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 Quasi-Cyclic LDPC Codes of Column-Weight Two Using a Search Algorithm | Hindawi Publishing Corporation EURASIP Journal on Advances in Signal Processing Volume 2007 Article ID 45768 8 pages doi 2007 45768 Research Article Quasi-Cyclic LDPC Codes of Column-Weight Two Using a Search Algorithm Gabofetswe Malema and Michael Liebelt School of Electrical and Electronic Engineering The University of Adelaide North Terrace Adelaide 5005 SA Australia Received 16 February 2006 Revised 11 August 2006 Accepted 6 February 2007 Recommended by Richard Heusdens This article introduces a search algorithm for constructing quasi-cyclic LDPC codes of column-weight two. To obtain a submatrix structure rows are divided into groups of equal sizes. Rows in a group are connected in their numerical order to obtain a cyclic structure. Two rows forming a column must be at a specified distance from each other to obtain a given girth. The search for rows satisfying the distance is done sequentially or randomly. Using the proposed algorithm regular and irregular column-weight-two codes are obtained over a wide range of girths rates and lengths. The algorithm which has a complexity linear with respect to the number of rows provides an easy and fast way to construct quasi-cyclic LDPC codes. Constructed codes show good bit-error rate performance with randomly shifted codes performing better than sequentially shifted ones. Copyright 2007 G. Malema and M. Liebelt. 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 Gallager has shown that column-weight-two codes have minimum distance increasing logarithmically with code length compared to a linear increase when the column-weight is at least three 1 . Despite the low increase in minimum distance these codes have shown potential in some applications such as partial response channels 2 3 . These codes also have less computation because columns .
