Wireless Channels

In wireless communication systems, the electromagnetic wave propagation is affected by the physical phenomenon such as reflection, diffraction, and scattering. Propagation models are used to characterize these propagation mechanisms and categorized into large scale and small scale fading models. Propagation models that characterize the signal strength over large transmitter receiver separation are called large scale propagation models. The large scale propagation models are used to predict the coverage area of the transmitter. Propagation models that used to characterize the signal strength over short distances (a few wavelengths) or short time duration (a few milliseconds to a few seconds) are called small scale fading models.

Channel modeling plays an important role in designing and analyzing wireless communication systems. For an example, the distribution of envelope of small scale fading is modeled as Rayleigh and Rician distributions; and the large-scale fading is modeled as Log-Normal distribution.