Tuyển tập báo cáo các nghiên cứu khoa học quốc tế ngành hóa học dành cho các bạn yêu hóa học tham khảo đề tài: Research Article Characterization and Optimization of LDPC Codes for the 2-User Gaussian Multiple Access Channel | Hindawi Publishing Corporation EURASIP Journal on Wireless Communications and Networking Volume 2007 Article ID 74890 10 pages doi 2007 74890 Research Article Characterization and Optimization of LDPC Codes for the 2-User Gaussian Multiple Access Channel Aline Roumy1 and David Declercq2 1 Unite de recherche INRIA Rennes Irisa Campus universitaire de Beaulieu 35042 Rennes Cedex France 2 ETIS ENSEA University of Cergy-Pontoise CNRS 6 Avenue du Ponceau 95014 Cergy-Pontoise France Received 25 October 2006 Revised 6 March 2007 Accepted 10 May 2007 Recommended by Tongtong Li 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. Copyright 2007 A. Roumy and D. Declercq. 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. 1. INTRODUCTION In this paper we address the problem of designing good LDPC codes for the Gaussian multiple access channel MAC . The corner points of the capacity region have long been known to be achievable by single-user decoding. This idea was also used to achieve any point of the capacity region by means of rate splitting 1 . Here we focus on the design of multiuser .
