When OFDM or multitone modulation is used, the dispersiveness ofthe channel is usually circumvented by means of the guard timetechnique. As an alternative it is possible not to use a guard time butdesign receivers able to equalize the intersymbol interference (ISI) andinter-carrier interference (ICI). We show how to design fractionallyspaced linear or decision-feedback MIMO equalizers for multitone systemswithout the guard time. Full complexity and reduced complexity solutionsare investigated. The design is made for an MMSE criterion and thesteady-state performance is analyzed. It is shown that MIMO equalizationoutperforms the guard time technique, that fractionally spaced devicesare very effective and the complexity reduction produces a performancedegradation which is negligible compared to full complexity fractionallyspaced devices, especially when the processing rate is larger than thesymbol rate
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