A Unifying Statistical Model for Atmospheric Optical Scintillation

Atmospheric optical communication has been receiving considerable attention recently for use in high data rate wireless links Considering their narrow beamwidths and lack of licensing requirements as compared to microwave systems, atmospheric optical systems are appropriate candidates for secure, high data rate, cost-effective, wide bandwidth communications. Furthermore, atmospheric free space optical (FSO) communications are less susceptible to the radio interference than radio-wireless communications. Thus, FSO communication systems represent a promising alternative to solve the last mile problem, above all in densely populated urban areas. However, even in clear sky conditions, wireless optical links may experience fading due to the turbulent atmosphere. In this respect, inhomogeneities in the temperature and pressure of the atmosphere lead to variations of the refractive index along the transmission path. These random refractive index variations can lead to power losses at the receiver and eventually to fluctuations in both the intensity and the phase of an optical wave propagating through this medium Such fluctuations can produce an increase in the link error probability limiting the performance of communication systems. In this particular scenario, the turbulence-induced fading is called scintillation. The reliability of an optical system operating in an environment as the mentioned above can be deduced from a mathematical model for the probability density function (pdf) of the randomly fading irradiance signal. For that reason, one of the goals in studying optical wave propagation through turbulence is the identification of a tractable pdf of the irradiance under all irradiance fluctuation regimes. The purpose of this chapter is to develop a new tractable pdf model for the irradiance fluctuations of an unbounded optical wavefront (plane and spherical waves) propagating through a homogeneous, isotropic turbulence to explain the focusing and strong turbulence regimes where multiple scattering effects are important. Hence, the desired theoretical solution can be useful in studying the performance characteristics of any optical communication system operating through a turbulent atmosphere. We demonstrate through this chapter that our proposed model fits very well to the published data in the literature, and it generalizes in a closed-form expression most of the developed pdf models that have been proposed by the scientific community for more than four decades. 8 www.intechopen.com