采用导频子载波的OFDM系统频偏跟踪算法

为了进一步提高多径快衰落环境下,正交频分复用(orthogonal frequency-division multiplexing,OFDM)系统的载波频偏估计精度,研究了利用在OFDM符号中插入的导频子载波进行小数倍频偏跟踪的算法在多径快衰落信道下的频偏跟踪性能.通过与常规的基于循环前缀的跟踪算法进行比较,采用导频子载波的频偏跟踪算法,不仅在高斯白噪声信道下能达到很好的频偏跟踪性能,而且在多径快衰落信道下也能实现更准确的频偏估计,因此采用导频子载波的算法更适合用于多径快衰落信道下的频偏跟踪.     

采用导频子载波的OFDM系统频偏跟踪算法

为了进一步提高多径快衰落环境下,正交频分复用（orthogonal frequency division multiplexing,OFDM）系统的载波频偏估计精度,研究了利用在OFDM符号中插入的导频子载波进行小数倍频偏跟踪的算法在多径快衰落信道下的频偏跟踪性能。通过与常规的基于循环前缀的跟踪算法进行比较,采用导频子载波的频偏跟踪算法,不仅在高斯白噪声信道下能达到很好的频偏跟踪性能,而且在多径快衰落信道下也能实现更准确的频偏估计,因此采用导频子载波的算法更适合用于多径快衰落信道下的频偏跟踪。     

MIMO-OFDM系统的时域导频信道估计算法

多天线正交频分复用(M IM O-OFDM)系统作为一种高速率无线通信的有效方式,其信道估计技术占有非常重要的位置。基于M IM O-OFDM系统的导频设计准则及特性,该文提出一种多径M IM O信道下用于多径定位和时域信道估计的算法。该算法从时域出发,首先利用所设计导频在时域上的循环移位正交性来获取多径信道的定位,从而利用时域导频符号来获取多径信道时域响应信息。仿真实验结果表明相比传统的频域信道估计插值算法,该算法在较低运算复杂度下可以获得信道估计性能的明显改善,同时作为导频符号的G o lay互补码有效降低OFDM系统功率峰均比(PAPR)2~5 dB。     

基于压缩感知的MIMO双选择性衰落信道的估计

为了减少MIMO （multiple-input multiple-output）时频双选择性衰落信道估计过程中需要的导频符号数,文中对多径信道的时延和多普勒频移构成的时频二维有界区域进行量化,将该信道估计问题建模为压缩感知理论中的稀疏信号重构问题,提出了一种采用正交匹配追踪估计MIMO双选择性衰落信道的方法.仿真结果表明获得相同的估计性能,所提出的压缩信道感知方法比传统的最小二乘法能节省近50％的导频符号,且该方法在低信噪比的场景里也能获得较高的估计性能.     

联合循环前缀和Pilot的OFDM系统定时同步方法

提出了一种联合循环前缀和Pilot的定时同步方法，并将其用于高速传输的无线移动正交频分复用（OFDM）系统．算法首先利用循环前缀定时函数得到时偏的估计范围，然后在估计范围内利用导频定时函数得到时偏的精确估计．由于不需要加入训练序列，提出的定时同步方法最大限度地节省了系统开销，提高了系统的频带利用率，而且利用导频序列进行定时同步可以有效地克服符号间干扰的影响．仿真结果表明，该算法能够改进时频估计在多径信道下的精度，提高系统在多径衰落信道下的性能．     

适用于快衰落环境的OFDM/TDM信道估计算法

针对正交频分复用/时分复用(OFDM/TDM)系统现有导频结构和信道估计算法缺乏对信道快衰落实时跟踪能力的问题,提出一种改进信道估计算法。该算法利用相邻2个时域复用导频序列对信道特性进行估计得到信道传递函数,通过内插处理获得数据符号的信道状态信息,并利用最小均方误差准则的频域均衡算法补偿信道衰落。仿真结果表明,与现有信道估计算法相比,在相同数据传输效率情况下,提出算法不仅能够适用于慢衰落信道,同时对快衰落信道的实时变化有良好的跟踪能力,改善系统性能。     

基于简化单一导频结构的信道估计方法研究

不同信道模型对信道估计有很大的影响,导频结构的设计必须选择合理的导频间隔。针对传统信道模型难以全面描述多径衰落和噪声对信道估计的影响,以及传统导频结构存在导频数量过多、计算复杂高等问题。本文建立了自定义信道估计模型,该模型充分考虑了时变频率选择性和广义平稳信号的非相关散射特性;同时,提出了基于梳状导频图案的简化单一导频结构,该导频结构根据导频间隔等间距的交错截取导频信号。仿真表明:该方法减少了导频数量,提高了频带利用率。同时,与二维导频结构相比,有效降低了计算复杂度;与传统结构相比,误码率降低了1-2 d B,该方法可广泛应用于信道估计中的导频图案设计,具有很强的实用性。     

一种适用于高速多径信道下的OFDM联合同步算法

基于正交频分复用系统（OFDM）循环前缀（CP）,尾部数据的能量差分和集相关特性未受到多径衰落干扰的特点,提出了一种新的联合同步算法。仿真表明,与现有算法比较,联合同步算法在多径衰落信道下能够获得准确的频偏估计,且随着多普勒频移的增加,其同步性能会进一步提高,特别适合于高速多径衰落信道下的符号定时同步。     

一种适于小波包多载波系统导频信道估计的方法

提出了一种适于小波包多载波系统信道估计的导频插入方法．该方法结合小波包多载波系统树型结构的分解特性以及不同频率对相干时间的影响,将子载波在树型结构的基础上分成若干个组,并结合等差原理,引入时域不等间隔的导频模式,实现导频的合理分配．在上述方法中,高频部分插入了相对较多的导频,使得总的导频数减少的同时,能够更好地估计多普勒频移的影响．仿真结果表明,在载波调制过程中,采用不等间隔导频模式与传统的等间隔块状导频模式相比,当导频个数减少14％,信噪比为20dB时,误比特率降低了19．6％;并且不论多普勒频移如何变化,系统总能在多径瑞利衰落信道中保持良好的性能．     

基于导频的SD-method信道估计算法研究

简要介绍SD-method调制方法及其与一般OFDM方法的关系,描述了基于导频信道估计的系统模型,分析并仿真验证了多径衰落信道模型下,SD-method系统的信道估计算法,对LS估计算法和MMSE估计算法的性能进行了对比,仿真结果验证了理论分析的正确性.     

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.     

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     

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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