Performance analysis and network path characterization for scalable internet streaming

Delivering high-quality of video to end users over the best-effort Internet is a challenging task since quality of streaming video is highly subject to network conditions. A fundamental issue in this area is how real-time applications cope with network dynamics and adapt their operational behavior to offer a favorable streaming environment to end users. As an effort towards providing such streaming environment, the first half of this work focuses on analyzing the performance of video streaming in best-effort networks and developing a new streaming framework that effectively utilizes unequal importance of video packets in rate control and achieves a near-optimal performance for a given network packet loss rate. In addition, we study error concealment methods such as FEC (Forward-Error Correction) that is often used to protect multimedia data over lossy network channels. We investigate the impact of FEC on the quality of video and develop models that can provide insights into understanding how inclusion of FEC affects streaming performance and its optimality and resilience characteristics under dynamically changing network conditions. In the second part of this thesis, we focus on measuring bandwidth of network paths, which plays an important role in characterizing Internet paths and can benefit many applications including multimedia streaming. We conduct a stochastic analysis of an end-to-end path and develop novel bandwidth sampling techniques that can produce asymptotically accurate capacity and available bandwidth of the path under non-trivial cross-traffic conditions. In addition, we conduct comparative performance study of existing bandwidth estimation tools in non-simulated networks where various timing irregularities affect delay measurements. We find that when high-precision packet timing is not available due to hardware interrupt moderation, the majority of existing algorithms are not robust to measure end-to-end paths with high accuracy. We overcome this problem by using signal de-noising techniques in bandwidth measurement. We also develop a new measurement tool called PRC-MT based on theoretical models that simultaneously measures the capacity and available bandwidth of the tight link with asymptotic accuracy

Controlling Cavity Magnon Polariton Properties in Frequency and Time Domain

The cavity-magnon-polariton (CMP) is the quasi-particle of a hybrid system that connects photonic excitations to magnonic ones. With this connection, the CMP is an ideal candidate to build a bridge between the promising fields of quantum computing and magnonics. However, for the CMP to fulfill its role as an effective interface, a robust control of its underlying physical properties is imperative. Here, we show how the coupling strength can be manipulated within the experiment by a second continuous drive tone applied directly to the magnon system. Furthermore, switching into the time-domain, we demonstrate a coherent control over the different CMP modes based on ns-short pulses to both oscillating systems. At last, frequency fluctuations are investigated with the future goal of improving magnon coherence times

Modular wireless networks for infrastructure-challenged environments

While access to Internet and cellular connectivity is easily achieved in densely-populated areas, provisioning of communication services is much more challenging in remote rural areas. At the same time Internet access is of critical importance to residents of such rural communities. People's curiosity and realization of the opportunities provided by Internet and cellular access is the key ingredient to adoption. However, poor network performance can easily impede the process of adoption by discouraging people to access and use connectivity. With this in mind, we evaluate performance and adoption of various connectivity technologies in rural developing regions and identify avenues that need immediate attention to guarantee smoother technology adoption. In light of this analysis we propose novel system designs that meet these needs. In this thesis we focus on cellular and broadband Internet connectivity. Commercial cellular networks are highly centralized, which requires costly backhaul. This, coupled with high price for equipment, maintenance and licensing renders cellular network access commercially-infeasible in rural areas. At the same time rural cellular communications are highly local: 70% of the rural-residential calls have an originator-destination pair within the same antenna. In line with this observation we design a low-cost cellular network architecture dubbed Kwiizya, to provide local voice and text messaging services in a rural community. Where outbound connectivity is available, Kwiizya can provide global services. While commercial networks are becoming more available in rural areas they are often out of financial reach of rural residents. Furthermore, these networks typically provide only basic voice and SMS services and no mobile data. To address these challenges, our proposed work allows Kwiizya to operate in coexistence with commercial cellular networks in order to extend local coverage and provide more advanced services that are not delivered by the commercial networks. Internet connectivity in rural areas is typically provided through slow satellite links. The challenges in performance and adoption of such networks have been previously studied. We add a unique dataset and consequent analysis to this spectrum of work, which captures the upgrade of the gateway connectivity in the rural community of Macha, Zambia from a 256kbps satellite link to a more capable 2Mbps terrestrial link. We show that the improvement in performance and user experience is not necessarily proportional to the bandwidth increase. While this increase improved the network usability, it also opened opportunities for adoption of more demanding services that were previously out of reach. As a result the network performance was severely degraded over the long term. To address these challenges we employ white space communication both for connectivity to more capable remote gateways, as well as for end user connectivity. We develop VillageLink, a distributed method that optimizes channel allocation to maximize throughput and enables both remote gateway access as well as end user coverage. While VillageLink features lightweight channel probing, we also consider external sources of channel availability. We design a novel approach for estimation of channel occupancy called TxMiner, which is capable of extracting transmitter characteristics from raw spectrum measurements. We study the adoption and implications of network connectivity in rural communities. In line with the results of our analyses we design and build system architectures that are geared to meet critical needs in these communities. While the focus of analysis in this thesis is on rural sub-Saharan Africa, the proposed designs and system implementations are more general and can serve in infrastructure-challenged communities across the world

MediaSync: Handbook on Multimedia Synchronization

This book provides an approachable overview of the most recent advances in the fascinating field of media synchronization (mediasync), gathering contributions from the most representative and influential experts. Understanding the challenges of this field in the current multi-sensory, multi-device, and multi-protocol world is not an easy task. The book revisits the foundations of mediasync, including theoretical frameworks and models, highlights ongoing research efforts, like hybrid broadband broadcast (HBB) delivery and users' perception modeling (i.e., Quality of Experience or QoE), and paves the way for the future (e.g., towards the deployment of multi-sensory and ultra-realistic experiences). Although many advances around mediasync have been devised and deployed, this area of research is getting renewed attention to overcome remaining challenges in the next-generation (heterogeneous and ubiquitous) media ecosystem. Given the significant advances in this research area, its current relevance and the multiple disciplines it involves, the availability of a reference book on mediasync becomes necessary. This book fills the gap in this context. In particular, it addresses key aspects and reviews the most relevant contributions within the mediasync research space, from different perspectives. Mediasync: Handbook on Multimedia Synchronization is the perfect companion for scholars and practitioners that want to acquire strong knowledge about this research area, and also approach the challenges behind ensuring the best mediated experiences, by providing the adequate synchronization between the media elements that constitute these experiences

The Dipole Response of an Ionization Threshold within Ultrashort and Strong Fields

In this work, the strong-field-modified dipole response at the ionization threshold of helium is studied. The dipole response is induced by an attosecond pulse in the extreme ultraviolet spectral range and is manipulated by an ultrashort and strong femtosecond pulse in the near-infrared. To probe the response, the transient absorption spectrum of helium is recorded for different time delays between both pulses and different intensities of the femtosecond pulse. From the spectra, the dipole response of the ionization threshold is reconstructed, which is linked to the dynamics of excited electrons with energies in the transition region from bound to free. To identify the underlying processes of light-matter interaction leading to the observed structures in the time and spectral domain, different quantum-mechanical model simulations are conducted. As a result, the measured dipole response reveals light-induced energy shifts of the photoelectron’s kinetic energy close to the parent ion, signatures for field-driven recollisions of a photoelectron into the parent ion, and a temporal amplitude and phase gating mechanism. With the latter, the build-up dynamics of complex spectral structures are temporally resolved, which are the time-dependent separation and line-shape modification of the doubly excited Rydberg series as well as the temporal build-up of the ionization threshold

Light-matter interactions

Understanding light-matter interaction is important to control the electron and nuclear dynamics of quantum-mechanical systems. The present work investigates this in the form of angular dependent tunnel ionization and different control mechanisms for nuclear, electron and coupled dynamics. With the help of close collaboration with experimental groups several control mechanisms could be examined and explained. The refined methods and models for these studies can be expanded for different experiments or more general concepts. The first part of this thesis focuses on tunnel ionization as one of the fundamental quantum-mechanical light-matter interactions while the second and third part investigates the control of nuclear and electron dynamics in depth. The angular dependent tunnel ionization of small hydrocarbons and the impact of their field dressed orbitals are researched in chapter 3. Advanced quantum chemical methods are used to explain experimental findings that could not be recognized by only looking at the Highest Occupied Molecular Orbital (HOMO). The so studied molecules show the importance to consider field dressed instead of field free orbitals to understand the light-matter interaction, to replicate experimental findings with theoretical models and to predict the behavior of different molecules. The influence of Rydberg character in virtual orbitals, that can become populated in a field dressed picture, can explain the difference in the angular dependent tunnel ionization for two similar derivates of Cyclohexadiene (CHD) and the lobed structure for C2H4 . This chapter also shows the success of adapting a previous used model for diatomic systems to polyatomic systems. The second part (chapter 4) investigates the deprotonation and isomerization reaction of acetylene (C2H2) and allene (C3H4) and the potential control with laser pulses over theses reaction. The first control mechanism utilizes the light field to suppress the reaction barrier, which allows molecules with lower energy to undergo isomerization and therefore increase the rate of the reaction. The second scheme controls the asymmetry of the reaction, so that either the left to right or right to left isomerization is preferred. This control is exercised by directly manipulating the nuclear wave packet with the Carrier–Envelope–Phase (CEP) of the laser pulse. The mechanism relies on forming a superposition of different normal modes that are excited by different means and therefore have a phase difference. One or more normal modes are excited by the light field and get the CEP imprinted in their phase while the other important normal modes are indirectly excited by the ionization process. This enables directional control of the nuclear dynamics in symmetric molecules. The concept of forming the superposition is general enough to be used in different reactions and molecules. In the last part (chapter 5) the control of electron dynamics with laser pulses is studied. The test case is the selective population of dressed states (SPODS) in the potassium dimer (K2). There a first pulse will populate an electronic superposition between the ground and first excited state. Depending on the relative phase of the second pulse to the oscillating dipole created by the electronic wave packet, the upper or lower dressed state will be populated. Excitation from the two different dressed states leads to two distinguishable final states. Although the scheme focuses on the control of the electron dynamics, the whole mechanism is also heavily influenced by the associated nuclear dynamics

Ultrafast electron dynamics and the role of screening

This thesis focuses on the ultrafast dynamics of electronic excitations in solids and how they are influenced by the screening of the Coulomb interaction between charged particles. The impact of screening on electron dynamics is manifold, ranging from modifications of electron-electron scattering rates over trapping of excess charges to massive renormalisation of electronic band structures. The timescales of these dynamical processes are directly accessible by femtosecond time-resolved photoemission and optical spectroscopy. Three exemplary systems are investigated to shed light onto these fundamental processes: Vanadiumdioxide undergoes a phase transition from a monoclinic insulator to a rutile metal. Apart from temperature, doping and other influences, the insulator-to-metal transition can also be driven by photoexcitation. This, in the past, gave rise to a controversy about the timescales of structural and electronic transition and raised the question which of them constitutes the driving mechanism. Using time-resolved photoelectron spectroscopy, it is shown that the electronic band gap of the insulator collapses instantaneously with photoexcitation and without any structural involvement. The reason is a change of screening due to the generation of photoholes. At the same time, the symmetry of the lattice potential changes, as seen by coherent phonon spectroscopy. This potential change is likely to initiate the structural phase transition from monoclinic to rutile structure. However, the initial non-equilibrium situation can be described by a metallic electronic structure with the atoms still in the monoclinic lattice positions. The SrTiO3/vacuum interface exhibits a two-dimensional electron gas (2DEG), which is delocalised within the surface plane, but localised perpendicular to it. The lower dimensionality changes the form of the screened Coulomb interaction and the phase space within the 2DEG, leading to modified hot carrier lifetimes. These are investigated by time-resolved photoemission spectroscopy: The predicted 2D behaviour is confirmed and two distinct final states within the unoccupied electronic band structure are discovered. Furthermore, the population of the 2DEG is transiently increased by photoexcitation from localised in-gap states into the 2DEG. A different type of screening by dipole moments in amorphous ice layers, is exploited to stabilise and trap electrons within the polar medium in front of a metal surface. Thereby, the mean free path of low energy electrons in amorphous ice is estimated. Moreover, the trapped electrons are used to drive a chemical reaction: A persistent modification of the surface electronic structure of the ice layer is explained via the `dielectron hydrogen evolution reaction'. Understanding the role of screening in these systems allows to explain seemingly unrelated effects, like trapping of excess electrons in ice and the insulator-to-metal transition in VO2, within the same concept

Ultrafast Laser Control of Molecular Quantum Dynamics from a Core-Electron Perspective

This work introduces two experimental approaches to control quantum dynamics in molecules, employing core electrons as messengers. A laser source providing ultrashort pulses has been developed to access the timescale of electronic and structural dynamics inside molecules. Pulses of few-cycle durations in the 1 µm to 2 µm short-wavelength infrared (SWIR) spectral region provide intensities up to 1015 W/cm2 . In combination with a vacuum beamline, this experimental setup allows for ultrafast laser control of molecular dynamics probed by core-electron transitions via x-ray absorption spectroscopy (XAS). The first experiment investigates the manipulation of molecular electronic structure. Here, a soft x-ray (SXR) pulse probes simultaneously to an SWIR pulse of variable intensity. The measured intensityvii dependent absorbance changes in SF6 reveal an increased effective electronic-exchange energy. This demonstrates the alteration of this purely quantum-mechanical component of the electron-electron interaction for the first time. In a second experiment, an SWIR pulse induces coherent molecular vibrations with amplitudes of ten times the diameter of the nucleus. Subsequently, a time-delayed SXR pulse probes the bond-length changes via core-level transitions. This enables an unprecedented 14 femtometer precision which paves the way for site-specific vibrational metrology in gas-phase molecules. Overall, these results enable ultrafast chemical control on a quantum level

Technology 2004, Vol. 2

Proceedings from symposia of the Technology 2004 Conference, November 8-10, 1994, Washington, DC. Volume 2 features papers on computers and software, virtual reality simulation, environmental technology, video and imaging, medical technology and life sciences, robotics and artificial intelligence, and electronics

Radio Communications

In the last decades the restless evolution of information and communication technologies (ICT) brought to a deep transformation of our habits. The growth of the Internet and the advances in hardware and software implementations modified our way to communicate and to share information. In this book, an overview of the major issues faced today by researchers in the field of radio communications is given through 35 high quality chapters written by specialists working in universities and research centers all over the world. Various aspects will be deeply discussed: channel modeling, beamforming, multiple antennas, cooperative networks, opportunistic scheduling, advanced admission control, handover management, systems performance assessment, routing issues in mobility conditions, localization, web security. Advanced techniques for the radio resource management will be discussed both in single and multiple radio technologies; either in infrastructure, mesh or ad hoc networks