Editing Rayleigh fading (section)

===Level crossing rate===
The level crossing rate is a measure of the rapidity of the fading. It quantifies how often the fading crosses some threshold, usually in the positive-going direction. For Rayleigh fading, the level crossing rate is:<ref name="rappaport">{{cite book|title=Wireless Communications: Principles and Practice|edition=2nd|author=T. S. Rappaport|date=December 31, 2001|publisher=Prentice Hall PTR|isbn=978-0-13-042232-3}}</ref>
:<math>\mathrm{LCR} = \sqrt{2\pi}f_d\rho e^{-\rho^2}</math>
where <math>f_d</math> is the maximum Doppler shift and <math>\,\!\rho</math> is the threshold level normalised to the [[root mean square]] (RMS) signal level:
:<math>\rho = \frac{R_\mathrm{threshold}}{R_\mathrm{rms}}.</math>