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I'm trying to understand OFDM modulation using Matlab Simulink and I've built the following system

OFDM TX

I sent to the input of the OFDM block a frame of 15 samples that comes from the 16-QAM modulator. The OFDM modulator also receives a frame of 15 pilot symbols that I have chosen (see below)

PILOT

Now, My OFDM block has the following settings:

OFDM settings

My question is, why the frequency spectrum of the output signal of the OFDM block has huge spikes?

freq

I have supposed to be the short FFT length compared to the number of pilot subcarriers but, I'm not sure about that

Thanks

NicoCaldo
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  • hm, what *are* your pilot symbols? And the spectrum you show, how much did you average to get that spectrum? How white is your data? – Marcus Müller Jun 11 '21 at 14:37
  • @MarcusMüller pilot symbols are shown in the 2nd image. About the spectrum, I just used the Spectrum Analyzer of Simulink (it uses 1 Ohm as reference load) – NicoCaldo Jun 11 '21 at 14:51
  • ah, I thought that was just a snapshot of a single realization of the pilots; Hm. Could you give us an overall overview of the full graph from sources to spectrum analyzer, not just the excerpt? – Marcus Müller Jun 11 '21 at 16:02
  • @MarcusMüller the spectrum analyzer is connected directly at the last buffer on the right – NicoCaldo Jun 12 '21 at 06:42

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