Explain three propagation mechanism which impacts propagation in mobile communication system.
Reflection occurs when a propagating electromagnetic wave impinges upon an object that has very large dimensions compared to the wavelength of propagating wave. Reflection occurs from the surface of the ground, from walls, and from furniture. When reflection occurs, the wave may also be partially refracted. The coefficients of reflection and refraction are functions of material properties of the medium, and generally depend on the wave polarization, the angle of incidence, and the frequency of propagation wave.
Diffraction
Diffraction occurs when the radio path between the transmitter and receiver is obstructed by a surface that has sharp edges.The waves produced by the obstructing surface are present throughout space and even behind the obstacle, giving rise to the bending of waves around the obstacle, even when a Line Of Sight (LOS) path does not exist between the transmitter and receiver. At high frequencies, diffraction-like reflection-depends on the geometry of the object, as well as on the amplitude, phase and polarization of the incident wave at the point of diffraction.
Scattering
Scattering occurs when the medium through which the wave propagates consists 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 produced by rough surfaces, small objects, or by other irregularities in the channel. In practice, foliage, streetsigns, lampposts and stairs within buildings can induce scattering in mobile-communication systems. A sound knowledge of the physical details of the objects can be used to accurately predict the scattered signal strength.
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