TowardsaReal‐TimeCommunica3onFrameworkforWirelessSensorNetworks

ChenyangLuDepartmentofComputerScienceandEngineering

Applica3onchallenges

  Highdatarate  Lowlatency  Priori;za;on  Predictability

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Structural Health Monitoring Process Monitoring

Outline

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  Conflict‐freetransmissionscheduling  Op;mizedforqueriesinsensornetworks.

  Priority‐basedreal‐;mescheduling  Trade‐offbetweenpriori;za;onandthroughput.

  Worst‐casedelayanalysis  Bridgingthegapbetweensensornetandreal‐;meschedulingtheory.

  Otherprojects

Querymodel

  Query–periodicdatacollec;onfromasetofsensors

  Queryinstance–instanceofqueryinasamplingperiod

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SELECT acceleration FROM accelerators SAMPLE RATE 10Hz DEADLINE 0.1s

Networkmodel

  Interference‐Communica;onGraph•  Communica;onedge(AB):A’stransmissionmaybereceivedbyB

•  Interferenceedges(AD):DcannotreceivewhenAtransmits,eventhoughDcannotdecodeA’stransmission

  TransmissionsABandCDareconflictfreeif:•  ADandCBarenotpresentinthegraph

  CanbeconstructedusingtheRIDprotocol[Zhou2005]

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A B

C D

Overview:queryscheduling

  Planner:Offlineorwhenaqueryarrives

•  Constructascheduleforasinglequeryinstance

•  Reducequerylatencybasedontransmissiondependency

  Scheduler:Run;me

•  Dynamicallyschedulemul)pleconcurrentqueryinstances

  Improvethroughput

  Maintainconflictfree

•  Priority‐basedreal‐;meschedulers

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Planner

  Plan:asequenceofsteps  Scheduleforasinglequeryinstance

•  Independentofotherqueryinstances

  Astepincludesasetofconflict‐freetransmissions  Respectinter‐transmissiondependenciesincurredbyrou;ngor

aggrega;on.

  Planningalgorithm•  Constructareversedplan

  Assignpriori;estonodesbasedon(depth,numbersofchildren,IDs).  Assignatransmissiontothenodewiththehighestprioritytothecurrent

step,ifnoconflictwithprevioustransmissionsassignedtothesamestep.

•  Reversetheplan

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Exampleofaplan

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0 q

1 n p

2 f k o z s

3 e l h t r

4 c j g w

5 b m

6 d

senders

s t e p s

a

b

c

d

f

g

h s

r

k

t

j

z

w

m

l

n

p q

e

o

0 1

2

Concurrentinstancesconflicts

9

1

0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 Slots:

Q1:

Q2:

0 1 2 3 4 5 6

0 1 2 3 4 5 6

0 1 2 3 4 5 6

conflicts?

Reduced throughput!

Minimumstepdistance

  MinimumstepdistanceisthesmallestΔsuchthat:ifthedistancebetweenanytwosteps≥Δconflict‐free

  Scheduler:EnforceagapofΔbetweeninstances=>conflict‐free

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0 1 2 3 4 5 6

0 Δ Δ Δ Δ Δ Δ 1 Δ Δ Δ Δ Δ Δ 2 Δ Δ Δ Δ Δ Δ 3 Δ Δ Δ Δ Δ Δ 4 Δ Δ Δ Δ Δ Δ 5 Δ Δ Δ Δ Δ Δ 6 Δ Δ Δ Δ Δ Δ

0 1 2 3 4 5 6

0 Δ Δ Δ Δ Δ Δ Δ 1 Δ Δ Δ Δ Δ Δ Δ 2 Δ Δ Δ Δ Δ Δ Δ 3 Δ Δ Δ Δ Δ Δ Δ 4 Δ Δ Δ Δ Δ Δ Δ 5 Δ Δ Δ Δ Δ Δ Δ 6 Δ Δ Δ Δ Δ Δ Δ

0 1 2 3 4 5 6

0 Δ Δ Δ Δ Δ 1 Δ Δ Δ Δ 2 Δ Δ Δ Δ 3 Δ Δ Δ Δ 4 Δ Δ Δ Δ 5 Δ Δ Δ Δ 6 Δ Δ Δ Δ Δ

0 1 2 3 4 5 6

0 Δ Δ Δ Δ 1 Δ Δ Δ 2 Δ Δ 3 Δ Δ 4 Δ Δ 5 Δ Δ Δ 6 Δ Δ Δ Δ

0 1 2 3 4 5 6

0 Δ Δ Δ 1 Δ Δ 2 Δ 3

4 Δ 5 Δ Δ 6 Δ Δ Δ

0 1 2 3 4 5 6

0

1

2

3

4

5

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Min. step distance: Δ = 0 Min. step distance: Δ = 1 Min. step distance: Δ = 2 Min. step distance: Δ = 3 Min. step distance: Δ = 4

Conflict table:

NS2simula3on:throughput

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58.6%

NS2simula3on:latency

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74.8%

Real‐3mequeryscheduling

  Trade‐offbetweenpriori3za3onandthroughput

  Non‐preemp;veQueryScheduler(NQS)•  highthroughput,priorityinversion

  Preemp;veQueryScheduler(PQS)•  lowerthroughput,nopriorityinversion

  Slack‐stealingQueryScheduler(SQS)•  usespreemp;ononlywhennecessary•  Improvethroughputwithoutmissingdeadlines

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Nonpreemp3veQueryScheduler(NQS)

  Orderpendingqueriesbasedonpriority

  EnforceΔbetweenthestart)mesofconsecu;veinstances  High‐priorityinstancedoesnotpreemptlow‐priorityinstancesthathave

alreadystarted

  Planlength=15,Δ=8

Suffers from priority inversion

  High‐priorityinstancepreemptslow‐priorityinstanceiftheywouldconflict.

Preemp3veQueryScheduler(PQS)

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NQS/PQSComparison

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Prioritization without preemption

Prioritization with preemption

Higher priority query has lower latency

NQS/PQSComparison

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Prioritization without preemption

Prioritization with preemption

Lower query throughput

  SQScombinesbenefitsofNQSandPQS  Usepreemp;ononlywhennecessarytomeetdeadlines  Improvethroughputwhilemee;ngalldeadlines

  Slack‐themaximum;meaqueryinstancemaybedelayedwithoutmissingitsdeadline

  SQSschedulingalgorithm  Ifithasenoughslack,ahigherpriorityinstanceallowsalowerpriority

instancetocompleteitsfirstΔsteps

  Otherwise,thehigherpriorityinstancepreemptsthelowpriorityinstanceimmediately

Slackstealingqueryscheduling(SQS)

0

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NS2simula3on:Priori3za3on

NQS PQS

NS2simula3on:SQS

SQS

Worst‐casedelayanalysis

  Assump;on:period<=deadline

  MaptoResponseTimeAnalysisinreal‐;meschedulingtheory  Execu;on;me:lengthoftheplanL  Interferencefromahigh‐priorityinstance:Δ  Blocking;me:Δ‐1

  Response;me:

  Assump;on:period<=deadline

  MaptoResponseTimeAnalysisinreal‐;meschedulingtheory  Execu;on;me:lengthoftheplanL  Interferencefromahigh‐priorityinstance:Δ  Blocking;me:Δ‐1

  Response;me:

Worst‐casedelayanalysis

executiontime

  Assump;on:period<=deadline

  MaptoResponseTimeAnalysisinreal‐;meschedulingtheory  Execu;on;me:lengthoftheplanL  Interferencefromahigh‐priorityinstance:Δ  Blocking;me:Δ‐1

  Response;me: worst‐casedelaybeforeinstancelstarts

Worst‐casedelayanalysis

  Assump;on:period<=deadline

  MaptoResponseTimeAnalysisinreal‐;meschedulingtheory  Execu;on;me:lengthoftheplanL  Interferencefromahigh‐priorityinstance:Δ  Blocking;me:Δ‐1

  Response;me:

Worst‐casedelayanalysis

blockingtime

Worst‐casedelayanalysis

  Assump;on:period<=deadline

  MaptoResponseTimeAnalysisinreal‐;meschedulingtheory  Execu;on;me:lengthoftheplanL  Interferencefromahigh‐priorityinstance:Δ  Blocking;me:Δ‐1

  Response;me:

interference

Worst‐casedelayanalysis

  Assump;on:period<=deadline

  MaptoResponseTimeAnalysisinreal‐;meschedulingtheory  Execu;on;me:lengthoftheplanL  Interferencefromahigh‐priorityinstance:Δ  Blocking;me:Δ‐1

  Response;me:

Conclusions

  Conflict‐freetransmissionscheduling  Op;mizedforqueriesinsensornetworks.

  Adap;vetoworkloadchanges.

  Priority‐basedreal‐;meschedulers  Trade‐offbetweenpriori;za;onandthroughput.

  Worst‐casedelayanalysis  Bridgingthegapbetweensensornetandreal‐;meschedulingtheory.

27

O.Chipara,C.Lu,J.A.Stankovic,DynamicConflict‐freeQuerySchedulingforWirelessSensorNetworks,ICNP’06.

O.Chipara,C.Lu,G.‐C.Roman,Real‐;meQuerySchedulingforWirelessSensorNetworks,RTSS’07.

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MLA:MACLayerArchitecture

  Separa;onofpowermanagementfromradiocore[IPSN’07]

  Componentsforsleepschedulingprotocols[SenSys’07]  ReusableeasedevelopmentandmaintenanceofMACprotocols  Plapormindependentreducepor;ngeffort

RadioCoreTimers

PowerManagement

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ReusabilityofComponents

B-MAC X-MAC SCP-Wustl Pure-TDMA SS-TDMA Channel Poller LPL Listener Preamble Sender Time Synchronization TDMA Slot Handler CSMA Slot Handler Low Level Dispatcher Async I/O Adapter Alarm Local Time Radio Core Other Components 3 3 4 2 2 Reused Components 6 6 8 7 8

SolveMACProblems

  HardtodevelopnewMACprotocols?

  Example:RI‐MAC(SenSys’08)builtontopofMLA  Hardtomaintainmul;pleMACstacksasOSevolves?

  UpgradingMLAforTinyOS2.0.1‐>2.0.2‐>2.1tookseveralhours

  Mul;pleMACprotocolssurvivedupgradewithoutanychange!  Protocolsnotreusableacrossradio/processorplaporms?

  SupportsbothTelosandMicaZ

  TinyOS2.1versionavailablefromTinyOS“contrib”CVS

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K.Klues,G.Hackmann,O.Chipara,andC.Lu,AComponentBasedArchitectureforPower‐EfficientMediaAccessControlinWirelessSensorNetworks,SenSys’07.

ClinicalMonitoring

  Wirelesspulseoximeter

  Low‐powermeshnetwork  Barnes‐JewishHospitalDeployment

  Ordersofmagnitudehighergranularitythancurrentprac;ce•  1reading/minvs.severalmanual

readings/day)

  Enablesearlydetec;onofclinicaldeteriora;on

  Highlyreliablenetwork(99.92%)

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O.Chipara,C.Brooks,S.Bhazacharya,C.Lu,R.D.Chamberlain,G.‐C.Roman,T.C.Bailey,ReliableReal‐;meClinicalMonitoringUsingSensorNetworkTechnology,AMIA’09.

StructuralHealthMonitoring

  Co‐designofdistributedsensornetworkarchitectureandstructuralengineeringalgorithms

  Successfuldamagelocaliza;ononlabstructures

  Advantagesovercentralizedapproaches  reducelatencyby88%  increasinglife;mebyafactorof

3.4underanhourlyschedule

G.Hackmann,W.Guo,G.Yan,C.Lu,S.Dyke,Cyber‐PhysicalCodesignofDistributedStructuralHealthMonitoringWithWirelessSensorNetworks,ICCPS'10.

G.Hackmann,F.Sun,N.Castaneda,C.LuandS.Dyke,AHolis;cApproachtoDecentralizedStructuralDamageLocaliza;onUsingWirelessSensorNetworks,RTSS’08.