  In this paper, we investigate noncoherent multiple-input multiple-output
(MIMO) ultra-wideband (UWB) systems where the signal is encoded by differential
space-time block code (DSTBC). DSTBC enables noncoherent MIMO UWB systems to
achieve diversity gain. However, the traditional noncoherent symbol-by-symbol
differential detection (DD) for DSTBC-UWB suffers from performance degradation
compared with the coherent detection. We introduce a noncoherent multiple
symbol detection (MSD) scheme to enhance the performance of DSTBC-UWB system.
Although the MSD scheme can boost the performance more as the observation
window size gets to larger, the complexity of the exhaustive search for MSD
also exponentially increases in terms of the window size. To decrease the
computational complexity, the concept of decision-feedback (DF) is introduced
to MSD for DSTBC-UWB in this paper. The resultant DF-MSD yields reasonable
complexity and also solid performance improvement. We provide the bit error
rate (BER) analysis for the proposed DF-MSD. Both theoretical analysis and
simulation results validate the proposed scheme.
