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I am sorry I am an amature in OFDM I just created a rayleigh filter using that function and passed the data bits on to it before taking the fft at the receiver..
And that would implement frequency selective fading..
Thought that I can share this with you as I did that only.
the behavior of the channel is generally specific to the radio environment. the frequency selectivity of the channel only depends on the system bandwidth. in other words, given the same channel (environment), it can be either frequency-selective (if the system bandwidth is large) or frequency-flat (if the system bandwidth is narrow).
Therefore, in order to simulate the frequency-selective channel, you just need to simulate multiple taps with the maximum delay larger than the sampling time.
I am actually lookin at Freq Selective fading... But I have an elementary question.
Assuming I have an array of mapped data (QPSK) 2x256 ..
After using IFFT operation I would now have OFDM data sized [1x640] ..
I have found out the channel coefficients seperately..
How do I perform Convolution operation between the two(OFDM and Channel Coeff) ?
(Coz, the ch coeff are supposed to change for every time period greater than Nyquist time...)
You cannot use the Matlab conv here but if you really understand the convolution technique here's what you can do.
1. pre-pend and append n-1 zeros to your post-ifft ofdm signal. n = channel length
2. form an n-length vector from the zero-appended ofdm signal.
3. start a loop for m iterations. m= n+k-1. k=length of raw ofdm signal
4. for every iteration i -
output(i)= ofdm(i:i+n)*transpose(channel(i,)
end
now I am assuming that ofdm signal and channel(i, are both row-vectors
hope this helps
Added after 1 minutes:
ok the editor screwed up " : ) " and turned it into smileys
I was trying to use the SUI channel model for the simulation...
I have attached a file ChannelModels.pdf which shows how fading coeffs in SUI channel models are calculated....
The following were the steps I found in an online source( not sure if it works )
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