1 wireless sensor networks 巨型机说： “...

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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”。

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Outline

• General Comments

• Wireless Sensor Network Applications

• Architecture of WSN

• Overview of Sensor Hardware

• Characteristic of WSN

• Our Work

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Outline






• Hot Issues

• Our Work

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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

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Faster, Smaller, Numerous• Moore’s Law– “Stuff” (transistors,

etc) doubling every 1-2 years

• Bell’s Law– New computing class

every 10 years

year

log

(p

eo

ple

pe

r c

om

pu

ter)

Source: The Mote Revolution:Low Power Wireless Sensor Network Devices

Streaming Data to/from the

Physical World

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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.

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Enabling Technologies

Embedded Networked

Sensing

Control system w/Small form factorUntethered nodes

ExploitcollaborativeSensing, action

Tightly coupled to physical world

Embed numerous distributed devices to monitor and interact with physical world

Network devices to coordinate and perform higher-level tasks

Exploit spatially and temporally dense, in situ, sensing and actuation

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Outline






• Hot Issues

• OUR WORK

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Wireless Sensor Network Applications

• Military Applications

• Environmental Applications

• Health Applications

• Home Applications

• Industrial Applications

• Other Commercial Applications

Application <——> WSN

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

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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.

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民用领域

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

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。

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

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科技领域

了解火山习性

研究鸟类习性

海洋环境监测

• 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.

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Industrial Applications

地面上的

传感节点

立柱上的

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

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Outline






• Hot Issues

• OUR WORK

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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

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Architecture of WSN(cont'd)• nodes are still

stationary.• multiple, mobile

sinks defined as users.

• sinks may collect data at any time, any place.

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无线传感网络无线传感网络无线传感网络无线传感网络接入网络接入网络接入网络接入网络核心网络核心网络核心网络核心网络

Architecture of WSN(cont'd)

From Talk of YunHao Luo

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A general work process of WSN

Deploy Organize into network

Sensing and monitoring Data collection and dissemination

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Outline






• Hot Issues

• OUR WORK

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Sensor Hardware

• Fundamental Components– Various Sensing,Processing,Storing, Transceiver,Power

• Application dependent components – Locating, Mobilizer, Power generator

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Sensor Node SamplesLWIM III

UCLA, 1996

Geophone, RFM

radio, PIC, star

network

AWAIRS I

UCLA/RSC 1998

Geophone, DS/SS

Radio, strongARM,

Multi-hop networks

Sensor Mote

UCB, 2000

RFM radio,

Atmel

Medusa, MK-2

UCLA NESL

2002

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Mote Evolution

Source: The Mote Revolution:Low Power Wireless Sensor Network Devices

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Outline






• Hot Issues

• OUR WORK

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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

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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.

S Dd

kTx/Rc electronics

Tx amplifier

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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)

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Outline






• Hot Issues

• OUR WORK

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Communication Protocols

• 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

Event

Sensor sources

Sensor sink

Directed Diffusion

A sensor field

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Coverage Control

• 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

Communicating radius

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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

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Outline






• Hot Issues

• OUR WORK

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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

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监测平台运行示意图

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两层网络架构

骨干网络

子网子网

采集终端

线路监测子站

变电站

监控中心

图例：

Zigbee

802.11b/g

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Geographic Routing for Sensor Networks

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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

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Geographic Routing: Greedy Routing

S D

Closest to D

A

- Find neighbors who are the closer to the destination- Forward the packet to the neighbor closest to the destination

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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

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Dealing with Void

Apply the right-hand rule to traverse the edges of a voidPick the next anticlockwise edgeTraditionally used to get out of a maze

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Impact of Sensing Coverage on Greedy Geographic Routing Algorithms

Guoliang Xing, Chenyang Lu, Robert Pless, Qingfeng Huang

IEEE Trans. Parallel Distributed System

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Theorem.• Definition: A network is

sensing-covered if any point in the deployment region of the network is covered by at least one node.

•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.

Rc / Rs >= 2

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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).

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Theorem

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

1 wireless sensor networks 巨型机说： “...

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