Optimum performance of zero-forcing and minimum mean-square-error equalization for spatial combining diversity over mobile radio channels

Equalization techniques based on zero forcing (ZF) and minimum mean-square-error (MMSE) equalization for optimum combining diversity reception are presented and compared. Computer simulations of equalizer with and without diversity are carried out for a typical quadrature amplitude modulation (QAM) mobile radio system under various frequency-selective multipath fading conditions. We evaluate the theoretical performance bounds for such a diversity receiver as the equalization length goes to infinity. A common conclusion presented in many papers is that MMSE equalizers significantly outperform the corresponding ZF equalizers using either a linear (LE) or a decision-feedback (DFE) structure. However, our results indicate that, under multipath fading, the ZF-DFE performs approximately the same as the MMSE-DFE, particularly in combining diversity reception