Department of Information Engineering University of Padova{fasoloel, zanella, zorzi}@dei.unipd.it

An Effective Broadcast Scheme for Alert Message Propagationin Vehicular Ad Hoc Networks

E. Fasolo, A. Zanella and M. Zorzi

Speaker Stefano Tomasin

June, 14th 2006.

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 reliabilityMinimize the delivery latency

To propose an analytical model in orderTo evaluate the protocol performanceTo optimize the protocol parameters

Compare the proposed solution with other broadcast protocols by means of simulations

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

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

S1Sn …

Propagation direction

Not considered area

Positive advancement towards the propagation

direction

AIM: Support the maximum advancement

of the broadcast message towards the propagation direction

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

S1Sn …Not considered area

Propagation direction

b11

b12

bn2

bn1

bj1

NEXT RELAY

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

SBP: Collision Resolution

S1

Sn

…

Not considered area

Propagation direction

b11

b11

bn2

bn1

bj1

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

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

Theoretical Analysis: Initial Assumptions

qh = the number of nodes that pick the same backoff value h in W

qh = 0 IDLE (I) No node transmits

qh > 0 COLLISION (C) A collision occurs

qh = 1 BROADCAST (B) A node wins the

contention and transmits the broadcast message

nU = number of unsuccessful events before the completion of the procedure

TU = average duration of an unsuccessful countdown step

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 = TC / TI

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

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

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 cwopt

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 = cwopt)

Good matching between analytical model and simulations High node densities assure the maximum progress

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

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 work123

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.

Department of Information Engineering University of Padova{fasoloel, zanella, zorzi}@dei.unipd.it

An Effective Broadcast Scheme for Alert Message Propagationin Vehicular Ad Hoc Networks

E. Fasolo, A. Zanella and M. Zorzi

Speaker Stefano Tomasin

June, 14th 2006.

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

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

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

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

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

FloodingHigh Data Redundancy Collision Problem

MCDS-based algorithms Minimize the retransmitting node numberSolve the collision problemNot 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 thatThe time wasted on re-broadcast procedure is minimized

Some theoretical observations