Communication Systems/Fading Channels
Over large distances, signal quality is shown to degrade even without the presence of large quantities of AWGN. This degradation is known as fading, and channels that exhibit these properties are known as fading channels.
What Causes Fading
Fading can be caused by natural weather disturbances, such as rainfall, snow, fog, hail and extremely cold air over a warm earth. Fading can also be created by man made disturbances, such as irrigation, or from multiple transmission paths, irregular earth surfaces, and varying terrains.
Fading Channel Models
Scales of Fading
is called frequency selective fading??
Small-Scale Fading Types
In flat fading, the coherence bandwidth of the channel is larger than the bandwidth of the signal. Therefore, all frequency components of the signal will experience the same magnitude of fading.
Fast fading occurs when coherant time of the channel is small relative to the delay constraint of the channel. Amplitude and phase changes imposed by the channel varies considerably over period of use.