多层叠加LDPC码编码调制技术

 本文提出了一种多层叠加LDPC码编码调制系统.与传统的基于速率分配的多层编码调制技术相比,多层叠加编码调制系统具有很好的对称性和可扩展性.通过分析比较Turbo码译码算法与LDPC码的译码算法的复杂度,本文指出了多层叠加LDPC码编码调制系统具有译码简单,易于实现的优点.实验结果表明,多层叠加LDPC码编码调制系统可以在不牺牲带宽的同时获得较好的性能.     

Next Generation FEC for High-Capacity Communication in Optical Transport Networks

Codes on graphs of interest for next generation forward error correction (FEC) in high-speed optical networks, namely turbo codes and low-density parity-check (LDPC) codes, are described in this invited paper. We describe both binary and nonbinary LDPC codes, their design, and decoding. We also discuss an FPGA implementation of decoders for binary LDPC codes. We then explain how to combine multilevel modulation and channel coding optimally by using coded modulation. Also, we describe an LDPC-coded turbo-equalizer as a candidate for dealing simultaneously with fiber nonlinearities, PMD, and residual chromatic dispersion.      

基于LDPC码的小波图像传输码率优化

LDPC码是一种具有低复杂度,强纠错能力的信道分组编码结构,SPIHT算法是嵌入式小波图像压缩编码中性能较好的一种。文中充分考虑SPIHT算法和LDPC码的特性,提出了根据信源编码后的数据在解码重建时的重要程度进行不等纠错保护的信源信道联合编码方案。实验表明,该方案有利于压缩图像在噪声信道上的可靠传输,提高系统整体纠错性能。     

基于低密度校验码的OFDM编码调制译码算法

低密度校验码(LDPC)具有编码增益高、译码速度快、性能接近Shannon限的优点。LDPC码应用于OFDM，能有效地提高多径环境下OFDM的BER性能。本文首先简单介绍LDPC码及其概率域上的译码算法，在此基础上对译码算法作融合，阐述概率似然比的译码算法。为了把LDPC应用于OFDM系统上，提出了多电平调制下的LDPC译码的算法。仿真结果表明，在AWGN和Rayleigh信道下，此算法正确有效。     

On coded modulation using LDPC convolutional codes

A new construction combining LDPC convolutional codes and multilevel coding/modulation is suggested and analyzed. In the case of QPSK, we demonstrate that it has a better performance than an LDPC convolutional code combined with conventional Gray mapping.     

A new multilevel coding method using error-correcting codes

A new multilevel coding method that uses several error-correcting codes is proposed. The transmission symbols are constructed by combining symbols of codewords of these codes. Usually, these codes are binary error-correcting codes and have different error-correcting capabilities. For various channels, efficient systems can be obtained by choosing these codes appropriately. Encoding and decoding procedures for this method are relatively simple compared with those of other multilevel coding methods. In addition, this method makes effective use of soft-decisions to improve the performance of decoding. The decoding error probability is analyzed for multiphase modulation, and numerical comparisons to other multilevel coding systems are made. When equally complex systems are compared, the new system is superior to other multilevel coding systems.     

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。     

LDPC码在802.16a协议中的应用

基于LDPC码的优越性能,找出一组优秀的非正则LDPC码应用于IEEE802．16a OFDM环境中,并对其性能进行仿真。仿真结果表明,LDPC码在衰落信道下具有良好的纠错能力,适用于WMAN等采用OFDM的无线通信系统。     

Performance of joint multilevel/AES‐LDPCC‐CPFSK schemes over wireless sensor networks

In wireless sensor networks, data encryption and channel coding are considered together for ensuring secure and robust communication. In order to achieve this purpose, we introduce a new joint scheme, namely ‘Multilevel/Advanced Encryption Standard‐Low Density Parity Check Coded‐Continuous Phase Frequency Shift Keying (ML/AES‐LDPCC‐CPFSK)’. AES algorithm is the most powerful and widely used symmetric key cryptography in providing secure data transmission. LDPC codes have very large Euclidean distance and use iterative decoding algorithms. In this study, we have increased error performance employing multilevel structure to AES and LDPC. In all communications systems, phase discontinuities of modulated signals result in extra bandwidth requirements. CPFSK, which is a special type of continuous phase modulation, is a powerful solution for this problem. In this paper, we simulate error performance of ML/AES‐LDPCC‐CPFSK for regular LDPC codes. Simulation results are drawn for 4CPFSK, 8CPFSK and 16CPFSK over wireless cooperative sensor networks. Using this scheme, we are able to improve bit error performance, channel throughput, security level of communication and reduction in complexity compared with related schemes such as various turbo code structures. Copyright © 2009 John Wiley & Sons, Ltd.     

Euclidean Geometry LDPC-VBLAST System Design and Performance Evaluation

Among popular multi-transmit and multi-receive antennas techniques, the VBLAST (Vertical Bell Laboratories Layered Space-Time) architecture has been shown to be a good solution for wireless communications applications that require the transmission of data at high rates. Recently, the application of efficient error correction coding schemes such as low density parity-check (LDPC) codes to systems with multi-transmit and multi-receive antennas has shown to significantly improve bit error rate performance. Although irregular LDPC codes with non-structure are quite popular due to the ease of constructing the parity check matrices and their very good error rate performance, the complexity of the encoder is high. Simple implementation of both encoder and decoder can be an asset in wireless communications applications. In this paper, we study the application of Euclidean geometry LDPC codes to the VBLAST system. We assess system performance using different code parameters and different numbers of antennas via Monte-Carlo simulation and show that the combination of Euclidean geometry LDPC codes and VBLAST can significantly improve bit error rate performance. We also show that interleaving data is necessary to improve performance of LDPC codes when a higher number of antennas is, used in order to mitigate the effect of error propagation. The simplicity of the implementation of both encoder and decoder makes Euclidean geometry LDPC codes with VBLAST system attractive and suitable for practical applications.     

LDPC-Coded MIMO Optical Communication Over the Atmospheric Turbulence Channel

In this paper, coded multiple-input-multiple-output (MIMO) communication schemes for data transmission over the optical atmospheric turbulence channels are studied. Two strategies are proposed and compared. The first is based on repetition coding, and the second on space-time (ST) coding. Both approaches employ low-density parity-check (LDPC) codes. The LDPC codes are designed using the concept of pairwise balanced design (PBD), balanced incomplete block design (BIBBD), and block-circulant (array) codes. To improve the spectral efficiency, we employ a bit-interleaved (BI) LDPC-coded modulation based on the pulse amplitude modulation (PAM). A better bit error rate (BER) performance is achieved by the iteration of extrinsic information between a demapper and LDPC decoder. The simulations show that the LDPC-coded MIMO schemes can operate under a strong atmospheric turbulence and at the same time provide excellent coding gains compared with the transmission of uncoded data. To verify the efficiency of the proposed coding schemes, achievable information rates are computed when the turbulence is modeled by a gamma-gamma distribution.     

联合信道网络编码研究综述

网络编码技术可以提高网络吞吐量和传输性能,均衡网络负载。在无线传感器网络中,应用网络编码和信道编码联合编码技术可以降低节点数据处理复杂度,大幅提升系统整体性能。基于传统网络编码模型,在节点中加入数据调制功能,可以实现网络编码和信道编码的联合编码,信道编码则采用各方面性能较好的Turbo码和LDPC码。结果表明,在10-4误码率下,联合编码方案的信噪比相比于传统编码方案有1.5 dB的节省。     

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.     

LDPC codes and convolutional codes with equal structural delay: a comparison

We compare convolutional codes and LDPC codes with respect to their decoding performance and their structural delay, which is the inevitable delay solely depending on the structural properties of the coding scheme. Besides the decoding performance, the data delay caused by the channel code is of great importance as this is a crucial factor for many applications. Convolutional codes are known to show a good performance while imposing only a very low latency on the data. LDPC codes yield superior decoding performance but impose a larger delay due to the block structure. The results obtained by comparison will also be related to theoretical limits obtained from random coding and the sphere packing bound. It will be shown that convolutional codes are still the first choice for applications for which a very low data delay is required and the bit error rate is the considered performance criterion. However, if one focuses on a low signal-to-noise ratio or if the obtained frame error rate is the base for comparison, LDPC codes compare favorably.     

具有不等错误保护特性的LDPC 编码调制方案

针对LDPC（low-density parity-check）编码调制系统，提出了一种新的具有不等错误保护特性的调制方案，在一个码字内，利用不同的调制方式对于重要的比特给予较强的保护，对于次要的比特给予较弱的保护，该方案既适用于非规则LDPC码，也适用于规则LDPC码。计算机仿真结果表明，新方案的性能是传统16QAM及4QAM的折衷，当采用1／2码率时，其频带利用率与8PSK相同，但是误码率性能优于8PSK。新方案的性能优于现有文献中基于比特可靠性的调制映射方案，并采用EXIT（extrinsic information transfer）图对新方案的优异性能给出了解释。     

Approaching V-BLAST Capacity With Adaptive Modulation and LDPC Encoding

This paper presents a practical implementation of the vertical Bell Laboratories layered space-time (V-BLAST) type system, in which the multiple-input multiple-output (MIMO) open-loop capacity can be approached with conventional scalar coding, using adaptive modulation with appropriate channel codes, e.g., low-density parity-check (LDPC) codes and optimum successive detection (OSD). The density evolution (DE) technique is employed to determine the maximal achievable rate of an LDPC code for each transmit antenna for a given channel realization at a given SNR. Numerical results show that the average sum rate of the adaptively modulated LDPC-encoded system is quite close to the V-BLAST capacity with both rate and power adaptations. Considering the performing degradation caused by error propagation due to the imperfect feedback and relatively long decoding delay in the OSD, we use parallel interference cancellation (PIC) followed by minimum mean square error (MMSE) filtering in the bit error rate (BER) performance simulation. Simulation results show that a target BER of 10-5 can be achieved by the optimally designed LDPC codes. To simplify the code design, we replace the LDPC codes optimally designed for each channel realization with rate-compatible punctured LDPC codes, at the cost of a slight sum rate loss. If the fading process is nonergodic, the outage capacity corresponding to a given outage probability is used to measure the channel performance. As an example, we design the LDPC codes for an adaptively modulated 2 × 2 V-BLAST system to approach its outage capacity for a given outage probability.      

Channel coding with multilevel/phase signals

A coding technique is described which improves error performance of synchronous data links without sacrificing data rate or requiring more bandwidth. This is achieved by channel coding with expanded sets of multilevel/phase signals in a manner which increases free Euclidean distance. Soft maximum--likelihood (ML) decoding using the Viterbi algorithm is assumed. Following a discussion of channel capacity, simple hand-designed trellis codes are presented for 8 phase-shift keying (PSK) and 16 quadrature amplitude-shift keying (QASK) modulation. These simple codes achieve coding gains in the order of 3-4 dB. It is then shown that the codes can be interpreted as binary convolutional codes with a mapping of coded bits into channel signals, which we call "mapping by set partitioning." Based on a new distance measure between binary code sequences which efficiently lower-bounds the Euclidean distance between the corresponding channel signal sequences, a search procedure for more powerful codes is developed. Codes with coding gains up to 6 dB are obtained for a variety of multilevel/phase modulation schemes. Simulation results are presented and an example of carrier-phase tracking is discussed.     

Multilevel coded modulation for unequal error protection andmultistage decoding .I. Symmetric constellations

In this paper, theoretical upper bounds and computer simulation results on the error performance of multilevel block coded modulations for unequal error protection (UEP) and multistage decoding are presented. It is shown that nonstandard signal set partitionings and multistage decoding provide excellent UEP capabilities beyond those achievable with conventional coded modulation. The coding scheme is designed in such a way that the most important information bits have a lower error rate than other information bits. The large effective error coefficients, normally associated with standard mapping by set partitioning, are reduced by considering nonstandard partitionings of the underlying signal set. The bits-to-signal mappings induced by these partitionings allow the use of soft-decision decoding of binary block codes. Moreover, parallel operation of some of the staged decoders is possible, to achieve high data rate transmission, so that there is no error propagation between these decoders. Hybrid partitionings are also considered that trade off increased intraset distances in the last partition levels with larger effective error coefficients in the middle partition levels. The error performance of specific examples of multilevel codes over 8-PSK and 64-QAM signal sets are simulated and compared with theoretical upper bounds on the error performance     

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。     

中短波信道中基于LDPC码的迭代解调译码方案

针对数字调幅广播系统,首次提出了基于迭代解调的低密度奇偶校验(LDPC)编码的比特交织编码调制(BICM)方案.首先研究了LDPC码的映射方式,然后基于复杂度分析,考察了LDPC码、Turbo码及国际标准中码率匹配的删除卷积码(RCPC)方案在中、短波广播信道中的性能.研究结果可为我国调幅波段的数字广播系统提供参考.