1

TBD: Trajectory-Based Data Forwardingfor Light-Traffic Vehicular Networks

IEEE ICDCS’09, Montreal, Quebec, Canada

Jaehoon Jeong, Shuo Gu, Yu Gu, Tian He and David DuComputer Science and Engineering

University of Minnesota{jjeong,sguo,yugu,tianhe,du}@cs.umn.edu

June 23rd, 2009

Motivation2

The vehicular networking is getting a hot research topic. Internet Access, Driving Safety, Data Dissemination, etc.

The environments for the vehicular networks Every vehicle has a DSRC device for wireless

communication. Every vehicle has a GPS-based navigation system for

driving information. The Internet Access Points (APs)

are sparsely deployed in road networks.

The objective in this paper The vehicles can deliver their packets to APs through the

multi-hop forwarding with the help of other vehicles.

Problem Definition3

Next hop?

Carrier-1’sMoving

Trajectory

Carrier-2’sMoving

Trajectory

Light-Traffic Road Network

Forwarding Path

Delay-1

Delay-2

Delay-1 < Delay-2

Problem Definition4

Road Network with Unbalanced Traffic Density

Light Traffic Path

Heavy Traffic Path

Heavy T

raffic PathNext hop?

Forwarding Path

Delay-1

Delay-2

Delay-1 > Delay-2

Contribution and Challenges

5

Contribution Data forwarding based on Vehicle Trajectory

With vehicle trajectory, TBD outperforms the existing scheme (VADD, Infocom’06) only using vehicular traffic density.

Challenges A more accurate link delay model than VADD’s

Mathematical model for the link delay

End-to-End delay model based on vehicle trajectory E2E delay modeling based on (i) vehicular traffic

density and (ii) individual vehicle trajectory

v

Link Delay Model6

Objective To compute the expected link delay over a one-way road

segment.

Road Segment for Link Delay Model Given the vehicle arrival rate and the vehicle speed ,

How to compute the Forwarding Distance ?

fl

v

Forwarding Distance for Vehicle Arrivals

7

Forwarding Distance over Time Forwarding

Distance

)Distance Forwarding(fl

Rnndist ),( 01

Vehicle arrives

at time .

1kn1kt

vRttdist /),( 01

Forwarding Distance for Vehicle Arrivals

8

Forwarding Distance

vRT

Tvl

h

k

hhf

/ where1

vRttdist /),( 01

Forwarding Distance

vRttdistT /),( 010

Link Delay Model Comparison between VADD and TBD9

VADD Link Delay Model Given the vehicle arrival rate and the vehicle speed ,

the forwarding distance is the sum of the network components.

This model is inaccurate since it misses the following fact Only the first network component can be used for data

forwarding.

Performance Comparison For Average Forwarding

Distance, TBD is much closerto the Simulation resultthan VADD.

v

E2E Delay Model10

Objective To compute the expected end-to-end delay

from a Vehicle to an Internet Access Point (AP).

Road Network Graph for Data Forwarding Given a vehicle’s

trajectory,how to compute the E2E delay? Since node1 and node2 have different trajectories, their E2E delays are different.

:Expected Delivery Delay (EDD)at Intersection 1 Where a packet is sent towards Intersection 2.

11

Expected Delivery Delayat Intersection (VADD Model)

2,1D

7,27,23,23,21,21,22,12,1 DPDPDPdD

Link Delay for

Road Segment

(1,2)]carryor forwardingby at delay delivery [ jEdD ijij

Expected Delivery Delayat Intersection (VADD Model)

12

Average Forwarding Probability ( ) The probability that a packet at intersection

i can be delivered towards neighboring intersection j.

We consider all the possible moving directions of the current packet carrier at intersection i.

How to compute ?

ijP

3,2P

Packet Delivery Direction

Moving Direction-3

Moving Direction-1

Moving Direction-2 j. towardsmovingcarrier

another packet to its forward

can iat carrier packet the that

y probabilit forwarding :'ijP

Limitation of EDD at Intersection The vehicle trajectory is not used to

compute the EDD. Node1 and Node2 have the same EDD regardless of

their different trajectories. Thus, we cannot determine which node is a better

next carrier.

How to involve the vehicle trajectory into EDD computation? The main idea is to divide the delivery process

recursively into two steps:1. The packet forwarding process at the current carrier. 2. The packet carry process by the current carrier.

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Expected Delivery Delayat Intersection (VADD Model)

They are very close to each other.

Expected Delivery Delay for Vehicle Trajectory (TBD Model)

14

Vehicle Trajectory:

Case 1: The packet is forwarded at intersection 1. Case 2: The packet is carried to intersection 2 and

is forwarded at intersection 2. Case 3: The packet is carried to intersection 3 and

is forwarded at intersection 3.

321

15

)(

)(

8,3'8,34,3

'4,32,3

'2,33,13,22,1

7,2'

7,23,2'

3,21,2'1,22,12,1

6,1'6,12,1

'2,1

DPDPDPCPP

DPDPDPCP

DPDPD

cc

c

k.1path for delay carry :

and j),(i,for y probabilitcarry :

j),(i,for y probabilit forwarding : where

,1

,

k

cji

'i,j

C

P

P

Expected Delivery Delay for Vehicle Trajectory

Forwarding Protocol16

TBD Forwarding Rule Within a connected component, packets

are forwarded to the vehicle with a minimum EDD.

Performance Evaluation17

Evaluation Setting Performance Metric: Average Delivery Delay Parameters: (i) Vehicular traffic density, (ii)

Vehicle speed, and (iii) Vehicle speed deviation.

Simulation Environments 36-intersection road network (4.2 miles X 3.7

miles) Vehicle mobility model: Random-Way Point Vehicle speed distribution: N(40,5) MPH Communication range: 200 meters Time-To-Live (TTL): infinite (i.e., no timeout)

Average Delivery Delay Comparison between TBD and VADD18

TBD outperforms VADD under the light traffic, such 20~50 vehicles.

As the traffic density increases, two schemes are converged.

Conclusion19

In this talk, the data forwarding scheme called TBD is introduced based on the vehicle trajectory: Data Forwarding from Vehicle to AP.

Also, the link delay model is introduced for TBD data forwarding scheme: This link delay model can be used for other VANET

routing or forwarding schemes.

As future work, the multiple-hop Internet access will be investigated in the vehicular networks: Vehicle trajectory will be used for the data

forwarding for the Internet access.

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Target Point

Future Work: Reverse Data Forwardingfor Internet Access

Challenge in Reverse Data Forwarding

21

As packet destination, the vehicle is moving, not static. The packet from AP needs to be delivered to

the vehicle, considering the rendezvous point along the vehicle trajectory.

Target Point

Target Missin

g!

The reason of the target missing? Inaccurate estimation of the

vehicle arrival How to

provide this reverse

forwarding?