LAR uses location information to reduce routing overhead in mobile ad hoc networks. It minimizes the search zone for route discovery by using the expected zone based on the destination's last known location and speed. The route request is restricted to this request zone to limit flooding. Variations include alternative definitions of the request zone and allowing intermediate nodes to update the zone based on more recent location data or initiate local repair if a route breaks. Simulation results show LAR performs better than flooding in networks with varying node speeds, transmission ranges, densities, and location errors.

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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