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Vehicular Communication Technology

Vehicular Communication Technology. Motivation. Safety and transport efficiency In Europe around 40 , 000 people die and more than 1.5 millions are injured every year on the roads Traffic jams generate a tremendous waste of time and of fuel

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Vehicular Communication Technology

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  1. Vehicular Communication Technology Vehicular Communication Technology

  2. Motivation • Safetyandtransportefficiency • InEuropearound 40,000 peopledieandmore than 1.5 millionsare injuredeveryyearontheroads • Trafficjamsgenerate a tremendouswasteoftimeandoffuel • Mostoftheseproblemscanbesolvedbyprovidingappropriateinformationtothedriverortothevehicle Vehicular Communication Technology

  3. VehicleCommunication (VC) • VC promisessaferroads, • … more efficient driving, Vehicular Communication Technology

  4. VehicleCommunication (VC) • … more fun, • … and easier maintenance. Vehicular Communication Technology

  5. Smart Vehicle Vehicular Communication Technology

  6. Approaches to vehicular communication Communication using Communication using dedicated infrastructures cellular systems Direct Communication Vehicular Communication Technology

  7. Vehicular Ad Hoc Network (VANET) • Ad-Hoc Network: • A networkwithminimalornoinfrastructure • Self-organizing • Eachnodecanactasthesourceofdata, the destinationfordataandanetwork router • VehicularAdHocnetwork (VANET) • Usesequippedvehiclesasthenetworknodes • Nodesmoveatwillrelativetoeachotherbut withintheconstraintsoftheroadinfrastructure Vehicular Communication Technology

  8. Differences VANETs from MANETs • RapidTopologyChanges • Highrelativespeedofvehicles => short link life • FrequentFragmentation • Chunks of the net are unable to reach nodes in nearby regions • SmallEffectiveNetworkDiameter • Apathmaycease toexistalmostasquicklyasitwasdiscovered (reactive routing) • LimitedRedundancy • The redundancy in MANETs is critical to providing additional bandwidth • In VANETs the redundancy is limited both in time and in function Vehicular Communication Technology

  9. Vehicular Ad Hoc Network (VANET) • Messagepropagatestodestinationusing a numberofintermediatelinks Vehicular Communication Technology

  10. Vehicular Ad Hoc Network (VANET) • If vehicle mobility causes links to break, message rerouted using a different path Vehicular Communication Technology

  11. Why use VANETS? • Easierdeployment • Decreased dependency on fixed infrastructure • Sparsenetworkofroadsidebeacons • Permitgradualintroductionoftechnology • Location-orientedservicescanbeprovidedwithlittleor norunningcoststotheusers Vehicular Communication Technology

  12. Lot of Involved Parties Vehicular Communication Technology

  13. Major problems in this area • Communication / Networking • Localization Vehicular Communication Technology

  14. Requirements on vehicular communication • Mobility • Delaybounded (real-time) • Scalability • Bandwidth efficiency • Cost • Fairness • Any time, any place, any hosts (GPS unequipped vehicles, standardization between cars’ manufactures) Vehicular Communication Technology

  15. Addressing the challenges • PhysicalLayer • limited bandwidth • Link Layer • congestioncontrol, latency, throughput, fairness andscalability • Network (Routing) Layer • rapidtopology changesandnetwork fragmentation Vehicular Communication Technology

  16. Dedicated ShortRangeCommunications(DSRC) • DSRC operates at 5.9 GHz Vehicular Communication Technology

  17. DSRC – Operating Characteristics • IEEE 802.11p protocol (802.11a modification for VC) • Maximumrange: 1000m • Vehicle speeds up to 100 mph • Low latency: 50 ms • Application priority: 8 levels • Channel 172: vehicle safety only Vehicular Communication Technology

  18. Howdoes DSRC work? • Road-Side Unit (RSU) • Announces to OBUs 10 times per second applicationsitsupportson whichchannel • On-Board Unit (OBU) • Listenson Channel 172 • Executessafetyapplicationsfirst • Then switches channels • Executes non-safety applications • Returns to Channel 172 and listens Vehicular Communication Technology

  19. Channel allocation (MAC) • Existing MAC protocols (CSMA/CA, MACA, MACA-BI) are contention-based => not delay bounded • Proposed MCS/CDMA • Each vehicle senses all the spreading codes, finds a code that is not used by nearby vehicles, and transmits data using the selected code • Search for free code, contention for free code (if vehicles > codes) => large delays Vehicular Communication Technology

  20. Channel allocation (MAC) • Location-based Channel Access (LCA) • The geographical area is divided into a cellular structure • Each cell has a unique channel associated with it • Multiple access scheme, such as CSMA/CA and MCS/CDMA, can be used within each cell • Maindesignparameters: cellsizeandchannelreuse distance • Advantages: no central station for channel assignment, no wait before transmit, no contention for free channels, reuse of channels => delay bounded, fairness, bandwidth efficiency, scalability and mobility Vehicular Communication Technology

  21. Routing Schemes • Proactive (table-driven) • Eachnodeattempts tomaintainacurrent representationofthenetworktopology • Advantage: lowermessagelatency (routes are immediately available) • Disadvantage: bandwidth overhead (to maintain routes), restricted scalability • Reactive (source-driven, on-demand) • Routesarerequestedbysourcenodesonlywhen needed • Advantage: bandwidth economy (no control messages for non-active routes) • Disadvantage: latency (establishing a route) • Hybrid • ZRP – proactive within zone, reactive outside zone Vehicular Communication Technology

  22. Major problems in this area • Communication / Networking • Localization Vehicular Communication Technology

  23. GPS Vehicular Communication Technology

  24. Space Segment Vehicular Communication Technology

  25. How does GPS work? Vehicular Communication Technology

  26. How do we compute Position? • GPS is a Distance (Range) Measuring System • Stable Frequency Standards in the Satellites and Receivers • Able to compute a Clock Offset • Velocity of Radiowave is known • Thus Distance = V x T • Since the coordinates of the Satellites are known at any point of time, with 4 ranges the position of the GPS Antenna can be computed • 3-D Trilateration: Distance, Distance, Distance and Distance Intersection Vehicular Communication Technology

  27. DGPS • Differential GPS can improve accuracy from several meters to a fewcentimeters Vehicular Communication Technology

  28. However… • Vehicles may be unequipped with GPS or sometimes cannot obtain line-of-sight access to satellites (in tunnels) • In order to discover their position (or at least driving direction), GPS-U vehicles can use communication with GPS-E vehicles • GPS-U periodically broadcasts PREQ message to its one-hop neighbors • When GPS-E receives PREQ, it sends back PREP message including its current position • The knowledge of the exact position depends on the number of neighbors sending PREP messages • GPS-U can compute its exact position if it receives at least three PREP from three different vehicles (by triangulation) Vehicular Communication Technology

  29. Thank You! Vehicular Communication Technology

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