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Lars Wischhof et al. Technical University of Hamburg-Harburg, Hamburg, Germany

Adaptive Broadcast for Travel and Traffic Information Distribution Based on Inter-Vehicle Communication. Lars Wischhof et al. Technical University of Hamburg-Harburg, Hamburg, Germany. Presented by Long Vu CS598JH – Fall 07. Traffic and Travel Information System (TTI).

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Lars Wischhof et al. Technical University of Hamburg-Harburg, Hamburg, Germany

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  1. Adaptive Broadcast for Travel and Traffic Information Distribution Based on Inter-Vehicle Communication Lars Wischhof et al. Technical University of Hamburg-Harburg, Hamburg, Germany Presented by Long Vu CS598JH – Fall 07

  2. Traffic and Travel Information System (TTI) Self Organizing Traffic Information System (SOTIS) How to broadcast information among cars efficiently?

  3. Challenges • Mobile nodes • Node density is not uniform • Highway vs. traffic jam • Possible solutions • Periodically broadcast with fixed broadcast interval • Adaptively tune broadcast interval How to broadcast information among cars efficiently?

  4. Next… • Self-Organizing Traffic Information System • Provoked Broadcast • Provoked Broadcast • Provocation vs.Mollification • Influence of Distance on Provoked Broadcast • Simulation • Settings • Cumulated number of dropped packets • Required Bandwidth • Conclusion

  5. Self-Organizing Traffic Information System • All nodes in a segment broadcast their velocities to all other nodes in the same segment  all nodes can compute average velocity and put into TTI record of this segment • Transmission range: 1000m • Fixed broadcast interval: 5 seconds No Segment Leader Intra-road segment communication

  6. Self-Organizing Traffic Information System Inter-road segments communication (SOTIS packet) N = 100 km/500m = 200 Each record is the average velocity of cars in the corresponding segment

  7. Next… • Self-Organizing Traffic Information System • Provoked Broadcast • Provoked Broadcast • Provocation vs.Mollification • Influence of Distance on Provoked Broadcast • Simulation • Settings • Cumulated number of dropped packets • Required Bandwidth • Conclusion

  8. Provoked Broadcast (1) • Step 1: Each car broadcast its velocity to its neighbors in the same road segment  avg. velocity is computed • Step 2: Cars update TTI for this road segment. Put it into SOTIS packet • A TTI record has averagevelocity and time stamp • Step 3: Car broadcasts the SOTIS packet to neighboring road segments

  9. Provoked Broadcast (2) • Step 4: Upon receiving SOTIS packet, car updates TTI records in its memory (knowledge base) • Step 5: Depending on the difference between received SOTIS packet and its knowledge base, car performs provocation or mollification on broadcast interval

  10. Compare received SOTIS packet to car’s knowledge base: • Provocation • Mollification vi- vi’ ti- ti’ Car’s Knowledge base Received SOTIS packet

  11. S Distinct Overlapped Road Segments • qinfo and qdate are constants

  12. Provocation vs. Mollification • If wm,n < wmol T = T + tmol • If wm,n > wprov T = T - tprov Too many constants and parameters !

  13. How it Actually Works ? Increase Tupd Decrease Tupd

  14. Interdependence of Provocation and Mollification • M close nodes (in trans. range) • Have a similar view of network • N broadcasts new information • All nodes provoke • Nodes are unsynchronized • A broadcasts, other nodes perform mollification

  15. Next… • Self-Organizing Traffic Information System • Provoked Broadcast • Provoked Broadcast • Provocation vs.Mollification • Influence of Distance on Provoked Broadcast • Simulation • Settings • Cumulated number of dropped packets • Required Bandwidth • Conclusion

  16. Influence of Distance on Provoked Broadcast • The farthest node in the broadcast range should broadcast next to utilize bandwidth dtx,max: the max trans. range If wm,n > wprov T = T – qdist(dtx)

  17. Next… • Self-Organizing Traffic Information System • Provoked Broadcast • Provoked Broadcast • Provocation vs.Mollification • Influence of Distance on Provoked Broadcast • Simulation • Settings • Cumulated number of dropped packets • Required Bandwidth • Conclusion

  18. Simulation Settings No justification about values of parameters NS2 simulation

  19. Cumulated Number of Dropped Packets

  20. Required Bandwidth

  21. Conclusion • Pros • A threshold-based adaptive broadcast protocol • Tune broadcast interval according to changes of SOTIS packet • Cons • Too many control parameters

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