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.
13
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.
20
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?