Re: Peaks when increasing the FFT lenght ofdm example
Did you repost this accidentally, or is this a new question? On Thu, Jan 6, 2022 at 12:15 PM Pedro Viegas wrote: > 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 >
Re: Peaks when increasing the FFT lenght ofdm example
Hi Johannes, First of all thanks for the quick response and time with my problem. I've made a text file with all specifications of my OFDM example that can be found in the attachments of this mail. Thanks again with your help and anything more just let me know. Best regards, Pedro Viegas Citando Johannes Demel : Hi Pedro, we'd need more info to tell why you observe these peaks. How large are your input packets? Do they span multiple OFDM symbols? How many subcarriers are active? Your peaks hint at some kind of repetition or lot's of zeros. Cheers Johannes On 14.12.21 13:07, Pedro Viegas wrote: 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. Thanks in advance, Pedro Viegas -- Pedro Viegas DSP Engineer Koala Tech phone: +351 917 354 070 e-mail: p...@koalatech.pt 512 carriers GRC Description: Binary data
Re: Peaks when increasing the FFT lenght ofdm example
Hi Pedro, we'd need more info to tell why you observe these peaks. How large are your input packets? Do they span multiple OFDM symbols? How many subcarriers are active? Your peaks hint at some kind of repetition or lot's of zeros. Cheers Johannes On 14.12.21 13:07, Pedro Viegas wrote: 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. Thanks in advance, Pedro Viegas