I need to ask about insertion of Zero Symbols after QAM modulation in a OFDM system. Such that the 4 QAM has a constellation with 4 corner and 1 center symbol indicating zero. What advantages or disadvantages woild that offer ?
Is this done for guard bits or as pilot or what ?
So I need to add more information to the question. I just had a tutorial on OFDM system on MATLAB and what my Tutor told was that in addition to the Cyclic Prefix, we may also include these zero symbols after we have modulated the bits with QAM. Which appear as Zero Points in Constellation. He was saying that they have the purpose of controlling the ISI as well. But I was confused because ISI was controlled by Cyclic Prefix. ?
Also I am not sure about what effects this would have on OFDM Spectrum.