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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