1. Department of Information Engineering University of Padova {fasoloel, zanella, zorzi}@dei.unipd.it An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks E. Fasolo, A. Zanella and M. Zorzi Speaker Stefano Tomasin June, 14 th 2006.

2. An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks Main aims of this study  To develop and improve a broadcast protocol to deliver alert messages as soon as possible in a vehicular scenario [3]  Maximize the reliability  Minimize the delivery latency  To propose an analytical model in order  To evaluate the protocol performance  To optimize the protocol parameters  Compare the proposed solution with other broadcast protocols by means of simulations

3. An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks Smart Broadcast Protocol (SBP)  Main Features  Position-based scheme  Using only position information  Running on the top of an IEEE 802.11-like system  Completely distributed  Absence of control traffic  System Model  Long and narrow rectangular area (street)  Nodes placed according to a Poisson distribution  Nodes known own position

4. An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks SBP: Initial Assumptions  The current source coverage area is split into n sub areas  At each sub area is associated a time interval named contention windows according to S1S1 SnSn … Propagation direction Not considered area Positive advancement towards the propagation direction AIM: Support the maximum advancement of the broadcast message towards the propagation direction

5. An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks  The source sends the an RTB (Request To Broadcast) message  Each node that receives correctly the RTB message  Determine the sector it belongs to  Schedules the retransmission of a CTB (Clear To Broadcast) message after a backoff time b selected in the contention window according to a uniform probability distribution function  Listen to the channel  Source send the message to the node which has transmitted the CTB message SBP: Relay Election S1S1 SnSn … Not considered area Propagation direction b 11 b 12 b n2 b n1 b j1 NEXT RELAY

6. An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks SBP: Collision Resolution S1S1 SnSn … Not considered area Propagation direction b 11 b n2 b n1 b j1  If a node receives correctly another RTB message adjusts its backoff time according to the position of the new source  If a collision occurs (  two or more nodes select the same backoff time and send at the same time a CTB message) the procedure continue. NEXT RELAY A COLLISION OCCURS

7. An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks Theoretical Analysis: Initial Assumptions  q h = the number of nodes that pick the same backoff value h in W  q h = 0  IDLE (I)  No node transmits  q h > 0  COLLISION (C)  A collision occurs  q h = 1  BROADCAST (B)  A node wins the contention and transmits the broadcast message  n U = number of unsuccessful events before the completion of the procedure  T U = average duration of an unsuccessful countdown step

8. An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks Theoretical Analysis: One-hop latency  The one-hop latency is defined as the mean time required before the broadcast message is successfully forwarded to the next relay node where the last terms accounts for the extra time spent to restart the procedure is negligible  Finally, we have the simplify equation for the one-hop latency where K = T C / T I

9. An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks Theoretical Analysis: One-hop message progress  The one–hop message progress, δ, is defined as the additional distance covered by the message in a rebroadcast phase, on average  We only need to determine the statistic of J:  We evaluate the conditioned probability that s = h, given that s in W  Ps(h)  And we use Ps(h) to evaluate Pj(r) and the the mean value of J

10. An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks Theoretical Analysis: Optimization  Consider the following cost function defined as the time required to get the success retransmission over the successful probability COST FUNCTION Single solution in [1/K, 1]If we fix Ns

11. An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks Validation of the theoretical analysis  One hop latency at varying of node density for different cw (assuming Ns = 10)  Lines refer to the theoretical results  Marks refer to the simulation outcomes  The interpolation of the minimum values correspond to the line obtained with cw opt

12. An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks Analytical Model versus Simulations  Average one–hop progress δ and propagation speed v versus the node density λ (assuming cw = cw opt ) Good matching between analytical model and simulations High node densities assure the maximum progress

13. An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks Protocol comparison From the figure we can observe that the propagation speed achieved by SB is almost constant when varying the node density SB may lead to a slightly lower advancement than the other schemes. This is due to the fact that SB balances both the message progress and the latency. SB is compared with MCDS-based, GeRaF and UMB

14. An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks Conclusions  We designed a protocol for message dissemination which guarantee high reliability and low latency  The developed analytical model assures good matching with the simulation results  SB outperforms the other message dissemination mechanisms.  Future work  1  2  3

15. An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks References  [1] D. Cottingham, “Research Directions on Inter-vehicle Communication,” http://www.cl.cam.ac.uk/users/dnc25/references.html, Dec. 2004.  [2] M. Rudack, M. Meincke, K. Jobmann, and M. Lott, “On traffic dynamical aspects intervehicle communication (IVC),” in 57th IEEE Semiannual Vehicular Technology Conference (VTC03 Spring), Jeju, South Korea, Apr. 2003, http://portal.acm.org/citation.cfm?id=778434.  [3] Fasolo, E. and Furiato, R. and Zanella, A., “Smart Broadcast for inter–vheicular communications,” in Proc. of WPMC05, Sep. 2005.  [4] Zanella, A. and Pierobon, G. and Merlin, S., “On the limiting performance of broadcast algorithms over unidimensional ad-hoc radio networks,” in Proceedings of WPMC04, Abano Terme, Padova, Sep. 2004.  [5] Korkmaz, G. and Ekici, E. and O¨ zgu¨ner, F. and O¨ zgu¨ner, U¨., “Urban multi-hop broadcast protocol for inter–vehicle communication systems,” in Proc. of the first ACM workshop on Vehicular ad hoc networks, 2004.  [6] M. Zorzi and R. Rao, “Geographic Random Forwarding (GeRaF) for ad hoc and sensor networks: energy and latency performance,” IEEE Transaction on Mobile Computing, vol. 2, no. 4, Oct.–Dec. 2003.  [7] B. Williams and T. Camp, “Comparison of broadcasting techniques for mobile ad hoc networks,” in MOBIHOC, 2002.  [8] K.M. Alzoubi and P.J. Wan and O. Frieder, “New distributed algorithm for connected dominating set in wireless ad hoc networks,” in Proc. Of 35th Hawaii Int’l Conf. on System Sciences (HICSS-35), Jan. 2002.  [9] P.J. Wan and K. Alzoubi and O. Frieder, “Distributed construction of connected dominating set in wireless ad hoc networks,” in Proc. of IEEE INFOCOM’2002, June 2002.  [10] S. Giordano and I. Stojmenovic, Position based routing algorithms for ad hoc networks: a taxonomy. Kluwer, 2004, pp. 103–136.  [11] I. Stojmenovic, “Position-based routing in ad hoc networks,” IEEE Communications Magazine, vol. 40, no. 7, pp. 128–134, July 2002.

16. Department of Information Engineering University of Padova {fasoloel, zanella, zorzi}@dei.unipd.it An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks E. Fasolo, A. Zanella and M. Zorzi Speaker Stefano Tomasin June, 14 th 2006.

17. An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks

21. Inter-vehicular networks (IVNs)  Applications and services  Emergency notification  Cooperative driving assistance  Car to car audio/video communications  Internet access  Traffic control  Topical features  No energy constraints  High mobility  Availability of timing and localization information  Main Issues  New paradigm (physical, MAC, routing layer solutions)  New broadcast propagation mechanisms Efficient Reliable Low latency

22. An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks The Broadcast Storm Problem  Flooding  High Data Redundancy  Collision Problem  MCDS-based algorithms  Minimize the retransmitting node number  Solve the collision problem  Not feasible in high dynamic networks

23. An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks Broadcast Protocol Overview  Probabilistic Schemes  Not solve collision and redundancy problem  Neighbor-based Schemes  Require control traffic, depend on the network topology  Topology-based Schemes  More efficient but require a complete topology knowledge (not feasible for high dynamic networks)  Cluster-based Schemes  High cost to maintain clustering structure in mobile networks  Position-based Schemes  Flat, not require control traffic Urban Multi-hop Protocol (UMBP)

24. An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks  The time wasted during the re-broadcast procedure depends on  The collision probability  The probability that the furthest sub-areas are empty  Fixed Ns, for each node density, there is an optimum contention window size such that  The time wasted on re-broadcast procedure is minimized Some theoretical observations