Differential Unitary Space-Time Modulation (DUSTM), which is a multi-antenna modulation technique for time-varying fading channels, can obtain full diversity gains without channel state information at the receiver in slowly fading channels. For fast fading channels, however, its performance degrades considerably and suffers an irreducible error floor. In this paper, a novel Sub-Matrix Interleaved Differential Unitary Space-Time Modulation (SMI-DUSTM) scheme is proposed, in which matrix-segmentation and sub-matrix based interleaving are combined with conventional DUSTM. The constellation design criteria of SMI-DUSTM are also derived in this paper, based on the calculation of Pairwise Error Probability (PEP). The performance analysis and simulation results demonstrate that SMI-DUSTM can not only inherit the merit of DUSTM in slowly fading channels, but also maintain a good performance in fast fading channels.
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