Nowadays, with a worldwide market penetration of over 50% in the mobile telecommunications sector, there is also an unrelenting demand from the subscribers for ever increasing transmission rates and availability of broadband-like experience on the handset. Due to this, research in next-generation networks is rife. Such systems are expected to achieve peak data rates of up to 1 Gbps through the use of innovative technologies such as multiple-input and multipleoutput (MIMO) and orthogonal frequency division multiple access (OFDMA). Two more ways of boosting capacity have also been identified: shrinking cell sizes and greater reuse of resources in the same area. This forms the foundation of the research presented in this thesis. For operators, the costs involved with planning and deploying additional network infrastructure to provide a dense coverage of small, high capacity cells cannot be justified. Femto-cells, however, promise to fulfil this function. These are user-deployed mini base stations (BSs), known as home evolved NodeBs (HeNBs), which are envisaged to be commonplace in homes and offices in the coming years. Since they drastically reduce communication distances to user equipments (UEs) and reuse the resources already utilised in the macro-cell, they help boost the system capacity significantly. However, there are issues to be addressed with the deployment of femto-cells, such as increased interference to the system and methods of access. These and other problems are discussed and analysed in this thesis. One of the first steps towards femtocell research has been the study of the time division duplex (TDD) underlay concept, whereby an indoor UE acts as a relay between the evolved NodeB (eNB) and other indoor UEs. In order to gain a deeper understanding of how and under what conditions such a self-organising network can be deployed, a mathematical analysis of the distribution of path losses in a network of uniformly distributed nodes has been performed. In connection with this, research has also been done in the identification of well connected nodes in such networks. Next, extensive simulations on traditional cellular networks with embedded femto-cells have been carried out in order to demonstrate the benefits of femto-cell deployment. This research has shown that femto-cells can cause severe downlink (DL) interference to badly placed macro UEs. Finally, a novel interference avoiding technique that addresses this problem is investigated.

Les communications sans fil prolifèrent dans presque chaque aspect de la société humaine : puissants ‘smart-phones' et ‘tablets', accès haut débit sans fil, et communications ‘machine-to-machine' ont généré des volumes de trafic de données imprévisibles quelques années en arrière. Dans ce nouveau paradigme, l'industrie des télécommunications se doit de garantir à la fois la durabilité économique des communications sans fil à large bande ainsi que la qualité de son service. En outre, il y a une forte incitation sociale à réduire les émissions de C02 duent aux communications mobiles, qui a augmenté notamment dans la dernière décennie. Dans ce contexte, l'intégration des ‘femtocells' dans les réseaux cellulaires est une solution à faible coût pour offrir une qualité de service élevée et en même temps de décharger le réseau macrocellule. Cependant, le déploiement massif et chaotique des points d'accès femtocell et leurs opérations non coordonnées peuvent conduire à une augmentation de l'interférence co-canal. De plus, un nombre élevé de cellules faiblement chargées augmente la consommation énergétique du réseau. Dans cette thèse, nous avons étudié les effets du déploiement de femtocells sur l'efficacité énergétique du réseau cellulaire. Par ailleurs, nous investiguons sur les mécanismes d'adaptation pour les réseaux des femtocells comme un moyen pour améliorer l'efficacité des communications mobiles. Notre objectif est de répondre dynamiquement à la demande des ressources afin de limiter la consommation d'énergie moyenne et l'interférence co-canal, tout en garantissant la qualité de service. Nous profitons du contexte inhabituel de communication ‘femtocellulaire' pour proposer des mécanismes d'allocation des ressources et des systèmes de gestion de réseau qui coordonne l'activité des points d'accès, la consommation d'énergie et de la couverture. Les résultats des simulations montrent que nos propositions améliorent l'efficacité énergétique et les performances perçues par les utilisateurs du système dans les réseaux ‘femtocellulaires' coopératives et autonomes. / Wireless communication proliferates into nearly each aspect of the human society, driving to the exponential growth in number of permanently connected devices. Powerful smart-phones and tablets, ubiquitous wireless broadband access, and machine-to-machine communications gen- erate volumes of data traffic that were unpredictable few years back. In this novel paradigm, the telecommunication industry has to simultaneously guarantee the economical sustainability of broadband wireless communications and users' quality of experience. Additionally, there is a strong social incentive to reduce the carbon footprint due to mobile communications, which has notably increased in the last decade. In this context, the integration of femtocells in cellular networks is a low-power, low-cost solution to offer high data rates to indoor customers and simultaneously offload the macrocell network. However, the massive and unplanned deployment of femtocell access points and their uncoordinated operations may result in harmful co-channel interference. Moreover, a high number of lightly loaded cells increases the network energy consumption. In this thesis, we investigate the effects of femtocells deployment on the cellular network energy efficiency. Moreover, we look into adaptive mechanisms for femtocell networks as a means to pave the way towards agile and economically viable mobile communications. Our goal is to dynamically match resource demand and offered capacity in order to limit the average power consumption and co-channel interference while guaranteeing quality of service constraints. We take advantage of the unusual communication context of femtocells to propose resource allocation and network management schemes that coordinate the access points activity, power consumption, and coverage. Simulation results show that our proposals improve system energy efficiency and users' performance in both networked and stand-alone femtocell deployment scenarios.