基于小波包变换和BP神经网络的DSSS系统干扰抑制算法

 提出功率分布优势小波包变换(PDP-WPT)和扩展BP神经网络(EBPNN),并基于两者提出针对直扩系统(DSSS)的变换域信息信号提取(TISI)干扰抑制算法。首先采用PDP-WPT高效跟踪直扩系统中的敌意干扰,提高算法收敛速度;然后通过EBPNN对变换系数进行信息信号的自适应识别达到干扰抑制的目的,具有复杂度低、鲁棒性好的特点。理论分析得到采用TISI后的扰信比(ISR)抑制量、信噪比(SNR)损失量和误码率(BER)的数学表达式。仿真结果表明：在相同干扰信号的情况下,与两种传统算法相比较,本算法的扰信比抑制量分别提高了43.8%和20.8%,信噪比损失量分别降低了62.5%和34.8%。     

单频干扰对周期序列DSSS通信系统性能影响分析

在论述单频干扰对DSSS通信系统性能影响的传统的基于标准高斯近似(SGA)的分析方法的基础上，结合国内外最新研究成果成果，对其进行了进一步的理论分析与仿真.结果表明，传统的基于SGA的分析方法对于周期序列DSSS通信系统并不适用，单频干扰对周期序列DSSS通信系统的符号判决变量的影响呈现固定电平或单频波动.由于干扰频偏的不同，符号判决变量的干扰分量分布为离散值或连续值.     

基于 RIE 的自适应窄带干扰抑制算法

针对直接序列扩频(direct sequence spread spectrum,DSSS)通信系统中窄带干扰(narrow-band interference,NBI)抑制问题,将窄带干扰存在性识别技术(recognition of interference existence,RIE)和变换域窄带干扰抑制算法相结合,提出了一种自适应窄带干扰抑制算法.该算法能根据接收到的信号,利用基于能限因子的RIE算法判断接收信号中是否含有窄带干扰信号,从而决定是否需要对其进行干扰抑制处理.理论分析表明,当接收信号中不合窄带干扰或干扰信号较小时,既可减少由于窄带干扰抑制算法对有用信号造成的损伤,提高误码率性能,又能降低系统处理的复杂度.仿真结果表明,自适应窄带干扰抑制方案抑制干扰误码率性能明显优于非自适应窄带干扰抑制方案.     

基于Simulink的直接序列扩频通信系统抗干扰的仿真实现

主要研究了直接序列扩频通信系统( DSSS)的抗干扰能力。利用Simulink对直接序列扩频通系统的发射机模块和接收机模块进行仿真设计,在高斯信道中加入不同中心频率、幅度的窄带干扰。通过传输过程中各个波形和频谱变换图,研究直扩系统误码率、信噪比和扩频增益的关系。当窄带干扰强度超过系统抗干扰容限时,使用自适应滤波器中的LMS(最小均方差)和RLS(最小递推二乘)滤波器来抑制窄带干扰。仿真结果表明：自适应滤波具有良好放任窄带干扰抑制效果,但RLS算法复杂仿真时间长,LMS收敛速度较慢。     

短波信道下直扩信号检测与载频盲估计

针对通信侦察识别中广泛遇到的短波信道下直接序列扩频信号(DSSS)的检测与参数估计问题,提出了一种利用广度优先搜索邻居(BFSN)聚类分析提取未知信号高阶循环累积量循环频率的算法。该算法通过聚类比较截获信号的各类峰值,剔除干扰和奇异类信号,克服了短波信道中常见的多径效应引起的码间串扰(ISI)影响,从而实现了在低信噪比条件下,对直扩信号进行检测和载频的盲估计。对算法进行了理论分析,并通过计算机仿真验证了该算法在低信噪比下具有较好的稳健性。     

直扩通信系统中的窄带干扰抑制及仿真

该文针对直扩通信系统在抗窄带干扰方面的局限性,提出在解扩前应用自适应窄带干扰抑制技术,并进行了仿真,仿真结果表明,直扩通信系统中采用自适应窄带干扰抑制技术,可有效的抑制强窄带干扰,保证通信系统数据传输的正确性。     

扩频通信系统的抗干扰特性分析

从直扩和跳频通信系统工作原理出发,定量分析了直扩和跳频通信系统的接收机灵敏度、系统电平余量和干扰电平余量。分析发现:在保持接收灵敏度和系统电平余量保持不变的情况下,直扩和跳频通信系统通过分别采用"隐蔽"和"躲避"均降低了干扰电平余量,与抗干扰的系统设计目的相符。     

CPLD在DS-FH混合扩频通信系统中的应用

直接序列扩频通信技术具有抗多径干扰等许多优点，跳频通信技术具有很强的抗部分带宽干扰的能力．结合这两种通信技术的特点，重点介绍了一种由m序列和Walsh函数构成的DS—FH混合扩频系统，该系统利用Walsh函数的频谱特性实现跳频，同时具有直扩技术和跳频技术的优点，并且实现简单．在系统实现中扩频码和跳频图案的产生部分用CPLD来完成，并对此进行了详细的介绍．     

一种基于DSP的双模水声通信系统

由于海洋中恶劣传输条件的影响,采用一种调制解调技术往往难以同时实现高数据传输率、大传输距离以及良好的信道适应性.为适应不同信道下的通信要求,利用直接序列扩频技术(DSSS)和正交频分复用技术(OFDM)设计并实现了基于TMS320C6713 DSP芯片的双模水声通信系统,给出了DSSS和OFDM通信参数设定以及模式转换协议设计.海上实验结果验证了该系统的有效性.     

基于Speex和深度编码的移动水声语音通信

为实现收发节点相对运动下的语音信息交互，提出一种基于Speex和深度编码的移动水声语音通信算法。针对水下信道带宽有限、语音传输低效及数据丢失问题，采用Speex算法，对语音信息进行压缩，提升语音信息传输效率和质量。针对水声信道中时变多途干扰和相位跳变问题，采用深度编码策略，在比特级，采用低复杂度的卷积编码，对信息比特进行编码以获得冗余编码比特，用以对抗时变多途干扰；在符号级，采用基于相位差的编码，令两个相邻符号的相位差作为传输符号，从而消除相位跳跃的影响。Speex算法实现了8.53倍的压缩率，有效节省了信道带宽；深度编码有效解决了多途干扰和相位跳变问题，在相同信噪比下使误码率大大降低。在胶州湾使用水声通信机(Seatrix Modem)对本文算法在通信距离为5.5 km、收发器之间相对运动速度为0.5 m/s、通信带宽为4 kHz条件下进行验证，结果表明了本文算法的有效性。     

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.     

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