A model for the received irradiance statistical distribution for turbulence induced fading channels is derived. The derivation is based on expanding the extended Rytov method by associating a doubly stochastic process to model large scale scintillation. In particular, the large scale induced fluctuations are modeled as the product of arbitrary numbers of gamma and inverse gamma random variables, while the small scale induced irradiance fluctuations are modeled as a single gamma random variable. Closed form expressions for the probability density function (pdf), cumulative distributions, and moment generating function are given. Also, a procedure is proposed for associating the pdf parameters with the large and small scale induced variances. The proposed model is seen to contain many previously published models, such as gamma–gamma (GG) and Fischer–Snedicor F , as special cases. Moreover, two new fading distributions are introduced and analyzed, and plots for the proposed pdfs are generated and compared with often used models and measurements, thus showing the accuracies of the derived models.
Summary Deep space exploration missions require the modelling of deep space communication channels. Due to the turbulent nature of space channels, propagating electromagnetic waves suffer from fading‐induced turbulence. In particular, scintillation effects are imparted on the intensity of electromagnetic beam wave propagating through the solar corona. Thus, it is imperative to determine the wave intensity distribution. Often, distributions derived and verified for terrestrial channels are applied to wave propagation through deep space channels. However, this neglects the specific nature of the physical processes in the channel. For example, to incorporate the events of solar inferior and solar superior conjunctions, the introduced statistical distribution should be valid over a large‐range, spanning weak to strong, scintillation conditions. Moreover, the solar corona physical parameters should be clearly related to the distribution parameters. Such a theoretical model can be derived based on Rytov solution, the solar wind speed distribution and the space permeating plasma electron density variation. The resultant wave intensity distribution is compared with the Rician, the Nakagami and the inverse Gaussian–gamma distributions for different scintillation conditions.
A model for the irradiance probability density function for turbulence induced fading in free space optical communications is derived. The derivations are based on expanding on the extended Rytov method by associating a doubly stochastic process to model large scale scintillation. In particular, the small scale induced irradiance fluctuations are modeled by a single gamma distribution, while the large scale induced fluctuations are modeled as a doubly stochastic process of gamma and inverted gamma distributions, thus better approximating the lognormal distribution. The resultant distribution’s probability density and cumulative density functions are both given in closed forms. Moreover, the resultant model parameters are given based on strong scintillation theory. Through comparison with previously published results and experimental data, including lognormal and gamma–gamma distributions, it is concluded that the proposed model agrees well with measurements for weak and strong scintillation conditions in cases of both aperture averaging and a point like receiver. Therefore, the proposed model can be used for the performance analysis of optical wireless systems.
The derivation of the probability density of irradiance for the received electromagnetic wave propagating through random inhomogeneities has applications in many diverse fields such as optical wireless communications, radar, and imaging systems, to name few. The conventional approach in this regard is to combine distribution models, with each found valid under different conditions, in a modulation process, e.g. the extended Rytov theory. However, in these techniques, the nature of the physical processes responsible for the randomness is not considered directly. Moreover, it is not clear how the model parameters are related to the physical environment. Recent researches found that in random media, such as underwater, the exact physical processes in effect can significantly alter the distribution of the received signal intensity. In this paper, a novel intensity distribution model is derived based on Rytov theory of propagation through weak turbulence. The physical parameters of the medium are directly included into the model parameters. Therefore, the resultant model is general enough to describe different physical environments. The utility of the model is validated by studying the effect of the medium parameters on the distribution through simulations.
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