一种自适应速率的UWB MAC协议

在超宽带（UWB）通信中,跳时冲激无线电（TH-IR）技术具有系统结构简单、成本低、功率小等优点,得到广泛的研究及应用探索。基于TH-IR UWB技术,提出了一种能够保证链路误码率及传输速率的自适应速率跳时（Rate-Adaptive Time Hopping,RATH）介质访问控制（MAC）协议,该协议利用跳时码管理多用户的信道访问,依据接收节点的信干比控制链路的建立,并采用自适应速率算法调节链路的传输速率。NS2平台下的仿真实验表明,与U-MAC等已有的固定速率协议相比较,RATH MAC协议能够使网络有效吞吐量和传输时延得到明显改善。     

联合动态聚合帧长机制的速率自适应算法

在IEEE 802.11n协议中引入帧聚合机制能够提高无线局域网MAC层的效率,但会增加速率自适应算法对信道变化的反应时间,降低网络吞吐量。针对该问题,提出一种改进的速率自适应算法JodaRA。引入权重思想统计聚合帧的发送情况,设计基于子帧丢失加权和的速率选择方案。采取混合型速率选择策略,利用发送端的RSSI与接收端的传感器信息进行链路状态感知,根据链路状态选取合适的速率选择方案并动态设定聚合帧的最大长度,以提高算法的实时性与准确性。仿真结果表明,在不同的节点移动状态下,与RRAA、MinstrelHT和SampleLite 3种算法相比,JodaRA算法的平均UDP吞吐量分别提高90%、57%和22%。     

Ad hoc网络中基于MAC层拥塞控制的速率自适应策略*

对现有AAR(adaptive auto rate)协议进行改进,将POCC算法应用于AAR协议,提出了AAR-CC(AAR-congestion control)协议,从而在MAC层实现了拥塞控制的速率自适应机制。AAR-CC协议源节点根据每时链路的总拥塞信息确定当时数据发送速率,适用于动态变化的多跳Ad hoc网络;本协议只对MAC帧稍作修改并增加一个字节的拥塞指示CI,具有可扩展性和低开销性。AAR-CC利用背靠背数据传输方式,充分发挥高质量通信信道利用率,能有效缓解控塞程度,从而提高网络的端到端饱     

基于接收端信号的水声网络MAC协议

水声网络的信道具有数据速率低以及传播时延长的特点,如果采用握手机制减少数据冲突,将降低信道利用率和网络的吞吐量。提出了一种基于接收节点发送短信号告知邻居节点其接收状态的水声网络MAC协议,即当接收节点接收数据时,向邻居节点发送短信号通知其当前时刻不要发送数据,解决了隐藏终端和暴露终端的问题,并提高了网络吞吐量;除此之外,使用短信号还能够降低能量损耗。仿真结果表明该协议能够实现上述目的。     

LPR MAC:一种采用并行协商机制的低功耗多信道MAC协议

本文通过分析不同类型的多信道MAC协议的特点,指出了并行协商类多信道MAC协议存在的消失节点问题和通信竞争问题。针对上述问题,基于无线传感器网络节点的能量有效性,本文提出了一种新的多信道MAC协议：LPR MAC。本协议采用全网同步,时间上划分为多个时间片,节点在网络建立时随机选择某个时间片作为自己的固定接收周期,在接收周期按各自的伪随机序列在多个信道之间进行跳跃,并行协商,在其余时间片休眠。仿真结果表明,该协议减少了通信竞争程度,降低了能量消耗。     

LPR-MAC:一种采用并行协商机制的低功耗多信道MAC协议

本文通过分析不同类型的多信道MAC协议的特点,指出了并行协商类多信道MAC协议存在的消失节点问题和通信竞争问题。针对上述问题,基于无线传感器网络节点的能量有效性,本文提出了一种新的多信道MAC协议:LPR-MAC。本协议采用全网同步,时间上划分为多个时间片,节点在网络建立时随机选择某个时间片作为自己的固定接收周期,在接收周期按各自的伪随机序列在多个信道之间进行跳跃,并行协商,在其余时间片休眠。仿真结果表明,该协议减少了通信竞争程度,降低了能量消耗。     

适用于水声传感网络的多链路传输MAC协议

针对水声传感网络存在的高时延、低信道利用率等问题,提出一种新的多链路传输介质访问控制协议。该协议节点通过RTS/CTS握手协议交互时延信息和传输计划,实现多条链路传输数据。在汇聚节点接收多个节点的数据时,汇聚节点根据节点的时延和接收的数据帧大小规划节点之间的发送顺序,避免传输冲突造成的能量损失和低信道利用率,同时为得到最大网络吞吐量,给出最优退避窗口值的理论表达式。仿真结果表明,与RC-FAMA、S-FAMA等协议相比,该协议能有效提高水声传感网络的吞吐量,降低传输冲突,从而延长水下节点的工作时间。     

一种针对树形拓扑网络的混合MAC协议

在树形拓扑水声传感网络中,时分多址(TDMA)机制存在信道利用率低的问题。为此,提出一种轻量级的流量自适应随机访问与TDMA的混合MAC协议。该协议在网络流量较低时采用S-ALOHA竞争机制提高信道利用率,运用最优化算法计算分配给簇内子节点的最大发送概率,通过流量自适应的灵活时隙分配机制以适应不同的网络流量。实验结果表明,该协议不仅能够提高树形拓扑网络中节点的通信效率,能减少子节点的等待时间。     

一种适用于Ad Hoc网络的多信道能量高效MAC协议

对多信道条件下MAC协议功率控制机制进行了分析,提出一种能够根据各个接收节点的通信状况,动态地调整数据信道上数据帧的传输功率和控制信道上CTS帧的发送功率的多信道Ad Hoc网络能量高效的MAC协议(MPEMAC).仿真表明,该协议有效的节省了节点能耗,延长了网络节点的生存时间,同时还能够增大空间信道的利用率,从而进一步提高网络的平均吞吐量.     

多速率Ad hoc网络MAC层公平性的分析与改进

在多速率Ad hoc网络中,利用自适应速率调整算法,网络节点可以根据信道质量选择不同的传输速率,从而提高网络的总体通信能力。对多速率Ad hoc网络MAC层公平性进行了仿真和分析,实验结果表明基于IEEE 802.11的多速率Ad hoc网络中存在严重的公平性问题。通过对吞吐率公平和时间公平的讨论,指出在多速率Ad hoc网络中进行MAC层公平性研究,时间公平性标准是较优的选择。另外提出一种针对多速率Ad hoc网络的改进公平回退（EFB）算法,仿真实验的结果表明该算法能够明显提高多速率Ad hoc网络的MAC层公平性。     

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QTE的蒙古文显示机制研究与实现

蒙古语言是中国蒙古族使用的通用语言,由于蒙古文区别于其他文字的书写方式和其自身变形机制等特点,在很多通用的文字处理引擎中都不被支持。在嵌入式产品开发与应用领域中Linux加QTE已经成为流行方式。该文给出了一种在QTE环境上实现基于标准Unicode的蒙古文点阵显示和变形算法, 并自定义了支持蒙古文的QTE组件,扩展了QTE功能,为在Linux加QTE方式的嵌入式体系结构中处理蒙古文提供了一种解决方法。     

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。