Mobility and resource management for 5G heterogeneous networks

The conventional topology of current cellular networks is a star structure, where central control points usually serve as base stations (BSs). This provides the advantage of simplicity while still providing quality of service (QoS). For next-generation networks, however, this topology is disadvantageous and difficult to use due to the insufficient availability of network access. The hybrid topology radio network will thus naturally be the future mobile access network that can help to overcome current and future challenges efficiently. Therefore, relay technology can play an important role in a hybrid cellular network topology. Today, with the recent long-term evolution-advanced (LTE-A) standards, the 3rd Generation Partnership Project (3GPP) supports a single-hop relay technology in which the radio access link between the BS and users is relayed by only one relay station (RS). With the help of multi-hop relay, however, the radio link between the BS and users can be extended to more than two hops to improve the coverage and network capacity. Multiple hops to transmit data to and from the corresponding BS results in the reduction of path loss. However, using a multi-hop relay system requires more radio resources to transmit data through different hops. More interference is also created due to a greater number of simultaneous transmissions in the network. New mobility and resource management schemes are thus important for achieving a high QoS while increasing the whole network capacity. In the first part, the problem of relay selection and radio resource allocation is studied, and choosing how the bandwidth should be shared between direct, backhaul, and access links in multi-hop relay networks is discussed. In such a network, resource allocation plays a critical role because it manages channel access in both time and frequency domains and determines how resources are allocated for different links. The proposed solution includes a nonlinear programming technique and a heuristic method. First, the problem formulation of resource allocation and relay selection is presented to provide an integrated framework for multi-hop relay networks. Second, an analytical solution to the problem is presented using a nonlinear programming technique. Finally, an iterative two-stage algorithm is presented to address the joint resource allocation and relay selection problem in multi-hop relay networks Under backhaul and capacity limitation constraints. In particular, the first stage proposed a fast approximation analytical solution for a resource allocation algorithm that takes into account the trade-off between the optimality and the complexity of the multi-hop relay architecture; the second stage presented a heuristic relay selection strategy that considers the RS load and helps to keep the relay from being overloaded is proposed. In the second part, the mobility problem in downlink multi-hop relay networks is addressed. In addition to the resource allocation issue, the relay selection problem is studied from a network layer perspective. Therefore, this part includes the issue of radio path selection. As an alternative to the heuristic algorithm developed in the previous part, the presented work describes the development and evaluation of a relay-selection scheme based on a Markov decision process (MDP) that considers the RS load and the existing radio-link path to improve handoff performance. First, the problem formulation of resource allocation and relay selection is presented. Second, an MDP mathematical model is developed to solve the relay selection problem in a decentralized way and to make the selection process simple. This relay selection scheme has the objective of maintaining the throughput and ensuring seamless mobility and service continuity to all mobile terminals while reducing the handoff frequency and improving handoff performance. In the third part, the admission and power control problem of a general heterogeneous network (HetNet) consisting of several small cells (SCs) is solved. Compared to the first two parts of this work, the system is expanded from a multi-hop RS to a general SC context. This part therefore focuses only on the access link problem, assuming the capacity of the SC backhaul links are large enough not to be bottlenecks. This part mainly deals with the problem of how to maximize the number of admitted users in an overloaded system while minimizing the transmit power given a certain QoS level. First, the problem is formulated to address concerns about QoS requirements in a better way. Second, a Voronoi-based user association scheme for maximizing the number of admitted users in the system under QoS and capacity limitation constraints is proposed to find near-optimal solutions. Finally, a twostage algorithm is presented to address the joint admission and power control problem in a downlink heterogeneous SC network. In particular, the first stage proposes a dynamic call admission control policy that considers the SC load and call-level QoS while also helping to keep the system from being overloaded. The second stage presents an adaptive power allocation strategy that considers both user distribution and the density of SCs in HetNets. Finally, the proposed solutions are evaluated using extensive numerical simulations, and the numerical results are presented to provide a comparison with related works found in the literature

Handoff vertical entre réseau UMTS et WLAN

Un des principaux défis majeurs des prochaines générations des systèmes de communication sans fil serait d'utiliser les ressources limitées des réseaux de communications d'une manière efficace à l'effet d'obtenir une qualité et une capacité qui soient suffisantes pour faire face à des demandes sans cesse croissante de services. En effet, les besoins en bande passante des utilisateurs ont augmenté en raison des résultats satisfaisants relevés des différentes applications telles que la vidéo et la navigation sur Internet. Ceci a permit à plusieurs technologies de voir le jour et qui ne cessent de s'améliorer afin de répondre aux besoins des utilisateurs. C'est notamment le cas des réseaux hétérogènes qui servent à interconnecter les réseaux WIFI, GSM/UMTS et Satellitaires. Ce progrès va permettre de répondre à la demande des utilisateurs en leurs offrants une très grande mobilité dans le monde et une connexion n'importe où et n'importe quand. L'objectif de ce présent mémoire de maîtrise est d'étudier la problématique de gestion de mobilité entre les deux réseaux et de combiner ces techniques afin d'exploiter au mieux les avantages inhérents à ces deux réseaux : cellulaire (UMTS) et local sans fil (WLAN) et de pouvoir intégrer ces deux technologies de telle sorte que le changement de technologie soit transparent. Dans le cadre de la première partie de ce mémoire, nous avons traité particulièrement les aspects de gestion de mobilité. Les deux différentes architectures d'interconnexion au contexte des réseaux hétérogènes UMTS/WLAN sont relatées ainsi que différents algorithme sont également mis en évidence principalement l'algorithme RSS, SNR et SINR. La plupart des contributions faites dans ce contexte prennent en considération juste la maximisation du débit à travers les deux réseaux. Par contre la minimisation de nombre de handoff durant un appel ou transfert de données joue un rôle très prépondérant, afin d'éviter tout handoff inutile et d'éliminer par voie de conséquence l'effet ping-pong qui dégrade la qualité de service. C'est pourquoi, dans la seconde partie de notre mémoire, nous avons proposé une nouvelle stratégie intégrant pour la réalisation d'un handoff vertical des utilisateurs mobiles entre les deux réseaux tout en minimisant le nombre de handoff la probabilité de perdre des paquets et d'atteindre un débit plus élevé avec meilleur prix conespondant. Dans ce cadre nous avons présenté et nous avons testé plusieurs algorithmes de handoff et nous avons comparé ces algorithmes avec notre solution proposée. Tous les algoritlmies entrepris ont été validés et évalués par des simulations