Location-Aided Routing (LAR) in Mobile Ad Hoc

Networks

Young-Bae Ko and Nitin H. VaidyaRecipient of the MOBICOM'98 Best Student Paper Award

Problem

A

B

E

C

XS D

D

C

XS D

C

S

D

C

XS

t0t1

Route Discovery Using Flooding

A

B

C

E

XS D

route request

route reply

Location-Aided Routing Main Idea

Using location information to reduce the number of nodes to whom route request is propagated.

Location-aided route discovery based on “limited” flooding

Location Information Consider a node S that needs to find a route to

node D. Assumption:

each host in the ad hoc network knows its current location precisely (location error considered in one of their simulations)

node S knows that node D was at location L at time t0, and that the current time is t1

Location services in ad hoc networks, refer to A survey on position-based routing in mobile ad hoc net

works, M. Mauve, J. Widmer, and H. Hartenstein, IEEE Network, Vol. 15 No. 6,  2001.

Expected Zone

expected zone of D ---- the region that node S expects to contain node D at time t1, only an estimate made by node S

Request Zone LAR’s limited flooding

A node forwards a route request only if it belongs to the request zone

The request zone should include

expected zone other regions around the

expected zone No guarantee that a path

can be found consisting only of the hosts in a chosen request zone.

timeout expanded request zone

Trade-off between latency of route

determination the message overhead

Membership of Request Zone

How a node determine if it is in the request zone for a particular route request

•LAR scheme 1

•LAR scheme 2

LAR Scheme 1

LAR Scheme 2

S knows the location (Xd, Yd) of node D at time t0

Node S calculates its distance from location (Xd, Yd): DISTs

Node I receives the route request, calculates its distance from location (Xd, Yd): DISTi

For some parameter δ, If DISTs + δ ≥ DISTi, node I replaces DISKs by DISKi and forwards the request to its neighbors; otherwise discards the route request

Error in Location Estimate Let e denote the maximum error in the

coordinates estimated by a node. Modified LAR scheme 1

D (Xd, Yd)

e+v(t1-t0) Expected Zone

Evaluation Comparing

Flooding LAR scheme 1 LAR scheme 2

Study Cases on Varying number of nodes in the network

15, 30, 50 nodes transmission range of each node

200, 300, 400, or 500 units moving speed

consider average speed (v) in range 1.5 to 32.5 units/sec

Definition of Evaluation Metric

DP: data packets data packets received by the destination

RP: routing packets routing related packets (i.e., route request,

route reply and route error) received by various nodes

#Routing packets per Data packet

Varying the Average Speed

Varying the Transmission Range

Varying the Number of Nodes

# Routing Packets per Route Discovery

Impact of Location Error (I)

Impact of Location Error (II)

Variations and Optimizations

Alternative Definitions of Request Zone increasing the request zone gradually?

Adaptation of Request Zone Propagation of Location and Speed

Information Local Search

More Recent Work on Forwarding Strategy & Work on Location Service

see A survey on position-based routing in mobile ad hoc networks, M. Mauve, J. Widmer, and H. Hartenstein, IEEE Network, Vol. 15 No. 6,  2001.