# TBD Trajectory-Based Data Forwarding for Light-Traffic Vehicular

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TBD: Trajectory-Based Data Forwarding
for Light-Traffic Vehicular Networks
Jaehoon Jeong, Shuo Gu, Yu Gu, Tian He and David Du
Computer Science and Engineering
University of Minnesota
{jjeong,sguo,yugu,tianhe,du}@cs.umn.edu

June 23rd, 2009     IEEE ICDCS’09, Montreal, Quebec, Canada
Motivation
2

   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)
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 Definition
3

Forwarding Path
Carrier-1’s
Moving
Trajectory
Delay-1
Carrier-2’s
Moving
Delay-1 < Delay-2   Next hop?                Trajectory

Delay-2
Problem Definition
4

Road Network with Unbalanced Traffic Density

Light Traffic Path

Heavy Traffic Path
Delay-1
Forwarding Path
Delay-1 > Delay-2    Next hop?

Delay-2
Heavy Traffic Path
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
 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
6
   Objective
   To compute the expected link delay over a one-way road segment.
   Given the vehicle arrival rate      and the vehicle speed   v,
                                                     v

 How to compute the Forwarding Distance l f ?
Forwarding Distance for Vehicle Arrivals
7

Vehicle nk 1 arrives
at time t k 1 .

dist (n1 , n0 )  R

l f (ForwardingDistance)
Forwarding Distance over Time
Forwarding Distance

dist (t1 , t0 )  R / v
Forwarding Distance for Vehicle Arrivals
8
Forwarding Distance

dist (t1 , t0 )  R / v

T0  dist (t1 , t0 )  R / v
Forwarding Distance
k
l f  v  Th
h1
whereTh  R / v
9
 Given  the vehicle arrival rate  and the vehicle speed v,
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 closer
to the Simulation result
E2E Delay Model
10

   Objective
 Tocompute 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
11
   D1,2 :Expected Delivery Delay (EDD)
at Intersection 1
 Where   a packet is sent towards Intersection 2.

D1,2  d1,2  P2,1D2,1  P2,3 D2,3  P2,7 D2,7

Dij  dij  E[delivery delay at j by forwardingor carry]
Expected Delivery Delay
12
   Average Forwarding Probability ( Pij )
 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 P2,3 ?
Pij' : forwardingprobability
Moving Direction-1       that the packet carrier at i can
Moving Direction-3    Moving Direction-2
forward its packet to another
carrier moving towards j.
Packet Delivery
Direction
Expected Delivery Delay
13
    Limitation of EDD at Intersection
 The vehicle trajectory is not used to     They are very close to
compute the EDD.                               each other.
 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.
Expected Delivery Delay for
Vehicle Trajectory (TBD Model)
14

   Vehicle Trajectory: 1  2  3

 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.
Expected Delivery Delay for
Vehicle Trajectory
15

D  P ', 2 D1, 2  P ',6 D1,6
1              1

 P c2 (C1, 2  P2' ,1D2,1  P2' ,3 D2,3  P2' ,7 D2,7 )
1,

 P c2 P2c,3 (C1,3  P3', 2 D3, 2  P3', 4 D3, 4  P3',8 D3,8 )
1,
'
where Pi,j : forwarding probability for (i, j),
Picj : carry probability for (i, j), and
,

C1,k : carry delay for path 1  k.
Forwarding Protocol
16

   TBD Forwarding Rule
 Within a connected component, packets are forwarded
to the vehicle with a minimum EDD.
Performance Evaluation
17

   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
18

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

As the traffic density increases, two schemes are converged.
Conclusion
19

   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.
Future Work: Reverse Data Forwarding
for Internet Access
20

Target Point
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.

 The reason of the
target missing?
 Inaccurate estimation
of the vehicle arrival
Target Point
 How to provide this
Target                       reverse forwarding?
Missing!

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