OFDM schemes with non-overlapping time waveforms

For orthogonal frequency division multiplexing (OFDM) schemes, the time waveform plays a major role not only in shaping the spectrum of the transmitted signal but also in separating the signal subcarriers at the receiver. The selection of such waveform is then very important and can make a big difference in spectrum utilization and system performance. The difficulty in using pulse shaping with OFDM appears in the detector design since smooth time waveforms destroy the orthogonality between subcarriers and introduce inter-channel interference (ICI). This paper investigates the use of non-overlapping signal waveforms for OFDM schemes. It is shown that pulse shaping for such schemes can be equivalently achieved using a discrete shaping matrix. Such a shaping structure is very suitable for digital implementation and can be combined with OFDM schemes without affecting their IDFT/DFT operators. It therefore makes the use of guard time interval (cyclic prefix) for OFDM schemes possible with any kind of non-overlapping shaping waveform.