Long Cheng ∗† , Sajal K. Das † , Mario Di Francesco † , Canfeng Chen ‡ and Jian Ma ∗§

1. Scalable and Energy-Efficient Broadcasting in Multi-hop Cluster-Based Wireless Sensor Networks Long Cheng∗†, Sajal K. Das†, Mario Di Francesco†, Canfeng Chen‡ and Jian Ma∗§ ∗State Key Lab of Networking & Switching Tech., Beijing Univ. of Posts and Telecomm., China †Center for Research in Wireless Mobility and Networking (CReWMaN), University of Texas at Arlington, USA ‡Nokia Research Center, Beijing, China §Wuxi SensingnetIndustralization Research Institute, Wuxi, China

2. Outline • Introduction • Network Model • Distributed heuristic broadcasting over CHs (BOCH) Protocol Description • Simulation • Conclusions • References

3. Introduction • In large scale WSNs, in order to extend network lifetime and achieve the network scalability and robustness objectives, one common approach is to group sensor nodes into clusters, forming the hierarchical clustering structure (called cluster-based WSNs) • Each cluster has a leader, referred to as the cluster head (CH) • A CH may simply collect sensed data in its cluster or perform aggregation/fusion of collected sensed data, sleep scheduling, etc

4. Introduction • Cluster-based WSNs have many advantages • First, the energy consumption can be significantly reduced since only one representative node per cluster needs to be involved routing • In addition, cluster of nodes can be managed more easily • Finally, communication bandwidth is conserved since redundant exchange of messages among sensor nodes is avoided

5. Introduction • Existing works either assume that CHs are richer in resources, i.e., have longer radio ranges than ordinary nodes, so that a direct link between CHs is available, or that clusters are constructed within very limited hops • However, these are not always realistic assumptions since the CH may be a regular sensor node and the sink is often not directly reachable • CHs communicate with each other by using multi-hop communication through the sensor nodes inside the clusters

6. Network Model • Each sensor node has a fixed level of transmission power and the wireless channel is bidirectional • The network has already been clustered by adopting an existing multi-hop clustering algorithm • Each sensor node can be a member of only a single cluster • The role of being a CH may be rotated periodically among the nodes of the cluster

7. Network Model • Each cluster member has a route to its CH and knows the hop distance • Each node maintains a 1-hop neighbor table thus knows whether it is a border node or not, border nodes are those nodes that have at least one neighbor that belongs to other clusters

8. BOCH Protocol – Cross CHs route construction • Cdeg(v) : ClusterDegreeof a border node v as the number of different clusters its immediate neighboring nodes belong to • In a cluster, each border node independently starts a backoff timer to send a GATEWAYCLAIM message to its CH • Once receiving such a message, the CH knows the existence of at least one neighboring CH and the corresponding path toward it (including the hopcount)

9. BOCH Protocol – Cross CHs route construction • H(a) : denote the hopcount from A to its CH • normalized hopcount1 Nhc(a,CH1, CH2) from CH1 to CH2 through border node A • v is A’s immediate neighbor which belongs to CH2

10. BOCH Protocol – Cross CHs route construction • Ahc(a) denote the average normalized hopcount from CH1 to all neighboring CHs that can be connected through the border node A where CHjis a CH1’s neighboring CH that is connected through A

11. BOCH Protocol – Cross CHs route construction • denotethe backoff delay for the border node A where τ is a time slot unit • A GATEWAYCLAIM message sent from a border node j includes its Ahc(j) value, and the neighboring CH set it can connect, denoted as Nch(j)

12. BOCH Protocol – Cross CHs route construction

13. BOCH Protocol – Broadcasting over CHs

14. BOCH Protocol – Local recovery mechanism • Once the CH changes, the border nodes of the cluster will initiate a new cross-CHs path construction process • At the same time, the CH rotation will also trigger that the border nodes of neighboring clusters send notification messages to their CHs

15. Simulation metric • Control message transmissions as the total number of control message transmissions to establish the routes spanning all CHs • Broadcasting transmissions metric is also measured as the total number oftransmissions when a source CH broadcasts a single packet toall other CHs • The clustersize is set to 5×5

16. Simulationresult

17. Simulationresult

18. Simulationresult

19. Simulationresult

20. Conclusion • The proposed solution for broadcasting over CHs is designed for the scenario where a direct link between CHs is not available • After the multi-hop clusters have been formed, each CH efficiently establishes the inter-cluster routes to its neighboring CHs • An efficient broadcasting over CHs scheme is performed whenever a source CH has a packet to broadcast to other CHs

21. References Long Cheng; Das, S.K.; Di Francesco, M.; Canfeng Chen; Jian Ma; , "Scalable and Energy-Efficient Broadcasting in Multi-Hop Cluster-Based Wireless Sensor Networks," Communications (ICC), 2011 IEEE International Conference on , vol., no., pp.1-5, 5-9 June 2011