Research on Rate-Compatible LDPC Codes

低密度奇偶校验（low-densityparity-checkcode，LDPC）码具有逼近Shannon限的性能、较低的误码平台（errorfloor）和线性的译码复杂度，在现代信道纠错编码领域中备受关注。随着现代通信服务从单一的低速话音业务迈向各种高速多媒体业务，传输速率与传输条件多样性日益增长，使得通信系统的信道编码技术不仅要具备纠错功能，而且还必须能够根据传输速率和传输条件的变化而自适应地改变码率。面对这一新需求，研究码率自适应LDPC（rate-compatibleLDPC，RC-LDPC）码，使其在延续LDPC码各项优势的同时，码率能够自适应地灵活调整，对于进一步推动LDPC码的应...Low-density parity-check (LDPC) codes have attracted significant attention in the area of modern error correcting codes (ECC) due to their capacity-approaching performance, low error floors and linear-time complexity of encoding. Along with the development of modern communication service from low-rate voice transmission to high-rate multimedia application, the variety of transmission rate under di...学位：工学博士院系专业：信息科学与技术学院通信工程系_通信与信息系统学号：2332007015387

一种改进的MET-LDPC码的译码算法

在迭代译码算法的基础上,进一步分析平均迭代译码算法,并将平均迭代译码算法用于MET-ldPC码型仿真,改善了传统迭代译码算法的性能,起到了降低误码平台的作用,并对今后译码算法的研究提出了展望

Design of rate-compatible protograph LDPC codes

无线通信信道的时变性,使得纠错编码必须具备码率自适应的功能。原模图低密度奇偶校验码(lOW dEnSITy PArITy CHECk COdE,ldPC)可通过删余和扩展实现码率自适应,并能解决传统ldPC码编码复杂度高的难题。将具有原模图结构的Ar4JA码(ACCuMulATE rEPEAT-4 JAggEd-ACCuMulATE COdE)作为母码,提出“逐节点删余“算法,实现Ar4JA码率从0.5~0.8的变化,利用矩阵扩展实现码率从0.5~0.25的降低。在加性高斯白噪声信道(AddITIVE WHITE gAuSSIAn nOISE,AWgn)下的仿真结果表明,在bEr为10-6数量级处,结合删余和扩展方法构造的码率自适应Ar4JA码并未出现错误地板。Over time-varying wireless channel,it is necessary for error-correction codes to be rate-compatible.Protograph LDPC codes can achieve rate-compatibility through puncturing and extending;and solve the problem that the encoders of tradition LDPC codes are more complex.With the AR4JA code which can be represented by protograph,we construct a rate-compatible family of AR4JA codes with rates ranging from 0.5 to 0.8 using the algorithm of "puncturing node by node".To obtain the lower rates from 0.5 to 0.25,matrix expansion is also used.Simulation results over AWGN channel show that using both puncturing and extending we can construct rate-compatible family of AR4JA codes which do not suffer from error floor when BER is 10-6.国家自然科学基金(60972053)---

LAS在滇池典型入湖河口缺氧水体中的生物降解

利用"河水衰减法"研究了不同培养条件下阴离子表面活性剂LAS在滇池典型入湖河口(海河口)缺氧水体中的生物降解及其动力学,探讨了温度、pH值、LAS的初始浓度、添加营养盐(NH4Cl或NaH2PO4)以及曝气等因素对LAS生物降解的影响.结果表明,在河口水体中的不同条件下,试验26 d后LAS的生物降解率都达95%以上,且降解服从二级动力学模型.温度、LAS的初始浓度、添加营养盐以及曝气均对LAS的降解有一定的影响.当水温从10℃增至25℃时,其降解速率p从0.21 d-1增至0.90 d-1;在连续曝气

Advances of the error-floor study of LDPC codes

低密度奇偶校验(ldPC)码在迭代译码下具有优越的性能,但是在高信噪比区呈现出误码平台(ErrOrflOOr)现象。综合分析了低密度奇偶校验码的误码平台现象及其产生的原因,重点描述了陷阱集及其对ldPC码误码平台的影响,同时阐述了估计和降低ldPC码误码平台的方法,并对今后ldPC码误码平台研究的重点和方向提出了展望。Low-density parity check(LDPC)codes are known to perform very well under iterative decoding.However,these codes often exhibit an error floor phenomenon in the high signal-to-noise(SNR)region.This paper provides a comprehensive description of the cause of the error floor phenomenon of LDPC codes.It presents a detailed description of the trapping sets,describes the methods to estimate and reduce the error floor of LDPC codes.Finally,it proposes the future development of the error floor of LDPC codes

FPGA Implementation of Irregular LDPC Code Decoder

LDPC(低密度奇偶校验码)是一种优秀的线性分组码,是目前距香农限最近的一类纠错编码。与Turbo码相比,LDPC码能得到更高的译码速度和更好的误码率性能,从而被认为是下一代通信系统和磁盘存储系统中备选的纠错编码。简要介绍了适于硬件实现的LDPC码译码算法,并基于软判决译码规则,使用Verilog硬件描述语言,在X ilinx V irtex2 6000 FPGA上实现了码率为1/2、帧长504bit的非规则LDPC码译码器。Low Density Parity Check(LDPC) code is a good linear block code,which performs at a rate extremely close to the Shannon limit capacity.Compared with Turbo code,LDPC code performs faster decoding speed and better BER performance and is considered to be one of suitable codes for 4G communication system and storage system.This paper introduces a decode algorithm which is suitable for hardware implementation and a fully parallel decoder based on a frame of 504 bits for irregular LDPC codes is implemented on Xilinx FPGA XC2V6000 device with Verilog language

Puncturing Algorithm for Design Rate-Compatible LDPC Code

鉴于无线通信信道的时变特性,信道纠错编码必须具备码率自适应的功能.现有的分组拣选算法尽管能构造出性能优秀的码率自适应删余型ldPC码,但达到的最高删余码率受到限制.对此,该文提出一种新的删余算法-分层拣选算法,解决了最高删余码率受限的问题,使码率能够无限接近1,且适用于任意ldPC码.AWgn信道下的仿真结果表明,所提出的算法较分组拣选算法具有更好的性能.Rate compatibility of forward error correction codes is required to accomplish high throughput and reliability over time-varying wireless channels.The grouping and sorting(GS) algorithm can produce rate-compatible puncturing LDPC(RCP-LDPC) codes with good performance.However,there is a limit in the achievable highest puncturing rate.In this paper,a novel layer-by-layer sorting algorithm is proposed to design RCP-LDPC without any limitation in the highest puncturing rate.The algorithm can be applied to an arbitrary LDPC code to obtain a code rate infinitely close to one.Simulation over AWGN channels shows that the proposed algorithm has superior performance as compared to the GS algorithm.国家自然科学基金(No.60972053);福建省自然科学基金(No2008J0035)资

Computation of the minimum distance of low-density parity-check codes

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。Low-density parity-check (LDPC) codes are a good liner block parity codes. In this paper, the fundamental of LDPC codes are introduced briefly first. Then an algorithm called the minimum-weight codeword searching is discussed, which can be used to compute the minimum distance of LDPC codes. The effectiveness and the practicability of the algorithm are demonstrated by some examples. It is significant for us to analyze and optimize the design of LDPC codes.国家"863"计划项目(2001AA123061);; 国家自然科学基金项目(60272005)资

基于FPGA的规则(3,6)LDPC码译码器

基于软判决译码规则,采用完全并行的解码结构,使用Verilog硬件描述语言,在Xilinx公司的FPGA(Virtex-2 xcv 1000)上实现了码率为1/2、帧长为20bit的规则(3,)LDPC码的译码器,最大传输速率可达20Mbps。对LDPC码的实际应用具有重要的推动作用

Joint Optimization Algorithm for Protograph LDPC Codes

根据深空通信的特点及需求,JPl实验室提出了性能比常规奇偶校验码更优的原模图低密度奇偶校验码,即原模图ldPC(lOW-dEnSITy PArITy-CHECk)码.该文提出一种原模图ldPC码的联合优化算法,在不增加编译码复杂度的前提下能兼顾瀑布区性能,设计出地板区性能更好的码型.理论分析和仿真结果表明,用该算法设计出的新型重复积累码与新型重复-积累-重复码与传统码型(重复积累码和Ar4JA码)相比,可在高信噪比区域获得显著的编码增益,降低了错误地板.According to the requirements and characteristic of space communication,protograph low-density parity-check(LDPC) codes have been proposed by Jet Propulsion Laboratory(JPL),which have better performance than conventional LDPC codes.In this paper,we propose a joint optimization algorithm for protograph LDPC codes,aiming at lowering the error floor of protograph LDPC codes,while maintaining good performance at waterfall region without increasing encoding and decoding complexity.Theoretical analysis and simulation indicate that the repeat accumulate(RA) and accumulate repeat accumulate(ARA) codes designed by using the proposed algorithm have a remarkable coding-gain,and a lower error floor,as compared with the conventional RA and accumulated repeat by-4-jagged accumulate(AR4JA) codes at the high SNR region.国家自然科学基金(No.60972053;No.61001073)资