A Dead-End Free Topology Maintenance Protocol for Geographic Forwarding in Wireless Sensor Networks IEEE Transactions on Computers, vol. 60, no. 11, November 2011 Chih-Hsun Anthony Chou 1, Kuo-Feng Ssu 2, Hewijin Christine Jiau 2, Wei-Tong Wang 2 and Chao Wang 2 1 Institute for Information Industry, Taiwan 2 National Cheng Kung University, Taiwan

Outline  Introduction  Assumptions and Background  Dead-End Free Topology Maintenance (DFTM) Protocol  Discussions and Analysis  Experimental Results  Conclusion

Introduction  Topology management schemes have emerged as a promising strategy for prolonging the lifetimes of wireless sensor networks.  Several schemes construct a virtual communication backbone by turning off redundant sensor nodes. a connected dominating set (CDS)

Introduction  The CDS is constructed in such a way Each node is either a member of the subset or is a neighbor of one of the nodes in the subset. S D

Introduction  Dead-End Node Problem  This paper proposes a topology maintenance scheme for the construction of dead-end free topologies in WSNs.

Assumptions and Background  There are many stationary sensors distributed over the monitoring region.  The network is assumed to be sufficiently dense to construct a dead-end free topology.  Each sensor can be in either an active mode or a sleep mode.  Each sensor knows both its own and all its neighbors’ coordinates.

DFTM Scheme  Dead-End Free Verification  Dead-End Free Topology Construction  Dead-End Free Topology Maintenance

Dead-End Free Verification  Global Dead-End Free (GDF) Condition The dead-end situation does not occur at any node in the network  Local Dead-End Free (LDF) Condition N A Sleeping neighbors Active neighbors Node N does not satisfy the LDF condition. Node N satisfies the LDF condition. Transmission range

A Dead-End Free Topology Construction N Sleeping neighbors Active neighbors Transmission range Undecided neighbors B C D E Active Neighbor Set (ANS) A B C Tentative Neighbor Set (TNS) D E F F Node N does not satisfy the LDF condition. Active Node Selection Algorithm

E A Dead-End Free Topology Construction N Sleeping neighbors Active neighbors Transmission range Undecided neighbors B C D F Active Neighbor Set (ANS) A B C F Tentative Neighbor Set (TNS) D E F

Active Node Selection Algorithm  Rule d The distance between the candidate node and the initiator A N B C D F E F

Active Node Selection Algorithm  Rule s The length of the new covered segment A N B C D F E F

Active Node Selection Algorithm  Preference weighting i: initiator r: the node’s transmission range ncs a : the length of the new covered segment of node a : the distance from node i to node a rule d rule s

Dead-End Free Topology Maintenance  Global Topology Maintenance For energy balancing All nodes change modes to undecided every T global seconds. The sink node randomly chooses a node to be the initiator. Every node has an equal probability of becoming an active node.

F Dead-End Free Topology Maintenance  Local Topology Maintenance Some of the active nodes may suddenly become unavailable. A N B C D E E

Discussions and Analysis  Discussions Lemma 1. A network topology is fully connected if it satisfies the Global Dead-End Free (GDF) condition. Theorem 1. A network topology constructed by the proposed DFTM scheme is fully connected.

Discussions and Analysis  Analysis The total number of active nodes required in GAF and DFTM. GAF

Discussions and Analysis  Analysis The total number of active nodes required in GAF and DFTM. DFTM – Best Case

Discussions and Analysis  Analysis The total number of active nodes required in GAF and DFTM. DFTM – Worst Case

Discussions and Analysis  Analysis The total number of active nodes required in GAF and DFTM. d

Experimental Results  ns2 Simulator  50, 75, or 100 static nodes were randomly distributed within a sensing area measuring 60*30 m.  Transmission range of each node: 15 m.  Comparisons: GPSR, GAF and SPAN The length of each GAF square was set to m. SPAN: backbone infrastructure

Number of Active Nodes 50 nodes 75 nodes 100 nodes

Number of Survived Nodes 50 nodes 75 nodes 100 nodes

Packet Delivery Ratio 50 nodes 75 nodes 100 nodes

Energy Consumption and Path Length

Comparison for Dead-End Occurrence 50 nodes 100 nodes

Conclusion  This paper presented a distributed dead-end free topology maintenance protocol, namely DFTM.  DFTM can be integrated with any geographic routing Low energy consumption A minimum number of dead-end events  The performance of DFTM has been benchmarked against that of GAF and SPAN using the ns2 simulator.

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