LDPC码在非相干BFSK系统中的性能分析

通过理论分析和计算机仿真研究了LDPC码在非相干BFSK系统中的性能.首先证明单输入双输出的非相干BFSK系统满足信道对称条件,然后分别利用离散密度进化(DDE)和高斯近似(GA)算法给出了LDPC码的性能下界,后者与前者相比性能非常接近而且计算量要小很多.通过仿真得到几种常用LDPC码的性能并与译码门限以及香农极限进...     

LDPC码的优化设计

通过码结构优化设计,可以得到性能接近香农限的LDPC好码,其关键是寻找好的次数分布对。本文阐述了几种有效分析LDPC码性能的方法：密度演进分析,高斯近似分析及基于EXIT图的方法,在此基础上给出了LDPC码优化设计的过程。LDPC码结构设计的研究对提高码的性能和进一步推动LDPC码的实际应用有着重要的意义。     

半双工中继信道下联合LDPC码设计

为了提高解码前传半双工中继通信系统的编码增益,提出了一种联合LDPC码编码结构及其度分布优化方法。该结构视信源和中继子码为联合LDPC码的一部分,目的端根据从信源和中继接收的消息进行联合译码,同时获得信源和中继的信息。为了分析联合LDPC码的渐进性能,推导了AWGN信道下联合LDPC码的高斯近似密度进化算法。结合译码收敛条件和度分布约束关系,提出联合LDPC码的度分布优化问题。仿真结果表明：联合LDPC码的渐进性能及误码性能优于BE-LDPC码和独立处理（SP）码。     

基于EXIT图和自适应微粒群算法的度分布对优化方法

综合EXIT图法和自适应微粒群优化(APSO)算法的优点,该文提出了一种基于EXIT图和APSO算法的非正则LDPC码度分布对优化方法。该方法设计了衡量EXIT曲线匹配程度的全局代价函数,并运用APSO算法对度分布对进行快速迭代优化,迭代过程中不需要固定CND曲线,可以获得EXIT曲线更加匹配的优化度分布对,以及更高的噪声门限。仿真结果表明,该方法在码结构优化方面有着很好的性能,且优化速度较高斯逼近法有了较大提高。     

CMMB系统中LDPC码研究和性能分析

LDPC码是一种已被证明可接近香农极限的信道编码技术。该文研究了中国移动多媒体广播系统（China Mobile Multimedi aBroadcasting,CMMB）中的LDPC码结构特点,并且采用LU分解编码算法和BP译码算法在AWGN信道中进行了仿真。仿真结果表明,LDPC应用于CMMB系统中极大地提高了系统...     

高阶调制系统下LDPC码优化设计

为了提高编码调制系统的整体编码增益,提出一种高阶调制系统下LDPC码的度分布优化方法.根据高阶调制符号中不同比特的误比特特性,将调制符号所经历信道建模为一组对称二进制输入加性高斯信道.在此基础上,推导了高阶调制系统下LDPC码高斯近似密度进化分析方法,并得到译码收敛条件.结合度分布约束关系及译码收敛条件,提出高阶调制系统下LDPC码的度分布优化问题及差分进化实现方法.仿真结果表明,设计的LDPC码在高阶调制系统中的渐进性能和误码性能优于基于比特优化映射的编码调制方案.     

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.     

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。     

LMMSE频域均衡系统中的最优LDPC码设计

首先介绍了基于LMMSE准则的频域均衡算法的基本原理及其信噪比演进技术,进而采用高斯近似的方法引出了LDPC码的最优设计问题,并通过将优化问题分解为线性优化对其进行迭代求解.针对优化所得的LDPC码进行仿真,结果表明其性能优于已有文献中给出的LDPC码性能,并且更加接近系统容量.     

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.     

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。     

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。     

Serial concatenation of LDPC codes and differential modulations

In this paper, we consider serially concatenated schemes with outer novel and efficient low-density parity-check (LDPC) codes and inner modulations effective against channel impairments. With a pragmatic approach, we show how to design LDPC codes tailored for simple and robust modulation formats, such as differentially encoded (DE) modulations. The LDPC codes are optimized through the use of a recently proposed analysis technique based on extrinsic information transfer (EXIT) charts. In particular, we optimize, through a "clever" random walk in the parametric space, the degree distributions of the outer LDPC codes, obtaining significant insights on the impact of such distributions on the performance of the proposed concatenated schemes. The optimization is carried out for transmission over both the additive white Gaussian noise channel and a noncoherent channel. The performance predicted by the EXIT chart-based optimization is confirmed by results obtained via computer simulations, considering phase-shift keying and quadrature amplitude modulation at the transmitter side, and iterative demodulation/decoding at the receiver side. The significance of the proposed optimized design of LDPC-coded schemes with DE modulations is validated by the fact that standard nonoptimized LDPC codes perform poorly when used together with inner DE modulations.     

Optimization of LDPC codes for modulation and detection in layered multi-antenna architectures

In this paper we first perform the density evolution of LDPC codes in layered multi-antenna architectures using bitinterleaved coded modulation and detection based on successive decoding and interference cancellation. The noise thresholds of LDPC codes are shown to be achieved within 1.2 dB of the capacity for these architectures. We then present a rate allocation method which optimizes the performance of a layered architecture and find good degree distributions for LDPC codes with the rates allocated by our method. Simulation results show that the performance for an optimized layered architecture is better by 4 dB than that for the layered architecture using LDPC codes with the same rate in all layers.     

一种低密度奇偶校验码的环数统计方法

对于Tanner图中给定码长的序列,LDPC码的短环对码的性能有重要影响.本文在分析LDPc码在Tanner图中的环在校验矩阵中的形状的基础上,提出了一种统计LDPC码中不同环长的环数的方法.首先对校验矩阵中一定数目的行组合中的环数进行统计,然后将所有行组合中的环数相加即得到校验矩阵中的环数.该方法可根据LDPC码的短环分布情况对其性能进行评估.应用提出的方法分别对MacKay的随机码和Fossorier的准循环码进行了环数统计.BER性能显示,尽管随机码环数特性比准循环码要差,但它的误码率性能比准循环码要好.     

Constraining LDPC degree distributions for improved error floor performance

The error floor performance of finite-length irregular low-density parity-check (LDPC) codes can be very poor if code degree distributions are chosen to optimize the threshold performance. In this paper we show that by constraining the optimization process, a balance between threshold and error floor' performance can be obtained. The resulting degree distributions give the best threshold performance subject to some minimum requirement on the error floor.     

Analysis of sum-product decoding of low-density parity-check codesusing a Gaussian approximation

Density evolution is an algorithm for computing the capacity of low-density parity-check (LDPC) codes under message-passing decoding. For memoryless binary-input continuous-output additive white Gaussian noise (AWGN) channels and sum-product decoders, we use a Gaussian approximation for message densities under density evolution to simplify the analysis of the decoding algorithm. We convert the infinite-dimensional problem of iteratively calculating message densities, which is needed to find the exact threshold, to a one-dimensional problem of updating the means of the Gaussian densities. This simplification not only allows us to calculate the threshold quickly and to understand the behavior of the decoder better, but also makes it easier to design good irregular LDPC codes for AWGN channels. For various regular LDPC codes we have examined, thresholds can be estimated within 0.1 dB of the exact value. For rates between 0.5 and 0.9, codes designed using the Gaussian approximation perform within 0.02 dB of the best performing codes found so far by using density evolution when the maximum variable degree is 10. We show that by using the Gaussian approximation, we can visualize the sum-product decoding algorithm. We also show that the optimization of degree distributions can be understood and done graphically using the visualization     

截断式原模图低密度奇偶校验卷积码边扩展优化

截断式原模图低密度奇偶校验(LDPC)卷积码(P-LDPC-CCs)结合了原模图LDPC (P-LDPC)码和卷积码的特点,具有多变的编码构造方式和优异的纠错性能,实现了编译码低时延特性。边扩展作为构造截断式原模图LDPC卷积码基础矩阵关键步骤,是影响其性能的重要因素。该文提出了一种边扩展优化方法。该方法利用原模图外信息转移(P-EXIT)算法理论分析基础矩阵的译码门限,引入差分进化思想搜索一定条件下最优的边扩展方式。理论分析与系统仿真结果均表明所提边扩展优化方法比现有的方法具有更好的性能。     

Doubly Generalized LDPC Codes over the AWGN Channel

In this paper, the design of doubly generalized low-density parity-check (DGLDPC) codes is proposed. This approach generalizes the structure of LDPC codes at both check and variable nodes. The performance of DGLDPC codes over the AWGN channel is analyzed using EXIT charts. Combined with differential evolution optimization, this analysis provides thresholds for DGLDPC codes that are better than that of LDPC and GLDPC codes with the same maximum variable degree. These theoretical thresholds are verified via simulations. Furthermore DGLDPC codes exhibit a lower error floor compared with their LDPC and GLDPC counterparts.