«Reflexión electromagnética/Índice/Métodos de Propagación»

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Métodos de Propagación editar

La reflexión, la difracción y la dispersión son los tres mecanismos básicos de propagación que influyen en la propagación en un sistema de comunicaciones móviles. Estos mecanismos se explican brevemente en esta sección, y los modelos de propagación que describen estos mecanismos se analizan posteriormente en este capítulo. La potencia recibida (o su recíproca, la pérdida de trayectoria) es generalmente el parámetro más importante predicho por los modelos de propagación a gran escala basados en la física de la reflexión, la dispersión y la difracción. El desvanecimiento a pequeña escala y la propagación por trayectos múltiples (discutidos en el capítulo 4) también pueden describirse mediante la física de estos tres mecanismos básicos de propagación.

Mobile Radio Propagation: Large-Scale Path Loss editar

The Three Basic Propagation Mechanisms Reflection, diffraction, and scattering are the three basic propagation mech-anisms which impact propagation in a mobile communication system. These mechanisms are briefly explained in this section, and propagation models which describe these mechanisms are discussed subsequently in this chapter. Received power (or its reciprocal, path loss) is generally the most important parameter predicted by large-scale propagation models based on the physics of reflection, scattering, and diffraction. Small-scale fading and multipath propagation (dis-cussed in Chapter 4) may also be described by the physics of these three basic propagation mechanisms. Reflection occurs when a propagating electromagnetic wave impinges upon an object which has very large dimensions when compared to the wavelength of the propagating wave. Reflections occur from the surface of the earth and from buildings and walls. Diffraction occurs when the radio path between the transmitter and receiver is obstructed by a surface that has sharp irregularities (edges). The sec-ondary waves resulting from the obstructing surface are present throughout the space and even behind the obstacle, giving rise to a bending of waves around the obstacle, even when a line-of-sight path does not exist between transmitter and receiver. At high frequencies, diffraction, like reflection, depends on the geome-try of the object, as well as the amplitude, phase, and polarization of the incident wave at the point of diffraction. Scattering occurs when the medium through which the wave travels con-sists of objects with dimensions that are small compared to the wavelength, and where the number of obstacles per unit volume is large. Scattered waves are pro-duced by rough surfaces, small objects, or by other irregularities in the channel. In practice, foliage, street signs, and lamp posts induce scattering in a mobile communications system.