rayleigh fading and AWGN

rayleigh fading rice

If one considers a channel which has only rayleigh fading and no ISI (no freq selective fading) then the signal will only have flat fading or simply amplitude variations

I wonder what causes these amplitude fluctuations, one thing is of course distance dependent fading between Tx and Rx and also multipath signals adding and subtracting each other at receiver, but i wonder if AWGN is added to this fading or not/

if no then do we have to add AWGN noise to each multipath when modelling rayleigh fading ?


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selective fading rayleigh

In channel model for wireless communication, noise is modeled separately to the fading. If you have flat fading channel plus noise, it means that you have to generate one random variable fulfilling rayleigh distribution and MULTIPLY the transmit signal with it, then you ADD the noise (usually Gaussian distributed).

If you have frequency selective fading channel, i.e. the channel is modeled as FIR filter with each tap fulfilling rayleigh distributed, then you have to CONVOLVE the transmit signal with this FIR filter, and then ADD the noise.

So, for either flat fading channel or frequency selective fading channel, the Gaussaian noise model is the same.

Rayleigh fading is only due to multipath signals and it is refered to as fast fading (small scale fading), whereas the distance between Tx & Rx introduce slow fading (large scale fading). You consider large scale fading for designing cell, power control, etc. But if you only consider designing equalizer or modulation technique, then you only consider small-scale fading (Rayleigh, Rice)

best

Please understand...
What is the source of noise?
the noise is due to thermal noise at the receivers.
the reason..receive antennas respond to the electromagnetic waves which may vary slightly. i think it is called shot noise.
But amplifier noise is the main one where external temperature results in fluctuations in the voltage gain. thats why the front end has low noise amplifier..which is not sensitive to temperature.
there is no noise from the channel as such (if we assume no interference, even if there is interference we can model separately.)

awgn channel means no signal distortion and only additional white noise.

fading channel means signal distortion that may follow rayleigh distribution + awgn noise

Added after 1 minutes:

all the multipath is captured in the signal distortion otherwise known as fading.

i agree with mimomod and darock they have provided u a very good and information and awgn and rayleigh fading..

if u not satisfied with there information refer to digital communication by john g proakis

I think that this fading might come from tension of media and you should study rayleigh disc(or disk) to undertand it's figure, this opinion come from when I had study acoustic engineering and go to https://en.wikipedia.org/wiki/Rayleigh_fading for orther useful information.

sincerely,
Phongphan Porana.
Phongphanp@yahoo.com

please guide how to write a matlab code to introduce rayleigh and than awgn ....
the signal is sound signal ..
secondly i than have to filter it... for that adaptive fir filter gona work ????

Consult "Concrete Mathematics" By D.E. nuth and study "Finite Element" for simulation .