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。     

一种适用于分布式MIMO信道测量系统的最优导频设计

研究适用于分布式MIMO无线通信信道测量系统的低峰均功率比导频信号优化方法和低复杂度多天线信号发送方案.为使发送信号的峰均功率比最低,采用OFDM技术,根据导频的长度、离散傅里叶变换的尺寸和子载波的映射方式,搜索最优的恒模零自相关(CAZAC)序列作为基序列.由最优基序列生成的OFDM发送信号峰均功率比低至2.556 dB.对第1根天线发送信号的采样点逐个移相,就可生成其余多根天线的发送信号.为支持分布式MIMO信道测量,采用所设计的信号帧格式的发送信号在时域和频域都可分离.与现有方案相比,所提出方案具有发送信号峰均功率比小和实现复杂度低的优点.     

基于导频的OFDM系统信道估计

本文介绍了基于导频的OFDM系统信道估计的基本方法,并给出在不同估计准则、不同导频图案下,信道估计性能的对比分析。采用广义平非相关散射下的多径时变瑞利信道模型,对各个算法进行仿真,得出不同算下信道估计的均方误差曲线。仿真结果表明：在快变信道中,梳状导频较块导频有更好的性能;基于MMSE准则的信道估计比基于LS准则的估计有更的性能,但前者复杂度较高。     

正交频分复用系统中基于子空间跟踪的信道估计

基于导频的正交频分复用（OFDM）系统信道估计方法是通过在确定的时频位置发送已知的导频符号来获取信道参数的,通常包括导频位置的最小二乘估计和内插滤波两步。如果能够提高导频位置信道频域特性的估计精度,那么后续内插滤波的精度也就能相应地得到提高,为此,在建立通用参数化信道模型的基础上,提出一种子空间跟踪的改进算法,该算法通过基于Givens旋转的时延子空间跟踪和基于RLS滤波的幅度跟踪,提高了导频符号信道估计的精度,降低了跟踪算法的复杂度。仿真结果表明,基于子空间跟踪的信道估计方法具有较低的复杂度和较高的估计精度。     

基于反转相移导频的OFDM系统信道估计

针对两发一收的OFDM系统,引入具有反转相移特性的导频序列,提出了一种新颖的基于离散余弦变换的信道估计方法.该方法有效地降低了不同发送天线上的导频信号之间的相互干扰,大大提高了信道估计精度.利用COST207TU信道模型进行仿真,结果表明,与传统梳状导频和相移导频方法相比,在同样的信噪比下,该方法得到的均方误差更小.     

水声通信CE-OFDM系统降低峰均功率比研究

正交频分复用(OFDM)系统存在着较高的峰均功率比(PAPR).针对这个问题,研究了恒包络正交频分复用(CEOFDM)系统,该系统通过相位调制得到恒包络的信号,消除了PAPR较高的问题.与传统降低PAPR的方法相比,相位调制的复杂度低,性能更好.仿真和水池实验结果表明:CE-OFDM系统将信号的PAPR降低至0,比传统降低PAPR的方法优越,是具有一定鲁棒性的高速水声通信解决方案.     

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。     

低压电力线载波通信压缩感知信道估计方法

针对低压电力线载波通信多径信道,建立了正交频分复用(OFDM)基带传输系统和低压电力线载波通信多径信道传输特性模型,并根据传输特性模型与模型参数,实验得出了低压电力线载波通信信道的冲击响应 h(n);在此基础上,分析推导了满足压缩感知条件的 OFDM 低压电力线载波通信多径传输数学模型,提出了低压电力线载波通信压缩感知信道估计方法,解决了最小二乘(LS)信道估计方法和最小均方误差(MMSE)信道估计方法精度差的缺点。 实验结果表明:在采用相同导频数 128 和相同信噪比 SNR 为 14 dB 的情况下,压缩感知(CS)信道估计方法与 LS 及 MMSE 信道估计方法中较优者相比,得出的信道均方误差降低 16 dB,接收端的误码率降低 3 倍,并且随着信噪比的增加性能提升更明显。     

基于双边偏差补偿隐藏导频UWB系统信道估计方法

在隐藏导频系统中,导频和数据的分离过程需要大量的计算,而且分离的导频并不纯净.针对这种情况,提出双边偏差补偿信道估计方法,即:数据预先经过双边偏差补偿,使数据的均值为零并叠加导频信息,接收端用传统的均值方法就能分离出纯净的导频信息,由于使用更少的数据运载导频,所以减少了导频分离过程的计算量.仿真结果表明,双边偏差补偿信道估计方法可以显著降低误码率,减少计算量,在发射功率和峰均功率比方面也有所改善.     

3D多输入多输出正交频分复用系统中基于奇异值分解的信道估计方法

在3D多输入多输出正交频分复用(MIMO-OFDM)系统模型中,分析了基于导频的信道估计方案.针对线性最小均方误差方法的算法复杂度高的问题,应用奇异值分解(SVD)算法降低信道自相关矩阵的维数,以减小算法的复杂度.仿真结果表明:所提出的基于奇异值分解的信道估计算法,能够在保证误码率(BER)性能的情况下,具有更低的算法复杂度.     

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     

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