A note on the use of these ppt slides: We’re making these slides freely available to all, hoping...

A note on the use of these ppt slides:We’re making these slides freely available to all, hoping they might be of use for researchers and/or

students. They’re in PowerPoint form so you can add, modify, and delete slides (including this one) and slide content to suit your needs. In return for use, we only ask the following:

If you use these slides (e.g., in a class, presentations, talks and so on) in substantially unaltered form, that you mention their source.

If you post any slides in substantially unaltered form on a www site, that you note that they are adapted from (or perhaps identical to) our slides, and put a link to the authors webpage:

www.dei.unipd.it/~zanella

Thanks and enjoy!

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


E. Fasolo, A. Zanella and M. ZorziE. Fasolo, A. Zanella and M. Zorzi

Special Interest Group on NEtworking & Telecommunications

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


E. Fasolo, A. Zanella and M. Zorzi

Speaker Stefano Tomasin

June, 14th 2006.

Special Interest Group on NEtworking & Telecommunications

www.dei.unipd.it/ricerca/signet

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


Smart Broadcast Protocol (SBP)

Main Features Position-based scheme Running on top of IEEE 802.11-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


SBP: Initial Assumptions

Coverage area is split into n sectors Si

Sectors are assigned adjacent contention windows Wj, j=1...,n

S1Sn …

Propagation direction

Forbiddenarea

Positive advancement in the propagation direction

AIM: Maximize broadcast-message

advancement along propagation line

Msg propagation direction

W1 Wn

cwi

0

W2

cw1+ cw2+... cwn

Wi


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

Countdown @ 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

S1Sn …


b11

b12

bn2

bn1

bj1

Source

Contention Winner

Backing off node


SBP: Collision Resolution

S1

Sn

…


b11

b11

bn2

bn1

bj1

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


Theoretical Analysis: Initial Assumptions

Nodes are distributed with density in each sector

Nodes in sector Sj select backoff slots in Wj independently and uniformly

Let qh be the number of nodes that select the same backoff slot hWi qh is a Poisson random variable with

parameter icw/

~


Theoretical Analysis: Events probability

Let’s focus on events that may occur in slot h: qh = 0 IDLE (I) No nodes transmit

qh > 0 COLLISION (C) A collision occurs

qh = 1 BROADCAST (B) A node wins the

contention and gets the broadcast message to be

forwarded

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

TU = average duration of an unsuccessful countdown stepIdle slot duration

Collision duration


Theoretical Analysis: One-hop latency

Def: One-hop latency mean time before broadcast message is

successfully forwarded to the next relay node

UUB TnTT 0

B

CIIB P

KPPTTT

0

K = TC / TI


Theoretical Analysis: One-hop message progress

One–hop message progress, δ: average one-hop covered distance

Next Relay sectorTotal number of

sectorsSector size (along the propagation direction)


Theoretical Analysis: Optimization

Optimize the Cost Function One-hop delay/success probability

COST FUNCTION

Single solution in [1/K, 1]


Validation of the theoretical analysis

Impact of CW setting on per-hop latency(Ns = 10)

TheoreticalSimulation

Setting cw=cwopt() we interpolate the minima of curves obtained with fixed cw


Analytical Model versus Simulations

• Good matching between analytical model & simulations• High node densities assure maximum progress

Average one–hop progress δ Average propagation speed v

, cw = cwopt()


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


Conclusions

Smart Broadcast provides good performance in message dissemination along mono-dimensional networks of vehicles

Analytical model permits in-depth analysis and optimization

Future work1. Consider contention with other broadcast flows

2. Include more realistic radio channel model


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


E. Fasolo, A. Zanella and M. Zorzi

Speaker Stefano Tomasin

June, 14th 2006.


Spare Slides


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


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


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)


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


S1

SNs S1SJ


SourceContention WinnerBacking off nodeCollided node

A

(J)


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

A note on the use of these ppt slides: We’re making these slides freely available to all, hoping...

Documents

Transcript of A note on the use of these ppt slides: We’re making these slides freely available to all, hoping...