1. Location-Aided Routing (LAR)
in Mobile Ad Hoc Networks
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2. Basic Idea
 Route discovery using flooding algorithm:
C
S
A D
X
B
E
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3. Basic Idea (cont.)
 Location information
 Minimize the search zone
 Reduce the number of routing messages
 Speed and direction information
 More minimization of the search zone
 Increases the probability to find a node
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4. 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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5. Definitions
 Expected zone
 S 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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6. Expected Zone
No direction information Direction information:
moving toward north
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7. Definitions (cont.)
 Request zone
 S defines a request zone for the route
request
 The request zone includes expected zone
 The 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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8. Request Zone
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9. 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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10. LAR Scheme 1 (example)
A (Xs, Yd+R) B (Xd+R, Yd+R)
Expected zone
R
Request zone
D (Xd, Yd)
J (Xj, Yj) I (Xi, Yi)
D (Xd+R, Ys)
S (Xs, Ys)
Network Space
Source node outside the expected zone
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11. LAR Scheme 1 (example)
A (Xd-R, Yd+R) B (Xd+R, Yd+R)
Expected zone
S (Xs, Ys)
R
D (Xd, Yd)
Request zone
C (Xd-R, Yd-R) D (Xd+R, Yd-R)
Network Space
Source node within the expected zone
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12. 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
DISTs 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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13. LAR Scheme 2 (example)
D (Xd, Yd)
DISTs
DISTn
DISTi
N
DISTk
I
K
S (Xs, Ys)
Network Space
Parameter δ= 0
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14. 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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15. # of Routing packets per Data packet
Simulation Result
Percentage of Improvement
Different average speed of nodes
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16. # of Routing packets per Data packet
# of Routing packets per Data packet
Simulation Result (cont.)
Different transmission range of nodes
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17. # of Routing packets per Data packet
# of Routing packets per Data packet
Simulation Result (cont.)
Different number of nodes in network
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18. Simulation Result (cont.)
Different location error
# of Routing packets per Data packet
Percentage of Improvement
Location Error (units) Location Error (units)
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19. 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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20. Variations and Optimizations
 Alternative definition of request zone in
LAR scheme 1
Expected Zone
D
Original Request Zone
S
Alternative Request Zone
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21. 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
Adapted Request Zone
as per node I D
J
Adapted Request Zone
Initial Request Zone
I as per node J
S 21

22. Variations and Optimizations (cont.)
 Adaptation of request zone
 Even 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
DISTs
DISTi
I
S
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23. Variations and Optimizations (cont.)
 Local search
 Allow any intermediate node I detecting
route error to initiate a route discovery
 Node I uses a request zone based on its
own location information for node D
D D
I I
S S
Request Zone determined by S Request Zone determined by I
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24. Conclusion
 Location information significantly lower
routing overhead
 Various optimizations can be done to
adjust LAR to a certain network
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