Technologies, Beaconing, and Routing in Vehicular...
Transcript of Technologies, Beaconing, and Routing in Vehicular...
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MicheleSegata,RenatoLoCigno - UniversityofTrento
withspecialthankstoFalko Dressler,ChristophSommer,BastianBloessl,Stefan Joerer,DavidEckhoff
WirelessMeshandVehicularNetworks
Technologies,Beaconing,andRoutinginVehicularNetworks
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Motivation
• TaxonomyofUseCases
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Vehicle-to-X
Non-Safety
Comfort
ContextualInformation Entertainment
TrafficInformationSystems
OptimalSpeedAdvisory
Congestion,Accident
Information
Safety
SituationAwareness
AdaptiveCruiseControl
BlindSpotWarning
WarningMessages
TrafficLightViolation
ElectronicBrakeLight
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Technology
• Communicationparadigmsandmedia
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[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
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Anoutline
A(rough)outlineoftheVehicularNetworkstopics• Application:whyVN?• Communication:technologies,alternatives,protocols,challenges• Simulation: evaluatingvehicularnetworkswithoutvehiclesand
withoutnetworks.Toolsandmodels
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COMMUNICATIONTECHNOLOGIES(Someofthem)
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Cellularnetworks
• Concept– Divideworldintocells,eachservedbybasestation– Allows,e.g.,frequencyreuseinFDMA
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Cellularnetworks
• Stricthierarchyofnetworkcomponents
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UE
Core Network
RNC
Cell
NodeB
Cell Cell Cell Cell
NodeB
Cell
RNC
Cell
NodeB
Cell Cell Cell Cell
NodeB
Cell
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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
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Cellularnetworks
• FACH– Timeslotsmanagedbybasestation– Delayontheorderof10ms per40ByteandUE– Capacityseverelylimited(innon-multicastnetworks)– NeedtoknowcurrentcellofUE
• RACH– SlottedALOHA– randomaccessbyUEs
• PowerrampingwithAcquisitionIndication– Delayapprox.50ms
per60ByteandUE– Massiveinterference
withotherUEs
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Cellularnetworks
• DCH– Delay:approx.250ms /2s/10sforchannelestablishment
• Dependsonhowfine-grainedUEpositionisknown– MaintainingaDCHisexpensive
• Closed-LoopPowerControl(nointerferenceofotherUEs)• Handoverbetweencells
– Upperlimitofapprox.100UEs
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Cellularnetworks
• So:canUMTSsupportCar-to-Xcommunication?– Atlowmarketpenetration:yes– Eventually:
• Needtoinvestinmuchsmallercells(e.g.,alongfreeways)• Needtoimplementmulticastfunctionality(MBMS)
– MainusecaseforUMTS:centralizedservices• Ex.:GoogleMapsTraffic
– CollectinformationfromUMTSdevices– Storageofdataoncentralserver– DisseminationviaInternet(⇨ idealforcellularnetworks)
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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
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[1]FayHui,Prasant Mohapatra.„ExperimentalCharacterizationofMultihop CommunicationsinVehicularAdHocNetwork“.InProceedingsofthe2ndACMinternationalworkshoponVehicularadhocnetworks,2005
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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• ...
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IEEE802.11p- OFDMSignal
• Howdoesitlooklike?
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IEEE802.11p
• ClassicIEEE802.11BasicServiceSet(BSS)– Dividesnetworksintologicalunits
• Nodesbelongto(exactlyone)BSS• PacketscontainBSSID• Nodesignorepacketsfrom“foreign”BSSs• Exception:Wildcard-BSSID(-1)forprobes• Adhocnetworksemulateinfrastructuremode
– JoiningaBSS• AccessPointsendsbeacon• Authenticationdialogue• Associationdialogue• NodehasjoinedBSS
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BSSSSID “A”
BSSSSID “B”
BSSSSID “C”
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IEEE802.11p
• New:802.11OCBMode(OutsideoftheContextofaBSS)– DefaultmodeofnodesinWAVE– NodesmayalwaysuseWildcardBSSinpackets– NodeswillalwaysreceiveWildcardBSSpackets– MayjoinBSSandstilluseWildcardBSS
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BSSSSID “A”
BSSSSID “B”
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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)
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• Map8userpriorities⇨ 4accesscategories⇨ 4queues• Queuescompeteindependentlyformediumaccess
IEEE802.11p
AC0
AC1
AC2
AC3
virt
ual c
ollis
ion
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• 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
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AC_VO AC_VI AC_BE AC_BK
ChannelAccess
Backoff:0 0 0 0
IEEE802.11p
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AC_VO AC_VI AC_BE AC_BK
Backoff:0 0 0 0
Channelbusy?
StartContention
WaitforIdle
IEEE802.11p
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ChannelAccess
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AC_VO AC_VI AC_BE AC_BK
0 0 0
Backoff0?
WaitAIFS(SIFS+AIFSn *Slotlen)
Waitforbackoff=0
Backoff:0
IEEE802.11p
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ChannelAccess
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Backoff:0
AC_VO AC_VI AC_BE AC_BK
Backoff:2 0 0 0
TransmissionOver
PostTransmitBackoff
IEEE802.11p
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ChannelAccess
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2
AC_VO AC_VI AC_BE AC_BK
Backoff:2 0 0 0
AC_VIQueuereadytosend…waitAIFS Backoff
Ch becomesbusy
IEEE802.11p
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ChannelAccess
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Backoff:2 21
AC_VO AC_VI AC_BE AC_BK
Backoff:1 0 0Channelidle
Channelbusy
[Slottimepassed]/DecrementBackoff
Channelstatechanges
Backoff:0 0
IEEE802.11p
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ChannelAccess
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3Backoff:0 0
AC_VO AC_VI AC_BE AC_BK
0 0
Queuereadytosend
InternalContentionBackoff
Higherprio
rity
queu
eready
IEEE802.11p
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ChannelAccess
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• 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:
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• ProsofUMTS/LTE– Easyprovisionofcentralizedservices– Quickdisseminationofinformationinwholenetwork– Pre-deployedinfrastructure– Easymigrationto(andintegrationinto)smartphones
• ConsofUMTS/LTE– Highshortrangelatencies(mightbetoohighforsafety)– Networkneedsfurtherupgrades(smallercells,multicastservice)– Highdependenceonnetworkoperator– Highloadincorenetwork,evenforlocalcommunication
UMTS/LTEvs.IEEE802.11p
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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
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HIGHERLAYERPROTOCOLS
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HigherLayerStandardsforIEEE802.11p
• Channelmanagement– Dedicatedfrequencybandat5.9GHzallocatedtoWAVE
• ExclusiveforV2VundV2Icommunication• Nolicensecost,butstrictrules• 1999:FCCreserves7channelsof10MHz(“U.S.DSRC”)
– 2reservedchannels,1+4channelsforapplications• ETSIEuropereserves5channelsof10MHz
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[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
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HigherLayerStandardsforIEEE802.11p
• Needforhigherlayerstandards– Unifiedmessageformat– Unifiedinterfacestoapplicationlayer
• U.S.– IEEE1609.*– WAVE(“WirelessAccessinVehicularEnvironments“)
• Europe– ETSI– ITSG5(“IntelligentTransportationSystems”)
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IEEE1609
• IEEE1609.*upperlayers(buildingonIEEE802.11p)– IEEE1609.1:“Operatingsystem”– IEEE1609.2:Security– IEEE 1609.3:Networkservices– IEEE1609.4:Channelmgmt.
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[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
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IEEE1609
• Channelmanagement– WAVEallowsforbothsingleradiodevices&multiradiodevices– DedicatedControlChannel(CCH)formgmtandsafetymessages⇨ singleradiodevicesneedtoperiodicallylistentoCCH
– Timeslots• SynchronizationenvisionedviaGPSreceiverclock• Standardvalue:100mssyncinterval(with50msonCCH)• Shortguardintervalatstartoftimeslot
– Duringguard,mediumisconsideredbusy(⇨ backoff)
Wireless Mesh & Vehicular Networks - Technologies, Beaconing, and Routing in Vehicular Networks 34
[1]IEEEVehicularTechnologySociety,"IEEE1609.4(Multi-channelOperation),"IEEEStd,November,2006
CCHinterval
CCHinterval
“SCH”interval
“SCH”interval
t = n × 1s
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IEEE1609
• Packettransmission– SortintoACqueue,basedonWSMP(orIPv6)EtherTypefield,destination
channel,anduserpriority– Switchtodesiredchannel,setupPHYpoweranddatarate– Startmediumaccess
Wireless Mesh & Vehicular Networks - Technologies, Beaconing, and Routing in Vehicular Networks 35
CC
HSC
HAC0AC1AC2AC3 vi
rt. C
ollis
ion
AC0AC1AC2AC3 vi
rt. C
ollis
ion
Cha
nnel
Rou
ter
Cha
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Cha
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ess
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IEEE1609
• Channelmanagement– ControlChannel(CCH):
• Defaultchanneluponinitialization• WAVEserviceadvertisements(WSA),WAVEshortmessages(WSM)
• Channelparameterstakefixedvalues
– ServiceChannel(SCH):• OnlyafterjoiningWAVEBSS• WAVEshortmessages(WSM),IPdatatraffic(IPv6)
• Channelparameterscanbechangedasneeded
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IEEE1609
• WAVEserviceadvertisement(WSA)– BroadcastonControlChannel(CCH)– IdentifiesWAVEBSSsonServiceChannels(SCHs)– Canbesentatarbitrarytimes,byarbitrarynodes– OnlypossibilitytomakeothersawareofdatabeingsentonSCHs,aswellas
therequiredchannelparameterstodecodethem
Wireless Mesh & Vehicular Networks - Technologies, Beaconing, and Routing in Vehicular Networks 37
NodeA NodeB
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ETSIITSG5
• Motivation– EuropeanstandardizationeffortbasedonIEEE802.11p– StandardizationtoincludelessonslearnedfromWAVE– Differentinstrumentationoflowerlayers– Differentupperlayerprotocols– Differentchannelassignment
• ITS-G5A(safety)• IST-G5B(nonsafety)
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ETSIITSG5
• Protocolstack– PHYandMACbasedonIEEE802.11p– Mostprominentchange:
crosslayerDecentralizedCongestionControl(DCC)
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ETSIITSG5
• Channelmanagement– Multiradio,multiantennasystem
• Noalternatingaccess⇨ Circumventsproblemswithsynchronization⇨ Noreductioningoodput
• DirectresultofexperienceswithWAVE
– OneradiotunedtoCCH• ServiceAnnouncementMessage(SAM)• Periodic:CooperativeAwarenessMessages(CAM)• Eventbased:DecentralizedEnvironmentNotificationMessage(DENM)
– Addl.radiotunedtoSCH• Userdata
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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)
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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
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BEACONING:1-HOPBROADCAST
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Beaconing:1-hopBroadcast
• ETSIITSCAMs(CooperativeAwarenessMessages)– Periodic(upto10Hz)safetymessage– Informationonstateofsurroundingvehicles:
• Speed,location,…– Messageagehighlyrelevantforsafety
• Needmechanismstodiscardoldmessages
• IEEE1609BSMs(BasicSafetyMessages)
• …but
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Beaconing:1-hopBroadcast
• Openissues– Infrastructure-lessoperation:needshighmarkedpenetration– Required/tolerablebeaconintervalhighlydependentonscenario– Designneedsdedicatedchannelcapacity
• Realnetworksareheterogeneous– Roadsideinfrastructurepresentvs.absent– Freewayscenariovs.innercity– Ownprotocol⇔ other,future,andlegacyprotocols
• Howtodobetter?– Dynamicallyadaptbeaconinterval– Dynamicallyuseallfree(!)channelcapacity
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DecentralizedCongestionControl(DCC)
• CorefeatureofETSIITSG5• Adaptiveparameterizationtoavoidoverload• ConfigurableparametersperAC:
– TXpower(TransmitPowerControl,TPC)– Minimumpacketinterval(TransmitRateControl,TRC)– Datarate(TransmitDatarateControl,TDC)– SensitivityofClearChannelAssessment(DCCSensitivityControl,DSC)
• Statemachinedetermineswhichparametersetisselected;availablestates:– Relaxed– Active(multiplesubstates)– Restrictive
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DecentralizedCongestionControl(DCC)
• Measuremin/maxChannelLoad(x)– Min/maxchannelloadin [tnow-x..tnow]– Channelload:fractionoftimethatchannelwassensedbusyduring
measuringinterval(ex:𝑇m ≈ 1s)– Channelbusy:Averagereceivedpower(signalornoise)duringprobing
interval(ex:𝑇p ≈ 10μs)abovecarriersensethreshold
• StatemachineforControlChannel:
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DecentralizedCongestionControl(DCC)
• Example:ControlChannel– TXpower:relaxed:33dBm ⇨ active:ref⇨ restrictive:-10dBm– “ref”:Valueremainsunchanged– Remember:
• 33dBm ⇨ 10%.% mW⇨ 2000mW• -10dBm ⇨ 10'( mW ⇨ 0.1mW
Wireless Mesh & Vehicular Networks - Technologies, Beaconing, and Routing in Vehicular Networks 48
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
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DecentralizedCongestionControl(DCC)
• Oscillatingchannelload(bothlocalandglobal!)– …causedbychannelaccessbeingtoorestrictive(standardparameters)
Wireless Mesh & Vehicular Networks - Technologies, Beaconing, and Routing in Vehicular Networks 49
[1]DavidEckhoff,Nikoletta Sofra andReinhardGerman,"APerformanceStudyofCooperativeAwarenessinETSIITSG5andIEEEWAVE,"Proceedingsof10thIEEE/IFIPConferenceonWirelessOndemandNetworkSystemsandServices(WONS2013),Banff,Canada,March2013.
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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]
Wireless Mesh & Vehicular Networks - Technologies, Beaconing, and Routing in Vehicular Networks 50
[1]ChristophSommer,StefanJoerer,MicheleSegata,OzanK.Tonguz,RenatoLoCignoandFalkoDressler,"HowShadowingHurts VehicularCommunicationsandHowDynamicBeaconingCanHelp,"Proceedingsof32ndIEEEConferenceonComputerCommunications(INFOCOM2013),Mini-Conference, Turin,Italy,April2013
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DynB– DynamicBeaconing
• wrt.handlingdynamicsintheenvironment– Assumingtwolargerclustersofvehiclesmeetingspontaneously(e.g.,at
intersectionsinsuburbanorwhentwobigtrucksleavethefreeway)
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Application-based:JerkBeaconing
• Jerk:– physicalquantitymeasuringvariationofaccelerationovertime
– usinganestimationofjerkwecomputethebeaconinterval
– tunableparameters:• minimumbeaconinterval• maximumbeaconinterval• sensitivity
• Mainidea:– themoreconstantthesystem,thelowertherequirement– sendupdatesonlywhenneeded,usepredictionotherwise
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JerkBeaconing
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Evaluation:Strongshockwaves
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3m
45 %
4m
17%
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Evaluation:Moderateshockwaves
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4.5m
40%
4.5m
10%
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MULTI-HOPFORWARDINGRoutingtechniquesinVehicularNetworks
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Classicalrouting
• MightnotbesuitedforVehicularNetworks…– Distancevector
• Eachnodestoresavectorof(dst,cost,next-hop)– Linkstate
• Knowntopology+Dijkstra• Fastconvergencevs.overhead
– Reactive(ondemand)• Establishroutesonlywhenneeded
– Proactive(tabledriven)• Continuouslymaintainroutesuptodate
– Hopbyhop• Intermediatenodeschosethenexthopforapacket
– Sourcerouting• Packetsincludethefullroute
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Georouting
• Primarymetrics:position/distancetodestination• Requiresnodepositionstobeknown(atleastforthedestination)• Twooperationmodes(typ.):
– Greedymode:choosenexthopaccordingtomaxprogress– Recoverymode:escapedeadends(localmaxima)
• Mustensurethatmessagenevergetslost
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Routing
• Q:Can(classical)routingworkinVANETs?• A:Onlyinsomecases.• Commonlyneedmulticastcommunication,lowload,lowdelay• Additionalchallengesandopportunities:
networkpartitioning,dynamictopology,complexmobility,…
Wireless Mesh & Vehicular Networks - Technologies, Beaconing, and Routing in Vehicular Networks 59
[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
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Flooding:Broadcastsuppression
• Motivation– Needsnoneighborinformation– Needsnocontrolmessages– Maximizesdistanceperhop– Minimizespacketloss
• Approach– Nodereceivesmessage,estimatesdistancetosender– Selectivelysuppressesre-broadcastofmessage– Alternatives
• weightedp-persistence• slotted1-persistence• slottedp-persistence
Wireless Mesh & Vehicular Networks - Technologies, Beaconing, and Routing in Vehicular Networks 61
[1]Wisitpongphan,Nawaporn andTonguz,OzanK.andParikh,J.S.andMudalige,Priyantha andBai,FanandSadekar,Varsha,"BroadcastStormMitigationTechniquesinVehicularAdHocNetworks,"IEEEWirelessCommunications,vol.14(6),pp.84-94,December2007
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Flooding:Broadcastsuppression
• Estimatedistancetosenderas0≤ρij ≤1
• GPSbased
• RSSbased
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Flooding:Broadcastsuppression
• Weightedp-persistence– Probabilisticfloodingwithvariablepij forre-broadcast– Thus,higherprobabilityforlargerdistanceperhop
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pij
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Flooding:Broadcastsuppression
• Weightedp-persistence– WaitWAIT_TIME(e.g.,2ms)– choosep=min(ρij)ofallreceivedpackets
(probabilityforre-broadcastofpacket)– Ensurethatatleastoneneighborhasre-broadcastpacket
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idle wait 2 msrcv
dup
sendp
wait δ ms
¬p
dup expired
dup
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Flooding:BroadcastSuppression
• Slotted1-persistence– Suppressionbasedonwaitingandoverhearing– Dividelengthofroadintoslots– Moredistantslotssendsooner– Closerslotssendlater(orifmoredistantslotsdidnotre-broadcast)– Thus,higherprobabilitytotransmitoverlongerdistance
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pij
t=0 t=τ t=2τ t=3τ
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Flooding:BroadcastSuppression
• Slotted1-persistence– Divide“communicationrange“intoNsslotsoflengthτ– Nodeswaitbeforere-broadcast,waitingtimedependingonslot– Duplicateeliminationtakescareofsuppressionofbroadcasts
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idle wait Tijrcv
dup
send¬dup
dup
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Flooding:BroadcastSuppression
• Slottedp-persistence– Cf.slotted1-persistence– Fixedforwardingprobabilityp(insteadof1)
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pij
t=0 t=τ t=2τ t=3τ
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Flooding:BroadcastSuppression
• Slottedp-persistence– WaitforTij (insteadoffixedWAIT_TIME)– Useprobabilityp(insteadof1)– Ensurethatatleastoneneighborhasre-broadcastthepacket
bywaitingforδ’>max(Tij)
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idle wait Tijrcv
dup
sendp
wait δ’
¬p
dup expireddup
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Flooding:Remainingproblems
• Temporarynetworkfragmentation
• Undirectedmessagedissemination
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Flooding+X:DV-CAST
• Idea:detectcurrentscenario,switchbetweenprotocols• Checkforfragmentednetwork
– Networkconnectedà performbroadcastsuppression
– Networkfragmentedà performStore-Carry-Forward
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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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Flooding:Remainingproblems
• Temporarynetworkfragmentation
• Undirectedmessagedissemination
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Geocast:TO-GO
• Step1:Findbestnexthop(TargetNode,T)– FindN:Furthestneighbortowardsdestination– FindJ:Furthestneighbortowardsdestination,currentlyonjunction– FindNJ:Furthestneighbortowardsdestination,asseenbyJ– ifN,NJ areonthesameroad,
pickNelse,pickJ
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N
NJ
J
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Geocast:TO-GO
• Step2:FindForwardingSet(FS)– NodesintheFSwillcompeteforrelayingofthemessage– OnlyonenodeinFSshouldrelay
thus,allnodesinFSmustheareachother– FindingoptimalsolutionisNPcomplete– TO-GOusesapproximation
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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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Flooding:Remainingproblems
• Temporarynetworkfragmentation
• Undirectedmessagedissemination
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