传感网原理及应用chapter1-yyb

1、Principles and Practical Application of Wireless Sensor Networks传感网原理及应用Your Lecturer/MentorLecturer： Name：Yanbing Yang （杨彦兵） Email: .sg Tel: Research Interest： Internet of Things，Wireless Sensor Networks, Visible Light Communication and Sensing. Video DemoVideo DemoVideo DemoCourse R

2、esourcesText book: English version：Fundamentals of Wireless Sensor Networks: Theory and PracticeWaltenegus Dargie, Christian Poellabauer. Chinese Version：德 Waltenegus Dargie 美 Christian Poellabauer 著；孙利民译，无线传感网网络基础：理论与实践，清华大学出版社.Others: ACM Sensys: ACM : Course Description Highlights 1Syllabus:Motiv

3、ation for a Network of Wireless Sensor NodesApplicationsNode ArchitectureOperating SystemsPHY Layer Medium Access ControlNetwork LayerPower ManagementTime SynchronizationLocalizationSecuritySensor Network ProgrammingCourse Description Highlights 2Teaching Method: Lectures mainly using PPT slides.Hom

4、ework & experiments.Grading:Homework & attendance & presentation: 32%Experiments or course project： 20% Final： 48%Answers to FAQCourse material focuses on concepts rather than technologies. There are no make ups for missed homework or final exam under any circumstance. So do not be absent.Exams will

5、 be closed notes and books and they will be time-limited.Course material is NOT all from the text book. Answers to FAQFocus of exam and homework will be on conceptual understanding, and problem-solving skill.ALL homework will be counted.Every student HAS TO attend the class he/she registered in. Ple

6、ase DO NOT ASK for changing classes internally.Attendance is mandatory. If you are absent for 8 classes or more then you will be banned form the final exam.Chapter 1: Motivation for a Network of Wireless Sensor NodesChapter 1: RoadmapDefinitions and backgroundChallenges and constraintsOverview of to

7、pics covered Sensing and SensorsSensing: technique to gather information about physical objects or areas.Sensor (transducer): object performing a sensing task; converting one form of energy in the physical world into electrical energy.Examples of sensors from biology: the human bodyeyes: capture opt

8、ical information (light).ears: capture acoustic information (sound).nose: captures olfactory information (smell).skin: captures tactile information (shape, texture).Sensing (Data Acquisition)Sensors capture phenomena in the physical world.Signal conditioning prepare captured signals for further use

9、(amplification, attenuation, filtering of unwanted frequencies, etc.).Analog-to-digital conversion (ADC) translates analog signal into digital signal.Digital signal is processed and output is often given (via digital-analog converter and signal conditioner) to an actuator (device able to control the

10、 physical world).Sensor ClassificationsPhysical property to be monitored determines type of required sensorTypeExamplesTemperatureThermistors, thermocouplesPressurePressure gauges, barometers, ionization gaugesOpticalPhotodiodes, phototransistors, infrared sensors, CCD sensorsAcousticPiezoelectric r

11、esonators, microphonesMechanicalStrain gauges, tactile sensors, capacitive diaphragms, piezoresistive cellsMotion, vibrationAccelerometers, mass air flow sensorsPositionGPS, ultrasound-based sensors, infrared-based sensors, inclinometersElectromagneticHall-effect sensors, magnetometersChemicalpH sen

12、sors, electrochemical sensors, infrared gas sensorsHumidityCapacitive and resistive sensors, hygrometers, MEMS-based humidity sensorsRadiationIonization detectors, Geiger-Mueller countersOther ClassificationsPower supply:active sensors require external power, i.e., they emit energy (microwaves, ligh

13、t, ultrasonic/sound) to trigger response or detect change in energy of transmitted signal (e.g., electromagnetic proximity sensor).passive sensors detect energy in the environment and derive their power from this energy input (e.g., passive infrared sensor).Other ClassificationsElectrical phenomenon

14、:resistive sensors use changes in electrical resistivity () based on physical properties such as temperature (R = *l/A).capacitive sensors use changes in capacitor dimensions or permittivity () based on physical properties (C = *A/d).inductive sensors rely on the principle of inductance (electromagn

15、etic force is induced by fluctuating current).piezoelectric sensors rely on materials (crystals, ceramics) that generate a displacement of charges in response to mechanical deformation.Example: Wheatstone Bridge CircuitR1, R2, and R3 known (R2 adjustable)Rx is unknownWireless Sensor Network (WSN)Mul

16、tiple sensors (often hundreds or thousands) form a network to cooperatively monitor large or complex physical environments. GreenOrbs： Acquired information is wirelessly communicated to a base station (BS), which propagates the information to remote devices for storage, analysis, and processing.Hist

17、ory of Wireless Sensor NetworksDARPA: Distributed Sensor Nets Workshop (1978).Distributed Sensor Networks (DSN) program (early 1980s).Sensor Information Technology (SensIT) program.UCLA and Rockwell Science CenterWireless Integrated Network Sensors (WINS).Low Power Wireless Integrated Microsensor (L

18、WIM) (1996).UC-BerkeleySmart Dust project (1999).concept of “motes”: extremely small sensor nodes.Berkeley Wireless Research Center (BWRC).PicoRadio project (2000).MITAMPS (micro-Adaptive Multidomain Power-aware Sensors) (2005).History of Wireless Sensor NetworksRecent commercial effortsCrossbow ( )

19、Sensoria ( )Worldsens (worldsens.citi.insa-lyon.fr)Dust Networks ( )Ember Corporation ( )WSN CommunicationCharacteristics of typical WSN:low data rates (comparable to dial-up modems)energy-constrained sensorsIEEE 802.11 family of standardsmost widely used WLAN protocols for wireless communications i

20、n generalcan be found in early sensor networks or sensors networks without stringent energy constraintsIEEE 802.15.4 is an example for a protocol that has been designed specifically for short-range communications in WSNslow data rateslow power consumptionwidely used in academic and commercial WSN so

21、lutionsSingle-Hop versus Multi-HopStar topology:every sensor communicates directly (single-hop) with the base station.may require large transmit powers and may be infeasible in large geographic areas.Mesh topologysensors serve as relays (forwarders) for other sensor nodes (multi-hop).may reduce powe

22、r consumption and allows for larger roduces the problem of routing.Challenges in WSNs: EnergySensors typically powered through batteriesreplace battery when depleted.recharge battery, e.g., using solar power.discard sensor node when battery depleted.For batteries that cannot be recharged

23、, sensor node should be able to operate during its entire mission time or until battery can be replaced.Energy efficiency is affected by various aspects of sensor node/network design.Physical layer:switching and leakage energy of CMOS-based processors.Challenges in WSNs: EnergyMedium access control

24、layer:contention-based strategies lead to energy-costly collisionsproblem of idle listeningNetwork layer:responsible for finding energy-efficient routesOperating system:small memory footprint and efficient task switchingSecurity:fast and simple algorithms for encryption, authentication, etc.Middlewa

25、re:in-network processing of sensor data can eliminate redundant data or aggregate sensor readingsChallenges in WSNs: Self-ManagementAd-hoc deploymentmany sensor networks are deployed “without design”sensors dropped from airplanes (battlefield assessment).sensors placed wherever currently needed (tra

26、cking patients in disaster zone).moving sensors (robot teams exploring unknown terrain).sensor node must have some or all of the following abilitiesdetermine its location.determine identity of neighboring nodes.configure node parameters.discover route(s) to base station.initiate sensing responsibili

27、ty.Challenges in WSNs: Self-ManagementUnattended operationonce deployed, WSN must operate without human interventiondevice adapts to changes in topology, density, and traffic loaddevice adapts in response to failuresOther terminologyself-organization is the ability to adapt configuration parameters

28、based on system and environmental stateself-optimization is the ability to monitor and optimize the use of the limited system resourcesself-protection is the ability recognize and protect from intrusions and attacksself-healing is the ability to discover, identify, and react to network disruptionsCh

29、allenges in WSNs: Wireless NetworksWireless communication faces a variety of challengesAttenuation:limits radio rangeMulti-hop communication:increased latencyincreased failure/error probabilitycomplicated by use of duty cyclesChallenges in WSNs: DecentralizationCentralized management (e.g., at the b

30、ase station) of the network often not feasible to due large scale of network and energy constraints.Therefore, decentralized (or distributed) solutions often preferred, though they may perform worse than their centralized counterparts.Example: routingCentralized: BS collects information from all sen

31、sor nodesBS establishes “optimal” routes (e.g., in terms of energy)BS informs all sensor nodes of routescan be expensive, especially when the topology changes frequentlyCloud Computing? Challenges in WSNs: DecentralizationDecentralized:each sensors makes routing decisions based on limited local info

32、rmationroutes may be nonoptimal, but route establishment/management can be much cheaperEdge Computing? Challenges in WSNs: Design ConstraintsMany hardware and software limitations affect the overall system designExamples include:Low processing speeds (to save energy)Low storage capacities (to allow

33、for small form factor and to save energy)Lack of I/O components such as GPS receivers (reduce cost, size, energy)Lack of software features such as multi-threading (reduce software complexity)Challenges in WSNs: SecuritySensor networks often monitor critical infrastructure or carry sensitive informat

34、ion, making them desirable targets for attacksAttacks may be facilitated by:remote and unattended operationwireless communicationlack of advanced security features due to cost, form factor, or energyConventional security techniques often not feasible due to their computational, communication, and st

35、orage requirementsAs a consequence, sensor networks require new solutions for intrusion detection, encryption, key establishment and distribution, node authentication, and secrecyComparisonTraditional NetworksWireless Sensor NetworksGeneral-purpose design; serving many applicationsSingle-purpose des

36、ign; serving one specific applicationTypical primary design concerns are network performance and latencies; energy is not a primary concernEnergy is the main constraint in the design of all node and network componentsNetworks are designed and engineered according to plansDeployment, network structur

37、e, and resource use are often ad-hoc (without planning)Devices and networks operate in controlled and mild environmentsSensor networks often operate in environments with harsh conditionsMaintenance and repair are common and networks are typically easy to accessPhysical access to sensor nodes is often difficult or even impossibleComponent failure is addressed through maintenance and repairComponent failure is expected and addressed in the design of the