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Wireless Sensor Networks

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  1. Wireless Sensor Networks 巨型机说:“我认为全球大概只需要五台计算机就够了”; PC机说:“每个家庭的桌面上都应该有一台电脑”; Pocket PC说:“太大了,应该每人口袋里放一台”; WSN说:“每粒沙子都应该是一台计算机”。

  2. Outline • General Comments • Wireless Sensor Network Applications • Architecture of WSN • Overview of Sensor Hardware • Characteristic of WSN • Our Work

  3. Outline • General Comments • Wireless Sensor Network Applications • Architecture of WSN • Overview of Sensor Hardware • Characteristic of WSN • Hot Issues • Our Work

  4. Sensor network: A new research hotspot August 2003 Business Week projects "Sensors and Sensor Networks". to be one of 4 Key Technology Waves of the Future 《国家中长期科学和技术发展规划纲要》将传感器网络列为重点研究领域

  5. Moore’s Law “Stuff” (transistors, etc) doubling every 1-2 years Bell’s Law New computing class every 10 years Faster, Smaller, Numerous Streaming Data to/from the Physical World log (people per computer) year Source: The Mote Revolution:Low Power Wireless Sensor Network Devices

  6. What’s are Wireless Sensor Networks • Wireless networks are usually composed of small, low-cost devices that communicate wirelessly and have the capabilities of Processing, Sensing and Storing • The purpose is to measure different physical parameters in a given environment, in order to characterize its properties, or to take decisions depending on these measurements.

  7. Enabling Technologies Embednumerous distributed devices to monitor and interact with physical world Networkdevices tocoordinate and perform higher-level tasks Networked Embedded Exploitcollaborative Sensing, action Control system w/ Small form factor Untethered nodes Sensing Tightly coupled to physical world Exploit spatially and temporally dense, in situ, sensing and actuation

  8. Outline • General Comments • Wireless Sensor Network Applications • Architecture of WSN • Overview of Sensor Hardware • Characteristic of WSN • Hot Issues • OUR WORK

  9. Wireless Sensor Network Applications • Military Applications • Environmental Applications • Health Applications • Home Applications • Industrial Applications • Other Commercial Applications Application <——> WSN

  10. Military Applications • enemy tracking, battlefield surveillance • target detection and classification

  11. An Example:Counter Sniper System Using the arrival times of the acoustic events at different sensor locations, the shooter position can be accurately calculated using the speed of sound and the location of the sensors.

  12. 民用领域 森林防火:节点实时 监测周围温度情况, 并在探测到温度过高 时发出警报。 土壤湿度、温度、成 份监测,节点对土壤 进行周期性采样将数 据发送给远端用户 医疗看护:将传感器 配置在身体上,可以 将身体情况传输给远 端监控中心。GE公司

  13. 科技领域 海洋环境监测 研 究 鸟 类 习 性 • sensors and vehicles are deployed to perform collaborative monitoring tasks over a given area under ocean. • Large number of sensor nodes collect data from the ocean and forward to a master node. 了 解 火 山 习 性

  14. Industrial Applications 立柱上的 传感节点 地面上的 传感节点 无线传感网络原型系统拓扑图: 矿井安全检测和防护系统 From talk of Yunhao Luo

  15. Outline • General Comments • Wireless Sensor Network Applications • Architecture of WSN • Overview of Sensor Hardware • Characteristic of WSN • Hot Issues • OUR WORK

  16. Architecture of WSN • Sensor nodes are scattered in a sensor field(object field) • Sensor nodes can self organize to form a sensor network • Data are collected by these scattered nodes and routed back to the sink in a multi-hop way • The user communicate with the sink via Internet

  17. Architecture of WSN(cont'd) • nodes are still stationary. • multiple, mobile sinks defined as users. • sinks may collect data at any time, any place.

  18. Architecture of WSN(cont'd) 接入网络 无线传感网络 核心网络 From Talk of YunHao Luo

  19. A general work process of WSN Deploy Organize into network Sensing and monitoring Data collection and dissemination

  20. Outline • General Comments • Wireless Sensor Network Applications • Architecture of WSN • Overview of Sensor Hardware • Characteristic of WSN • Hot Issues • OUR WORK

  21. Sensor Hardware • Fundamental Components • Various Sensing,Processing,Storing, Transceiver,Power • Application dependent components • Locating, Mobilizer, Power generator

  22. Sensor Node Samples AWAIRS I UCLA/RSC 1998 Geophone, DS/SS Radio, strongARM, Multi-hop networks LWIM III UCLA, 1996 Geophone, RFM radio, PIC, star network Sensor Mote UCB, 2000 RFM radio, Atmel Medusa, MK-2 UCLA NESL 2002

  23. Mote Evolution Source: The Mote Revolution:Low Power Wireless Sensor Network Devices

  24. Outline • General Comments • Wireless Sensor Network Applications • Architecture of WSN • Overview of Sensor Hardware • Characteristic of WSN • Hot Issues • OUR WORK

  25. Characteristic of WSN • Resource Constraints • battery equipped,recharging the batteries is impossible or unfeasible • Radio and embedded CPU • Self configuring • Randomly deployed, unattended. • Dynamic Topology • Data centric • Different from traditional network • Unique traffic model • Application specific

  26. Power Consumption • Power is of most important and directly influencing the lifetime of WSN • Consumption in three domains: • Sensing, communication and data processing • Energy consumed by Comm. is dominating • The energy cost of transmitting 1Kb a distance of 100 m is approximately the same as that for executing 3 million instructions by a 100 million instructions per second (MIPS)/W processor. k S D Tx/Rc electronics Tx amplifier d

  27. MANET vs WSN: Differences • Low density vs. high density • Address centric (IP) vs. content centric (no IP) • Resource (constraint vs critical) • Mobile vs stationary • First criterion of performance (QoS vs. Power)

  28. Outline • General Comments • Wireless Sensor Network Applications • Architecture of WSN • Overview of Sensor Hardware • Characteristic of WSN • Hot Issues • OUR WORK

  29. Directed Diffusion Communication Protocols A sensor field • MAC Protocol • Fairness vs. Energy • Routing Protocol • Energy-aware routing • Geo-routing • Transport Control Protocol • Congestion Control • Reliability • End-to-end vs. Hop-by-hop Event Sensor sources Sensor sink

  30. Coverage Control Communicating radius • Problem • Given a set of sensors deployed in a target area, we want to determine if the area is sufficiently k-covered, in the sense that every point in the target area is covered by at least k sensors, where k is a predefined constant. • Two Motivations • One of the measurements of the QoS • Energy efficient • Two conflicting objectives: • minimizing the number of active sensors to minimize the energy consumption. • maintaining the coverage. • Two metrics • Connectivity and Coverage Sensing radius

  31. Data and Query Dissemination • Problem • The sensor network is a distributed database. • How to collect or query the interested data detected by some nodes in a energy-efficient way? • Application-specific • Area-based • Attribute-based • Pull vs. Push

  32. Outline • General Comments • Wireless Sensor Network Applications • Architecture of WSN • Overview of Sensor Hardware • Characteristic of WSN • Hot Issues • OUR WORK

  33. 自组织的无源无线Zigbee-WiFi输电线路在线监测自组织的无源无线Zigbee-WiFi输电线路在线监测 • 监测功能 • 图像采集:线下图像、塔架塔基图像、导线及绝缘子图像 • 弧垂和导线温度的采集 • 两级数据传输 • 监测数据和报警信息从采集终端上传到塔架上监测子站采用无线Zigbee技术 • 数据和信息从塔架监测子站接力上传到监控中心(运行值班、变电站)采用无线WiFi技术 • 监控中心的控制命令可以下传 • 监控功能 • 监控中心采集监测数据、存储并进行综合分析处理

  34. 监测平台运行示意图

  35. 两层网络架构 802.11b/g Zigbee

  36. Geographic Routing for Sensor Networks

  37. Motivation • A sensor net consists of hundreds or thousands of nodes • Scalability is the issue • Existing ad hoc net protocols, e.g., DSR, AODV, ZRP, require nodes to cache e2e route information • Dynamic topology changes • Mobility • Reduce caching overhead • Hierarchical routing is usually based on well defined, rarely changing administrative boundaries • Geographic routing • Use location for routing • Assumptions • Every node knows its location • Positioning devices like GPS • Localization • A source can get the location of the destination

  38. Closest to D A Geographic Routing: Greedy Routing S D • Find neighbors who are the closer to the destination • Forward the packet to the neighbor closest to the destination

  39. Greedy Forwarding does NOT always work • If the network is dense enough that each interior node has a neighbor in every 2/3 angular sector, GF will always succeed GF fails

  40. Dealing with Void • Apply the right-hand rule to traverse the edges of a void • Pick the next anticlockwise edge • Traditionally used to get out of a maze

  41. Impact of Sensing Coverage on Greedy Geographic Routing Algorithms Guoliang Xing, Chenyang Lu, Robert Pless, Qingfeng Huang IEEE Trans. Parallel Distributed System

  42. Theorem. • Definition: A network is sensing-covered if any point in the deployment region of the network is covered by at least one node. Rc / Rs >= 2 • In a sensing-covered network, GF can always find a routing path between any two nodes. Furthermore, in each step (other than the last step arriving at the destination), a node can always find a next-hop node that is more than Rc-2Rs closer (in terms of both Euclidean and projected distance) to the destination than itself.

  43. GF always finds a next-hop node • Since Rc >> 2Rs, point a must be outside of the sensing circle of si. • Since a is covered, there must be at least one node, say w, inside the circle C(a, Rs).

  44. Theorem • In a sensing-covered network, GF can always find a routing path between source u and destination v no longer than hops.