Measurements, Models, Systems and Design

531 s.

Magnetless circulators based on linear time-varying circuits

In a crowded electromagnetic spectrum with an ever‐increasing demand for higher data rates to enable multimedia‐rich applications and services, an efficient use of the available wireless resources becomes crucial. For this reason, full‐duplex communication, which doubles the transmission rate over a certain bandwidth compared to currently deployed half-duplex radios by operating the uplink and the downlink simultaneously on the same frequency, has been brought back into the spotlight after decades of being presumed impractical. This long‐held assumption has been particularly due to the lack of high performance low-cost and small-size circulators that could mitigate the strong self-interference at the RF frontend interface of full-duplex transceivers while, at the same time, permitting low-loss bi-directional communication using a single antenna. Traditionally, such non-reciprocal components were almost exclusively based on magnetic biasing of rare-earth ferrite materials, which results in bulky and expensive devices that are not suitable for the vast majority of commercial systems. Despite significant research efforts over the past few decades, none of the previous works managed to eliminate the magnet while satisfying all the challenging requirements dictated by the standards of real systems. In this dissertation, we introduce several newly invented magnetless circulators based on linear time-varying circuits that can overcome for the first time the limitations of all previous approaches. We analyze the presented circuits rigorously and validate them through simulations and measurements, showing unprecedented performance in all relevant metrics, thus holding the promise to enable full-duplex radios in the near futur

Spatial diversity in MIMO communication systems with distributed or co-located antennas

The use of multiple antennas in wireless communication systems has gained much attention during the last decade. It was shown that such multiple-input multiple-output (MIMO) systems offer huge advantages over single-antenna systems. Typically, quite restrictive assumptions are made concerning the spacing of the individual antenna elements. On the one hand, it is typically assumed that the antenna elements at transmitter and receiver are co-located, i.e., they belong to some sort of antenna array. On the other hand, it is often assumed that the antenna spacings are sufficiently large, so as to justify the assumption of independent fading. In this thesis, the above assumptions are relaxed. In the first part, it is shown that MIMO systems with distributed antennas and MIMO systems with co-located antennas can be treated in a single, unifying framework. In the second part this fact is utilized, in order to develop appropriate transmit power allocation strategies for co-located and distributed MIMO systems. Finally, the third part focuses on specific synchronization problems that are of interest for distributed MIMO systems

Control analysis and design of medium voltage converter with multirate techniques

This work aims to unify the current knowledge about multirate controllers with design techniques for grid-tied converters, in this occasion, connected to Medium Voltage AC grid. Therefore, the multirate contributions, that have been given so far, are studied, as well as everything related to modulation techniques for power converters. The temporal implications of the DSPWM actuator will be correlated to multirate analysis, in addition to possible alternatives for applications with a lower sampling frequency than modulation one. Finalizing with explanations and result demonstrations of controllers working between two frequencies or rates, by means of the available power converter in laboratory.Este trabajo pretende unir el conocimiento actual sobre controladores multitasa o multifrecuencia (multirate) con técnicas de diseño para convertidores conectados a la red, en este caso concreto, a la red alterna (AC) de Media Tensión. Por tanto, se estudian las contribuciones multirate realizadas hasta la fecha, así como todo lo relacionado con la modulación de la señal de control para los convertidores. Las implicaciones temporales del actuador DSPWM se relacionarán con el análisis multitasa, así como se explicarán posibles alternativas para aplicaciones con una frecuencia de muestreo menor que la de modulación. Finalizando con la explicación y presentación de resultados de controladores trabajando entre dos frecuencias o tasas, mediante simulaciones del convertidor disponible en laboratorio.Máster Universitario en Ingeniería Industrial (M141