Technologies, Beaconing, and Routing in Vehicular...

MicheleSegata,RenatoLoCigno - UniversityofTrento

withspecialthankstoFalko Dressler,ChristophSommer,BastianBloessl,Stefan Joerer,DavidEckhoff

WirelessMeshandVehicularNetworks

Technologies,Beaconing,andRoutinginVehicularNetworks

Motivation

• TaxonomyofUseCases

Wireless Mesh & Vehicular Networks - Technologies, Beaconing, and Routing in Vehicular Networks 2

Vehicle-to-X

Non-Safety

Comfort

ContextualInformation Entertainment

TrafficInformationSystems

OptimalSpeedAdvisory

Congestion,Accident

Information

Safety

SituationAwareness

AdaptiveCruiseControl

BlindSpotWarning

WarningMessages

TrafficLightViolation

ElectronicBrakeLight

Technology

• Communicationparadigmsandmedia


[1] Dar, K. and Bakhouya, M. and Gaber, J. and Wack, M. and Lorenz, P., "Wireless Communication Technologies for ITS Applications," IEEE Communications Magazine, vol. 48 (5), pp. 156-162, May 2010

WirelessCommunicationTechnologies

Infrastructure-based

Broadcast

FMRadio,DAB/DVB,

…

Cellular

GSM

2GCellular

UMTS

3GCellular

LTE/WiMAX

4GCell.

Infrastructureless

ShortRange

Millimeter,Infrared,Visible

802.15.1Bluetooth

802.15.4ZigBee

MediumRange

802.11Wi-Fi

DSRC/WAVE

Anoutline

A(rough)outlineoftheVehicularNetworkstopics• Application:whyVN?• Communication:technologies,alternatives,protocols,challenges• Simulation: evaluatingvehicularnetworkswithoutvehiclesand

withoutnetworks.Toolsandmodels


COMMUNICATIONTECHNOLOGIES(Someofthem)


Cellularnetworks

• Concept– Divideworldintocells,eachservedbybasestation– Allows,e.g.,frequencyreuseinFDMA


f0

f1

f2

f0f2

f1

f2

f0

f1

f0

f1

f2

f0

f1

f2

f0

f1

f2

f0f2

f0f2

f0f2

f0

f1

f2

f0

Cellularnetworks

• Stricthierarchyofnetworkcomponents


UE

Core Network

RNC

Cell

NodeB

Cell Cell Cell Cell

NodeB

Cell

RNC

Cell

NodeB

Cell Cell Cell Cell

NodeB

Cell

Cellularnetworks

• CanUMTSsupportCar-to-Xcommunication?– Ex:UTRAFDDRelease99(W-CDMA)– Speedofvehiclesnotalimitingfactor

• Fieldoperationaltestsat290km/hshowsignaldropsonlyaftersuddenbraking(⇨ handoverpredictionfailures)

– Openquestions• Delay• Capacity

• ChannelsinUMTS– Sharedchannels

• E.g.,RandomAccessChannel(RACH),uplinkandForwardAccessChannel(FACH),downlink

– Dedicatedchannels• E.g.,DedicatedTransportChannel(DCH),up-/downlink


Cellularnetworks

• FACH– Timeslotsmanagedbybasestation– Delayontheorderof10ms per40ByteandUE– Capacityseverelylimited(innon-multicastnetworks)– NeedtoknowcurrentcellofUE

• RACH– SlottedALOHA– randomaccessbyUEs

• PowerrampingwithAcquisitionIndication– Delayapprox.50ms

per60ByteandUE– Massiveinterference

withotherUEs


Cellularnetworks

• DCH– Delay:approx.250ms /2s/10sforchannelestablishment

• Dependsonhowfine-grainedUEpositionisknown– MaintainingaDCHisexpensive

• Closed-LoopPowerControl(nointerferenceofotherUEs)• Handoverbetweencells

– Upperlimitofapprox.100UEs


Cellularnetworks

• So:canUMTSsupportCar-to-Xcommunication?– Atlowmarketpenetration:yes– Eventually:

• Needtoinvestinmuchsmallercells(e.g.,alongfreeways)• Needtoimplementmulticastfunctionality(MBMS)

– MainusecaseforUMTS:centralizedservices• Ex.:GoogleMapsTraffic

– CollectinformationfromUMTSdevices– Storageofdataoncentralserver– DisseminationviaInternet(⇨ idealforcellularnetworks)


IEEE802.11p

• IEEE802.11{a,b,g,n,ac}forCar-to-Xcommunication?– Can’tbeininfrastructuremodeand

adhocmodeatthesametime– Switchingtimeconsuming– Associationtimeconsuming– Nointegralwithin-networksecurity– (Massively)shared

spectrum(⇨ ISM)– NointegralQoS– Multi-patheffects

reducerangeandspeed


[1]FayHui,Prasant Mohapatra.„ExperimentalCharacterizationofMultihop CommunicationsinVehicularAdHocNetwork“.InProceedingsofthe2ndACMinternationalworkshoponVehicularadhocnetworks,2005

IEEE802.11p

• Newlowerlayersfor“WirelessAccessinVehicularEnvironments”(WAVE)– PHYlayermostlyidenticaltoIEEE802.11a

• VariantwithOFDMand16QAM• Higherdemandsontolerances• Reductionofintersymbolinterference

becauseofmulti-patheffects– Doubletimingparameters– Channelbandwidthdownto10MHz(from20MHz)– Throughputdownto3...27Mbit/s(from6...54Mbit/s)– Rangeupto1000m,speedupto200km/h

– MAClayerofIEEE802.11aplusextensions• RandomMACAddress• QoS (EDCApriorityaccess,cf.IEEE802.11e,...)• Multi-FrequencyandMulti-Radiocapabilities• NewAdHocmode• ...


IEEE802.11p- OFDMSignal

• Howdoesitlooklike?


IEEE802.11p

• ClassicIEEE802.11BasicServiceSet(BSS)– Dividesnetworksintologicalunits

• Nodesbelongto(exactlyone)BSS• PacketscontainBSSID• Nodesignorepacketsfrom“foreign”BSSs• Exception:Wildcard-BSSID(-1)forprobes• Adhocnetworksemulateinfrastructuremode

– JoiningaBSS• AccessPointsendsbeacon• Authenticationdialogue• Associationdialogue• NodehasjoinedBSS

Wireless Mesh & Vehicular Networks - Technologies, Beaconing, and Routing in Vehicular Networks15

BSSSSID “A”

BSSSSID “B”

BSSSSID “C”

IEEE802.11p

• New:802.11OCBMode(OutsideoftheContextofaBSS)– DefaultmodeofnodesinWAVE– NodesmayalwaysuseWildcardBSSinpackets– NodeswillalwaysreceiveWildcardBSSpackets– MayjoinBSSandstilluseWildcardBSS


BSSSSID “A”

BSSSSID “B”

IEEE802.11p- MAC

• IEEE802.11HybridCoordinationFunction(HCF)– cf.IEEE802.11eEDCA– DIFS⇨ AIFS(ArbitrationInter-FrameSpace)

• DCF⇨ EDCA(EnhancedDistributedChannelAccess)

– Classifyuserdatainto4ACs(AccessCategories)• AC0(lowestpriority)• …• AC3(highestpriority)

– EachACshasdifferent...• CWmin,CWmax,AIFS,TXOPlimit(max.continuoustransmissions)

– ManagementdatausesDIFS(notAIFS)



• Map8userpriorities⇨ 4accesscategories⇨ 4queues• Queuescompeteindependentlyformediumaccess

IEEE802.11p

AC0

AC1

AC2

AC3

virt

ual c

ollis

ion


• Parameterization

• Samplequeueconfiguration

IEEE802.11p

Parameter Value

SlotTime 13µs

SIFS 32µs

CWmin 15

CWmax 1023

Bandwidth 3..27mbit/s

Parameter AC_BK AC_BE AC_VI AC_VO

CWmin CWmin CWmin (CWmin+1)/2-1 (CWmin+1)/4-1

CWmax CWmax CWmax CWmin (CWmin+1)/2-1

AIFSn 9 6 3 2

AC_VO AC_VI AC_BE AC_BK

ChannelAccess

Backoff:0 0 0 0

IEEE802.11p



Backoff:0 0 0 0

Channelbusy?

StartContention

WaitforIdle

IEEE802.11p


ChannelAccess


0 0 0

Backoff0?

WaitAIFS(SIFS+AIFSn *Slotlen)

Waitforbackoff=0

Backoff:0

IEEE802.11p


ChannelAccess

Backoff:0


Backoff:2 0 0 0

TransmissionOver

PostTransmitBackoff

IEEE802.11p


ChannelAccess

2


Backoff:2 0 0 0

AC_VIQueuereadytosend…waitAIFS Backoff

Ch becomesbusy

IEEE802.11p


ChannelAccess

Backoff:2 21


Backoff:1 0 0Channelidle

Channelbusy

[Slottimepassed]/DecrementBackoff

Channelstatechanges

Backoff:0 0

IEEE802.11p


ChannelAccess

3Backoff:0 0


0 0

Queuereadytosend

InternalContentionBackoff

Higherprio

rity

queu

eready

IEEE802.11p


ChannelAccess


• QoSinWAVE– meanwaitingtimeforchannelaccess,givensampleconfiguration(and

TXOPLimit=0⇨ singlepacket)

IEEE802.11p

[1]Eichler,S.,"PerformanceevaluationoftheIEEE802.11pWAVEcommunicationstandard,"Proceedingsof66thIEEEVehicularTechnology Conference(VTC2007-Fall),Baltimore,USA,October2007,pp.2199-2203

AC CWmin CWmax AIFS TXOP tw (inμs)

0 15 1023 9 0 264

1 7 15 6 0 152

2 3 7 3 0 72

3 3 7 2 0 56

n Single Node: n Multiple Nodes:


• ProsofUMTS/LTE– Easyprovisionofcentralizedservices– Quickdisseminationofinformationinwholenetwork– Pre-deployedinfrastructure– Easymigrationto(andintegrationinto)smartphones

• ConsofUMTS/LTE– Highshortrangelatencies(mightbetoohighforsafety)– Networkneedsfurtherupgrades(smallercells,multicastservice)– Highdependenceonnetworkoperator– Highloadincorenetwork,evenforlocalcommunication

UMTS/LTEvs.IEEE802.11p

UMTS/LTEvs.IEEE802.11p

• Prosof802.11p/Adhoc– Smallestpossiblelatency– Cansustainoperationwithoutnetworkoperator/provider– Networkloadhighlylocalized– Betterprivacy(⇨ laterslides)

• Consof802.11p/Adhoc– Needsgatewayforprovisionofcentralservices(e.g.,RSU)– Nopre-deployedhardware,andhardwareisstillexpensive

• Thesolution?– hybridsystems:

deploybothtechnologiestovehiclesandroad,decidedependingonapplicationandinfrastructureavailability


HIGHERLAYERPROTOCOLS


HigherLayerStandardsforIEEE802.11p

• Channelmanagement– Dedicatedfrequencybandat5.9GHzallocatedtoWAVE

• ExclusiveforV2VundV2Icommunication• Nolicensecost,butstrictrules• 1999:FCCreserves7channelsof10MHz(“U.S.DSRC”)

– 2reservedchannels,1+4channelsforapplications• ETSIEuropereserves5channelsof10MHz


[1]ETSIES202663V1.1.0(2010-01):IntelligentTransportSystems(ITS);EuropeanprofilestandardforthephysicalandmediumaccesscontrollayerofIntelligentTransportSystemsoperatinginthe5GHzfrequencyband

…

CriticalSafety of

Life

ch1725.860GHz

SCH

ch1745.870GHz

SCH

ch1765.880GHz

ControlChannel(CCH)

ch1785.890GHz

SCH

ch1805.900GHz

SCH

ch1825.910GHz

Hi-PowerPublicSafety

ch1845.920GHz

…

SCH

ch1725.860GHz

SCH

ch1745.870GHz

SCH

ch1765.880GHz

SCH

ch1785.890GHz

CCH

ch1805.900GHz

HigherLayerStandardsforIEEE802.11p

• Needforhigherlayerstandards– Unifiedmessageformat– Unifiedinterfacestoapplicationlayer

• U.S.– IEEE1609.*– WAVE(“WirelessAccessinVehicularEnvironments“)

• Europe– ETSI– ITSG5(“IntelligentTransportationSystems”)


IEEE1609

• IEEE1609.*upperlayers(buildingonIEEE802.11p)– IEEE1609.1:“Operatingsystem”– IEEE1609.2:Security– IEEE 1609.3:Networkservices– IEEE1609.4:Channelmgmt.


[1]Jiang,D.andDelgrossi,L.,"IEEE802.11p:Towardsaninternationalstandardforwirelessaccessinvehicularenvironments,"Proceedingsof67thIEEEVehicularTechnologyConference(VTC2008-Spring),MarinaBay,Singapore,May2008[2]Uzcátegui,RobertoA.andAcosta-Marum,Guillermo,"WAVE:ATutorial,"IEEECommunicationsMagazine,vol.47(5),pp.126-133,May2009

TCP/UDP

WAVEPHY

ChannelCoordination,WAVEMAC

IPv6WSMP

Managem

ent

Security LLC

802.

11p 16

09.

4

1609

.3

1609

.2

WAVEPHY

IEEE1609

• Channelmanagement– WAVEallowsforbothsingleradiodevices&multiradiodevices– DedicatedControlChannel(CCH)formgmtandsafetymessages⇨ singleradiodevicesneedtoperiodicallylistentoCCH

– Timeslots• SynchronizationenvisionedviaGPSreceiverclock• Standardvalue:100mssyncinterval(with50msonCCH)• Shortguardintervalatstartoftimeslot

– Duringguard,mediumisconsideredbusy(⇨ backoff)


[1]IEEEVehicularTechnologySociety,"IEEE1609.4(Multi-channelOperation),"IEEEStd,November,2006

CCHinterval

CCHinterval

“SCH”interval

“SCH”interval

t = n × 1s

IEEE1609

• Packettransmission– SortintoACqueue,basedonWSMP(orIPv6)EtherTypefield,destination

channel,anduserpriority– Switchtodesiredchannel,setupPHYpoweranddatarate– Startmediumaccess


CC

HSC

HAC0AC1AC2AC3 vi

rt. C

ollis

ion

AC0AC1AC2AC3 vi

rt. C

ollis

ion

Cha

nnel

Rou

ter

Cha

nnel

sel

ectio

n an

d se

tup

Cha

nnel

acc

ess

IEEE1609

• Channelmanagement– ControlChannel(CCH):

• Defaultchanneluponinitialization• WAVEserviceadvertisements(WSA),WAVEshortmessages(WSM)

• Channelparameterstakefixedvalues

– ServiceChannel(SCH):• OnlyafterjoiningWAVEBSS• WAVEshortmessages(WSM),IPdatatraffic(IPv6)

• Channelparameterscanbechangedasneeded


IEEE1609

• WAVEserviceadvertisement(WSA)– BroadcastonControlChannel(CCH)– IdentifiesWAVEBSSsonServiceChannels(SCHs)– Canbesentatarbitrarytimes,byarbitrarynodes– OnlypossibilitytomakeothersawareofdatabeingsentonSCHs,aswellas

therequiredchannelparameterstodecodethem


NodeA NodeB

ETSIITSG5

• Motivation– EuropeanstandardizationeffortbasedonIEEE802.11p– StandardizationtoincludelessonslearnedfromWAVE– Differentinstrumentationoflowerlayers– Differentupperlayerprotocols– Differentchannelassignment

• ITS-G5A(safety)• IST-G5B(nonsafety)


ETSIITSG5

• Protocolstack– PHYandMACbasedonIEEE802.11p– Mostprominentchange:

crosslayerDecentralizedCongestionControl(DCC)


ETSIITSG5

• Channelmanagement– Multiradio,multiantennasystem

• Noalternatingaccess⇨ Circumventsproblemswithsynchronization⇨ Noreductioningoodput

• DirectresultofexperienceswithWAVE

– OneradiotunedtoCCH• ServiceAnnouncementMessage(SAM)• Periodic:CooperativeAwarenessMessages(CAM)• Eventbased:DecentralizedEnvironmentNotificationMessage(DENM)

– Addl.radiotunedtoSCH• Userdata


ETSIITSG5

• CooperativeAwarenessMessage– Periodic(upto10Hz)safetymessage– Informationonstateofsurroundingvehicles:

• Speed,location,…– Messageagehighlyrelevantforsafety

• Needmechanismstodiscardoldmessages– SafetyapplicationsrelyonCAMs:

• Tailendofjam• Rearendcollision• Intersectionassistance…

– SentonCCH– Generatedevery100ms..1s,butonlyif

∆angle(>4°),∆position(>5m),∆speed(>1m/s)


ETSIITSG5

• DecentralizedEnvironmentalNotificationMessage(DENM)– Eventtriggered(e.g.,byvehiclesensors)

• Hardbraking• Accident• Tailendofjam• Constructionwork• Collisionimminent• Lowvisibility,highwind,icyroad,…

– Messageshave(tight)localscope,relaybasedon• Area(definedbycircle/ellipse/rectangle)• Roadtopology• Drivingdirection


BEACONING:1-HOPBROADCAST


Beaconing:1-hopBroadcast

• ETSIITSCAMs(CooperativeAwarenessMessages)– Periodic(upto10Hz)safetymessage– Informationonstateofsurroundingvehicles:

• Speed,location,…– Messageagehighlyrelevantforsafety

• Needmechanismstodiscardoldmessages

• IEEE1609BSMs(BasicSafetyMessages)

• …but


Beaconing:1-hopBroadcast

• Openissues– Infrastructure-lessoperation:needshighmarkedpenetration– Required/tolerablebeaconintervalhighlydependentonscenario– Designneedsdedicatedchannelcapacity

• Realnetworksareheterogeneous– Roadsideinfrastructurepresentvs.absent– Freewayscenariovs.innercity– Ownprotocol⇔ other,future,andlegacyprotocols

• Howtodobetter?– Dynamicallyadaptbeaconinterval– Dynamicallyuseallfree(!)channelcapacity


DecentralizedCongestionControl(DCC)

• CorefeatureofETSIITSG5• Adaptiveparameterizationtoavoidoverload• ConfigurableparametersperAC:

– TXpower(TransmitPowerControl,TPC)– Minimumpacketinterval(TransmitRateControl,TRC)– Datarate(TransmitDatarateControl,TDC)– SensitivityofClearChannelAssessment(DCCSensitivityControl,DSC)

• Statemachinedetermineswhichparametersetisselected;availablestates:– Relaxed– Active(multiplesubstates)– Restrictive



• Measuremin/maxChannelLoad(x)– Min/maxchannelloadin [tnow-x..tnow]– Channelload:fractionoftimethatchannelwassensedbusyduring

measuringinterval(ex:𝑇m ≈ 1s)– Channelbusy:Averagereceivedpower(signalornoise)duringprobing

interval(ex:𝑇p ≈ 10μs)abovecarriersensethreshold

• StatemachineforControlChannel:



• Example:ControlChannel– TXpower:relaxed:33dBm ⇨ active:ref⇨ restrictive:-10dBm– “ref”:Valueremainsunchanged– Remember:

• 33dBm ⇨ 10%.% mW⇨ 2000mW• -10dBm ⇨ 10'( mW ⇨ 0.1mW


StateRelaxed Active Restrictive

AC_VI AC_VO AC_BE AC_BK

TXpower 33dBm ref 25dBm 20dBm 15dBm -10dBm

Minpkt interval 0.04s ref ref ref ref 1s

Datarate 3Mbit/s ref ref ref ref 12Mbit/s

CCAthreshold -95 dBm ref ref ref ref -65 dBm


• Oscillatingchannelload(bothlocalandglobal!)– …causedbychannelaccessbeingtoorestrictive(standardparameters)


[1]DavidEckhoff,Nikoletta Sofra andReinhardGerman,"APerformanceStudyofCooperativeAwarenessinETSIITSG5andIEEEWAVE,"Proceedingsof10thIEEE/IFIPConferenceonWirelessOndemandNetworkSystemsandServices(WONS2013),Banff,Canada,March2013.

DynB– DynamicBeaconing

• Consideralltheradioshadowingeffectstoadaptveryquicklytothecurrentchannelquality

• Mainidea:continuouslyobservetheloadofthewirelesschanneltocalculatethecurrentbeaconinterval𝐼

• Basecalculationof𝐼 on:– Channelbusytimefraction𝑏+– Numberofneighbors𝑁– Desiredinterval𝐼-./– Desiredchannelbusytimefraction𝑏-./

• 𝐼 = 𝐼-./ + 𝑟× 𝐼456 − 𝐼-./– With𝐼456 = 𝑁 + 1 ×𝐼-./

andr=(bt /bdes)- 1clippedin[0,1]


[1]ChristophSommer,StefanJoerer,MicheleSegata,OzanK.Tonguz,RenatoLoCignoandFalkoDressler,"HowShadowingHurts VehicularCommunicationsandHowDynamicBeaconingCanHelp,"Proceedingsof32ndIEEEConferenceonComputerCommunications(INFOCOM2013),Mini-Conference, Turin,Italy,April2013

DynB– DynamicBeaconing

• wrt.handlingdynamicsintheenvironment– Assumingtwolargerclustersofvehiclesmeetingspontaneously(e.g.,at

intersectionsinsuburbanorwhentwobigtrucksleavethefreeway)


Application-based:JerkBeaconing

• Jerk:– physicalquantitymeasuringvariationofaccelerationovertime

– usinganestimationofjerkwecomputethebeaconinterval

– tunableparameters:• minimumbeaconinterval• maximumbeaconinterval• sensitivity

• Mainidea:– themoreconstantthesystem,thelowertherequirement– sendupdatesonlywhenneeded,usepredictionotherwise


JerkBeaconing


Evaluation:Strongshockwaves


3m

45 %

4m

17%

Evaluation:Moderateshockwaves


4.5m

40%

4.5m

10%

MULTI-HOPFORWARDINGRoutingtechniquesinVehicularNetworks


Classicalrouting

• MightnotbesuitedforVehicularNetworks…– Distancevector

• Eachnodestoresavectorof(dst,cost,next-hop)– Linkstate

• Knowntopology+Dijkstra• Fastconvergencevs.overhead

– Reactive(ondemand)• Establishroutesonlywhenneeded

– Proactive(tabledriven)• Continuouslymaintainroutesuptodate

– Hopbyhop• Intermediatenodeschosethenexthopforapacket

– Sourcerouting• Packetsincludethefullroute


Georouting

• Primarymetrics:position/distancetodestination• Requiresnodepositionstobeknown(atleastforthedestination)• Twooperationmodes(typ.):

– Greedymode:choosenexthopaccordingtomaxprogress– Recoverymode:escapedeadends(localmaxima)

• Mustensurethatmessagenevergetslost


Routing

• Q:Can(classical)routingworkinVANETs?• A:Onlyinsomecases.• Commonlyneedmulticastcommunication,lowload,lowdelay• Additionalchallengesandopportunities:

networkpartitioning,dynamictopology,complexmobility,…


[1]Toor,YasserandMühlethaler,PaulandLaouiti,Anis andFortelle,ArnauddeLa,"VehicleAdHocNetworks:ApplicationsandRelatedTechnicalIssues,"IEEECommunicationsSurveysandTutorials,vol.10(3),pp.74-88,2008

Car-to-X

Non-Safety

Comfort

ContextualInformation Entertainment

TrafficInformationSystems

OptimalSpeedAdvisory

Congestion,Accident

Information

Safety

SituationAwareness

AdaptiveCruiseControl

BlindSpotWarning

WarningMessages

TrafficLightViolation

ElectronicBreakLight

<!><!>

<!>

<!>

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<!>

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idle send

rcvdup

“Smart”Flooding

• Flooding:Multi-HopBroadcast• Simplestprotocol:“SmartFlooding“:

– Problem:BroadcastStorm• Superfluousre-broadcastsoverloadchannel

60Wireless Mesh & Vehicular Networks - Technologies, Beaconing, and Routing in Vehicular Networks

Flooding:Broadcastsuppression

• Motivation– Needsnoneighborinformation– Needsnocontrolmessages– Maximizesdistanceperhop– Minimizespacketloss

• Approach– Nodereceivesmessage,estimatesdistancetosender– Selectivelysuppressesre-broadcastofmessage– Alternatives

• weightedp-persistence• slotted1-persistence• slottedp-persistence


[1]Wisitpongphan,Nawaporn andTonguz,OzanK.andParikh,J.S.andMudalige,Priyantha andBai,FanandSadekar,Varsha,"BroadcastStormMitigationTechniquesinVehicularAdHocNetworks,"IEEEWirelessCommunications,vol.14(6),pp.84-94,December2007


• Estimatedistancetosenderas0≤ρij ≤1

• GPSbased

• RSSbased



• Weightedp-persistence– Probabilisticfloodingwithvariablepij forre-broadcast– Thus,higherprobabilityforlargerdistanceperhop


pij


• Weightedp-persistence– WaitWAIT_TIME(e.g.,2ms)– choosep=min(ρij)ofallreceivedpackets

(probabilityforre-broadcastofpacket)– Ensurethatatleastoneneighborhasre-broadcastpacket


idle wait 2 msrcv

dup

sendp

wait δ ms

¬p

dup expired

dup

Flooding:BroadcastSuppression

• Slotted1-persistence– Suppressionbasedonwaitingandoverhearing– Dividelengthofroadintoslots– Moredistantslotssendsooner– Closerslotssendlater(orifmoredistantslotsdidnotre-broadcast)– Thus,higherprobabilitytotransmitoverlongerdistance


pij

t=0 t=τ t=2τ t=3τ


• Slotted1-persistence– Divide“communicationrange“intoNsslotsoflengthτ– Nodeswaitbeforere-broadcast,waitingtimedependingonslot– Duplicateeliminationtakescareofsuppressionofbroadcasts


idle wait Tijrcv

dup

send¬dup

dup


• Slottedp-persistence– Cf.slotted1-persistence– Fixedforwardingprobabilityp(insteadof1)


pij

t=0 t=τ t=2τ t=3τ


• Slottedp-persistence– WaitforTij (insteadoffixedWAIT_TIME)– Useprobabilityp(insteadof1)– Ensurethatatleastoneneighborhasre-broadcastthepacket

bywaitingforδ’>max(Tij)


idle wait Tijrcv

dup

sendp

wait δ’

¬p

dup expireddup

Flooding:Remainingproblems

• Temporarynetworkfragmentation

• Undirectedmessagedissemination


Flooding+X:DV-CAST

• Idea:detectcurrentscenario,switchbetweenprotocols• Checkforfragmentednetwork

– Networkconnectedà performbroadcastsuppression

– Networkfragmentedà performStore-Carry-Forward

70

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Wireless Mesh & Vehicular Networks - Technologies, Beaconing, and Routing in Vehicular Networks

[1] Tonguz, Ozan K. and Wisitpongphan, N. and Bai, F., "DV-CAST: A distributed vehicular broadcast protocol for vehicular ad hoc networks," IEEE Wireless Communications, vol. 17 (2), pp. 47-57, April 2010





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Geocast:TO-GO

• Step1:Findbestnexthop(TargetNode,T)– FindN:Furthestneighbortowardsdestination– FindJ:Furthestneighbortowardsdestination,currentlyonjunction– FindNJ:Furthestneighbortowardsdestination,asseenbyJ– ifN,NJ areonthesameroad,

pickNelse,pickJ


N

NJ

J

Geocast:TO-GO

• Step2:FindForwardingSet(FS)– NodesintheFSwillcompeteforrelayingofthemessage– OnlyonenodeinFSshouldrelay

thus,allnodesinFSmustheareachother– FindingoptimalsolutionisNPcomplete– TO-GOusesapproximation


Geocast:TO-GO

• Step3:MulticastmessagetoallnodesinFS– NodesintheFScompeteforrelayingofthemessage– EnsuremaximumprogresswithinFS– Delayre-broadcastby𝑡– Suppressre-broadcastifanothernodesforwardswithin𝑡– 𝑡 = 𝜏×𝑑;/𝑑456

with:• 𝜏:Maximumdelayperhop• 𝑑;:DistancetoTargetNode• 𝑑456:DistancefromlasthoptoTargetNode






✓

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