Connectivity Aware Routing for Vehicular Ad Hoc Networks

1
Connectivity Aware Routing for Vehicular Ad Hoc
Networks

• Qing Yang, Alvin Lim, Prathima Agrawal

Auburn University
IEEE Wireless Communications Networking
Conference March 31 April 3, 2008, Las Vegas
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Outline

• Goals
• Basic concepts
• Related works
• Assumptions
• Model of the connectivity
• Validation with VanetMobiSim
• Routing strategy
• Simulations and result analysis
• Conclusions

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Goals

• Achieves routing between two ends

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Basic concepts

• Model the probability of connectivity of each
  road segment
• Find the route with the highest probability of
  connectivity
• Carry-and-forward the packet while facing network
  partitions

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Related Works

• VADD (06Infocom)
• Vehicle-Assisted Data Delivery
• MURU (06MobiQuitous)
• Multi-Hop Routing for Urban Vanet
• GSR (05MC2R)
• Geographic source routing
• GPSR (00MobiCom)

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Assumption

• GPS on each vehicle
• Standard component
• Digital maps 1,2
• Vehicle density
• Vehicle speed
• Traffic light period

1. http//www.mapmechanics/ 2. http//www.yahoo.co
m/
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Model of connectivity

• One lane road segment
• road segment (length is L) is equally divided
  into m cells
• each cell can contain only one node
• communication range is size of n0 cells

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Multiple lanes case

• One lane road segment
• Number of empty cells is m-n
• Multiple lanes road segment
• Number of lanes is n
• Number of empty cells ranges m-n, m-n/n

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Problem formulation

• Problem formulation
• What is the probability that network is connected
• The probability that no gap in networks is larger
  than the communication range
• Random Allocation (RA) theory

1
0
1
1
0
0
1
0
1
1
1
1
2
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Probability of connectivity

• P1 (exists exactly k empty cells)
• P2 (exists more than n0 continuous empty cells)
• Pcon (Probability of connectivity)

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VanetMobiSim

• Feature
• multi-lane roads
• separate directional flows
• traffic signs at intersections
• Intersection management
• Lane changing
• VanetMobiSim3 mobility patterns have been
  validated against TSIS-CORSIM
• a well known and validated traffic generator

3. http//vanet.eurecom.fr
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Validation of connectivity model

• Length of road
• 1000m, 1800m
• Traffic light period
• 60sec., 120sec.
• Average velocity
• 7.5m/s, 10m/s

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Result of validation

• 1000m, 7.5m/s and 60sec

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Result of validation (cont)

• 1800m, 10m/s and 120sec

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Probability of connectivity of route
p3
p8
p1
p11
p6
p4
p9
p1p4p7p12Max?
p2
p7
p12
p5
p10

• Pi probability of connectivity of road segment i
• Pcon probability of connectivity of selected
  route (path)
• Defined as ?Pi

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Computation of Pr

• Define of Pr
• sequence of road segments from source to
  destination
• Modified Dijkstra Algorithm
• Final goal maximize the probability of whole
  path
• Each step add one more edge, the probability of
  new path decrease
• Can be computed
• Centralized
• Distributed

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Computation of Pr (cont)

• Centralized
• Path Pr was computed only by source node
• Size of packet header is proportionate to hop
  number
• Distributed
• Every node who received packet computes Pr
• More processing on vehicles

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Routing strategy

• Compute Pr
• Find hops on road segment along Pr
• Every node beacons its current position
• Predict neighbors position while choosing next
  hop
• Carry and forward
• Buffered packet if no available next hop
• Send buffered packet when new next hop is in range

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Carry and forward strategy

• Buffer packets which cannot be forwarded
• Send out buffered packet if new next hop is
  available
• Good for VANET
• Lots of holes in VANET
• On path Pr, higher probability of obtaining a new
  next hop
• Big buffer is feasible in cars

Wisitpongphan, N. Bai, F. Mudalige, P. Tonguz,
O. K., "On the Routing Problem in Disconnected
Vehicular Ad-hoc Networks," INFOCOM 2007. 26th
IEEE International Conference on Computer
Communications. IEEE , vol., no., pp.2291-2295,
May 2007
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Simulation

• Nodes movement
• VanetMobiSim
• Map
• TIGER/LINE
• Real map from Tennessee
• Network simulation
• Ns2 setup
• Result analysis

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Map information

• TIGER4
• Topologically Integrated Geographic Encoding and
  Referencing
• A format used by the United States Census Bureau
  to describe land attributes
• Roads, buildings, rivers, and lakes
• Can be read by Tivec5

4. http//www.census.gov/geo/www/tiger/ 5.
http//www.triusinc.com/latest.htm
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Map in simulation

• Centered at
• Long -84877562
• Lat 35162102
• Size
• Width 2000m
• Length 2000m

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Ns2 setup

• Simulation Area 2000m2000m
• Number of nodes 100, 200
• Communication range 250m
• Packet size 512 Byte
• CBR rate 0.1 1packet/sec.
• Random selected source and fixed destination
• Buffer size 64kBytes
• Beacon interval 1.0 sec.
• Velocity 15 35 MPH

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Data delivery ratio (100nodes)
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Data delivery ratio (200nodes)
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Networking delay (100nodes)
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Networking delay (200nodes)
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Throughput
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Conclusions

• Connectivity issue is very important in VANET
• CAR performs well and is independent on the
  network density
• Perimeter mode of GPSR suffers in frequently
  disconnected networks

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Questions and comments

• Thanks!