【作者】 王玲；

【导师】 赵力；

【作者基本信息】 东南大学 ， 信号与信息处理， 2006， 硕士

【摘要】 纠错编码技术是移动通信、卫星通信、光纤通信和磁盘存储等系统中的关键技术之一。其中,由Gallager在1962年首先提出的低密度奇偶校验码(LDPC)码,在沉寂了多年之后,受到Turbo码的启发,Mackey和Wiberg等人对Gallager码重新进行了研究发现Gallager码优异性能,LDPC码再次成为通信技术研究的热点。LDPC码是一种具有稀疏校验矩阵的线性分组码,研究结果表明,采用迭代的概率译码算法,LDPC码可以达到接近香农极限的性能。本论文较为系统的介绍了LDPC码的构造、编码和译码。重点是LDPC码的译码算法和其在数字电视系统中的应用。本文首先研究了LDPC码理论基础,如图结构、线形分组码。之后介绍了几种构造方法,包括Mackay随即构造、有限几何的EG构造,以及相应的编码算法。本文介绍了BF、WBF、LP-WBF、BP、BP_based和Normalized BP_based算法,详细的推导了BP译码的各个步骤。给出了AWGN信道下几种LDPC码在不同译码算法下的仿真性能。同时,本文在BF译码算法的基础上提出了改进算法Iterate F-BF算法,仿真结果表明其对低列重的码有明显的改善。最后,本论文对LDPC码在数字电视地面广播系统中的应用进行了研究。文中仔细分析了BP软译码的初始化问题,并且给出了AWGN信道,多进制调制系统下的仿真结果。然后,将LDPC和OFDM结合,在Rayleigh信道下仿真了LDPC-OFDM系统的误码率性能,选用的系统是时域同步正交频分复用(Time Domain Synchronous OFDM,TDS-OFDM)系统。更多还原

【Abstract】 Error-correcting codes are widely used in many fields, such as mobile communication, satellite communication, and so on.‘Low-Density Parity codes (LDPC)’, one kind of Error-correction codes, is defined in terms of very sparse matrices, and can be decoded by iteration algorithms. It were first investigated in 1962 by Gallager, but appear to have been largely forgotten. Mackey and Wiberg rediscovered their excellent property of achieving information rates up to the Shannon limit, after the extreme success of Turbo codes.This dissertation presents a systematic investigation of LDPC codes. We introduce the theory foundation of LDPC, firstly, including Tanner graph, several constructions and responded encoding methods. Than we study the major decoding algorithms, BF, WBF, LP-WBF, BP and two other improved BP algorithms. Some simulation results for additive white Gaussian noise ( AWGN ) channel are given.As one of contributions of this dissertation, an improved decoding algorithm based on the BF algorithm (Iterate F-BF) is proposed. Compared with BF algorithm, it achieves considerable improvement for low column weight LDPC with almost the same complexity.The applications of LDPC codes are studied. We apply the LDPC to the Time Domain Synchronous OFDM(TDS-OFDM) system in Rayleigh fading channels. The OFDM parameters are selected according to Chinese Digital TV Terrestrial broadcasting standards.更多还原