  This paper investigates the design of precoders for single-user
multiple-input multiple-output (MIMO) channels, and in particular for
finite-alphabet signals. Based on an asymptotic expression for the mutual
information of channels exhibiting line-of-sight components and rather general
antenna correlations, precoding structures that decompose the general channel
into a set of parallel subchannel pairs are proposed. Then, a low-complexity
iterative algorithm is devised to maximize the sum mutual information of all
pairs. The proposed algorithm significantly reduces the computational load of
existing approaches with only minimal loss in performance. The complexity
savings increase with the number of transmit antennas and with the cardinality
of the signal alphabet, making it possible to support values thereof that were
unmanageable with existing solutions. Most importantly, the proposed solution
does not require instantaneous channel state information (CSI) at the
transmitter, but only statistical CSI.
