Principles of Wireless Sensor Networkscarlofi/teaching/pwsn-2009/...Fall 2009 Principles of Wireless Sensor Networks Carlo Fischione Evaluation Ph.d. version: ¾The course is worth

Fall 2009 Principles of Wireless Sensor Networks Carlo Fischione

Principles of Wireless Sensor NetworksPrinciples of Wireless Sensor Networks

http://http://www.ee.kth.se/~carlofi/teaching/wsn_course.shtmlwww.ee.kth.se/~carlofi/teaching/wsn_course.shtml

Lecture 1Stockholm, September 9 2009

Carlo Fischione

Royal Institute of Technology - KTHStockholm, Swedene-mail: [email protected]


TodayToday’’s lectures lecture

Course OverviewIntroduction to WSNsNode ArchitectureNetwork Architecture


Practical InformationPractical Information

Office: Osquldas väg 10, floor 6.

Meeting times: Wednesdays, 13.15-15.00. Exception: Tuesday September 22, 13.15-15:00, and Tuesday October 21, 10:00-11:00.

Office Times: By appointment.

Class Room: Himmelriket, floor 8, Osquldas väg 10, KTH, Stockholm.

Work load: 2h per lecture + research work.

Prerequisites: Familiarity with linear algebra and analysis. Knowledge of optimization theory may be useful.


Course ContentCourse Content

Lec 1: Introduction (course overview, applications, WSNs node architecture, protocols, operating systems). Lec 2: WSN Programming: from abstractions to running code.

Invited lecture, Luca Mottola, SICSLec 3: Iterative Methods for Parallel Computation. Lec 4: Decentralized Radio Power Control. Lec 5: Medium Access Control, Routing, Duty Cycle.Lec 6: IEEE802.15.4, ZigBee, WirelessHART, ISA SP-100, ROLL.Lec 7: Invited Lecture, TBD. Lec 8: Consensus Algorithms. Lect 9: Distributed Estimation. Lect 10: Localization and Positioning.


Course GoalCourse Goal

After finishing the course, the attendant willKnow the essential theoretical tools to cope with WSNs. Know the basics of WSNs. Know how to design WSNs. Develop a research project. Develop presentation skills.


EvaluationEvaluation

Ph.d. version: The course is worth 5 credits plus 2.5 optional credits based on an original research project. Grades (pass/fail) will be based on attendance (50%) and exercises plus presentations (50%).

Master students version: The course is worth 5 credits Grades (pass/fail) will be based on attendance, exercises, presentation (3 credits) and a research project (2 credit). Less exercises than the Ph.D. version.

Exercises Contain theoretical as well as practical parts (mainly through simulations and possible implementation on test-bed).Have to be delivered before the next lecture following the assignment.


Student PresentationsStudent Presentations

Each students has to present a paper/book chapter during the course.

See the list on the course website http://www.ee.kth.se/~carlofi/teaching/wsn_course.shtml

Choose papers/book chapter from the list.Send me an e-mail with the preferred papers by tomorrow Sept. 10You can propose to present a paper that is not in the list, but I reserve to check if it is relevant to the course flow before accepting. I will then assign the papers to the presenters by Sept 11.

http://www.ee.kth.se/~carlofi/teaching/wsn_course.shtml


Research projectsResearch projects

The project title must be communicated to the teacher by September 30 2009.You can propose your own project, or ask the teacher to give to you a project. A project can be developed in collaboration with max 2 students. The project has to be presented on November 18The project has to be summarized in a paper max 5 pages long, IEEE conference format. The paper has to be delivered by November 25.


Text booksText books

D. P. Bertsekas, J. N. Tsitsiklis, Parallel and Distributed Computation: Numerical methods, Athena Scientific, 1997. http://dspace.mit.edu/handle/1721.1/3719

H. Karl and A. Willig, Protocols and Architectures for Wireless Sensor Networks, Wiley, 2005. http://www.cs.uni-aderborn.de/index.php?id=1119&L=1


Useful LinksUseful Linkshttp://www.hartcomm.org/http://www.ieee802.org/15/pub/TG4.htmlhttp://www.ietf.org/dyn/wg/charter/roll-charter.html WSNs Standardhttp://www.ipso-alliance.org/Pages/Front.phphttp://www.isa.org/http://www.tinyos.net/http://www.sics.se/contiki/http://www.zigbee.org/

http://www.wsnblog.com/ Blogshttp://www.wsn-security.info/index.htm

http://www.dustnetworks.com/http://www.sensinode.com/ Industrieshttp://www.sentilla.com/http://www.xbow.com/Home/wHomePage.aspx

http://www.ee.kth.se/~mikaelj/wsn_course.shtmlhttp://www.cs.berkeley.edu/~culler/eecs194/http://bwrc.eecs.berkeley.edu/Research/energy_efficient_systems.htm University courseshttp://wsnl.stanford.edu/http://courses.csail.mit.edu/6.885/spring06/readings.htmlhttp://www.eecs.harvard.edu/~mdw/course/cs263/fa04/http://www.cs.sunysb.edu/~jgao/CSE595-spring09/

http://www.hartcomm.org/

http://www.cs.sunysb.edu/~jgao/CSE595-spring09/

Fall 2009 Principles of Wireless Sensor Networks Carlo FischioneUCB, October 26, 2007 Design Challenges in Wireless Sensor Networks

Definition of WSNsDefinition of WSNs

Wireless Sensor Networks are networks for communication, control, sensing, and actuation. WSNs are composed by nodes equipped by reduced processing and power resources and communicating through wireless.


DARPA DSN node, 1960 Mica2 mote, 2002

Tmote-sky mote, 2003Smart Dust, 200?

History of WSNsHistory of WSNs


Application of Wireless Sensor NetworksApplication of Wireless Sensor Networks

Marine monitoring

TransportationIndustrial control

Economist

Health care

Environmental monitoring


Applications: Applications: Building MonitoringBuilding Monitoring

Sensors used to measure response to traffic, tidal and seismic activityDeployed on Golden Gate Bridge

http://www.cs.berkeley.edu/~binetude/ggb/


Habitat MonitoringHabitat Monitoring

Non-intrusive monitoring of animal habitat. Example: Nesting of Leach’s Storm Petrels

A. Mainwaring, J. Polastre, R. Szewczyk, and D. Culler, "Wireless Sensor Networks for Habitat Monitoring," Intel Research, IRB-TR-02-006, Jun. 19, 2002.

Storm petrel chick

Sensor node


Smart BuildingsSmart Buildings

WSNs to Control of temperature, light intensity, air and humidity.

Source: Ed Arenswww.instablogsimages.com


Smart gridsSmart grids

Smart grids: “Smart Grids: It's All About Wireless Sensor Networks”(http://stanford.wellsphere.com)

source: http://deviceace.com/


The project aims to close the control loop over wireless networks by deriving and applying a co-design framework that allows the integration of communication, control, computation and energy management aspects in a holistic way.

KEYWORDS: co-design, communication, control, computation, energy

FeedNetBackFeedNetBack European ProjectEuropean Project

Closing the loop over wireless networks

Fall 2009 Principles of Wireless Sensor Networks Carlo FischioneUCB, October 26, 2007 Design Challenges in Wireless Sensor Networks

WSNs in Industrial AutomationWSNs in Industrial Automation

Several advantages with wireless networking control systems:

Added flexibilitySensor and actuator nodes can be placed more appropriatelyLess restrictive maneuvers and control actionsMore powerful control through distributed computations

Reduced installation and maintenance costsLess cablingMore efficient monitoring and diagnosis


Distributed Camera CalibrationDistributed Camera Calibration

•WSN allows one to perform distributed camera calibration•Application: massive graphic effects in film production


Old Market Forecasts for WSNsOld Market Forecasts for WSNs

WSNs population forecast 2010WSNs population forecast 2010

300 MillionPC’s:

1+ Trillion

500 Billion

2 Billion

1 Billion Info Devices:

Smart Devices:AppliancesMachineryVehiclesBldg. Eqpt.

etc.

Microprocessors:

4-64+ bits CPU’s etc.

RFID/Sensors:

LocationHumidityTemperatureVibrationLiquidWeight etc.

Forecast of installed base, 2010The FocalPoint Group, LLC 2003http://www.thefpgroup.com

Mobile PhonesPDA’sWeb Tablets etc.


New Market Forecasts for WSNsNew Market Forecasts for WSNs

On World Expert survey “WSN Market size in 2007 and Active RFID and Sensor Networks 2007-2017”:

industrial applications of WSN: 4.6 Billion $ by 2011 smart building applications of WSN: 2.5 Billion $ by 2011.

IDTechEx: WSNs and active RFID of about 4B$ by 2012.

WSNs R&D investments: from 522Million $ in 2007 to 1.3Billion $ in 2012.

30 millions WirelessHART wireless sensors installed so far worldwide.


OutlineOutline

Course OverviewIntroduction to WSNs

Infrastructure for wireless?Requirements & mechanisms

Node ArchitectureNetwork Architecture

The following slides are adapted from H. Karl’s companion book webpage http://www.cs.uni-paderborn.de/index.php?id=1119&L=1


Possible applications for Possible applications for infrastructureinfrastructure--free networksfree networks

Factory floor automation

Disaster recovery

Car-to-car communication

ad ho

c

ad ho

c

Military networking: Tanks, soldiers, …Finding out empty parking lots in a city, without asking a serverSearch-and-rescue in an avalanche Personal area networking (watch, glasses, PDA, medical appliance, …)…


Solution: (Wireless) ad hoc Solution: (Wireless) ad hoc networksnetworks

Try to construct a network without infrastructure, using networking abilities of the participants

This is an ad hoc network – a network constructed “for a special purpose”

Simplest example: Laptops in a conference room –a single-hop ad hoc network


Problems/challenges for ad hoc Problems/challenges for ad hoc networksnetworks

Without a central infrastructure, things become much more difficultProblems are due to

Lack of central entity for organization availableLimited range of wireless communicationMobility of participantsBattery-operated entities

?


Wireless sensor networksWireless sensor networks

Participants in the previous examples were devices close to a human user, interacting with humans

Alternative concept: Instead of focusing interaction on humans, focus on interacting with environment

Network is embedded in environmentNodes in the network are equipped with sensing and actuation to measure/influence environment Nodes process information and communicate it wirelessly

! Wireless sensor networks (WSN)Or: Wireless sensor & actuator networks (WSAN)


Roles of participants in WSN Roles of participants in WSN

Sources of data: Measure data, report them “somewhere”Typically equip with different kinds of actual sensors

Sinks of data: Interested in receiving data from WSN May be part of the WSN or external entity, PDA, gateway, …

Actuators: Control some device based on data, usually also a sink


Structuring WSN application Structuring WSN application typestypes

Interaction patterns between sources and sinks classify application types

Event detection: Nodes locally detect events (maybe jointly with nearby neighbors), report these events to interested sinks• Event classification additional option

Periodic measurementFunction approximation: Use sensor network to approximate a function of space and/or time (e.g., temperature map)Edge detection: Find edges (or other structures) in such a function (e.g., where is the zero degree border line?)Tracking: Report (or at least, know) position of an observed intruder (“pink elephant”)


Deployment options for WSNDeployment options for WSN

How are sensor nodes deployed in their environment? Dropped from aircraft → Random deployment• Usually uniform random distribution for nodes over finite area is

assumed• Is that a likely proposition?

Well planned, fixed → Regular deployment• E.g., in preventive maintenance or similar• Not necessarily geometric structure, but that is often a convenient

assumptionMobile sensor nodes • Can move to compensate for deployment shortcomings• Can be passively moved around by some external force (wind,

water)• Can actively seek out “interesting” areas


Maintenance optionsMaintenance options

Feasible and/or practical to maintain sensor nodes?E.g., to replace batteries?Or: unattended operation? Impossible but not relevant? Mission lifetime might be very small

Energy supply? Limited from point of deployment? Some form of recharging, energy scavenging from environment?• E.g., solar cells


Characteristic requirements for Characteristic requirements for WSNsWSNs

Type of service of WSNNot simply moving bits like another networkRather: provide answers (not just numbers)Issues like geographic scoping are natural requirements, absent from other networks

Quality of serviceTraditional QoS metrics do not applyStill, service of WSN must be “good”: Right answers at the right time

Fault toleranceBe robust against node failure (running out of energy, physical destruction, …)

LifetimeThe network should fulfill its task as long as possible – definition depends on applicationLifetime of individual nodes relatively unimportantBut often treated equivalently


Characteristic requirements for Characteristic requirements for WSNsWSNs

ScalabilitySupport large number of nodes

Wide range of densitiesVast or small number of nodes per unit area, very application-dependent

ProgrammabilityRe-programming of nodes in the field might be necessary, improve flexibility

MaintainabilityWSN has to adapt to changes, self-monitoring, adapt operationIncorporate possible additional resources, e.g., newly deployed nodes


Mechanisms to meet requirementsMechanisms to meet requirements

Multi-hop wireless communicationEnergy-efficient operation

Both for communication and computation, sensing, actuating

Auto-configurationManual configuration just not an option

Collaboration & in-network processingNodes in the network collaborate towards a joint goalPre-processing data in network (as opposed to at the edge) can greatly improve efficiency


OutlineOutline




Network ArchitectureNetwork Architecture

Survey the main components of the composition of a node for a wireless sensor network

Controller, radio modem, sensors, batteriesUnderstand energy consumption aspects for these components

Putting into perspective different operational modes and what different energy/power consumption means for protocol design


Enabling technologies for WSN Enabling technologies for WSN

Cost reduction For wireless communication, simple microcontroller, sensing, batteries

MiniaturizationSome applications demand small size“Smart dust” as the most extreme vision

Energy scavengingRecharge batteries from ambient energy (light, vibration, …)


Sensor node architectureSensor node architecture

Main components of a WSN nodeControllerCommunication device(s)Sensors/actuatorsMemoryPower supply Memory

Controller Sensor(s)/actuator(s)

Communicationdevice

Power supply


Memory power consumptionMemory power consumption

Crucial part: FLASH memoryPower for RAM almost negligible

FLASH writing/erasing is expensiveExample: FLASH on Mica motesReading: ≈ 1.1 nAh per byteWriting: ≈ 83.3 nAh per byte


ControllerController

Main options: Microcontroller – general purpose processor, optimized for embedded applications, low power consumptionDSPs – optimized for signal processing tasks, not suitable hereFPGAs – may be good for testingASICs – only when peak performance is needed, no flexibility

Example microcontrollersTexas Instruments MSP430

• 16-bit RISC core, up to 4 MHz, versions with 2-10 kbytes RAM, several DACs, RT clock, prices start at 0.49 US$

• Fully operational 1.2 mW• Deepest sleep mode 0.3 μW – only woken up by external interrupts (not

even timer is running any more)Atmel ATMega

• 8-bit controller, larger memory than MSP430, slower• Operational mode: 15 mW active, 6 mW idle• Sleep mode: 75 μW


Transceiver statesTransceiver states

Transceivers can be put into different operational states, typically: TransmitReceiveIdle – ready to receive, but not doing so• Some functions in hardware can be switched off, reducing energy

consumption a littleSleep – significant parts of the transceiver are switched off• Not able to immediately receive something• Recovery time and startup energy to leave sleep state can be

significant

Research issue: Wakeup receivers – can be woken via radio when in sleep state (seeming contradiction!)


Example radio transceiversExample radio transceivers

Almost boundless variety availableSome examples

RFM TR1000 family• 916 or 868 MHz• 400 kHz bandwidth• Up to 115,2 kbps• On/off keying or ASK • Dynamically tuneable output

power• Maximum power about 1.4 mW• Low power consumption

Chipcon CC1000• Range 300 to 1000 MHz,

programmable in 250 Hz steps • FSK modulation• Provides RSSI

Chipcon CC 2400• Implements 802.15.4• 2.4 GHz, DSSS modem • 250 kbps• Higher power consumption

than above transceivers Infineon TDA 525x family

• E.g., 5250: 868 MHz• ASK or FSK modulation• RSSI, highly efficient

power amplifier• Intelligent power down,

“self-polling” mechanism • Excellent blocking

performance


Energy supply of mobile/sensor Energy supply of mobile/sensor nodesnodes

Goal: provide as much energy as possible at smallest cost/volume/weight/recharge time/longevity

In WSN, recharging may or may not be an optionOptions

Primary batteries – not rechargeable Secondary batteries – rechargeable, only makes sense in combination with some form of energy harvesting

Requirements include Low self-dischargeLong shelf liveCapacity under load Efficient recharging at low currentGood relaxation properties (seeming self-recharging)Voltage stability (to avoid DC-DC conversion)


Energy scavengingEnergy scavenging

How to recharge a battery?A laptop: easy, plug into wall socket in the eveningA sensor node? – Try to scavenge energy from environment

Ambient energy sourcesLight → solar cells – between 10 μW/cm2 and 15 mW/cm2

Temperature gradients – 80 μ W/cm2 @ 1 V from 5K differenceVibrations – between 0.1 and 10000 μ W/cm3

Pressure variation (piezo-electric) – 330 μ W/cm2 from the heel of a shoe Air/liquid flow (MEMS gas turbines)


Energy scavenging Energy scavenging –– overview overview


Energy consumptionEnergy consumption

A “back of the envelope” estimation

Number of instructionsEnergy per instruction: 1 nJSmall battery (“smart dust”): 1 J = 1 WsCorresponds: 109 instructions!

LifetimeOr: Require a single day operational lifetime = 24·60·60 =86400 s1 Ws / 86400s ≈ 11.5 μW as max. sustained power consumption!

Not feasible!


Multiple power consumption modesMultiple power consumption modes

Way out: Do not run sensor node at full operation all the timeIf nothing to do, switch to power safe modeQuestion: When to throttle down? How to wake up again?

Typical modesController: Active, idle, sleepRadio mode: Turn on/off transmitter/receiver, both

Multiple modes possible, “deeper” sleep modesStrongly depends on hardwareTI MSP 430, e.g.: four different sleep modesAtmel ATMega: six different modes


Start processing

Switching between modesSwitching between modes

Simplest idea: Greedily switch to lower mode whenever possibleProblem: Time and power consumption required to reach higher modes not negligible

Introduces overhead Switching only pays off if Esaved > Eoverhead

Example: Event-triggered wake up from sleep modeScheduling problem with uncertainty (exercise)

Pactive

Psleep

timeteventt1

Esaved

Eoverhead

τdown τup


Transmitter power/energy Transmitter power/energy consumption for n bitsconsumption for n bits

Amplifier power: Pamp = αamp + βamp PtxPtx radiated power αamp, βamp constants depending on model Highest efficiency (η = Ptx / Pamp ) at maximum output power

In addition: transmitter electronics needs power PtxElecTime to transmit n bits: n / (R · R

code)

R nomial data rate, Rcode

coding rate To leave sleep mode

Time Tstart, average power Pstart

→ Etx

= Tstart

Pstart

+ n / (R · Rcode

) (PtxElec + αamp + βamp Ptx)

Simplification: Modulation not considered


Receiver power/energy Receiver power/energy consumption for n bitsconsumption for n bits

Receiver also has startup costsTime Tstart, average power P

startTime for n bits is the same n / (R · R

code)

Receiver electronics needs PrxElec

Plus: energy to decode n bits EdecBits

→ Erx = Tstart

Pstart

+ n / (R · Rcode

) PrxElec + EdecBits ( R )


Some transceiver numbers Some transceiver numbers


Controlling transceiversControlling transceivers

Similar to controller, low duty cycle is necessaryEasy to do for transmitter – similar problem to controller: when is it worthwhile to switch offDifficult for receiver: Not only time when to wake up not known, it also depends on remote partners → Dependence between MAC protocols and power consumption is

strong!

Only limited applicability of techniques analogue to DVS Dynamic Modulation Scaling (DSM): Switch to modulation best suited to communication – depends on channel gainDynamic Coding Scaling – vary coding rate according to channel gainCombinations


Computation vs. communication Computation vs. communication energy costenergy cost

Tradeoff?Directly comparing computation/communication energy cost not possibleBut: put them into perspective!Energy ratio of “sending one bit” vs. “computing one instruction”: Anything between 220 and 2900 in the literatureTo communicate (send & receive) one kilobyte = computing three million instructions!

Hence: try to compute instead of communicate whenever possibleKey technique in WSN – in-network processing!

Exploit compression schemes, intelligent coding schemes, …


Summary Summary

For WSN, the need to build cheap, low-energy, (small) devices has various consequences for system design

Radio frontends and controllers are much simpler than in conventional mobile networksEnergy supply and scavenging are still (and for the foreseeable future) a premium resourcePower management (switching off or throttling down devices) crucial


OutlineOutline


Optimization goalsDesign principlesGateway concepts



Network ArchitectureNetwork Architecture

Having looked at the individual nodes in the, we now look at general principles and architectures how to put these nodes together to form a meaningful networkWe will look at design approaches to both the more conventional ad hoc networks and the non-standard WSNs


SingleSingle--hop vs. multihop vs. multi--hop hop networksnetworks

One common problem: limited range of wireless communicationEssentially due to limited transmission power, path loss, obstacles

Option: multi-hop networksSend packets to an intermediate nodeIntermediate node forwards packet to its destinationStore-and-forward multi-hop network

Basic technique applies to both WSN and MANETNote: Store&forward multi-hopping NOT the only possible solution

E.g., collaborative networking, network codingDo not operate on a per-packet basis

Source

Sink

Obstacle


Energy efficiency of multiEnergy efficiency of multi--hopping?hopping?

Obvious idea: Multi-hopping is more energy-efficient than direct communication

Because of path loss α > 2, energy for distance d is reduced from cdα to 2c(d/2)α• c some constant

However: This is usually wrong, or at least very over-simplified

Need to take constant offsets for powering transmitter, receiver into account

→ Multi-hopping for energy savings needs careful choice


WSN: Multiple sinks, multiple WSN: Multiple sinks, multiple sourcessources


Different sources of mobilityDifferent sources of mobility

Node mobilityA node participating as source/sink (or destination) or a relay node might move aroundDeliberately, self-propelled or by external force; targeted or at randomHappens in both WSN and MANET

Sink mobilityIn WSN, a sink that is not part of the WSN might moveMobile requester

Event mobility In WSN, event that is to be observed moves around (or extends, shrinks)Different WSN nodes become “responsible” for surveillance of such an event


Optimization goal: Quality of Optimization goal: Quality of ServiceService

In ad-hoc networks: Usual QoS interpretationThroughput/delay/jitterHigh perceived QoS for multimedia applications

In WSN, more complicatedEvent detection/reporting probabilityEvent classification error, detection delayProbability of missing a periodic reportApproximation accuracy (e.g, when WSN constructs a temperature map)Tracking accuracy (e.g., difference between true and conjecturedposition of the pink elephant)

Related goal: robustnessNetwork should withstand failure of some nodes


Optimization goal: Energy Optimization goal: Energy efficiencyefficiency

Umbrella term!Energy per correctly received bit

Counting all the overheads, in intermediate nodes, etc.Energy per reported (unique) event

After all, information is important, not payload bits!Typical for WSN

Delay/Reliability/energy tradeoffsNetwork lifetime

Time to first node failureNetwork half-life (how long until 50% of the nodes died?)Time to partitionTime to loss of coverageTime to failure of first event notification


Optimization goal: ScalabilityOptimization goal: Scalability

Network should be operational regardless of number of nodesAt high efficiency

Typical node numbers difficult to guessAd-hoc networks: 10s to 100s WSNs: 10s to 1000s, maybe more (although few people have seen such a network already …)

Requiring to scale to large node numbers has serious consequences for network architecture

Might not result in the most efficient solutions for small networks!Carefully consider actual application needs before looking for n → ∞ solutions!


Distributed organization Distributed organization

Participants in a WSN should cooperate in organizing the networkE.g., with respect to medium access, routing, …Centralistic approach as alternative usually not feasible – hinders scalability, robustness

Potential shortcomingsNot clear whether distributed or centralistic organization achieves better energy efficiency (when taking all overheads into account)

Option: “limited centralized” solutionElect nodes for local coordination/controlPerhaps rotate this function over time


InIn--network processingnetwork processing

WSNs are supposed to deliver bits from one end to the otherWSNs, on the other end, are expected to provide information, notnecessarily original bits

Gives additional optionsE.g., manipulate or process the data in the network

Main example: aggregation Apply composable aggregation functions to a convergecast tree in a network Typical functions: minimum, maximum, average, sum, …Not amenable functions: median


InIn--network processing: network processing: Aggregation exampleAggregation example

Reduce number of transmitted bits/packets by applying an aggregation function in the network

1

1

31

1

6

1

1

11

1

1


InIn--network processing: signal network processing: signal processingprocessing

Depending on application, more sophisticated processing of data can take place within the network

Example edge detection: locally exchange raw data with neighboring nodes, compute edges, only communicate edge description to far away data sinksExample tracking/angle detection of signal source: Conceive of sensor nodes as a distributed microphone array, use it to compute the angle of a single source, only communicate this angle, not all the raw data

Exploit temporal and spatial correlationObserved signals might vary only slowly in time → no need to transmit all data at full rate all the timeSignals of neighboring nodes are often quite similar → only try to transmit differences (details a bit complicated, see later)


Data centric networking?Data centric networking?

In typical networks (including ad hoc networks), network transactions are addressed to the identities of specific nodes

A “node-centric” or “address-centric” networking paradigm

In a redundantly deployed sensor networks, specific source of an event, alarm, etc. might not be important

Redundancy: e.g., several nodes can observe the same area

Thus: focus networking transactions on the data directly instead of their senders and transmitters → data-centric networking


Gateway concepts for WSN?Gateway concepts for WSN?

Gateways are necessary to the Internet for remote access to/from the WSN

Same is true for ad hoc networks; additional complications due to mobility (change route to the gateway; use different gateways)WSN: Additionally bridge the gap between different interaction semantics (data vs. address-centric networking) in the gateway

Gateway needs support for different radios/protocols, …

Gatewaynode

Internet Remoteusers

Wireless sensor network

Gatewaynode

Internet Remoteusers

Wireless sensor network


Gatewaynodes

Alice‘s desktop

Alice‘s PDA

Alert Alice

Internet

WSN to Internet communicationWSN to Internet communication

Example: Deliver an alarm message to an Internet hostIssues

Need to find a gateway (integrates routing & service discovery)Choose “best” gateway if several are availableHow to find Alice or Alice’s IP?


Gatewaynodes

Internet

Gateway

WSN tunnelingWSN tunneling

Use the Internet to “tunnel” WSN packets between two remote WSNs


SummarySummary

We have seen the most important aspects of wireless sensor networks

ApplicationsDifference from other networksNode architecture: controller, transceiver, memory, battery. Power consumption models. Design principles: distributed optimization, in-network processing

Next Lecture: Luca Mottola, SICS, “WSN Programming: from Abstractions to Running Code”.


HomeworkHomework

Mandatory reading: Chapter 1 and 2, H. Karl and A. Willig, Protocols and Architectures for Wireless Sensor Networks, Wiley. Appendix A, D. P. Bertsekas, J. N. Tsitsiklis, Parallel and Distributed Computation: Numerical methods, Athena Scientific, 1997.

Paper for presentation for next lecture: • A. Dunkels, B. Grönvall, T. Voigt, "Contiki - a Lightweight and

Flexible Operating System for Tiny Networked Sensors", IEEE Emnets 2004.

• P. Levis, S. Madden, D. Gay, J. Polastre, R. Szewczyk, A. Woo, E. Brewer, D. Culler, "The Emerging of Networking Abstractions and Techniques in TinyOS", ACM NSDI 2004.

• V. Kawadia, P. R. Kumar, "A Cautionary Perspective on Cross Layer Design", IEEE Wireless Communications Magazine, Feb. 2005.

Send me an e-mail with the preferred papers from the complete list by tomorrow Sept. 10I will then assign the papers to the presenters by Sept 11.

Documents

Principles of Wireless Sensor Networkscarlofi/teaching/pwsn-2009/...Fall 2009 Principles of Wireless Sensor Networks Carlo Fischione Evaluation Ph.d. version: ¾The course is worth