Section: New Results

Self-organization

Participants : Natale Guzzo, Valeria Loscri, Nathalie Mitton.

Self-organization encompasses several mechanisms. This year, the FUN research group has contributed to specific aspects; topology importance and clustering.

Impact of the topology

Wireless Sensor Networks (WSN) are composed of constrained devices and deployed in unattended and hostile environments. Most papers presenting solutions for WSN evaluate their work over random topologies to highlight some of their "good" performances. They rarely study these behaviors over more than one topology. Yet, the topology used can greatly impact the routing performances. [13] presents a study of the impact of the network topology on algorithm performance in WSNs and illustrate it with the geographic routing. Geographic routing relies on node coordinates to route data packets from source to destination. We measure the impact of different network topologies from realistic ones to regular and very popular ones through extensive simulation and experimentation campaigns. We show that different topologies can lead to a difference of up to 25% on delivery ratio and average route length and more than 100% on energy costs.

Clustering

Clustering in wireless sensor networks is an efficient way to structure and organize the network. It aims to identify a subset of nodes within the network and bind it a leader (i.e. cluster-head). This latter becomes in charge of specific additional tasks like gathering data from all nodes in its cluster and sending them by using a longer range communication to a sink or a Base Station (BS) which may be far away from the monitoring area. Many algorithms proposed in the literature compute the routing process by clustering the network and by designing new election mechanisms in which the cluster-heads are chosen taking account of the remaining energy, the communication cost and the density of nodes. However, they do not consider the connectivity to the BS, and assume that all the nodes or only few prefixed nodes are able to directly communicate with it. We believe that this assumption is not suitable for many applications of WSN and to tackle this problem we propose CESAR [14] , a multi-hop and energy-efficient routing protocol for large-scale WSN which includes a new cluster-head selection mechanism aware of the battery level and the connectivity to the BS. Furthermore, our solution employs an innovative hybrid approach to combine both clustering and on-demand techniques in order to provide an adaptive behavior for different dynamic topologies. Simulation results show that our solution outperforms in terms of energy consumption and data delivery other known routing algorithms in the literature. Note that CESAR is currently the object of two pending patents.