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Location-Aided Routing (LAR) in Mobile Ad Hoc Networks
Young-Bae Ko and Nitin H. Vaidya
Yu-Ta Chen
2006 Advanced Wireless Network
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Basic Idea
Route discovery using flooding algorithm:
C
D
B
S
E
A
X
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Basic Idea (cont.)
Location informationMinimize the search zoneReduce the number of routing messages
Speed and direction informationMore minimization of the search zone Increases the probability to find a node
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Basic Idea (cont.)
Each node knows its current location
Using last known location information and average speed for route discovery Limited destination zone – expected zone Restricted flooding – request zone
Route discovery is initiated when Source does not know a route to destination Previous route from source to destination is broken
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Definitions
Expected zoneS knows the location of D at time t0
Current time is t1
The location of D at t1 is the expected zone
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Expected Zone
No direction information Direction information: moving toward north
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Definitions (cont.)
Request zoneS defines a request zone for the route
requestThe request zone includes expected zoneThe route request messages only flood in
request zone If S can not find a route within the timeout
interval, create a expanded request zone
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Request Zone
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LAR Scheme 1
The request zone is the smallest rectangle to include the expected zone and the location of source
S Includes the coordinates of corners and location of D(t0) in routing messages
The node outside the rectangle should not forward route message to neighbors
When D receives the message, it replies a route reply message including its current location and current time
When S receives the route reply message, it records the location of node D.
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LAR Scheme 1 (example)
Network Space
Expected zone
A (Xs, Yd+R)
(Xd, Yd)
Request zone
B (Xd+R, Yd+R)
S (Xs, Ys)D (Xd+R, Ys)
R
Source node outside the expected zone
I (Xi, Yi)J (Xj, Yj)
D
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LAR Scheme 1 (example)
Network Space
Expected zone
A (Xd-R, Yd+R)
(Xd, Yd)
S (Xs, Ys)
Request zone
B (Xd+R, Yd+R)
C (Xd-R, Yd-R) D (Xd+R, Yd-R)
R
Source node within the expected zone
D
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LAR Scheme 2
The distance between S and D is DISTs
S includes DISTs and (Xd, Yd) in route request message
When node I receives route request Calculates its distance to D (DISTi) If DISTs+δ DISTi then forwards the request and replace DIS
Ts by DISTi
Otherwise, node I discards the route request
δ is a parameter for increasing the probability of finding a route or dealing with location error
The request is forwarded closer and closer to destination D
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LAR Scheme 2 (example)
Network Space
D (Xd, Yd)
S (Xs, Ys)
N
IK
DISTn
DISTs
DISTi
DISTk
Parameter δ= 0
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Error in Location Estimate
Impact of location error GPS may include some error With a larger location error, the size of request zone
increases Usually location error contributes to an increase in
routing overhead But routing overhead may decrease with increasing
error, why? In LAR scheme 1, radius of expected zone
= e + v(t1 – t0), e is location error In LAR scheme 2, there is no modification
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Simulation Result
Different average speed of nodes
# of Routing packets per Data packetPercentage of Improvement
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Simulation Result (cont.)
Different transmission range of nodes
# of Routing packets per Data packet # of Routing packets per Data packet
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Simulation Result (cont.)
Different number of nodes in network
# of Routing packets per Data packet # of Routing packets per Data packet
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Simulation Result (cont.)
Different location error
# of Routing packets per Data packetPercentage of Improvement
Location Error (units)
Location Error (units)
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Simulation Result (cont.)
LAR perform better in various speed Especially in high speed
LAR perform better in various transmission range Exception: very low transmission rate
LAR perform better in various amount of nodes Exception: small amount of nodes
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Variations and Optimizations
Alternative definition of request zone in LAR scheme 1
D
Expected Zone
Alternative Request Zone
Original Request Zone
S
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Variations and Optimizations (cont.)
Adaptation of request zone If an intermediate node I holds a more
recent location information of D, it can update the request zone
D
SI
J
Adapted Request Zone as per node J
Adapted Request Zone as per node I
Initial Request Zone
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Variations and Optimizations (cont.)
Adaptation of request zoneEven though LAR scheme 2 does not
explicitly define request zone, the zone that the source node ask can be seen as a circular zone
D
SI
DISTsDISTi
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Variations and Optimizations (cont.)
Local searchAllow any intermediate node I detecting
route error to initiate a route discoveryNode I uses a request zone based on its
own location information for node D
S
IS
I
D D
Request Zone determined by S Request Zone determined by I
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Conclusion
Location information significantly lower routing overhead
Various optimizations can be done to adjust LAR to a certain network