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Broadcasting in VANET

Speaker: Lin-You Wu

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Outline

1. Introduction

2. Different Regimes for Broadcasting in VANET

3. Distributed Vehicular Broadcast (DV-CAST)protocol

4. Conclusions

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1. Introduction(1/2)

Broadcasting in vehicular ad hoc networks

(VANET) is emerging as a critical area of

research.

This problem is the confinement of the

routing problem to vehicle-to-vehicle (V2V)

scenarios as opposed to also utilizing the

wireless infrastructure.

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1. Introduction(2/2)

We report the first comprehensive study on

the subject whereby the extreme traffic

situations such as dense traffic density, sparse

traffic density, and low market penetration of

cars using DSRCtechnology are specifically

taken into account.

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DSRC

DSRC

5.9GHz DSRCMACPHYIEEE802.11p.

802.11pIEEE2003802.11aWAVE(Wireless Access in the

Vehicular Environment)DSRC

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2. Different Regimes for Broadcasting

in VANET

Our previous research has identified three

different regimes of operation in VANET:

A. Dense Traffic Regime;

B. Sparse Traffic Regime;

C. Regular Traffic Regime.

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A. Dense Traffic Regime

When the traffic density is above a certainvalue, one of the most serious problems is thechoking of the shared medium by an excessive

number of the same safety broadcast messageby several consecutive cars.

Because of the shared wireless medium,blindly broadcasting the packets may lead tofrequent contention and collisions intransmission among neighboring nodes.

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Referred to as broadcast storm problem[1].

In [1], we (i) explore how serious the

broadcast storm is in VANET using a case study

for a four-lane highway scenario;

and (ii) propose three light-weight broadcast

techniques; i.e., weighted p-persistence,

slotted 1-persistence, and slotted p-

persistence,

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The basic broadcast techniques follow either a

1-persistence or a p-persistence rule.

Gossip-based approach, on the other hand,

follows the p-persistence rule which requires

that each node re-forwards with a pre-

determined probabilityp. This approach is

sometimes referred to as probabilistic flooding

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To make the situation worse, there might be

no cars within the transmission range of the

source in the opposite lane either, see Figure

3(c). Under such circumstances, routing and

broadcasting becomes a challenging task.

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We propose to cope with such extreme cases

via the so-called store-carry-forward

mechanism.

Our results show that depending on the

sparsity of vehicles or the market penetration

rate of cars using Dedicated Short Range

Communication (DSRC) technology.

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C. Regular Traffic Regime

For both sparse and dense traffic scenarios

previously considered, a vehicle in a dense

network is likely to observe a dense local

topology while vehicles in a sparse networkare likely to have zero or only a few neighbors

or observe a sparse local topology.

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3. Distributed Vehicular Broadcast

(DV-CAST) protocol

A. Design Goal

B. Design Principle C. DV-CAST Protocol

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A .Design Goal

A broadcast protocol for vehicular ad hoc

wireless networks should be reliable, robust,

and bandwidth efficient.

More specifically, the protocol should be able

to distribute broadcast information to all

intended recipients of the message.

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B. Design Principle

We propose to use a per-hop routing based

approach which uses only local connectivity

information (1-hop neighbor topology) to

make a routing decision.

The motivation for using local connectivity in

the broadcast protocol design is to ensure the

maximum reachability of the broadcastmessage.

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C. DV-CAST Protocol

We propose a new Distributed Vehicular

Broadcast protocol known as the DV-CAST

protocol that is entirely based on the local

information established by each node (car) viathe use of periodic hello messages.

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1) Routing Parameters: The most importantparameters for DV-CAST protocol are the local

topology information and the Region ofInterest.

In particular, each vehicle should be able to

(i) determine whether it is the intendedrecipient of the message that is moving in thesame direction as the source.

(ii) determine whether it is the last vehicle in the

group/cluster.

(iii) determine whether it is connected to atleast one vehicle in the opposite direction.

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These three parameters are denoted in this

paper as Destination Flag (DFlg), Message

Direction Connectivity (MDC), and Opposite

Direction Connectivity (ODC), respectively.

2) Routing Rules: In order to handle the

broadcast message properly, we propose that

each vehicle follows two basic routing rules:

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i) If DFlg is set to 1, vehicle should ignore any

duplicate broadcast or follow the diagram in

Figure 5 if the message is received for the first

time.

ii) If DFlg is set to 0, vehicle is a relay node and

should follow the routing diagram.

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Decision Tree for DV-CAST Protocol (ODN = Opposite Direction Neighbor).

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Case I: Well-Connected Neighborhood

A vehicle is said to be in well-connected

neighborhood if it has at least one neighbor in

the message forwarding direction (MDC = 1).

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According to Figure 6, each vehicle in Group 1,

except forA which is the last vehicle in the

cluster (MDC = 0), upon receiving the

broadcast message from S, will have thefollowing flags .

Vehicles in Group 3 except for B will also have

similar flags, i.e., .

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Case II: Sparsely-Connected

Neighborhood

A vehicle is operating in a sparse traffic regime

if it is the last one in a cluster.

Furthermore, a vehicle in this regime is said to

be in a sparsely-connected neighborhood if

there is at least one neighbor in the opposite

direction as in the case of vehiclesA and B in

Figure 7.

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The parameters for these

vehicle should be set to .

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Case III: Totally Disconnected

Neighborhood

A vehicle, operating in a sparse traffic regime,

is said to be in a totally disconnected

neighborhood if it has no neighbor in the

message forwarding direction and is notconnected to anybody in the opposite

direction, i.e., MDC = ODC = 0.

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4. Conclusions

we have proposed a new Distributed VehicularBroadcasting protocol (DV-CAST) design forsafety and transport efficiency applications in

VANET.

The proposed DV-CAST protocol is fully

distributed and relies on the local informationprovided by one-hop neighbors via periodichello messages.

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END