数字基带信号频谱特性的研究

本对数字基带信号的频谱进行了深入的分析，并得出了重要的结论。     

基于DFT的数字基带系统传输特性分析

将离散傅里叶变换(DFT)与反傅立叶变换(IDFT)变换应用到抽样序列分析中,得到适合抽样信号的DFT和IDFT关系.分析了广义基带系统对信号产生的码间串扰作用,得出抽样值无失真的广义基带系统的离散信号时域表示.根据抽样信号的DFT和IDFT关系,导出广义基带系统抽样值无失真的传输条件,并对几种基带系统进行了IDFT变换,分析了它们可能产生的码间串扰程度,讨论了基带系统的带宽与码元速率的对应关系.     

离散小波多音调制技术研究

离散多音调制(DMT)信号的频谱旁瓣功率过大，在噪声环境和信道特性变化的情况下会影响系统的传输性能。离散小波多音调制(DWMT)采用离散小波变换来代替DMT中的离散傅立叶变换，通过仔细地设计调制信号的频谱特性来提高系统的传输性能。文中在介绍DWMT技术基本原理的基础上，对DWMT系统的关键技术(比特与能量分配算法、基带滤波器设计等)进行了分析研究。通过对DWMT与DMT进行性能上的比较，说明DWMT性能优于DMT，有望用于宽带接入网技术。     

数字基带信号频谱特性的研究

本文对数字基带信号的频谱进行了深入的分析 ,并得出了重要的结论     

OFDM信号过采样率盲估计的新方法

针对低信噪比多径信道下过采样率估计性能低的问题,根据正交频分复用( OFDM)基带采样信号的频谱特性,提出了基于采样信号频谱逼近的过采样率盲估计方法.该方法首先利用改进的移动协方差方法估计信号的载波频率,采用修正的周期图平均法估计信号的功率谱;然后通过选择最佳的滚降系数,设计一个最佳余弦滚降滤波器,使余弦滚降滤波器的截止频率逼近信号的截止频率;最后根据过采样信号的频谱特性原理估计出接收信号的过采样率,实现了不同类型OFDM信号的过采样率的盲估计.仿真结果表明,在信噪比为-2 dB,多径信道条件下OFDM信号的过采样率估计的均方误差不超过0.2.可见该方法无需任何先验知识,在低信噪比多径信道下具有良好的估计性能.     

高动态测量系统中的自适应信号成形滤波器设计

针对航天测控和卫星导航领域中高动态信号测量的基带信号成形问题,提出一种改进的信号重采样滤波算法.该算法利用截短升余弦内插滤波器设计实现数字扩频信号的连续序列恢复,通过构建频谱自适应的分段抛物线内插函数滤波器实现基带信号的动态重采样处理,并采用Farrow结构降低成形滤波算法的运算量.仿真验证和实验测试结果表明,采用该算法设计的成形滤波器能够较好地适应动态多普勒频移,将基带伪码相位抖动导致的测量误差从亚米级降低至毫米级,有效抑制信号带外功率,为改善导弹航天试验靶场高动态信号的测量精度和稳定性提供了一种有效途径.     

基于多项式数字基带自适应预失真技术的研究

由于自适应数字预失真具有稳定性好、适应能力强等优点,被广泛应用于实现功率放大器的线性化.而本文正是研究了基于多项式数字基带自适应预失真技术.首先,介绍了基于多项式数字基带自适应预失真技术;其次,分析了间接学习结构理论;最后,对OFDM信号进行了仿真实验.结果表明:预失真可以有效地抑制带外频谱以及补偿功放的非线性失真和记忆效应.     

OFDM系统中记忆非线性功放基带预失真技术

研究了OFDM系统的自适应基带预失真技术。针对OFDM信号的高峰值平均功率比对非线性功率放大器敏感的特点,并考虑OFDM的宽带特性引起的功放记忆非线性效应,提出了一种基于辨识方案的非直接学习结构的自适应基带预失真技术,给出了自适应算法。仿真结果表明,该方案能有效抑制带外频谱扩散,减小带内失真,实现有记忆非线性大功率放大器(HPA)的自适应预失真。     

宽带多速率通用数字调制器的设计与实现

设计了宽带通用调制器结构,分析了该调制器硬件实现的关键技术,给出了基带脉冲成形数字滤波器、多速率插值的CIC滤波器及时钟信号产生的具体实现方法. 利用矢量信号分析仪对调制器进行了测试. 测试结果表明,该调制器可产生速率为0.5～50.0MS/s的通用数字调制信号,矢量幅度误差和频谱满足通信标准的要求.     

一种WCDMA基带信号处理方法的研究

无线基带信号的多模处理是目前宽带移动通信发展的趋势,WCDMA系统中典型的基带信号计算为有限序列的互相关运算。采用快速傅里叶变换(FFT)完成了WCDMA多径检测典型基带信号处理,与LTE基带信号典型的FFT运算统一,实现了WCDMA和LTE多种无线制式的基带多模共享处理资源。实验仿真结果表明,该方法在性能和计算量上都能满足实际应用需求。     

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.     

Design and analysis of generic LBS application developing platform

Location based services is promising due to its novel working style and contents.A software platform is proposed to provide application programs of typical location based services and support new applications developing efficiently. The analysis shows that this scheme is easy implemented, low cost and adapt to all kinds of mobile nework system.     

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