Advantage and implementation considerations of shaped OFDM signals

This paper presents the structure and measured performance of a modem designed to implement a variant of OFDM known as shaped OFDM. Individual complex sub-carriers matching the mutually orthogonal tones of a Fourier transform with time span of MT seconds form a standard OFDM signal. The amplitudes of the orthogonal sinusoids are obtained by a DFT of uniformly spaced samples of the time function. An interfering tone within the frequency span of the OFDM signal may interfere with all the OFDM channels. The interference can be isolated to a few OFDM channels by replacing the rectangle envelope with a shaped envelope. The shaping controls the side lobe levels of the individual channel spectra and thus suppress the projection of an inter channel interfering signal. To maintain a fixed system throughput, the time span of the OFDM frame is lengthened and the adjacent frames are overlapped.