  In this paper, the Hermite polynomials are employed to study linear
approximation models of narrowband multiantenna signal reception (i.e., MIMO)
with low-resolution quantizations. This study results in a novel linear
approximation using the second-order Hermite expansion (SOHE). The SOHE model
is not based on those assumptions often used in existing linear approximations.
Instead, the quantization distortion is characterized by the second-order
Hermite kernel, and the signal term is characterized by the first-order Hermite
kernel. It is shown that the SOHE model can explain almost all phenomena and
characteristics observed so far in the low-resolution MIMO signal reception.
When the SOHE model is employed to analyze the linear minimum-mean-square-error
(LMMSE) channel equalizer, it is revealed that the current LMMSE algorithm can
be enhanced by incorporating a symbol-level normalization mechanism. The
performance of the enhanced LMMSE algorithm is demonstrated through computer
simulations for narrowband MIMO systems in Rayleigh fading channels.
