基于PN码导频的FMT信道估计方法

针对FMT系统,提出了一种新的基于 PN 码的信道估计方法,既可用于慢变信道,又可用于快变信道.分析了新方法的计算复杂度和估计性能.仿真结果表明,在瑞利衰落信道下新估计方法的误比特性能优于最小二乘估计,与线性最小均方误差估计性能相似,但计算量远小于线性最小均方误差估计.     

快速时变信道下的基扩展模型信道估计性能分析

针对快速时变信道,提出了一种基于复指数基扩展模型(CE-BEM)的线性最小均方误差(LMMSE)信道估计方法,对信道估计的结果使用离散长椭球序列(DPSS)进行平滑处理,并相应提出了基于迭代的载波间干扰(ICI)消除信道均衡方法.仿真结果表明:在高多普勒信道场景下,该方法系统误码性能较传统信道估计方法有一定程度的提升.     

MIMO系统中的迭代时变信道估计

为了提高时变信道环境中MIMO信道估计的性能,利用Karhunen-Loeve基扩展模型(KL-BEM)建立MIMO系统中符合期望最大化(EM)算法框架的信号模型,从而得到MIMO时变信道的迭代估计方法.将EM算法应用于MIMO系统中进行迭代信道估计,一方面利用了EM迭代来提高信道估计的性能,另一方面利用了KL-BEM基函数的正交性来降低信道估计的运算复杂度.在2×2 MIMO系统下的仿真结果表明:算法经5次迭代即可收敛,而且迭代估计的信道脉冲响应与实际响应几乎重合;此外,迭代估计后系统的BER性能接近理想信道时的BER性能,在高信噪比区域,两者之间的差别在1 dB以内,比最小二乘信道估计有约2 dB的性能增益,可见迭代估计方法在时变信道条件下具有良好的估计性能.     

对称α稳定分布噪声下基于Kalman滤波迭代信道估计

为了提高加性脉冲噪声衰落信道环境下的通信传输性能,提出了一种适用于对称稳定分布噪声的基于Kalman滤波的迭代信道估计方法。该方法利用时变信道的先验统计信息将信道建模为一阶自回归模型,并将最小分散系数准则应用于Kalman滤波信道估计方法中,从而更充分地利用了时变信道和非高斯噪声的先验信息。在较为严重的时变脉冲信道下,该方法比最小平均p范数估计方法性能要优约2 dB。仿真结果表明:该方法能消除脉冲噪声和稳定分布二阶矩不存在等不利因素的影响,能快速准确地跟踪并预测时变信道的变化,且性能显著地优于传统的最小均方误差和最小平均p范数信道估计方法。     

基于EM的MIMO-OFDM系统LMMSE信道估计

最小均方误差(MMSE)信道估计算法应用于MIMO-OFDM系统时将带来高计算复杂度且不易实现,根据这个问题,提出了一种基于期望最大化(EM)的线性最小均方误差(LMMSE)信道估计算法,并分析了该算法的性能.EM算法可以把多输入多输出(MIMO)信道估计问题转化为一系列单输入单输出(SISO)信道估计问题,避免了大规...     

MC DS-CDMA系统中信道估计器的比较

首先介绍了几种多载波码分多址(CDMA)系统,然后建立了MC DS-CDMA系统模型,在该系统中进行最小二乘(LS),线性最小均方误差(LMMSE)和最大似然(ML)3种信道估计器的研究,并对其均方误差(MSE)和误码率(BER)性能进行了仿真,LS实现最简单,但性能最差,LMMSE计算量大,性能优于LS,ML性能最佳,且其计算复杂度低于LMMSE。     

基于信道分割级联的正交频分复用子载波干扰消除算法

在高频段正交频分复用（OFDM）系统中子载波间干扰（ICI）较大,运用信道分割方法,将线性时变信道近似等效为时不变信道与无时延时变信道的级联,从而在接收端实现一维均衡抑制ICI,避免了高复杂度的信道频域响应矩阵的计算和求逆过程.分析和仿真表明,相对于现有的利用ICI相邻载波分布特性的低复杂度最小均方误差算法,算法在几乎不损失系统性能的同时,可将复杂度降低到O(N).     

OFDM系统中基于基扩展模型的快时变信道估计算法

信道估计是正交频分复用(orthogonal frequency division multiplexing,OFDM)的关键技术。随着移动端速度的提高,信道会发生快速变化产生频率选择性衰落,针对此种情况,通过对传统信道估计算法搭建OFDM系统级仿真链路的基础上对不同的基扩展模型(basis expansion model,BEM)研究,针对复指数基扩展模型(complex exponential-BEM,CE-BEM)的部分基函数频率过高会产生较大误差的缺点,提出一种修正基函数系数的方法有效地去除了频率过高的基函数,通过仿真对信噪比和多普勒频移对模型均方误差性能的影响进行分析,结果表明提出算法能在不增加复杂度的前提下均方误差性能较CE-BEM低4～5 dB,有效地提高了拟合性能。     

TDS-OFDM时变信道估计和均衡的BEM-LSQR方法

中国地面高清数字电视(DTMB)在高速移动环境下的应用日益广泛.利用其多载波模式下的时域同步正交频分复用(TDS-OFDM)帧结构,提出三种利用基展开模型(BEM)的针对不同场合的时变信道估计方法,并利用正交分解最小二乘(LSQR)对帧体进行均衡.第一种信道估计方法针对400Hz及以下多普勒频移,分别估计帧体前后帧头的一阶信道冲击响应,映射得到基展开系数,第二种方法针对400Hz以上情况,利用帧头循环结构,估计帧头内部信道的时变性,第三种方法针对945模式,对同一帧头进行两次一阶估计.由于信道矩阵使用基展开系数进行表示,因此LSQR均衡可以实现O(Nlog N)的复杂度.仿真结果显示,该方法提高了系统在高速时变下的性能.     

应用基扩展模型的混合信号单通道盲分离算法

针对传统最小均方误差逐幸存路径处理(LMS-PSP)单通道盲分离算法在时变信道下性能差的问题,提出一种基于基扩展模型逐幸存路径处理(BEM-PSP)的单通道盲分离算法。首先对接收到的部分混合信号进行LMS-PSP单通道盲分离,得到部分准确的信道冲激响应(CIR);然后结合时变信道下基于基扩展模型进行信道估计的思想,完成整个时间周期CIR的估计;最后采用Viterbi算法对混合信号进行序列估计,从而实现时变信道下混合信号的单通道盲分离。仿真结果表明,对于2路混合QPSK信号,在相同仿真条件下,BEM-PSP算法较LMS-PSP算法能降低50%的复杂度且能获得更好的性能,在20dB处的误码率可达4×10-2,而LMS-PSP单通道盲分离算法的误码率只能达到1×10-1,并且在同等过采样倍数下,该算法能获得更高的性能提升。     

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.     

Features of Women's language

Language is a means of verbal communication. People use language to communicate with each other. In the society, no two speakers are exactly alike in the way of speaking. Some differences are due to age, gender, statue and personality. Above all, gender is one of the obvious reasons. The writer of this paper tries to describe the features of women＇s language from these perspectives： pronunciation, intonation, diction, subjects, grammar and discourse. From the discussion of the features of women＇s language, more attention should be paid to language use in social context. What＇s more, the linguistic phenomena in a speaking community can be understood more thoroughly.     

An Analysis of Catherine＇s Character——Wuthering Heights

Wuthering Heights, Emily Bronte＇s only novel, was published in December of 1847 under the pseudonym Ellis Bell. The book did not gain immediate success, but it is now thought one of the finest novels in the English language. Catherine is the key character of this masterpiece, because everybody and everything center on her though she had a short life. We can understand this masterpiece better if we know Catherine well.     

Lower Paleozoic oil relationships within Williston Basin, Canada

The Williston Basin is a significant petroleum province, containing oil production zones that include the Middle Cambrian to Lower Ordovician, Upper Ordovician, Middle Devonian, Upper Devonian and Mississippian and within the Jurassic and Cretaceous. The oils of the Williston Basin exhibit a wide range of geochemical characteristics defined as "oil families", although the geochemical signature of the Cambrian Deadwood Formation and Lower Ordovician Winnipeg reservoired oils does not match any "oil family". Despite their close stratigraphic proximity, it is evident that the oils of the Lower Palaeozoic within the Williston Basin are distinct. This suggests the presence of a new "oil family" within the Williston Basin. Diagnostic geochemical signatures occur in the gasoline range chromatograms, within saturate fraction gas chromatograms and biomarker fingerprints. However, some of the established criteria and cross-plots that are currently used to segregate oils into distinct genetic families within the basin do not always meet with success, particularly when applied to the Lower Palaeozoic oils of the Deadwood and Winnipeg Formation.     

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     

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