Doctor of Philosophy

dissertationHigh speed wireless communication systems (e.g., long-term evolution (LTE), Wi-Fi) operate with high bandwidth and large peak-to-average power ratios (PAPRs). This is largely due to the use of orthogonal frequency division multiplexing (OFDM) modulation that is prevalent to maximize the spectral efficiency of the communication system. The power amplifier (PA) in the transmitter is the dominant energy consumer in the radio, largely because of the PAPR of the input signal. To reduce the energy consumption of the PA an amplifier that simultaneously achieves high efficiency and high linearity. Furthermore, to lower the cost for high volume production, it is desirable to achieve a complete System-on-Chip (SoC) integration. Linear amplifiers (e.g., Class-A, -B, -AB) are inefficient when amplifying signals with large PAPR that is associated by high peak-to-average modulation techniques such as LTE. OFDM. Switching amplifiers (e.g., Class-D, -E, -F) are very promising due to their high efficiency when compared to their linear amplifier counterparts. Linearization techniques for switching amplifiers have been intensively investigated due to their limited sensitivity to the input amplitude of the signal. Deep-submicron CMOS technology is mostly utilized for logic circuitry, and the Moore's law scaling of CMOS optimizes transistors to operate as high-speed and low-loss switches rather than high gain transistors. Hence, it is advantageous to use transistors in switching mode as switching amplifies and use high-speed digital logic circuitry to implement linearization systems and circuitry. In this work, several linearization architectures are investigated and demonstrated. An envelope elimination and restoration (EER) transmitter that comprises a class-E power amplifier and a 10-bit digital-to-analog converter (DAC) controlled current modulator is investigated. A pipelined switched-capacitor DAC is designed to control an open-loop transconductor that operates as a current modulator, modulating the amplitude of the current supplied to a class-E PA. Such a topology allows for increased filtering of the quantization noise that is problematic in most digital PAs (DPA). The proposed quadrature and multiphase architecture can avoid the bandwidth expansion and delay mismatch associated with polar PAs. The multiphase switched capacitor power amplifier (SCPA) was proposed after the quadrature SCPA and it significantly improves the power efficiency

Power system applications of fiber optics

Power system applications of optical systems, primarily using fiber optics, are reviewed. The first section reviews fibers as components of communication systems. The second section deals with fiber sensors for power systems, reviewing the many ways light sources and fibers can be combined to make measurements. Methods of measuring electric field gradient are discussed. Optical data processing is the subject of the third section, which begins by reviewing some widely different examples and concludes by outlining some potential applications in power systems: fault location in transformers, optical switching for light fired thyristors and fault detection based on the inherent symmetry of most power apparatus. The fourth and final section is concerned with using optical fibers to transmit power to electric equipment in a high voltage situation, potentially replacing expensive high voltage low power transformers. JPL has designed small photodiodes specifically for this purpose, and fabricated and tested several samples. This work is described

Time domain analysis of switching transient fields in high voltage substations

Switching operations of circuit breakers and disconnect switches generate transient currents propagating along the substation busbars. At the moment of switching, the busbars temporarily acts as antennae radiating transient electromagnetic fields within the substations. The radiated fields may interfere and disrupt normal operations of electronic equipment used within the substation for measurement, control and communication purposes. Hence there is the need to fully characterise the substation electromagnetic environment as early as the design stage of substation planning and operation to ensure safe operations of the electronic equipment. This paper deals with the computation of transient electromagnetic fields due to switching within a high voltage air-insulated substation (AIS) using the finite difference time domain (FDTD) metho

Electronic and Photonic Systems WILGA 2014

Symposium Wilga 2014, in its 34th edition, was organized during the last week of May. Symposium is organized under the auspices of SPIE, IEEE, Photonics Society of Poland, WEiTI PW, and PKOpto SEP. The event gathered around 350 persons, mainly young researchers from the  whole country. There were presented around 250 speeches and communications. The main book of Symposium Proceedings is Proc. SPIE vol.9290 which contains around 130 papers. A few tens of papers were also published in technical journals. The leading topics of Wilga 2014 were gathered in key sessions: nano-materials for photonics and electronics, astronomy and space technology, biomedicine, computational intelligence, visualization and multimedia, and large research experiments. The paper presents a digest of some topical tracks, and chosen  work results presented during WILGA 2014 Symposium

Performance Comparison of Dual Connectivity and Hard Handover for LTE-5G Tight Integration in mmWave Cellular Networks

MmWave communications are expected to play a major role in the Fifth generation of mobile networks. They offer a potential multi-gigabit throughput and an ultra-low radio latency, but at the same time suffer from high isotropic pathloss, and a coverage area much smaller than the one of LTE macrocells. In order to address these issues, highly directional beamforming and a very high-density deployment of mmWave base stations were proposed. This Thesis aims to improve the reliability and performance of the 5G network by studying its tight and seamless integration with the current LTE cellular network. In particular, the LTE base stations can provide a coverage layer for 5G mobile terminals, because they operate on microWave frequencies, which are less sensitive to blockage and have a lower pathloss. This document is a copy of the Master's Thesis carried out by Mr. Michele Polese under the supervision of Dr. Marco Mezzavilla and Prof. Michele Zorzi. It will propose an LTE-5G tight integration architecture, based on mobile terminals' dual connectivity to LTE and 5G radio access networks, and will evaluate which are the new network procedures that will be needed to support it. Moreover, this new architecture will be implemented in the ns-3 simulator, and a thorough simulation campaign will be conducted in order to evaluate its performance, with respect to the baseline of handover between LTE and 5G.Comment: Master's Thesis carried out by Mr. Michele Polese under the supervision of Dr. Marco Mezzavilla and Prof. Michele Zorz

A novel approach for wide band high-efficiency power amplifier design

Wireless communication systems require an efficient and broadband RF frontend. RF Power Amplifiers (PA) are the most critical component in the RF frontend and are considered the bottleneck in high efficient wideband transmitters. The research starts with an investigation of high efficient operation modes based on waveform engineering. The outcome of the research can be divided into two main parts: The first concerns an analysis of high efficient modes of operation. The second part builds on first part looking at the PA’s efficiency-bandwidth perspective to design a wide band high efficient PA. The first part of the thesis, introduces a novel linear high efficient PA mode termed Injection Power Amplifier (IPA) that exceeds drain efficiency of 90% without relying on the nonlinearity of a PA at the compression region. This is achieved by presenting appropriate negative harmonic impedances to a transistor to reduce the dissipated power, thus, increasing the efficiency of conversion of DC to fundamental RF power. The theoretical analysis of this mode is presented and a validation measurement has been carried out using an active load-pull system. The measured results confirmed the theoretical predictions of achieving high efficiency in a linear PA operation. Furthermore, a PA structure that is based on two parallel PAs (main PA and auxiliary PA) has been proposed along with the practical circuit realization of the IPA mode. In addition, a PA prototype has been designed following a methodology of nonlinear PA design based on waveform engineering. The PA prototype has been characterized and built operating at 0.9 GHz with an output power of 10 W showing a high linear efficient operation of 80% drain efficiency at only 1 dB compression level. The second part of this work aims to tackle today’s limitation of high efficient wideband PAs beyond octave bandwidth. A conceptual system based on multimode operation has been proposed to overcome the need for bandlimiting passive harmonic termination. This novel approach is based on combining passive termination with active harmonic injection to get around the theoretical limitation of one octave for high efficiency harmonically tuned power amplifiers. Furthermore, a proof of concept PA prototype has been designed and built for a two octave bandwidth (4:1 bandwidth) operating from 0.63-2.56 GHz and providing the rated output power of a 10 W GaN device with a PAE greater than 50% at only 1 dB compression point. This multi-mode approach shows a promising technique for future wideband high efficiency wireless transmitters.EThOS - Electronic Theses Online ServiceGBUnited Kingdo