Stephen S. Yau, Wei Gao, and Dazhi Huang
Dept. of Computer Science and Engineering
Arizona State University
Nov. 29, 2006 GLOBECOM 2006
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Introduction
Overview of our approach
Three components of our approach
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Node Location Service based on Local
Coordinates
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Directional Route Request
Refinement on Intermediate Nodes
Simulation Results
Conclusions and Future Work
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Topology-based route discovery protocols
(AODV [3], DSR [4]) flood route requests, and hence cause
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Large route redundancy
Large overhead of route discovery
Challenge: How to reduce route redundancy and overhead of route discovery?
Some extra network information must be added to help
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Physical Locations of Nodes: Global/Localized
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 Purpose: to restrict the influencing range of route requests
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Greedy packet forwarding (GPSR [7], TBF [8])
Restricted directional flooding (DREAM [9], LAR [10])
 A prerequisite of location-based route discovery protocols is a node location service
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Use GPS receivers
GPS-free localization: RSSI [12], ToA/TDoA [13]
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Location-based Directional Route
Discovery (LDRD)
 LDRD consists of three components:
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A Node Location Service based on Local
Coordinates (NLS-LC)
An algorithm used by the route requesters to generate directional route requests
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A directional route request can only be processed and forwarded in allowed geographical areas
Its influencing range is only part of the entire network
An algorithm used by intermediate nodes to refine the directional route request to progressively reduce its influencing range
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 LDRD greatly reduces the route redundancy and overhead of route discovery by using and progressively refining directional route requests
 LDRD exploits a GPS-free node location service
 LDRD is insensitive to the accuracy of node locations
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Node Location Service based on Local
Coordinates (NLS-LC)
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Each node updates the locations of its neighbors periodically using physical measurements
Each node broadcasts updated location information to its neighbors.
Each node maintains a location table
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All the node coordinates are localized, i.e., are relative to the local coordinate system of table owner
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The location record of a node:
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origintime indicates the generation time of the localized coordinates
elapsetime is the elapsed time since origintime
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Node Location Service based on Local
Coordinates (NLS-LC) (cont.)
 An example:
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We consider the following fragment of network topology
A ↔ B ↔ C
B gets location of A by physical measurement at time t
1
, and broadcasts this information to C at t
2
C receives the information at time t
3
Records of A in B’s and C’s location tables:
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 The direction of forwarding a route request is determined by a destination area DST, and a respondable area RESP.
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DST:
R = (d max
+ elapsetime)

V max
DST: ( x – x d
) 2 + ( y – y d
) 2 = R 2
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RESP: k
1

2 x y d d
 
2( x d
2 
R
2
)

= 4x d
2 y d
2 k
2
– 4(x d
2

2 x y d d
 
2( x d
2 
R
2
)
– R 2 ) (y d
2 – R 2 )
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 LDRD is insensitive to the accuracy of node locations

( x y d d
)

((1
 
) x d
, (1
 
) y d
)
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The probability of missing the route destination is O

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Every receiver checks whether it is within the defined
DST or RESP
The intermediate node refines the route request according to its location information of the route destination
The intermediate node nearer to the route destination has more accurate location information of the route destination
N s original tangent lines
N i new tangent lines
D
D’
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Tradeoff on Frequency of Location
Updates
 The frequency of sending location updates needs to be selected carefully:
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Too large: LDRD is as bad as flooding-based approaches
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Too small: The allowed areas are too narrow to contain a qualified forwarder
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Decision making: user’s performance requirements
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50 nodes are randomly distributed in a 1000m 2 square area with 802.11 MAC
Mobility settings:
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V avg
: 2m/s – 10m/s
Network connectivity settings:
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Transmission range: 150m - 400m
Network traffic settings:
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Number of CBR traffic flows: 1 – 5
Frequency of Location Updates
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SIZE/10/V avg
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 LDRD can greatly reduce the route redundancy and overhead of route discovery
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 LDRD can maintain performance of route discovery without great degradation
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LDRD greatly reduces the route redundancy and overhead of route discovery.
LDRD is highly adaptable to the dynamic nature of
MANETs
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It exploits a GPS-free node location service
It is insensitive to the accuracy of node locations
Future work:
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Analyze the impact of location errors and the parameters used in NLS-LC
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Incorporate service discovery functionality with route discovery to achieve better efficiency
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Nov. 29, 2006
GLOBECOM 2006
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