Ad Hoc网络中一种空时协作中继方案的性能研究

在Ad Hoc网络中,数据通过多跳传输到达目的节点.因此,中继节点的选择在Ad Hoc网络中有着至关重要的作用.传统的中继方案往往根据信道状态的好坏,从源节点的邻居节点中选出一个状况最佳的节点作为中继节点,但是当中继与目的间的信道状态不好时,这种中继方案仍存在一定的问题.为了解决这一问题,考虑利用无线信道的广播特性,基于空时编码,给出了一种依赖于两个中继节点的空时协作中继方案;并基于有限状态Markov模型,对系统的误比特率、吞吐量、时延和丢包率等性能进行了分析.仿真结果表明,相比于传统的单中继方案,该方案能获得较好的性能增益.     

放大转发协作下多S-R-D节点网络中继选择策略

在多个信源、中继及目的端的环境中,研究了放大转发协作系统的中继选择策略与传输机制.为了求得最优解,在最优中继节点选择策略中使用了穷举算法,此方法计算复杂度会随着中继节点数目增加而大幅上升.在此基础上,提出了改进的中继节点选择策略,该策略先使系统的平均误码率最小,之后再使目的端中断容量最大化.仿真及分析结果表明,该策略除了能达到与最优算法类似的吞吐量之外,复杂度也大大降低.     

基于信道质量和网络寿命的最优中继选择策略

针对中继节点因剩余能量不足而不能长时间协作通信的问题,在HDAF协作系统中,提出了一种基于各中继节点信道状态信息(CSI)和剩余能量信息(REI)联合考虑的多中继集合选择方案.该方案根据节点CSI和REI构造加权函数,通过控制容量增益门限进行多节点选择.仿真结果表明,该方案在满足系统通信前提下,很大程度上提升了系统的网络寿命;与传统基于CSI中继选择方案相比,该方案网络生存时间最高提升约19.8%.     

基于组确认机制的车联网中最佳中继节点的选择

针对特定位置的车辆用户节点和Sink节点,通过选取最佳中继节点来最大限度提高车联网的端到端吞吐量.将上述问题纳入基于组确认机制的车联网模型中,结合数据重传技术及多跳中继技术,提出了最佳中继节点的选择算法OTNS.并借助非线性优化方法来求解,最终确定出车辆用户节点与Sink节点之间的最佳中继的位置,以使得该车辆用户节点与Sink节点间的端到端吞吐量达到最大值.最后通过仿真实验验证了OTNS算法的有效性,结果表明,最佳中继节点的选择方案有利于车联网性能的提高,相比于不使用中继节点,该方案使车联网端到端吞吐量的期望值得到了提高.     

功率分裂的无线信息与能量同传中继方案的优化

研究了无线信息与能量同时传输两跳协作中继系统中的传输方案优化问题.方案中,第1跳中继节点对接收到的源节点发送的信号进行功率分裂,一部分信号用于信息的译码;另一部分转换成能量用于第2跳的信息转发.中继采用译码转发协议,与常规方案不同,所提方案两跳采用不等时长方式,在传输总信息量一定的情况下,以两跳总传输时间最小化为目标,对功率分裂因子进行优化求解.由于无法直接完全通过解析求解获得优化结果,故采用部分解析求解和遍历搜索求解相结合的方法求解优化问题.仿真结果表明,在无线信息与能量同时传输中继模型下,所提方案的传输速率和系统吞吐量明显优于传统的两跳等时长的译码转发和放大转发方案.     

在中继选择系统中的发送功率和调制方式的联合优化方案

在传感器网络中,降低网络总功耗和延长网络寿命是网络设计和优化的重要要求.本文研究了采用机会性中继选择的解码前传系统,提出了一种能提高系统功率效率的中继选择、调制方式和发送功率的联合优化方案.该方案中,源节点和中继节点使用不同的发送功率.在给定误码率和系统参数的条件下,可以通过分布式的计算方法获得最优解.仿真结果表明所提方案能获得比协作MIMO系统更高的功率效率.     

基于剩余能量的多源无线协作网络中继选择策略设计

在多源多中继协作无线传感网中,单纯基于链路质量的中继选择策略往往会使最佳中继的能量被快速消耗完,造成节点能量消耗的不公平和整个网络寿命的减少。因此,提出了一种基于剩余能量的中继选择策略,重新定义了一个理论有效转发信息包数与中继剩余能量的内积,并以最大化该内积数值作为中继最优的选择标准。仿真结果表明提出的策略能有效平衡网络中各中继节点的剩余能量,以损失平均吞吐量10%左右为代价,换来网络总吞吐量的提升和平均网络寿命延长一倍左右。     

一种简单的适合无线Mesh网络的机会协作MAC机制

针对IEEE 802.11 MAC(medium access control)协议中通信模式的缺陷,提出了一种新的协作MAC机制.该机制重点研究了分布式中继节点的选择算法,并定义了一种新的控制帧(retran).目的节点通过发送retran帧启动协作机制,收到该帧的节点根据中继选择算法设置自身定时器,从而竞争产生"机会中继",使其在源节点与目的节点之间搭建通信桥梁,该方法简单可行.仿真表明,随着网络中节点数的增加,新的机制对网络吞吐量和误比特性能的改善效果明显,从而提高了通信质量.     

基于网络编码的多中继协作通信研究

本文介绍了基于两用户—两中继—单目的节点的协作中继模型,将协作分集与网络编码结合起来,针对传统的两中继方案、模拟网络编码的两中继方案以及机会式网络编码的两中继方案,分析比较了这3种方案的中断概率、信噪比和网络吞吐量等性能。经过仿真结果编码,在系统中断概率一定的情况下,机会式网络编码可以提升系统吞吐量,但编码要求复杂,其次是模拟网络编码。在信噪比一定的情况下,传统方案中断概率最低,但增加了时延,需要消耗更多的能量。     

基于功率加权的延长网络寿命的机会中继策略

针对采用解码-转发协议的无线协作中继网络,提出了一种基于功率加权的机会中继策略,即根据每个节点的剩余能量设定其功率的权重因子,每个源节点根据加权能量消耗最小准则选择最优的协作中继,并通过单纯型法得到源节点和中继节点之间的最优功率分配,以提高能量利用率和平衡网络中每个节点的能量消耗.仿真结果表明,与其它策略相比,文中策略可以有效延长整个协作中继网络的寿命.     

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