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How OFDM works
Because an IIFT is used for modulation in OFDM, this spacing of the subcarriers is done in such a way the frequency where we evaluate the received signal all other signals are zero thus allowing the subchannels to overlap. But because of this, for an OFDM system to work using this method, the receiver and the transmitter must be in perfect synch, and there can’t be any multipath fading, which is unusual since finding a fix to this is one of the main goals of OFDM.Luckily there is an easy way to solve this problem. If a guard interval is used, which is larger than the expected delay spread, which is done by artificially extending the symbol time and then removing this extension at the receiver, the problem is solved but with only a minimal loss in bandwidth.