Why are OFDM Subcarriers Sinc Functions?
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- Опубликовано: 23 авг 2024
- Explains the relationship between the time domain OFDM transmitted signal, and the orthogonal subcarriers in the frequency domain.
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Excellent explanation, thanks a lot sir
You are most welcome
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?
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.
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.
thank you very much,
You are welcome!
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.....
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
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.
Yes, you're right. I simplified the diagram, only showing the elements of the vector that relate to the data-carrying sub channels.
@@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.
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