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.

The work of Y. Wu was supported by a TUM University Foundation Fellowship. The work of D. W. K. Ng was supported by the Australian Research Councils Discovery Early Career Researcher Award funding scheme under Grant DE170100137 and in part by the Linkage Project under Grant LP160100708. The work of C.-K. Wen was supported by the Ministry of Science and Technology of Taiwan under Grant MOST 103-2221-E-110-029-MY3. The work of R. Schober was supported by the German Science Foundation under Grant SCHO 831/5-1. The work of A. Lozano was supported in part by the Project TEC2015-66228-P under Grant MINECO/FEDER, UE and in part by the European Research Council under the H2020 Framework Programme/ERC under Grant 694974. Part of this paper was presented in ICC 2016. The associate editor coordinating the review of this paper and approving it for publication was M. Uysal. (Corresponding author: Yongpeng Wu.)