1. RPB-MD: A Novel Robust Message Dissemination Method for VANETs Congyi Liu and Chunxiao Chigan Michigan Technological University GLOBECOM 2008

2. Outline Introduction RPB-MD: Relative Position Based Message Dissemination Performance Evaluation Conclusion

3. Introduction VANETs providing multi-hop wireless communication among vehicles, promises a broad applications. Robust message disseminations are desirable for most of safety-critical VANET applications.

4. Related Work To disseminate messages by delaying different times to avoid peak load  This scheme requires location service and does not consider the issue of partitions, which may affect the delivery ratio significantly. Carry and forward  Would result in high overhead (especially under the dense vehicular traffic), and high computation complexity because of the process of partition crossing.

5. Related Work (cont.) Considered the direction of vehicle movement to disseminate messages.  Can not ensure robust message dissemination.

6. Goal In this paper, we address the issue of robustly disseminating messages to all intended vehicles in the zone-of-relevance. Zone-of-relevance defines the area where the message is of interest to the drivers. The design of such mechanisms aims at high message delivery ratio with acceptable latency and overhead.

7. Assumptions We can get the precise relative distance between two neighbors (i.e. Based on received signal strength indication, RSSI.) The reference direction,which is used as a basis for the comparison of vehicles’ directions, can also be achieved in the highway scenario. Assume that two directional antennas are equipped for every vehicle to communicate with each other within 180 o

8. RPB Forwarding Strategy - Overview A C B D F E A C F Message Head Active State Intermediate State Inactive StateActive State Intermediate State Active State Intermediate StateActive State Inactive State Message Holder Implicit ACKExplicit ACK

9. The Next Candidate Message Head

10. A C B

11. Hold the message further with probability λ

12. Message Head abnormal modes handling – case1 A C B A C B

13. Message Head abnormal modes handling – case2 (t 1 ) A C B A D E D

14. Message Head abnormal modes handling – case3 (t 2 ) A C B A D C

15. Message Holder abnormal modes handling – case1(T’) A C B A D B

16. Message Holder abnormal modes handling – case2 (t 3 ) A C B A D B

17. Addressing Model r

18. Update of the total relative distance

19. Update of total relative distance AA B

20. Simulation Parameter ParameterValue 802.11 DCF data rate2Mbps Communication Range250m Number of lanes2/direction Vehicle density 5-100 cars/(km 。 lane) Average speed90km/h Waiting time T 0 50ms Waiting time T’1s Waiting time t 1 2s Waiting time t 2 2.5s Waiting time t 3 3s Simulation model12km Distance from S to D6.5km message size512bytes Simulatorns-2 (version 3.31)

21. Comparison: Epidemic routing M. Nekovee, and B.B. Bogason, “Reliable and Efficient Information Dissemination in Intermittently Connected Vehicular Adhoc Networks,” Proceedings of IEEE Vehicular Technology Conference, pp.2486–2490, April 2007. A. Vahdat, and D. Becker, “Epidemic Routing for Partially Connected Ad Hoc Networks,” Technical Report CS-200006, 2000. http://issg.cs.duke.edu/epidemic/epidemic.pdf

25. Conclusion This paper proposed a novel relative position based message dissemination scheme for VANETs. The scheme can ensure robust message dissemination and desirable performance under all VANET traffic densities.