Mobile networks are in the process of becoming the world’s leading medium for data traffic. This challenge has raised the bar for Quality of Services (QoS) provided by the mobile network operators. It requires methods and tools to verify the Service Level Agreement (SLA) and benchmark competitors by comparing metrics of QoS, e.g. the round-trip time and available bandwidth. For this purpose, Blixt™ has been developed, which is a property of InfoVista Sweden AB. Blixt™ is an Android application which measures the available bandwidth and the round-trip time for the latest generation of mobile networks. Blixt™ approach relies on a time-stamping protocol commonly known as Two-Way Active Measurement Protocol (TWAMP). This research work discusses how the packet probing parameters affect the accuracy of measurements and the level of intrusiveness. The performance of the technique was experimentally tested and compared to other tools and methods, namely, iPerf3, nPerf and FTP test.

As the Internet continues to evolve, without providing any performance guarantees or explicit feedback to applications, the only way to infer the state of the network and to dynamically react to congestion is through end-to-end measurements. The emph{available bandwidth} (avail-bw) is an important metric that characterizes the dynamic state of a network path. Its measurement has been the focus of significant research during the last 15 years. However, its estimation remained elusive for several reasons. The main contribution of this thesis is the development of the first estimation methodology for the avail-bw in a network path using end-to-end measurements. In more detail, our first contribution is an end-to-end methodology, called SLoPS, to determine whether the avail-bw is larger than a given rate based on the sequence of one-way delays experienced by a periodic packet stream. The second contribution is the design of two algorithms, based on SLoPS, to estimate the mean and the variation range, respectively, of the avail-bw process. These algorithms have been implemented in two measurement tools, referred to as PathLoad and PathVar. We have validated the accuracy of the tools using analysis, simulation, and extensive experimentation. Pathload has been downloaded by more than 6000 users since 2003. We have also used PathVar to study the variability of the avail-bw process as a function of various important factors, including traffic load and degree of multiplexing. Finally, we present an application of avail-bw estimation in video streaming. Specifically, we show that avail-bw measurements can be used in the dynamic selection of the best possible overlay path. The proposed scheme results in better perceived video quality than path selection algorithms that rely on jitter or loss-rate measurements.

Cette thèse s’inscrit dans le domaine de la caractérisation des systèmes de communication sans fil utilisant la diversité des antennes. En effet, ces systèmes permettent de lutter contre les évanouissements des signaux, lorsque le terminal est placé dans un environnement riche en multi-trajets. L’objectif d'une telle recherche est : d’étudier l'association de plusieurs antennes à l'émission et / ou la réception pour améliorer le bilan de liaison, et la capacité des systèmes sans fil, (diminution de BER (Bit Error Rate), augmentation de débit ...). Cette thèse s’intéresse à l'aspect électromagnétique et traitement du signal. Afin de comprendre les phénomènes mis en jeu, et de caractériser les performances du terminal, il doit être placé dans un environnement de propagation multi-trajets contrôlable dans le temps et dans l'espace.Cela nous amène à trouver des méthodes de mesures capables de reproduire des modèles de canaux de propagation réalistes. Dans le cadre de cette thèse la méthode utilisée est la chambre réverbérante. Dans cette thèse, nous nous intéressons à l'aspect temporel. La chambre réverbérante (RC) est considérée comme un outil utile pour émuler des environnements riches en multi-trajets. Dans cette contribution, ce dispositif est utilisé pour émuler des modèles canaux multi-trajets, et évaluer la performance des systèmes de communication sans fil. Cette évaluation est effectuée avec des mesures en temps réel et non temps réel. Parmi les objectifs de cette thèse est d'obtenir un modèle de simulation électromagnétique de la chambre réverbérante basé sur une approche circuit, afin de déterminer la fonction de transfert de canal en fonction des pertes. / This thesis is part of the field of the characterization of wireless communication systems using antennas diversity. Indeed, such systems allow fighting against the signals fading, when the terminal is inside a strong multipath environment. The issue of such research is: to study the association of multiple antennas at transmitting and/or receiving sides to improve the link budget, and the capacity of wireless systems, (decrease of BER (Bit Error Rate), increase of throughput …). This thesis takes an interest to the electromagnetic aspect, and signal processing. In order to understand the involved phenomena, and to characterize the terminal performance, it should be placed in a controlled multipath propagation environment in time, and in space. This brings us to find measurement methodologies able to reproduce models of realistic propagation channels. As part of this thesis the method used is the reverberation chamber. In this thesis we are interested in the time aspect. Reverberation chamber (RC) is considered as a useful tool to emulate rich multipath environments. In this contribution, this device is employed to emulate multi clusters channel models (cluster is defined as a group of multipath), and evaluate performance of wireless communication systems. This evaluation is performed with real time and not-real time measurements. It remains to note that among the objectives set out in this PhD thesis is to obtain electromagnetic simulation model of the reverberation chamber based on circuit approach, in order to determine the channel transfer function versus losses quantities.