伊落丹矩阵_Radio

Notes::small-scale fading

<伊落丹> illidan.modeler [at] gmail.com
Northern Capital, Republic of Pandaren


Of the Net, by the Net, for the Net

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 multipath induced fading. [1]

How
The effects of fading can be combated by using diversity 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

1. Web http://en.wikipedia.org/wiki/Fading
2. Web http://www.ylesstech.com/terminology.php?letter=all&id=15
   
3. [Rappaport 2001]
4. [Goldsmith 2005]
5. [Tse 2005]