A Cross Layered MAC and Clustering Scheme for Efficient Broadcast in VANETs

A Cross Layered MAC and Clustering Scheme for Efficient Broadcast in

VANETs

Luciano Bononi, Marco Di FeliceDepartment of Computer Science, University of B

ologna

IEEE MASS 2007

Outline

• Introduction

• System Model and Assumptions

• Cross-layered Protocol Scheme– Backbone Creation and Maintenance

– MAC Layer Support

• Performance evaluation

• Conclusion

Introduction

Introduction

• RVC (Road-vehicle Communication)

Introduction

• IVC (Inter-vehicle Communication)

Introduction

• Road-network coverage by wireless communication infrastructures is costly.• Road-safety applications based on IVC strictly rely on the assumption of

– Cooperation among vehicles

– Distributed coordination among vehicles

A

C

B

Introduction - Goal

• Design an algorithm for efficient broadcast of alert messag

es in VANETs.• Overhead reduction

• Reliability

System Model and Assumptions

In a multi-lane highway scenario Vehicles travelling in both directions Vehicles to be equipped with

Sensing capability Wireless communication Computation capability Storage capability GPS

Backbone

Normal Vehicle (NV) State

Backbone Member (BM) State

Backbone

Backbone

• Each chain member has at most two neighbors

AB

prev_hop

C

next_hop

Message Message

Direction

Backbone Creation Process

BEACON message：

<ID, (x,y), R, speed, dir, horizon>

BA

D C

Direction

Residual Time (RT)

v

BAdistRvsignBART

),())](,0[max(

),(

R： the transmission range of the sender vehicle Δv = vB - vA is the relative speed between nodes B and A dist(A,B)： the current estimated distance

1-

1)( vsign , if Δv > 0

, otherwise

Assume Vehicle A is following Vehicle B B

A

Residual Time (RT)

v

BAdistRvsignBART

),())](,0[max(

),(

B

A

= 1

R

dist(A, B)

v

BAdistR

),(

Direction

dist(A, B)

Residual Time (RT)

B

A

v

BAdistRvsignBART

),())](,0[max(

),(

= -1

v

BAdist

),(

Direction

Backbone Creation Process

BA

D C

Vehicle ID： BBackbone State： NVTime Residual： 2 sec

Vehicle ID： DBackbone State： NVTime Residual： 4 sec

Vehicle ID： CBackbone State： NVTime Residual： 5 sec

Direction

Fit Factor (FF)

R

REFRBBvBAdistAFF

_),()(

dist(A, B)B

A

Backbone Refresh Interval

Direction

Backbone Creation Process

BA

D C

Vehicle ID： DBackbone State： NVTime Residual： 4 secFit： 0.4

Vehicle ID： CBackbone State： NVTime Residual： 5 secFit： 0.9

Vehicle C sends a CANDIDATURE message to Vehicle AVehicle A sends an ACK_WINNER message to Vehicle C

Direction

Backbone Creation Process

BA

Vehicle A receives a BEACON message from Vehicle BVehicle A replies immediately with a CANDIDATURE message to Vehicle BVehicle B sends an ACK_WINNER message to Vehicle A

Direction

ACK

Fast Multi-Hop Forwarding (FMF)

ACK

Direction

ACK

Basic MAC Scheme

A

B

Direction

Performance evaluation

Simulation Parameters

Average Number of Retransmissions

Average Percentage of Collisions

MAC End-to-end Delay, 600 Vehicles

MAC Delay Percentiles, 200 Vehicles

MAC Delay Percentiles, 600 Vehicles

Conclusion

• The performance of the DBA-MAC has been compared with other schemes, by showing general advantages in – Performance

– Reliability– overhead reduction.