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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 Differentially Encoded LDPC Codes—Part II: General Case and Code Optimization | Hindawi Publishing Corporation EURASIP Journal on Wireless Communications and Networking Volume 2008 Article ID 367287 10 pages doi 10.1155 2008 367287 Research Article Differentially Encoded LDPC Codes Part II General Case and Code Optimization Jing Li Tiffany Electrical and Computer Engineering Lehigh University Bethlehem PA 18015 USA Correspondence should be addressed to Jing Li Tiffany jingli@ece.lehigh.edu Received 19 November 2007 Accepted 6 March 2008 Recommended by Yonghui Li This two-part series of papers studies the theory and practice of differentially encoded low-density parity-check DE-LDPC codes especially in the context of noncoherent detection. Part I showed that a special class of DE-LDPC codes product accumulate codes perform very well with both coherent and noncoherent detections. The analysis here reveals that a conventional LDPC code however is not fitful for differential coding and does not in general deliver a desirable performance when detected noncoherently. Through extrinsic information transfer EXIT analysis and a modified convergence-constraint density evolution DE method developed here we provide a characterization of the type of LDPC degree profiles that work in harmony with differential detection or a recursive inner code in general and demonstrate how to optimize these LDPC codes. The convergence-constraint method provides a useful extension to the conventional threshold-constraint method and can match an outer LDPC code to any given inner code with the imperfectness of the inner decoder taken into consideration. Copyright 2008 Jing Li Tiffany . 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 With an increasingly mature status of the sparse-graph coding technology in a theoretical context the very pervasive scope of their well-proven practical applications .