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Wireless Sensor Networks

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”。. Outline. General Comments Wireless Sensor Network Applications Architecture of WSN Overview of Sensor Hardware Characteristic of WSN OUR WORK. Outline.

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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. Internet Network Model Patch Network Sensor Node Sensor Patch Gateway Transit Network Client Data Browsing and Processing Basestation Base-Remote Link Data Service

  8. 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

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

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

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

  12. 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.

  13. 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

  14. 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

  15. 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

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

  17. 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

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

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

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

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

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

  23. 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

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

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

  26. 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

  27. 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

  28. 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)

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

  30. 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

  31. 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

  32. 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

  33. Time Synchronization • Link to the physical world • When does an event take place? • Key basic service of sensor networks • Fundamental to data fusion • Crucial to the efficient working of other basic services • Localization, Calibration, In-network processing, … • Several protocols require time synchronization • Cryptography, Topology management.

  34. ? ? ? ? ? Time Synchronization • Characteristics of SN • Cheap and Small • No Accurate Oscillator • Limited Energy • Need to Sleep • Work Together • Data Fusion • Conclusion • must initiate T-Sync in WSN

  35. Difficulties in Sensor Networks • No periodic message exchange is guaranteed • There may be no links between two nodes at all • Transmission delay between two nodes is hard to estimate • The link distance changes all the time • Energy is very limited • Nodes sleep most of the time to conserve power • Node need to be small and cheap • No expensive clock circuitry

  36. distance A B T1 T2 T3 T4 h i h j Basic Mechanism • Pair-wise synchronization • T2=T1+delay+offset • T4=T3+delay-offset • offset=((T2-T1)-(T4-T3))/2 • delay=((T2-T1)+(T4-T3))/2

  37. Localization • Critical service • A sensor reading consists of <time, location, measurement> • E.g., target tracking, disaster recovery, fire detection, patient location in a smart hospital, … • Needed for geographic routing • Too expensive for an individual sensor to have a GPS (Global Positioning System) • Reference nodes (called anchor or beacon nodes) + sensor nodes

  38. Range-based localization schemes • TOA (Time of Arrival) • Get range info via signal propagation delay • E.g., GPS • Expensive, power consuming, inaccurate • TDOA (Time Difference of Arrival) • Transmit both radio and ultrasonic signals at the same time to observe the arrival time difference • Extra hardware, i.e., ultrasonic channel, is required • Not only radio but also sound signals have multipath effects affected by humidity, temperature, …

  39. Range-based localization schemes • Received signal strength (RSS) • Distance estimation based on RSS • Hard due to radio signal vagaries • AoA (Angle of Arrival) • A node estimates the relative angles between neighbors • Requires directional antennae

  40. Range-free localization • Centroid algorithm • Anchors beacon their positions to neighbors (single hop broadcast) • A sensor node computes the centroid using all received beacon messages

  41. DV-HOP • Anchor locations are flooded through the network • Keep the running hop count • Estimate average one hop distance • Amorphous Positioning • Similar to DV-HOP • Use offline one hop distance estimation

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

  43. 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

  44. 监测平台运行示意图

  45. 两层网络架构 802.11b/g Zigbee

  46. 能源紧缺、环境污染 电荒、煤荒、油价上涨

  47. 新能源 • 电能是与我们严密不可分开的能源，还存在着很大的节能空间。 积少成多 • 同时，产生电能需要释放大量二氧化碳，造成环境污染。如果一个煤燃料的发电能力为44M瓦的发电厂，使用后会释放15吨二氧化碳。

  48. 细粒度计量： 节能的第一步 • 有报告称，72%的电能都消耗在家庭和商业建筑方面，其中30%的电能被浪费了。 • 研究表明，实时细粒度电器耗能反馈将能改变用户行为，使用电量降低10%到20%。 • 然而，当前的电表计量方式 为人们节能提供信息很少。

  49. 细粒度能耗计量无线传感器网络 • 目的 • 以可视化的方法实现每个电器任意时段的能耗 • 为实现节能减排提供基础 • 目前系统已稳定工作，并投入到与能耗相关的科研工作中。

  50. 细粒度能耗计量无线传感器网络

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