Clustering schemes can reduce energy consumption, prolong network lifetime and improve scalability in wireless sensor networks (WSNs). In a typical cluster-based WSN, sensor nodes are organized into clusters. Each cluster elects a cluster head (CH) node. The CH is responsible for collecting the sensed data from cluster members, aggregating data and transmitting data to the sink node via a multi-hop path through intermediate CHs. Thus, the use of cluster techniques not only shortens the transmission distances for sensor nodes but also reduces energy consumption; however, each cluster imposes a larger load on the CH. Under this situation, CHs closer to the sink node tend to use up their batteries faster than those farther away from the sink node due to imbalanced traffics among CHs. To overcome this problem, we contribute to the energy balancing issues in WSNs from two aspects. In the first work, we first analyze the corona model. Based on analysis results, we found that nearly balanced energy consumption of WSNs can be achieved with the additional help of arranging different initial conditions. We then propose the Energy-balanced Node Deployment with Balanced Energy (END-BE) scheme and Energy-balanced Node Deployment with Maximum Life-Time (END-MLT) scheme, which determine the cluster density for each corona according to the energy consumption of each CH. Simulation results show that energy consumption is nearly balanced by implementing END-BE, and the network lifetime is greatly improved by adopting END-MLT. In the second work, we development a novel cluster-based routing protocol for corona-structured wireless sensor networks in order to balance the energy consumption among CHs. Based on the relaying traffic of each CH conveys, adequate radius for each corona can be determined through nearly balanced energy depletion analysis, which leads to balanced energy consumption among CHs. Simulation results demonstrate that our clustering approach effectively improves the network lifetime, residual energy and reduces the number of CH rotations in comparison with the Multi-Layer Clustering Routing Algorithm (MLCRA).

Recent advances in Micro-Electro-Mechanical Systems (MEMS) and low-power short-range radios have enabled rapid development of wireless sensor networks. Future sensor networks are anticipated to include hundreds or thousands of these devices in many applications, such as capturing multimedia content for surveillance, structural health monitoring, tracking of accidental chemical leaks, machine failures, earthquakes and intrusion detection. With the increase of sensor applications, a number of challenging problems related to the network protocol design has emerged - the most important ones relating to energy efficiency and lifetime maximisation. Techniques devised for sensor networks should deal with a large number of sensors distributed in the field. Wireless sensor nodes are deployed with limited energy reserves, so the networks should operate with minimum energy overhead. In fact, the network should take into account not only individual node's energy efficiency but also consider the global picture, because surviving nodes' energy reserves in a failed network are wasted energy. This thesis examines a node organisation technique to deal with the above challenges. The focus is on improving network lifetime via organising the nodes in a distributed and energy efficient manner. The main goal is lowering wasted energy via energy balancing and exploiting node redundancy in case of node failure. In particular, this thesis proposes Energy Balanced Clustering (EBC) method for node self-organisation where network tasks (such as data aggregation and data forwarding) are shifted to high-energy neighbours to reduce the energy consumption of low energy nodes. After showing how to extend network lifetime by energy balanced node organisation, the effect of redundant node deployments on network lifetime is addressed. Redundant nodes consume energy by performing unnecessary tasks so a method called Self-Calculated Redundancy Check (SCRC) is proposed to deactivate redundant nodes. A deactivated redundant node can be used as a replacement for a failed node. The Asynchronous Failed Sensor node Detection (AFSD) proposed in this thesis uses the data packets exchanged between neighbours to identify failed neighbours. To restore coverage for network holes caused by failed nodes, policies are given for re-activating redundant nodes. Detailed analytical analysis and simulation of the proposed methods demonstrate that by taking into account energy balancing, eliminating redundant tasks and replacing failed nodes sensor network lifetime can significantly be improved.

Le challenge de la consommation d'énergie dans les réseaux de capteurs sans fil constitue un verrou technologique qui reste un problème ouvert encore aujourd'hui. Ces travaux de thèse s'inscrivent dans la problématique de la conservation de l'énergie dans les réseaux de capteurs et s'articulent autour de deux axes. Dans la première partie, nous abordons le dimensionnement des protocoles de découverte de voisinage. Nous proposons deux techniques de dimensionnement de ces protocoles qui visent à optimiser la consommation d'énergie des nœuds capteurs. La première technique, PPM-BM, consiste à dimensionner le protocole de découverte de voisins en fonction du niveau de batterie du nœud. La deuxième approche, ECoND, vise à ajuster la fréquence de découverte de voisins en fonction de la connectivité estimée à chaque instant. Cette technique tire profit des cycles temporels des modèles de mouvement des nœuds. La connectivité est estimée en se basant sur l'historique des rencontres. La découverte de voisins est ajustée en fonction du taux de connectivité estimé. Les résultats enregistrés mettent en évidence l'efficacité de ces deux techniques dans l'optimisation de la consommation d'énergie des nœuds sans affecter les performances de taux de livraison de messages et d'overhead. La deuxième partie de la thèse concerne l'optimisation des performances des réseaux de capteurs en termes de durée de vie. Nous reconsidérons dans cette partie certains protocoles de routage relevant du domaine des réseaux à connectivité intermittente et nous proposons le protocole EXLIOSE qui se base sur la capacité d'énergie résiduelle au niveau des nœuds pour assurer un équilibre énergétique, partager la charge et étendre à la fois la durée de vie des nœuds ainsi que celle du réseau / The challenge of energy consumption in wireless sensor networks is a key issue that remains an open problem. This thesis relates to the problem of energy conservation in sensor networks and is divided into two parts. In the first part, we discuss the design of neighbor discovery protocols. We propose two techniques for modulating these protocols in order to optimize the energy consumption of sensor nodes. The first technique, PPM-BM aims to modulate the neighbor discovery protocol based on the battery level of the node. The second approach ECoND aims to set up the frequency of neighbor discovery based on estimated connectivity. This technique takes advantage of the temporal cycles of nodes' movement patterns. Connectivity is estimated based on encounters' history. A neighbor discovery is set up based on the estimated rate of connectivity. The achieved results demonstrate the effectiveness of these techniques in optimizing the energy consumption of nodes while maintaining acceptable message delivery and overhead rates. In the second part of the thesis, we contribute to the optimization of the performance of sensor networks in terms of network lifetime. We review in this section some routing protocols for networks with intermittent connectivity and we propose EXLIOSE protocol which is based on residual energy to ensure energy-balancing, load sharing and network lifetime extending

The balance of the supply of renewable energy sources with electricity demand will become increasingly difficult with further penetration of renewable energy sources. Traditionally, large stationary batteries have been used to store renewable energy in excess of electricity demand and dispatch the stored energy to meet future electricity demand. Cool thermal energy storage is a feasible renewable energy balancing solution that has economic and environmental advantages over utility scale stationary lead-acid batteries. Two technologies, ice harvesters and internal-melt ice-on-coil cool thermal energy storage, have the capability to store excess renewable energy and use the energy to displace electricity used for building cooling systems. When implemented by a utility, cool thermal energy storage can replace large utility scale batteries for renewable energy balancing in utility regions with high renewable energy penetration. The California Independent System Operator (CAISO) region and the Electric Reliability Council of Texas (ERCOT) are utility regions with large solar and wind resources, respectively, that can benefit from installation of cool thermal energy storage systems for renewable energy balancing. With proper scheduling of energy dispatched from cool thermal energy storage, these technologies can be effective in displacing peak power capacity for the region, in displacing traditional building cooling equipment, and in recovering renewable energy that would otherwise be curtailed. / Master of Science