Forming optimal topologies for Bluetooth-based wireless personal area networks

In this paper, we address the problem of determining an optimal topology for Bluetooth wireless personal area networks (BT-WPANs). In BT-WPANs, multiple communication channels are available, through a frequency hopping technique. The way network nodes are grouped to share the same channel, and which nodes are selected to bridge traffic from a channel to another, has a significant impact on the capacity and throughput of the system, as well as the nodes' battery lifetime. The determination of an optimal topology is thus extremely important. Our approach is based on a min-max formulation of the optimization problem, which produces topologies that minimize the traffic load of the most congested node in the network (thus also minimizing energy consumption) while meeting the traffic requirements and the constraints posed by the BT-WPAN technology. We investigate the performance of the topologies produced by our optimization approach as the system requirements vary, and evaluate the trade-offs existing between system complexity and network efficiency. Results show that a topology optimized for some traffic requirements is remarkably robust to changes in the traffic pattern. Due to the problem complexity, the optimal solution is attained in a centralized manner. Although this implies severe limitations, a centralized solution can be applied whenever a network coordinator is elected, and provides a useful term of comparison for any distributed heuristics.     

QoS issues in ad hoc wireless networks

Ad hoc wireless networks consist of mobile nodes interconnected by multihop communication paths. Unlike conventional wireless networks, ad hoc networks have no fixed network infrastructure or administrative support. The topology of the network changes dynamically as mobile nodes join or depart the network or radio links between nodes become unusable. This article addresses some of the quality of service issues for ad hoc networks which have started to receive increasing attention in the literature. The focus is on QoS routing. This is a complex and difficult issue because of the dynamic nature of the network topology and generally imprecise network state information. We present the basic concepts and discuss some of the results. The article concludes with some observations on the open areas for further investigation     

Minimum latency joint scheduling and routing in wireless sensor networks

Wireless sensor networks are expected to be used in a wide range of applications from environment monitoring to event detection. The key challenge is to provide energy efficient communication; however, latency remains an important concern for many applications that require fast response. In this paper, we address the important problem of minimizing average communication latency for the active flows while providing energy-efficiency in wireless sensor networks. As the flows in some wireless sensor network can be long-lived and predictable, it is possible to design schedules for sensor nodes so that nodes can wake up only when it is necessary and asleep during other times. Clearly, the routing layer decision is closely coupled to the wakeup/sleep schedule of the sensor nodes. We formulate a joint scheduling and routing problem with the objective of finding the schedules and routes for current active flows with minimum average latency. By constructing a novel delay graph, the problem can be solved optimally by employing the M node-disjoint paths algorithm under FDMA channel model. We further present extensions of the algorithm to handle dynamic traffic changes and topology changes in wireless sensor networks.     

Virtual Topology Design and Reconfiguration of Virtual Private Networks (VPNs) over All-Optical WDM Networks

This paper studies the virtual topology design and reconfiguration problem of virtual private networks (VPNs) over all-optical WDM networks. To support VPN service, a set of lightpaths must be established over the underlying WDM network to meet the VPN traffic demands and this set of lightpaths must also be dynamically reconfigurable in response to changing VPN traffic. To achieve good network performance and meet the service requirements of optical virtual private networks (oVPNs), we formulate the problem as an integer programming problem with multi-objectives and present a general formulation of the problem. In the formulation, we take into account the average propagation delay over a lightpath, the maximum link load, and the reconfiguration cost with objectives to minimize the three metrics simultaneously. The formulated problem is NP-hard and is therefore not practical to have exact solutions. For this reason, we use heuristics to obtain approximate optimal solutions and propose a balanced alternate routing algorithm (BARA) based on a genetic algorithm. To make the problem computationally tractable, we approximately divide BARA into two independent stages: route computing and path routing. At the route computing stage, a set of alternate routes is computed for each pair of source and destination nodes in the physical topology. At the path routing stage, an optimal route is decided from a set of alternative routes for each of the lightpaths between a pair of source and destination nodes. A decision is subject to the constraints and objectives in the formulation. To improve the computational efficiency, we use a genetic algorithm in BARA. Through simulation experiments, we show the effectiveness of BARA and the evolution process of the best solution in a population of solutions produced by the genetic algorithm. We also investigate the impact of the number of alternative routes between each pair of source and destination nodes on the optimized solutions.     

Group key management scheme for large-scale sensor networks

Wireless sensor networks are inherently collaborative environments in which sensor nodes self-organize and operate in groups that typically are dynamic and mission-driven. Secure communications in wireless sensor networks under this collaborative model calls for efficient group key management. However, providing key management services in wireless sensor networks is complicated by their ad-hoc nature, intermittent connectivity, large scale, and resource limitations. To address these issues, this paper proposes a new energy-efficient key management scheme for networks consisting of a large number of commodity sensor nodes that are randomly deployed. All sensor nodes in the network are anonymous and are preloaded with identical state information. The proposed scheme leverages a location-based virtual network infrastructure and is built upon a combinatorial formulation of the group key management problem. Secure and efficient group key initialization is achieved in the proposed scheme by nodes autonomously computing, without any communications, their respective initial group keys. The key server, in turn, uses a simple location-based hash function to autonomously deduce the mapping of the nodes to their group keys. The scheme enables dynamic setup and management of arbitrary secure group structures with dynamic group membership.     

基于拓扑重构的水下移动无线传感器网络拓扑优化

针对水下移动无线传感器网络（MUWSN, mobile underwater wireless sensor networks）拓扑随洋流动态演化对其网络性能会产生很大影响,提出了一种基于拓扑重构的水下移动无线传感器网络拓扑优化方法,首先通过模拟鱼群行为对传感器节点位置进行调整,优化网络覆盖度;其次,利用冗余节点修复网络中不连通位置,消除关键节点,优化网络连通性,最后,通过仿真对比实验验证了该方法的合理性和有效性。实验结果表明,所提算法能在较低能耗下,保证网络覆盖度长期维持在97%左右,连通率达到89%以上。     

Genetic Algorithms With Immigrants and Memory Schemes for Dynamic Shortest Path Routing Problems in Mobile Ad Hoc Networks

In recent years, the static shortest path (SP) problem has been well addressed using intelligent optimization techniques, e.g., artificial neural networks, genetic algorithms (GAs), particle swarm optimization, etc. However, with the advancement in wireless communications, more and more mobile wireless networks appear, e.g., mobile networks [mobile ad hoc networks (MANETs)], wireless sensor networks, etc. One of the most important characteristics in mobile wireless networks is the topology dynamics, i.e., the network topology changes over time due to energy conservation or node mobility. Therefore, the SP routing problem in MANETs turns out to be a dynamic optimization problem. In this paper, we propose to use GAs with immigrants and memory schemes to solve the dynamic SP routing problem in MANETs. We consider MANETs as target systems because they represent new-generation wireless networks. The experimental results show that these immigrants and memory-based GAs can quickly adapt to environmental changes (i.e., the network topology changes) and produce high-quality solutions after each change.      

Automatic and dynamic network establishment for linear WSNs

The deployment of wireless sensor networks (WSNs) in the mostly linear large structures, such as rivers, pipelines, etc, suffers from being the worst case for classical addressing schemes, e.g. distributed address assignment mechanism (DAAM) or stochastic addressing for Zigbee. Using DAAM for physical topologies composed of long lines of nodes connected together wastes addresses and generates orphan nodes. We show in this paper the inherent limitations of classical (DAAM, stochastic) and specialized (usually cluster-orientated) addressing schemes for Linear WSNs. DiscoProto, is an addressing and routing scheme which builds a logical network corresponding to a corresponding physical linear network without any knowledge of physical topology. In this paper, we show thanks to a realistic simulation using Castalia (Omnet based simulator) that DiscoProto avoids waste of addresses and allows a high association ratio. We also propose a dynamic version of our protocol called Dynamic DiscoProto in the second part of the paper. Dynamic DiscoProto allows to add new nodes or new branches in an existing linear network.

     

Traffic grooming in an optical WDM mesh network

In wavelength-division multiplexing (WDM) optical networks, the bandwidth request of a traffic stream can be much lower than the capacity of a lightpath. Efficiently grooming low-speed connections onto high-capacity lightpaths will improve the network throughput and reduce the network cost. In WDM/SONET ring networks, it has been shown in the optical network literature that by carefully grooming the low-speed connection and using wavelength-division multiplexer (OADM) to perform the optical bypass at intermediate nodes, electronic ADMs can be saved and network cost will be reduced. In this study, we investigate the traffic-grooming problem in a WDM-based optical mesh topology network. Our objective is to improve the network throughput. We study the node architecture for a WDM mesh network with traffic-grooming capability. A mathematical formulation of the traffic-grooming problem is presented in this study and several fast heuristics are also proposed and evaluated     

可充电无线传感器网络动态拓扑问题研究

在可充电无线传感器网络中的能量补给设备兼任数据采集设备的情况下,提出了可充电无线传感器网络时变动态拓扑模型,并在此基础上根据最大化能量补给设备驻站时间比为目标提出了最优化问题。通过分析不同时刻不同传感器节点和无线能量补给/数据采集设备的工作情况及需要遵循的约束条件,得到与原问题具有等优性的多状态线性规划问题。求解该优化问题,获得可充电无线传感器网络动态拓扑下的周期动态路由和无线能量补给/数据采集设备的工作策略。与之前的研究成果相比,优化目标值均有20%以上的提升。     

Performance and testbed study of topology reconfiguration in IP over optical networks

With the widespread deployment of Internet protocol/wavelength division multiplexing (IP/WDM) networks, it becomes necessary to develop traffic engineering (TE) solutions that can effectively exploit WDM reconfigurability. More importantly, experimental work on reconfiguring lightpath topology over testbed IP/WDM networks is needed urgently to push the technology forward to operational networks. This paper presents a performance and testbed study of topology reconfiguration for IP/WDM networks. IP/WDM TE can be fulfilled in two fashions, overlay vs. integrated, which drives the network control software, e.g., routing and signaling protocols, and selects the corresponding network architecture model, e.g., overlay or peer-to-peer. We present a traffic management framework for IP over reconfigurable WDM networks. Three "one-hop traffic maximization"-oriented heuristic algorithms for lightpath topology design are introduced. A reconfiguration migration algorithm to minimize network impact is presented. To verify the performance of the topology design algorithms, we have conducted extensive simulation study. The simulation results show that the topologies designed by the reconfiguration algorithms outperform the fixed topology with throughput gain as well as average hop-distance reduction. We describe the testbed network and software architecture developed in the Defense Advanced Research Projects Agency (DARPA) Next Generation Internet (NGI) SuperNet Network Control and Management project and report the TE experiments conducted over the testbed.     

无线传感器网络多业务仿真平台的实现方案

在无线传感器网络中,由于传感器节点的能源十分有限,节能是设计的首要因素。然而,无线传感器网络的多业务在现实生活应用中对QoS(服务质量)都有不同的需求,这就使得WSN网络的QoS研究成为了专家学者们的主要研究方向。在WSN网络拓扑结构和业务类型的研究基础上,使用网络模拟器(Network Simulator Version 2,NS2)来搭建基于多业务共存的星型以及对等结构两种WSN网络仿真平台,建立多种业务流量模型,实现以无线传感器网络协议、流量模型、拓扑为基础的功能模块化设计;并对无线传感器网络关键性能进行了仿真模拟,实现延时、吞吐量、能耗等关键性能的分析。     

IMECN：一种新的无线传感器网络拓扑控制算法

 拓扑控制策略对减小无线传感器网络中节点的能量消耗,延长网络的生命期具有重要意义. 在已有的拓扑控制算法中,有代表性的是SMECN.本文在分析SMECN拓扑控制算法的缺点的基 础上,提出了一种新的拓扑控制算法—IMECN.IMECN利用极坐标中的极角,巧妙地将区域覆盖问题转化为角度叠加问题,通过判断多个圆心角的叠加和是否等于2π传输范围是否覆盖其直接传输区域.最后,我们理论分析了IMECN的计算复杂度,仿真分析了IMECN的节能特性.     

ad hoc网络组播对于DoS攻击畦抵抗策略分析

与固定有线网络相比,无线ad hoc网络动态的拓扑结构、脆弱的无线信道、网络有限的通信带宽以及节点兼备主机和路由功能等特点,使得网络容易遭受拒绝服务（DOS）攻击。文章针对ad hoc网络的组播应用在抵御DoS攻击方面的不足,提出外部和内部两种组播DoS泛洪攻击模型,同时针对ad hoc网络组播组内的攻击提出相应的两种抵抗策略和具体实现步骤。     

无线传感器网络拓扑结构研究

随着处理技术、存储技术以及无线传输技术的不断发展,由体积小、重量轻、价格低的无线传感器节点所组成的传感器网络已经充分具备了感知客观事物及自然现象,随时随地为用户提供精确信息的能力。通过对于星状网、网状网和混合网等几种常用传感器网络拓扑结构的比较,以及针对这些拓扑结构所形成的网络寿命的仿真,说明了对于常用的基站距离远、节点密度大的传感器网络,分层式的拓扑结构能够大大的节省网络能量,延长网络寿命,改善网络性能。     

Generalized Survivable Network

Two important requirements for future backbone networks are full survivability against link failures and dynamic bandwidth provisioning. We demonstrate how these two requirements can be met by introducing a new survivable network concept called the generalized survivable network (GSN), which has the special property that it remains survivable no matter how traffic is provisioned dynamically, as long as the input and output constraints at the nodes are fixed. A rigorous mathematical framework for designing the GSN is presented. In particular, we focus on the GSN capacity planning problem, which finds the edge capacities for a given physical network topology with the input/output constraints at the nodes. We employ fixed single-path routing which leads to wide-sense nonblocking GSNs. We show how the initial, infeasible formal mixed integer linear programming formulation can be transformed into a more feasible problem using the duality transformation. A procedure for finding the realizable lower bound for the cost is also presented. A two-phase approach is proposed for solving the GSNCPP. We have carried out numerical computations for ten networks with different topologies and found that the cost of a GSN is only a fraction (from 39% to 97%) more than the average cost of a static survivable network. The framework is applicable to survivable network planning for ASTN/ASON, VPN, and IP networks as well as bandwidth-on-demand resource allocation.     

System lifetime optimization for heterogeneous sensor networks with a hub-spoke technology

As a specific area of sensor networks, wireless in-home sensor networks differ from general sensor networks in that the network has nodes with heterogeneous resources and dissimilar mobility attributes. For example, sensor with different radio coverage, energy capacity, and processing capabilities are deployed, and some of the sensors are mobile and others are fixed in position. The architecture and routing protocol for this type of heterogeneous sensor networks must be based on the resources and characteristics of their member nodes. In addition, the sole stress on energy efficiency for performance measurement is not sufficient. System lifetime is more important in this case. We propose a hub-spoke network topology that is adaptively formed according to the resources of its members. A protocol named resource oriented protocol (ROP) was developed to build the network topology. This protocol principally divides the network operation into two phases. In the topology formation phase, nodes report their available resource characteristics, based on which network architecture is optimally built. We stress that due to the existence of nodes with limitless resources, a top-down appointment process can build the architecture with minimum resource consumption of ordinary nodes. In the topology update phase, mobile sensors and isolated sensors are accepted into the network with an optimal balance of resources. To avoid overhead of periodic route updates, we use a reactive strategy to maintain route cache. Simulation results show that the hub-spoke topology built by ROP can achieve much longer system lifetime.     

Effect of Selfish Node Behavior on Efficient Topology Design

The problem of topology control is to assign per-node transmission power such that the resulting topology is energy-efficient and satisfies certain global properties such as connectivity. The conventional approach to achieve these objectives is based on the fundamental assumption that nodes are socially responsible. We examine the following question: if nodes behave in a selfish manner, how does it impact the overall connectivity and energy consumption in the resulting topologies? We pose the above problem as a non-cooperative game and use game-theoretic analysis to address it. We study Nash equilibrium properties of the topology control game and evaluate the efficiency of the induced topology when nodes employ a greedy best response algorithm. We show that even when the nodes have complete information about the network, the steady state topologies are suboptimal. We propose a modified algorithm based on a better response dynamic and show that this algorithm is guaranteed to converge to energy-efficient and connected topologies. Moreover, the node transmit power levels are more evenly distributed and the network performance is comparable to that obtained from centralized algorithms.     

An integrated cross-layer study of wireless CDMA sensor networks

In this paper, we characterize analytically the multiaccess interference in wireless code-division multiple-access sensor networks with uniformly random distributed nodes and study the tradeoff between interference and connectivity. To provide a guideline for improving system behavior, three competitive deterministic topologies are evaluated along with the random topology in terms of link-level and network-level (routing) performance. The impact of signature code length and receiver design on the network performance for different topologies is also studied.     

Density‐adaptive network reprogramming protocol for wireless sensor networks

Network reprogramming is a process used to update program codes of sensor nodes that are already deployed. To deal with potentially unstable link conditions of wireless sensor networks, the epidemic approach based on 3‐way advertise‐request‐data handshaking is preferred for network reprogramming. Existing epidemic protocols, however, require a long completion period and high traffic overhead in high‐density networks, mainly due to the hidden terminal problem. In this paper, we address this problem by dynamically adjusting the frequency of advertisement messages in terms of the density of sensor nodes, which is the number of sensor nodes in a certain area. We compare the performance of the proposed scheme, called DANP (Density‐Adaptive Network Reprogramming Protocol), with a well‐known epidemic protocol, Deluge. Simulations indicate that, in the grid topologies, DANP outperforms Deluge by about 30% in terms of the completion time and about 50% in terms of the traffic overhead. Significant performance gain is observed in random topologies as well. The performance of DANP is further confirmed via measurements in an experimental test bed. Copyright © 2009 John Wiley & Sons, Ltd.