After IFFT you get a temporal signal which is expected because IFFT transforms the FFT bins where you placed your QAM symbols into time domain. Now if you use complex conjugate symbols on your frequency bins you will get a real temporal signal, however this technique is wasteful. So to efficiently use the available bins, the complex temporal signal is separated into real and imaginary signal which, then, can be sent over a cosine and sine carrier or in other words sent with a phase difference of pi/2.

Amit Pathania

--- On Mon, 11/3/08, Somayeh Mahmoodi wrote:
From: Somayeh Mahmoodi
Subject: Re: [matlab] ofdm simulation
To: m...
Date: Monday, November 3, 2008, 7:47 PM

hi dear,

yes, the output of IFFT is a time varying signal. infact in the output of IFFT are the samples of time domain signal. if you take for example 128-point IFFT, after IFFT you get 128 samples of time domain signal.

hope to be useful

--- On Sat, 11/1/08, mohamm1er wrote:

From: mohamm1er

Subject: [matlab] ofdm simulation

To: matlab@yahoogroups. com

Date: Saturday, November 1, 2008, 6:58 PM

hi all

I am simulatin ofdm using matlab,with 16QAM digital modulation.

now my out put from QAM is a complex number.when i apply this to IFFT i

am still getting a complex number(i was hoping to get time varying

signal).

any help

thanks
hi dear,
yes, the output of IFFT is a time varying signal. infact in the output of IFFT are the samples of time domain signal. if you take for example 128-point IFFT, after IFFT you get 128 samples of time domain signal.
hope to be useful

--- On Sat, 11/1/08, mohamm1er wrote:

From: mohamm1er
Subject: [matlab] ofdm simulation
To: m...
Date: Saturday, November 1, 2008, 6:58 PM

hi all
I am simulatin ofdm using matlab,with 16QAM digital modulation.
now my out put from QAM is a complex number.when i apply this to IFFT i
am still getting a complex number(i was hoping to get time varying
signal).
any help
thanks