Spectral analysis of OFDM signals and its improvement by polynomial cancellation coding

In orthogonal frequency division multiplexing (OFDM) systems, the subcarriers are generated by an inverse discrete Fourier transform. In the literature, the spectra of these subcarriers are often represented by a sequence of sinc functions of the same polarity. This is not consistent with the intercarrier interference (ICI) cancellation properties of polynomial cancellation coding (PCC) or similar self-ICI cancellation schemes in OFDM. This paper shows the spectra of these subcarriers are more accurately represented by a sequence of sinc functions with alternating polarity. It is shown that the spectral rolloff of OFDM signals can be improved by PCC and the resultant OOB power is much reduced.