subcarriers overlapping in OFDM...

[mashhur]

subcarriers

Hi all!

could somebody explains me even though the subcarriers overlap each other in frequency domain, the information doesn't mix at receiver?

 

[Communications_Engineer]

ofdm subcarriers plot

Actually if you look at the frequency domain plot, the peak of one carrier is on the point where the the two carriers; one on its right and one on its left have their zero crossing. And you know at zero crossing they would contribute to zero energy to the center carrier, And this is how, even after 'overlapping' they dont mix.

In fact if you look at this statement carefully, you'd also understand why we say that OFDM signals are extremely sensitive to Doppler shifts, as it violates the idea of non-overlapping carriers

I hope that helped you

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[Aya2002]

matlab ofdm overlap

Hi freind

see the attached file i think it is good to understand it

enjoy

 

[mashhur]

how the overlapping takes place in ofdm

thank you a lot, i had read them but didn't pay attention!

 

[Communications_Engineer]

ofdm+subcarrier+matlab code

From which book is that taken from Muntather. Its looks good. By the way do you have the codes used for those graphs. I'm not asking for pdfs and just the Matlab code, if you have

 

[mashhur]

subcarrier spectrum

i read it from this thesis but unfortunately there is not code. however, many times i saw this graph.

please check mathworks.com

 

[Aya2002]

subcarrier ofdm

the code to generate this figure is attached here

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) ) , '-*' ) ;