Editing Rayleigh fading (section)

===Applicability===
[[File:NYC Manhattan from Empire State Building 2003.jpg|thumb|left|Densely built Manhattan has been shown to approach a Rayleigh-fading environment.]]
[[File:Rayleigh fading doppler 10Hz.svg|thumb|250px|right|One second of Rayleigh fading with a maximum Doppler shift of 10 Hz]]
[[File:Rayleigh fading doppler 100Hz.svg|thumb|250px|right|One second of Rayleigh fading with a maximum Doppler shift of 100 Hz]]
The requirement that there be many scatterers present means that Rayleigh fading can be a useful model in heavily built-up city centres where there is [[NLOS|no line of sight]] between the transmitter and receiver and many buildings and other objects [[attenuation (electromagnetic radiation)|attenuate]], [[Reflection (physics)|reflect]], [[refraction|refract]], and [[diffraction|diffract]] the signal. Experimental work in [[Manhattan]] has found near-Rayleigh fading there.<ref>{{cite journal|title=Multiple-Input–Multiple-Output Measurements and Modeling in Manhattan|author1=Dmitry Chizhik |author2=Jonathan Ling |author3=Peter W. Wolniansky |author4=Reinaldo A. Valenzuela |author5=Nelson Costa |author6=Kris Huber  |name-list-style=amp |journal=IEEE Journal on Selected Areas in Communications|volume=21|issue=3|date=April 2003|pages=321&ndash;331|doi=10.1109/JSAC.2003.809457|url=http://dmitrychizhik.com/NYC_BLAST.pdf}}</ref> In [[tropospheric scatter|tropospheric]] and [[ionospheric reflection|ionospheric]] signal propagation the many particles in the atmospheric layers act as scatterers and this kind of environment may also approximate Rayleigh fading. If the environment is such that, in addition to the scattering, there is a strongly dominant signal seen at the receiver, usually caused by a [[Line-of-sight propagation|line of sight]], then the mean of the random process will no longer be zero, varying instead around the power-level of the dominant path. Such a situation may be better modelled as [[Rician fading]].

Note that Rayleigh fading is a small-scale effect. There will be bulk properties of the environment such as [[path loss]] and [[Shadow fading|shadowing]] upon which the fading is superimposed.

How rapidly the channel fades will be affected by how fast the receiver and/or transmitter are moving. Motion causes [[doppler effect|Doppler shift]] in the received signal components. The figures show the power variation over 1 second of a constant signal after passing through a single-path Rayleigh fading channel with a maximum Doppler shift of 10&nbsp;Hz and 100&nbsp;Hz. These Doppler shifts correspond to velocities of about 6&nbsp;km/h (4&nbsp;mph) and 60&nbsp;km/h (40&nbsp;mph) respectively at 1800&nbsp;MHz, one of the operating frequencies for [[Global System for Mobile Communications|GSM]] [[mobile phone]]s. This is the classic shape of Rayleigh fading. Note in particular the 'deep fades' where signal strength can drop by a factor of several thousand, or 30–40 [[decibel|dB]].