Amit Saha April 13 th , 2005 - PowerPoint PPT Presentation

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Amit Saha April 13 th , 2005

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  1. Amit SahaApril 13th, 2005 VANET: VEHICULAR AD HOC NETWORKS

  2. What is a VANET ? • Ad hoc network composed of vehicles • Individual nodes different from traditional wireless nodes • No power constraint • Nodes mostly mobile • Complements existing infrastructure • Extends existing infrastructure

  3. Medium Access Control • Dedicated Short Range Communication (DSRC) • FCC regulated 5.9 GHz • 10 MHz channels • 1 control, 6 service • MAC similar to 802.11, i.e., CSMA/CA • OFDM used in PHY • Speeds up to 120 mph • Up to 1000 m transmission range

  4. VANET 2004 • First conference of its kind • 9 papers, 7 posters • Safety applications (3) • Security (2) • Data dissemination (4)

  5. Sensors in VANET Nodes • Size and power no longer issues

  6. Applications • Traffic control • Automatic speed limit enforcement • Rerouting in traffic congestion • Safety • Notification of accident up ahead • Decentralized 911 service • Prioritized over non-safety applications • Extended communication • Infotainment

  7. Snowplowing Project • Project by Berkeley PATH • Snowplowing in total whiteout • Vehicle equipped with sensors for • Measuring steering angle and vehicle motion • Field of magnetic markers on roadway • Obstacle detection (radar sensors)

  8. Security Aspects • Somewhat similar to sensor networks • Sensors might report “incorrect” data • Undetected error • Detected error • Corrected error

  9. Data Collection • No aggregation • No hierarchy • Simple model for data collection

  10. Data Delivery • Opportunistic forwarding • Disconnection possible • Geographic forwarding • Trajectory based forwarding • A coordinate system is assumed • Nodes know position in this coordinate system • Route is a trajectory in this coordinate system

  11. Conclusion • Similar to mobile ad hoc networks • Has sensors but usage is mostly different • Accident notification similar to ‘fire !!!’ in sensor networks • Not power or size constrained

  12. Amit SahaApril 13th, 2005 MOBILITY MODELS

  13. Different Mobility Models • Random waypoint model • City section model • Obstacle-based model

  14. Random Waypoint Model • Convergence issues • Nodes tend to converge to center • Wrap around • Reflection • Average speed • Minimum speed has to be greater than zero • Many variations exist

  15. Example

  16. City Section Model • Simulates movement of vehicles on streets • Gets very complicated to make realistic • Lane change • Traffic light modeling • Widely used versions are simplistic • Grid structure

  17. Obstacle-based Model • Models obstacles • Restricts movement • Nodes do not reflect off surfaces • Restricts wireless propagation • Doors used to cross buildings • Movement on Voronoi Graph

  18. Example

  19. Problems • Steady state unknown • Existence is not known as well • When is steady state reached in simulation • Infocom 2005 best paper, EPFL, Lausanne • Conditions required for steady state behavior • Several mobility models • Steady state initialization