrews Larry
Department of Mathematics, University of Central Florida, Orlando, Florida 32816, USA.
Appl Opt. 2007 Jun 20;46(18):3780-9. doi: 10.1364/ao.46.003780.
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.
在大气中运行的激光通信系统的性能会因光学湍流而降低，光学湍流会导致接收信号的辐照度波动。结果是信号随机衰落。将从实验数据中获得的衰落统计数据与基于对数正态分布和伽马-伽马分布的理论预测进行了比较。根据沿水平路径在接近地面的中等至强光学湍流区域中传播的高斯光束波的辐照度波动，计算了衰落概率、每秒预期的衰落次数和平均衰落时间。在三个不同尺寸的接收孔径处同时收集辐照度数据。从测量中推断出大气传播参数，并将其用于理论分布的计算。结果发现，对于在中等至强波动区域收集的辐照度数据，伽马-伽马分布和对数正态分布做出的衰落预测分别为衰落概率和每秒衰落次数提供了上限和下限。基于伽马-伽马分布，开发了一种据信是预期衰落次数的新积分表达式。与现有的近似表达式相比，这个新表达式更紧密地跟踪了伽马-伽马分布的数据，并且导致了更多的衰落次数。
