The 5th generation (5G) of mobile networks is just around the corner. It is expected to bring extraordinary benefits to the population and to solve the majority of the problems of current 4th generation (4G) systems. The success of 5G, whose first phase of standardization has concluded, relies in three pillars that correspond to its main use cases: massive machine-type communication (mMTC), enhanced mobile broadband (eMBB), and ultra-reliable low latency communication (URLLC). This thesis mainly focuses on the first pillar of 5G: mMTC, but also provides a solution for the eMBB in massive content delivery scenarios. Specifically, its main contributions are in the areas of: 1) efficient support of mMTC in cellular networks; 2) random access (RA) eventreporting in wireless sensor networks (WSNs); and 3) cooperative massive content delivery in cellular networks. RegardingmMTC in cellular networks, this thesis provides a thorough performance analysis of the RA procedure (RAP), used by the mobile devices to switch from idle to connected mode. These analyses were first conducted by simulation and then by an analytical model; both of these were developed with this specific purpose and include one of the most promising access control schemes: the access class barring (ACB). To the best of our knowledge, this is one of the most accurate analytical models reported in the literature and the only one that incorporates the ACB scheme. Our results clearly show that the highly-synchronized accesses that occur in mMTC applications can lead to severe congestion. On the other hand, it is also clear that congestion can be prevented with an adequate configuration of the ACB scheme. However, the configuration parameters of the ACB scheme must be continuously adapted to the intensity of access attempts if an optimal performance is to be obtained. We developed

A Ph.D. Thesis

Exploring the microscopic origin of magnetic anisotropies with X-ray magnetic circular dichroism (XMCD) spectroscopy

Platinum metal was shock compressed to 660 GPa using a two‐stage light‐gas gun to qualify this material as an ultrahigh‐pressure standard for both dynamic and static experiments. The shock velocity data are consistent with most of the previously measured low‐pressure data, and an overall linear us−up relationship is found over the range 32–660 GPa. As a part of this work, we have also extended the Hugoniot of the tantalum standard we use to 560 GPa; we have included these data into a new linear fit of the tantalum Hugoniot between 55–560 GPa. We also present the results of a first‐principles theoretical treatment of compressed platinum. The fcc phase is predicted to remain stable to beyond 550 GPa. In addition, we have calculated the 300‐K pressure‐volume isotherm and the Hugoniot. The latter is in excellent agreement with experimental results and qualifies the former to at least 10% accuracy.

The equation of state of platinum to 660 GPa (6. 6 Mbar)

The semi-empirical Tight Binding model1,2 is the simplest scheme for describing the energetics of semi-conductors and transition metals within a quantum mechanical framework.

https://iopscience.iop.org/article/10.1088/0022-3719/21/1/007/pdf

The tight-binding bond model

In this paper, we review a large set of experimental data acquired over the past decade by several groups, and demonstrate how it can be used to construct a detailed picture of the low-temperature metallic state of the unconventional superconductor Sr2RuO4. We show how the normal state properties can be consistently and quantitatively explained in terms of Landau quasi-particles moving on a quasi-two-dimensional Fermi surface. Besides presenting our full and extensive data sets, we explain the details of some novel data analysis tools that can be used within the general context of quasi-two-dimensional metals. We then use the experimental Fermi surface and band dispersion to reassess several issues relevant to the unconventional superconductivity in Sr2RuO4, such as the spin-fluctuation spectrum, quasi-particle renormalization, interlayer dispersion and pressure dependence.

Quasi-two-dimensional Fermi liquid properties of the unconventional superconductor Sr2RuO4

Lifshitz, I. M. and Kaganov, M. I. Geometric concepts in the electron theory of metals. -- Wilkins, J. W. Understanding quasi-particles. -- Chambers, R. G. The generalized path-integral approach to transport problems. -- Pippard, A. B. The Shoenberg effect (magnetic interaction). -- Mackintosh, A. R. and Andersen, O. K. The electronic structure of transition metals. -- Lonzarich, G. G. Fermi surface studies of ground-state and magnetic excitations in itinerant electron ferromagnets. -- Fawcett, E. et al. The effect of strain on the Fermi surface. -- Coleridge, P. T. The de Haas-van Alphen effect in dilute alloys. -- Springford, M. Electron quasi-particle lifetimes in metals. -- Higgins, R. J. and Lowndes, D. H. Waveshape analysis in the de Haas-van Alphen effect. -- Coleridge, P. T. and Templeton, I. M. High precision measurements of de Haas-van Alphen frequencies.

Electrons at the Fermi Surface

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Electrons at the Fermi Surface