LGR: A Novel Location-fault-tolerant Geographic Routing Scheme for Wireless Ad Hoc Network

1. LGR: A Novel Location-fault-tolerant Geographic Routing Scheme for Wireless Ad Hoc Network PRESENTATION PREPARED BY: BABAN MAHMOOD

2. Outline • Introduction • Geographic routing and location inaccuracy problems • Location-fault-tolerant geographic routing • Simulation results • Limitations • Summary.

3. Outline • Introduction • Geographic routing and location inaccuracy problems • Location-fault-tolerant geographic routing • Simulation results • Limitations • Summary

4. Introduction • Geographic routing assumes wireless nodes can acquire location information. • To make forwarding decision, nodes need to know their positions and their one-hop neighbors’ positions. • Source node should know destination’s position. • Location information may not be accurate. • Nodes may move at any moment making it hard to update nodes’ positions in time.

5. Outline • Introduction • Geographic routing and location inaccuracy problems • Location-fault-tolerant geographic routing • Simulation results • Limitations • summary

6. Geographic routing and location inaccuracy problems • Location inaccuracy may result in • Wrong Greedy Decision • Planarization Collapse.

7. Geographic routing and location inaccuracy problems – Wrong Greedy Decision • Greedy Forwarding Strategy • Wrong decision • Packet dropping . • Packet looping.

8. Geographic routing and location inaccuracy problems – Planarization Collapse • In case of dead end or void, recovery is necessary. • An example of face routing protocol is GPSR. • GPSR is graph based scheme. • It should construct a planar graph that does not have a cross link among nodes. (RNG)

9. Geographic routing and location inaccuracy problems – Planarization Collapse • Due to location inaccuracy, possibility of correctly constructing planar graph is small. • In the figure, because of B’s mistakenly reckoned position by A, link between A and C is removed.

10. Geographic routing and location inaccuracy problems – Planarization Collapse • Connection between B and D is created because of incorrect recognition of C’s location. • Too many occurrences of similar phenomena will result in planarization collapse.

11. Outline • Introduction • Geographic routing and location inaccuracy problems • Location-fault-tolerant geographic routing • Simulation results • Limitations • Summary

12. Location-fault-tolerant geographic routing • Combines • position-based clustering with • geographic routing technology together. • Capitalizes on the fixed cluster’s position instead of node’s accurate positions needed in traditional geographic routing.

13. 1- Position based Clustering • The geographic area is divided in to m regular polygons • The edge of the regular polygon is multiple of radio radius R • The polygons’ shapes are hexagons, each is called a cluster.

14. 1-Position based Clustering • The coordinates of the cluster’s center called clusterpositionwhich is used as the ID of the cluster. • Based on its own position, each node knows which cluster it belongs to and gets the cluster position • There is no need to disseminate all the small changes in node positions to the whole network. • As long as node stays in the same cluster, only nodes within this cluster may be updated. • Whenever a node moves to new cluster, it should update its cluster position

15. 1- Position based Clustering (node’s position update description) • Initialization: Notify all nodes of the network center (NetCenterX,NetCenterY) • Algorithm Starts: • The node updates its position (X,Y) depending on localization scheme. • Calculates the number of cluster Cij • Then calculates the new fixed cluster position

16. 2-Geographic routing on Overlay Graph of Cluster Headers • Each cluster selects a Cluster Header (CH) • CH is the closest to the Cluster Center. • CH has lower mobility and more energy. • Every node broadcasts a message to its neighbors. • The message contains distance from Cluster Center to the node. • Each node compares distance metric with its neighbors to see whether it should be a CH.

17. The Routing Process • The routing process is divided into two steps: • Global geographic routing • Local gradient routing.

18. 1- Global Geographic Routing • The packet is transmitted from one cluster to another. • The next cluster is chosen based on its distance to destination cluster. • Distance is found depending on Cluster Positions. • If there is no closer neighbor cluster, then The packet is transmitted to another cluster by right-hand rule.

19. 2- Local Gradient Routing • Transmitting packets between clusters. • CH floods a short tree-building message to its neighbors to set up initial hop count. • The message contains a hop count cost of “zero” and cluster position • Every node in this cluster or its neighbor cluster maintains its minimum hop count to this cluster. • On receiving the first message, a node judges whether the message is coming from its own cluster or its neighbor one by cluster position. • If yes, it sets its hop count value to the message’s hop count value plus 1. • Otherwise, it discards this message without further broadcasting. • Finally, every node has a shortest path to its CH and its neighbor’s CHs

20. 2- Local Gradient Routing

21. Packet Header Fields • NCP is Next Cluster Position. • HCis Hop Count to next cluster position. • FM is Face Routing Mode. • DCP is Destination Cluster Position. • ID is Destination ID.

22. Routing process • Only source node sets the DCP field. • When a packet is received by a node U, • U determines whether the DCP is equal to its own cluster position or not. • If yes, • U transmits the packet to its CH by local gradient routing step. • CH sends the packet to destination node. • If not, U checks whether the NCP is set or not. • If yes and it is U’s cluster position, or if it is not set, then U calculates the NCP by the greedy forwarding strategy. • One of the neighbor clusters will be selected as next cluster by global geographic routing step

23. Outline • Introduction • Geographic routing and location inaccuracy problems • Location-fault-tolerant geographic routing • Simulation results • Limitations • Summary

24. Simulation (Settings) • Network of 50 nodes. • 802.11 physical and MAC layers. • Nodes uniformly placed in a region of (700m x 700m) • Nodes move with random velocity between (0-10 m/s) • Upon arriving at one destination, the node pauses for 10 seconds before moving to another destination. • Density of network is 10 nodes per unit radio range

25. Simulation Results • Packet delivery success rate (LGR with GPSR) • LGR decreases by about 8.75%

26. Simulation Results • End-to-end delay of (LGR with GPSR) without location inaccuracy • LGR has longer end-to-end delay due to clustering • But better in unstable environment; when facing too many inaccuracies

27. Simulation Results • Packet delivery success rate of the networks with different densities. • LGR is better than GPSR in sparse networks.

28. Outline • Introduction • Geographic routing and location inaccuracy problems • Location-fault-tolerant geographic routing • Simulation results • Limitations • Summary

29. Limitations • Too many nodes in a cluster may cause overhead due to the flooding feature inside clusters. • This may limit the scalability of the entire network. • When a cluster header moves outside its cluster, an alternative approach is required (hand over or reselection) • When a node becomes closer to the Cluster Position than the CH, what does the algorithm do? Does it consider this as new CH? How does the algorithm maintain this feature?

30. Outline • Introduction • Geographic routing and location inaccuracy problems • Location-fault-tolerant geographic routing • Simulation results • Limitations • Summary

31. Summary • Two ideas combined. • Traditional geographic routing with clustering. • Geographic routing is used on cluster based. • So the algorithm tolerates location inaccuracy. • Gradient (hop count) routing used within clusters. • So it uses predefined paths, no greedy problems. • Performs well in sparse network.

32. Thank you