I have to apply a window to an IFFT'ed signal (based on LTE standards, simulated for 1 symbol - 100 resource blocks - 1200 subcarriers). I have a signal which I have simulated till the IFFT. Now I have to apply a window function to it to analyse the Out of band emissions. How do I decide the window function length and then how do I apply it? e.g Hamming/Hanning/Blackman etc.
If allowed, I would view the signal in the frequency domain (2048 pt FFT for a single symbol, Fs=30.72Mhz).
Anything outside the central 1200 carriers in the symbol is "noise" and shouldn't be there.
You can filter the noise by setting the outer FFT bin amplitudes to 0, then convert back to the time-domain or perform other signal processing as desired.
Edit: that may not really help your cause, since analysis and demodulation is performed on the center 1200 carriers only... Setting outer carriers to 0 won't change the carriers/frequency content that matters... So maybe I'm missing your point?