Node scheduling is one of the most effective techniques to maximize the lifetime of a wireless sensor network. It is the process of selecting a subset of nodes to monitor the sensor field on behalf of redundant nodes. At every round of the scheduling a small group of nodes are active while the rest of the sensor nodes are in sleep mode. In this thesis, we propose a novel node scheduling solution for wireless sensor networks. The main characteristic of our approach is its independence from location information as well as distance information. Moreover, it does not rely on unrealistic circular radio propagation models. In order to have a comprehensive solution, we have considered different relations between sensing range and transmission range. When these ranges are equal in addition to the case that transmission range is higher than sensing range, we devise a node scheduling scheme based on the concept of Minimum Dominating Set. Two heuristics are presented to determine a collection of minimum dominating sets of the graph of the wireless sensor network. At each round of the scheduling only one set is active. Minimum dominating sets are scheduled to be rotated periodically. Moreover, every set is synchronized prior to the end of its active period in order to minimize the effect of clock drift of sensor nodes. Two components are considered to address node failures during the on-duty period of minimum dominating sets. These are probing environment and adaptive sleeping. The former is responsible for probing the working nodes of the active set to detect any node failure. The latter adjusts the frequency of probing for minimizing the overhead of probing while preserving an adequate level of robustness for discovery of node failure. This framework is based on the PEAS protocol that has been developed by Fan Ye et al. [98, 99]. We propose a different node scheduling scheme with a three-tier architecture for the case that sensing range is higher than transmission range. The coverage tier includes a set of nodes to monitor the region of the interest. We propose a heuristic to determine a collection of d-dominating sets of the graph of the wireless sensor network. At every round of the scheduling one d-dominating set forms the coverage tier. Connectivity tier consists of sensor nodes that relay the data collected at the coverage tier back to the base station. Finally, the coverage management tier is responsible for managing different patterns of coverage such as cyclic or uniform coverage.

Les protocoles de routage dans les réseaux peuvent être amenés à changer pour de nombreuses raisons : la détection d'un événement particulier, un changement de topologie planifié ou non, la mobilité des nœuds, l'obsolescence de version, etc. Ces changements ne pouvant être simultanément détectés ou pris en compte par tous les nœuds du réseau, il est nécessaire de considérer le cas où certains nœuds utilisent le protocole de routage initial, tandis que d'autres ont migré vers le nouveau protocole de routage. Les travaux de cette thèse portent sur le problème de boucles de routage susceptibles d'apparaître dans ce contexte, et qui dégradent considérablement les performances du réseau. Nous proposons des solutions d'ordonnancement des nœuds, dans le but de contrôler la migration afin d'éviter ces boucles. Premièrement, nous considérons le contexte des réseaux statiques et des protocoles centralisés avec pour cas particulier le changement de métriques dans le réseau. Nous proposons deux solutions d'évitement des boucles centralisées : SCH-m (amélioration mineure d'un protocole existant), et ACH (nouvelle contribution), basées sur l'identification des boucles de routage dans les composantes connexes que contient l'union des deux protocoles de routage. Nous accélérons la migration du réseau par une opération de fusion étape par étape des différentes transitions produites. Deuxièmement, nous évoluons vers les protocoles distribués en conservant le contexte statique du réseau, et considérons le cas particulier du retrait ou de la panne d'un nœud. Nous proposons également deux solutions : RTH-d (amélioration mineure d'un protocole existant) et DLF (nouvelle contribution traitant les boucles de taille 2) basées sur un échange de messages entre les nœuds tant pour la détection de la panne que pour la notification de la migration. Troisièmement, nous considérons le contexte de mobilité des nœuds, et étudions les performances de DLF-k (version améliorée de DLF qui prend en compte les boucles de taille inférieures ou égales à k, avec k >= 2) sur deux types d'applications : les applications avec un unique nœud mobile qui est la destination, et les applications avec un groupe de nœuds mobiles. / Routing protocols in networks may change for many reasons: detection of a particular event, planned or unplanned change of topology, mobility of nodes, version obsolescence, etc. As these changes can not be simultaneously detected or taken into account by all nodes of the network, it is necessary to consider the case where some nodes use the initial routing protocol, while others have migrated to the new routing protocol. The work of this thesis deals with the problem of routing loops that may appear in this context, and which considerably degrade the performance of the network. We propose node scheduling solutions to control migration to avoid these loops. First, we consider the context of static networks and centralized protocols with the particular case of changing metrics. We propose two centralized avoidance solutions: SCH-m (minor improvement of an existing heuristic), and ACH (new contribution), based on the identification of the routing loops in the strongly connected components contained in the union of the two routing protocols. We accelerate the migration of the network by a step-by-step merge operation of the different transitions produced. Second, we evolve towards the distributed protocols while preserving the static context of the network, and consider the particular case of the withdrawal or breakdown of a node. We also propose two solutions: RTH-d (minor improvement of an existing heuristic) and DLF (new contribution for loops of size 2) based on message exchange of nodes for both failure detection and for migration notification. Thirdly, we consider the context of nodes mobility, and study the performance of DLF- k (improved version of DLF which takes into account loops of size less than or equal to k, with k >= 2) on two types of applications: applications with a single mobile node that is the destination, and applications with a group of mobile nodes.

Nowadays most communication networks like GSM, WLan or WiMAX are based on pre-existing infrastructure. These infrastructures are complicated, costly and difficult to deploy in very short time. Whereas Wireless Ad Hoc Networks are infrastructure-free self organizing networks which consist of co-operating nodes. These networks are highly desirable for various emerging applications for military and to extend the range and capacity of infrastructure based wireless networks. One critical issue that we face in Ad Hoc Network is the problem of scheduling. Scheduling algorithms in an Ad Hoc Network allows the nodes to share the wireless channel efficiently. But on the other hand, the scheduling algorithm needs to be easily implementable in a distributed fashion with little, if any, coordination between nodes in the network. Spread spectrum technologies allow interference averaging and therefore are employed in Ad Hoc networks. There are two major types of spread spectrum physical layer, which are frequency hopping (FH) spread spectrum and direct sequence (DS) spread spectrum. FH-CDMA divides the bandwidth into M sub channels, the receiver only sees the interference from the transmitter side which is on the same sub channel whereas in DS-CDMA we increase the spreading code M to decrease the signal to interference plus noise ratio (SINR) requirement. The purpose of research is to study a hybrid spread spectrum based on physical layer, in which the direct sequence signal is also frequency hoped. The DS will reduce the region of dominating interferes, while frequency hopping will be used within this region intelligently and allow the dominating interferes to transmit on different frequencies. First the system bounds on the transmission capacity of the proposed scheme is evaluated, and than a comparative analysis of different multiple access schemes is done with our proposed model with respect to their transmission capacity to evaluate its performance.