Survey of computer communications loop networks: Part 2

Loop networks for computer communications have inherent advantages of performance, modularity and cost. In Part 1 several demand-shared loops, their configuration and topology were discussed. In the second part control distribution, timing and synchronization, reliability and performance are covered. The section on performance includes a comparison of loops with each other and with other topologies, particularly stars, random-access highways and polled highways.     

Synchronization of two different chaotic systems using Legendre polynomials with applications in secure communications

In this study, a new controller for chaos synchronization is proposed. It consists of a state feedback controller and a robust control term using Legendre polynomials to compensate for uncertainties. The truncation error is also considered. Due to the orthogonal functions theorem, Legendre polynomials can approximate nonlinear functions with arbitrarily small approximation errors. As a result, they can replace fuzzy systems and neural networks to estimate and compensate for uncertainties in control systems. Legendre polynomials have fewer tuning parameters than fuzzy systems and neural networks. Thus, their tuning process is simpler. Similar to the parameters of fuzzy systems, Legendre coefficients are estimated online using the adaptation rule obtained from the stability analysis. It is assumed that the master and slave systems are the Lorenz and Chen chaotic systems, respectively. In secure communication systems, observer-based synchronization is required since only one state variable of the master system is sent through the channel. The use of observer-based synchronization to obtain other state variables is discussed. Simulation results reveal the effectiveness of the proposed approach. A comparison with a fuzzy sliding mode controller shows that the proposed controller provides a superior transient response. The problem of secure communications is explained and the controller performance in secure communications is examined.     

基于演化图论的可靠的VANETs路由协议

车载网络（VANETs）属于移动无线网络的特例,具有鲜明的特性。传统无线网络的路由协议难以直接应用于VANETs。节点的高速移动,引起网络拓扑动态变化,导致VANETs的通信链路频繁断裂。高动态网络的链路可靠性问题引起广泛的关注。为此,针对高速公路VANETs的路由可靠性进行分析,对演化图论进行扩展,建立扩展后的演化图论模型（EEGM）,并利用EEGM获取VANETs拓扑的动态信息,从而预先获取可靠路由的信息。在此基础上,提出基于演化图论的可靠路由协议（EG-RAODV）。仿真结果表明,与同类的其他协议相比,提出的路由协议在分组传输率、端到端传输时延、路由请求消息率以及链路断裂数方面得到了提升。     

Command and control of the emergency services

Because of the increasing cost of salaries, it is becoming necessary to use as many emergency-services personnel as possible in operational rather than administrative roles.This demands good communications, and the paper describes several operational computerized command and control systems in use with UK police forces and fire brigades.Typical incident-handling procedures for police and fire emergencies are described. Management-information capabilities, personnel factors and reliability are discussed, together with selection criteria. In conclusion, the paper stresses the importance of systems interconnection to form larger networks.     

HARTS: a distributed real-time architecture

The design, implementation, and evaluation of a distributed real-time architecture called HARTS (hexagonal architecture for real-time systems) are discussed, emphasizing its support of time-constrained, fault-tolerant communications and I/O (input/output) requirements. HARTS consists of shared-memory multiprocessor nodes, interconnected by a wrapped hexagonal mesh. This architecture is intended to meet three main requirements of real-time computing: high performance, high reliability, and extensive I/O. The high-level and low-level architecture is described. The evaluation of HARTS, using modeling and simulation with actual parameters derived from its implementation, is reported. Fault-tolerant routing, clock synchronization and the I/O architecture are examined     

TCP协议在卫星网络中的问题研究

由于TCP协议直接应用到卫星网络中将可能会导致网络性能下降,因此针对卫星网络的特点,分析了传播时延、高误码率、非对称连接方式等特点对TCP协议性能的影响,对主要解决方法进行了分析、比较现有的几种解决方法利弊,应根据具体应用采用相应的解决方案。     

A comprehensive survey on control strategies of distributed generation power systems under normal and abnormal conditions

High energy demand, low cost requirements and higher reliability requirements increase the importance of distributed generation power systems (DGPSs). The large capacity DGPSs requires high performance control algorithms and synchronization techniques based positive-negative sequence (PNS) extractors to fulfil system reliability and power quality requirements under not only during normal operating conditions, but also under unbalanced grid conditions. The power quality problems caused by voltage unbalances, voltage sag/swell, voltage fluctuations, phase faults and harmonic distortions have critical influences on control of power converter devices interfaced DGPSs. In literature studies, novel control strategies with phase locked loops (PLLs) techniques based PNS extractors are used to overcome these problems. In this paper, a comprehensive review on various advanced control strategies and PNS extractors for interlinking three phase inverter in the DGPSs are comprehensively investigated and discussed under normal and abnormal conditions. Several PNS extractors have been overviewed to produce the sequences components required for reference current generation (RCG). The theoretical assessment of the RCG based flexible control strategies and overcurrent limitation control are also comprehensively analysed, surveyed and compared in detail to deal with power quality problems. Comparative analyses for PNS extractors, voltage/current regulation controllers and RCG based control strategies have been detailed presented and analysed. The presented detailed overview can be useful to researchers studying impact of normal and abnormal conditions on various control strategies with or without any using PLLs based PNS extractors for three-phase inverters interfaced DGPSs.     

Reliable Communication Networks for Smart Grid Transmission Systems

In this paper, we discuss the communications reliability requirements posed by the smart power grid with a focus on communications in support of wide area situational awareness. Implementation of wide area situational awareness relies on both transmission substation networks and wide area optical networks. We study the reliability of a sample communications network of the California Power Grid and find that its reliability falls short of proposed requirements. To overcome this issue, we consider the problem of designing the substation network and the wide area network to meet the reliability requirements while minimizing the network cost. For the wide area network design problem, we propose two alternate design approaches, namely: (1) following the power lines and (2) a mesh based design interconnecting the nodes. For the first approach we develop two greedy iterative heuristics and a heuristic integer linear programming (H-ILP) model using minimum cut-sets for network reliability optimization. The greedy iterative algorithms outperform the H-ILP approach in terms of cost, but require a larger amount of computing resources. Both proposed models are in fact complementary and thus provide a framework to optimize the reliability of smart grid communications networks restricted to following the power lines. In the second approach a greenfield mesh network method is proposed based on starting with a minimum spanning tree which is then augmented through a greedy heuristic into a mesh. Comparative numerical results show that the reliable mesh design has advantages in terms of the number of links and total link distance needed.     

Intelligent Agents for ATM Network Control and Resource Management: Experiences and Results from an Implementation on a Network Testbed

This paper presents the architecture and implementation of a distributed multi-agent system designed to provide flexible control and efficient resource management of a communications network. The system architecture enables different service providers and the network provider to use different control algorithms on the same logically partitioned physical infrastructure. All the mechanisms have been implemented and successfully tested on real experimental telecommunications networks. The system components are first described and then results from experiments and performance issues are discussed. The problem of interfacing a multi-agent system to network devices is then discussed. Interfacing agents with the network requires some form of programmable interface, since it is necessary, for example, to override conventional ATM signaling. At the moment programmable network device interfaces are not always available, particularly in commercially available devices and, thus, generic operations using management protocols have to be used. A generic architecture for embedding custom network control functionality into ATM networks is described.     

Neural network control of underwater vehicles

In this paper, recent research efforts in the field of the application of neural networks (NNs) for the control of (semi-)autonomous underwater vehicles are reviewed. Based on a literature review the authors propose a classification of approaches to control underwater vehicles using NNs and the presented articles are categorized according to the identified categories. Based on practical results as described in the discussed literature this paper presents a qualitative assessment regarding the performance of the control strategies. Per category, or control strategy, the major advantages and disadvantages are identified and discussed.     

基于超宽带无线传感网络的导频优化脉冲同步算法

超宽带(UWB)技术因具有低功耗、极高时间和空间分辨率等特点成为无线传感网络主要物理层技术之一.本文主要研究基于发送-参考超宽带(TR-UWB)方式的传感网络信号检测与同步技术,文中提出一种新型自适应脉冲同步算法.该算法实现复杂度低,能够快速实现脉冲帧级同步.同步时间仅需要几个符号周期,同时把基于SQP的约束非线性最优化理论应用于设计脉冲导频符号进一步提高同步性能.此外,文中给出了两种脉冲符号级同步方法,它们在不同Eb/No时展现不同性能,可根据实际环境选择最适合的符号级同步方法.脉冲帧级同步具有自适应性,可根据实际的同步性能要求动态调节帧级同步的递归次数.理论分析和计算机仿真验证了该同步算法的性能.     

移动对等网络体系结构的研究与设计

随着科学技术的进步,移动用户的日渐增多和移动网络应用环境的逐渐成熟,人们对移动网络的速度要求越来越高,使得无线网络上P2P技术的需求日渐强烈。众所周知,无线网络通信和终端的移动性使得网络在带宽、延迟、连接可靠性、连接维持可预期性等通信性能上与有线网络相比相差很远。可以利用移动P2P方式提供的视频点播、资源共享和移动协同计算等,提高网络的性能。     

Markov Chain-based performance analysis of multihop IEEE 802.15.4 wireless networks

In this paper, we propose a Markov chain-based analytical framework for modeling the behavior of the medium access control (MAC) protocol in IEEE 802.15.4 wireless networks. Two scenarios are of interest. First, we consider networks where the (sensor) nodes communicate directly to the network coordinator (the final sink). Then, we consider cluster-tree (CT) scenarios where the sources communicate to the coordinator through a series of intermediate relay, which forward the received packets and do not generate traffic on their own. In both scenarios, no acknowledgment messages are used to confirm successful data packet deliveries and communications are beaconed (i.e., they rely on synchronization packets denoted as “beacons”). In all cases, our focus is on networks where the sources and the relays have finite queues (denoted as buffers) to store data packets. The network performance is evaluated in terms of aggregate network throughput and packet delivery delay. The performance predicted by the proposed analytical framework is in very good agreement with realistic ns-2 simulation results.     

Synchronization of a Class of Improved Neural Networks Based on Periodic Intermittent Control

In this paper, the synchronization of a class of improved neural networks with variable time delay is concerned via intermittent control. Firstly, a class of modified delayed neural networks is introduced, in which communication delays between different neurons are considered and the intra-neuron delays are negligible. Secondly, using Lyapunov functional theory, inequality techniques, and multi-parameter method, the synchronization criteria are established based on p-norm via intermittent control, and a feasible synchronization control region is given. Besides, by means of the component analysis method, the reduction to absurdity, mathematical induction, the exponential synchronization of the addressed networks is discussed in terms of the infinite norm, some criteria and the feasible control region of synchronization are also derived. Finally, some numerical examples are provided to show the validity and effectiveness of the theoretical results.     

AVP: A Highly Efficient Transport Protocol for Low Bit Rate Multimedia Communications

Utilization of Internet communications in distance learning, distributed simulation, and distributed work groups involves multimedia transmission of animation, voice and video clips. Highly compressed audio-video data protocols are required for efficient Internet multimedia communications. Addressing this requirement, a new transport protocol called Audio-Video Protocol (AVP) for highly efficient multimedia communications on the Internet is presented. While providing similar real-time delivery functions as Real-Time Transport Protocol (RTP) and Real-Time Control Protocol (RTCP), AVP adopts a novel audio-based synchronization scheme. This synchronization scheme has two advantages. One is the overhead reduction through eliminating the timestamp in each transmitted data packet. The other is the packet rate reduction by putting multiple audio frames or mixed audio-video frames in a single AVP packet. As a result, the end-to-end media unit delay is reduced while achieving implicit synchronization. Furthermore, AVP provides adaptive quality of service (QoS) by the prioritized packetization scheme. Simulation results are presented to verify the advantages of the AVP protocol.     

利用Java即时编译器自动外提循环中的同步操作

同步开销是影响并行程序性能的一个重要方面,如果同步操作出现在循环中,将会使这种影响进一步扩大.为了降低循环中同步操作的开销,本文提出一种利用即时编译器外提Java程序中循环内同步操作的优化算法,并在实际的Java虚拟机中实现.该算法在保证程序语义不变的前提下,大量减少运行时实际执行的同步操作数量,降低同步开销,并能保证外提变换后同步代码块不会太大而降低程序的并发度.实验结果表明该算法能提高程序的整体性能,并且不降低程序的可扩放性.     

PROFIBUS-DP/MODBUS的网关结构设计

针对工业控制网络中的系统互连及扩展问题,提出将采用MODBUS协议的系统与采用PROFIBUS-DP协议的系统融合的解决方案。设计了PROFIBUS-DP/MODBUS网关,其体积小、功耗低、成本低且可靠性高,无缝连接了MODBUS网络和PROFIBUS-DP网络。对PROFIBUS-DP网络扩展的网关协议栈的实现以及网关实时性和可靠性措施进行了详细的说明,并对网关设备的性能进行了分析和测试。     

A boundary control for motion synchronization of a two-manipulator system with a flexible beam

A novel synchronization motion control method is proposed in this paper for the system in which two manipulators are constrained by a flexible beam. Different from the general synchronization control method, the coupling dynamics among various actuators is considered as the shear force, which results from the synchronization errors. Then a simple boundary control is introduced to realize the synchronization motion of actuators by suppressing the shear force. In order to avoid the drawbacks of assumed modes model, the dynamic model of flexible beam is described by a distributed parameter model in this paper. A Riesz basis method is used to prove that the proposed control law can guarantee the synchronization system to be exponential stability. Simulation results demonstrate that the proposed method can effectively improve the performance of synchronization motion compared with other methods.     

机会网络中元数据交换的改进方法

署名向量法在缓冲区有限的情况下,其数据同步性的表现不够理想。针对该问题,提出一种机会网络中元数据交换的改进方法,即动态署名向量法。改进方法对元数据的可信程度进行标识并增加超时预测机制。实验表明,在缓冲区有限的情况下,使用动态署名向量的元数据交换技术能改善署名向量中存在的同步问题,降低消息平均到达时间,从而提高数据转发的性能。     

多链接复杂网络指数同步的间歇事件触发控制

本文研究了基于间歇事件触发控制策略的延迟多链接复杂网络的指数同步问题, 设计了一种间歇动态事 件触发控制策略. 相比于间歇静态事件触发控制策略, 本文提出的控制策略是基于控制区间内的动态事件触发, 极 大地减少了事件触发次. 并且, 考虑的间歇控制的控制增益是自适应的, 这具有动态调整的作用. 基于图论和李雅 普诺夫方法, 本文给出了实现延迟多链接复杂网络指数同步的充分条件. 此外, 本文设计的控制策略能够排除Zeno 现象. 并且, 将理论结果应用于一类振子系统的指数同步问题. 最后, 文章给出相应的数值仿真来验证理论结果的有 效性和可行性.