Peaks when increasing the FFT lenght ofdm example

[Pedro Viegas]

Hi everyone,

I'm having a problem when I increase the number of carriers from 64 to 512 in the gnuradio OFDM example. When the number of carriers is 512, the complex envelope of the signal in the time domain has some peaks, which I can not have for the test I'm trying to make. Can anyone tell why there are those peaks and how I get rid of them?
A possible cause for the peaks, in my opinion, can be the fixed frame len of the header, that is filled with zeros when the FFT size increases, resulting in a peak in the beginning of each frame because of the ifft block. If this is the problem, how can I change that frame len?
To better show what I'm saying, there is an image on the attachments of the complex envelope with the peaks, and a .txt file with the specifications of the ofdm parameters.

Thanks in advance,
Pedro Viegas

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