无线传感器网络时钟同步的研究

在无线传感器网络中,时钟同步是十分必要的．有限的电池能量,存储以及带宽限制等传感器固有的特性的存在,导致传统的时钟同步算法不适合无线传感器网络．本文阐述了时钟同步问题和时钟同步的必要性,介绍了一些传感器网络的时钟同步算法,并深入研究了在考虑节点移动的情况下,利用节点的移动来传递时钟信息的思想,模拟证明我们的算法性能良好。     

无线传感器网络基于能量效率的系统设计

无线传感器网络是传感技术、计算技术和通信技术的融合.由于传感器节点的能量限制,能量效率是设计无线传感器网络所关注的一个主要内容.文章主要研究网络节点如何配置使系统能量效率提高.通过对传感器节点无线通信能耗模型的扩展,在两种线性网络模型下,分析并仿真实现了多数据源负载时的系统能耗;通过对比分析,在无线传感器网络节点配置时,提出两种有效可行的配置机制:节点等间距放置和优化间距放置.这两种机制对提高能量效率,延长网络寿命提供了很大的帮助.     

Effects of Optical Buffering on the Performance of Manhattan Street Networks

Multihop networks are strong candidates for the implementation of high-speed networks, ranging from back-plane networks for cluster computing to metropolitan-area networks. Besides using deflection routing for contention resolution, optical buffering may be used to enhance the performance of optical multihop networks and to reduce or even eliminate the need for optical-electrical conversions. The enhancements obtained by augmenting traditional MSN (Manhattan Street Networks) with optical buffering are evaluated. The MSN considered here is based on a novel 6 × 6 optical switching node with up to two fiber delay loops. Impact of the parameters associated with optical buttering, such as the number of delay loops and the loop length, are discussed in detail.     

A High Capacity Multihop Packet CDMA Wireless Network

Wireless multihop networks overlaid with cellular structure have the potential to support high data rate Internet traffic. In this paper, we consider techniques by which the system capacity of such networks can be increased. First, methods for increasing link capacity in single-user systems are explored. Subsequently, we consider a different set of techniques suitable for multiuser systems. We also investigate the effect of traffic dynamics on system capacity and ways to achieve the maximum throughput. Finally, we present capacity bounds which illustrate how these techniques help in trading off the conserved power for capacity advantage.     

A Constraint Formulation for Minimum-Energy Multicast Routing in Wireless Multihop Ad-hoc Networks

Energy conservation is a critical issue in wireless multihop ad-hoc networks, which have nodes powered by batteries only. One major metric for energy conservation is to route a communication session along the routes that require the lowest total energy consumption. To do this, we introduce in this paper a new concept called Virtual Relay. Based on this new concept, we present a constraint formulation for the minimum-energy multicast routing problem in terms of mixed integer linear programming. Experiment results show that in a typical multihop ad-hoc network with 50 nodes, the optimal solutions can always be solved in a timely manner, and it also provides a way to evaluate the realistic performance of different heuristic algorithms. Song Guo received the B.S. degree in computer science from Huazhong University of Science and Technology, Wuhan, China, in 1995 and the M.S. degree in electrical and computer engineering from Beijing University of Posts and Telecommunications, Beijing, China, in 1998. Since 2001 he has been a Ph.D. student in the School of Information Technology and Engineering at University of Ottawa, Canada. His main research interests lie in mobile ad-hoc routing protocols and algorithms, power-aware design and optimization for ad-hoc wireless networks, and performance evaluation. Oliver Yang is a Professor in the School of Information Technology and Engineering at University of Ottawa, Ontario, Canada. Dr. Yang received his Ph.D. degree in Electrical Engineering from the University of Waterloo, Ont., Canada in 1988. He has worked for Northern Telecom Canada Ltd. and has done various consulting. His research interests are in modeling, analysis and performance evaluation of computer communication networks, their protocols, services and interconnection architectures. The CCNR Lab under his leadership has been working on various projects in the traffic control, traffic characterization, switch architecture and traffic engineering issues in both wireless and photonic networks. This has been reported in more than 200 technical papers. Dr. Yang is also interested in queuing theory, simulations, computational algorithms and their applications such as reliability and traffic analysis. Dr. Yang is currently the editor of IEEE Communication Magazine.     

基于两个中继的多跳无线网中的编码协同

本文针对使用两个中继的多跳无线网,提出了一种新的编码协同方案.利用有线的方式,两个距离很近的中继终端被联接后形成一对虚拟天线阵.由于分布式Turbo码被融合到该网中,该方案便于单天线中继与其他中继共享天线,并且以较低硬件实现复杂度提高了系统在准静态衰落中继信道下的性能.     

Implicit hop-by-hop congestion control in wireless multihop networks

It has been shown that TCP and TCP-like congestion control are highly problematic in wireless multihop networks. In this paper we present a novel hop-by-hop congestion control protocol that has been tailored to the specific properties of the shared medium. In the proposed scheme, backpressure towards the source node is established implicitly, by passively observing the medium. A lightweight error detection and correction mechanism guarantees a fast reaction to changing medium conditions and low overhead. Our approach is equally applicable to TCP- and UDP-like data streams. We demonstrate the performance of our approach by an in-depth simulation study. These findings are underlined by testbed results obtained using an implementation of our protocol on real hardware.     

On computing the reliability of opportunistic multihop networks with Mobile relays

Opportunistic multihop networks with mobile relays recently have drawn much attention from researchers across the globe due to their wide applications in various challenging environments. However, because of their peculiar intrinsic features like lack of continuous connectivity, network partitioning, highly dynamic behavior, and long delays, it is very arduous to model and effectively capture the temporal variations of such networks with the help of classical graph models. In this work, we utilize an evolving graph to model the dynamic network and propose a matrix‐based algorithm to generate all minimal path sets between every node pair of such network. We show that these time‐stamped‐minimal‐path sets (TS‐MPS) between each given source‐destination node pair can be used, by utilizing the well‐known Sum‐of‐Disjoint Products technique, to generate various reliability metrics of dynamic networks, ie, two‐terminal reliability of dynamic network and its related metrics, ie, two‐terminal reliabilities of the foremost, shortest, and fastest TS‐MPS, and Expected Hop Count. We also introduce and compute a new network performance metric?Expected Slot Count. We use two illustrative examples of dynamic networks, one of four nodes, and the other of five nodes, to show the salient features of our technique to generate TS‐MPS and reliability metrics.     

基于Ad Hoc无线网的多跳交换算法分析及其仿真结果

论文对基于多跳无线局域网并应用多接入点技术(APs)进行通信的交换性能进行了分析。当一个移动终端不能跟任何接入点进行通信时,它就会用其他移动终端作为终端转发器(TRs)。这种交换标准是建立在绝对和相对信号强度基础上的,其性能指标即平均交换量和平均交换延迟。论文研究了当移动终端和终端转发器均处于移动状态下的交换标准及性能指标之间的联系。多次结果表明当终端转发器移动速度增大时平均交握延迟减小但平均交换量增大。     

Path selection with Nash Q‐learning for remote state estimation over multihop relay network

In this article, the security issue of remote state estimation is investigated for multihop relay networks interrupted by an attacker launching denial‐of‐service attacks. Since the presence of the relay enriches the communication topology, there might exist several paths connecting the sensor and the estimator, consisting of the corresponding channels. Thus, it is reasonable for the sensor to select the path with a lower dropout rate to enhance the system performance measured by the estimation error, due to the dropout rate changing with the channel. However, as an adversary, the objective of the jammer is to deteriorate the corresponding performance through launching attack on the communication path selectively. For addressing the problem on the behalf of both of the sensor and the jammer, we first formulate this problem as a two‐player zero‐sum stochastic game model, and then present a Nash Q‐learning algorithm to explore the equilibrium point for both players, under the assumption that both of them are rational players. Furthermore, the existence of equilibrium point for this problem is proved analytically. Moreover, a more general case of the channel attack, under which the jammer can attack any channels among this network, is considered. Finally, numerical results are presented to verify the effectiveness of the algorithm proposed and the theorem results.