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ofdm carriers discrete or analog

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bvishwanath

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1.how com discrete carriers(present in ifft) modulate input sequence?
2.which parameter of carrier is changing?(after modlation)
3.is this base band or band pass modulation?
4.why ofdm spectrum is continues? i,e sinc each having null at center of adjacent carrier..
 

1.how com discrete carriers(present in ifft) modulate input sequence?
Whay call the carriers "discrete". each of them is a continuous signal, they are at discrete frequencies, if you want.
Each individual carrier is modulated (eg QPSK) by the input data sequence.

2.which parameter of carrier is changing?(after modlation)
Phase and Amplitude (QPSK)

3.is this base band or band pass modulation?
band pass probably, since the spectrum is shifted to where the carrier is.

4.why ofdm spectrum is continues? i,e sinc each having null at center of adjacent carrier..
Each carrier's spectrum gets spread by the modulating sequence, look up spectrum of a QPSK signal. it is only that in OFDM you have lots of carriers.
 

3. Spectrum is shifted to the carrier a little bit later in the upconverter.
IFFT result is a baseband representation of signal.

4. Where 1st sinc has a null, at the adjacent carrier, the sinc of adajcent carrier has 1 and so on. The total envelope of multiple carriers will be rather continuous.
 

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