1. 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. 2 Basic Idea Route discovery using flooding algorithm: C D B S E A X

3. 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. 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. 5 Definitions Expected zone S knows the location of D at time t 0 Current time is t 1 The location of D at t 1 is the expected zone

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

7. 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. 8 Request Zone

9. 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(t 0 ) 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. 10 LAR Scheme 1 (example) Network Space Expected zone A (X s, Y d +R) (X d, Y d ) Request zone B (X d +R, Y d +R) S (X s, Y s ) D (X d +R, Y s ) R Source node outside the expected zone I (X i, Y i )J (X j, Y j ) D

11. 11 LAR Scheme 1 (example) Network Space Expected zone A (X d -R, Y d +R) (X d, Y d ) S (X s, Y s ) Request zone B (X d +R, Y d +R) C (X d -R, Y d -R) D (X d +R, Y d -R) R Source node within the expected zone D

12. 12 LAR Scheme 2 The distance between S and D is DIST s S includes DIST s and (X d, Y d ) in route request message When node I receives route request Calculates its distance to D (DIST i ) If DIST s +δ  DIST i then forwards the request and replace DIST s by DIST i 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. 13 LAR Scheme 2 (example) Network Space D (X d, Y d ) S (X s, Y s ) N I K DIST n DIST s DIST i DIST k Parameter δ= 0

14. 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(t 1 – t 0 ), e is location error In LAR scheme 2, there is no modification

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

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

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

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

19. 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. 20 Variations and Optimizations Alternative definition of request zone in LAR scheme 1 D Expected Zone Alternative Request Zone Original Request Zone S

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

22. 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 S I DIST s DIST i

23. 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 S I S I D D Request Zone determined by SRequest Zone determined by I

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