Precoding by Pairing Subchannels to Increase MIMO Capacity with Discrete Input Alphabets
Saif Khan Mohammed, Emanuele Viterbo, Yi Hong, Ananthanarayanan, Chockalingam

TL;DR
This paper introduces a novel precoding method for MIMO channels with discrete inputs, using subchannel pairing and rotation matrices to enhance mutual information while simplifying optimization and detection.
Contribution
It proposes a new pairing-based precoding scheme that improves mutual information in discrete-input MIMO channels and reduces complexity compared to existing methods.
Findings
Achieves mutual information close to the optimal precoder by Cruz et al.
Significantly outperforms Mercury/waterfilling strategy by Lozano et al.
Simplifies precoder optimization and detection for practical use.
Abstract
We consider Gaussian multiple-input multiple-output (MIMO) channels with discrete input alphabets. We propose a non-diagonal precoder based on the X-Codes in \cite{Xcodes_paper} to increase the mutual information. The MIMO channel is transformed into a set of parallel subchannels using Singular Value Decomposition (SVD) and X-Codes are then used to pair the subchannels. X-Codes are fully characterized by the pairings and a real rotation matrix for each pair (parameterized with a single angle). This precoding structure enables us to express the total mutual information as a sum of the mutual information of all the pairs. The problem of finding the optimal precoder with the above structure, which maximizes the total mutual information, is solved by {\em i}) optimizing the rotation angle and the power allocation within each pair and {\em ii}) finding the optimal pairing and…
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Taxonomy
TopicsAdvanced MIMO Systems Optimization · Energy Harvesting in Wireless Networks · Advanced Wireless Communication Techniques
