Location-Aided Routing (LAR) in Mobile Ad Hoc Networks

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Location-Aided Routing (LAR) in Mobile Ad Hoc
Networks

• Young-Bae Ko and Nitin H. Vaidya
• Recipient of the MOBICOM'98 Best Student Paper
  Award

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Problem
D
t0
t1
C
C
C
A
X
S
D
X
S
D
X
S
B
E
3
Route Discovery Using Flooding
route request
C
route reply
A
X
S
D
B
E
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Location-Aided Routing

• Main Idea
• Using location information to reduce the number
  of nodes to whom route request is propagated.
• Location-aided route discovery based on limited
  flooding

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Location Information

• Consider a node S that needs to find a route to
  node D.
• Assumption
• each host in the ad hoc network knows its current
  location precisely (location error considered in
  one of their simulations)
• node S knows that node D was at location L at
  time t0, and that the current time is t1
• Location services in ad hoc networks, refer to
• A survey on position-based routing in mobile ad
  hoc networks, M. Mauve, J. Widmer, and H.
  Hartenstein, IEEE Network, Vol. 15 No. 6,  2001.

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Expected Zone
expected zone of D ---- the region that node S
expects to contain node D at time t1, only an
estimate made by node S
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Request Zone

• LARs limited flooding
• A node forwards a route request only if it
  belongs to the request zone
• The request zone should include
• expected zone
• other regions around the expected zone
• No guarantee that a path can be found consisting
  only of the hosts in a chosen request zone.
• timeout
• expanded request zone

• Trade-off between
• latency of route determination
• the message overhead

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Membership of Request Zone

• How a node determine if it is in the request zone
  for a particular route request

• LAR scheme 1
• LAR scheme 2

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LAR Scheme 1
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LAR Scheme 2
S knows the location (Xd, Yd) of node D at time
t0 Node S calculates its distance from location
(Xd, Yd) DISTs
Node I receives the route request, calculates its
distance from location (Xd, Yd) DISTi For some
parameter d, If DISTs d DISTi, node I
replaces DISKs by DISKi and forwards the request
to its neighbors otherwise discards the route
request
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Error in Location Estimate

• Let e denote the maximum error in the coordinates
  estimated by a node.
• Modified LAR scheme 1

ev(t1-t0)
Expected Zone
D (Xd, Yd)
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Evaluation

• Comparing
• Flooding
• LAR scheme 1
• LAR scheme 2
• Study Cases on Varying
• number of nodes in the network
• 15, 30, 50 nodes
• transmission range of each node
• 200, 300, 400, or 500 units
• moving speed
• consider average speed (v) in range 1.5 to 32.5
  units/sec

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Definition of Evaluation Metric

• DP data packets
• data packets received by the destination
• RP routing packets
• routing related packets (i.e., route request,
  route reply and route error) received by various
  nodes
• Routing packets per Data packet

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Varying the Average Speed
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Varying the Transmission Range
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Varying the Number of Nodes
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Routing Packets per Route Discovery
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Impact of Location Error (I)
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Impact of Location Error (II)
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Variations and Optimizations

• Alternative Definitions of Request Zone
• increasing the request zone gradually?
• Adaptation of Request Zone
• Propagation of Location and Speed Information
• Local Search

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• More Recent Work on Forwarding Strategy Work on
  Location Service
• see A survey on position-based routing in mobile
  ad hoc networks, M. Mauve, J. Widmer, and H.
  Hartenstein, IEEE Network, Vol. 15 No. 6,  2001.