Structural Optimization And Design Of LDPC Codes

Mobile communication is one of the most promising branches in the communication area. In the next generation communication systems, in order to satisfy the ever increasing high-quality requirements for high-speed data transmission, we need to further improve the existing key techniques in the physical layer. For instance, the revolutionary Turbo codes and LDPC codes which boast better performance are thus given more attention for channel coding. With the carrying out of further research, people discovered that Turbo codes are in reality a kind of LDPC codes; in addition, the long-length LDPC codes even outperform Turbo codes while maintaining a much lower decoding complexity. As a result of their superior error-correcting abilities and efficient iterative decoding algorithms, LDPC codes become the focus of coding community once again.The purpose of this paper is to combine the theoretical research results and practical experiences of LDPC codes, to summarize and improve the existing optimizing design algorithms, and finally to design LDPC codes which have good performance and relatively low encoding complexity as well as decoding complexity.The basic definition and relating concepts of LDPC codes are introduced in this paper. The main factors which can influence the performance of LDPC codes are summarized and used as the primary guidance in designing the structures of LDPC codes. Based on the comprehension of the existing optimizing design methods, a revised algorithm which can significantly improve both the ring distribution and minimum distance is proposed, and supported simulation results are given. The idea of constructing rate-compatible LDPC codes is introduced, and an effective yet simple puncturing algorithm is given. Fundamental concepts and constructing principles of protograph, an optimizing design method which is relatively new, are introduced in detail. A series of efficiently-encodable LDPC codes are also designed by using carefully selected protographs. Finally, the traditional definition of LDPC codes is generalized and the concept of multi-edge type LDPC codes is given.