Design of Wireless Sensor Networks

(1)

Energy

-

Efficiency Issues in Cross

-

Layer

Design of Wireless Sensor Networks

Sergio Palazzo

[email protected]

Sensor

Networks

: a

small

world

Main

Features

f

fsmall in size f

fsmall transmission ranges f flow-powered f fcheap f fcost-effective

Energy

Efficiency

is

a major

issue

!

Università degli Studi di Catania

Dipartimento di Ingegneria Informatica e delle Telecomunicazioni

Design Guidelines (1/3)

f

fProduction Production CostsCosts::consideringconsideringthatthatsensorsensornetworksnetworksare are composedcomposedof a of a large

largenumbernumberof of sensorsensordevicesdevices, , reducingreducingthe the costcostof a single of a single nodenodeisisveryvery important

important f

fHardware Hardware ConstraintsConstraints::a a sensorsensornodenodeisismademadeup of up of fourfourbasic basic components

components

SensingSensingUnitUnit::ititperformesperformes sensing

sensingtaskstasksand and analoganalogtoto digital

digitalconversionconversion

Processing Processing UnitUnit::ititisiscomposedcomposed of a

of a processorprocessorand of a and of a smallsmall storage

storageunitunit

TransceiverTransceiverUnitUnit::ititisisa radio a radio frequency

frequencymodem modem thatthatusesuses more

more thanthanone one codingcodingtechniquetechnique to

toconnectconnectthe the nodenodetotothe the network network Sensor ADC POWER UNIT POWER UNIT SENSING UNIT SENSING UNIT Processor PROCESSING UNIT PROCESSING UNIT Storage TRANSCEIVER TRANSCEIVER UNIT UNIT POWER GENERATION POWER GENERATION

Power Power UnitUnit::ititmaymaybebesupportedsupportedbybysolarsolarcellscells

GPS GPS UnitUnit::optionallyoptionallya GPS a GPS unitunitmaymaybeberequiredrequired

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Design Guidelines (2/3)

f

fNetwork Network TopologyTopology::changeschangesin in sensorsensornetworknetwork’’s s topologytopologycan can happenhappen during

duringprepre--deploymentdeploymentand and deploymentdeploymentphasephase, , postpost--deploymentdeploymentphasephaseand and re

re--deploymentdeploymentphasephase. . TheyTheyare are causedcausedbybymisfunctioningmisfunctioning, , lowlowavailableavailable energy

energy, , etcetc, , ThenThen, in a network , in a network withwitha high a high numbernumberof of nodesnodesthatthatcan can failfail, , itit is

isnecessarynecessarytotoimplementimplementspecial special routingroutingprotocolsprotocolsthatthatrere--route route packetspackets and

and rere--organizeorganizethe networkthe network f

fTransmissionTransmissionMedia:Media:wirelesswirelessconnection connection betweenbetweensensorssensorscan can bebe performed

performedthroughthrough

radio radio linkslinks

infraredinfraredlinkslinks

opticalopticallinkslinks Much

Muchof the of the currentcurrenthardware hardware forforsensorsensornodesnodesisisbasedbaseduponuponRF RF circuitcircuit design.

design. InfraredInfraredmode mode isislicenselicense--freefreeand and robustrobusttotointerferenceinterferencefromfrom electrical

electricaldevicesdevices. . OpticalOpticaltransmissiontransmissionisisunder under developmentdevelopment. . NonethelessNonetheless, , the

the transmittedtransmittedinformationinformationmustmustbebeprotectedprotectedthrough through robustrobustcodingcodingand and modulation

modulationschemesschemes

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Design Guidelines (3/3)

f

fOperatingOperatingEnvironmentEnvironment::a a biologicallybiologicallyor or chemicallychemicallycontaminatedcontaminated field

field, the , the bottombottomof of ananoceanocean, a , a riverrivermovingmoving, fast , fast movingmovingvehiclesvehicles, , animals

animals’’bodybody f

fPower Power ConsumptionConsumption::sensorssensors’’lifetimelifetimeisisstronglystronglydependentdependenton on battery

batterylifetimelifetime. A . A wirelesswirelesssensorsensornodenodeisistypicallytypicallyequippedequippedwithwitha a limited

limitedpower power sourcesource(< 0.5 Ah, 1.2 V) (< 0.5 Ah, 1.2 V) totomaintainmaintainlowlowthe the sizesizeand and weightweight. . Power

Power conservationconservationand power management are of and power management are of primaryprimaryimportanceimportance: : researchers

researchersare are currentlycurrentlyfocusingfocusingon the design of on the design of powerpower--awareaware protocols

protocolsand and algorithmsalgorithmsforforsensorsensornetworksnetworks f

fScalabilityScalability::nodesnodesdensity density dependsdependson the on the particularparticularapplicationapplication(the (the number

numberof of sensorsensornodesnodescan can varyvaryfromfromhundredshundredstotothousandsthousandsdevicesdevices f

fFault Fault tolerancetoleranceand and ReliabilityReliability::the fault the fault tolerancetolerancelevelleveldependsdependson on the

the applicationapplication. . InfactInfact, , ififthe the environmentenvironment, , wherewherethe the sensorsensornodesnodesare are

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Energy

-

Efficiency related issues

Application requirements Application requirements

Sensing accuracySensing accuracy

ReliabilityReliability

CoverageCoverage

Wireless TechnologyWireless Technology

Network ConnectivityNetwork Connectivity

MAC ProtocolsMAC Protocols

Routing and Forwarding schemesRouting and Forwarding schemes

Positioning and Localization AlgorithmsPositioning and Localization Algorithms

Congestion controlCongestion control

Data aggregationData aggregation

(2)

Energy

Conserving

in the

layered

framework

f

fIn principleIn principle, , energyenergyconservingconservingstrategiesstrategiescan becan beeffectivelyeffectively introduced

introducedat allat allindividualindividuallayerslayersof the of the traditionaltraditional“layered“layered architecture

architecture””frameworkframework At the

At the physicalphysicallayerlayerenergyenergycan can bebesavedsavedbybyproperproperselectionselection of

of batteriesbatteries, hardware (, hardware (forforexampleexample, power , power amplifiersamplifiers), ), antennas

antennas((diversitydiversity, , beamsteeringbeamsteering, MIMO , MIMO techniquestechniques), ), codingcoding (

(turbocodesturbocodes, turbo , turbo trellistrelliscodedcodedmodulationmodulation), ), transmissiontransmission power control (

power control (waterfillingwaterfillingstrategiesstrategies), ), multiusermultiuserdetection. detection. In the

In the followingfollowing, , onlyonlystrategiesstrategiesthatthatcoarselycoarselyreferrefertotoMAC and MAC and network

network layerslayerswillwillbebeconsideredconsidered..

Energy

Conserving

Approaches

f

To meet energy conserving requirements in ad hoc networks, To meet energy conserving requirements in ad hoc networks, three approaches have been mostly used so far:

three approaches have been mostly used so far: 1.

1. Power save protocolsPower save protocolsattack the problem of high idle state energy attack the problem of high idle state energy consumption by maximizing the amount of time nodes spend in consumption by maximizing the amount of time nodes spend in the sleep state

the sleep state 2.

2. Power control techniquesPower control techniquesincrease network capacity and reduce increase network capacity and reduce energy consumption by allowing nodes to determine the minimum energy consumption by allowing nodes to determine the minimum transmit power level required to maintain network connectivity transmit power level required to maintain network connectivity and forward traffic with least energy cost

and forward traffic with least energy cost 3.

3. Maximum lifetime routingMaximum lifetime routingselects paths that maximize network selects paths that maximize network lifetime by balancing energy consumption across the nodes of lifetime by balancing energy consumption across the nodes of the network

the network

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Operating Modes of a Sensor Node (1/2)

The energy consumed by an interface depends on its

operating mode

Sleep Mode:

an interface can neither transmit nor

receive

¨

very low energy consumption

Idle Mode:

an interface can transmit or receive data at

any time (this requires time and energy)

¨

it

consumes more energy than it does in the sleep state

Receive Mode and Transmit Mode:

the energy

consumption is of the same order of magnitude than

idle state. Transmitting requires more energy than

receiving, but the difference is generally less than a

factor of two

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Power consumption of node subsystems

0 5 10 15 20 Po w er ( m W )

Sensing Unit Processing Unit TX RX IDLE SLEEP

Transceiver Unit SLEEP IDLE RX TX

E

≈

>>

Operating Modes of a Sensor Node (2/2)

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Power

-

Save Switch

-

off Approaches

f

To save energy the nodes must

spend

more time in the

sleep

mode

f

The

unavailability

of

sleeping

nodes

may

interrupt

the

flow

of

traffic

through a

multihop

ad hoc network

f

Power

-

save

protocols

have

been

introduced

at MAC and

network

layers

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MAC layer Power

-

Save mechanisms

The nodes periodically wake up to listen the announcements of pe The nodes periodically wake up to listen the announcements of pending nding traffic and, if it is necessary, they remain awake to receive an traffic and, if it is necessary, they remain awake to receive and exchange d exchange traffic

traffic

It is important to determine time windows to maximize energy sav It is important to determine time windows to maximize energy saving ing while minimizing impact on throughput and latency

while minimizing impact on throughput and latency In this approach the nodes must also maintain a globally synchro In this approach the nodes must also maintain a globally synchronized nized sleep

sleep--wakeup cyclewakeup cycle Practical Problem

Practical Problem xx to establish the phase synchronization in a to establish the phase synchronization in a dynamic multi

(3)

Signalling

-

based Power

-

Save Protocols

MACA

-

based protocols exploit the media access control

process to find intervals during which the network interface

does not need to be awake

While a packet is being transmitted, nearby nodes, whose

transmissions might interfere with the ongoing

transmission, must remain silent

Therefore these nodes can sleep with little or no impact on

throughput

PAMAS

f

PAMAS (Power

Aware

Multi

-

Access

with

Signalling

for

Ad

Hoc

Networks

)

uses

an

RTS/CTS

mechanism

as

the IEEE

802.11 MAC

f

It relies on a separate control signaling channel (busy tone)It relies on a separate control signaling channel (busy tone)

f

A node that is going to transmit or is in the process of receiving a A node that is going to transmit or is in the process of receiving a transmission causes other nodes to go to sleep by generating a transmission causes other nodes to go to sleep by generating a busy tone

busy tone

f

When a sleeping node wakes up, it has no information about the When a sleeping node wakes up, it has no information about the state of channel, then it transmits a sequence of probe messages state of channel, then it transmits a sequence of probe messages and awaits a response on the control channel

and awaits a response on the control channel

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Power

-

Save Based on Network Topology (1/2)

A subset of nodes that are topologically representative of the f

A subset of nodes that are topologically representative of the full network is ull network is selected

selected

This covering set must be chosen so as to maintain the effective This covering set must be chosen so as to maintain the effectivecapacity of capacity of the network and minimize the impact of the power save protocol o the network and minimize the impact of the power save protocol on n throughput and latency

throughput and latency

A few selected nodes in the covering set remain in the idle stat A few selected nodes in the covering set remain in the idle state and are e and are responsible to forward traffic in the network

responsible to forward traffic in the network

Other nodes spend most of their time sleeping, consuming much le Other nodes spend most of their time sleeping, consuming much less ss energy. They wake up periodically to participate in

energy. They wake up periodically to participate in ““subset electionsubset election””or to or to receive pending traffic in the sleep state

receive pending traffic in the sleep state

The rotation between the two roles among nodes in the network is The rotation between the two roles among nodes in the network is necessary to maximize the network lifetime

necessary to maximize the network lifetime

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Power

-

Save Based on Network Topology (2/2)

Selecting the optimal covering set is a non

Selecting the optimal covering set is a non--trivial problem, especially trivial problem, especially when it is based on localized computation with minimal overhead when it is based on localized computation with minimal overhead and and when it must be recomputed in response to nodes

when it must be recomputed in response to nodes’’failure and mobilityfailure and mobility The protocols that use this approach are inherently asynchronous The protocols that use this approach are inherently asynchronous, but , but they may rely on synchronized mechanisms for buffering traffic f they may rely on synchronized mechanisms for buffering traffic for or sleeping nodes.

sleeping nodes.

In the asynchronous protocols In the asynchronous protocols

¾

¾Connectivity information can be used to determine the covering sConnectivity information can be used to determine the covering set: et: the nodes that are not currently part of the covering set must the nodes that are not currently part of the covering set must exchange traffic to determine their connectivity.

exchange traffic to determine their connectivity. ¾

¾It is also possible to select a covering set indirectly, for exaIt is also possible to select a covering set indirectly, for example, by mple, by using position information

using position information

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Topology

-

Based Power

-

Save Protocols:

Dominating Sets (1/3)

•

• In a In a clustercluster--basedbasedalgorithmalgorithm--namednamedCEDAR CEDAR --eacheachnodenodeselectsselects a

a corecore--nodenodeasasdominatordominator, , whichwhichwillwillgivegiveaccess access totothe the servicesservices offered

offeredbybythe core the core ÎÎEachEachcore core nodenodehashasa a domaindomainof non of non corecore- -nodes

nodes

A subset of

A subset of nodesnodes, S , S ⊂⊂V, V, isisa a

dominating

dominatingset set forforV V ififeacheach node

nodein V in V isisincludedincludedin S or in S or it

itisisdistantdistant1 hop 1 hop fromfromS. The S. The dominating

dominatingset set withwiththe the minimum

minimum numbernumberof of nodesnodesisis called

calledminimum minimum dominatingdominating set (MDS)

set (MDS)

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Topology

-

Based Power

-

Save Protocols:

Dominating Sets (2/3)

Heavy

Heavycomputationcomputationisisrequiredrequiredtotofindfinda a minimalminimal--sizesize dominating

dominatingset: set: totothisthispurposepurposedistributeddistributedalgorithmsalgorithmsare are necessary

necessary Most

Mostof theseof thesealgorithmsalgorithmsuseusea twoa twophasephaseapproachapproach

In the first

In the first phasephase nodes exchange neighbor information and any node that has two unconnected neighbors marks itself as

The

The secondsecondphasephase

eliminates any marked node that is redundant (its one-hop neighborhood is contained within the one-hop neighborhood of an adiacent marked

(4)

Topology

-

Based Power

-

Save Protocols:

Dominating Sets (3/3)

Whenever

Wheneverpossible, the possible, the nodenodewithwiththe the lowerlowerenergyenergysuppliessuppliesisis preferentially

preferentiallyremovedremovedfromfromthe the dominatingdominatingset: set: thisthisallowsallowstoto increase

increasenetwork network lifetimelifetime The

The incrementalincrementalcostcostof a of a dominatingdominatingnodenodeisisspecifiedspecifiedasasa a function

functionof theof theroutingroutingoverheadoverhead(proportional(proportionaltotothe the numbernumberof of nodes

nodes) and the ) and the forwardingforwardingoverheadoverhead((inverselyinverselyproportionalproportionaltotothe the number

numberof of forwardersforwarders): the relative ): the relative magnitudemagnitudeof of thesethesefactorsfactors depends

dependson the averageon the averagenodenodedegreedegree, , pathpathlengthlength, , pathpathlifetimelifetime(i.e. (i.e. mobility

mobility) and the relative ) and the relative costscostsof of transmittingtransmittingand receivingand receiving PERFORMANCE

PERFORMANCE Simulation

Simulationresultsresultsshow show thatthatafter the after the eliminationeliminationphasephase3030--40% of the 40% of the nodesnodesare in the are in the dominating

dominatingset and the network set and the network lifetimelifetimeisislongerlonger When

Whenno no usingusingpowerpower--savesaveprotocolsprotocols, , forforallallvaluesvaluesof of routingroutingoverheadoverheadand and forforallall mobility

mobilitylevelslevels, network , network lifetimelifetimedecreasesdecreasesasymptoticallyasymptoticallyasasthe the nodenodedensity density increaseincrease; ; instead

instead, , fixedfixedenergyenergyconsumptionconsumptionmodelsmodelsyieldyielda a linearlinearincreaseincreasein network in network lifetimelifetimeasasa a function

functionof density (SPAN and GAF of density (SPAN and GAF protocolprotocol))

Topology

-

Based Power

-

Save Protocols: SPAN (1/3)

The

covering

set in SPAN

is

a

connected

dominating

set,

whose

nodes

are

called

“

coordinators

”

Coordinators

are in the

idle

state.

They

act

as

low

latency

routing

backbone

nodes

and

buffer

traffic

for

sleeping

destinations

(

using

mechanisms

derived

from

IEEE 802.11)

Non

-

coordinator

nodes

wake

up

periodically

to

exchange

traffic

with

the

coordinator

nodes

and

participate

in

coordinator

election

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Topology

-

Based Power

-

Save Protocols: SPAN (2/3)

The

The coordinatorcoordinatorelectionelectionalgorithmalgorithm A.

A.The The nodesnodesperiodicallyperiodicallyexchangeexchangeHELLO HELLO messagesmessagestotodiscoverdiscover

their

theirtwotwo--hophopneighborhoodneighborhood

B.

B.A A nodenodemarksmarksitselfitselfasaseligibleeligiblecoordinatorcoordinatorififititdiscoversdiscoversthatthattwotwo

neighbors

neighborscannotcannotcomunicate comunicate directlydirectlyor via or via otherothercoordinatorscoordinators

C.

C.EachEachmarkedmarkednodenodeschedulesschedulesa a backoffbackoffintervalinterval((itithashasbothbothrandomrandom

and

and adaptiveadaptiveelementselements), ), duringduringwhichwhichititlistenslistensforforannouncementsannouncements from

fromotherothernodesnodes

D.

D.IfIfafter after thisthisintervalintervalthe the nodenodeisisstillstilleligibleeligible, , ititsendssendsitsitsownown

coordinator

coordinatorannouncementannouncement. The . The nodesnodeswithwithgreatergreaterconnectivityconnectivity and

and higherhigherenergyenergyreservesreservesannounceannouncethemselvesthemselvesasascoordinatorscoordinators more

more quicklyquickly

E.

E.After After spendingspendingsome time some time asasa a coordinatorcoordinator, a , a nodenodewithdrawswithdraws

The

The rotation of the rotation of the coordinatorcoordinatorroleroletendstendstotobalancebalancenodes’nodes’ energy

energyreserves, reserves, evenevenin the case of in the case of initiallyinitiallyunequalunequaldistributiondistribution

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Topology

-

Based Power

-

Save Protocols: SPAN (3/3)

SPAN

SPAN isisa a synchronoussynchronouspower power savesaveprotocolprotocolforfortwotworeasonsreasons 1.

1.the the bufferingbufferingand and announcementsannouncementsare are basedbasedon the on the synchronoussynchronous

IEEE 802.11 power

IEEE 802.11 power savesavemechanismmechanism, , alsoalsosome some formformof of

asynchronous

asynchronouspollingpollingisisa a possiblepossiblealternativealternative

2.

2.the the nodesnodesmustmustbebeawakeawakesimultaneouslysimultaneouslytotoexchangeexchangetraffictraffictoto

determine

determinetheirtheirconnectivityconnectivityand and participateparticipatein in coordinatorcoordinatorelectionelection

PERFORMANCE PERFORMANCE Simulations

Simulationsand and experimentalexperimentalenergyenergymeasurementsmeasurementscorroborate corroborate thatthat

SPAN

SPAN providesprovidesaboutabout50% 50% energyenergysavingsavingin dense in dense networksnetworks, , withwithonlyonlyminimal minimal impact on

impact on throughputthroughputand and packetpacketlossloss Network

Network lifetimelifetimeincreasesincreasesroughlyroughlylinearlylinearlywithwithnetwork densitynetwork density Also

Alsolatencylatencyincreasesincreaseswithwithnodenodedensitydensity Rotation of the

Rotation of the rolesrolesallowsallowsa 50a 50--100% 100% increaseincreaseof the network of the network lifetimelifetime

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Topology

-

Based Power

-

Save Protocols:

Geographic

Adaptive

Fidelity

-

GAF (1/2)

GAF

GAF isisa power a power savesaveprotocolprotocolthatthatselectsselectsitsitsrepresentativerepresentativenodesnodesbasedbasedon on

position

position((bybyGPS GPS receiverreceiver, , forforexampleexample), ), ratherratherthanthanmembershipmembershipin a in a dominating

dominatingsetset GAF

GAF partitionspartitionsthe network the network usingusinga a geographicgeographicgridgrid

The

The gridgridsizesizeof R/of R/√√55, , wherewhereR R isisthe the nodesnodes’’transmissiontransmissionrangerange, , guaranteesguarantees that

thateacheachnodenodein a in a gridgridsquaresquareisiswithinwithinthe the transmissiontransmissionrangerangeof of everyevery node

nodein in eacheachadjacentadjacentgridgridsquaresquare All

Allnodesnodesin a in a gridgridsquaresquareare are regardedregardedasasequivalentequivalentwithwithrespectrespecttototheirtheir ability

abilityof of forwardingforwardingpacketspackets One

One nonnon--sleepingsleepingnodenodein in eacheachgridgridsquaresquareisissufficientsufficienttotomaintainmaintainthe the connectivity

connectivityof the of the originaloriginalnetworknetwork

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Topology

-

Based Power

-

Save Protocols:

Geographic

Adaptive

Fidelity

-

GAF (2/2)

Each

Eachnodenodepassespassesamongamongthreethreestatesstates: : sleepsleep, , discoverydiscoveryand and activeactive

Sleep Sleep State State Discovery Discovery State State Active Active State State B Sleeping

Sleepingnodesnodesin the in the gridgridperiodicallyperiodically wake

wakeupupand go and go totothe the discoverydiscoverystatestate

(A): in

(A): in thisthisstate a state a nodenodesendsenda a

discovery

discoverymessagemessagecontainingcontainingitsitsgridgrid positon

positonID and ID and energyenergystatus, and status, and listens

listensforforotherotherdiscoverydiscoverymessagesmessages. . IfIf the

the nodenodehearshearsno no ““higherhigherrankingranking”” announcements

announcements, , ititpassespassestotothe the activeactive state

state(B), (B), otherwiseotherwiseititgoesgoesback back totothe the sleep

sleepstate state (C)(C) If

Ifananactiveactivenodenodehearshearsa a discoverydiscoverymessagemessagefromfromananactiveactivenodenodeof of higherhigherrankrank, , it

itimmediatelyimmediatelygoesgoestotothe the sleepsleepstate state (D). After (D). After spendingspendingsome time in the some time in the activeactive state, a

state, a nodenodepassespassestotothe the discoverydiscoverystatestate(E), (E), allowingallowingthe the activeactiverolerole’’s rotation s rotation between

betweenthe the nodesnodesin the in the gridgridsquaresquare A C D E

(5)

Power Control Techniques

With these techniques, nodes modify their transmit power to

reduce energy consumption and increase network capacity

Low power transmissions reduce contention and increase Low power transmissions reduce contention and increase

network capacity, while at the same time consuming less

energy

This implies that a route with a larger number This implies that a route with a larger number of low power hops may be more energy of low power hops may be more energy efficient than one with fewer high power hops efficient than one with fewer high power hops

Minimum Energy Routing Problem

The problem is to minimize the energy consumed in forwarding a p

The problem is to minimize the energy consumed in forwarding a packet acket

from source to destination

Minimum energy routing can exploit exponential path loss by forw

Minimum energy routing can exploit exponential path loss by forwarding arding

traffic using a sequence of low power transmissions rather than

traffic using a sequence of low power transmissions rather than a single a single

direct transmission

In a basic path loss model, received signal strength decreases

exponentially with distance: therefore the minimum transmit powe

exponentially with distance: therefore the minimum transmit power r

required to transmit from node

required to transmit from node iito node to node jjmust bemust be P

Pminmin_ij_ij∝∝dd_i,j_i,jαα

with

with 22≤α≤4≤α≤4. Besides, the signal to noise ratio (SNR) at the receiver must . Besides, the signal to noise ratio (SNR) at the receiver must

be greater than some threshold, which depends on the target bit

be greater than some threshold, which depends on the target bit error rateerror rate In general, because of the effects of terrain and other obstacle

In general, because of the effects of terrain and other obstacles, a node s, a node

can not determine the transmission power level required for node

can not determine the transmission power level required for nodes to s to

communicate given their position

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Topology Control Problem

This problem consists of assigning per

This problem consists of assigning per-

-node transmit

node transmit

powers that minimize the total transmit power, while still

maintaining network connectivity

Most strategies are focused on increasing throughput

by reducing interference, with the associated reduction

in energy consumption as a beneficial side effect

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Examples

of

Topology

Control

Strategies

1.

1.Link state topology informationLink state topology informationis used to maintain a connected topology. is used to maintain a connected topology.

When a route update indicates a

When a route update indicates a link failurelink failure, the appropriate nodes increase , the appropriate nodes increase

their transmission power (using slotted

their transmission power (using slotted backoffbackoff) until the network is ) until the network is

connected. In the

connected. In the absence of topology informationabsence of topology information, each node increases its , each node increases its transmission power until its degree is sufficiently large, based

transmission power until its degree is sufficiently large, basedon estimated on estimated

node density

2.

2.Each node modifies its transmission power until it has discovereEach node modifies its transmission power until it has discovered at least d at least

one neighbor in every direction with cones of angle

one neighbor in every direction with cones of angle αα≤≤22ππ/3: these /3: these neighbors

neighbors’’combined wireless coverage provides connectivity (this combined wireless coverage provides connectivity (this

guarantees to each node to be connected to the network). Besides

guarantees to each node to be connected to the network). Besides, thanks to , thanks to

topology of this

topology of this neighbor setneighbor set, nodes can further reduce their transmission , nodes can further reduce their transmission

power by eliminating redundant nodes from the set

3.

3.Given a Given a broadcast source nodebroadcast source node, the minimum energy broadcast problem is , the minimum energy broadcast problem is

to select a set of re

to select a set of re--broadcasters and transmission powers, such that the broadcasters and transmission powers, such that the

message is distributed to all nodes with minimum total energy co

message is distributed to all nodes with minimum total energy cost. This st. This

type of strategies is not very used because minimum energy broad

type of strategies is not very used because minimum energy broadcast is an cast is an

NP

NP--complete problemcomplete problem

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Maximum

Lifetime

Routing

Problem

of

Maximum

Lifetime

Routing

Saving energy in the whole network is so much important as Saving energy in the whole network is so much important as doing it at the individual nodes. This may be done balancing doing it at the individual nodes. This may be done balancing

energy consumption across the nodes of the network energy consumption across the nodes of the network

three

threemainmainRoute Route MetricsMetrics used

usedin in selectingselectingenergyenergyawareaware

alternative alternative approachesapproaches have

havealsoalsobeenbeenproposedproposed

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Route Selection Metrics (1/2)

Minimum Energy Routing

This metric minimizes the total energy consumed as a packet is forwarded on a route

It does not maximize network lifetime

Nodes’ residual energy is not taken into account, therefore the nodes will suffer early failure due to their heavy forwarding load

Max

Max--Min RoutingMin Routing

It selects the route which maximizes the minimumresidual energy of any node on the route itself

The routes selected may be longer or have higher total energy consumption than the minimum energy route

(6)

Route Selection Metrics (2/2)

Minimum Cost Routing

It minimizes the total cost of forwarding the packet at each node, selecting the route that minimizes the sum of the link costs cij

The cost function controls the presence of a high-cost node on a route which may deflect traffic from that route

In general, the cost function is increasing, so reflecting a node’s increasing “reluctance” to forward traffic, as its residual energy decreases Alternatively, a capacity cost function incorporates both the link energy cost and the residual energy at a node: so it has ability to balance to maximize energy reserves and to minimize forwarding cost

MACRO: a MAC/

ROuting

cross

-

layer

protocol

for

WSNs

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MACRO is a cross

MACRO is a cross--layer protocol developed at the WiNelayer protocol developed at the WiNe--Lab (Wireless Network Lab (Wireless Network Laboratory) of the University of Catania. Unlike former solution

Laboratory) of the University of Catania. Unlike former solutions (e.g. s (e.g. GeRaFGeRaF) it ) it doesn

doesn’’t involve any location information exchanging. Each node only net involve any location information exchanging. Each node only needs to know eds to know its own position in the coverage area. The metric to establish t

its own position in the coverage area. The metric to establish the next hop is:he next hop is:

R’’ R’ ) ' ( 1R S Weighted Progress Factor (WPF)

Set of power levels and coverage range

D ) ' ( 2R S ) ' ( 3R S

Î

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Advantages

of

using

different

power

levels

M=4 ⇒ ⇒ PP11=0.0011W=0.0011W––RR11=62.5m=62.5m ⇒ ⇒ PP22=0.0176W=0.0176W––RR22=125m=125m ⇒ ⇒ PP33=0.0892W=0.0892W––RR33=182.5m=182.5m ⇒ ⇒ PP44=0.2818W=0.2818W––RR44=250m=250m M=3 ⇒ ⇒ PP11=0.0035W=0.0035W––RR11=83.4m=83.4m ⇒ ⇒ PP22=0.0556W=0.0556W––RR22=166.7m=166.7m ⇒ ⇒ PP33=0.2818W=0.2818W––RR33=250m=250m M=2 ⇒ ⇒ PP11=0.0176W=0.0176W––RR11=125m=125m ⇒ ⇒ PP22=0.2818W=0.2818W––RR22=250m=250m M=1 ⇒ ⇒ PP11=0.2818w=0.2818w––RR11=250m=250m

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R’’ R’ D ) ' ( 1R S •

• To select the next relay node RTo select the next relay node R’’triggers triggers a competition

a competition •

• Let RLet R’’’’be the winner of the competition be the winner of the competition in the set S

in the set S11(R(R’’) and G) and GRR’’R1R1’’’’its WPFits WPF •

• If RIf R’’estimates that a higher WPF can estimates that a higher WPF can be obtained increasing P, a new be obtained increasing P, a new competition is triggered in the set S competition is triggered in the set S22(R(R’’)) •

• The procedure is repeated until no The procedure is repeated until no better relay nodes can be found better relay nodes can be found

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MACRO

–

MAC Functionalities

•

• Nodes periodically switch ON and OFF to Nodes periodically switch ON and OFF to reduce energy consumption

reduce energy consumption •

• Synchronization is not neededSynchronization is not needed •

• A wake up phase is required for RA wake up phase is required for R’’to identify to identify the best relay node in S

the best relay node in Sii(R(R’’)) •

• To this purpose RTo this purpose R’’transmits several short transmits several short WAKE

WAKEUPUPmessages for a period Tmessages for a period TCycleCycle •

• Then RThen R’’sends a GO MESSAGE which triggers sends a GO MESSAGE which triggers competition among nodes in S

competition among nodes in Sii(R(R’’) ) •

• A node in SA node in Sii(R(R’’) hearing the WAKE) hearing the WAKEUPUP messages calculates its WPF and stays awake messages calculates its WPF and stays awake waiting for the GO MESSAGE

waiting for the GO MESSAGE •

• Then, upon hearing the GO MESSAGE, a node Then, upon hearing the GO MESSAGE, a node sends randomly to R

sends randomly to R’’its WPF so that Rits WPF so that R’’ performs the choice of the best relay in S performs the choice of the best relay in Sii(R(R’’))

Cycle

T

ON T TX WU ON In WU T T T ≤ −2

(7)

MACRO

–

Analytic Framework

g P R i i_≤ +1 g P R i i> +1 What is the probability that outside the coverage area obtained

What is the probability that outside the coverage area obtained using using PPii, exists at , exists at least one node whose WPF is higher than

least one node whose WPF is higher than gg, provided that , provided that GGii(M(M))= = GGii??

Where

Wherezzisisthe the nodesnodes’’density and density and a(a(g|Gg|Gii))isisthe area the area wherewherea a nodenodeB B mustmustbebelocatedlocatedin in order

ordertotobelongbelongtotoSSi+1i+1(R(R’’))and and havehavea WPF a WPF higherhigherthanthang.g.

Where is the probability density functi

Where is the probability density function which can be evaluated on which can be evaluated using the previous results as

using the previous results as

Once the probability is known, when is it worth enlarging the co Once the probability is known, when is it worth enlarging the coverage area?verage area?

) | ( ) ( ) ( 1|G i G g G f M i M i+

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Performance

Evaluation

GPSR (with STEMGPSR (with STEM--B MAC protocol)B MAC protocol)

⇒

⇒ B. Karp and H.T. Hung, GPSR: Greedy Perimeter Stateless Routing B. Karp and H.T. Hung, GPSR: Greedy Perimeter Stateless Routing for for Wireless Networks.

Wireless Networks. Proc. of ACM Proc. of ACM MobicomMobicom2000.2000.

⇒

⇒ C. C. SchurgersSchurgers, V. , V. TsiatisTsiatis, G. , G. GaneriwalGaneriwal, and M. , and M. SrivastavaSrivastava. Optimizing . Optimizing Sensor Networks in the Energy

Sensor Networks in the Energy--LatencyLatency--Density Design Space. Density Design Space. IEEE IEEE Transactions on Mobile Computing

Transactions on Mobile Computing. Vol. 1, No. 1, January. Vol. 1, No. 1, January--March 2002.March 2002.

GeRaFGeRaF(same MAC as MACRO)(same MAC as MACRO)

⇒

⇒ M. M. ZorziZorziand R.R. and R.R. RaoRao. Geographic Random Forwarding (. Geographic Random Forwarding (GeRaFGeRaF) for Ad ) for Ad Hoc and Sensor Networks:

Hoc and Sensor Networks: MultihopMultihopPerformance. Performance. IEEE Transactions on IEEE Transactions on Mobile Computing

Mobile Computing. Vol. 2, No. 4. October. Vol. 2, No. 4. October--December 2003.December 2003.

⇒

⇒ M. M. ZorziZorziand R.R. and R.R. RaoRao. Geographic Random Forwarding (. Geographic Random Forwarding (GeRaFGeRaF) for Ad ) for Ad Hoc and Sensor Networks: Energy and Latency Performance. Hoc and Sensor Networks: Energy and Latency Performance. IEEE IEEE Transactions on Mobile Computing

Transactions on Mobile Computing. Vol. 2, No. 4. October. Vol. 2, No. 4. October--December December 2003.

2003.

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•Area 1000 x 1000 mArea 1000 x 1000 m22

•

•Number of nodes in the range [50,250]Number of nodes in the range [50,250]

•

•Four traffic sources; packet rate Four traffic sources; packet rate rrin the range [0.2,2]; packet size 512 bytesin the range [0.2,2]; packet size 512 bytes

•

•Duty cycle time 0.1 s, TDuty cycle time 0.1 s, TONONthree times three times WakeWakeUPUPmessage transmission timemessage transmission time

•

•Signal propagation model Signal propagation model twotwo--ray ground model ray ground model (accurate in outdoor environment)(accurate in outdoor environment)

•

•Two nodes in the radio coverage if the received signal is higheTwo nodes in the radio coverage if the received signal is higher than 0.365er than 0.365e--6 W6 W

•

•Four possible transmission power levelsFour possible transmission power levels

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Impact of node density

Average power consumption Average number of hops

MACRO GPSR+STEM GeRaF MACRO GeRaF GPSR+STEM

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Impact of node density

Average power consumption Average power consumption vs

vsnodes nominal radio areanodes nominal radio area

MACRO GPSR+STEM

GeRaF

Ninra=N Ninra=NππRR22_/_/_Ξ_Ξ22

(8)

Number of packets delivered at destination

GPSR+STEM MACRO GeRaF MACRO GPSR+STEM GeRaF

Data

Aggregation

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Scenario

ApplicationsApplications: Sensor Networks for phenomenon monitoring : Sensor Networks for phenomenon monitoring

Sensor nodes notify the sink about the phenomenon they senseSensor nodes notify the sink about the phenomenon they sense

The sink uses this data to create a map of the phenomenon (spatiThe sink uses this data to create a map of the phenomenon (spatial al propagation, temporal evolution, etc.)

propagation, temporal evolution, etc.)

Data is funneled towards the sink and causes congestionData is funneled towards the sink and causes congestion

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Aggregation

Due Due totosensorssensors’’density and the density and the kindkindof of applicationsapplications, , redundantredundantand and highly

highlycorrelatedcorrelateddata (data (bothbothin space and time) are in space and time) are oftenoftenpropagatedpropagated throughout

throughoutthe network.the network.

ThisThiscan can leadleadtotoenergyenergywastewastewhichwhichreducesreducesnetwork network lifetimelifetime

MechanismsMechanismsforforcombiningcombiningdata at data at forwardingforwardingintermediate intermediate nodesnodesso so as

astotopropagate propagate onlyonlyusefulusefuland and notnotredundantredundantinformationinformationshouldshouldbebe considered

considered

Data Data aggregationaggregationisisaimedaimedat at aggregatingaggregatingdata data comingcomingfromfrommultiple multiple sensors

sensorsintointousefulusefulnon non redundantredundantfusedfuseddatadata

Data Data aggregationaggregation= = gatheringgathering+ + fusionfusion

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Relevant

Metrics

MetricsMetricstotobebeconsideredconsideredwhenwhenperformingperformingaggregationaggregationareare

⇒

⇒ EnergyEnergyefficiency: efficiency: fairnessfairnessin in energyenergyconsumptionconsumptionat at eacheachaggregationaggregation round

round isistotobebesearchedsearched. .

⇒

⇒ Network Network lifetimelifetime: the : the numbernumberof of roundsroundsuntiluntilthe first the first sensorsensorisisdepleteddepletedof of energy

energyshouldshouldbebemaximizedmaximized

⇒

⇒ Fidelity/Fidelity/distortiondistortionraterate: : differencedifferencebetweenbetweenthe data the data collectedcollectedat the at the sinksink when

whenno no aggregationaggregationisisperformedperformedand and whenwhenititisis, , shouldshouldbebeevaluatedevaluated

⇒

⇒ LatencyLatency: : aggregationaggregationimpliesimpliesadditionaladditionalprocessing of data. The processing of data. The delaydelay introduced

introducedbybythesetheseoperationsoperationsshouldshouldbebeconsideredconsideredand and shouldshouldnotnothavehave excessive

excessiveimpact on the impact on the timelinesstimelinessof the systemof the system

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Direct

Diffusion

TwoTwo--phasephasepullpullmechanismmechanism: :

⇒

⇒ PhasePhase1: the 1: the sinksinkpullspullsforforinformationinformationfromfromsourcessourcesusingusingthe the propagationpropagation of

of interestsinterestsforforspecificspecificinformationinformation. . SourcesSourcesansweranswerusingusingmultiple multiple pathspaths

⇒

⇒ PhasePhase2: the 2: the sinksinkinitiatesinitiatesreinforcementreinforcement, i.e. , i.e. asksaskssome some specificspecificnodesnodes (

(basedbasedon on considerationsconsiderationsrelatedrelatedtotodelaydelay, , qualityquality, , etcetc.) .) totoincreaseincreasetheirtheir event

eventsendingsendingraterate

Data Data arrivingarrivingat intermediate at intermediate nodesnodesand and comingcomingfromfrommultiple multiple sourcessourcescan can bebe aggregated

aggregatedwhenwhenreferringreferringtotothe the samesameinterestinterest

ReinforcementReinforcementcan can bebeincorporatedincorporatedintointoPhasePhase1, so the 1, so the twotwophasephaseprocessprocesscan can become

becomeone one phasephase

Direct Direct DiffusionDiffusioncan can bebecostlycostlybecausebecauseallallnodesnodesare are requiredrequiredtotosendsendtheirtheirdata data to

(9)

LEACH

ToToreduce the reduce the overheadoverheadof of eacheachnodenodetransmittingtransmittingdata data directlydirectlytotothe the sinksink, , clusterhead

clusterheadsolutionssolutionshavehavebeenbeenproposedproposed. . TheseTheseallowallowtotodrasticallydrasticallyreduce reduce energy

energyconsumptionconsumption

In LEACH In LEACH sensorsensornodesnodesorganizeorganizethemslevesthemslevesintointoclustersclusters. In . In eacheachone, a one, a nodenode, , denoted

denotedasasclusterheadclusterhead(CH)(CH), , takestakescare of care of fusingfusingdata data comingcomingfromfromotherothernodesnodesin in the

the clusterclusterand and sendssendsthe the fusedfuseddata data totothe the sinksink..

LEACH LEACH isisusefulusefulforforconstantconstantmonitoringmonitoringand and periodicperiodicdata data reportingreportingapplicationsapplications

2 2 phasesphases::

⇒

⇒ Set up: nodesSet up: nodesorganizeorganizethemselvesthemselvesintointoclustersclustersand and CHsCHsare are randomlyrandomly selected

selected

⇒

⇒ Steady state: Steady state: CHsCHsperformperformdata data aggregationaggregation

LimitationsLimitations::

⇒

⇒ NodesNodesassumedassumedtotohavehavethe the samesameenergyenergycapabilitiescapabilitiesso so thatthatrandomrandomrotation rotation of leadership can

of leadership can bebeperformedperformed

⇒

⇒ ConsequentlyConsequentlyallallnodesnodesare thoughtare thoughttotobebeCHsCHsand are assumedand are assumedtotobebeableabletoto reach

reachthe sinkthe sinkin one hop in one hop transmissiontransmission

CONCERT:

focus

on

congestion

control

CongestionCongestiontypicallytypicallyoccursoccursin in nodesnodescloseclosetotothe the sinksinkand and causescauseswastewasteof of bandwidth

bandwidthand and energyenergyresourcesresources

CongestionCongestionleadsleadstotolosseslossesand and thusthuscausescausesinaccuracyinaccuracyin in phenomenonphenomenon monitoring

monitoring

New New approachapproachtotosolve the solve the congestioncongestionproblemproblemin in sensorsensornetworksnetworksusingusing adaptive

adaptivedatadata--aggregationaggregation

PreviousPreviousworksworkson on congestioncongestioncontrol control usedusedbackback--pressurepressuretotoregulateregulatesourcessources’’ transmission

transmissionrate rate --> > decreasedecreasein in sourcessources’’throughputthroughputand and increaseincreasein in signalingsignaling

Data Data aggregationaggregationhashasbeenbeenusedusedforforincreasingincreasingnetwork network lifetimelifetime

Positive Positive effectseffectson the on the distributiondistributionof the of the loadloadin the network in the network havehavebeenbeenobservedobserved

DataData--aggregationaggregationusedusedforforcounteractingcounteractingcongestioncongestionproblemproblemand and guaranteingguaranteing

fidelity

fidelityin the networkin the network

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AggregationAggregationforforcongestioncongestioncontrol control purposespurposesshouldshouldbebedonedonewhilewhilepreservingpreserving information

informationentropyentropy

ToTothisthispurposepurposewewefocusfocuson on losslosslesslessaggregationaggregationwhichwhichexploitsexploitsspatialspatial correlation

correlationof data of data

WeWestudystudythe impact of the impact of aggregatoraggregatornodesnodespositioningpositioningon network performance in on network performance in terms

termsof of losslossprobabilityprobabilityand network and network overloadoverload

WeWeestimate the impact of data estimate the impact of data aggregationaggregationon on energyenergyconsumptionconsumptionbothbothat at aggregator

aggregatornodesnodesand and overalloverallin the network in the network

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Aggregator

nodes

positioning

:

Example

0 50 100 150 200 250 0 50 100 150 200 250 1 2 3 4 5 6 7 8 9 sink

The The loadloaddue due totocontrol control packetspacketsforwardingforwardingforforaggregatoraggregatornodesnodescontrol and control and management

management cannotcannotbebeneglectedneglected

AggregatingAggregatingone hop one hop awayawayfromfromthe the funneledfunnelednodesnodes(i.e. (i.e. nodenode9) 9) performsperformswellwell especially

especiallyforforhigh high valuesvaluesof the of the aggregationaggregationfunctionfunction(i.e. g=5)(i.e. g=5)

ThereThereisisnotnotgreatgreatadavntageadavntagein in aggregatingaggregatingat at allallnetwork network nodesnodeswithwithrespectrespecttoto aggregating

aggregatingonlyonlyat few at few nodesnodes. . ItItalsoalsoresultsresultscheapercheaper!!

0 0,02 0,04 0,06 0,08 0,1 0,12 0,14 0,16 1 2 3 4 5 6 7 8 9 Nodes P Lo ss g=2 g=5 No aggr 0 0,02 0,04 0,06 0,08 0,1 0,12 0,14 0,16 1 2 3 4 5 6 7 8 9 Nodes PLos s g=2 g=5 No aggr 0 0,02 0,04 0,06 0,08 0,1 0,12 0,14 0,16 1 2 3 4 5 6 7 8 9 Nodes PLos s g=2 g=5 No aggr 0 0,02 0,04 0,06 0,08 0,1 0,12 0,14 0,16 1 2 3 4 5 6 7 8 9 Nodes P Los s g=2 g=5 No aggr 0,08 0,1 0,12 0,14 0,16 0,18 0,2 P Los s g=2 g=5 No aggr 0,08 0,1 0,12 0,14 0,16 0,18 0,2 P Los s g=2 g=5

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Energy

Cost

1 2 3 4 5 6 7 8 9 10 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 αMAX C os t [W ] Aggr=9 Aggr=3 Aggr=4 Aggr=7 Aggr=3, 9 Aggr=3, 4 Aggr=3, 7 Aggr=4, 9 Aggr=4, 7 Aggr=7, 9 Aggr=3, 4, 7 Aggr=3, 7, 9 Aggr=4, 7, 9 Aggr=3, 4, 7, 9

Design of Wireless Sensor Networks

Energy

Energy

-

-

Efficiency Issues in Cross

Efficiency Issues in Cross

-

-

Layer

Layer

Design of Wireless Sensor Networks

Design of Wireless Sensor Networks

Sergio Palazzo

[email protected]

Sensor

Sensor

Networks

Networks

: a

: a

small

small

world

world

Main

Main

Features

Features

Energy

Energy

Efficiency

Efficiency

is

is

a major

a major

issue

issue

!

!

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Design Guidelines (1/3)

Design Guidelines (1/3)

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Design Guidelines (2/3)

Design Guidelines (2/3)

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Design Guidelines (3/3)

Design Guidelines (3/3)

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Energy

Energy

-

-

Efficiency related issues

Efficiency related issues

Energy

Energy

Conserving

Conserving

in the

in the

layered

layered

framework

framework

Energy

Energy

Conserving

Conserving

Approaches

Approaches

f

f

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Operating Modes of a Sensor Node (1/2)

Operating Modes of a Sensor Node (1/2)



