Open Access

Characterization and Optimization of LDPC Codes for the 2-User Gaussian Multiple Access Channel

EURASIP Journal on Wireless Communications and Networking20072007:074890

https://doi.org/10.1155/2007/74890

Received: 25 October 2006

Accepted: 10 May 2007

Published: 26 June 2007

Abstract

We address the problem of designing good LDPC codes for the Gaussian multiple access channel (MAC). The framework we choose is to design multiuser LDPC codes with joint belief propagation decoding on the joint graph of the 2-user case. Our main result compared to existing work is to express analytically EXIT functions of the multiuser decoder with two different approximations of the density evolution. This allows us to propose a very simple linear programming optimization for the complicated problem of LDPC code design with joint multiuser decoding. The stability condition for our case is derived and used in the optimization constraints. The codes that we obtain for the 2-user case are quite good for various rates, especially if we consider the very simple optimization procedure.

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Authors’ Affiliations

(1)
Unité de recherche INRIA Rennes, Irisa
(2)
ETIS/ENSEA, University of Cergy-Pontoise/CNRS

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Copyright

© A. Roumy and D. Declercq. 2007

This article is published under license to BioMed Central Ltd. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.