A Low-Cost Flooding Algorithm for Wireless Sensor Networks Department of Electrical and Computer Systems Engineering Monash University, Australia WCNC 2007, Hong Kong Ou Liang, Ahmet Sekercioglu and Nallasamy Mani

2 Sections 1.Flooding in WSNs. 2.Our Low-Cost Flooding algorithm. 3.Simulation study. 4.Conclusion and future work.

3 Flooding in WSNs Flooding is the simplest way of routing. It requires each node in the network to broadcast a packet upon receiving it for the first time. Flooding is widely used in WSNs by many applications. Problems : Redundant packets — nodes receive multiple copies of a packet. Contention and collision — happen when using a contention MAC layer like IEEE Energy wastage — redundant retransmissions consume energy. Section 1Section 2Section 3Section 4

4 Redundant flooding S Section 1Section 2Section 3Section 4

5 An efficient way of flooding S A C B Section 1Section 2Section 3Section 4

6 Low-Cost Flooding Algorithm It aims to form a Connected Dominating Set (CDS) in a given network. It operates in two steps: Elects cluster-heads (dominators). Generates connectors to link all the dominators. Section 1Section 2Section 3Section 4

7 Electing dominators Initially, all nodes in the network mark themselves as white nodes, and only the nodes in the white node state participate dominator election. Section 1Section 2Section 3Section 4 A node announces itself as the dominator if it has the largest node degree among its white node neighbors. Nodes that are covered by the dominators change their states to dominatees.

8 Dominator election example DB F A E C G H I J O P N L K M T Node | Node degree D 6 h 5 P 5 Dominators are two hops or three hops apart from each other. Section 1Section 2Section 3Section 4

9 Generating connectors Two types of connectors: Active-Connector – selected by dominators Passive-Connector – selected by dominators and active connectors. Section 1Section 2Section 3Section 4 Passive-Connectors connect two-hop away dominators. Active-Connectors + Passive-connectors connect three-hop away dominators.

10 Connecting two-hop away dominators A dominator U selects a dominatee V as a passive- connector to connect two-hop away dominators based on two rules: U has a bigger node ID than all its two-hop away dominators that are covered by V. V covers the most number of two-hop away dominators of U. Section 1Section 2Section 3Section 4

11 Selecting passive connectors W B A V U Dominator W Node A: { V } Node B: { U, V } Dominator V Node A: { W } Node B: { U, W } Dominator UNode B: { V, W } I am a Passive connector Selected by W Section 1Section 2Section 3Section 4

12 Connecting three-hop away dominators Two steps to connect three-hop away dominators: A dominator U selects an active-connector V. Active-connector V selects other passive connectors to connect three-hop away dominators. Section 1Section 2Section 3Section 4

13 New definitions Special-dominatee: A dominatee V marks another dominatee W as a special dominatee if W has no shared one-hop dominator with V. CA B VW U Dominatee U and V have a shared dominator C. Dominatee V and W have no shared dominators. V and W mark each other as the special-dominatees. Section 1Section 2Section 3Section 4

14 New definitions Special-dominator: Dominatee V marks all the one-hop dominators of a special- dominatee W as the special-dominators. CA B VW U Dominatee V marks dominator A as the special-dominator. Dominatee W marks dominator B and C as the special-dominators. Section 1Section 2Section 3Section 4

15 New definitions Isolated-dominator: A dominator C marks a special-dominator A of dominatee V as the isolated-dominator if A is neither a two-hop away dominator of C, nor a two-hop away dominator of any node in D 2 (C). Use D 2 (C) to represent the set of two-hop away dominators of a dominator C. CA B VW U Section 1Section 2Section 3Section 4

16 Selecting active-connectors A dominator U selects a dominatee V as an active-connector if: U has marked some isolated-dominator from V. U has larger node ID than those marked isolated dominators. Dominator U will inform active-connector V about the isolated-dominators V needs to connect. Section 1Section 2Section 3Section 4

17 Selecting passive-connectors (by active-connectors) An active-connector V selects a dominatee W as the passive-connector if: W connects to the most number of isolated-dominators. CA B VW U Connect isolated- dominator A I am a passive- connector Section 1Section 2Section 3Section 4

18 Simulation study Section 1Section 2Section 3Section 4 SimulatorOMNeT++ with Mobility Framework. MAC protocolAssume a perfect MAC layer (error and collision free). Network area100m x 100m two dimensional area. Topology generation Randomly distribute nodes in the area. Each node is placed within the transmission range of a previously placed node to make sure connectivity. Total nodesRange from 100 to 500. Transmission range Two transmission ranges: 15m and 25m. Performance metrics Number o forwarding nodes, number of signaling messages, and signaling message size. Number of runs11 random topologies simulated for each network size.

19 Simulation study Section 1Section 2Section 3Section 4 Number of forwarding nodes generated

20 Simulation study Section 1Section 2Section 3Section 4 Number of signaling messages generated

21 Simulation study Section 1Section 2Section 3Section 4 Signaling message size (in bytes) R=15m Total number of nodes in the network LCF MOA GMPR MPR SIMPR EMPR EEMPR

22 Simulation study Section 1Section 2Section 3Section 4 Signaling message size (in bytes) R=25m Total number of nodes in the network LCF MOA GMPR MPR SIMPR EMPR EEMPR

23 Conclusion and future work Section 1Section 2 Section 3Section 4 We have proposed a Low-Cost Flooding (LCF) algorithm for wireless senor networks. The algorithm aims to minimize the redundant retransmissions in the network by generating a Connected Dominating Set (CDS). Future work: Design efficient routing protocols for sensor networks. Implement a real world sensor network test bed.

24 Thank you for your attention!

25 Flooding protocol designing considerations Scalability — flooding algorithms for WSNs need to be distributed and depends on localized information. Simplicity — flooding algorithms need to be simple in both computation and communication. Efficiency — flooding algorithms can dramatically reduce unnecessary redundant transmissions and save energy. Section 1Section 2Section 3Section 4