模糊控制在垂直切换判决算法中的应用

为了满足用户的各种通信需求,垂直切换判决算法中考虑的因素越来越多,判决因素的增加,使得切换判决所需的时间延长,不能够实现快而有效的切换判决,影响了移动终端的实用性。并行模糊控制系统使得各判决因素同时进行模糊推理且大大减少模糊规则的数量,降低了切换判决的时延。把网络可用带宽、用户移动速度及网络的服务费用作为判决因素进入并行模糊控制系统,通过用户服务类型的不同,对各判决因素动态地计算相应的权值,同时各判决因素通过模糊控制系统的输出值与权值对应相乘相加,从而得到最优的切换目标网络。仿真结果表明,该算法增强了切换的准确性,减少了不必要的切换,增强了系统性能。     

基于移动用户位置预测的垂直切换算法

针对异构无线网络环境中现有垂直切换算法存在难以实现移动用户接入网络的无缝切换,无法向用户提供稳定通信服务的问题,提出一种基于移动用户位置预测的垂直切换算法。首先利用用户移动轨迹的相似性,使用用户轨迹数据离线训练LSTM模型以学习各用户普遍具有的移动规律;然后在线加载LSTM模型进行用户位置预测,从而使用模糊逻辑分析计算下一时刻用户对应候选网络的回报值,并选取回报值最高的网络进行切换。实验结果表明,该算法与已有垂直切换算法相比,在不同的用户移动速度和用户规模条件下的切换次数、切换失败次数和切换时延均有明显下降,内存消耗较低,能够实现无缝切换。     

一种新型的异构无线网络呼叫接纳控制算法研究

在CDMA2000蜂窝网络和WLAN组成的异构无线网络中,呼叫接纳控制算法对于提高系统资源的利用率有着非常重要的作用。根据WLAN的网络负载情况和移动用户的速度来判决是否接入WLAN;提出一种基于概率机制的CAC算法,WLAN能够限制来自于蜂窝网的VHO呼叫,减少不必要的VHO处理负荷;对新呼叫阻塞率和DVHO呼叫阻塞率进行理论分析和推导。仿真结果表明,该CAC算法能够减少不必要的重复上下垂直切换,同时将DVHO呼叫阻塞率控制在可接受的范围内。算法保证了较高的系统吞吐量,提高了系统整体性能。     

基于声望模型的联合呼叫接纳控制算法

为了弥补异构无线网络中呼叫接纳控制研究场景的局限性,降低终端选择接入网时的盲目性,将研究场景从两个接入网延伸为多个接入网,提出一种基于声望模型的联合呼叫接纳控制算法。将声望模型应用于网络选择过程,增加了网络反馈机制。在用户侧,终端根据网络声望值大小选择接入网;在网络侧,采用动态带宽分配和缓冲队列策略来提高接入成功率。仿真结果表明,该算法有效降低了新呼叫阻塞率和切换呼叫掉线率。     

异构融合网络中的垂直切换机制研究

针对移动终端有限的电量以及现有垂直切换机制往往忽略终端电能因素,提出了基于终端能耗的垂直切换机制。网络发现阶段,提出一种自适应调整网络接口激活时间间隔的网络发现策略。切换判决阶段,对采样点进行预判决,减少进入后续模块的采样点;为实时业务和非实时业务分别设计相应的模糊逻辑处理方法;实时业务引入权重因子完成切换判决,非实时业务通过差值门限算法进行切换判决。仿真结果显示,相比传统策略,该机制在网络发现阶段能够降低网络发现时间,减少网络接口激活次数;在切换判决阶段能够降低掉话率,减少网络切换次数以及乒乓效应发生次数,具有有效性。     

无线多媒体网络中一种基于测量网络状态的动态呼叫接纳控制算法

提出了一种无线多媒体网络中基于测量网络状态的动态呼叫接纳控制算法.它区分了实时和非实时业务,在网络带宽资源不足时可通过降低非实时业务带宽确保实时业务呼叫连接的可靠性;还可根据当前网络状况调整预留带宽大小,使小区实时业务切换呼叫掉线率低于设定的门限值.大量仿真结果显示该算法具有低实时业务切换呼叫掉线率和与固定预留方案相当的带宽利用率,而只以略高的新呼叫阻塞率为代价,适合各种不同概率发生时实际应用的情况.     

融合分层呼叫协议与GCM-FIFO的移动管理方案

针对节点高速移动的UAVS通信网络中的移动性管理问题,提出了基于分层呼叫协议的位置管理方案以及融合滞后余量与门限结合的切换判决方法、UAV节点自主决策的紧急切换控制策略和GCM-FIFO信道分配策略的切换管理方案。通过相关理论分析和图形化的测试与仿真,结果表明:分层呼叫协议解决了UAVS通信网中节点高移动性问题;针对系统切换业务量高但信道数有限的特点提出了GCM-FIFO信道分配方案,在满足一定的新呼叫阻塞的同时减小了UAV节点切换失败的概率;针对中继机节点可能被击毁而提出的UAV节点自主决策的紧急切换策略,弥补了一般性切换方案的不足。     

面向异构网的呼叫控制体系研究

促进多网融合是下一代网络工作的主要研究方向,如何把握切换时机,在异构网络中进行准确切换是保证用户获取最佳的通信质量的核心.提出了基于无线局域网即有资源以及用户所出位置决定切换策略的机制,对用户的移动进行预测,能够掌握较为准确的切换时机,在两个不同模式的网络之间进行切换.在此机制下,可以根据用户个性化的数据,计算获得根据新呼叫失败概率以及呼叫切换失败概率数据,从而为切换提供理论数据.通过仿真实验表明了新切换机制的有效性.     

基于等效SINR的VLC与WiFi垂直切换算法

针对室内可见光异构通信网络中,现有切换算法无法感知不同网络服务质量,不能保证用户始终获得最优网络服务的问题,提出一种基于等效SINR的VLC（visible light communication,可见光通信）与WiFi垂直切换算法。算法将达到相同最大传输速率作为转换条件,把VLC SINR转换为等效的WiFi SINR,在此基础上实现切换触发和判决。首先,根据目标网络和服务网络SINR差值与设定切换门限的对比结果进行切换触发;然后,考虑到VLC易受遮挡干扰影响的特点,引入驻留定时器进行切换判决,保证判决准确性。仿真实验表明,该切换算法能保证用户接入到提供最大传输速率的网络中,并且对于不同VLC网络布设和室内光环境影响都具有较好的适应性,更加适合室内融合VLC异构通信网络。     

基于预判决和改进灰关联的异构网络切换算法

传统异构网络切换算法容易引起乒乓效应和切换准确度不高等问题; 同时,现有异构网络切换算法存在网络属性权重确定不合理问题,容易增加不必要的切换次数。因此,针对异构网络切换算法判决不准确带来的乒乓效应问题进行了研究,提出了一种基于差值门限比率和改进灰色关联分析相结合的异构网络切换算法。首先采用差值门限比率进行预判决,初步确定网络是否切换;再利用改进灰色关联分析算法选取目标切换网络,从而决定是否切换网络。搭建了WLAN和UMTS融合的异构网络环境,采用了MATLAB、OPNET等仿真工具。仿真结果表明：该算法有效提高了网络切换判决的准确性,减少了网络切换次数,降低了网络切换失败率。     

European Community policy and the market

Abstract This paper starts with some reflections on the policy considerations and priorities which are shaping European Commission (EC) research programmes. Then it attempts to position the current projects which seek to capitalise on information and communications technologies for learning in relation to these priorities and the apparent realities of the marketplace. It concludes that while there are grounds to be optimistic about the contribution EC programmes can make to the efficiency and standard of education and training, they are still too technology driven.     

一种自适应子融合集成多分类器方法

融合集成方法已经广泛应用在模式识别领域,然而一些基分类器实时性能稳定性较差,导致多分类器融合性能差,针对上述问题本文提出了一种新的基于多分类器的子融合集成分类器系统。该方法考虑在度量层融合层次之上通过对各类基多分类器进行动态选择,票数最多的类别作为融合系统中对特征向量识别的类别,构成一种新的自适应子融合集成分类器方法。实验表明,该方法比传统的分类器以及分类融合方法识别准确率明显更高,具有更好的鲁棒性。     

Explanation and prediction: an architecture for default and abductive reasoning

Although there are many arguments that logic is an appropriate tool for artificial intelligence, there has been a perceived problem with the monotonicity of classical logic. This paper elaborates on the idea that reasoning should be viewed as theory formation where logic tells us the consequences of our assumptions. The two activities of predicting what is expected to be true and explaining observations are considered in a simple theory formation framework. Properties of each activity are discussed, along with a number of proposals as to what should be predicted or accepted as reasonable explanations. An architecture is proposed to combine explanation and prediction into one coherent framework. Algorithms used to implement the system as well as examples from a running implementation are given.     

Three Process Perspectives: Organizations, Teams, and People

This paper provides the author's personal views and perspectives on software process improvement. Starting with his first work on technology assessment in IBM over 20 years ago, Watts Humphrey describes the process improvement work he has been directly involved in. This includes the development of the early process assessment methods, the original design of the CMM, and the introduction of the Personal Software Process (PSP)^SM and Team Software Process (TSP){^SM}. In addition to describing the original motivation for this work, the author also reviews many of the problems he and his associates encountered and why they solved them the way they did. He also comments on the outstanding issues and likely directions for future work. Finally, this work has built on the experiences and contributions of many people. Mr. Humphrey only describes work that he was personally involved in and he names many of the key contributors. However, so many people have been involved in this work that a full list of the important participants would be impractical.     

基于复小波噪声方差显著修正的SAR图像去噪

提出了一种基于复小波域统计建模与噪声方差估计显著性修正相结合的合成孔径雷达(Synthetic Aperture Radar,SAR)图像斑点噪声滤波方法。该方法首先通过对数变换将乘性噪声模型转化为加性噪声模型,然后对变换后的图像进行双树复小波变换(Dualtree Complex Wavelet Transform,DCWT),并对复数小波系数的统计分布进行建模。在此先验分布的基础上,通过运用贝叶斯估计方法从含噪系数中恢复原始系数,达到滤除噪声的目的。实验结果表明该方法在去除噪声的同时保留了图像的细节信息,取得了很好的降噪效果。     

How do children do mathematics with LOGO?

Abstract  This paper considers some results of a study designed to investigate the kinds of mathematical activity undertaken by children (aged between 8 and 11) as they learned to program in LOGO. A model of learning modes is proposed, which attempts to describe the ways in which children used and acquired understanding of the programming/mathematical concepts involved. The remainder of the paper is concerned with discussing the validity and limitations of the model, and its implications for further research and curriculum development.     

Editorial: Special issue on recent advances in hybrid control theory and applications

正The demands of a rapidly advancing technology for faster and more accurate controllers have always had a strong influence on the progress of automatic control theory.In recent years control problems have been arising with increasing frequency in widely different areas,which cannot be addressed using conventional control techniques.The principal reason for this is the fact that a highly competitive economy is forcing systems to operate in regimes where     

Information for Authors

正Aim The Journals of Zhejiang University-SCIENCE(A/B/C)areedited by the international board of distinguished Chinese andforeign scientists,and are aimed to present the latest devel-opments and achievements in scientific research in China andoverseas to the world’s scientific circles,especially to stimulateand promote academic exchange between Chinese and for-eign scientists everywhere.     

Enhancing a leaf radiative transfer model to estimate concentrations and in vivo specific absorption coefficients of total carotenoids and chlorophylls a and b from single-needle reflectance and transmittance

The relative concentrations of different pigments within a leaf have significant physiological and spectral consequences. Photosynthesis, light use efficiency, mass and energy exchange, and stress response are dependent on relationships among an ensemble of pigments. This ensemble also determines the visible characteristics of a leaf, which can be measured remotely and used to quantify leaf biochemistry and structure. But current remote sensing approaches are limited in their ability to resolve individual pigments. This paper focuses on the incorporation of three pigments—chlorophyll a, chlorophyll b, and total carotenoids—into the LIBERTY leaf radiative transfer model to better understand relationships between leaf biochemical, biophysical, and spectral properties.Pinus ponderosa and Pinus jeffreyi needles were collected from three sites in the California Sierra Nevada. Hemispheric single-leaf visible reflectance and transmittance and concentrations of chlorophylls a and b and total carotenoids of fresh needles were measured. These data were input to the enhanced LIBERTY model to estimate optical and biochemical properties of pine needles. The enhanced model successfully estimated reflectance (RMSE = 0.0255, BIAS = 0.00477, RMS%E = 16.7%), had variable success estimating transmittance (RMSE = 0.0442, BIAS = 0.0294, RMS%E = 181%), and generated very good estimates of carotenoid concentrations (RMSE = 2.48 µg/cm², BIAS = 0.143 µg/cm², RMS%E = 20.4%), good estimates of chlorophyll a concentrations (RMSE = 10.7 µg/cm², BIAS = − 0.992 µg/cm², RMS%E = 21.1%), and fair estimates of chlorophyll b concentrations (RMSE = 7.49 µg/cm², BIAS = − 2.12 µg/cm², RMS%E = 43.7%). Overall root mean squared errors of reflectance, transmittance, and pigment concentration estimates were lower for the three-pigment model than for the single-pigment model. The algorithm to estimate three in vivo specific absorption coefficients is robust, although estimated values are distorted by inconsistencies in model biophysics. The capacity to invert the model from single-leaf reflectance and transmittance was added to the model so it could be coupled with vegetation canopy models to estimate canopy biochemistry from remotely sensed data.     

Mr. Twinn’s bombes

This article discusses the history and design of the special versions of the bombe key-finding machines used by Britain’s Government Code & Cypher School (GC&CS) during World War II to attack the Enigma traffic of the Abwehr (the German military intelligence service). These special bombes were based on the design of their more numerous counterparts used against the traffic of the German armed services, but differed from them in important ways that highlight the adaptability of the British bombe design, and the power and flexibility of the diagonal board. Also discussed are the changes in the Abwehr indicating system that drove the development of these machines, the ingenious ways in which they were used, and some related developments involving the bombes used by the U.S. Navy’s cryptanalytic unit (OP-20-G).