基于并行级联LDPC码的递增冗余HARQ方案及性能分析

并行级联LDPC码是由多个码率不同的子码,经并行级联后得到的码率可变的LDPC码.本文提出了基于并行级联:LDPC码的递增冗余HARQ方案,给出了这种方案的吞吐量性能封闭解.在AWGN信道和Rayleigh衰落信道下,通过仿真将新方案的性能和随机LDPC码的性能进行了比较.结果显示,并行级联LDPC码的递增冗余HARQ方案性能接近随机LDPC码,但编、译码更简单,参数选择范围更广.     

非规则全分集LDPC码的构造方法

提出一种基于渐进边增长（Progressive Edge．Growth,PEG）算法的非规则全分集低密度奇偶校验（Low—Density Parity—Check,LDPC）码的构造方法。首先根据度分布和码率,对非规则全分集LDPC码中的节点进行度分配;然后对PEG算法中校验节点的选择标准加以约束,生成消除短环的非规则全分集LDPC码;进一步,通过改变局部校验节点剩余度的方法,解决在特殊度分布下算法失效的问题。仿真结果表明,构造的非规则全分集LDPC码在瑞利块衰落信道下能够实现全分集;在码长、码率相同的情况下与规则全分集LDPC码相比,非规则全分集LD—PC码能够获得更高的编码增益。     

结构半随机LDPC码的递增冗余HARQ方案

提出了结构半随机LDPC码，分析了其在不同码率时，编、译码具有兼容性的特性。介绍了基于结构半随机LDPC码的递增冗余HARQ方案，给出了这种方案的吞吐量性能封闭解。在AWGN信道和Rayleigh衰落信道下，通过仿真将新方案的性能和随机LDPC码的性能进行了比较，结果显示，结构半随机LDPC码的递增冗余HARQ方案性能接近随机LDPC码，但编、译码更简单，参数选择范围更广。     

不规则LDPC码构造方法研究及其改进

通过对码的度数分布进行设计,非规则LDCP码能获得比规则LDPC码更好的性能,但非规则LDPC码在高SNR区会出现错误平层.在本文中,利用ACE算法,对非规则LDPC码的构造方法PEG算法进行改进,以降低非规则LDPC码的错误平层.最后Matlab模拟证明此算法有效提高了非规则LDPC码在加性高斯白噪声通道中的纠错性能.     

一种非规则卷积低密度校验码的构造和短环去除方法

该文研究了使用为分组低密度校验(Low-Density Parity-Check,LDPC)码优化的度序列分布来构造卷积低密度(Low-Density Convolutional,LDC)码的方法,详细讨论了LDC码的编码、译码和短环的消除算法,实验结果说明用为分组LDPC码优化的非规则度序列分布所构造的LDC码,其性能要优于目前文献上提出的规则(homogeneous)LDC码。     

基于差分进化的非规则LDPC码分布对优化

讨论了基于差分进化的非规则LDPC码分布对优化方法。在分布对的优化搜索过程当中,联合使用了差分进化算法(EA)与密度进化算法,并对这种联合技术的实现方法和约束条件处理做了研究。用密度进化算法作为差分进化算法的目标函数,优化搜索出了一组AWGN信道下好的非规则LDPC码分布对,且计算出了各分布对的近似门限值。该方法充分利用差分进化算法的健壮性、有效性以及搜索结果全局最优的特点,是一种有效的好LDPC码搜索技术。     

基于LDPC码率自适应的HARQ系统

在对LDPC码及常用的不等差错保护策略分析的基础上,提出了一种新的码率调整策略,并对该策略的BER和迭代性能进行了分析,证明了其有效性.在该策略的基础上设计了一种基于不等差错保护方法的结合SPIHT和LDPC码的HARQ无线图像传输方案,通过计算机仿真表明该系统的能够起到较好的图像传输保护效果.     

数字调幅广播中基于LDPC码的多级编码方案

研究了DAMB系统中基于LDPC码的多级编码方案。首先,设计了MLC分量码的码率,从而给出一种具有自适应特性的以LDPC码为分量码的多级编码方案。提出了基于可靠信息传播的多级译码方案,该方案不会造成信息丢失,且不需要重编码。构造了一组性能优异的非正则LDPC码并在DAMB信道进行了差错率仿真,结果表明基于LDPC码的MLC方案全面优于标准中RCPC/MLC方案。     

不规则LDPC码度分布的优化设计研究

针对非规则LDPC码的度分布优化,研究了差分进化算法,并利用差分进化算法得到了最大门限的度分布序列,同时在AWGN信道下,通过高斯近似方法得到了在该度分布对下的较精确的LDPC译码门限。通过仿真发现,在改进后的优化算法中的度分布对得到了更高的门限值。同时高斯近似还能应用到其他高效纠错码,对现代高效纠错码具有重要的指导意义。     

Optimization Design of Degree Distributions for Irregular LDPC Codes

针对非规则LDPC码的度分布优化,研究了差分进化算法,并利用差分进化算法得到了最大门限的度分布序列,同时在AWGN信道下,通过高斯近似方法得到了在该度分布对下的较精确的LDPC译码门限.通过仿真发现,在改进后的优化算法中的度分布对得到了更高的门限值.同时高斯近似还能应用到其他高效纠错码,对现代高效纠错码具有重要的指导意义.     

可分解的RC-LDPC码以及HARQ的设计

该文提出了一种可分解的码率兼容LDPC码的构造方法, 该方法构造所得到的一个高码率LDPC码的校验矩阵中包含有若干低码率LDPC码的校验矩阵,而且一个高码率的LDPC码又可以分解成多个性能优异的低码率的LDPC码进行编译码;结合该特性设计了一种基于可分解的码率兼容LDPC码的混合自动重传方案。与普通的ARQ方案相比,该重传方案不单能够通过重传获得更多的信息,而且能够通过降低纠错码的码率来提高纠错码的性能。仿真结果表明,当所采用LDPC码的码长为2000左右,码率为1/2和2/3时,与一般的ARQ相比,该方案的误帧率以及吞吐量(小于0.5的时候)均能获得近1.5dB的增益。     

Rice信道下LDPC码密度进化的研究

应用低密度奇偶校验(LDPC)码译码消息的密度进化可以得到码集的噪声门限,依此评价不同译码算法的性能,并可以用来优化非正则LDPC码的次数分布对。该文首先以Rice信道下正则LDPC码为例,讨论了不同量化阶数及步长时BP,BP-based 和offset BP-based 3种译码算法的DDE(Discrete Density Evolution)分析,接着在offset BP-based译码算法的DDE分析基础上,采用差分进化方法对Rice信道下非正则LDPC码的次数分布对进行了优化,得出了相应的噪声门限。最后,给出了Rice信道下码率为1/2的优化非正则LDPC码的概率聚集函数(PMF)进化曲线。     

Performance of degree distribution based HARQ scheme for LDPC-coded OFDM system

This article studies the degree distribution property of low density parity check (LDPC) codes by Gaussian approximation (GA) and presents an efficient hybrid automatic repeat quest (HARQ) scheme for LDPC-coded orthogonal frequency division multiplexing (OFDM) system. In the scheme, the important bits with large degrees have high retransmission priorities and are mapped to the sub-carriers with better channel quality indicator (CQI) levels in the OFDM system. The new scheme provides more protection to the bits with large degrees and thus contributes more to the decoding process by offering more transmission power. In this way the system performance would be improved. The statistics and simulation results also prove the new scheme.     

Construction of Irregular LDPC Codes by Quasi-Cyclic Extension

In this correspondence, we propose an approach to construct irregular low-density parity-check (LDPC) codes based on quasi-cyclic extension. When decoded iteratively, the constructed irregular LDPC codes exhibit a relatively low error floor in the high signal-to-noise ratio (SNR) region and are subject to relatively few undetected errors. The LDPC codes constructed based on the proposed scheme remain efficiently encodable     

Design of efficiently encodable moderate-length high-rate irregular LDPC codes

This paper presents a new class of irregular low-density parity-check (LDPC) codes of moderate length (10/sup 3//spl les/n/spl les/10/sup 4/) and high rate (R/spl ges/3/4). Codes in this class admit low-complexity encoding and have lower error-rate floors than other irregular LDPC code-design approaches. It is also shown that this class of LDPC codes is equivalent to a class of systematic serial turbo codes and is an extension of irregular repeat-accumulate codes. A code design algorithm based on the combination of density evolution and differential evolution optimization with a modified cost function is presented. Moderate-length, high-rate codes with no error-rate floors down to a bit-error rate of 10/sup -9/ are presented. Although our focus is on moderate-length, high-rate codes, the proposed coding scheme is applicable to irregular LDPC codes with other lengths and rates.     

Finite-length rate-compatible LDPC codes: a novel puncturing scheme - [transactions letters]

In this paper, we study rate-compatible puncturing of finite-length low-density parity-check (LDPC) codes. We present a novel rate-compatible puncturing scheme that is easy to implement. Our scheme uses the idea that the degradation in performance is reduced by selecting a puncturing pattern wherein the punctured bits are far apart from each other in the Tanner graph of the code. Although the puncturing scheme presented is tailored to regular codes, it is also directly applicable to irregular parent ensembles. By simulations, the proposed rate-compatible puncturing scheme is shown to be superior to the existing puncturing methods for both regular and irregular LDPC codes over the binary erasure channel (BEC) and the additive white Gaussian noise (AWGN) Channel.     

Transactions papers evaluation and design of irregular LDPC codes using ACE spectrum

The construction of finite-length irregular LDPC codes with low error floors is currently an attractive research problem. In particular, for the binary erasure channel (BEC), the problem is to find the elements of selected irregular LDPC code ensembles with the size of their minimum stopping set being maximized. Due to the lack of analytical solutions to this problem, a simple but powerful heuristic design algorithm, the approximate cycle extrinsic message degree (ACE) constrained design algorithm, has recently been proposed. Building upon the ACE metric associated with a cycle in a code graph, we introduce the ACE spectrum of LDPC codes as a useful tool for evaluation of codes from selected irregular LDPC code ensembles. Using the ACE spectrum, we generalize the ACE constrained design algorithm, making it more flexible and efficient. We justify the ACE spectrum approach through examples and simulation results.     

HIGH-PERFORMANCE SIMPLE-ENCODING GENERATOR-BASED SYSTEMATIC IRREGULAR LDPC CODES AND RESULTED PRODUCT CODES

Low-Density Parity-Check (LDPC) code is one of the most exciting topics among the coding theory community.It is of great importance in both theory and practical communications over noisy channels.The most advantage of LDPC codes is their relatively lower decoding complexity compared with turbo codes,while the disadvantage is its higher encoding complexity.In this paper,a new ap- proach is first proposed to construct high performance irregular systematic LDPC codes based on sparse generator matrix,which can significantly reduce the encoding complexity under the same de- coding complexity as that of regular or irregular LDPC codes defined by traditional sparse parity-check matrix.Then,the proposed generator-based systematic irregular LDPC codes are adopted as con- stituent block codes in rows and columns to design a new kind of product codes family,which also can be interpreted as irregular LDPC codes characterized by graph and thus decoded iteratively.Finally, the performance of the generator-based LDPC codes and the resultant product codes is investigated over an Additive White Gaussian Noise (AWGN) and also compared with the conventional LDPC codes under the same conditions of decoding complexity and channel noise.