Why are OFDM Subcarriers Sinc Functions?

Explains the relationship between the time domain OFDM transmitted signal, and the orthogonal subcarriers in the frequency domain.
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[@koteshsharma2950]

Excellent explanation, thanks a lot sir

[@iain_explains]

You are most welcome

[@user-dh9qf4eu7i]

Thank you for your explanation. I have a question. Is it correct to make OFDM symbol and then go through the pulse shaping filter? If so, will the shape of the waveform change?

[@JaySmith91]

I am wondering why it ends up as the modulus of the sinc function, i.e. why there's no negative values over there in the frequency domain.

[@iain_explains]

Generally people only plot the magnitude, in the frequency domain. There is a corresponding phase plot, which flips by 180 degrees in the frequency ranges where the “amplitude” is negative.

[@theoryandapplication7197]

thank you very much,

[@iain_explains]

You are welcome!

[@pitmaler4439]

The vector C_n represents just integer values of the base function f1 - ist that right?
Or can use other step sizes e.g. f2 = 1.5*f1; f3 = 3*f1.....

[@iain_explains]

They need to be integer, in order to maintain the orthogonality between the subcarriers. Hopefully this video explains it: "OFDM Waveforms" ruclips.net/video/F6B4Kyj2rLw/видео.html

[@AbhayNarasimhaKS]

2:04 If only the first element is nonzero, the output of IDFT has to be the DC value, not the sinusoid of fundamental frequency. The subcarriers range from C_0 to C_{N-1}. C_0 will correspond to the DC value at the output and C_1 will give the fundamental sinusoid of period = N. Please respond if I am wrong.

[@iain_explains]

Yes, you're right. I simplified the diagram, only showing the elements of the vector that relate to the data-carrying sub channels.

[@028gnanadathareddy4]

@@iain_explains I did not understood how output of IDFT is sinusoidal with .output of IDFT will be all of same elements for given example right.

[@iain_explains]

Try running these lines of code in Matlab:
X=zeros(1,40); % Frequency domain vector
X(2)=1; % Put data into the first subcarrier (only) ... note that X(1) corresponds to f=0
x=ifft(X); % Use IFFT to generate time domain signal
stem(real(x)) % plot the time domain signal