Location-Aided Routing (LAR)
in Mobile Ad Hoc Networks
Young-Bae Ko and Nitin H. Vaidya
Yu-Ta Chen
2006 Advanced Wireless Network
1
Basic Idea

Route discovery using flooding algorithm:
C
A
S
D
X
B
E
2
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

3
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
4
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

5
Expected Zone
No direction information
Direction information:
moving toward north
6
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

7
Request Zone
8
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.
9
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
10
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
11
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
12
LAR Scheme 2 (example)
D (Xd, Yd)
DISTs
DISTn
DISTi
N
DISTk
I
K
S (Xs, Ys)
Network Space
Parameter δ= 0
13
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
14
Percentage of Improvement
# of Routing packets per Data packet
Simulation Result
Different average speed of nodes
15
# of Routing packets per Data packet
# of Routing packets per Data packet
Simulation Result (cont.)
Different transmission range of nodes
16
# of Routing packets per Data packet
# of Routing packets per Data packet
Simulation Result (cont.)
Different number of nodes in network
17
Simulation Result (cont.)
Percentage of Improvement
# of Routing packets per Data packet
Different location error
Location Error (units)
Location Error (units)
18
Simulation Result (cont.)

LAR perform better in various speed


LAR perform better in various transmission
range


Especially in high speed
Exception: very low transmission rate
LAR perform better in various amount of
nodes

Exception: small amount of nodes
19
Variations and Optimizations

Alternative definition of request zone in
LAR scheme 1
Expected Zone
D
Original Request Zone
S
Alternative Request Zone
20
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
Initial Request Zone
S
I
Adapted Request Zone
as per node J
21
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
I
S
DISTi
22
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
23
Conclusion

Location information significantly lower
routing overhead

Various optimizations can be done to
adjust LAR to a certain network
24