不含小环的低密度校验码的代数构造方法

该文提出了一种构造不含小环的规则低密度校验(LDPC)码的代数方法,使用这种方法可以构造出最小环长为8的规则LDPC码．仿真结果显示,在AWGN信道中其性能优于随机构造的规则LDPC码．     

基于稀疏二进制序列的低密度奇偶校验码

通过对低密度奇偶校验(LDPC)码构造的研究,提出了一种利用稀疏二进制序列构造规则LDPC码的新颖而简单的方法。在构造中,还提出了奇偶校验矩阵里元素‘1’的分布矩阵的概念。为了确保码Tanner图的最小圈长为8,利用了序列的周期自相关函数和周期互相关函数。通过仿真表明构造的新码在和积算法下进行迭代解码性能优异。由于产生的LDPC码本身固有的准循环结构,还能得到较低的编码复杂度。     

低密度奇偶校验码码字构造的消环算法

低密度奇偶校验码(LDPC)的性能取决于多种因素,包括度分布对、码字的长度以及环的分布。环的存在会影响LDPC码的译码门限和误码平层,尤其是长度比较小的环对LDPC码的性能影响很大。因此,有必要在构造LDPC码时消去长度比较小的环。文中提供了一种有效的消环算法,降低了LDPC码的误码平层。     

MLC存储信道下的双层LDPC码优化设计

大数据及云存储的发展对传统的存储技术提出了更高的要求。为了进一步提升多级存储单元的存储效率,提出了一种双层低密度奇偶校验(Low-Density Parity-Check, LDPC)码的优化设计方法。该方法针对多层单元(Multi-level Cell, MLC)信道的非对称性特性,对存储单元的单页添加额外校验比特以提高存储单元闪存信道的译码性能,并对单层LDPC码和本算法的性能进行了分析。仿真结果表明,在多级存储单元信道中使用BP译码算法进行译码,误码率为10;时,基于双层LDPC码构造的纠错码算法比单层LDPC码有约额外4 000次的擦除次数的提升,且译码复杂度也相应降低。     

非规则LDPC码的不等错误保护性能研究

提出了一种具有不等错误保护性能的非规则低密度校验(LDPC,low-density parity-check)码信道编码方案, 构造了重量递增校验(weight-increasing parity-check)矩阵,系统编码时,重要信息比特映射到LDPC码的“精华”比特上。AWGN和Rayliegh衰落信道的仿真结果表明,与随机构造的非规则LDPC码相比,WICP-LDPC码具有好的UEP性能。     

LDPC码的最小汉明距离估算

低密度奇偶校验码(LDPC)是一种优秀的线性分组奇偶校验码。在简要阐述LDPC码原理上,给出了一种叫“最小码字搜索法”的算法来估算LDPC码的最小汉明距离。并用相应的实例给予验证,显示了该方法的正确性与实用性,对分析与优化LDPC码设计具有重要参考价值。     

基于EXIT Chart的码率兼容LDPC码的构造

提出了一种码率兼容LDPC(Rate-Compatible LDPC,以下简称RC-LDPC)码的构造方法.通过该方法构造所得到的一个高码率LDPC码的校验矩阵(H矩阵)中所包含的其它低码率LDPC码的度分布对都是通过码率兼容约束EXIT Chart优化得到.仿真结果表明这样优化得到的各个码率的LDPC码性能与采用普通的最优约束EXIT Chart优化所得到的LDPC码的性能接近.     

低密度校验码及其在图像传输中的应用

低密度校验(Low-Density Parity-Check,LDPC)码是一种基于图和迭代译码的信道编码方案,性能非常接近Shannon极限且实现复杂度低,具有很强的纠错抗干扰能力。该文深入研究了LDPC码的编码和译码基本原理,并将其应用于移动衰落信道图像的传输中,仿真结果表明LDPC码能为图像传输带来显著的性能提高,且系统复杂度低,译码时延短。     

非规则LDPC码简化译码算法研究

主要介绍了低密度奇偶校验码(LDPC)的基本概念及规则和非规则两种典型的LDPC码的结构,简要介绍了LDPC码的译码算法,在此基础上,引出两种非规则LDPC码的简化译码算法,仿真验证算法较大地降低了译码复杂度,并在高信噪比下性能损失较小.     

卫星激光通信中基于Fibonacci数列与GCD序列的非规则QC-LDPC码构造方法

为提高卫星激光通信系统的可靠性,节约其硬件资源,提出一种基于斐波那契(Fibonacci)数列与最大公约数(GCD)序列的非规则准循环低密度奇偶校验(Quasi-Cyclic Low-Density Parity-Check, QC-LDPC)码构造方法。该方法通过由Fibonacci数列与GCD序列组合构造的循环移位矩阵扩展原模图基矩阵,从而得到校验矩阵。所构造的校验矩阵围长至少为6且码长码率可灵活选择,需存储元素少,利于硬件实现,较适用于卫星激光通信系统。仿真结果表明,采用该方法构造的非规则QC-LDPC码与相同码率码长的基于完备差集的非规则Type-I QC-LDPC码、基于消除陷阱集的有限长度非规则FL-QC-LDPC码、基于GCD可快速编译的非规则GL-QC-LDPC码以及基于矩阵扩展的非规则RC-LDPC码相比,其净编码增益均有一定提高。     

Construction of nonsystematic Low-Density Parity-Check codes based on Symmetric Balanced Incomplete Block Design

This paper studies the nonsystematic Low-Density Parity-Check（LDPC）codes based on Symmetric Balanced Incomplete Block Design（SBIBD）.First,it is concluded that the performance degradation of nonsystematic linear block codes is bounded by the average row weight of generalizedinverses of their generator matrices and code rate.Then a class of nonsystematic LDPC codes constructed based on SBIBD is presented.Their characteristics include：both generator matrices and parity-check matrices are sparse and cyclic,which are simple to encode and decode;and almost arbitrary rate codes can be easily constructed,so they are rate-compatible codes.Because there are sparse generalized inverses of generator matrices,the performance of the proposed codes is only 0.15dB away from that of the traditional systematic LDPC codes.     

REGULAR LOW-DENSITY PARITY-CHECK CODES BASED ON SHIFTED IDENTITY MATRICES

This paper extends the class of Low-Density Parity-Check （LDPC） codes that can be constructed from shifted identity matrices. To construct regular LDPC codes, a new method is proposed. Two simple inequations are adopted to avoid the short cycles in Tanner graph, which makes the girth of Tanner graphs at least 8. Because their parity-check matrices are made up of circulant matrices, the new codes are quasi-cyclic codes. They perform well with iterative decoding.     

Sparse sequence construction of LDPC codes

This letter proposes a novel and simple construction of regular Low-Density Parity-Check （LDPC） codes using sparse binary sequences. It utilizes the cyclic cross correlation function of sparse sequences to generate codes with girth 8. The new codes perform well using the sumproduct decoding. Low encoding complexity can also be achieved due to the inherent quasi-cyclic structure of the codes.     

QuaSi-Systematic Block-Circulant LDPC codes

A class of Quasi-Systematic Block-Circulant Low-Density Parity-Check （QSBC-LDPC） codes is proposed. Block-circulant LDPC codes have been studied a lot recently, because the simple structures of their parity-check matrices are very helpful to reduce the implementation complexities. QSBC-LDPC codes are special block-circulant LDPC codes with quasi-systematic parity-check matrices. The memories for encoders of QSBC-LDPC codes are limited, and the encoding process can be carried out in a simple recursive way with low complexities. Researches show that the QSBC-LDPC codes can provide remarkable performances with low encoding complexities.     

有限长不规则LDPC码的构造和编码的优化

该文分析了影响有限长低密度校验(LDPC)码性能的主要因素,在此基础上从度分布参数的优选为起点,结合改进的循序边增长(PEG)算法构造出初步的校验矩阵,提出一种实用的编码优化算法对该校验矩阵进一步优化,最终得到错误平底低且编码复杂度准线性的有限长不规则LDPC码。该优化方法可以容易地推广到一般的信道条件下。     

删余低密度奇偶校验码的分析与设计

通信系统中在不同的信道条件下常采用不同的编码速率,删余码是实现这种策略的有效方式。该文基于高斯近似思想,分析了高斯白噪声信道上删余LDPC码的消息传递译码算法,并在推导出消息均值迭代公式的基础上提出了一种优化删余分布的方法。仿真结果表明,根据此优化方法设计的删余LDPC码在消息传递译码算法下,消息均值增长较快并且消息传递译码算法具有较快的收敛速度。     

DESIGN OF LDPC-CODED BICM USING A SEMI-GAUSSIAN APPROXIMATION

This paper investigates analysis and design of Low-Density Parity-Check （LDPC） coded Bit Interleaved Coded Modulation （BICM） over Additive White Gaussian Noise （AWGN） channel. It focuses on Gray-labeled 8-ary Phase-Shift-Keying （8PSK） modulation and employs a Maximum A Posteriori （MAP） symbol-to-bit metric calculator at the receiver. An equivalent model of a BICM communication channel with ideal interleaving is presented. The probability distribution function of log-likelihood ratio messages from the MAP receiver can be approximated by a mixture of symmetric Gaussian densities. As a result semi-Gaussian approximation can be used to analyze the decoder. Extrinsic information transfer charts are employed to describe the convergence behavior of LDPC decoder. The design of irregular LDPC codes reduces to a linear programming problem on two-dimensional variable edge-degree distribution. This method allows irregular code design in a wider range of rates without any limit on the maximum node degree and can be used to design irregular codes having rates varying from 0.5275 to 0.9099. The designed convergence thresholds are only a few tenths, even a few hundredths of a decibel from the capacity limits. It is shown by Monte Carlo simulations that, when the block length is 30,000, these codes operate about 0.62-0.75 dB from the capacity limit at a bit error rate of 10s.     

Design of irregular LDPC code with unequal error protection property and its performance analysis on image transmission

Based on the property that high degree variable nod.es within an irregular LowDensity Parity-Check （LDPC） code have more powerful error-correcting capability than that of low degree variable nodes, a group of irregular LDPC codes with Unequal Error Protection （UEP） property is designed in this letter. Simulation results show that the transmission quality of the image may be effectively improved with this class of irregular LDPC code.     

Design of Quasi-Cyclic LDPC codes based on Euclidean Geometries

A new method for constructing Quasi-Cyclic (QC) Low-Density Parity-Check (LDPC) codes based on Euclidean Geometry (EG) is presented. The proposed method results in a class of QC-LDPC codes with girth of at least 6 and the designed codes perform very close to the Shannon limit with iterative decoding. Simulations show that the designed QC-LDPC codes have almost the same performance with the existing EG-LDPC codes.