Low-complexity MIMO detector with 1024-QAM

In this paper, dual-layer multiple-input multiple-output (2 × 2 MIMO) systems that use 1024-QAM constellations are studied. Using the layered orthogonal lattice detector (LORD) algorithm, which achieves optimal maximum-likelihood (ML) performance at the expense of high complexity, we argue that the low-complexity version of LORD (LC-LORD) introduces a significant performance degradation, especially with high channel correlation. We propose several approaches that outperform LC-LORD at a lower complexity. These approaches are based on improving the location of a reduced region of search within a 1024-QAM constellation, as well as optimizing the bit log likelihood ratio (LLR) approximation. The proposed approaches were studied in the context of non-iterative and iterative detection and decoding, and significant gains were achieved in both cases.