Propagation Effects in Optical and Wireless Communications Channels, Noise Sources, and Channel Impairments

Abstract

This chapter discusses the propagation effects, noise sources, and channel impairments for wireless communications, free-space optical communications, and fiber-optics communications. The key idea of the chapter is to derive the wave equation for a given medium from Maxwell’s equation and determine its solution subject to corresponding boundary conditions. After the introduction of the vector derivatives in orthogonal curvilinear, cylindrical polar, and spherical coordinate systems, we study vectorial nature of the light, derive Snell’s law of refraction from Maxwell’s equations, study total internal reflection, and explain the light confinement in step-index optical fibers. We also describe how arbitrary polarization state can be generated by employing three basic polarizing elements, namely, polarizer, phase shifter (retarder), and rotator. We then introduce the electromagnetic potentials to simplify the study of generation of electromagnetic waves, followed by antenna theory basics. We then discuss interference, coherence, and diffraction in optics. After that the detailed description of laser beam propagation effects over the atmospheric turbulence channels is provided, including the description of simulation models. In the section on wireless communication channel effects, we study path loss, shadowing, and multipath fading propagation effects. Both ray theory-based and statistical multipath wireless communication channel models are described. We then move to signal propagation effects in optical fibers and describe (1) fiber attenuation and insertion loss, (2) chromatic dispersion effects, (3) polarization-mode dispersion effects, and (4) fiber nonlinearities. Regarding the fiber nonlinearities, both Kerr nonlinear effects (self-phase modulation, cross-phase modulation) and nonlinear scattering effects, such as stimulated Raman scattering, are described. The generalized nonlinear Schrodinger equation is then described for both single-mode and few-mode fibers as well as the corresponding split-step Fourier algorithms to solve it. The following noise sources related to optical communication are described: mode partition noise, relative intensity noise, laser phase noise, modal noise, thermal noise, spontaneous emission noise, noise beating components, quantum shot noise, dark current noise, and cross talk. Finally, in section on indoor optical wireless communications, the channel models for both infrared and visible light communications are described.