Hi, I'm trying to visualize the sub-carriers in my ofdm model. What I do is I generate a BPSK OFDM symbol and after IFFT I plot the FFT of transmitter output. I only get one Sinc graph not the overlapping sub-channels. Could you please correct me to get a proper view of sub-carriers? Best regards Shahin

# OFDM Spectrum

Started by ●July 24, 2006

Reply by ●August 8, 20062006-08-08

Hi Shahin, In simplistic terms, there must be something else going on here. If you plot your frequency domain OFDM symbol, then you IFFT it, then you FFT it, you should see pretty much the same thing as you started with. I'd check: 1) the BPSK OFDM symbol before you IFFT it. Does it look like what you expect? 2) what else are you doing to the time domain signal before you FFT it? Hope this helps (as a starting point). Ron Murias On 2006-07-24 05:41:22 -0600, "Shahin" <gheitanchi@gmail.com> said:> > > Hi, > > I'm trying to visualize the sub-carriers in my ofdm model. What I > do is I generate a BPSK > OFDM symbol and after IFFT I plot the FFT of transmitter output. I > only get one Sinc graph > not the overlapping sub-channels. > > Could you please correct me to get a proper view of sub-carriers? > > Best regards > Shahin

Reply by ●August 9, 20062006-08-09

Hi Shahin, I guess u need to increase the resolution of ur FFT by padding zeros. I suggest u try out this piece of Matlab code and try to understand it. N = 16; % Number of subcarriers. a = sign(randn(N, 1)); % Generate BPSK symbols. b = diag(a); % This helps to plot overlapping subcarrier spectrum. c = ifft(b); % Do IFFT along each column--(each column is a subcarrier). f = fft(c, N*16); % Do FFT of 16x resolution. plot(abs(f)); % U get the spectrum corresponding to each subcarrier. grid on; hold on; plot(abs(sum(f, 2)), '-*'); % This is the spectrum with all the subcarriers superimposed. Note that this curve matches with the previous plot at every peak, corresponding to a subcarrier frequency. hope this helps, JohnP