联合解调与Viterbi译码算法的改进

本文分析了在第三代移动通信系统中，将数据解调和卷积码译码结合的译码方法，并与传统的Viterbi软判决译码和硬判决译码算法进行了比较。在3GPP所规定使用的调制和编码方式下进行了仿真，结果表明，在不增加复杂度和保持相同的误码率的条件下系统所需信噪比比Viterbi软判决译码降低1—2dB。本文给出的方法也可推广到其它通信系统中。     

基于数字信号处理的体全息视频体存储方案研究

合理有效的存储方案能在有限的硬件条件下，充分挖掘存储系统的潜力，达到用户对存储数据误码率的要求。本文从通信系统的观点出发，并充分结合体全息存储系统的特性，设计和实现了一套基于数字信号处理的体全息视频存储方案。针对体全息存贮系统中噪声干扰复杂的特点，提出了一些新的具体数字信号处理方法，包括二维渐进循环移位交织器、调制一阵列码的编译码方法及其相应的软判决度量方法等，从而形成了一套存储方案。实验结果表明，该存储方案可以有效地抑制体全息系统中的噪声干扰，对于一段包含音频和视频的多媒体数据，采用本方案进行全息存储和重构数据的回放取得了成功。     

移动信道下采用软判决译码的自适应多级编码系统

基于信道容量规则和分组分割,构造自适应于AWGN和Rayleigh两种信道特征的多级编码系统,分量码选用删除型卷积码,系统性能与未编码系统和BCH码为分量码的系统作比较.在多阶段译码中提出利用信道状态信息的软判决支路度量计算公式,比较软、硬判决译码对系统性能的影响,为移动信道编码调制系统的最佳设计度量提供参考.     

RS码短码的软判决方法

RS码是差错控制领域中一种重要的线性分组码,而相对于普通的硬判决来说,软判决译码具有纠错能力强的优势。针对RS码(15,11),提出了使用Chase算法实现非二进制码的软判决译码方法,并通过计算机模拟,给出在AWGN信道中的译码结果。     

衰落信道下多级编码方案的软判决译码

研究Rayleigh衰落信道下,软判决译码对三种不同映射方案多级编码系统性能的影响.基于信道容量规则,构造卷积码为分量码的8ASK多级编码系统,在多阶段译码中提出利用信道状态信息的软判决支路度量计算公式,并探讨系统的误码传播特性,研究结果可为衰落信道编码调制方案的最佳设计度量提供参考.     

基于MRF的高性能二进制LDPC码译码算法

二进制LDPC码译码改进算法主要是提升硬判决性能或者降低软判决计算复杂度。本文应用高斯-马尔可夫随机场(Markov Random Field,MRF)模型实现信源参数估计,对信道译码端接收的比特序列进行对数似然比修正,在译码时加入信源的残留冗余信息来增加译码器的纠错能力。信源估计修正系数自适应可变,是由误码率参数调控。在计算复杂度不变的情况下,基于MRF的LDPC码译码算法有效提高了译码性能,降低误比特率     

Rayleigh衰落信道中分组码最大似然译码的性能

摆脱了传统代数译码方法,对分组码进行基于广义阵列码（ＧＡＣ）结构的网格译码（Ｔｒｅｌｌｉｓ ｄｅｃｏｄｉｎｇ）,研究了Ｒａｙｌｅｉｇｈ衰落信道中分组码与这种软判决最大似然译码方法相结合的性能。模拟结果显示。分组码采用网格译码,可为移动衰落信道带来显著的性能改善。     

OFDM系统中低复杂度联合译码和信道估计方法研究

本文针对OFDM(Orthogonal Frequency Division Multiplexing)系统提出了一种低复杂度联合译码和信道估计算法的接收机。接收机首先通过导频对信道进行估计，然后使用Turbo码译码输出判决信息对信道参数进行稳健的估计。仿真结果表明，即使系统误码率大于10^-2，经过3次迭代估计，系统性能提高仍有0．5-1dB；在高信噪比下，可显著地降低系统的误码底限。本文同时还给出了译码迭代次数对系统性能的影响。     

软信息辅助硬判决译码在自由空间光通信中的应用

由于在性能和复杂度之间的良好折中,软信息辅助硬判决译码近年来受到了光通信领域的高度关注,其中包括了软信息辅助比特标记(Soft-Aided Bit-Marking,SABM)算法.为了易于硬件实现,本文基于阶梯码(Staircase Code,SCC)提出了一种改进型SABM算法(improved SABM,iSABM),称为iSABM-SCC.iSABM-SCC利用信道软信息,通过两个可信度阈值将硬判决输出比特标记为三种可信度等级,用以辅助硬判决译码识别译码错误和扩展纠错能力,达到提升阶梯码性能的目的.在受大气湍流影响的自由空间光通信中的仿真表明,iSABM-SCC性能显著优于标准SCC和RS码.以强湍流信道为例,码率为0.75的iSABM-SCC在4-PAM调制下较标准SCC产生的性能增益可达4.37 dB,在8-PAM调制下较RS码产生的性能增益可达11.06 dB.     

衰落信道下卷积码的软判决译码

本文将交织、信道输出软信息、信道特征软信息相结合,研究Rayleigh衰落信道下卷积码的Viterbi软判决译码,在利用和不利用信道状态信息(CSI)两种情况下给出软判决的支路度量计算公式和性能仿真结果,计算了卷积码的性能上界;研究了解调器输出量化门限(量化级数目、量化间距)对译码性能的影响.结果与硬判决译码及AWGN信道的相关结论进行了比较.     

BER performance with soft and hard decision decoder for coherentoptical DPSK systems corrupted by phase noise

The performance of coherent optical communication systems is significantly degraded by semiconductor laser phase noise. A rate 1/2, constraint length K=7, convolutional error correcting code with Viterbi decoding is used to improve a 3.5-10 Mbit/s DPSK system. Error correcting coding demonstrates the reduction of the influence of phase noise on BER performance, and significantly lowers the BER floor. Soft decision decoding and hard decision decoding performance is investigated and compared     

FSO中分层空时编码的误码性能

分层空时编码(BLAST)虽然具有极高的频谱效率,能成倍提高光通信系统的信息传输速率,但BLAST系统的误码率较大,严重影响了光通信系统的可靠性。在描述了湍流信道中多输入多输出(MIMO)系统的信道模型后,针对多进制脉冲位置调制(Q-PPM)技术,推导出了采用线性译码算法时分层空时码的极大似然判决准则及其误码率公式,并比较了最大似然译码算法、线性译码算法、串行干扰消除译码算法的误码性能。最后,利用仿真实验进行了验证。结果表明:在自由空间光通信(FSO)中,串行干扰消除译码算法的误码性能更接近最大似然译码算法的性能,明显优于线性译码算法。在4×4系统中,当误比特率为2×10-2时,相对于最小均方误差(MMSE)译码算法,最大似然译码算法和MMSE-SIC译码算法的信噪比分别改善了约14.5 dB和7 dB。理论分析与实验结果相一致。     

基于MSK和LT码的联合迭代译码算法

传统的简单级联编码调制系统在译码时会造成软信息损失.提出了一种基于MSK和LT码的联合软迭代译码算法,设计了算法的系统模型.利用LT码的软译码和MSK调制的SISO算法,进行联合软迭代译码,提高了编码调制系统的性能.仿真结果表明:在误码率为10-4时,提出的算法比传统的简单级联编码调制算法约有1.5 dB的编码增益.     

SVD iterative detection of turbo-coded multiantenna unitary differential modulation

A new suboptimal demodulator based on a singular value decomposition for estimation of unitary matrices is introduced. Noncoherent communication over the Rayleigh flat fading channel with multiple transmit and receive antennas, where no channel state information is available at the receiver is investigated. Codes achieving bit-error rate (BER) lower than 10/sup -4/ at bit energy over the noise spectral density ratio (E/sub b//N/sub 0/) of 1.6-1.9 dB from code restricted capacity limit were found. At higher data rates, computation of code restricted capacity is impractical. Therefore, the mutual information upper bound of the capacity attaining isotropically random unitary transmit matrices was used. The codes achieve BER lower than 10/sup -4/ at E/sub b//N/sub 0/ of 3.2-6 dB from this bound, with coding rates of 1.125-5.06 bits per channel use, and different modulation decoding complexities. The codes comprise a serial concatenation of turbo code and a unitary matrix differential modulation code. The receiver employs the high-performance coupled iterative decoding of the turbo code and the modulation code. Information theoretic arguments are harnessed to form guidelines for code design and to evaluate performance of the iterative decoder.     

基于G.9960协议的高阶QAM调制与解调

G.9960是国际电信联盟(ITU-T)制定的下一代家用网络标准,采用正交频分复用(OFDM)和高阶QAM调制相结合的技术,实现高速可靠的数据传输.将讨论高阶QAM调制和软解调的算法.偶数阶调制使用方形星座图,将格雷码形式排列的二进制序列,映射成复数点;奇数阶调制使用十字型星座,将格雷码形式的二进制序列映射为复数点后,再依据一定的规则加以旋转.基于Bahl等人提出的逐符号最大后验概率译码算法,推导了对数似然比计算公式;由于对数似然比计算涉及对数运算,因此利用取最大值代替指数对数运算来进行简化.仿真结果表明,在AWGN信道下,信噪比为8 dB时,使用简化的软解调算法,2048QAM-LDPC系统的误码率可达到3×10-5,4096QAM-LDPC系统的误码率可达到5×10-4.简化的软解调算法,计算量较小,误码率低,具有良好的性能.     

一种差分高阶调制联合LDPC编码方案及其FPGA实现

针对复杂环境中通信系统误码率高和硬件实现复杂度高的问题,提出基于正交频分复用( Orthogonal Frequency Division Multiplexing, OFDM)时域差分和 16 进制幅度差分相移键控( 16 Multilevel Differential Amplitude and Phase Shi...     

有限长度量子密钥的纠错误码率估计仿真分析

基于奇偶检错-汉明纠错算法的误码率后验分布参数，用仿真数据直接估计纠错后的误码率及其置信区间。实验利用了两个伪随机二进制序列替代原始量子密钥，长度为1.4×10-7，误码呈二项分布，通过奇偶检错后利用(7,4)汉明码对奇偶性不一致的码字进行纠错。实验结果表明：当初始误码率为3%时，通过一次检错、纠错，误码率降至2.47×10-3，置信度为95%的上限值为2.77×10-3；当初始误码率为0.1%时，通过一次纠错，误码率降至1.43×10-7，置信度为95%的上限值为10.54×10-7。该方法有效地估计了奇偶-汉明纠错码对有限长度原始量子密钥纠错后的误码率，为量子密钥分配后续处理提供了可靠的数据支持。     

Performance of BICM-SC and BICM-OFDM systems with diversity reception in non-gaussian noise and interference

In this paper, we present a general mathematical framework for performance analysis of single?carrier (SC) and orthogonal frequency division multiplexing (OFDM) systems employing popular bit?interleaved coded modulation (BICM) and multiple receive antennas. The proposed analysis is applicable to BICM systems impaired by general types of fading (including Rayleigh, Ricean, Nakagami-m, Nakagami-q, and Weibull fading) and general types of noise and interference with finite moments such as additive white Gaussian noise (AWGN), additive correlated Gaussian noise, Gaussian mixture noise, co-channel interference, narrowband interference, and ultra-wideband interference. We present an approximate upper bound for the bit error rate (BER) and an accurate closed-form approximation for the asymptotic BER at high signal-to-noise ratios for Viterbi decoding with the standard Euclidean distance branch metric. For the standard rate-1/2 convolutional code the proposed approximate upper bound and the asymptotic approximation become tight at BERs of 10-6 and 10-12, respectively. However, if the code is punctured to higher rates (e.g. 2/3 or 3/4), the asymptotic approximation also becomes tight at a BER of 10-6. Exploiting the asymptotic BER approximation we show that the diversity gain of BICM systems only depends on the free distance of the code, the type of fading, and the number of receive antennas but not on the type of noise. In contrast their coding gain strongly depends on the noise moments. Our asymptotic analysis shows that as long as the standard Euclidean distance branch metric is used for Viterbi decoding, BICM systems optimized for AWGN are also optimum for any other type of noise and interference with finite moments.     

Optimum soft decision decoding with channel state information inthe presence of fading

The article first presents the formulation for computing the optimum soft decision metrics for decoding of convolutional codes on fading channels and then demonstrate the performance gains achieved in using the optimum soft decision metrics. The optimum soft decision metrics use channel state information to account for signal strength variations due to fading. The formulation for computing the optimum soft decision metrics is given for the general case in which the statistics of the additive noise on the channel is nonstationary. However, the formulation is applied to a more simple case in which the noise is assumed to be stationary. The results indicate that at moderate signal-to-noise ratios, the 2 dB advantage usually claimed for soft decision decoding over hard decision decoding on Gaussian channels is achievable on fading channel, with the rate 3/4 code used, if the channel state information is incorporated in the soft decision metrics