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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: Optimized Irregular Low-Density Parity-Check Codes for Multicarrier Modulations over Frequency-Selective Channels | EURASIP Journal on Applied Signal Processing 2004 10 1546-1556 2004 Hindawi Publishing Corporation Optimized Irregular Low-Density Parity-Check Codes for Multicarrier Modulations over Frequency-Selective Channels Valerian Mannoni ETIS ENSEA UCP CNRS 8051 6 Avenue du Ponceau 95014 Cergy-Pontoise Cedex France Laboratory of Decision and Communications Systems DeCom University of Reims Champagne-Ardenne UFR Sciences Moulin de la Housse 51687 Reims Cedex2 France Email valerian.mannoni@univ-reims.fr David Declercq ETIS ENSEA UCP CNRS 8051 6 Avenue du Ponceau 95014 Cergy-Pontoise Cedex France Email declercq@ensea.fr Guillaume Gelle Laboratory of Decision and Communications Systems DeCom University of Reims Champagne-Ardenne UFR Sciences Moulin de la Housse 51687 Reims Cedex2 France Email guillaume.gelle@univ-reims.fr Received 1 March 2003 Revised 30 October 2003 This paper deals with optimized channel coding for OFDM transmissions COFDM over frequency-selective channels using irregular low-density parity-check LDPC codes. Firstly we introduce a new characterization of the LDPC code irregularity called irregularity profile. Then using this parameterization we derive a new criterion based on the minimization of the transmission bit error probability to design an irregular LDPC code suited to the frequency selectivity of the channel. The optimization of this criterion is done using the Gaussian approximation technique. Simulations illustrate the good performance of our approach for different transmission channels. Keywords and phrases orthogonal frequency division multiplexing frequency-selective channel optimized channel coding irregular LDPC codes density evolution. 1. INTRODUCTION In this paper we address the problem of designing codes for transmissions over frequency-selective channels when orthogonal frequency division multiplexing OFDM modulation technique is used. Multicarrier modulations are good candidates for the emerging high rate transmissions either wired .