OFDM modulator

Hi,

I have problem concerning process of generating OFDM signal. From what I
know, the real part of IFFT is sampled OFDM signal. So why after IFFT block
is IQ modulator that uses real and imaginalis part of IFFT? Why we do not
take the real part of IFFT and then convert it to analog signal and then
upconvert to the IF frequency? And what about real part of OFDM signal at
the output of IQ modulator? It should changed after IQ modulation, am I
right?

On May 22, 12:00 pm, "marko1" <marcin_bl...@o2.pl> wrote:
> Hi,
>
> I have problem concerning process of generating OFDM signal. From what I
> know, the real part of IFFT is sampled OFDM signal. So why after IFFT block
> is IQ modulator that uses real and imaginalis part of IFFT? Why we do not
> take the real part of IFFT and then convert it to analog signal and then
> upconvert to the IF frequency? And what about real part of OFDM signal at
> the output of IQ modulator? It should changed after IQ modulation, am I
> right?

You need to learn about "complex baseband" representation of signals.
You need both real and imaginary parts because the signal generated
at the output of an IFFT is in general complex-valued.

You may want to review some of the literature by Richard Lyons,
- Paper, "Quadrature Signals: Complex, But not Complicated"
- Book, "Understanding Digital Signal Processing", Chapter 8.

These should give you more information on creating signals in the
frequency domain that will be only real in the time domain.