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7/29/2019 Lecture3.1Factors Influencing Sensor Network
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Factors Influencing Sensor NetworkFactors Influencing Sensor Network
DesignDesign
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Factors Influencing Sensor NetworkFactors Influencing Sensor Network
DesignDesign
A. Hardware ConstraintsA. Hardware Constraints
B. Fault Tolerance (Reliability)B. Fault Tolerance (Reliability)
C. ScalabilityC. Scalability
D. Production CostsD. Production CostsE. Sensor Network TopologyE. Sensor Network Topology
F. Operating Environment (Applications)F. Operating Environment (Applications)
G. Transmission MediaG. Transmission Media
H. Power Consumption (Lifetime)H. Power Consumption (Lifetime)
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Sensor Node HardwareSensor Node Hardware
Power UnitPower Unit AntennaAntenna
Sensor ADCSensor ADC
ProcessorProcessor
MemoryMemory
TransceiverTransceiver
Location Finding SystemLocation Finding System MobilizerMobilizer
SENSING UNIT PROCESSING UNIT
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Fault ToleranceFault Tolerance
(Reliability)(Reliability)
Sensor nodes may fail due to lack of power,Sensor nodes may fail due to lack of power,physical damage or environmental interferencephysical damage or environmental interference
The failure of sensor nodes should not affect theThe failure of sensor nodes should not affect the
overall operation of the sensor networkoverall operation of the sensor network
This is calledThis is calledRELIABILITY or FAULT TOLERANCE,RELIABILITY or FAULT TOLERANCE,
i.e., ability to sustain sensor network functionalityi.e., ability to sustain sensor network functionality
without any interruptionwithout any interruption
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Fault Tolerance (Reliability)Fault Tolerance (Reliability)
Reliability R (Fault Tolerance) of a sensor node k isReliability R (Fault Tolerance) of a sensor node k ismodeled:modeled:
i.e., by Poisson distribution, to capture the probability ofi.e., by Poisson distribution, to capture the probability ofnot having a failure within the time interval (0,t) with lnot having a failure within the time interval (0,t) with l kk isisthe failure rate of the sensor node k and t is the time period.the failure rate of the sensor node k and t is the time period.
)()(
t
kketR
=
G. Hoblos, M. Staroswiecki, and A. Aitouche,G. Hoblos, M. Staroswiecki, and A. Aitouche, Optimal Design of Fault Tolerant SensorOptimal Design of Fault Tolerant SensorNetworks,Networks, IEEE Int. Conf. on Control ApplicationsIEEE Int. Conf. on Control Applications, pp. 467-472, Sept. 2000., pp. 467-472, Sept. 2000.
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Fault Tolerance (Reliability)Fault Tolerance (Reliability)
Reliability (Fault Tolerance) of a broadcast rangeReliability (Fault Tolerance) of a broadcast rangewith N sensor nodes is calculated fromwith N sensor nodes is calculated from
])(1[1)(1
=
=N
k
k tRtR
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Fault Tolerance (Reliability)Fault Tolerance (Reliability)
EXAMPLE:EXAMPLE:
How many sensor nodes are needed within aHow many sensor nodes are needed within abroadcast radius (range) to have 99% fault toleratedbroadcast radius (range) to have 99% fault tolerated
network?network?
Assuming all sensors within the radio range haveAssuming all sensors within the radio range havesame reliability, previous equation becomes:same reliability, previous equation becomes:
Drop t and substitute f = (1-R) 0.99 = (1 fN) N=2
NtRtR )](1[1)( =
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Fault Tolerance (Reliability)Fault Tolerance (Reliability)
REMARKREMARK::
1. Protocols and algorithms may be designed to1. Protocols and algorithms may be designed toaddress the level of fault tolerance required byaddress the level of fault tolerance required by
sensor networks.sensor networks.
2. If the environment has little interference, then2. If the environment has little interference, thenthe requirements can be more relaxed.the requirements can be more relaxed.
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Fault Tolerance (Reliability)Fault Tolerance (Reliability)
Examples:Examples:1.1. HouseHouse to keep track of humidity and temperatureto keep track of humidity and temperature
levelslevels the sensors cannot be damaged easily orthe sensors cannot be damaged easily orinterfered by environmentinterfered by environment lowlow fault tolerancefault tolerance(reliability) requirement!!!!(reliability) requirement!!!!
2.2. BattlefieldBattlefield for surveillance the sensed data are criticalfor surveillance the sensed data are criticaland sensors can be destroyed by enemiesand sensors can be destroyed by enemies highhigh faultfault
tolerance (reliability) requirement!!!tolerance (reliability) requirement!!!
Bottom line:Bottom line: Fault Tolerance (Reliability)Fault Tolerance (Reliability)
depends heavily on applications!!!depends heavily on applications!!!
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ScalabilityScalability
The number of sensor nodes may reach thousandsThe number of sensor nodes may reach thousandsin some applicationsin some applications
The density of sensor nodes can range from few toThe density of sensor nodes can range from few toseveral hundreds in a region (cluster) which can beseveral hundreds in a region (cluster) which can be
less than 10m in diameterless than 10m in diameter
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Node DensityNode Density:: The number of expected nodes per unit areaThe number of expected nodes per unit area::
N is the number of scattered sensor nodes in region AN is the number of scattered sensor nodes in region A
Node DegreeNode Degree: The number of expected nodes in the transmission range of a: The number of expected nodes in the transmission range of anodenode
R is the radio transmission rangeR is the radio transmission range
Basically:Basically: mm(R(R)) is the number of sensor nodes within the transmissionis the number of sensor nodes within the transmissionradius R of each sensor node in region A.radius R of each sensor node in region A.
ScalabilityScalability
AN/=
2)( RR =
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ScalabilityScalability
EXAMPLE:EXAMPLE:
Assume sensor nodes are evenly distributed in the sensorAssume sensor nodes are evenly distributed in the sensor
field. Determine the node density and node degree if 200 sensorfield. Determine the node density and node degree if 200 sensornodes are deployed in a 50x50 mnodes are deployed in a 50x50 m22 region where each sensorregion where each sensor
node has a broadcast radius of 5m.node has a broadcast radius of 5m.
Use the eq.Use the eq.
6508.0)( 2 = R
08.0)5050/(200 ==
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ScalabilityScalabilityExamples:Examples:
1.1. Machine Diagnosis Application:Machine Diagnosis Application:less than 50 sensor nodes in a 5 m x 5 m region.less than 50 sensor nodes in a 5 m x 5 m region.
2.2. Vehicle Tracking Application:Vehicle Tracking Application:Around 10 sensor nodes per cluster/region.Around 10 sensor nodes per cluster/region.
3.3. Home Application:Home Application: tens depending on the size of the house.tens depending on the size of the house.
4.4. Habitat Monitoring Application:Habitat Monitoring Application:Range from 25 to 100 nodes/clusterRange from 25 to 100 nodes/cluster
5.5. Personal Applications:Personal Applications:Ranges from tens to hundreds, e.g., clothing, eye glasses, shoes,Ranges from tens to hundreds, e.g., clothing, eye glasses, shoes,watch, jewelry.watch, jewelry.
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Production CostsProduction Costs
Cost of sensors must be low so that sensorCost of sensors must be low so that sensornetworks can be justified!networks can be justified!
PicoNode: less than $1PicoNode: less than $1
Bluetooth system: around $10,-Bluetooth system: around $10,- THE OBJECTIVE FOR SENSOR COSTSTHE OBJECTIVE FOR SENSOR COSTS
must be lower than $1!!!!!!!must be lower than $1!!!!!!!
CurrentlyCurrently ranges from $25 to $180ranges from $25 to $180(STILL VERY EXPENSIVE!!!!)(STILL VERY EXPENSIVE!!!!)
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Sensor Network TopologySensor Network Topology
Internet,Internet,Satellite, UAVSatellite, UAV
Sink
Sink
Task
Manager
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Sensor Network TopologySensor Network Topology
Topology maintenance and change:Topology maintenance and change:
Pre-deployment and Deployment PhasePre-deployment and Deployment Phase
Post Deployment PhasePost Deployment Phase Re-Deployment of Additional NodesRe-Deployment of Additional Nodes
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Sensor Network TopologySensor Network Topology
Pre-deployment and Deployment PhasePre-deployment and Deployment Phase
Dropped from aircraft(Random deployment) Well Planned, Fixed (Regular deployment) Mobile Sensor Nodes
Adaptive, dynamicCan move to compensate for deployment
shortcomings
Can be passively moved around by some
external force (wind, water)Can actively seek out interesting areas
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Sensor Network TopologySensor Network Topology
Initial Deployment SchemesInitial Deployment Schemes
Reduce installation costReduce installation cost
Eliminate the need for any pre-organization andEliminate the need for any pre-organization andpre-planningpre-planning
Increase the flexibility of arrangementIncrease the flexibility of arrangement
Promote self-organization and fault-tolerancePromote self-organization and fault-tolerance
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Sensor Network TopologySensor Network Topology
POST-DEPLOYMENT PHASEPOST-DEPLOYMENT PHASE
Topology changes may occur:Topology changes may occur:
PositionPosition
Reachability (due to jamming, noise, movingReachability (due to jamming, noise, moving
obstacles, etc.)obstacles, etc.)Available energyAvailable energy
MalfunctioningMalfunctioning
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Operating EnvironmentOperating Environment
* SEE ALL THE APPLICATIONS discussed before* SEE ALL THE APPLICATIONS discussed before
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TRANSMISSION MEDIATRANSMISSION MEDIA
Radio, Infrared, Optical, Acoustic, Magnetic MediaRadio, Infrared, Optical, Acoustic, Magnetic Media
ISMISM (Industrial, Scientific and Medical)(Industrial, Scientific and Medical) Bands (433Bands (433
MHz ISM Band in Europe and 915 MHz as well asMHz ISM Band in Europe and 915 MHz as well as2.4 GHz ISM Bands in North America)2.4 GHz ISM Bands in North America)
REASONS:REASONS: Free radio, huge spectrum allocationFree radio, huge spectrum allocation
and global availability.and global availability.
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POWER CONSUMPTIONPOWER CONSUMPTION
Sensor node has limited power sourceSensor node has limited power source
Sensor node LIFETIME depends on BATTERY lifetimeSensor node LIFETIME depends on BATTERY lifetime
Goal: Provide as much energy as possible at smallestGoal: Provide as much energy as possible at smallestcost/volume/weight/rechargecost/volume/weight/recharge
Recharging may or may not be an optionRecharging may or may not be an option
OptionsOptions
Primary batteries not rechargeablePrimary batteries not rechargeable
Secondary batteries rechargeable, only makesSecondary batteries rechargeable, only makes
sense in combination with some form of energysense in combination with some form of energyharvestingharvesting
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Battery ExamplesBattery Examples
Energy per volume (Joule per cubic centimeter):Energy per volume (Joule per cubic centimeter):Primary batteries
Chemistry Zinc-air Lithium Alkaline
Energy (J/cm3) 3780 2880 1200
Secondary batteries
Chemistry Lithium NiMHd NiCd
Energy (J/cm3) 1080 860 650
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Energy ScavengingEnergy Scavenging (Harvesting)(Harvesting)Ambient Energy Sources (their power density)Ambient Energy Sources (their power density)
Solar (Outdoors)Solar (Outdoors) 15 mW/cm 15 mW/cm22 (direct sun)(direct sun)
Solar (Indoors)Solar (Indoors) 0.006 mW/cm 0.006 mW/cm22 (office desk)(office desk)
0.57 mW/cm0.57 mW/cm22
(
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POWER CONSUMPTIONPOWER CONSUMPTION
Sensors can be aSensors can be a DATA ORIGINATORDATA ORIGINATOR or aor a DATADATAROUTER.ROUTER.
Power conservation and power management arePower conservation and power management areimportantimportant
POWER AWARE COMMUNICATION PROTOCOLSPOWER AWARE COMMUNICATION PROTOCOLSmust be developed.must be developed.
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POWER CONSUMPTIONPOWER CONSUMPTION
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Power ConsumptionPower Consumption
Power consumption in a sensor network can bePower consumption in a sensor network can bedivided into three domainsdivided into three domains
SensingSensingData Processing (Computation)Data Processing (Computation)
CommunicationCommunication
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Power ConsumptionPower Consumption
Power consumption in a sensor network can bePower consumption in a sensor network can bedivided into three domainsdivided into three domains
SensingSensingData Processing (Computation)Data Processing (Computation)
CommunicationCommunication
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Power ConsumptionPower Consumption
SensingSensing
Depends onDepends on
ApplicationApplication
Nature of sensing: Sporadic or ConstantNature of sensing: Sporadic or Constant
Detection complexityDetection complexity
Ambient noise levelsAmbient noise levels
Rule of thumb (ADC power consumption)Rule of thumb (ADC power consumption)
FFss - sensing frequency, ENOB - effective number of bits- sensing frequency, ENOB - effective number of bits
PsFS2
EN
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Power ConsumptionPower Consumption
Power consumption in a sensor network can bePower consumption in a sensor network can bedivided into three domainsdivided into three domains
SensingSensingData Processing (Computation)Data Processing (Computation)
CommunicationCommunication
Power Consumption inPower Consumption in
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Power Consumption inPower Consumption in
Data Processing (Computation)Data Processing (Computation)(Wang/Chandrakarasan: Energy Efficient DSPs for Wireless Sensor(Wang/Chandrakarasan: Energy Efficient DSPs for Wireless Sensor
Networks. IEEE Signal Proc. Magazine, July 2002. also from Shih paper)Networks. IEEE Signal Proc. Magazine, July 2002. also from Shih paper)
)(***/2 TVndd
dd
V
OddP eIVVCfP +=
The power consumption in data processing (PThe power consumption in data processing (Ppp) is) is
f clock frequency
C is the aver. capacitance switched per cycle (C ~ 0.67nF);
Vdd is the supply voltage
VT is the thermal voltage (n~21.26; Io ~ 1.196 mA)
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Power Consumption inPower Consumption in
Data ProcessingData Processing (Computation)(Computation)
The second term indicates the power loss due toThe second term indicates the power loss due toleakage currentsleakage currents
In general, leakage energy accounts for about 10%In general, leakage energy accounts for about 10%of the total energy dissipationof the total energy dissipation
In low duty cycles, leakage energy can becomeIn low duty cycles, leakage energy can become
large (up to 50%)large (up to 50%)
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Power Consumption inPower Consumption in
Data ProcessingData Processing
This is much less than in communication.This is much less than in communication.
EXAMPLE:EXAMPLE: (Assuming: Rayleigh Fading wireless(Assuming: Rayleigh Fading wireless
channel; fourth power distance loss)channel; fourth power distance loss)
Energy cost of transmittingEnergy cost of transmitting 1 KB1 KB over a distance ofover a distance of100 m is approx. equal to executing100 m is approx. equal to executing 0.25 Million0.25 Millioninstructionsinstructions by a 8 million instructions per secondby a 8 million instructions per secondprocessor (MicaZ).processor (MicaZ).
Local data processing is crucial in minimizingLocal data processing is crucial in minimizingpower consumption in a multi-hop networkpower consumption in a multi-hop network
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Memory Power ConsumptionMemory Power Consumption
Crucial part: FLASH memoryCrucial part: FLASH memory
Power for RAM almost negligiblePower for RAM almost negligible
FLASH writing/erasing is expensiveFLASH writing/erasing is expensiveExample: FLASH on Mica motesExample: FLASH on Mica motes
Reading: 1.1 nAh per byteReading: 1.1 nAh per byte
Writing: 83.3 nAh per byteWriting: 83.3 nAh per byte
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Power ConsumptionPower Consumption
Power consumption in a sensor network can bePower consumption in a sensor network can bedivided into three domainsdivided into three domains
SensingSensingData Processing (Computation)Data Processing (Computation)
CommunicationCommunication
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Power Consumption forPower Consumption for
CommunicationCommunication
A sensor spends maximum energy in dataA sensor spends maximum energy in datacommunication (both for transmission and reception).communication (both for transmission and reception).
NOTE:NOTE:
For short range communication with low radiationFor short range communication with low radiationpower (~0 dbm), transmission and reception powerpower (~0 dbm), transmission and reception powercosts are approximately the same,costs are approximately the same,
e.g., modern low power short range transceiverse.g., modern low power short range transceiversconsume betweenconsume between 15 and 300 mW15 and 300 mW of power whenof power when
sending and receivingsending and receiving Transceiver circuitry has both active and start-upTransceiver circuitry has both active and start-up
power consumptionpower consumption
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Power Consumption forPower Consumption for
CommunicationCommunication
Power consumption forPower consumption fordata communicationdata communication (P(Pcc))
PPcc = P= P00 + P+ Ptxtx + P+ Prxrx
PPte/rete/re is the power consumed in the transmitter/receiveris the power consumed in the transmitter/receiver
electronics (including the start-up power)electronics (including the start-up power)
PP00 is the output transmit poweris the output transmit power
TX RXTX RX
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Power Consumption forPower Consumption for
CommunicationCommunication
START-UP POWER/ START-UP TIMESTART-UP POWER/ START-UP TIME
A transceiver spends upon waking up from sleep mode,A transceiver spends upon waking up from sleep mode,e.g., to ramp upe.g., to ramp up phase locked loops or voltagephase locked loops or voltagecontrolled oscillatorscontrolled oscillators..
During start-up time, no transmission or reception ofDuring start-up time, no transmission or reception ofdata is possible.data is possible.
Sensors communicate in short data packetsSensors communicate in short data packets
Start-up power starts dominating as packet size isStart-up power starts dominating as packet size isreducedreduced
It is inefficient to turn the transceiver ON and OFFIt is inefficient to turn the transceiver ON and OFFbecause a large amount of power is spent in turning thebecause a large amount of power is spent in turning thetransceiver back ON each time.transceiver back ON each time.
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Wasted EnergyWasted Energy
Fixed cost of communication:Fixed cost of communication: Startup TimeStartup Time High energy per bit for small packetsHigh energy per bit for small packets (from Shih paper)(from Shih paper)
Parameters: R=1 Mbps; TParameters: R=1 Mbps; Tstst ~ 450 msec, P~ 450 msec, Ptete~81mW; P~81mW; Poutout = 0 dBm= 0 dBm
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Energy vs Packet SizeEnergy vs Packet Size
TR 1000 (115kbps)
0
1020
30
40
50
60
10 100 1000 10000
Packet Size (bits)
E
bit(p
J)
Energy per Bit
(pJ)
As packet size is reduced the energy consumption is dominated by the startup time on the orderof hundreds of microseconds during which large amounts of power is wasted.
NOTE: During start-up time NO DATA CAN BE SENT or RECEIVED by the
transceiver.
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Start-Up and SwitchingStart-Up and Switching
Startup energy consumptionStartup energy consumption
EEstst = P= PLOLO x tx tstst
PPLOLO, power consumption of the circuitry (synthesizer, power consumption of the circuitry (synthesizer
and VCO); tand VCO); tstst, time required to start up all, time required to start up allcomponentscomponents
Energy is consumed when transceiver switchesEnergy is consumed when transceiver switchesfrom transmit to receive modefrom transmit to receive mode
Switching energy consumptionSwitching energy consumptionEEswsw = P= PLOLO x tx tswsw
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Start-Up Time and Sleep ModeStart-Up Time and Sleep Mode
The effect of the transceiver startup time willThe effect of the transceiver startup time willgreatly depend on the type of MAC protocol used.greatly depend on the type of MAC protocol used.
To minimize power consumption, it is desirable toTo minimize power consumption, it is desirable tohave the transceiver in ahave the transceiver in a sleep modesleep mode as much asas much aspossiblepossible
Energy savings up to 99.99% (59.1mWEnergy savings up to 99.99% (59.1mW 33mmW)W) BUTBUT
Constantly turning on and off the transceiver alsoConstantly turning on and off the transceiver alsoconsumes energy to bring it to readiness forconsumes energy to bring it to readiness fortransmission or reception.transmission or reception.
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Receiving and Transmitting EnergyReceiving and Transmitting Energy
ConsumptionConsumption
Receiving energy consumptionReceiving energy consumption
EErxrx = (P= (PLOLO + P+ PRXRX ) t) trxrx
PPRXRX, power consumption of active components, e.g.,, power consumption of active components, e.g.,
decoder, tdecoder, trxrx, time it takes to receive a packet, time it takes to receive a packet Transmitting energy consumptionTransmitting energy consumption
EEtxtx = (P= (PLOLO + P+ PPAPA ) t) ttxtx
PPPAPA, power consumption of power amplifier, power consumption of power amplifier
PPPAPA = 1/= 1/ PPoutout ,, power efficiency of power amplifier, Ppower efficiency of power amplifier, Poutout, desired, desired
RF output power levelRF output power level
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RF output powerRF output power
http://memsic.com/support/documentation/wireless-sensor-networks/category/7-datasheets.html?download=148%3Amicazhttp://memsic.com/support/documentation/wireless-sensor-networks/category/7-datasheets.html?download=148%3Amicaz
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Power Amplifier Power ConsumptionPower Amplifier Power Consumption
Receiving energy consumptionReceiving energy consumption
PPPAPA = 1/= 1/ PAPA rr ddnn
PAPA, amplifier constant (antenna gain, wavelength,, amplifier constant (antenna gain, wavelength,thermal noise power spectral density, desiredthermal noise power spectral density, desiredsignal to noise ratio (SNR) at distance d),signal to noise ratio (SNR) at distance d),
r, data rate,r, data rate,
n, path loss exponent of the channel (n=2-4)n, path loss exponent of the channel (n=2-4)
d, distance between nodesd, distance between nodes
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Lets put it togetherLets put it together
Energy consumption for communicationEnergy consumption for communication
EEcc = E= Estst + E+ Erxrx + E+ Eswsw + E+ Etxtx
= P= PLOLO ttstst + (P+ (PLOLO + P+ PRXRX)t)trxrx + P+ PLOLO ttswsw + (P+ (PLOLO+P+PPAPA)t)ttxtx
Let tLet trxrx = t= ttxtx = l= lPKTPKT/r/r
EEcc = P= PLOLO (t(tstst+t+tswsw)+(2P)+(2PLOLO + P+ PRXRX)l)lPKTPKT/r + 1//r + 1/ PAPA llPKTPKT ddnnDistance-independentDistance-independent Distance-dependentDistance-dependent
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A SIMPLE ENERGY MODELA SIMPLE ENERGY MODEL
Operation EnergyDissipated
Transmitter Electronics ( ETx-elec)
Receiver Electronics ( ERx-elec)
( ETx-elec = ERx-elec = Eelec )
50 nJ/bit
Transmit Amplifier {eamp} 100pJ/bit/m2
TransmitElectronics
TxAmplifier
ETx (k,D)
Eelec * keamp* k* D
2
k bit packet
ReceiveElectronics
Eelec * k
k bit packet
D
tx (k,D) = Etx-elec (k) + Etx-amp (k,D)
tx (k,D) = Eelec * k + eamp * k * D2
ERx (k) = Erx-elec (k)
ERx (k) = Eelec * k
ERx (k)
ETx-elec (k) ETx-amp (k,D)
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Power ConsumptionPower Consumption(A Simple Energy Model)(A Simple Energy Model)
Assuming a sensor node is only operating in transmit andreceive modes with the following assumptions:Energy to run circuitry:
Eelec = 50 nJ/bit
Energy for radio transmission:
eamp = 100 pJ/bit/m2
Energy for sending k bits over distance D
ETx
(k,D) = Eelec
* k + eamp
* k * D2
Energy for receiving k bits:
ERx (k,D) = Eelec * k
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Example using the Simple Energy ModelExample using the Simple Energy Model
What is the energy consumption if 1 Mbit ofinformation is transferred from the source to the sinkwhere the source and sink are separated by 100meters and the broadcast radius of each node is 5meters?
Assume the neighbor nodes are overhearing each
others broadcast.
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EXAMPLEEXAMPLE
100 meters / 5 meters = 20 pairs of transmitting andreceiving nodes (one node transmits and one node receives)
ETx (k,D) = Eelec * k + eamp * k * D2
ETx = 50 nJ/bit . 106 + 100 pJ/bit/m2 . 106 . 52 =
= 0.05J + 0.0025 J = 0.0525 J
ERx (k,D) = Eelec * k
ERx = 0.05 J
Epair = ETx + ERx = 0.1025J
ET = 20 . Epair = 20. 0.1025J = 2.050 J
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VERY DETAILED ENERGY MODEL
sleepsleepononTPTPE +=
Simple Energy Consumption Model
A More Realistic ENERGY MODEL*
( ) LTPTPBTGP
BT
LNE trsynoncond
b
on
BT
L
BT
L
f
on
on /2
214
ln123
41
2
2
++
+=
* S. Cui, et.al., Energy-Constrained Modulation* S. Cui, et.al., Energy-Constrained ModulationOptimization,Optimization, IEEE Trans. on Wireless CommunicationsIEEE Trans. on Wireless Communications,,September 2005.September 2005.
fD t il f th R li ti M d l
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Details of the Realistic ModelDetails of the Realistic Model
onTB
L
M
MM
=
+
=
=
2
113
1
L packet lengthL packet length
B channel bandwidthB channel bandwidth
NNff receiver noise figure receiver noise figure
22 power spectrum energy power spectrum energyPPbb probability of bit error probability of bit error
GGdd power gain factor power gain factor
PPcc circuit power consumption circuit power consumption
PPsynsyn frequency synthesizer power frequency synthesizer power
consumptionconsumption
TTtrtr frequency synthesizer settling time (duration of frequency synthesizer settling time (duration of
transient mode)transient mode)TTonon transceiver on time transceiver on time
M Modulation parameterM Modulation parameter
ANOTHER EXAMPLE
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Enery Consumption: Important Variables:Enery Consumption: Important Variables:
PPrere 4.5 mA4.5 mA (energy consumption at receiver)(energy consumption at receiver)PPtete 12.0 mA12.0 mA (energy consumption at transmitter)(energy consumption at transmitter)PPclcl 12.0 mA12.0 mA(basic consumption without radio)(basic consumption without radio)PPslsl 8mA (0.008 mA)8mA (0.008 mA) (energy needed to sleep)(energy needed to sleep)
ANOTHER EXAMPLE
EXAMPLE
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Capacity (Watt) = Current (Ampere) * Voltage (Volt)Capacity (Watt) = Current (Ampere) * Voltage (Volt)Rough estimation for energy consumption and sensor lifetime:Rough estimation for energy consumption and sensor lifetime:
Let us assume that each sensor should wake up once aLet us assume that each sensor should wake up once a
second, measure a value and transmit it over the network.second, measure a value and transmit it over the network.
a) Calculations needed: 5K instructions (for measurement anda) Calculations needed: 5K instructions (for measurement and
preparation for sending)preparation for sending)
b) Time to send information: 50 bytes for sensor data,b) Time to send information: 50 bytes for sensor data,
(another 250 byte for forwarding external data)(another 250 byte for forwarding external data)
c) Energy needed to sleep for the rest of the time (sleepc) Energy needed to sleep for the rest of the time (sleep
mode)mode)
EXAMPLE
EXAMPLE
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Time for Calculations and Energy Consumption:Time for Calculations and Energy Consumption:
MSP430 running at 8 MHz clock rateMSP430 running at 8 MHz clock rate one cycleone cycletakes 1/(8*10takes 1/(8*1066) seconds) seconds
1 instruction needs an average of 3 cycles1 instruction needs an average of 3 cycles 3/3/(8* 10(8* 1066) sec, 5K instructions, 15/(8*10) sec, 5K instructions, 15/(8*1033) sec) sec
15/(8*1015/(8*1033) * 12mA = 180/8000 = 0.0225 mAs) * 12mA = 180/8000 = 0.0225 mAs
EXAMPLE
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Time for Sending Data and Energy Consumption:Time for Sending Data and Energy Consumption:
Radio sends with 19.200 baud (approx. 19.200 bits/sec)Radio sends with 19.200 baud (approx. 19.200 bits/sec)
1 bit takes 1/19200 seconds1 bit takes 1/19200 seconds
We have to send 50 bytes (own measurement)We have to send 50 bytes (own measurement)
and we have to forward 250 bytes (externaland we have to forward 250 bytes (external
data): 250+50=300 which takesdata): 250+50=300 which takes
300*8/19200s*24mA (energy basic + sending) = 3mAs300*8/19200s*24mA (energy basic + sending) = 3mAs
EXAMPLE
EXAMPLE
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Energy consumed while sleeping:Energy consumed while sleeping:
Time for calculation 15/8000 + time for transmissionTime for calculation 15/8000 + time for transmission
300*8/19200 ~ 0.127 sec300*8/19200 ~ 0.127 sec Time for sleep mode = 1 sec 0.127 = 0.873 sTime for sleep mode = 1 sec 0.127 = 0.873 s
Energy consumed while sleepingEnergy consumed while sleeping
0.008mA * 0.873 s = 0.0007 mAs0.008mA * 0.873 s = 0.0007 mAs
EXAMPLE
EXAMPLE
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Total Amount of energy and resulting lifetimeTotal Amount of energy and resulting lifetime::
The ESB needs to be supplied with 4.5 V so we needThe ESB needs to be supplied with 4.5 V so we need
3 * 1.5V AA batteries.3 * 1.5V AA batteries.
3*(0.0225 + 3 + 0.007) ~ 3 * 3.03 mWs3*(0.0225 + 3 + 0.007) ~ 3 * 3.03 mWs
Energy of 3AA battery ~ 3 * 2300 mAh = 3*2300*60*60 mWsEnergy of 3AA battery ~ 3 * 2300 mAh = 3*2300*60*60 mWs
Total lifetimeTotal lifetime 3*2300*60*60/3*3.03 ~ 32 days.3*2300*60*60/3*3.03 ~ 32 days.
EXAMPLE
EXAMPLE
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NOTES:NOTES:
Battery suffers from large current (losing about 10% energy/year)Battery suffers from large current (losing about 10% energy/year)
Small network (forwarding takes only 250 bytes)Small network (forwarding takes only 250 bytes)
Most important:Most important:
Only sending was taken into account, not receivingOnly sending was taken into account, not receiving
If we listen into the channel rather than sleeping 0.007 mA has to beIf we listen into the channel rather than sleeping 0.007 mA has to bereplaced by (12+4.5)mAreplaced by (12+4.5)mA
which results in a lifetime of ~ 5 days.which results in a lifetime of ~ 5 days.
EXAMPLE
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Power Consumption forPower Consumption forCommunicationCommunication(Detailed Formula)(Detailed Formula)
)]([)]()([stonreRonOstonteTc
RRPNTPTTPNP ++++=
wherewherePPtete is power consumed by transmitteris power consumed by transmitter
PPrere is power consumed by receiveris power consumed by receiver
PPOO is output power of transmitteris output power of transmitter
TTonon is transmitter on timeis transmitter on time
RRonon is receiver on timeis receiver on timeTTstst is start-up time for transmitteris start-up time for transmitter
RRstst is start-up time for receiveris start-up time for receiver
NNTT is the number of times transmitteris the number of times transmitter
is switched on per unit of timeis switched on per unit of time
NNRRis the number of times receiveris the number of times receiver
is switched on per unit of timeis switched on per unit of time
E. Shih et al.,Physical Layer Driven Protocols and Algorithm Design forE. Shih et al.,Physical Layer Driven Protocols and Algorithm Design forEnergy-Efficient Wireless Sensor Networks, ACM MobiCom, Rome, JulyEnergy-Efficient Wireless Sensor Networks, ACM MobiCom, Rome, July2001.2001.
P C ti fP C ti f
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Power Consumption forPower Consumption for
CommunicationCommunication
TTonon = L / R= L / R
where L is the packet size in bits and R is thewhere L is the packet size in bits and R is thedata rate.data rate.
NNTT and Nand NRR depend on MAC and applications!!!depend on MAC and applications!!!
What can we do to Reduce Energy ConsumptionWhat can we do to Reduce Energy Consumption
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What can we do to Reduce Energy ConsumptionWhat can we do to Reduce Energy Consumption
Multiple Power Consumption ModesMultiple Power Consumption Modes
Way out:Way out: Do not run sensor node at full operation all theDo not run sensor node at full operation all thetimetime
If nothing to do, switch toIf nothing to do, switch topower safe modepower safe mode
Question: When to throttle down? How to wake upQuestion: When to throttle down? How to wake up
again?again? Typical modesTypical modes
Controller: Active, idle, sleepController: Active, idle, sleep
Radio mode: Turn on/offRadio mode: Turn on/off
transmitter/receiver, bothtransmitter/receiver, both
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Multiple Power Consumption ModesMultiple Power Consumption Modes
Multiple modes possibleMultiple modes possible Deeper sleep modesDeeper sleep modes
Strongly depends on hardwareStrongly depends on hardwareTI MSP 430, e.g.: four different sleep modesTI MSP 430, e.g.: four different sleep modes
Atmel ATMega: six different modesAtmel ATMega: six different modes
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Multiple Power Consumption ModesMultiple Power Consumption Modes
MicrocontrollerMicrocontroller
TI MSP 430TI MSP 430
Fully operation 1.2 mWFully operation 1.2 mW
Deepest sleep mode 0.3Deepest sleep mode 0.3 W only woken up byW only woken up byexternal interrupts (not even timer is running anyexternal interrupts (not even timer is running anymore)more)
Atmel ATMegaAtmel ATMega
Operational mode: 15 mW active, 6 mW idleOperational mode: 15 mW active, 6 mW idle
Sleep mode: 75Sleep mode: 75 WW
S it hi b t M d
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Switching between ModesSwitching between Modes
Simplest idea: Greedily switch to lower mode wheneverSimplest idea: Greedily switch to lower mode wheneverpossiblepossible
Problem: Time and power consumption required to reachProblem: Time and power consumption required to reachhigher modes not negligiblehigher modes not negligible
Introduces overheadIntroduces overhead
Switching only pays off if ESwitching only pays off if Esavedsaved > E> Eoverheadoverhead
S i hi b M dS it hi b t M d
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Switching between ModesSwitching between Modes
Example: Event-triggered wake up from sleep modeExample: Event-triggered wake up from sleep mode
Scheduling problem with uncertaintyScheduling problem with uncertainty
Pactive
Psleeptimeteventt1
Esaved
tdown tup
Eoverhead
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Alternative: Dynamic Voltage ScalingAlternative: Dynamic Voltage Scaling
Switching modes complicated by uncertainty onSwitching modes complicated by uncertainty onhow long a sleep time is availablehow long a sleep time is available
Alternative: Low supply voltage & clockAlternative: Low supply voltage & clock
Dynamic Voltage Scaling (DVS)Dynamic Voltage Scaling (DVS)
A controller running at a lower speed, i.e., lowerA controller running at a lower speed, i.e., lowerclock rates, consumes less powerclock rates, consumes less power
Reason: Supply voltage can be reduced at lowerReason: Supply voltage can be reduced at lowerclock rates while still guaranteeing correctclock rates while still guaranteeing correct
operationoperation
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Alternative: Dynamic Voltage ScalingAlternative: Dynamic Voltage Scaling
Reducing the voltage is a very efficient way toReducing the voltage is a very efficient way toreduce power consumption.reduce power consumption.
Actual power consumption P depends quadraticallyActual power consumption P depends quadraticallyon the supply voltage Von the supply voltage VDDDD, thus,, thus,
P ~ VP ~ VDDDD22
Reduce supply voltage to decrease energyReduce supply voltage to decrease energyconsumption !consumption !
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Alternative: Dynamic Voltage ScalingAlternative: Dynamic Voltage Scaling
Gate delay also depends on supply voltageGate delay also depends on supply voltage
K and a are processor dependent (a ~ 2)K and a are processor dependent (a ~ 2)
Gate switch periodGate switch period TT00=1/f=1/f
For efficient operationFor efficient operation
TTgg
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Alternative: Dynamic Voltage ScalingAlternative: Dynamic Voltage Scaling
)(~)(
cVKVdd
VVKf dd
a
thdd
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Computation vs. Communication EnergyComputation vs. Communication Energy
costcost
Tradeoff?Tradeoff?
Directly comparing computation/communicationDirectly comparing computation/communicationenergy cost not possibleenergy cost not possible
But: put them into perspective!But: put them into perspective!
Energy ratio of sending one bit vs. computingEnergy ratio of sending one bit vs. computingone instruction: Anything between 220 and 2900one instruction: Anything between 220 and 2900
in the literaturein the literature
To communicate (send & receive)To communicate (send & receive) one kilobyteone kilobyte ==
computingcomputing three million instructions!three million instructions!
C t ti C i ti EComputation vs Communication Energy
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Computation vs. Communication EnergyComputation vs. Communication Energy
CostCost
BOTTOMLINEBOTTOMLINE
Try to compute instead of communicateTry to compute instead of communicatewhenever possiblewhenever possible
Key technique in WSN Key technique in WSN in-network processingin-network processing!!
Exploit compression schemes, intelligent codingExploit compression schemes, intelligent codingschemes, aggregation, filtering, schemes, aggregation, filtering,
BOTTOMLINE
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BOTTOMLINE:BOTTOMLINE:
Many Ways to Optimize Power ConsumptionMany Ways to Optimize Power Consumption
Power aware computingPower aware computing
Ultra-low power microcontrollersUltra-low power microcontrollers
Dynamic power management HWDynamic power management HW
Dynamic voltage scaling (e.g Intels PXA, TransmetasDynamic voltage scaling (e.g Intels PXA, TransmetasCrusoe)Crusoe)
Components that switch off after some idle timeComponents that switch off after some idle time
Energy aware softwareEnergy aware software
Power aware OS: dim displays, sleep on idle times, powerPower aware OS: dim displays, sleep on idle times, poweraware schedulingaware scheduling
Power management of radiosPower management of radios
Sometimes listen overhead larger than transmit overheadSometimes listen overhead larger than transmit overhead
O OBOTTOMLINE
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BOTTOMLINE:BOTTOMLINE:
Many Ways to Optimize Power ConsumptionMany Ways to Optimize Power Consumption
Energy aware packet forwardingEnergy aware packet forwarding
Radio automatically forwards packets at a lowerRadio automatically forwards packets at a lowerpower level, while the rest of the node is asleeppower level, while the rest of the node is asleep
Energy aware wireless communicationEnergy aware wireless communication
Exploit performance energy tradeoffs of theExploit performance energy tradeoffs of thecommunication subsystem, better neighborcommunication subsystem, better neighbor
coordination, choice of modulation schemescoordination, choice of modulation schemes
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COMPARISONCOMPARISON
Technology Data RateTx
CurrentEnergy per
bitIdle
CurrentStartup
time
Mote 76.8 Kbps 10 mA 430 nJ/bit 7 mA Low
Bluetooth 1 Mbps 45 mA 149 nJ/bit 22 mA Medium
802.11 11 Mbps 300 mA 90 nJ/bit 160 mA High
IEEE 802.11
Bluetooth
Mote
Energyper bit
Startuptime
Idlecurrent