1. A Distributed Algorithm for the Dead End Problem of Location Based Routing in Sensor Networks Le Zou, Mi Lu, Zixiang Xiong, Department of Electrical Engineering, Texas A&M University IEEE Transactions,Vehicular Technology 2005

2. Outline Introduction Network Model The PAGER (partial-partition avoiding geographic routing) Algorithm Simulation Conclusions

3. Introduction Base Station Sensor nodes Sensor nodes forward data packets to BS in a multihop manner

4. Introduction Base Station The dead end problem x y Greedy forwarding z g Concave Node: distance(x,BS) < distance(y,BS ) ∀ y ∈ N(x),

5. Introduction Sink Destination GPSR (RHR)

6. Introduction st Face Routing

7. Network Model A number of sensor nodes randomly deployed on an unobstructed two-dimensional sensing field with a BS. All sensor nodes within communication range r The BS is located either adjacent to the sensing field or inside it Each node knows the location information of the BS.

8. The PAGER Algorithm The Shadow Spread Phase Divides a connected graph into subgraphs originated from concave nodes The Cost Spread Phase Establishes paths on a given subgraph obtained in the first phase

9. The Shadow Spread Phase Base Station A B C D E F concave node

10. The Shadow Spread Phase Base Station A B C D E F shadow node bright nodes Shadow Area Bright Area

11. The Shadow Spread Phase Nodes exchange information by means of periodically broadcasting beacon messages beacon(status, location) the shadow spread phase converges in n rounds in terms of beacon broadcast interval B

12. The Cost Spread Phase 5 12 7 16 20 Base Station 18 8 15 16 20 19 23 A B C D E F Euclidian distance to the BS 19+∆ ∆ should be set to the average Euclidean distance between neighboring sensor nodes ∆ is set to 3 in this example 22

13. The Cost Spread Phase 5 12 7 16 20 Base Station 18 8 15 16 20 19 23 A B C D E F 22+∆ 22 25

14. The Cost Spread Phase 5 12 7 16 20 Base Station 18 8 15 16 20 19 23 A B C D E F 23+∆ 22 25 26

15. The Cost Spread Phase 5 12 7 16 20 Base Station 18 8 15 16 20 19 23 A B C D E F 26+∆ 26 25 22 29

16. The Cost Spread Phase Once the status of a sensor node turns from bright to shadow, the cost spread phase can be triggered on that node immediately The convergence length of the cost spread algorithm in the whole sensor network is only associated with the maximum size of these shadow areas

17. Multiple BS BS 1BS 2

18. PAGER-M The shadow spread and cost spread processes begin

19. PAGER-M A changes its status to “bright”, then sends out beacon message

20. Path Redundancy We use path redundancy to reduce forwarding failure Choosing the neighbor with closest arrival time among available forwarding candidates

21. Simulation ~PAGER-S

25. Simulation ~PAGER-M

28. Conclusions PAGER has the loop free guarantee delivery property The mobility adaptability of PAGE make it suitable for use in mobile sensor networks with frequent topology changes