一种新的OFDM系统自适应调制算法

提出了一种新的用于正交频分复用(OFDM)系统的自适应调制算法,它在保持恒吞吐量的前提下对OFDM系统进行自适应比特分配和自适应功率分配．与使用固定调制方法的OFDM系统相比,使用该算法系统的误码率性能和吞吐量有了很大的提高．该算法计算量较小,是一种实用的自适应调制算法．模拟结果表明引入子载波分组后系统性能依然保持良好,并且信道估计偏差对本算法的影响较小.     

低复杂度的MIMO-OFDM系统自适应调制方案

以最小化发射总功率为目标,提出了一种低复杂度的MIMO-OFDM无线通信系统的自适应调制方案.在发射端,基于已知信道状态信息,应用奇异值分解将空分复用信道转化为并行的子信道,并将表征信道增益的信道矩阵特征值用于子信道自适应调制优化设计中.针对MQAM调制,采用变步长的贪婪算法得到优化的子信道比特加载及功率分配方案.仿真结果表明,所提出的简化算法与一种近似最优的自适应调制算法性能接近,但复杂度降低了30%以上.     

采用数据扩展技术的OFDM自适应调制算法

在传统的OFDM系统中,实现自适应调制需要传输大量的有关子载波调制参数信息,致使传输效率下降.文中分析了采用数据扩展技术的自适应调制OFDM系统的特征,发现最优算法就是在原始数据符号之间平均分配比特和功率,在此基础上提出了以用户需求为目标的最小化总功率的自适应调制算法.此算法的原始数据符号最多采用两种调制阶数,并且可以在原始数据符号之间按顺序分配,这样不仅降低了算法复杂度,而且大大减少了有关调制参数信息的传输.仿真结果表明该算法具有良好的性能,在复杂度相近的前提下,该算法比采用自适应功率控制的传统OFDM系统节省功率(用子载波的平均信噪比表示)约2 dB.     

一种新的MIMO系统功率比特自适应算法

目的发射功率受限的自适应调制系统,由于调制方式有限,实际使用的发射功率通常小于受限的发射功率,对这一部分剩余功率进行再分配和利用,从而提高频谱效率。方法针对自适应调制MIMO系统,提出对剩余功率在空域及空时域联合进行再分配的自适应算法。结果仿真结果表明,在空域采用等功率分配,再进行空域剩余功率再分配,能够提高频谱效率。结论该算法复杂度低,易于实现。     

OFDM系统中一种改进的低复杂度自适应比特功率分配算法

针对正交频分复用(orthogonal frequency division multiplexing,OFDM)系统在进行自适应比特功率分配时存在过高复杂度的问题,提出了一种基于边缘自适应(margin adaptive,MA)准则的改进低复杂度自适应比特功率分配算法.与贪婪(Greedy)算法相比,提出的改进算法通过预分配和迭代分配2部分来降低算法的计算量.改进算法先在预分配中根据信道条件预先分配部分比特,在迭代分配中通过增大内存开销的方法减少Greedy算法中计算和比较每个子信道功率增量的次数,从而降低算法的复杂度.仿真结果表明,在相同的仿真环境下算法的自适应分配效果和Greedy算法的自适应分配效果基本一致,同时该算法和Greedy算法具有几乎相同的误比特性能.且随着子信道数量的增加,与Greedy算法相比,该算法的运行时间更短,进而说明所提出的算法具有较低的复杂度.     

空间复用MIMO系统的功率分配新算法

研究空间复用多输入多输出系统的功率分配问题,提出一种新的功率分配算法--残余功率再分配. 在满足服务质量要求的前提下充分利用星座图尺寸的离散性,将残余功率按照各子信道的不同优先级进行二次分配,并结合自适应调制编码技术改善低信噪比时的系统吞吐量. 仿真结果表明,在准静态平坦衰落信道下,与传统算法(如注水算法)相比,新算法能进一步改善系统的吞吐量,提高发射功率的使用效率,减少不可用子信道个数,且无附加复杂度.     

基于MIMO-OFDM系统的自适应调制算法研究

为了提高MIMO-OFDM系统的数据传输率和频谱利用率,提出一种新的自适应调制算法.该算法在信道传输质量满足一定系统误码率下,根据信道状态信息自适应地调整每个子载波的调制方式,使系统的发射总功率尽量最小.理论分析得出,该算法降低了MIMO-OFDM系统的运算复杂度,并使系统的整体性能得到了优化.     

低压电网基于发射效率的OFDM比特分配算法

低压电网信道衰减特性变化剧烈,正交频分复用（OFDM）系统的自适应调制技术根据每个子载波的信道状况和用户需求,为每个用户分配最佳的子载波,为每个子载波分配最佳的调制方式,这样可以更好地利用信道资源,提高传输速率．以低压电网为对象,利用多项式函数拟合的低压电网信道模型,从基于SNR门限的比特分配算法出发,提出了一种基于发射效率的OFDM比特分配算法,并与固定调制方式和固定功率分配的OFDM系统进行对比．结果表明该算法能够根据各个子信道的实际传输情况灵活地分配发送功率和信息比特,使更多的子载波可以使用性能好的调制方式,从而有效地利用了低压电网信道资源．     

一种基于延时信道状态信息的MIMO-OFDM系统自适应功率分配算法

在基于正交频分复用的多输入多输出（multiple-input-multiple-output-orthogonal frequency divided multiplexing,MIMO-OFDM）系统中,适当的功率分配方案能够显著提高系统吞吐量,但是其复杂度往往较高。研究MIMO-OFDM系统的自适应功率分配问题。以系统的和速率最大化为目标,根据延时的信道状态信息在所有空间子信道之间分配功率,同时满足各子信道的误码率约束与系统总功率约束。根据MIMO空间子信道的特点提出了一种复杂度很低的功率分配算法,并分析了算法复杂度。在IMT-2000信道中的仿真表明,提出算法的性能优于已有的次佳算法。     

FMT系统中的动态比特分配算法性能分析

提出了一种基于滤波多音（FMT）系统的自适应比特分配算法，在发射端等功率发射的基础上，通过测量每个子载波的信号失真比（SDR），确定每个子载波的比特分配方式和传输参数. 仿真结果表明，该算法提高了FMT系统的抗衰落性能.     

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