VANETs - Unict · Università degli Studi di Catania Dipartimento di Ingegneria Informatica e delle Telecomunicazioni VANETs Vehicular Ad-hoc NETworks (VANETs) can be considered as

Università degli Studi di CataniaDipartimento di Ingegneria Informatica e delle Telecomunicazioni

VANETsVANETs

Ing. Alessandro Leonardi


VANETsVANETs

Vehicular Ad-hoc NETworks (VANETs) can be considered as asubset of Mobile Ad hoc NETworks (MANETs) with uniquecharacteristics.

A typical VANET consists of vehicles and access points along theroad. Vehicles move on the roads sharing information betweenthemselves and with the Internet through the access points.


Vehicles communicationVehicles communication

Vehicle-to-vehicle communication

Vehicle-to-infrastructure communicationMulti-hop communication


VANETs vsVANETs vs. . MANETsMANETs

Vehicles mobility⇒⇒ Vehicles often move at high speed but their mobility is rather regular andVehicles often move at high speed but their mobility is rather regular and

predictablepredictable

Network topology⇒⇒ High speed movement creates scenarios characterized by a veryHigh speed movement creates scenarios characterized by a very

dynamic network topologydynamic network topology

No significant power constraint⇒⇒ Vehicles can always rely on recharging batteriesVehicles can always rely on recharging batteries

Localization⇒⇒ AnAn accurate estimate of accurate estimate of vehiclesvehicles position can position can bebe mademade availableavailable through through

GPS GPS systemssystems or on-board or on-board sensorssensors


PHY/MACPHY/MAC


DSRC/802.11p (1/2)DSRC/802.11p (1/2)

Dedicated Short Range Communication (DSRC) wasreleased in 2002 by the American Society for Testing andMaterials (ASTM)

In 2003 the standardization moved to IEEE Forum andchanged the name from DSRC to WAVE (Wireless Ability inVehicular Environments) also known as 802.11p


DSRC/802.11p (2/2)DSRC/802.11p (2/2)

The standard is based on IEEE 802.11a PHY layer andIEEE 802.11 MAC layer

Seven 10 MHz channels at 5.9GHz

one control channel and six service channels


DSRC/802.11p DSRC/802.11p vsvs. 802.11a (1/3). 802.11a (1/3)

802.11a is designed for high data rate multimedia communications in indoorenvironment with low user mobility

DSRC PHY uses a variation of OFDM modulation scheme to multiplex data

high spectral efficiency, simple transceiver design and avoids multi-path fading



DSRC/802.11p reduces the signal bandwidth from 20MHz to 10MHz

all parameter values are doubled in time domain in order to increasethe robustness to ISI caused by the multi-path delay spread andDoppler spread effect

Data rates from 6 up to 27 Mbps

Transmit power level are changed to fit requirements of outdoor vehicularcommunications

communication ranges up to 1000 meters




DSRC/802.11p MACDSRC/802.11p MAC

MAC layer of DSRC is very similar to the IEEE 802.11 MACbased on CSMA/CA with some minor modifications

DSRC involves vehicle-to-vehicle and vehicle-to-infrastructure communications


DSRC/802.11p scenariosDSRC/802.11p scenarios

relative speed between vehicles islow despite high absolutespeed – the effect of mobility can beignored and considered only multi-hopaspects

the key attribute necessary for communications in this kind of scenariois the need for very high download ratesover a short duration


802.11 MAC problems802.11 MAC problems

Scenario a)⇒ Starvation due to hidden terminal – exposed terminal

• Solutions: limiting data transmission duration by using small maximum TCP window

size MAC layer approaches (MACAW)

Scenario b)⇒ Low efficiency and instability due to shortened connection time

• Solutions: low overhead protocol (no RTS/CTS handshake) no variable rates because this leads to overestimation or underestimation

of the NAV used in future


MAC issuesMAC issues

Priority, response time and reliability should be assuredbecause are basic requirements of safety applications

Approaches:

Different CWs and backoff increase parameters for differentpriority classes in data traffic (e.g., DFS)

Assigning shorter CWs to low-delay real-time service

Static slot assignment for high-priority traffic and dynamicassignment for the low-priority traffic


RoutingRouting


Routing Protocols for Routing Protocols for VANETs VANETs (1/3)(1/3)

Proactive algorithms (table-driven)⇒⇒ better performance in terms of delay but they need abetter performance in terms of delay but they need a

considerable amount of control traffic (e.g., OLSR)considerable amount of control traffic (e.g., OLSR)

Reactive algorithms (on-demand)⇒⇒ minimize the number of broadcast packets by creating routesminimize the number of broadcast packets by creating routes

only on demand (e.g., AODV)only on demand (e.g., AODV)

Several studies demonstrate that neither of the two protocolclasses outperform the other in every vehicular scenarios.



Traditional MANETs routing protocols require an explicitroute establishment phase before the data transmissionbegins

They are not adequate to low delivery-latency requirement forsafety applications

Routing protocols for VANETs⇒⇒ should rely on packet forwarding based on geographic locationshould rely on packet forwarding based on geographic location

of sender and receiverof sender and receiver⇒⇒ should be broadcast orientedshould be broadcast oriented



Position-based unicast routing (geographical forwarding)⇒⇒ these routing protocols exploit the availability of accuratethese routing protocols exploit the availability of accurate

location informationlocation information⇒⇒ more suited to dense networks and to frequent networkmore suited to dense networks and to frequent network

disconnections (e.g., GPSR)disconnections (e.g., GPSR)

Geocast routing⇒⇒ a a kindkind of of multicastmulticast routingrouting wherewhere the the destinationdestination nodesnodes are are

characterizedcharacterized byby theirtheir geographicalgeographical coordinatescoordinates⇒⇒ in in VANETsVANETs nodesnodes interestedinterested in in notificationsnotifications of of traffictraffic

congestionscongestions or or warningswarnings are are locatedlocated in the in the samesame placeplace


Broadcast (1/2)Broadcast (1/2)

Majority of applications for VANETs rely on broadcastdissemination of information in the applications area

Blind flooding is the first approach to achieve broadcastingsince it does not require local or global topology information

Broadcasting has a strong influence on network performance⇒⇒ Serious redundancy, contention and collision problems canSerious redundancy, contention and collision problems can

occur as a result of floodingoccur as a result of flooding

An efficient broadcast protocol should minimize the totalnumber of packet retransmissions, while at the same timepreserving network connectivity


Broadcast (2/2)Broadcast (2/2) A trade-off between robustness and redundancy should be found Different approaches:

⇒⇒ probability-basedprobability-based•• a node forwards the packet with a probability a node forwards the packet with a probability p p which dependswhich depends

on network scenarioon network scenario⇒⇒ location-basedlocation-based

•• the idea is to select as relays those nodes that permit to coverthe idea is to select as relays those nodes that permit to coverthe widest additional areathe widest additional area

⇒⇒ neighbor-basedneighbor-based•• the nodes decide whether broadcasting the message or not onthe nodes decide whether broadcasting the message or not on

the status of their neighborsthe status of their neighbors⇒⇒ cluster-basedcluster-based

•• nodesnodes are are groupedgrouped intointo smallsmall clustersclusters eacheach one one managedmanaged byby a aparticualrparticualr nodenode calledcalled cluster-headcluster-head whichwhich hashas the task of the task ofretransmittingretransmitting broadcastbroadcast messagesmessages


Classes of ApplicationsClasses of Applications

Assistance for Safe Navigation

Internet Connectivity


Assistance for Safe Navigation (1/4)Assistance for Safe Navigation (1/4)

Traffic safety

It is possible to detect dangerous situations It is possible to detect dangerous situations through on-through on-board board sensorssensors

Warning messages Warning messages propagate propagate to other vehicles to other vehicles through through ad-ad-hoc networkinghoc networking

Traffic management services

Access Access points along points along the road the road distribute information aboutdistribute information abouttraffic congestiontraffic congestion, , weather forecastweather forecast, road , road worksworks, etc., etc.



Forward radar

Computing platform

Event data recorder (EDR)Positioning system

Rear radar

Communication facility

Display

Smart vehicle’s onboard instrumentation:•• Newer cars Newer cars include include features as recordingfeatures as recording, processing,, processing, positioning positioning and location and location capabilitiescapabilities..

•• Communication facility supports wireless Communication facility supports wireless data data exchangeexchangewith other vehicles with other vehicles or or fixed stationsfixed stations..


A potential danger scenario :

The system The system automatically triggers automatically triggers the the propagation propagation of of warning messageswarning messages

by exploiting multi-hop ad-hoc communications by exploiting multi-hop ad-hoc communications


Roadside base station

Emergency event

Inter-vehiclecommunication

Vehicle-to-roadsidecommunication



Overview of some vehicular safety and communication projects:

European European Community Community has recently funded has recently funded a forum a forum to support to support the the developmentdevelopment

of a network system of a network system offering assistance to offering assistance to the the driversdrivers..

Many interesting features Many interesting features are are presented presented in the in the following projectsfollowing projects::

•• CarTalk CarTalk 20002000

•• FleetNetFleetNet


CarTalk CarTalk 2000 (1/5)2000 (1/5)

•• ObjectivesObjectives::

- - DevelopmentDevelopment of co-operative driver of co-operative driver assistanceassistance systemssystems basedbased uponupon inter-vehicleinter-vehicle communicationcommunication

- - DevelopmentDevelopment of a mobile of a mobile ad-hocad-hoc radio network radio network asas a a communicationcommunication platformplatform withwith the the aimaim of of preparingpreparing a future a future standard standard

PARTNERS: Centro Ricerche Fiat, PARTNERS: Centro Ricerche Fiat, DaimlerChryslerDaimlerChrysler, , SiemensSiemens Mobile, Mobile, BoschBosch


CarTalk CarTalk 2000 (2/5)2000 (2/5)•• ApplicationsApplications::

- - InformationInformation and and WarningWarning FunctionsFunctions:: transmissiontransmission of of warningwarning messagesmessages duringduring breakdownbreakdown, high, high traffictraffic density or density or congestioncongestion, or , or dangerousdangerous road road surfacesurface conditionsconditions.. ThisThis allowsallows anan earlyearly warningwarning of the driver of of the driver of followingfollowing vehiclesvehicles on on the the samesame road. road.


CarTalk CarTalk 2000 (3/5)2000 (3/5)

•• ApplicationsApplications::

- - Communication-basedCommunication-based LongitudinalLongitudinal Control System: Control System: ExistingExisting AdaptiveAdaptive CruiseCruise Control Control systemssystems onlyonly reactreact on the on the vehiclevehicle directlydirectly in front. in front. ByBy integratingintegrating communicationcommunication, , thesethese systemssystems maymay adaptadapt longitudinallongitudinal control control toto the the traffictraffic in front and can in front and can allowallow anticipatinganticipating toto anan earlyearly brakingbraking maneuvermaneuver whenwhen anan invisibleinvisible vehiclevehicle beyondbeyond the direct the direct predecessorpredecessor in front in front isis brakingbraking. . ThisThis leadsleads toto a a more more naturalnatural followingfollowing behaviorbehavior..


CarTalk CarTalk 2000 (4/5)2000 (4/5)


- Co-operative - Co-operative AssistanceAssistance SystemsSystems:: A A typicaltypical scenario scenario forfor co-operationco-operation isis the highway entry and the highway entry and mergingmerging scenario. scenario. TodayToday, , misunderstandingsmisunderstandings betweenbetween driversdrivers on on the highway and on the entry-lane cause the highway and on the entry-lane cause criticalcritical situationssituations.. ByBy exchangingexchanging informationinformation up up toto simplesimple trajectorytrajectory plansplans, , criticalcritical situationssituations can can bebe foreseenforeseen and and solvedsolved byby the the vehiclesvehicles themselvesthemselves..


CarTalk CarTalk 2000 (5/5)2000 (5/5)

•• Technologies:Technologies:

- - CommunicationCommunication System: System: A A keykey technologytechnology forfor CarTALKCarTALK 2000 2000 isis the the developmentdevelopment of a of a mobile mobile multi-hopmulti-hop ad-hocad-hoc radio radio communicationcommunication system system thatthat meetsmeets the the requirementsrequirements set set byby the the applicationsapplications.. ItIt willwill bebe basedbased on a UMTS radio access on a UMTS radio access technologytechnology, , usingusing a a spatial-awarespatial-aware position-basedposition-based multi-hopmulti-hop routingrouting protocolprotocol..


FleetNet FleetNet (1/6)(1/6)

•• ObjectivesObjectives::

- - DevelopmentDevelopment of a of a communicationcommunication platformplatform forfor inter-vehicleinter-vehicle communicationscommunications

- - ImplementationImplementation of of demonstratordemonstrator applicationsapplications

- - DevelopmentDevelopment and and standardizationstandardization of of promisingpromising strategiesstrategies and and solutionssolutions in in orderorder toto improveimprove driversdrivers’’ and and passengerspassengers’’ safetysafety and comfort and comfort

PARTNERS: PARTNERS: DaimlerChryslerDaimlerChrysler AG, AG, FraunhoferFraunhofer FOKUS, NEC FOKUS, NEC EuropeEurope LtdLtd,, RobertRobert BoschBosch GmbHGmbH, , SiemensSiemens AG, TEMIC AG, TEMIC TelefunkenTelefunken, , microelectronicmicroelectronic GmbHGmbH, , UniversitiesUniversities of of MannheimMannheim, , Hamburg-HarburgHamburg-Harburg, , KarlsruheKarlsruhe, Hannover., Hannover.




- Cooperative driver - Cooperative driver assistanceassistance : :

- - EmergencyEmergency notificationnotification

- - OvertakingOvertaking assistanceassistance

- - ObstacleObstacle warningwarning




- - DecentralizedDecentralized floatingfloating carcar data data ::

- - TrafficTraffic jamjam monitor monitor

- - DynamicDynamic navigationnavigation

- Route - Route weatherweather forecastforecast




- - UserUser communicationscommunications and and informationinformation servicesservices ::

- - Hot-spotHot-spot Internet access Internet access

- - Inter-vehicleInter-vehicle chatchat

- - DistributedDistributed gamesgames



•• KeyKey FeaturesFeatures::

- - WirelessWireless multi-hopmulti-hop ad hoc ad hoc networkingnetworking

- - UnlicensedUnlicensed radio radio frequencyfrequency bandsbands

- - AllowsAllows forfor lowlow costcost data data transmissiontransmission

- - Position-basedPosition-based routingrouting and and location-basedlocation-based servicesservices

- Internet access and - Internet access and integrationintegration

- Open - Open solutionsolution



•• Technologies:Technologies:

- - FleetNetFleetNet plansplans toto useuse a UTRA TDD radio hardware: a UTRA TDD radio hardware: UMTS UMTS TerrestrialTerrestrial Radio Access system Radio Access system willwill bebe enhancedenhanced or or replacedreplaced byby FleetNetFleetNet protocolsprotocols enablingenabling operationoperation ad ad hoc mode. hoc mode.

- - Radar-basedRadar-based communicationcommunication currentlycurrently under under feasibilityfeasibility studystudy willwill focusfocus on on safety-relatedsafety-related applicationsapplications..

- - DuringDuring the the FleetNetFleetNet developmentdevelopment processprocess IEEE 802.11 IEEE 802.11 wirelesswireless LAN LAN componentscomponents willwill bebe usedused intermediatelyintermediately forfor testingtesting and and verificationverification purposespurposes..


Internet Connectivity (1/2)Internet Connectivity (1/2)

Internet-based services

Access Access to emailto email, web , web browsingbrowsing, etc., etc.

Video and audio Video and audio applicationsapplications

P2P

ChattingChatting, , multiplayer gamesmultiplayer games

On board file On board file sharingsharing


Internet Connectivity (2/2)Internet Connectivity (2/2)

Some proposed systems :

•• Drive-thru Drive-thru InternetInternet

•• CarTorrentCarTorrent


Drive-thru (1/5)Drive-thru (1/5)•• Proposed Architecture Proposed Architecture ::

One or more One or more locally interconnected locally interconnected access access points form points form a so-a so- called called connectivity-islandconnectivity-island, , several several of of them along them along a road or in thea road or in the same same area area may be interconnected may be interconnected and cooperate and cooperate to provideto provide network access network access with with intermittentintermittent connectivity to drivers connectivity to drivers inin a a larger larger area.area.


Drive-thru (2/5)Drive-thru (2/5)

•• FeaturesFeatures::

- - Investigation about Investigation about the the feasibility feasibility of of providing providing networknetwork connectivity connectivity and, and, ultimatelyultimately, Internet access , Internet access to to mobilemobile users users in in vehicles by testing vehicles by testing UDP and TCP performance inUDP and TCP performance in a a real vehicular real vehicular scenario scenario using using IEEE 802.11b and 802.11gIEEE 802.11b and 802.11g hardware hardware

- Hot - Hot spots along spots along the road the road will provide will provide WLAN access WLAN access forfor some (some (relatively relatively short) short) period period of time of time to vehicles drivingto vehicles driving by by..

- - Conventional client-server approachConventional client-server approach



•• Measurement Measurement scenario and scenario and findingsfindings::



•• Findings from measurementsFindings from measurements::

- - Both Both UDP and TCP UDP and TCP tests performed tests performed over IEEE 802.11b andover IEEE 802.11b and 802.11g hardware 802.11g hardware suggest to subdivide suggest to subdivide a a connectivityconnectivity session into three distinct phases session into three distinct phases::

•• Entry Entry phasephase•• Production Production phasephase•• Exit Exit phasephase

Only Only in the production in the production phase phase a a stable connectivity jointlystable connectivity jointly with with a a maximum throughput value is possiblemaximum throughput value is possible, , while while in thein the entry and exit entry and exit phases performances decrease phases performances decrease due due to to aa higher number higher number of of lost packets lost packets and and link-layer retransmissionslink-layer retransmissions..



•• Results Results and impact on Internet and impact on Internet applicationsapplications::

- - Usability Usability of of exsisting exsisting IEEE 802.11 radio hardware IEEE 802.11 radio hardware toto transmit transmit a a significant amount significant amount of data of data during during aa connectivity sessionconnectivity session

- - Limited connectivity period Limited connectivity period and and variable transmissionvariable transmission characteristics limit characteristics limit the the usage usage of the system of the system forfor continous communications such as continous communications such as IP IP telefony whiletelefony while transaction based application like sending an email transaction based application like sending an email could be performed exploiting could be performed exploiting more more than than oneone connectivity connectivity windowwindow


CarTorrent CarTorrent (1/11)(1/11)

•• KeyKey FeaturesFeatures::

- Cooperative P2P - Cooperative P2P vehicularvehicular strategystrategy proposedproposed forfor contentcontent delivery of delivery of largelarge multimedia multimedia filesfiles

- - ““CommunicationCommunication efficientefficient”” swarmingswarming protocolprotocol whichwhich usesuses a gossip a gossip mechanismmechanism toto propagate propagate contentcontent avalaibilityavalaibility informationsinformations thatthat leveragesleverages the the broadcastbroadcast nature of nature of wirelesswireless medium medium

- - Piece-selectionPiece-selection strategystrategy whichwhich takestakes proximityproximity intointo account account forfor the the exchangeexchange of of informationinformation piecespieces



•• KeyKey factorsfactors forfor usingusing opportuninisticopportuninistic ad hoc ad hoc networkingnetworking modelsmodels::

- - ProblemsProblems:: SStopping at gas station for full download is a nuisancetopping at gas station for full download is a nuisance

Downloading from GPRS/3G too slow and quite expensive Downloading from GPRS/3G too slow and quite expensive

- - Observation:Observation: Many other drivers are interested in download sharing (like Many other drivers are interested in download sharing (like in the Internet) in the Internet)

- Solution:- Solution: Co-operative P2P Downloading via Car-Torrent Co-operative P2P Downloading via Car-Torrent



•• InfostationInfostation model model : : downloadsdownloads onlyonly at at infostationinfostation


Download pieces

InternetInternetVehicle-to-roadsidecommunication



•• Basic idea:Basic idea:•• Co-operative Co-operative downloaddownload –– phasephase 1 1


Download pieces

Vehicle-to-roadsidecommunication

InternetInternet



Inter-vehiclecommunication

InternetInternet


•• Basic idea:Basic idea:•• Co-operative Co-operative downloaddownload –– phasephase 2 2



•• A Bit A Bit TorrentTorrent reviewreview::

-- SwarmingSwarming:: ParallelParallel downloadsdownloads amongamong a a meshmesh of of cooperatingcooperating peerspeers

-- Scalable:Scalable: System capacity increases with increase in System capacity increases with increase in number of peers number of peers

-- Tracker:Tracker: Handles peer discovery Handles peer discovery Centralized Tracker:Centralized Tracker: single point of failure single point of failure

Observation: Observation: Might not work for Wireless scenarios, because of Might not work for Wireless scenarios, because of intermittent connectivity intermittent connectivity

Issue: Issue: Mobility increases churn of nodes participating in Mobility increases churn of nodes participating in a download a download



•• A A picturepicture of Bit of Bit TorrentTorrent system: system:

Uploader/downloader

Uploader/downloader

Uploader/downloader

Uploader/downloader

TrackerUploader/downloader



•• Gossip Gossip protocolprotocol : : FIlesFIles are are divideddivided in in chunkschunks. . A Gossip message containing TorrentA Gossip message containing Torrent

ID, Chunk list and Timestamp is ID, Chunk list and Timestamp is ““propagatedpropagated”” by each peer. by each peer.



•• PeerPeer SelectionSelection StrategiesStrategies::

Problem: Problem: how to select the peer for downloading? how to select the peer for downloading?

Possible selections schemes:Possible selections schemes:

1) Rarest First: 1) Rarest First: BitTorrentBitTorrent-like policy of searching for the rarest -like policy of searching for the rarest bitfieldbitfield in your in your peerlistpeerlist and downloading it and downloading it

2) Closest Rarest: download closest missing piece (break ties on 2) Closest Rarest: download closest missing piece (break ties on rarity) rarity)

3) Rarer 3) Rarer vsvs Closer: weights the rare pieces based on the distance to Closer: weights the rare pieces based on the distance to the closest peer who has that piece. the closest peer who has that piece.



•• Impact of Impact of SelectionSelection StrategyStrategy : :



•• AttractiveAttractive aspectsaspects of of CarTorrentCarTorrent solutionssolutions::

- - Bandwidth at the Bandwidth at the infostationinfostation is limited and is limited and ““not convenientnot convenient”” - It can become congested if all vehicles stop - It can become congested if all vehicles stop - It is a nuisance as I must stop and waste time - It is a nuisance as I must stop and waste time

- GPRS and 3G bandwidth is also limited and expensive - GPRS and 3G bandwidth is also limited and expensive - The car to car bandwidth on the freeway is huge and - The car to car bandwidth on the freeway is huge and practically unlimited! practically unlimited!

- Car to car radios already paid for by safe navigation - Car to car radios already paid for by safe navigation requirement requirement

- - CarTorrentCarTorrent transmissions are reliable - they involve only transmissions are reliable - they involve only few hops (proximity routing) few hops (proximity routing)


Vehicular mobility models and simulatorsVehicular mobility models and simulators

Modeling vehicular traffic

Vehicular simulators


Modeling vehicular traffic (1/5)Modeling vehicular traffic (1/5)

Issues:

One One key problem key problem in the in the study study of of VANETs is VANETs is the the need toneed tocharacterize vehicular nodes mobility characterize vehicular nodes mobility and and traffic patterns traffic patterns ininorder to order to produce produce mobility models that reflect as close asmobility models that reflect as close aspossible possible the the real behaviour real behaviour of mobile of mobile systemssystems

Mobility Mobility model model affects affects the the simulation resultssimulation results



Approaches:

Based Based on a on a level-of- detaillevel-of- detail classification classification, , traditionallytraditionally, , three typesthree types

of of approaches have been usedapproaches have been used::

Microscopic modelsMicroscopic models

Kinetic modelsKinetic models

Macroscopic modelsMacroscopic models



Microscopic models:

The The most most basic and basic and detailed approaches detailed approaches are are microscopic microscopic ororcar following modelscar following models, , modeling modeling the the actual response actual response ofofindividual vehicles to their predecessorindividual vehicles to their predecessor

Each vehicle is described Each vehicle is described on the on the ““microscopic microscopic scalescale”” by itsby itsspace space x(t)x(t) and and speed speed v(t)v(t) coordinates coordinates at time at time tt



Kinetic models:

PresentPresent anan intermediate intermediate stepstep betweenbetween the the otherother twotwo modelsmodels

PartiallyPartially derivedderived fromfrom microscopicmicroscopic modelsmodels and and usedused toto obtainobtain

fluidfluid dynamicdynamic equationsequations, so , so leadingleading toto macroscopicmacroscopic modelsmodels

EffectiveEffective approachapproach forfor the the derivationderivation of of validvalid vehicularvehicular traffictraffic

modelsmodels whichwhich takestakes alsoalso intointo account account forfor the the psycho-psycho-

physiologicalphysiological nature of driver interaction ( nature of driver interaction (microscopicmicroscopic levellevel))

A A distributiondistribution functionfunction f(x,v,t)f(x,v,t) describesdescribes the the numbernumber of of vehiclesvehicles

withwith a a certaincertain location and location and speedspeed at time at time tt



Macroscopic models:

Coarsest level Coarsest level of of descriptiondescription

In In most applications most applications one one is neither interested is neither interested in the in the exactexact

evolution evolution of the of the singles vehicle nor singles vehicle nor in the in the distribution function distribution function ff

Use fluid dynamic equationsUse fluid dynamic equations

Main quantities Main quantities are the densityare the density,, the the mean speed mean speed and and speedspeed

variance variance of of vehiclesvehicles


Vehicular simulators (1/3)Vehicular simulators (1/3)

Issues:

While it is crucial to While it is crucial to test and test and evaluate protocolevaluate protocolimplementations implementations in a in a real testbed environmentreal testbed environment, , simulationssimulationsare are still commonly used as still commonly used as a first a first step step in in any protocolany protocoldevelopment for VANETs researchdevelopment for VANETs research

VANETs imply specific motion patterns that make VANETs imply specific motion patterns that make thethecommon common random mobility models used random mobility models used in in MANETsMANETsunrealisticunrealistic



A quick overview :

Recently Recently new new open-source tools open-source tools are are available for available for generation ofgeneration of

vehicular mobility patternsvehicular mobility patterns. . Most Most of of them them are are capable capable ofof

producing traces for producing traces for network network simulators such as simulators such as ns-2ns-2 or or OpNetOpNet

STRAW: The Street STRAW: The Street Random Waypoint tool provides Random Waypoint tool provides roadroadtopology extraction from topology extraction from the the maps maps of the TIGER database of the TIGER database asaswell as micromobility supportwell as micromobility support. The . The main drawback is that itmain drawback is that itproduces traces not usable by different well-known produces traces not usable by different well-known networknetworksimulators but only by simulators but only by the SWANS the SWANS platform platform on on which it iswhich it isbasedbased



A quick overview :

CanuMobiSimCanuMobiSim: : is is a a tool for tool for the generation of the generation of movement tracesmovement tracesin a in a variety variety of of conditionsconditions. . Extrapolation Extrapolation of of real topologiesreal topologiesfrom detailed Geographical from detailed Geographical Data Data Files Files (GDF) are (GDF) are possiblepossible,,many different mobility models many different mobility models are are implementedimplemented, a GUI , a GUI isispresentpresent, and the , and the tool tool can generate can generate mobility traces for mobility traces for ns-2ns-2 and andother simulatorsother simulators..

Micromobility is Micromobility is consideratedconsiderated, , implementing several car-to-implementing several car-to-car modelscar models..


Future research and challengesFuture research and challenges Solutions proposed for VANETs are inspired to well-known paradigms

defined for ad hoc networks and they do not fully exploit the peculiar featurescharacterizing VANETs

Most current research on multi-hop networks assumes fixed or very slowvarying network topology⇒⇒ the the effect effect of high of high mobility mobility in ad hoc in ad hoc networks should be fully investigatednetworks should be fully investigated⇒⇒ new new mobility models should be developedmobility models should be developed

New algorithms should be designed taking into consideration severe delay-constraints of safety applications and real-time applications⇒⇒ new MAC new MAC schemesschemes⇒⇒ routing schemes should provide routing schemes should provide a a good tradeoff between reliability good tradeoff between reliability and and overheadoverhead

Location privacy schemes should be designed to prevent or mitigate trackingof vehicles during their communication with other vehicles or the road-sideinfrastructure

Documents

VANETs - Unict · Università degli Studi di Catania Dipartimento di Ingegneria Informatica e delle Telecomunicazioni VANETs Vehicular Ad-hoc NETworks (VANETs) can be considered as