Performance and EXIT analysis of parallel concatenated space time trellis codes

Space time trellis coding （STTC） techniques have been proposed to achieve both diversity and coding gains in multiple input multiple output （MIMO） fading channels. But with more transmit antennas STTCs suffer from the design dificulty and complexity increasing. This paper proposes a scheme, named parallel concatenated space time trellis codes （PC-STTC）, to achieve the tradeoff between the performances and complexity of STTCs for a large number of transmit antennas. Simulation results and complexity comparison are provided to demonstrate the performance and superiority of the proposed scheme over conventional schemes in fast fading channels in low signal-to-noise ratio （SNR） regions. And an EXIT （extrinsic information transform） chart is given to analyze the iterative convergence of the proposed scheme. It shows that PC-STTC has better iterative convergence in low SNR regions.

Numerical Investigation on the Deformation of the Free Interface During Water Entry and Exit of a Circular Cylinder by Using the Immersed Boundary-Multiphase Lattice Boltzmann Flux Solver

In this work,the deformation of free interface during water entry and exit of a circular cylinder is investigated numerically by using the two-dimensional(2D)immersed boundary-multiphase lattice Boltzmann flux solver(IB-MLBFS).The fluid domain is discretized by finite volume discretization,and the flux on the grid interface is evaluated by lattice Boltzmann equations.Both the implicit velocity correction and the surface flux correction are implemented by using the immersed boundary-method to consider the fluid-structure interaction and the contact interface between the multiphase fluids and the structure.First,the water entry of a circular cylinder is simulated and the results are compared with the experiment,which considered the length-diameter ratio of the circular cylinder.The reliability of 2D simulation is verified and the deformation of the free interface is well investigated.Afterward,the water exit of a circular cylinder with constant velocity is simulated,which is less researched.In addition,the results show the advantage of present IB-MLBFS to some extent.Finally,the water exit and re-entry of a circular cylinder are presented,and the results present the complex deformation of the free interface and the dynamic response of the moving structure.Based on the numerical results,the free interface of the multiphase fluids is well captured,and the contact interface on the boundary of the moving structure is accurately presented by the IB-MLBFS.

Connectivity Analysis of Vehicles in Highway with One Entry/Exit and One RSU

In this paper, we consider a unidirectional highway road with one entry/exit uniformly distributed on the road interval. One road side unit (RSU) is located on the position of the entry/exit. We build an analytical model to study the network connectivity problem. In building the analytical model, we take into account several parameters, such as vehicle arrival rate, vehicle moving speed, vehicle communication radius, RSU communication radius, highway road length and the probability of vehicles driving through the entry/exit. The analytical model is verified by using simulation tools.

A Study of How Market Entry and Exit Matter for Productivity in China＇s 426 Industries

Based on extensive micro data sets, this paper examines the relationship among large-scale entry and exit, competition and total factor productivity （TFP） growth of China＇s industry during economic transition and market opening. We have arrived at these findings： market opening spurs entry and exit of large numbers of non-state-owned enterprises （non-SOEs） and facilitates dynamic competition; through the stimulation effect of competition, entry and exit push TFP growth on the part of enterprises; through the resource reallocation effect, entry and exit promote growth of the aggregate TFP. However, results indicate that the resource allocation efficiency remains very low in capital-intensive industries where the government intervenes a lot. To conclude, promoting open competition is significant to the growth of industrial sectors ＇productivity.

基于EXIT图的正则LDPC码性能分析研究

EXIT(EXtrinsic Information Transfer)图分析方法可以看作密度进化技术的一种简化,具有实现简单的优点,并且在不同的信道、调制方案以及检测器中都可以使用。在详细阐述了EXIT图分析方法的基础上,给出了基于EXIT图的正则LDPC码的门限判决算法,进一步通过计算机仿真分别给出了变量节点译码器和校验节点译码器的EXIT曲线,以及不同的信道信噪比下(3,6)正则LDPC码EXIT图的变化规律,直观地对迭代译码过程中的互信息变化进行了描述分析。

基于EXIT图的SCMA通信系统多用户检测算法收敛性分析

消息传递算法(message passing algorithm,MPA)是基于稀疏码多址接入(sparse code multiple access,SCMA)技术中码本的稀疏性,提出的一类接近联合最优的多用户检测算法。针对现有的基于并行策略和串行策略的MPA算法,存在算法收敛性论述缺乏理论分析的问题,该文通过外信息转移图(extrinsic information transfer,EXIT)技术分析MPA算法的收敛性。首先将SCMA接收机检测器分为函数节点译码器和变量节点译码器,然后给出译码器的EXIT图的理论分析,最后通过比较两类算法的EXIT曲线估算出达到收敛状态所需的迭代次数。仿真结果验证了EXIT图分析的正确性。

基于EXIT图分析的BICM-ID系统SNR估计失配研究

研究了基于LDPC码的BICM-ID系统中,信道的SNR估计失配对于接收机性能的影响.提出了采用EX-IT图的分析方法,比较SNR过估计和欠估计对于解调器以及LDPC码译码器性能的影响,该方法不需要BER性能的仿真,简单直观.仿真结果表明不管是对于解调器还是LDPC码译码器,SNR过估计的影响相对较大,而欠估计则对性能的影响较小.

基于EXIT图分析的PCGC译码器最优设计

PCGC(Parallel Concatenated Gallager Code,并行级联Gallager码)是一种将LDPC(Low Density Parity Check,低密度奇偶校验)码与并行级联编码相结合的信道编码。传统的PCGC译码器参数通过仿真获得,有可能导致不必要的译码迭代。通过分析PCGC码的边信息转移图,以获得PCGC码子译码器的最优参数。仿真结果表明,通过EXIT(Extrinsic Information Transfer,边信息转移)图分析获得的译码器最优参数设置可以在不影响误码率性能的基础上,有效地节省译码器运算量。

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。

纠删信道中LDPC码EXIT曲线匹配设计

基于单检码和重复码EXIT图面积特性的分析,介绍了在二元纠删信道中,采用EXIT曲线匹配设计LDPC码度分布序列的最佳性:当内外码的EXIT曲线完全匹配时,所设计的度分布序列对应的速率能够达到信道容量;而当内外码EXIT曲线之间有间隔时,所设计的度分布序列对应的速率严格小于信道容量,并且间隔面积越大,所损失的速率越大。

对基于EXIT图的LDPC码优化算法的改进

就Brink方法不能自动搜索的不足,文中提出了一种基于EXIT曲线匹配的改进优化算法:DE-EXIT算法.该算法构造了衡量EXIT曲线匹配程度的代价函数,利用差分进化技术由初始的矢量集开始,迭代更新集合中的每一个矢量,直至监督矢量发现最优的代价函数值.算法在给定码率的情况下,可以进行优化次数分布对的自动搜索,同时获得相应的码集噪声门限.仿真结果表明,提出的优化算法在码结构优化方面有着很好的性能,并且可以用于不同情况下的结构优化.

两种级联空时格码方案的EXIT分析

级联空时格码方案可以有效地提高空时格码系统的性能。研究了两种级联空时格码方案:PC-STTC和ST-Turbo-TC。由于两种级联方案都使用了迭代译码方法,而外信息转移(EXIT)图是分析迭代译码性能的有利工具,主要分析比较了PC-STTC和ST-Turbo-TC的EXIT性能,比较了不同信噪比和编码多项式对于译码外信息转移特性的影响。研究结果显示,PC-STTC方案比ST-Turbo-TC方案有着更好的迭代收敛性能,同时给出了BER仿真图证明了EXIT图的分析结论。

基于EXIT图的连续变量密钥分发数据协调优化

在量子密码通信中,未优化的低密度奇偶校验（LDPC）码的度分布性能较差,得到的协调效率较低,且传输距离较短。针对上述问题,提出一种基于连续变量的量子密钥分发数据协调算法。利用外信息转移图分析特点,从基于粒子群的高斯近似算法得到的度分布中,通过比较门限值大小筛选出性能更好的度分布,进而优化低密度奇偶校验码。仿真结果表明,与密度进化算法和高斯近似算法相比,外信息转移图可以有效地优化LDPC码度分布,同时,当连续变量分组数为2×105时,与未优化的LDPC码相比,优化的LDPC码能降低收敛信噪比,提高协调效率,延长传输距离。

基于EXIT函数的自适应OFDM-LDPC调制编码方案设计

推导了瑞利衰落信道下,LDPC迭代译码的互信息公式,采用数值积分的方法计算校验节点外部信息,避免了信噪比较低时校验节点的LLR服从高斯分布的不精确假设带来的误差。分析了该编码系统的EX IT函数,以EX IT误差函数为代价函数,提出了自适应OFDM-LDPC编码方案。该方案与传统自适应方案相比,不需要确定切换门限,数值计算简单,而且避免了计算子信道信噪比带来的误差,适用于高速通信系统。最后在802.16e协议的仿真平台上进行了仿真验证。

累积码EXIT曲线的高效数值求法

累积码作为非规则RA码的分量码之一,除了在纠删信道上具有显式的EXIT函数之外,在一般信道上其EXIT曲线均由仿真获得。由仿真获得累积码EXIT曲线不但增加了非规则RA码的设计复杂度,而且使得整个设计过程无法实时完成。首先证明对于累积码而言,串行和积算法与BCJR算法是等价的;在此基础上,证明了累积码在串行和积译码时,与译码中间变量相关的互信息具有平稳特性;利用该平稳特性,推导了累积码EXIT函数的隐式表达式,从而给出一种求解累积码EXIT曲线的高效数值算法。采用该方法获得的EXIT曲线与仿真结果一致,能够显著降低非规则RA码的设计复杂度,并使非规则RA码的设计实时化。

LDPC码EXIT曲线图分析方法研究

EXIT曲线图是ten Brink发明的分析迭代和积译码收敛性能的有效工具。在描述了LDPC码迭代译码器结构基础上,详细地推导和研究了在AWGN信道中EXIT曲线图性能分析方法的计算方法。利用此方法确定了多种度分布LDPC码的收敛门限,并与利用高斯近似和密度进化得到的仿真结果进行比较分析,探讨EXIT曲线图的优点和进一步应用前景。

利用EXIT图分析信源码率对双LDPC码系统的影响

双LDPC(DLDPC)码系统是一种高性能的信源信道联合编码系统,但是其性能在很大程度上受到信源码率的影响。为了从理论上分析信源码率对DLDPC码系统的影响,推导了外信息转移(EXIT)函数,并利用EXIT图分析了信源码率对DLDPC码系统的影响,理论分析结果与实际仿真结果一致。进而利用EXIT图估算出DLDPC码系统在不同信源熵情况下的信源码率门限值,该门限值可以用来指导实际系统中信源码率的选取。所提出的分析方法比传统的蒙特卡罗仿真法更加简捷、直观。

基于EXIT图的TET-LDPC码优化分析

两边类型低密度奇偶校验码(two-edge type low density parity check,TET-LDPC码)是一种高效的信道纠错码,其性能受到删余变量节点度(punctured variable node degree,PVN度)的影响.为了分析PVN度对TET-LDPC码纠错性能的影响,基于外信息转移图(extrinsic information transfer,EXIT图)估算了TET-LDPC码在不同PVN度情况下的门限值,利用门限值的好坏来分析纠错性能的优劣,进而通过选取门限值好的PVN度优化TET-LDPC码.仿真结果显示,经过EXIT图优化的TET-LDPC码具有更好的纠错性能.利用EXIT图优化分析TET-LDPC码的方法,比现有的仿真试值法更加简捷、直观.

Design of Irregular QC-LDPC Code Based Multi-Level Coded Modulation Scheme for High Speed Optical Communication Systems

In this paper, we focus on the design of irregular QC-LDPC code based multi-level coded modulation(MLCM) scheme by jointly optimizing the component code rate and the degree distribution of the irregular QC-LDPC component code. Firstly, the sub-channel capacities of MLCM systems is analyzed and discussed, based on which the optimal component code rate can be obtained. Secondly, an extrinsic information transfer chart based two-stage searching algorithm is proposed to find the good irregular QC-LDPC code ensembles with optimal component code rates for their corresponding sub-channels. Finally, by constructing the irregular QC-LDPC component codes from the designed ensembles with the aim of possibly enlarging the girth and reducing the number of the shortest cycles, the designed irregular QC-LDPC code based 16QAM and 64QAM MLCM systems can achieve 0.4 dB and 1.2 dB net coding gain, respectively, compared with the recently proposed regular QC-LDPC code based 16QAM and 64QAM MLCM systems.

Optimized LDPC differential-encoded 16QAM scheme for high-speed transmission systems

The 16-ary quadrature amplitude modulation （16QAM） is a high spectral efficient scheme for high-speed transmission systems. To remove the phase ambiguity in the coherent detection system, differential-encoded 16QAM （DE-16QAM） is usually used, however, it will cause performance degradation about 3 dB as compared to the conventional 16QAM. To overcome the performance loss, a serial concatenated system with outer low density parity check （LDPC） codes and inner DE-16QAM is proposed. At the receiver, joint iterative differential demodulation and decoding （ID） is carried out to approach the maximum likelihood performance. Moreover, a genetic evolution algorithm based on the extrinsic information transfer chart is proposed to optimize the degree distribution of the outer LDPC codes. Both theoretical analyses and simulation results indicate that this algorithm not only compensates the performance loss, but also obtains a significant performance gain, which is up to 1 dB as compared to the conventional non-DE-16QAM.