基于陷阱集的比特翻转二阶段qc-ldpc 码译码算法研究.docx

Classified Index: :
Dissertation for the Master’s Degree in Engineering
RESEARCH ON BITS FLIPPING TWO-PHASE DECODING ALGORITHM OF QC-LDPC CODES BASED ON TRAPPING SETS
Candidate:
Li Bin
Supervisor:
Prof. Wang Xuedong
Academic Degree Applied for:
Master of Engineering
Specialty:
Electronic munication Engineering
Affiliation:
School of Electronics and Information Engineering
Date of Defence:
July, 2013
Degree-Conferring-Institution:
Harbin Institute of Technology
摘 要
LDPC(Low-Density-Parity-Check)码是一种性能逼近香农限的编码,并成为近年来在信道编码领域尤其是无线通信领域中的主要技术和研究热点之一, 目前已广泛应用于卫星数字视频、光通信、音频广播和深空通信等领域。LDPC 码在构造上难以避免的会造成陷阱集结构,从而迭代译码时在高信噪比区域会形成误码平层现象,即误码率难以随信噪比的提高而明显下降,这阻碍了码字译码性能的进一步提升。现在越来越多的应用需要更低的误码率以满足更高的应用要求。
为了降低误码平层追求更低的误码率,本文主要针对 LDPC 码的码字构造中的陷阱集结构对迭代译码算法进行了分析和改进来纠正译码时的遇到的陷阱集问题。通过对陷阱集模式的实际分析,研究改进了比特翻转二阶段迭代的译码算法来纠正陷阱集差错以及降低误码平层,得到更低误码率的 LDPC 译码方案,是逼近 LDPC 码性能极限的一种有效方式。
本文设计了 LDPC 码比特翻转二阶段译码算法仿真系统,使用准对角线循环置换矩阵构造满秩校验矩阵的方法构造了多种不同码长码率的准循环
LDPC(QC-LDPC)码并挑选使用了其中的四个码字。使用本文研究的比特翻转二阶段译码算法对码字进行编译码仿真,分析不同陷阱集模式下比特翻转二阶段译码发挥的作用及取得的改进效果。使用本文提出的翻转尝试算法可以获
得更高的陷阱集纠正概率,并改进迭代译码的误码率性能。使用比特翻转二阶段改进译码能够比传统迭代译码纠正更多的错误,从而
在高信噪比区域能达到更低的误码平层,实现更低的误码率,可以满足更多的新的实际应用对更低误码率的要求。
关键词: QC-LDPC;误码平层;陷阱集;BP 迭代译码;比特翻转二阶段译码
Abstract
LDPC(Low-Density-Parity-Check) code is a coding method with a performance closed to Shannon limit, which has e the main technology and hot researching in field of channel coding and especially in field of munications in recent years, and currently has been widely used in satellite digital video, munications, audio broadcasting and deep munications. It’s hard to avoid the trapping sets problem in constructing LDPC code, which is the reason of error-floor in high SNR(signal-to-noise ratio) region during decoding, that the BER(bit error rate) decreases very slowly with the increasing of signal-to-noise ratio, and it hinders the further increase of code performance. Now more and municating applications need lower BER to meet the higher requirements of t