Performance of MMSE MIMO Receivers in Frequency-Selective Channels

This paper investigates the performance of the minimum mean-square error (MMSE) equalizers in MIMO frequency selective channels under zero-padding (ZP) transmission. It was previously known that the SISO linear ZP receiver achieves full diversity; this paper shows that the MIMO version of this receiver is suboptimal in diversity. It is shown that the MMSE MIMO receiver exhibits an intricate error behavior that depends not only on channel memory and antenna configuration, but also on transmission rate. This behavior is fully characterized in closed form, revealing that the MMSE ZP receiver attains the (optimal) diversity of a ML receiver but only at small spectral efficiencies.