Location-Aided Routing (LAR) in Mobile Ad Hoc Networks

1. 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

2. D C S Problem D t0 t1 C C C A S S S X X X D D B E

3. Route Discovery Using Flooding route request C route reply A S X D B E

4. 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

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

6. 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

7. 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

8. 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

9. LAR Scheme 1

10. 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

11. Error in Location Estimate • Let e denote the maximum error in the coordinates estimated by a node. • Modified LAR scheme 1 e+v(t1-t0) Expected Zone D (Xd, Yd)

12. 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

13. 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

14. Varying the Average Speed

15. Varying the Transmission Range

16. Varying the Number of Nodes

17. # Routing Packets per Route Discovery

18. Impact of Location Error (I)

19. Impact of Location Error (II)

20. 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

21. 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.