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 Yu-Ta Chen 2006 Advanced Wireless Network

2. C S A D X B E Basic Idea • Route discovery using flooding algorithm:

3. Basic Idea (cont.) • Location information • Minimize the search zone • Reduce the number of routing messages • Speed and direction information • More minimization of the search zone • Increases the probability to find a node

4. 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

5. Definitions • Expected zone • S knows the location of D at time t0 • Current time is t1 • The location of D at t1 is the expected zone

6. Direction information: moving toward north No direction information Expected Zone

7. Definitions (cont.) • Request zone • S defines a request zone for the route request • The request zone includes expected zone • The route request messages only flood in request zone • If S can not find a route within the timeout interval, create a expanded request zone

8. Request Zone

9. 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.

10. A (Xs, Yd+R) B (Xd+R, Yd+R) Expected zone R Request zone D (Xd, Yd) J (Xj, Yj) I (Xi, Yi) D (Xd+R, Ys) S (Xs, Ys) Network Space Source node outside the expected zone LAR Scheme 1 (example)

11. A (Xd-R, Yd+R) B (Xd+R, Yd+R) Expected zone S (Xs, Ys) R (Xd, Yd) D Request zone D (Xd+R, Yd-R) C (Xd-R, Yd-R) Network Space Source node within the expected zone LAR Scheme 1 (example)

12. 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 DISTs 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

13. D (Xd, Yd) DISTs DISTn DISTi N DISTk I K S (Xs, Ys) Network Space Parameter δ= 0 LAR Scheme 2 (example)

14. 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

15. Different average speed of nodes Percentage of Improvement # of Routing packets per Data packet Simulation Result

16. Different transmission range of nodes # of Routing packets per Data packet # of Routing packets per Data packet Simulation Result (cont.)

17. Different number of nodes in network # of Routing packets per Data packet # of Routing packets per Data packet Simulation Result (cont.)

18. Different location error Percentage of Improvement # of Routing packets per Data packet Simulation Result (cont.) Location Error (units) Location Error (units)

19. 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

20. Expected Zone D Original Request Zone S Alternative Request Zone Variations and Optimizations • Alternative definition of request zone in LAR scheme 1

21. 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 Adapted Request Zone as per node I D J Adapted Request Zone as per node J Initial Request Zone I S

22. Variations and Optimizations (cont.) • Adaptation of request zone • Even 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 DISTs DISTi I S

23. Variations and Optimizations (cont.) • Local search • Allow any intermediate node I detecting route error to initiate a route discovery • Node I uses a request zone based on its own location information for node D D D I I S S Request Zone determined by S Request Zone determined by I

24. Conclusion • Location information significantly lower routing overhead • Various optimizations can be done to adjust LAR to a certain network