浅海水声信道中Turbo码性能研究

针对复杂多变、强多途和大起伏的浅海水声信道,本文建立了包括时变衰落、多途和加性干扰在内的信道仿真模型及Turbo码编/译码结构.通过计算机仿真,研究了浅海水声信道中的Turbo码性能及Turbo码性能随多途效应、衰落率和信道交织器等的变化.结果表明:在水声通信可接受的信噪比范围内(10～20 dB),Turbo码具有良好的性能(误比特率小于10-4);浅海水声信道中,Turbo码性能随多途路径数的增加而下降;Turbo码性能随衰落率的减小而略有下降;浅海水声信道中,信道交织器可改善Turbo码性能,并弥补由于衰落率不同而造成的性能差异.     

卷积Turbo码技术在WiMAX系统中的应用

信道鳊码技术是保证移动通信传输质量的关键技术。卷积Turbo码（简称CTC）是很灵活的码字,帧长和码率的变化范围很大,这也是选它做为WiMAX（W0rId Interoperability for Microwavc Access）标准中的信道鳊码方案之一的主要原因。它采用递归系统卷积码作为子码,相对于经典Turbo码,它具有鳊码效率高,相同复杂度译码器下纠错性能好以及译码时延小等优点。本文将首先介绍卷积Turbo码的基本鳊译码原理,并在多径衰落环境下,对WiMAX系统中的卷积Turbo码性能进行了仿真验证。     

信道编码在无人机数据链中的应用研究

针对无人机（unmanned aerial vehicle, UAV)平台数据链机栽端机所要求的信道编码算法简单、运算速度快、糾错能力强和实时性高等特点,研究分析了适用于无人机数据链系统的卷积码、Turbo码、LDPC(low density parity check code)码等信道编码的编译码特点,采用基于信道编码的OFDM( orthogonal frequency division multiplexing)传输方案设计了高速无人机数据链系统,并针对不同的编码方案分别进行了在Rayleigh衰落和Rician衰落信道下的性能仿真分析,仿真结果表明,在高速无人机信道下,不论在短码和长码情况下,综合考虑编译码实现复杂度和性能2个方面,LDPC码均表现出了比卷积码和Turbo码较优异的性能,可作为无人机数据链系统中较好的信道编码方案。LDPC码相比卷积码与Turbo码具有更好的误码率性能,是较好的解决方案。     

Turbo码在瑞利慢衰落信道中的性能仿真与分析

介绍瑞利衰落信道的编码信道模型，给出与这些模型相对应的仿真方法．然后针对充分交织瑞利平坦慢衰落信道，在未知信道状态信息的情况下，对Turbo码的译码算法Log—MAP进行修正，并进一步对影响Turbo码性能的主要参数：迭代次数、交织器长度、编码效率、分量编码器结构进行仿真与分析，得出的仿真结果可以指导实际无线信道中设计合理的通信Turbo码。     

Turbo 码的基本介绍及其在第三代移动通信系统中的应用

介绍了 Turbo码的基本构造原理、性能曲线、优缺点及其在第三代移动通信系统中的应用。     

一种基于最大比合并的Turbo乘积码自适应编码调制方法

为了增强高速多媒体无线通信系统在衰落环境中的传输效率,提出了一种基于最大比合并的Turbo乘积码自适应编码调制的通信方法;通过采用信道补偿最佳速率自适应策略,研究了优化的模式切换门限;分析了在瑞利信道环境中自适应传输的系统容量性能.研究表明:所设计的自适应系统具有较强的抗衰落能力;随着分集阶数的增加,其频谱利用率将可以逼近高斯信道香农容量限.     

用于移动多媒体通信的双重自适应Turbo编码调制技术

给出了一种应用于移动多媒体通信的跨层的双重自适应编码调制技术.该技术采用Turbo码,并同时自适应于时变的信道特征和不同媒体业务的服务质量(QoS),以充分提高系统的平均吞吐量.首先给出经优化设计的实用信道自适应Turbo编码调制方案,该方案距Shannon极限仅2.5 dB;然后将一个QoS自适应方案加载其上,构成跨层的双重自适应结构.仿真结果表明,在假设所有媒体业务以等概率出现、业务持续时间服从指数分布时,该新颖的双重自适应技术可达到距衰落信道容量2 dB的优异性能.     

Turbo码在3G中的应用与DSP实现

Turbo码以其优越的性能逐渐在通信系统受到人们的重视,因此在概述了Turbo码的编译码算法原理以后,针对其在第三代移动通信系统(3G)中的应用,对其迭代译码进行了DSP定点仿真实现,并与Matlab浮点仿真进行了比较,在SNR为0.2dB时,误码率已近似为0,已成为3G中的首选方案.     

Nakagami衰落信道的信噪比估计及其在Turbo译码中的应用

在Turbo译码中,需要精确的信噪比信息来计算子译码器生成的外信息,而在无线衰落信道中,Nakagami衰落信道具有通用性,文中对Summer信噪比估计算法进行了改进,使之能够应用于Nakagami衰落信道。最后,对应用了改进Summer信噪比的Turbo译码进行了性能仿真。从结果可以看出,改进的Summer信噪比估计算法能够成功应用到Turbo译码中,使得Turbo译码获得良好的性能。     

Turbo码的高效调制方案

Turbo码由于其接近香农限的特性而倍受关注,但标准的Turbo码是低码率码,其频带效率低,为了利用Turbo码低误码率的特点,同时又能提高其频带利用率,一个简单的方法是让其与高效率的高阶调制方案M－QAM相结合,本在高斯信道和瑞利平坦衰落信道条件下对数域最大后验概率（log－MAP）解码算法进行了研究和修改,使之适合这2种信道和高阶调制方案,通过采用一种实用方法,使得编、解码系统具有通用性,同时推导出精确计算高斯信道下调制码元对数似然值（LLR）的计算公式,并与近似算法进行了比较,仿真结果表明,在2种信道中,该方案具有很高的编码增益,同时频带效率也得到了提高。     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that     

On the Thermodynamic Limit for Responses to Static Electromagnetic Fields

For molecular systems,the quantum-mechanical treatment of their responses to static electromagnetic fields usually employs a scalar-potential treatment of the electric field and a vector-potential treatment of the magnetic field.Although the potential for each field separately is associated with the choice of an(unphysical)origin,the precise choice of the origin for the electrostatic field has little consequences for the results.This is different for the     

An affordable accurate evaluation of the binding conformations predicted by molecular docking studies in bio-system

Franck-Condon factors bridge the gap between theoretical modeling and experimental observations for molecular electronic spectroscopy and electron transfer.Under the displaced harmonic oscillator approximation,multidimensional Franck-Condon factors are decomposed into a product of many one-dimensional(1D)Franck-Condon(FC)factors,and each 1D-FC factor is associated with one Huang-Rhys factor that determines the leading contribution of     

Call for Papers

<正>"The Journal of Shanghai Normal University:Mathematics"is published by Shanghai Normal University as regular issues of The Journal of Shanghai Normal University each year from 2014 in English.The editors-in-chief of the issues are professors Yuhao Cong and Maoan Han.The Journal of Shanghai Normal University was started in 1958 with     

Journal of Donghua University ( English Edition) Contents of Volume 31

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