Location-Aided Routing (LAR) in Mobile Ad Hoc Networks Young-Bae Ko and Nitin H. Vaidya Recipient of the MOBICOM'98 Best Student Paper Award

Problem A B E C XSD D C XSD C S D C XS t0t0 t1t1

Route Discovery Using Flooding A B C E XSD 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 t 0, and that the current time is t 1  Location services in ad hoc networks, refer to A survey on position-based routing in mobile ad hoc networks, M. Mauve, J. Widmer, and H. Hartenstein, IEEE Network, Vol. 15 No. 6, A survey on position-based routing in mobile ad hoc networks

Expected Zone expected zone of D ---- the region that node S expects to contain node D at time t 1, 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 (X d, Y d ) of node D at time t 0 Node S calculates its distance from location (X d, Y d ): DIST s Node I receives the route request, calculates its distance from location (X d, Y d ): DIST i For some parameter δ, If DIST s + δ ≥ DIST i, node I replaces DISK s by DISK i 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 (X d, Y d ) e+v(t 1 -t 0 ) 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.A survey on position-based routing in mobile ad hoc networks