  In this paper, we propose a multiple-input multipleoutput (MIMO) transmission
strategy that is closer to the Shannon limit than the existing strategies.
Different from most existing strategies which only consider uniformly
distributed discrete input signals, we present a unified framework to optimize
the MIMO precoder and the discrete input signal distribution jointly. First, a
general model of MIMO transmission under discrete input signals and its
equivalent formulation are established. Next, in order to maximize the mutual
information between the input and output signals, we provide an algorithm that
jointly optimizes the precoder and the input distribution. Finally, we compare
our strategy with other existing strategies in the simulation. Numerical
results indicate that our strategy narrows the gap between the mutual
information and Shannon limit, and shows a lower frame error rate in
simulation.
