ABSTRACT
The wireless channel experiences deep fade in time or frequency. Fading effects related to mobile communications can be classified in two spatial scales: large-scale fading and small-scale fading. Large-scale fading refers to variations in received power over large distances. A very important type of fading normally considered in wireless communication systems is related to rapid changes in the signal’s amplitude and phase that occur over very short variations in time or in the spatial area between the receiver and the transmitter. Different transmitted signals are subjected to different effects of fading. In fact, the type of fading “sensed” by the transmitted signal is defined by a relation between the properties of the signal and the characteristics of the channel. Multipath propagation leads to the time dispersion of the transmitted symbol within the channel, leads to frequency-selective fading. The statistical characteristics of the channel exhibiting small-scale fading can be modeled by several probability distribution functions.
