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Post by aya2002 on Feb 26, 2009 17:55:53 GMT -5
it is very good for any new ofdm reader
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Post by jwardojo on Mar 4, 2009 10:31:12 GMT -5
I like the explanation on why we use IFFT. That's true that most people got lost in here, I was confused for a while until I started thinking that all these processing of the orthogonal carriers are done in DSP,so it can be viewed as modulating the carriers in frequency domain, and convert back to time domain for further processing (mix up in frequency) for transmission over the channel.
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Post by binzhou75 on Sept 8, 2009 1:24:15 GMT -5
hi,i am new member to this site,maybe i found here too later, can anybody help me to find the tutorial on ofdm, i can't find it, or i need some pass?
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Post by norbert on Aug 12, 2011 2:37:42 GMT -5
True, tutorial about OFDM is excellent. Only question i have, relate to sentence whitch say that BER for OFDM is far better than for wide band signal of exactly same modulation in fading channel. Could You show some plot (or matlab code) whitch confirm this thesis. I found on the network this kind of compraison but only for flat fading channel where results are the same!!
Thanks in advance,
Norbert Krzysztofik
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Post by charan langton on Aug 17, 2011 15:36:26 GMT -5
The BER in a fading channel is given by
Pe == 1/2SNR, where as in AWGN is given by
Pe = Q(2SNR)^1/2
The fading Pe is much worse for same SNR. MIMO is one way to mitigate this because the data travels through several independent channels and hence on the average has better SNR than the worse case. Depending on the antennas used, we can bring the flatter (see figure 8 in MIMO tutorial).
The OFDM channelization in frequency does the same thing. Each sub-carrier has its own fading performance, so again on the average the SNR will be better than the worst case.
So we conclude that OFDM just as MIMO improve performance in a fading channel.
Charan Langton
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