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Department of Information Engineering University of Padova {fasoloel, zanella, 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 Special Interest Group on NEtworking & Telecommunications

An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks Aim of the study  Design a broadcast protocol for alert message delivery in a vehicular scenario  Maximize reliability  Minimize delivery latency  Analytical modeling of the protocol  Evaluate protocol performance  Optimize protocol parameters  Comparison with other broadcast protocols

An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks Smart Broadcast Protocol (SBP)‏  Main Features  Position-based scheme  Running on top of IEEE like system  Completely distributed  Limited control traffic  System Model  Street: Long and narrow rectangular area  Nodes: placed according to a Poisson distribution  Nodes known their own position only x

An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks SBP: Initial Assumptions  Coverage area is split into n sectors S i  Sectors are assigned adjacent contention windows W j, j=1...,n S1S1 SnSn … Propagation direction Forbidden area Positive advancement in the propagation direction AIM: Maximize broadcast-message advancement along propagation line Msg propagation direction W1W1 WnWn cw i 0 W2W2 cw 1 + cw cw n WiWi

An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks  Source sends an RTB (Request To Broadcast) message  Nodes that receive RTB message  Determine the sector they belong to  Schedule the retransmission of a CTB (Clear To Broadcast) message after a random backoff time b uniformly selected in their contention window  each idle slot, freeze in busy slots  Node that first transmits successfully a CTB (Clear To Broadcast) message becomes the Next Relay SBP: Relay Election NEXT RELAY S1S1 SnSn … Propagation direction b 11 b 12 b n2 b n1 b j1 Source Contention Winner Backing off node

An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks SBP: Collision Resolution S1S1 SnSn … Propagation direction b 11 b n2 b n1 b j1  If two or more nodes select the same backoff time, CTB messages will collide  After collisions, procedure is resumed by the other backing off nodes (if any)‏  If any CTB message is received before the maximum backoff period has elapsed, procedure is started anew NEXT RELAY A COLLISION OCCURS Source Contention Winner Backing off node Collided node

An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks Theoretical Analysis: Initial Assumptions  Nodes are distributed with density in each sector  Nodes in sector S j select backoff slots in W j independently and uniformly  Let q h be the number of nodes that select the same backoff slot h  W i  q h is a Poisson random variable with parameter

An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks Theoretical Analysis: Events probability  Let’s focus on events that may occur in slot h:  q h = 0  IDLE (I)  No nodes transmit  q h > 0  COLLISION (C)  A collision occurs  q h = 1  BROADCAST (B)  A node wins the contention and gets the broadcast message to be forwarded  n U = average number of unsuccessful events before the completion of the procedure  T U = average duration of an unsuccessful countdown step Idle slot duration Collision duration

An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks Theoretical Analysis: One-hop latency  Def: One-hop latency   mean time before broadcast message is successfully forwarded to the next relay node K = T C / T I

An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks Theoretical Analysis: One-hop message progress  One–hop message progress, δ: average one-hop covered distance Next Relay sector Total number of sectors Sector size (along the propagation direction)‏

An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks Theoretical Analysis: Optimization  Optimize the Cost Function  One-hop delay/success probability COST FUNCTION Single solution in [1/K, 1]

An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks Validation of the theoretical analysis Impact of CW setting on per-hop latency (Ns = 10)‏ Theoretical Simulation Setting cw=cw opt ( )  we interpolate the minima of curves obtained with fixed cw

An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks Analytical Model versus Simulations Good matching between analytical model & simulations High node densities assure maximum progress Average one–hop progress δAverage propagation speed v , cw = cw opt ( )‏

An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks Protocols comparison SB propagation speed is almost constant when varying the node density SB may lead to slightly lower advancement than other schemes  (SB balances both the message progress and the latency)‏ SB vs MCDS-based, GeRaF and UMB

An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks Conclusions  Smart Broadcast provides good performance in message dissemination along mono- dimensional networks of vehicles  Analytical model permits in-depth analysis and optimization  Future work 1.Consider contention with other broadcast flows 2.Include more realistic radio channel model

An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks References  [1] D. Cottingham, “Research Directions on Inter-vehicle Communication,” Dec  [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,  [3] Fasolo, E. and Furiato, R. and Zanella, A., “Smart Broadcast for inter–vheicular communications,” in Proc. of WPMC05, Sep  [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  [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,  [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  [7] B. Williams and T. Camp, “Comparison of broadcasting techniques for mobile ad hoc networks,” in MOBIHOC,  [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  [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  [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.

Department of Information Engineering University of Padova {fasoloel, zanella, 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.

An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks Spare Slides

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

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

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)‏

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

An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks S1S1 S Ns S1S1 SJSJ Propagation direction Source Contention Winner Backing off node Collided node A  (J)‏

An Effective Broadcast Scheme for Alert Message Propagation in Vehicular Ad Hoc Networks Theoretical Analysis: One-hop message progress  One–hop message progress, δ: average one-hop covered distance  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