Wireless Sensor Wireless Sensor NetworksNetworks

- overview -- overview -

Wireless Sensor Wireless Sensor NetworksNetworks

IntroductionIntroduction TerminologyTerminology ApplicationsApplications Technical ChallengesTechnical Challenges Examples Examples ConclusionConclusion

IntroductionIntroduction

A Wireless sensor network (WSN) is a network A Wireless sensor network (WSN) is a network that is formed when a set of small sensor devices that is formed when a set of small sensor devices that are deployed in an ad hoc fashion cooperate that are deployed in an ad hoc fashion cooperate for sensing a physical phenomenon.for sensing a physical phenomenon.

Wireless Sensor Network consists of base Wireless Sensor Network consists of base stations and a number of wireless sensors.stations and a number of wireless sensors.

Wireless Sensor NetworkWireless Sensor Network

IntroductionIntroduction-basic features--basic features-

Self-organizing capabilitiesSelf-organizing capabilities Short-range broadcast Short-range broadcast

communication and multihop routingcommunication and multihop routing Dense deployment and cooperative Dense deployment and cooperative

effort of sensor nodeseffort of sensor nodes Frequently changing topology due to Frequently changing topology due to

fading and node failurefading and node failure Limitation in energy, transmit power, Limitation in energy, transmit power,

memory, and computing powermemory, and computing power

TerminologyTerminology

Sensor: The deviceSensor: The device Observer: The end user/computerObserver: The end user/computer Phenomenon: The entity of interest Phenomenon: The entity of interest

to the observerto the observer

ApplicationsApplications

General engineeringGeneral engineering AgriAgriculture and enivronmental culture and enivronmental

monitoringmonitoring Civil engineeringCivil engineering MMilitary applicationsilitary applications HHealth monitoring and surgeryealth monitoring and surgery

ApplicationsApplications -general engineering--general engineering-

AAutomotive telematics (cars networked)utomotive telematics (cars networked) FFingertip accelerometer virtual keybordsingertip accelerometer virtual keybords SSensing and maintenance in industrial plantsensing and maintenance in industrial plants AAircraft drag reductionircraft drag reduction SSmart office spacesmart office spaces TTracking of goods in retail storesracking of goods in retail stores TTracking of containers and boxesracking of containers and boxes SSocial studies (human interaction and social ocial studies (human interaction and social

behavior)behavior) CCommercial and residential securityommercial and residential security

ApplicationsApplications -agr-agriculture and iculture and eenvironmental nvironmental

mmonitoringonitoring-- PPrecision agriculture (crop and livestock recision agriculture (crop and livestock

management)management) PPlanetary exploration (inhospitable lanetary exploration (inhospitable

environments)environments) GGeophysical monitoring (seismic activity)eophysical monitoring (seismic activity) MMonitoring of freshwater qualityonitoring of freshwater quality Zebranet Zebranet project project HHabitat monitoringabitat monitoring DDisaster detection (forest fires and floods)isaster detection (forest fires and floods) CContaminant transportontaminant transport

Applications Applications -c-civil ivil eenginneeringnginneering--

MMonitoring of structuresonitoring of structures UUrban planing (groundwater rban planing (groundwater

paterns, percent of COpaterns, percent of CO2 2 cities are cities are expelling,...)expelling,...)

DDisaster recovery (locating signs of isaster recovery (locating signs of life after earthquake)life after earthquake)

Applications Applications -m-military ilitary aapplicationspplications--

AAsset monitoring and managementsset monitoring and management SSurveillance and battle-space urveillance and battle-space

monitoringmonitoring UUrban warfare (sensors in buildings, rban warfare (sensors in buildings,

movement of friend and foe, movement of friend and foe, localizing snipers,...)localizing snipers,...)

PProtection (for sensitive objects)rotection (for sensitive objects) SSelf-healing minefieldself-healing minefields

Applications Applications -h-health ealth mmonitoring and onitoring and ssurgeryurgery--

MMedical sensing (physiological data edical sensing (physiological data transmitted to a computer otransmitted to a computer or r physician, wireless sensing physician, wireless sensing bandages worn of infection, sensors bandages worn of infection, sensors in the blood stream which prevent in the blood stream which prevent coagulation and thrombosis)coagulation and thrombosis)

MMicro-surgery (swarm of MEMS-icro-surgery (swarm of MEMS-based robots)based robots)

Technical challengesTechnical challenges-performance metrics--performance metrics-

Energy efficiency/System LifetimeEnergy efficiency/System Lifetime LatencyLatency AccuracyAccuracy Fault toleranceFault tolerance ScalabilityScalability Transport capacity/throughput Transport capacity/throughput Production costsProduction costs Sensor network topologySensor network topology Transmission mediaTransmission media Power supply Power supply Communication architectureCommunication architecture Security Security

Technical challengesTechnical challenges-sensor network topology--sensor network topology-

Hundreds of nodes require careful handling Hundreds of nodes require careful handling of topology maintenance.of topology maintenance.

Predeployment and deployment phasePredeployment and deployment phase Numerous ways to deploy the sensors (mass, Numerous ways to deploy the sensors (mass,

individual placement, dropping from plane..)individual placement, dropping from plane..) Postdeployment phasePostdeployment phase

Factors are sensor nodes’ position change, Factors are sensor nodes’ position change, reachability due to jamming, noise, obstacles reachability due to jamming, noise, obstacles etc, available energy, malfunctioningetc, available energy, malfunctioning

Redeployment of additional nodes phaseRedeployment of additional nodes phase Redeployment because of malfunctioning of Redeployment because of malfunctioning of

unitsunits

Technical challengesTechnical challenges- transmission media -- transmission media -

In a Multihop sensor network nodes are linked In a Multihop sensor network nodes are linked by Wireless mediumby Wireless medium Radio Frequency (RF)Radio Frequency (RF)

Most of the current sensor node HW is based on itMost of the current sensor node HW is based on it Do not need Line of Sight Do not need Line of Sight Can hide these sensorsCan hide these sensors

Infrared (IR)Infrared (IR) License freeLicense free Robust to interferenceRobust to interference Cheaper and easier to buildCheaper and easier to build Require line of sightRequire line of sight Short Range SolutionShort Range Solution

Optical mediaOptical media Require Line of sightRequire Line of sight

Technical challengesTechnical challenges-power supply--power supply-

PowerPower supply usually the limiting supply usually the limiting factor in terms of size and cost and factor in terms of size and cost and life timelife time

Power sources can be classified asPower sources can be classified as Energy Reservoir (Energy storage in Energy Reservoir (Energy storage in

form of chemical energy; batteries)form of chemical energy; batteries) Power Distribution methodsPower Distribution methods Power Scavenging methodsPower Scavenging methods

Technical challengesTechnical challenges-power supply (contd.)--power supply (contd.)-

Power distributionPower distribution Distribution of power to nodes from a Distribution of power to nodes from a

nearby energy rich sourcenearby energy rich source Wires (defeats purpose of wireless Wires (defeats purpose of wireless

communication)communication) Acoustic waves (very low power level)Acoustic waves (very low power level) Light or lasers (Directed laser beams to Light or lasers (Directed laser beams to

large number of nodes very complicated )large number of nodes very complicated ) Electromagnetic (RF) power Electromagnetic (RF) power

distributiondistribution Example: Example: µ- chip developed µ- chip developed by Hitachi for RFID devicesby Hitachi for RFID devices

Technical challengesTechnical challenges-power supply (contd.)--power supply (contd.)-

Power ScavengingPower Scavenging

Energy provided depends on how long the Energy provided depends on how long the source is in operationsource is in operation

Used usually to charge secondary Used usually to charge secondary batteriesbatteries Photovoltaic CellsPhotovoltaic Cells Temperature gradientTemperature gradient Human Power (average human body burns Human Power (average human body burns

10.5 MJ of energy per day)10.5 MJ of energy per day) Wind / Air flowWind / Air flow VibrationsVibrations

Technical challengesTechnical challenges- power consumption -- power consumption -

SensingSensing CommunicationCommunication Data processingData processing

Components of a sensor nodeComponents of a sensor node

Technical challengesTechnical challenges- power consumption (contd.)-- power consumption (contd.)-

Key to Low Duty Key to Low Duty Cycle Operation:Cycle Operation: Sleep – majority of Sleep – majority of

the timethe time Wakeup – quickly Wakeup – quickly

start processingstart processing Active – minimize Active – minimize

work & return to work & return to sleepsleep

Technical challengesTechnical challenges --Communication architecture-Communication architecture-

Combines power and routing awareness,

Integrates data with networking protocols,

Communicates power efficiently through the wireless medium

promotes cooperative efforts of sensor nodes.

The sensor network protocol stack

Technical challengesTechnical challenges --communication architecture communication architecture

(contd.)-(contd.)-Application layerApplication layer

An application layer management protocol An application layer management protocol makes themakes the

hardware and software of the lower layers hardware and software of the lower layers transparent totransparent to

the sensor network management applications.the sensor network management applications. Sensor management protocol (SMP)Sensor management protocol (SMP) Task assignment and data advertisement Task assignment and data advertisement

protocol (TADAP)protocol (TADAP) Sensor query and data dissemination Sensor query and data dissemination

protocol (SQDDP)protocol (SQDDP)

Technical challengesTechnical challenges --communication architecture communication architecture

(contd.)-(contd.)-Transport layerTransport layer

This layer is especially needed when This layer is especially needed when the system is planned to be accessed the system is planned to be accessed through Internet or other external through Internet or other external networks. networks.

No attempt thus far to propose a No attempt thus far to propose a scheme or to discuss the issues scheme or to discuss the issues related to the transport layer of a related to the transport layer of a sensor network in literature.sensor network in literature.

Technical challengesTechnical challenges --communication architecture communication architecture

(contd.)-(contd.)-Network layerNetwork layer

Routing the data supplied by the transport layer. Power efficiency is always an important Power efficiency is always an important

consideration.consideration. Sensor networks are mostly data centric.Sensor networks are mostly data centric. Data aggregation is useful only when it does Data aggregation is useful only when it does

not hinder the collaborative effort of the sensor not hinder the collaborative effort of the sensor nodes.nodes.

An ideal sensor network has attribute-based An ideal sensor network has attribute-based addressing and location awareness.addressing and location awareness.

Technical challengesTechnical challenges --communication architecture (contd.)-communication architecture (contd.)-

Routing Routing Flooding Flooding : :

Broadcast basedBroadcast based -High Overhead-High Overhead -Data aggregation to reduce the overhead-Data aggregation to reduce the overhead -Less complex-Less complex

Unicast:Unicast: Sensors can communicate with the observer directly or Sensors can communicate with the observer directly or

with the cluster head using one to one unicast.with the cluster head using one to one unicast. MultiCast:MultiCast:

Sensors form application-directed groups and use Sensors form application-directed groups and use multicast to communicate among group members.multicast to communicate among group members.

Technical challengesTechnical challenges --communication architecture communication architecture

(contd.)-(contd.)-

•Maximum available power (PA) route: Route 2•Minimum energy (ME) route: Route 1•Minimum hop (MH) route: Route 3•Maximum minimum PA node route: Route 3

Selecting an energy efficient route

Technical challengesTechnical challenges --communication architecture communication architecture

(contd.)-(contd.)-Data link layerData link layer

The data link layer is responsible for the medium The data link layer is responsible for the medium access and error control. It ensures reliable point-access and error control. It ensures reliable point-to-point and point-to-multipoint connections in a to-point and point-to-multipoint connections in a communication network.communication network.

MAC (Medium Access Control)MAC (Medium Access Control) Creation of the network infrastructure Creation of the network infrastructure Fairly and efficiently share communication Fairly and efficiently share communication

resources between sensor nodesresources between sensor nodes Error controlError control

Forward Error Correction (FEC) Forward Error Correction (FEC) Automatic Repeat Request (ARQ).Automatic Repeat Request (ARQ).

Technical challengesTechnical challenges --communication architecture communication architecture

(contd.)-(contd.)-Physical layerPhysical layer

The physical layer is responsible for The physical layer is responsible for frequency selection, frequency frequency selection, frequency generation, signal detection, generation, signal detection, modulation and data encryption.modulation and data encryption.

Technical challengesTechnical challenges-security--security-

Technical challengesTechnical challenges-designed protocols--designed protocols-

Examples Examples MIT d'Arbeloff Lab – MIT d'Arbeloff Lab –

The ring sensorThe ring sensor Monitors the Monitors the

physiological status of physiological status of the wearer and transmits the wearer and transmits the information to the the information to the medical professional medical professional over the Internet over the Internet

Oak Ridge National Oak Ridge National LaboratoryLaboratory Nose-on-a-chip is a Nose-on-a-chip is a

MEMS-based sensor MEMS-based sensor It can detect 400 species It can detect 400 species

of gases and transmit a of gases and transmit a signal indicating the signal indicating the level to a central control level to a central control stationstation

ExamplesExamples- iButton -- iButton -

A 16mm computer chip armored in a stainless steel A 16mm computer chip armored in a stainless steel can can

Up-to-date information can travel with a person or Up-to-date information can travel with a person or objectobject

Types of i-ButtonTypes of i-Button Memory ButtonMemory Button Java Powered Cryptographic iButtonJava Powered Cryptographic iButton Thermochron iButtonThermochron iButton

Applications Applications Caregivers AssistanceCaregivers Assistance

Do not need to keep a bunch of keys. Only one Do not need to keep a bunch of keys. Only one iButton will do the workiButton will do the work

Elder AssistanceElder Assistance They do not need to enter all their personal They do not need to enter all their personal

information again and again. Only one touch of information again and again. Only one touch of iButton is sufficientiButton is sufficient

They can enter their ATM card information and They can enter their ATM card information and PIN with iButtonPIN with iButton

Vending Machine Operation AssistanceVending Machine Operation Assistance

ExamplesExamples- Berkeley Motes-- Berkeley Motes-

Small (under 1” Small (under 1” square) microcontroller square) microcontroller

It consists of:It consists of: MicroprocessorMicroprocessor A set of sensors for A set of sensors for

temperature, light, temperature, light, acceleration and motionacceleration and motion

A low power radio for A low power radio for communicating with communicating with other motesother motes

C compiler InclusionC compiler Inclusion Development ongoingDevelopment ongoing

ExamplesExamples-iBadge – UCLA--iBadge – UCLA-

Investigate behavior of children/patientInvestigate behavior of children/patient Features:Features:

Speech recording / replayingSpeech recording / replaying Position detectionPosition detection Direction detection /estimation (compass)Direction detection /estimation (compass) Weather data: Temperature, Humidity, Weather data: Temperature, Humidity,

Pressure, LightPressure, Light

ConclusionConclusion

Wireless Sensor Networks are ideal for Wireless Sensor Networks are ideal for remote sensing in various applicationsremote sensing in various applications

Due to the severe power constraints Due to the severe power constraints there is a need for a new set of there is a need for a new set of protocols for WSNprotocols for WSN

Power consumption in hardware and OS Power consumption in hardware and OS must be minimalmust be minimal

Data redundancy can be exploited to Data redundancy can be exploited to reduce power consumptionreduce power consumption

Technology of the future!!!!Technology of the future!!!!