Forums

alias in OFDM

Started by aizza ahmed October 31, 2011
Hi everyone,
                 Got Stuck with fresh doubt. I saw a very old post in
comp.dsp

http://www.dsprelated.com/showmessage/58605/1.php

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in that post, phil says
"This isn't quite right.  Keep in mind that frequencies that appear to
be beyond the Nyquist frequency will end up wrapping (aliasing) around
into the -ve frequencies.  So...

........................N/2........................: 0 + (N/2-1)/(N*T)
Hz
......................N/2+1......................: 0 - (N/2)/(N*T) Hz
...
........................N..........................: 0 - 1/(N*T) Hz

Also, the OFDM symbol period will be N*T + M*T, where M represents the
number of samples used for the cyclic prefix and suffix."

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i am wondering about this statement " Nyquist frequency will end up
wrapping (aliasing) around
into the -ve frequencies." At transmitters it is fine, but at receiver
how it is being recovered (basically it doesn't satisfy sampling
theorem)..i mean to say information is lost in terms of samples being
missed (with inadequate sampling).

Please explain,


Thanks
aizza ahmed