Precoding with X-codes to increase capacity with discrete input alphabets

Mohammed, SK and Viterbo, E and Hong, Yi and Chockalingam, A (2010) Precoding with X-codes to increase capacity with discrete input alphabets. In: 2010 IEEE International Symposium on Information Theory Proceedings (ISIT), 13-18 June 2010, Austin, TX.

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Abstract

We consider Gaussian multiple-input multiple-output (MIMO) channels with discrete input alphabets. We propose a non-diagonal precoder based on X-Codes in 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 the 2 × 2 real rotation matrices for each pair (parameterized with a single angle). This precoding structure enables 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 equivalent to i) optimizing the rotation angle and the power allocation within each pair and ii) finding the optimal pairing and power allocation among the pairs. It is shown that the mutual information achieved with the proposed pairing scheme is very close to that achieved with the optimal precoder by Cruz et al., and significantly better than mercury/waterfilling strategy by Lozano et al.. Our approach greatly simplifies both the precoder optimization and the detection complexity, making it suitable for practical applications.

Item Type:	Conference Paper
Publisher:	IEEE
Additional Information:	Copyright 2010 IEEE. Personal use of this material is permitted.However, permission to reprint/republish this material for advertising or promotional purposes or for creating new collective works for resale or redistribution to servers or lists, or to reuse any copyrighted component of this work in other works must be obtained from the IEEE.
Department/Centre:	Division of Electrical Sciences > Electrical Communication Engineering
Date Deposited:	20 Dec 2011 06:55
Last Modified:	20 Dec 2011 06:55
URI:	http://eprints.iisc.ac.in/id/eprint/38968

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