Reduced complexity fractionally spaced MIMO equalizers for multitone systems without guard time

When OFDM or multitone modulation is used, the dispersiveness of the channel is usually circumvented by means of the guard time technique. As an alternative it is possible not to use a guard time but design receivers able to equalize the intersymbol interference (ISI) and inter-carrier interference (ICI). We show how to design fractionally spaced linear or decision-feedback MIMO equalizers for multitone systems without the guard time. Full complexity and reduced complexity solutions are investigated. The design is made for an MMSE criterion and the steady-state performance is analyzed. It is shown that MIMO equalization outperforms the guard time technique, that fractionally spaced devices are very effective and the complexity reduction produces a performance degradation which is negligible compared to full complexity fractionally spaced devices, especially when the processing rate is larger than the symbol rate.