适用于飞行自组网的闲置时隙预约TDMA协议

在飞行自组网中,固定时隙分配时分多址接入（TDMA）协议存在闲置时隙无法成功使用的问题。通过对TDMA协议引入闲置时隙预约机制,提出一种支持业务优先级传输机制的闲置时隙预约TDMA协议。采用短帧长的方式满足协同与控制业务的低时延传输需求,并利用闲置时隙预约机制允许节点使用闲置时隙传输感知业务,从而满足感知业务的高吞吐量传输性能要求。仿真结果表明,与CF-MAC和CTMAC协议相比,该协议能够在降低传输时延的同时,有效提高信道利用率和网络吞吐量。     

采用渐进式预留机制的Ad Hoc网络MAC协议

实时业务传输的服务质量(QoS)保障问题一直是限制Ad Hoc网络发展的瓶颈.在分布式网络环境下,分组冲突十分普遍,节点很难在限定的时间内成功接入信道.现有很多算法(如FPRP)虽能很好的消除冲突,却需要非常多的控制分组,同样造成过高的接入时延.在研究动态时隙分配类MAC协议的基础上,设计了一种采用渐进式预留机制的MAC协议,协议通过分级预留、协同竞争和空闲时隙的时隙重构来达到分组冲突的充分化解,信道资源的高效利用,以及不同优先级业务的有效接入.仿真表明,与现有时隙类协议相比,新协议可以显著减少分组冲突,提高信道利用率,实现较低的分组接入延迟,并且能够较好的支持数据报业务.     

基于可变长时隙机制的水下传感器网络MAC协议

通过研究水声通信的特点,分析水下物体的运动特性,提出了一种基于可变长时隙机制的水下传感器网络MAC协议。新协议中,传感器节点会周期性获取邻居节点的位置信息,并根据节点间相互距离的变化自适应地调整信道预约时隙长度,当节点由于运动引起网络区域收缩,节点之间距离变小时,预约时隙长度变小,反之,时隙长度增大。可变长时隙机制,提高了信道时隙资源的利用率。仿真结果表明,动态环境下新协议相对现有的协议在有效网络吞吐量性能上提升15%左右。     

一种基于预约的无线传感器网络MAC协议

无线传感器网络要求的能量高效,低延时,使得MAC协议的设计充满挑战.近来已经提出了很多基于簇的MAC协议,为减少冲突在簇内部采用TDMA方式来协调簇内各个节点的传输.本文提出了一种在采用簇结构的基础上,使用预约方式来发送数据的R-MAC(Reservation-MAC)协议.当争用节点少的时候,采用随机争用方式来预约数据的发送;在争用节点多的时候,采用时隙争用方式来预约数据的发送.分析表明,R-MAC能够有效的降低能耗和减少延迟.     

一种新型的无竞争的基于TDMA的MAC协议

本文提出了一种无竞争的基于TDMA的MAC协议CA-TDMA.CA-TDMA协议通过对超帧中竞争时隙的直接分配和数据时隙的相互申请来实现在整个网络中无时隙竞争,并且通过添加新的申请消息(RTS、CTS、CTR)和提出新的时隙竞争机制、时隙续约机制和竞争时隙交换机制,来提高整个网络的性能.仿真结果表明,CA-TDMA相比动态TDMA协议在分组投递率和网络延迟等性能参数方面均有明显的提高.     

基于网络效用最大化与冲突避免的无线传感器网络MAC协议

针对周期汇报型无线传感器网络(WSN)中的无线信号冲突和能量利用效率问题,提出了一种基于网络效用最大化与冲突避免的媒体访问控制(UM-MAC)协议。该协议基于时分多路复用(TDMA)调度机制,将效用模型引入无冲突的节点工作时隙分配过程中,把链路可靠性、网络能耗归纳到一个统一的效用优化框架中;进而提出了一个启发式算法,使网络能够快速找到一个基于网络效用最大化与冲突避免的节点工作时隙调度方案。将UM-MAC协议与S-MAC协议和冲突避免MAC(CA-MAC)协议进行比较,在不同节点数量的网络环境中,UM-MAC获得的网络效用较大,平均数据包成功发送率较高,生命周期介于S-MAC与CA-MAC之间,在不同的网络负载下所有节点发数据包到汇聚节点的平均时延有所增加。仿真实验结果表明:UM-MAC协议较好地解决了冲突干扰问题,提高了网络的数据包成功发送率和能量利用效率等性能;在低网络负载时,TDMA类协议的性能并不比竞争类协议好。     

船舶通信网无线接入协议研究

本文提出了一种适用于船舶通信网的无线接入协议--基于优先级的时分多址协议（PTDMA）,它允许节点通过捎带预约的方式动态申请时隙,并采用基于优先级和网络负载的动态时隙分配算法分配时隙.此外,它还保证节点动态接入和退出.仿真结果表明,该协议有较好的网络性能     

认知车载网中基于TDMA/CSMA的混合多信道MAC协议研究

在传统车载自组网(Vehicular Ad Hoc Network, VANET)中采用认知无线电(Cognitive Radio, CR)技术可以解决无线电频谱资源短缺的问题,该技术形成了新兴的认知车载网络(CR-VANET),其关键技术之一是设计高效可靠的介质访问控制(Medium Access Control, MAC)协议。MAC协议在很大程度上影响着车载移动环境的吞吐量,丢包率和传输时延等性能,基于认知车载网中MAC协议的要求,提出了一种TDMA与CSMA相结合的多信道MAC协议(CRTC-MAC)。在固定时隙分配时采用基于无竞争的TDMA访问策略,在动态时隙分配时采用基于竞争的CSMA接入方案,并在此基础之上对传统的TDMA和CSMA访问方式进行了改进。性能分析和仿真结果表明,所提出的MAC协议能有效降低节点间数据包传输时所产生的碰撞,改善网络性能。     

LoRa无线网络MAC层TDMA时隙分配协议研究

轮询协议是一种经典的介质访问控制(MAC)层时分多址(TDMA)时隙分配协议,具有无冲突数据通信且功耗低的特点,但无法保证通信可靠性及实现有区别服务。为此,研究一种具有动态重传和差异服务机制的TDMA时隙分配协议。重新设计帧结构,根据终端节点数据包信息完成静态时隙分配,在数据传输失败时,利用重传时隙提高通信可靠性,通过影子时隙实现有区别服务。在无线抄表系统上的实验结果表明,与经典轮询协议相比,该协议的丢包率降低了3%。     

EDA-MAC:事件驱动应用感知的无线传感器网络MAC协议

MAC协议是无线传感器网络领域中的一个广泛研究的问题,然而,现有的MAC协议较少是针对具体的应用而设计.针对基于无线传感器网络的坡道转弯交通控制系统,设计并实现了一个事件驱动、应用感知的MAC协议EDA-MAC(Event Driven Application MAC).此协议使用竞争时隙分配算法选择优先级最高的汇报事件,根据此优先级作为可以汇报事件的基准,限制低优先级事件的汇报,有效降低数据包的碰撞,保证了数据传输的完整性和实时性.同时,提出一个时隙动态调整算法,根据已有汇报事件的信息,动态调整非竞争周期和非活动周期的时隙数目,减少节点的空闲监听时间,最大程度地使节点处于睡眠状态,有效降低了节点能耗.试验结果表明,该MAC协议支持优先事件传输,具有较好的实时性和能量高效性,适用于基于无线传感器网络的坡道转弯交通控制系统.     

Only connect: teaching, technology and telesis

Abstract This paper describes an approach to the design of interactive multimedia materials being developed in a European Community project. The developmental process is seen as a dialogue between technologists and teachers. This dialogue is often problematic because of the differences in training, experience and culture between them. Conditions needed for fruitful dialogue are described and the generic model for learning design used in the project is explained.     

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。     

Avoiding semantic and temporal gaps in developing software intensive systems

Development of software intensive systems (systems) in practice involves a series of self-contained phases for the lifecycle of a system. Semantic and temporal gaps, which occur among phases and among developer disciplines within and across phases, hinder the ongoing development of a system because of the interdependencies among phases and among disciplines. Such gaps are magnified among systems that are developed at different times by different development teams, which may limit reuse of artifacts of systems development and interoperability among the systems. This article discusses such gaps and a systems development process for avoiding them.     

Designing economic np control charts: A programmed simulation approach

This paper presents control charts models and the necessary simulation software for the location of economic values of the control parameters. The simulation program is written in FORTRAN, requires only 10K of main storage, and can run on most mini and micro computers. Two models are presented - one describes the process when it is operating at full capacity and the other when the process is operating under capacity. The models allow the product quality to deteriorate to a further level before an existing out-of-control state is detected, and they can also be used in situations where no prior knowledge exists of the out-of-control causes and the resulting proportion defectives.     

The development of robot art

Going through a few examples of robot artists who are recognized worldwide, we try to analyze the deepest meaning of what is called “robot art” and the related art field definition. We also try to highlight its well-marked borders, such as kinetic sculptures, kinetic art, cyber art, and cyberpunk. A brief excursion into the importance of the context, the message, and its semiotics is also provided, case by case, together with a few hints on the history of this discipline in the light of an artistic perspective. Therefore, the aim of this article is to try to summarize the main characteristics that might classify robot art as a unique and innovative discipline, and to track down some of the principles by which a robotic artifact can or cannot be considered an art piece in terms of social, cultural, and strictly artistic interest. This work was presented in part at the 13th International Symposium on Artificial Life and Robotics, Oita, Japan, January 31–February 2, 2008     

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.