Sensor Networks Introduction and Architecture

Details of fundamentals of Sensor networks and its applications

1. Unit II
Sensor Networks –
Introduction & Architectures
Dr.S.Periyanayagi
Professor & Head
Ramco Institute of Technology
20.08.2020

2. Topics
•Challenges for Wireless Sensor Networks
•Enabling Technologies for Wireless Sensor Networks
•WSN application examples
•Single-Node Architecture -Hardware Components
•Energy Consumption of Sensor Nodes
•Network Architecture -Sensor Network Scenarios
•Transceiver Design Considerations
•Optimization Goals and Figures of Merit
2

3. WSN -Introduction
•AWirelessSensorNetwork(WSN)isawirelessnetwork
consistingofalargenumberofspatiallydistributedsensor
nodes
•verysensitivetotheenvironment
•capableofcommunicationwitheachotherthrough
wirelesschannels
Picture Taken from: https://microcontrollerslab.com/wireless-sensor-networks-wsn-applications/
3

4. Sensor & Sensor Nodes
•SensorNetworkisaninfrastructurecomprisedofsensing,
computingandcommunicationelementsthatgivethe
abilityofobservingandreactingtoeventsinaspecified
environmenttoanadministrator.
•TheAdministratortypicallyisacivil,governmental,
commercialorindustrialentity.
•Theenvironmentcanbeaphysicalworld,abiological
system,oraninformationtechnologyframework.
4

5. Contd…
•SensingisaTechniqueusedtogatherinformationabout
physicalobjectorProcess,Includingoccurrenceofthe
event.
•AnObjectperformingsuchasensingtaskiscalleda
sensor.
•Foreg:RemoteSensors
•Thehumanbodyisequippedwithsensorsthatareableto
captureopticalinformationfromtheenvironment
•Acousticinformationsuchassounds(ears)andsmell(Nose)
•Asensorisadevicethattranslatesparametersoreventsin
thephysicalworldintosignalsthatcanbemeasuredand
analyzed.
5

6. •Asensorisaelectronicdevicethatmeasuresaphysical
quantityandconvertsitintoasignalwhichcanberead
byanobserverorbyaninstrument.
•SensorNode:BasicunitinSensorNetwork
Picture taken from : https://www.researchgate.net/publication/312332362_Application aware _ Energy _
Efficient_Centralized_Clustering_Routing_Protocol_for_Wireless_Sensor_Networks/figures?lo=1
6

7. Architecture of Sensor Node
7

8. Goal of a Sensor Node
•Thegoalfromthesensornodeis
•tocollectthedataatregularintervals
•thentransformthedataintoanelectricalsignal
•finallysendthesignaltothesinkorthebasenode
8

9. Early, wireless sensor networks functioned mainly with two important
application domains namely monitoringand tracking.
9

10. One Minute Paper
•List few Applications of WSNs –you are familiar with
10

11. Wireless Sensor Networks
Applications
•Forest fire detection
•Air pollution monitoring
•Water quality monitoring
•Land slide detection
•Automotive application
•Military application
•Animal Habitat Monitoring & Tracking
•Agriculture
•Health Care Monitoring
11

12. Contd…
•Disaster relief applications
–Sensor nodes are equipped with thermometersand can
determine their own location
–Drop sensor nodes from an aircraft over a wildfire
–Each node measures temperature
–Derive a “temperature map”of the area
•Biodiversity mapping
–Use sensor nodes to observe wildlife
Picture taken from: https://www.slideshare.net/shikhathegreat/ppt-on-low-power-wireless-sensor-network-
5th-sem
12

13. Forest fire detection
• A network of Sensor Nodes can be installed in a forest to
detect when a fire has started.
• The nodes can be equipped with sensors to measure
temperature, humidity and gases which are produced by
fire in the trees or vegetation.
• If the node detects fire,itsends an alarm message(along
with its location) to the base station
13

14. Air Quality monitoring
•Traditionalairqualitymonitoringmethods,suchas
buildingairqualitymonitoringstations,aretypically
expensive.
•Thesolutiontotheseisairqualitymonitoringsystem
basedonthetechnologyofwirelesssensornetworks
(WSNs).
•Wirelesssensornetworkshavebeendeployedinseveral
citiestomonitortheconcentrationofdangerousgasesfor
citizens.
14

15. Water Quality Monitoring
•Waterqualitymonitoringinvolvesanalyzingwater
propertiesindams,rivers,lakes&oceans,aswellas
undergroundwaterreserves.
•Parametersconsideredinclude–temperature,turbidity
andpH
Picture taken from: Paper by JungsuPark et al., ‘Recent Advances in Information and Communications
Technology (ICT) and Sensor Technology for Monitoring Water Quality’
15

16. Military Surveillance
•Enemy tracking, battlefield surveillance
•Target detection
•Monitoring, tracking and surveillance of borders
•Nuclear, biological and chemical attack detection
Picture taken from: https://www.researchgate.net/figure/WSNs-used-in-Military-
Applications_fig1_4365726
16

17. Landslidedetection system
•Alandslidedetectionsystemmakesuseofawireless
sensornetworktodetecttheslightmovementsofsoiland
changesinvariousparametersthatmayoccurbeforeor
duringalandslide.
•Throughthedatagathereditmaybepossibletoknowthe
occurrenceoflandslideslongbeforeitactuallyhappens.
17

18. Eruption
Picture Taken from: https://www.researchgate.net/figure/Monitoring-volcanic-eruptions-with-
a-WSN-24_fig3_230660610
18

19. Precision Agriculture
Picture Taken from: Article by uferahsafriet al, ‘Precision Agriculture Techniques and
Practices: From Considerations to Applications’
–Bring out fertilizer/pesticides/irrigation only where needed
19

20. Medical & Health Care
Monitoring
Picture taken from: https://www.slideshare.net/DeeptimanMallick/using-tiny-os-in-
wireless-sensor-network
–Post-operative or intensive care
–Long-term surveillance of chronically ill patients or the elderly
20

21. •Intelligent buildings (or bridges)
–Reduce energy wastage by proper humidity, ventilation, air
conditioning (HVAC) control
–Needs measurements about room occupancy,
temperature, air flow, …
–Monitor mechanical stress after earthquakes
•Facility management
–Intrusion detection into industrial sites
–Control of leakages in chemical plants, …
•Machine surveillance and preventive maintenance
–Embed sensing/control functions into places no cable has gone
before
–E.g., tire pressure monitoring
21

22. •Logistics
–Equip goods (parcels, containers) with a sensor node
–Track their whereabouts –total asset management
–Note: passive readout might sufficient –compare RF IDs
•Telematics
–Provide better traffic control by obtaining finer-grained
information about traffic conditions
–Intelligent roadside
–Cars as the sensor nodes
Picture taken from : https://www.semanticscholar.org/paper/Industry%3A-using-dynamic-WSNs-in-
smart-logistics-for-Bijwaard-Kleunen / 377f4ffcece496334f65255263b942f3509bbe7c /figure/0
22

23. A general work process of WSN
23

24. 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 assumption
Deployment options for WSN
24

25. •Mobile 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
Maintenanceoptions
•Feasibleand/orpracticaltomaintainsensornodes?
–E.g.,toreplacebatteries?
–Or:unattendedoperation?
–Impossiblebutnotrelevant?Missionlifetimemightbeverysmall
•Energysupply?
–Limitedfrompointofdeployment?
–Someformofrecharging,energyscavengingfromenvironment?
–E.g.,solarcells
25

26. Assignment
•Explain any one application of WSN (Agriculture,
Medical, Military, Under water, Animal Habitat,
IOT, IIOT etc..) in Detail
–What is WSN?
–Type of Sensor Used
–Application in Detail
–Working
–Refernces
26

27. Challenges for Wireless Sensor
Networks
21.08.2020

28. Design Challengesin WSN
•Heterogeneity
–Thedevicesdeployedmaybeofvarioustypesandneedto
collaboratewitheachother.
•DistributedProcessing
–Thealgorithmsneedtobecentralizedastheprocessingis
carriedoutondifferentnodes.
•LowBandwidthCommunication
–Thedatashouldbetransferredefficientlybetweensensors
•LargeScaleCoordination
–Thesensorsneedtocoordinatewitheachothertoproduce
requiredresults.
28

29. Contd…
•UtilizationofSensors
–Thesensorsshouldbeutilizedinawaysthatproducethe
maximumperformanceanduselessenergy.
•RealTimeComputation
–Thecomputationshouldbedonequicklyasnewdatais
alwaysbeinggenerated.
29

30. Challenges for WSNs
•Type of service of WSN
–Notsimplymovingbitslikeanothernetwork
–Rather:provideanswers(notjustnumbers)
–Issueslikegeographicscopingarenaturalrequirements,absent
fromothernetworks
•Qualityofservice
–TraditionalQoSmetricsdonotapply
–Still,serviceofWSNmustbe“good”:Rightanswersattheright
time
•Faulttolerance
–Berobustagainstnodefailure(runningoutofenergy,physical
destruction,…)
30

31. Contd..
•Lifetime
–Thenetworkshouldfulfillitstaskaslongaspossible–
definitiondependsonapplication
–Lifetimeofindividualnodesrelativelyunimportant
–Butoftentreatedequivalently
•Scalability
–Supportlargenumberofnodes
•Widerangeofdensities
–Vastorsmallnumberofnodesperunitarea,very
application-dependent
31

32. Contd..
•Programmability
–Re-programmingofnodesinthefieldmightbe
necessary,improveflexibility
•Maintainability
–WSNhastoadapttochanges,self-monitoring,adapt
operation
–Incorporatepossibleadditionalresources,e.g.,newly
deployednodes
32

33. Operational Challenges of Wireless Sensor
Networks
•EnergyEfficiency
•Limitedstorageandcomputation
•Lowbandwidthandhigherrorrates
•Errorsarecommon
–Wirelesscommunication
–Noisymeasurements
–Nodefailureareexpected
•Scalabilitytoalargenumberofsensornodes
•Survivabilityinharshenvironments
•Experimentsaretime-andspace-intensive
33

34. Required mechanisms to meet
requirements
•Multi-hopwirelesscommunication
•Energy-efficientoperation
–Bothforcommunicationandcomputation,sensing,actuating
•Auto-configuration
–Manualconfigurationjustnotanoption
•Collaboration&in-networkprocessing
–Nodesinthenetworkcollaboratetowardsajointgoal
–Pre-processingdatainnetwork(asopposedtoattheedge)can
greatlyimproveefficiency
34

35. Contd..
•Data centric networking
–Focusing network design on data, not on node identifies(id-
centric networking)
–To improve efficiency
•Locality
–Do things locally (on node or among nearby neighbors) as far
as possible
•Exploit tradeoffs
–E.g., between invested energy and accuracy
35

36. Enabling technologies for WSN
•Costreduction
–Forwirelesscommunication,simplemicrocontroller,
sensing,batteries
•Miniaturization
–Someapplicationsdemandsmallsize
–“Smartdust”asthemostextremevision
•Energyscavenging
–Rechargebatteriesfromambientenergy(light,
vibration,…)
36

37. Single Node Architecture
24.08.2020

38. Single-node Architecture
Goals
•Surveythemaincomponentsofthecompositionofanodefora
wirelesssensornetwork
–Controller,radiomodem,sensors,batteries
•Understandenergyconsumptionaspectsforthesecomponents
–Puttingintoperspectivedifferentoperationalmodesand
whatdifferentenergy/powerconsumptionmeansfor
protocoldesign
38

39. Main components of a WSN node
•Controller-Acontrollertoprocessalltherelevantdata,capableof
executingarbitrarycode.
•Memory-Somememorytostoreprogramsandintermediatedata;
usually,differenttypesofmemoryareusedforprogramsanddata.
•Communicationdevice(s)-Turningnodesintoanetworkrequiresa
deviceforsendingandreceivinginformationoverawirelesschannel
•Sensors/actuators-Theactualinterfacetothephysicalworld:devices
thatcanobserveorcontrolphysicalparametersoftheenvironment
•Powersupply-Asusuallynotetheredpowersupplyisavailable,some
formofbatteriesarenecessarytoprovideenergy.Sometimes,someformof
rechargingbyobtainingenergyfromtheenvironmentisavailableaswell
(e.g.solarcells).
39

40. Single-node Architecture
•Eachofthesecomponentshastooperatebalancingthetrade-off
betweenassmallanenergyconsumptionaspossibleontheone
handandtheneedtofulfilltheirtasksontheotherhand.
40

41. Controller
Main options:
•General purpose processor
–Used in Desktop Computers
–Highly over powered
–Energy Consumption is excessive
•Micro controller
–optimized for embedded applications
–Flexibility in connecting other devices
–low power consumption
–Build in Memory
–Freely programmable and flexible
–Going to Sleep State
41

42. Controller
Main options:
•DSPs
–optimized for signal processing tasks
–Advantages are not suitable here
•FPGAs (Field –Programmable Gate Arrays)
–may be good for testing
–Reprogrammed
•ASICs
–Specialized processor
–Custom Design for application
–only when peak performance is needed, no flexibility
42

43. Controller
Example microcontrollers
•Intel strong ARM
–High end Processor with PDAs
–SA-1100 model has 32 bit reduced Instruction Set Computer
(RISC) core, running at up to 206 MHz
•Texas Instruments MSP430
–16-bit RISC core, up to 4 MHz, versions with 2-10 kbytesRAM,
several DACs, RT clock, prices start at 0.49 US$
•Atmel ATMega
–8-bit controller
–Usage in embedded application with external interfaces.
43

44. 25.08.2020

45. Memory
•The memory component is fairly straightforward.
–Need for Random Access Memory (RAM) to store
intermediate sensor readings, packets from other nodes.
–While RAM is fast, disadvantage -loses its content if power
supply is interrupted.
•Program code can be stored in
–Read-Only Memory (ROM)
–Electrically Erasable Programmable Read-Only Memory
(EEPROM) or
–flash memory
45

46. Contd…
•Flash memory serve as intermediate storage of data in case
RAM is insufficient or when the power supply of RAM shut
down for some time.
•The long read and write access delays of flash memory need
high energy.
•Manufacturing costs and power consumption.
•Memory requirements are very much application
dependent.
46

47. Communication Devices
•Choice of transmission medium
•Transceivers
•Transceivers tasks and characteristics
•Transceiver structure
•Transceiver operational states
•Advanced Radio Concepts
•Nonradio frequency wireless communication
•Examples of radio transceivers
47

48. Choice of transmission medium
•The communication device is used to exchange data between
individual nodes.
•wired communication can actually be the method of choice and is
frequently applied in many sensor network like settings (using field
buses like Profibus, LON, CAN, or others).
•The first choice to make is that of the transmission medium
–Radio frequencies
–Optical communication
–Ultrasound
–other media like magnetic inductance are only used in very
specific cases
48

49. Contd..
•Radio Frequency (RF)-based communication -best fits the
requirements of most WSN applications
–It provides relatively long range and high data rates
–acceptable error rates at reasonable energy expenditure
–does not require line of sight between sender and receiver
•Wireless sensor networks typically use communication frequencies
between about 433 MHz and 2.4 GHz.
49
Picture taken from: https://www.britannica.com/science/radio-frequency-spectrum

50. Transceivers
•Forcommunication,bothatransmitterandareceiverare
requiredinasensornode.
•Theessentialtaskistoconvertabitstreamcomingfroma
microcontroller(orasequenceofbytesorframes)and
convertthemtoandfromradiowaves.
•Devicethatcombinesthesetwotasksinasingleentity-
transceivers.
50

51. Contd…
•Half-duplexoperationisrealized
•Arangeoflow-costtransceiversiscommerciallyavailable
thatincorporateallthecircuitryrequiredfortransmitting
andreceiving–modulation,demodulation,amplifiers,
filters,mixersetc
51

52. Transceiver tasks and characteristics
•Servicetoupperlayer
–Areceiverhastooffercertainservicestotheupperlayers,most
notablytotheMediumAccessControl(MAC)layer.
–Thisserviceispacketoriented;sometimes,
–Transceiveronlyprovidesabyteinterfaceorevenonlyabit
interfacetothemicrocontroller.
•Powerconsumptionandenergyefficiency
–Thesimplestinterpretationofenergyefficiencyistheenergy
requiredtotransmitandreceiveasinglebit.
–Transceiversshouldbeswitchablebetweendifferentstates-active
andsleeping.
52

53. Contd…
•Carrierfrequencyandmultiplechannels
–Transceiversareavailablefordifferentcarrierfrequencies-match
applicationrequirementsandregulatoryrestrictions.
–Channelshelpstoalleviatesomecongestionproblemsindense
networks.
–Suchchannelsor“subbands”arerelevant,forexample,forcertain
MACprotocols(FDMAormultichannelCSMA/ALOHAtechniques)
•Statechangetimesandenergy
–Atransceivercanoperateindifferentmodes:
•sendingorreceiving
•usedifferentchannels
•differentpower-safestates
53

54. Contd…
–Inanycase,thetimeandtheenergyrequiredtochangebetween
twosuchstatesareimportantfiguresofmerit.
–Theturnaroundtimebetweensendingandreceiving,forexample,
isimportantforvariousmediumaccessprotocols
•Datarates
–Carrierfrequencyandusedbandwidthtogetherwithmodulation
andcodingdeterminethegrossdatarate.
–Typicalvaluesareafewtensofkilobitspersecond
–Differentdataratescanbeachieved-byusingdifferent
modulationsorchangingthesymbolrate.
54

55. Contd…
•Modulations
–Thetransceiverstypicallysupportoneorseveralofon/off-keying,
ASK,FSK,orsimilarmodulations.
•Coding
–Sometransceiversallowvariouscodingschemestobeselected
•Transmissionpowercontrol
–Sometransceiverscandirectlyprovidecontroloverthe
transmissionpowertobeused;
–somerequiresomeexternalcircuitry.
–Maximumoutputpowerisusuallydeterminedbyregulations.
55

56. Contd…
•NoiseFigure
NFofanelementisdefinedastheratiooftheSignal-to-NoiseRatio
(SNR)ratioSNR
iattheinputoftheelementtotheSNRratioSNR
Oat
theelement’soutput:
NF=
�??????�??????
�??????�??????
ThedegradationofSNRduetotheelement’soperationandistypically
givenindB:NFdB=SNR
idB−SNR
OdB
56

57. Contd…
•Gain
–Thegainistheratiooftheoutputsignalpowertotheinputsignalpowerandis
typicallygivenindB.
–Amplifierswithhighgainaredesirabletoachievegoodenergyefficiency.
•Powerefficiency
–Theefficiencyoftheradiofrontendisgivenastheratiooftheradiatedpower
totheoverallpowerconsumedbythefrontend
–poweramplifier,theefficiencydescribestheratiooftheoutputsignal’spower
tothepowerconsumedbytheoverallpoweramplifier.
•Receiversensitivity
–Thereceiversensitivity(givenindBm)istheminimumsignalpoweratthe
receiverneededtoachieveaprescribedE
b/N
0
–Bettersensitivitylevelsextendthepossiblerangeofasystem.
57

58. Contd…
•Range
–Therangeisconsideredinabsenceofinterference;itevidently
dependsonthemaximumtransmissionpower,ontheantenna
characteristics,ontheattenuationcausedbytheenvironment,
whichinturndependsontheusedcarrierfrequency,onthe
modulation/codingschemethatisused,andonthebiterrorrate
thatoneiswillingtoacceptatthereceiver.
–Italsodependsonthequalityofthereceiver–basedon
sensitivity.
–Theproductswithrangesbetweenafewmetersandseveral
hundredsofmetersareavailable
58

59. Contd…
•Blockingperformance
–Theblockingperformanceofareceiverisitsachievedbiterror
rateinthepresenceofaninterferer.
–Blockingperformancecanbeimprovedbyinterposingafilter
betweenantennaandtransceiver.
–Animportantspecialcaseisanadjacentchannelinterfererthat
transmitsonneighboringfrequencies.
–Theadjacentchannelsuppressiondescribesatransceiver’s
capabilitytofilteroutsignalsfromadjacentfrequencybands(and
thustoreduceadjacentchannelinterference)hasadirectimpact
ontheobservedSignaltoInterferenceandNoiseRatio(SINR).
59

60. Contd…
•Outofbandemission
–Theinversetoadjacentchannelsuppressionistheoutofband
emissionofatransmitter.
–Tolimitdisturbanceofothersystems,oroftheWSNitselfina
multichannelsetup,thetransmittershouldproducelittle
transmissionpower
•CarriersenseandRSSI
–Theprecisesemanticsofthiscarriersensesignaldependsonthe
implementation.
–Forexample,theIEEE802.15.4standard[468]distinguishesthe
followingmodes:
60

61. Contd..
•Acarrierhasbeendetected,thatis,somesignalwhich
complieswiththemodulation.
•Carrierdetectedandenergyispresent.
•Thesignalstrengthatwhichanincomingdatapackethas
beenreceivedcanprovideusefulinformation(e.g.arough
estimateaboutthedistancefromthetransmitterassuming
thetransmissionpowerisknown);
•AreceiverhastoprovidethisinformationintheReceived
SignalStrengthIndicator(RSSI).
61

62. Contd..
•FrequencyStability
–Thefrequencystabilitydenotesthedegreeofvariation
fromnominalcenterfrequencieswhenenvironmental
conditionsofoscillatorsliketemperatureorpressure
change
–Poorfrequencystabilitycanbreakdowncommunication
links
•Voltagerange
–Transceiversshouldoperatereliablyoverarangeof
supplyvoltages
–Inefficientvoltagestabilizationcircuitryisrequired
62

63. Transceiver structures
•Radiofrequencyfrontend
–PerformsAnalogsignalprocessingintheactualradio
frequencyband
•BasebandProcessor
–PerformsallSignalProcessingindigitaldomain
–Communicateswithasensornodeprocessororother
digitalcircuitry
Betweenthesetwopartsafrequencyconversion
constitutedbyDACsandADCs
63

64. •ThePowerAmplifier(PA)acceptsupconvertedsignalsfromtheIFor
basebandpartandamplifiesthemfortransmissionovertheantenna.
TheLowNoiseAmplifier(LNA)amplifiesincomingsignalsupto
levelssuitableforfurtherprocessingwithoutsignificantlyreducing
theSNR[470].
64

65. •Therangeofpowersoftheincomingsignalsvariesfromvery
weaksignalsfromnodesclosetothereceptionboundaryto
strongsignalsfromnearbynodes;thisrangecanbeupto100
dB.
•LNAisactiveallthetimeandcanconsumeasignificantfraction
ofthetransceiver’senergy.
•Elementslikelocaloscillatorsorvoltage-controlledoscillators
andmixersareusedforfrequencyconversionfromtheRF
spectrumtoIFortothebaseband.
•TheincomingsignalatRFfrequenciesf
RFismultipliedina
mixerwithafixed-frequencysignalfromthelocaloscillator
(frequencyf
LO).
•IF=f
LO−f
RF.
65

66. Transceiver Operational States
•TransmitState:
–Inthetransmitstate,thetransmitpartofthetransceiverisactive
andtheantennaradiatesenergy.
•ReceiveState:
–thereceivepartisactive.
•IdleState:
–Atransceiverthatisreadytoreceivebutisnotcurrentlyreceiving
anythingissaidtobeinanidlestate.
–manypartsofthereceivecircuitryareactive,andotherscanbe
switchedoff.
66

67. Contd..
–Forexample,inthesynchronizationcircuitry,someelements
concernedwithacquisitionareactive,whilethoseconcernedwith
trackingcanbeswitchedoffandactivatedonlywhenthe
acquisitionhasfoundsomething.
–Amajorsourceofpowerdissipationisleakage.
•SleepState:
–significantpartsofthetransceiverareswitchedoff.
–Therearetransceiversofferingseveraldifferentsleepstates.
–Thesesleepstatesdifferintheamountofcircuitryswitchedoff
–associatedrecoverytimesandstartupenergy
67

68. Activity: Brainstorming
68

69. Advanced Radio Concepts
–Wakeupradio
•Oneofthemostpower-intensiveoperationsiswaitingfora
transmissiontocomein,readytoreceiveit.
•Duringthistime,thereceivercircuitmustbepoweredup-to
observewirelesschannelneedsspendingenergywithoutany
immediatebenefit.
•Areceiverstructureisnecessarythatdoesnotneedpowerbut
candetectwhenapacketstartstoarrive.
•Tokeepthisspecializedreceiversimple,itshouldraisean
eventtonotifyothercomponentsofanincomingpacket;upon
suchanevent,themainreceivercanbeturnedonandperform
theactualreceptionofthepacket.
•Such receiver concepts are called wakeup receivers
•Each packet –power consumption is 1 microwatt
69

70. Contd…
–Spreadspectrumtransceivers
•ASK,FSKhaslimitedPerformancewhenlotofinterference.
•ToovercomeSpreadspectrumtransceivers–DSSS(Direct
Sequencespreadspectrum,FrequencyHoppingSpread
Spectrum
•Complexhardwareandcostly
–Ultrabandcommunication
•Usingsuchalargebandwidth,anultrawideband
communicationwilloverlapwiththespectrumofa
conventionalradiosystem.
•But,becauseofthelargespreadingofthesignal,averysmall
transmissionpowersufficesUWBtransmitterisactually
relativelysimplesinceitdoesnotneedoscillatorsorrelated
circuitryfoundintransmittersforacarrier-frequency-based
transmitter.
•Thereceiversrequirecomplextimingsynchronization.
70

71. Non radio frequency wireless
communication
–Optical
–Opticallinkbetweensensors
–Advantage–verysmallenergyperbit
–LEDs–Highefficiencysenders
–Disadvantages:Stronglyinfluencedbywhethercondition
–LineofSight
–Ultrasound
–Forunderwatercommunication:Ultrasoundcommunication
issuitable
–Travelsforlongdistances
–Differentpropagationspeed
71

72. Examples of radio Transceiver
–RFMTR1000family
–Hardwareaccelerators(Micamotes)
–ChipconCC100andCC2420family
–InfineonTDA525xfamily
–IEEE802.15.4/EmberEM2420RFTransceiver
–NationalSemiconductorLMX3162
–ConexantRDSSS9M
72

73. Contd..
–RFMTR1000family
•TheTR1000familyofradiotransceiversfromRF
Monolithics2isavailableforthe916MHzand868MHz
frequencyrange.
•Itworksina400kHzwidebandcenteredat,for
example,916.50MHz.
•Itisintendedforshort-rangeradiocommunicationwith
upto115.2kbps.
•Low-powerconsumptioninbothsendandreceivemodes
andespeciallyinsleepmode.
73

74. Contd..
–Hardwareaccelerators(Micamotes)
•TheMicamotesusetheRFMTR1000transceiverand
containalsoasetofhardwareaccelerators.
•Thetransceiveroffersaverylow-levelinterface,giving
themicrocontrollertightcontroloverframeformats,
MACprotocols,andsoforth.
•Ontheotherhand,framingandMACcanbevery
computationintensive,forexample,forcomputing
checksums,formakingbytesoutofseriallyreceivedbits
orfordetectingStartFrameDelimiters(SFDs)ina
streamofsymbols
74

75. •ChipconCC1000
–Range 300 to 1000 MHz, programmable in 250 Hz steps
–FSK modulation
–Provides RSSI
•ChipconCC2400
–Implements 802.15.4
–2.4 GHz, DSSS modem
–250 kbps
–low power consumption than above transceivers

76. •Infineon TDA 525x family
–provides flexible, single-chip, energy-efficient transceivers
–E.g., TDA5250: 868 -870 MHz transceiver
–ASK or FSK modulation
–RSSI, highly efficient power amplifier
–Intelligent power down, “self-polling” mechanism(define
data rate)
–Excellent blocking performance (quite resistant to
interference)

77. Example radio transceivers for ad hoc networks
•Adhocnetworks:Usually,higherdataratesarerequired
•Typical:IEEE802.11b/g/aisconsidered
–Upto54MBit/s
–Relativelylongdistance(100sofmeterspossible,typical10sof
metersathigherdatarates)
–Worksreasonablywell(butcertainlynotperfect)inmobile
environments
–Problem:expensiveequipment,quitepowerhungry

78. Sensors and actuators
01.09.2020

79. Contd…
•Sensors
–Sensors can be roughly categorized into three categories
•Passive,omnidirectionalsensors
–Thesesensorscanmeasureaphysicalquantityatthepointofthe
sensornodewithoutactuallymanipulatingtheenvironmentby
activeprobing–inthissense,theyarepassive.
–Moreover,someofthesesensorsactuallyareself-poweredinthe
sensethattheyobtaintheenergytheyneedfromtheenvironment
–energyisonlyneededtoamplifytheiranalogsignal.Thereisno
notionof“direction”involvedinthesemeasurements.

80. Contd…
–Typicalexamplesforsuchsensorsincludethermometer,light
sensors,vibration,microphones,humidity,mechanicalstress
ortensioninmaterials,chemicalsensorssensitiveforgiven
substances,smokedetectors,airpressure,andsoon.
•Passive,narrow-beamsensors
–Thesesensorsarepassiveaswell,buthaveawell-defined
notionofdirectionofmeasurement.
–Atypicalexampleisacamera,whichcan“take
measurements”inagivendirection,buthastoberotatedif
needbe.

81. Contd…
•Active sensors
–Thislastgroupofsensorsactivelyprobesthe
environment,forexample,asonarorradarsensoror
sometypesofseismicsensors,whichgenerateshock
wavesbysmallexplosions.
•Obvioustrade-offsincludeaccuracy,dependability,energy
consumption,cost,size,andsoon–allthiswouldmakea
detaileddiscussionofindividualsensorsquiteineffective.
•Overall,mostofthetheoreticalworkonWSNsconsiders
passive,omnidirectionalsensors.

82. Contd…
•Narrow-beam-typesensorslikecamerasareusedinsomepractical
testbeds,butthereisnorealsystematicinvestigationonhowto
controlandschedulethemovementofsuchsensors.
•Eachsensornodehasacertainareaofcoverageforwhichitcan
reliablyandaccuratelyreporttheparticularquantitythatitis
observing.

83. Actuators
•Inprinciple,allthatasensornodecandoistoopenorclosea
switchorarelayortosetavalueinsomeway.
•Whetherthiscontrolsamotor,alightbulb,orsomeother
physicalobjectisnotreallyofconcerntotheway
communicationprotocolsaredesigned.
•Inarealnetwork,however,carehastobetakentoproperly
accountfortheidiosyncrasiesofdifferentactuators.
•Also,itisgooddesignpracticeinmostembeddedsystem
applicationstopairanyactuatorwithacontrollingsensor–
followingtheprincipleto“nevertrustanactuator”

84. Power supply of sensor nodes
•Goal:toprovideasmuchenergyaspossibleatsmallestcost/volume/
weight/rechargetime/longevity
–InWSN,rechargingmayormaynotbeanoption
•Options
–Primarybatteries–notrechargeable
–Secondarybatteries–rechargeable,onlymakessensein
combinationwithsomeformofenergyharvesting
•Storingpowerisconventionallydoneusingbatteries.
•Asaroughorientation,anormalAAbatterystoresabout2.2–2.5Ah
at1.5V.
•Batterydesignisascienceandindustryinitself,andenergy
scavenginghasattractedalotofattentioninresearch.

85. Contd…
Storing energy: Batteries
•Traditional batteries
–Thepowersourceofasensornodeisabattery,either
nonrechargeable(“primarybatteries”)or,ifanenergyscavenging
deviceispresentonthenode,alsorechargeable(“secondary
batteries”).
–Insomeformorother,batteriesareelectro-chemicalstoresfor
energy–thechemicalsbeingthemaindeterminingfactorof
batterytechnology.

86. Contd…
Battery examples
•Energy per volume (Joule per cubic centimeter):

87. Contd…
Upon these batteries, very tough requirements are imposed:
Capacity
•They should have high capacity at a small weight, small
volume, and low price.
•The main metric is energy per volume, J/cm3. Above table
shows some typical values of energy densities, using
traditional, macroscale battery technologies.

88. Contd…
Capacity under load
•Theyshouldwithstandvarioususagepatternsasasensor
nodecanconsumequitedifferentlevelsofpowerovertime
andactuallydrawhighcurrentincertainoperationmodes.
•Inmosttechnologies,thelargerthebattery,themore
powercanbedeliveredinstantaneously.
•Inaddition,theratedbatterycapacityspecifiedbya
manufacturerisonlyvalidaslongasmaximumdischarge
currentsarenotexceeded,lestcapacitydropsoreven
prematurebatteryfailureoccurs

89. Contd…
Self-discharge
•Theirself-dischargeshouldbelow;theymightalsohaveto
lastforalongtime(usingcertaintechnologies,batteriesare
operationalonlyforafewmonths,irrespectiveofwhether
powerisdrawnfromthemornot).
•Zinc-airbatteries,forexample,haveonlyaveryshort
lifetime(ontheorderofweeks),whichoffsetstheir
attractivelyhighenergydensity.

90. Contd…
Efficientrecharging
•Rechargingshouldbeefficientevenatlowand
intermittentlyavailablerechargepower;consequently,the
batteryshouldalsonotexhibitany“memoryeffect”.
•Someoftheenergy-scavengingtechniquesareonlyableto
producecurrentintheμAregion(butpossiblysustained)at
onlyafewvoltsatbest.
•Currentbatterytechnologywouldbasicallynotrechargeat
suchvalues.

91. Contd…
Relaxation
•Theirrelaxationeffect–theseemingself-rechargingofan
emptyoralmostemptybatterywhennocurrentisdrawnfrom
it,basedonchemicaldiffusionprocesseswithinthecell–should
beclearlyunderstood.
•Batterylifetimeandusablecapacityisconsiderablyextendedif
thiseffectisleveraged.
•example,itispossibletousemultiplebatteriesinparalleland
“schedule”thedischargefromonebatterytoanother,depending
onrelaxationpropertiesandpowerrequirementsofthe
operationstobesupported

92. Contd…
Energy scavenging
•Someoftheunconventionalenergystores–fuelcells,microheat
engines,radioactivity–convertenergyfromsomestored,secondary
formintoelectricityinalessdirectandeasytousewaythananormal
batterywoulddo.
•Theentireenergysupplyisstoredonthenodeitself–oncethefuel
supplyisexhausted,thenodefails.
•Toensuretrulylong-lastingnodesandwirelesssensornetworks,such
alimitedenergystoreisunacceptable.
•Rather,energyfromanode’senvironmentmustbetappedintoand
madeavailabletothenode–energyscavengingshouldtakeplace.
Severalapproachesexist

93. Photovoltaics
•Thewell-knownsolarcellscanbeusedtopowersensornodes.
•Theavailablepowerdependsonwhethernodesareusedoutdoorsor
indoors,andontimeofdayandwhetherforoutdoorusage.
•Differenttechnologiesarebestsuitedforeitheroutdoororindoor
usage.
•Theresultingpowerissomewherebetween10μW/cm
2
indoorsand
15mW/cm
2
outdoors.
•Singlecellsachieveafairlystableoutputvoltageofabout0.6V(and
havethereforetobeusedinseries)aslongasthedrawncurrentdoes
notexceedacriticalthreshold,whichdepends,amongotherfactors,
onthelightintensity.
•Hence,solarcellsareusuallyusedtorechargesecondarybatteries.

94. Temperaturegradients
•Differencesintemperaturecanbedirectlyconvertedtoelectrical
energy.
•Theoretically,evensmalldifferenceof,forexample,5Kelvincan
produceconsiderablepower,butpracticaldevicesfallveryshortof
theoreticalupperlimits(givenbytheCarnotefficiency).
•Seebeckeffect-basedthermoelectricgeneratorsarecommonly
considered;oneexampleisagenerator,whichwillbecommercially
availablesoon,thatachievesabout80μW/cm
2
atabout1Vfroma5
Kelvintemperaturedifference

95. Vibrations
•Onealmostpervasiveformofmechanicalenergyisvibrations:
•wallsorwindowsinbuildingsareresonatingwithcarsortrucks
passinginthestreets,machineryoftenhaslowfrequencyvibrations,
ventilationsalsocauseit,andsoon.
•Theavailableenergydependsonbothamplitudeandfrequencyofthe
vibrationandrangesfromabout0.1μW/cm
3
upto10,000μW/cm
3
forsomeextremecases(typicalupperlimitsarelower).
•Convertingvibrationstoelectricalenergycanbeundertakenbyvarious
means,basedonelectromagnetic,electrostatic,orpiezoelectric
principles.

96. Pressurevariations
•Somewhatsimilartovibrations,avariationofpressurecan
alsobeusedasapowersource.Suchpiezoelectric
generatorsareinfactusedalready.
•Onewell-knownexampleistheinclusionofapiezoelectric
generatorintheheelofashoe,togeneratepowerasa
humanwalksabout.
•Thisdevicecanproduce,onaverage,330μW/cm
2
.Itis,
however,notclearhowsuchtechnologiescanbeappliedto
WSNs.

97. Flowofair/liquid
•Anotheroften-usedpowersourceistheflowofairorliquid
inwindmillsorturbines.
•Thechallengehereisagaintheminiaturization,butsomeof
theworkonmillimeterscaleMEMSgasturbinesmightbe
reusable.
•However,thishassofarnotproducedanynotableresults.

99. Comparison of energy sources

100. •Astheseexamplesshow,energyscavengingusuallyhastobe
combinedwithsecondarybatteriesastheactualpower
sourcesarenotabletoprovidepowerconsistently,
uninterruptedly,atarequiredlevel;rather,theytendto
fluctuateovertime.
•Thisrequiresadditionalcircuitryforrechargingofbatteries,
possiblyconvertingtohigherpowerlevels,andabattery
technologythatcanberechargedatlowcurrents