I am trying to understand why exponential decay power delay profiles are used to model fading. In other words, why power of taps of channel impulse response decays exponentially and not, for instance, linearly.
The only explanation I could come up was that since taps are modeled as circularly symmetric Gaussian random variables, their magnitude is Rayleigh distributed and their power is Chi-squared distributed with two degrees of freedom, or in other words, exponentially distributed. But this does not sound correct. I suppose this has something to do with channel acting as low pass filter, but I was not able to figure out exact relation.