1. Amit Saha April 13 th, 2005 VANET : V EHICULAR A D HOC NET WORKS

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 Saha April 13 th, 2005 M OBILITY M ODELS

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