Notes on small-scale fading

What
Fading is the distortion that a carrier-modulated telecommunication signal experiences over certain propagation media.

Propagation models that characterize the rapid fluctions of the received signal strength over very short travel distances (a few wavelengths) or short time duration (on the order of seconds) are called small-scale or fading models. (Page  106 of [3])

Why
In wireless systems, fading is due to multipath propagation and is sometimes referred to as induced fading. [1]

How
The effects of fading can be combated by using to transmit the signal over multiple channels that experience independent fading and coherently combining them at the receiver.

Miscellaneous
The coherence time is a measure of the minimum time required for the magnitude change of the channel to become decorrelated from its previous value.

There's a good summary of large-scale and small-scall fadings on Page 40 and 41 of [5].


References

3. Theodore S.Rappaport ：Wireless Communications: Principles and Practice, 2nd Ed, Prentice Hall, Dec 2001
4. Andrea Goldsmith, Wireless Communications, Cambridge University Press, Aug 2005
5. David Tse, Pramod Viswanath, Fundamentals of Wireless Communication, Cambridge University Press, May 2005