Re: Questions about OFDM.
malaylah said:
received_signal=rayleigh_flat_fading_variable*transmitted_signal+gaussian_noise
And the rayleigh_flat_fading_variable .....I can generate easily with a very basic rayleigh distribution theorem.....
Yes, right.
malaylah said:
which is without consideration of doppler frequency and so on.......Am I right? Pls clarify.....
This is not right. Even flat fading channel may experience Doppler effect.
The Doppler PSD (power spectral density) captures the time variation of the channel.
See "Mobile Fading Channels" by Matthias Paetzold for further explaination. The book has been uploaded in this forum.
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Added after 22 minutes:
moustafahussein said:
It suffers from both, as OFDM was created to over the raylieh fading and frequency selective fading.
To summarize my knowledge on fading channel:
1) Channels can be divided into flat fading and frequency selective fading channels. Flat fading channel will be experienced by communication signal having symbol period larger than delay spread, i.e. the maximum delay of paths taken by signal from the sender to the receiver. If the symbol period is shorter than the delay spread, then the signal experiences frequency selective fading which causes intersymbol interference (ISI). Thus, flat fading channel has only one path and frequency selective fading channel has multiple paths.
2) From the experiments, each path of fading channel has a certain distribution, i.e. either Rayleigh (if no line of sight), Rice (if there is line of sight), or Nakagami (more general). For example in the rural area (RA), the first path (lowest delay) of a frequency selective fading channel has the Rice distribution, whereas the other paths have the Rayleigh distribution.
3) Furthermore, due to the movement of the sender or receiver, there will be time variation of the channel due to Doppler effect. This Doppler effect will be zero only when there is no movement of the sender/receiver.
So the type of a wireless channel could be the combination of three items discussed above. Examples:
a) flat fading channel with Rayleigh distribution and no Doppler effect
b) frequency selective fading channel with all paths having Rayleigh distribution with Doppler effect.
c) etc.....
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