The reliable internet stream transport (RIST) protocol is used for streaming video over the internet and requires time synchronisation to ensure that each frame is played out at the correct time. One method to ensure time synchronisation today in RIST productions is by utilizing the network time protocol (NTP). NTP has several issues and requirements that makes it a not ideal time synchronisation method in RIST productions and this thesis proposes a dynamic average time synchronisation (DATS) method as an option for using NTP in RIST productions. The DATS method uses a two-way synchronisation scheme to estimate the time offset between a video sender node and a video receiver node which is added to an average used as the time offset value. Additionally, it is explored whether or not a Kalman filter can further increase performance in DATS. Furthermore, the Kalman filter parameters were attempted to be optimized with a genetic algorithm. With a simulated \textit{testsrc FFmpeg} stream, the performance of DATS is evaluated and compared with the NTP implementation \textit{Chrony}. The metrics used in the evaluation was the playout delay and the error in time synchronisation which were calculated by periodical messages between a sender and receiver node. The results reveal that DATS performs slightly better without a Kalman filter but is slightly less robust without it. The results also indicated that DATS is comparable to NTP in an unloaded network, but is outperformed by NTP in a congested network.

Background. Speed is getting more and more critical in modern Software Engineering to be able to respond to users’ expectations of product development. One practice that takes a significant amount of time in the process of releasing software to the customers is testing. It is a clear trend that organizations are increasing the amount of test automation compared to manual testing. However, manual testing is still prominent in GUI-based testing due to challenges interacting with a GUI from test scripts. One of the most prominent challenges is synchronizing test script execution with the system under test. Objectives. This research aims to compare static and dynamic synchronization of GUI-based tests. This comparison will be conducted by replicating an existing Selenium test suite using static synchronization to Playwright, which will use dynamic synchronization and run the test suites against a web-based application. These test suites will then be used to compare the two types of synchronization from the perspective of test execution efficiency, test output correctness, and maintenance cost.Methods. The research methodology we chose is experiment. We have chosen Selenium to represent static synchronization and Playwright to represent dynamic synchronization. We used an existing test suite in Selenium that was translated into Playwright. There are a total of 81 tests in the test suite. The test suites were used to compare test scripts that use static and dynamic synchronization from the perspective of test execution efficiency, test output correctness, and maintenance cost.Results. The data collected from the experiments shows that execution efficiency for test scripts using dynamic synchronization is significantly faster than static synchronization. A mean difference between the test suites showed a decrease of 87%. For defect identification, ten defects where used and both test suites managed to identify all of them, resulting in no difference could be found. Test maintenance cost was found that test scripts using dynamic synchronization had a positive effect with an average of 60% less time spent on maintenance.Conclusions. Based on the result, we found that test scripts using dynamic synchronization improved execution efficiency and maintenance costs without sacrificing the test output correctness.

No description available.

Model Driven Engineering (MDE) has gained a considerable attention in the software engineering domain in the past decade. MDE proposes shifting the focus of the engineers from concrete artifacts (e.g., code) to more abstract structures (i.e., models). Such a change allows using the human intelligence more efficiently in engineering software products. Model Transformation (MT) is one of the key operations in MDE and plays a critical role in its successful application. The current MT approaches, however, usually miss either one or both of the two essential features: 1) declarativity in the sense that the MT definitions should be expressed at a sufficiently high level of abstraction, and 2) formality in the sense that the approaches should be based on precise underlying semantics. These two features are both critical in effectively managing the complexity of a network of interrelated models in an MDE process. This thesis tackles these shortcomings by promoting a declarative MT approach that is built on mathematical foundations. The approach is called Query Structured Transformation (QueST) as it proposes a structured orchestration of diagrammatic queries in the MT definitions. The aim of the thesis is to make the QueST approach –that is based on formal foundations– accessible to the MDE community. This thesis first motivates the necessity of having declarative formal approaches by studying the variety of model synchronization scenarios in the networks of interrelated models. Then, it defines a diagrammatic query framework (DQF) that formulates the syntax and the semantics of the QueST collection-level diagrammatic operations. By a detailed comparison of the QueST approach and three rule-based MT approaches (ETL, ATL, and QVT-R), the thesis shows the way QueST contributes to the development of the following aspects of MT definitions: declarativity, modularity, incrementality, and logical analysis of MT definitions. / Thesis / Doctor of Philosophy (PhD)

Impulse-based Ultra Wideband (UWB) radio technology has recently gained significant research attention for various indoor ranging, sensing and communications applications due to the large amount of allocated bandwidth and desirable properties of UWB signals (e.g., improved timing resolution or multipath fading mitigation). However, most of the applications have focused on indoor environments where the UWB channel is characterized by tens to hundreds of resolvable multipath components. Such environments introduce tremendous complexity challenges to traditional radio designs in terms of signal detection and synchronization. Additionally, the extremely wide bandwidth and shared nature of the medium means that UWB receivers must contend with a variety of interference sources. Traditional interference mitigation techniques are not amenable to UWB due to the complexity of straight-forward translations to UWB bandwidths. Thus, signal detection, synchronization and interference mitigation are open research issues that must be met in order to exploit the potential benefits of UWB systems. This thesis seeks to address each of these three challenges by first examining and accurately characterizing common approaches borrowed from spread spectrum and then proposing new methods which provide an improved trade-off between complexity and performance. / Ph. D.

The demand for access to information when and where you need has motivated the transition of wireless communications from a fixed infrastructure based cellular communications technology to a more pervasive adhoc wireless networking technology. Challenges still remain in wireless adhoc networks in terms of meeting higher capacity demands, improved reliability and longer connectivity before it becomes a viable widespread commercial technology. Present day wireless mesh networking uses node-to-node serial multi-hop communication to convey information from source to destination in the network. The performance of such a network depends on finding the best possible route between the source and destination nodes. However the end-to-end performance can only be as good as the weakest link within a chosen route. Unlike wired networks, the quality of point-to-point links in a wireless mesh network is subject to random fluctuations. This adversely affects the performance resulting in poor throughput and poor energy efficiency. In recent years, a new paradigm for communication called cooperative communications has been proposed for which initial information theoretic studies have shown the potential for improvements in capacity over traditional multi-hop wireless networks. Cooperative communication involves exploiting the broadcast nature of the wireless medium to form virtual antenna arrays out of independent single-antenna network nodes for transmission. In this research we explore the fundamental performance limits of cooperative communication under more practical operating scenarios. Specifically we provide a framework for computing the outage and ergodic capacities of non identical distributed MIMO links, study the effect of time synchronization error on system performance, analyze the end-to-end average bit error rate (ABER) performance under imperfect relaying, and study range extension and energy efficiency offered by the system when compared to a traditional system. / Ph. D.

As chip vendors are increasingly manufacturing a new generation of multi-processor chips called multicores, improving software performance requires exposing greater concurrency in software. Since code that must be run sequentially is often due to the need for synchronization, the synchronization abstraction has a significant effect on program performance. Lock-based synchronization — the most widely used synchronization method — suffers from programability, scalability, and composability challenges. Transactional memory (TM) is an emerging synchronization abstraction that promises to alleviate the difficulties with lock-based synchronization. With TM, code that read/write shared memory objects is organized as transactions, which speculatively execute. When two transactions conflict (e.g., read/write, write/write), one of them is aborted, while the other commits, yielding (the illusion of) atomicity. Aborted transactions are re-started, after rolling-back changes made to objects. In addition to a simple programming model, TM provides performance comparable to lock-based synchronization. Software transactional memory (STM) implements TM entirely in software, without any special hardware support, and is usually implemented as a library, or supported by a compiler or by a virtual machine. In this thesis, we present ByteSTM, a virtual machine-level Java STM implementation. ByteSTM implements two STM algorithms, TL2 and RingSTM, and transparently supports implicit transactions. Program bytecode is automatically modified to support transactions: memory load/store bytecode instructions automatically switch to transactional mode when a transaction starts, and switch back to normal mode when the transaction successfully commits. Being implemented at the VM-level, it accesses memory directly and uses absolute memory addresses to uniformly handle memory. Moreover, it avoids Java garbage collection (which has a negative impact on STM performance), by manually allocating and recycling memory for transactional metadata. ByteSTM uses field-based granularity, and uses the thread header to store transactional metadata, instead of the slower Java ThreadLocal abstraction. We conducted experimental studies comparing ByteSTM with other state-of-the-art Java STMs including Deuce, ObjectFabric, Multiverse, DSTM2, and JVSTM on a set of micro- benchmarks and macro-benchmarks. Our results reveal that, ByteSTM's transactional throughput improvement over competitors ranges from 20% to 75% on micro-benchmarks and from 36% to 100% on macro-benchmarks. / Master of Science

[ES] Actualmente, existe una gran variedad de tecnologías de distribución de contenidos multimedia, de dispositivos de consumo, así como de tipos de contenidos. En cuanto a tecnologías de distribución, dichos contenidos se pueden enviar bien a través de redes broadcast, como las redes DVB, o bien a través de redes broadband, como las redes IP (por ejemplo, a través de Internet). La coordinación y convergencia entre los dos tipos de tecnologías para distribuir contenidos relacionados ofrece un gran potencial a los proveedores de contenidos, así como grandes beneficios a los consumidores (una prueba de ello es el estándar Hybrid Broadcast Broadband TV o HbbTV). Sin embargo, la recepción de contenidos relacionados procedentes de diferentes redes híbridas (broadcast/broadband) conlleva una variabilidad de retardos significativa, por lo que se deben superar una serie de retos importantes, como, por ejemplo, la necesidad de mecanismos que garanticen un consumo sincronizado de dichos contenidos, bien en un mismo dispositivo o bien en distintos dispositivos (locales o remotos). Se han especificado, implementado y evaluado soluciones de sincronización de los procesos de reproducción de contenidos híbridos (prevenientes de redes broadcast y/o broadband) tanto en entornos multidispositivo, entre dispositivos locales (Inter-Device Synchronization o IDES), como en entornos multiusuario, entre destinatarios distribuidos en red (Inter-Destination Media Synchronization o IDMS), incluyendo la sincronización de efectos multisensoriales. Se ha diseñado e implementado una plataforma extremo-a-extremo para la generación, distribución (adaptativa) y consumo de contenidos híbridos relacionados, tanto en un mismo dispositivo como en múltiples dispositivos locales (por ejemplo, escenario multipantalla) o remotos (por ejemplo, TV Social). Se han generado y preparado contenidos multimedia tradicionales (2D) y omnidireccionales (360), enriquecidos con efectos multisensoriales que mejoran el grado de realismo y la inmersividad de los usuarios. La plataforma es compatible con el estándar HbbTV y, además, incluye soluciones eficientes para aspectos clave que no están especificados en dicho estándar, pero que son necesarios para la implementación satisfactoria de servicios de TV híbridos y multidispositivo en la misma, como, por ejemplo: la necesidad de un buffer para el contenido broadcast (existente y opcional hasta la especificación HbbTV 2.0.2); mecanismos de señalización, asociación y descripción de contenido disponible y relacionado con el contenido principal; mecanismos de coordinación e interacción entre los dispositivos de consumo; o soluciones de sincronización para alinear en el tiempo el consumo de contenidos de forma satisfactoria. Los resultados obtenidos en la evaluación realizada muestran que el nivel de sincronización adquirido entre los procesos de reproducción de los diversos tipos de contenido disponibles a través de distintas tecnologías de transmisión alcanza unos valores suficientes para proporcionar al usuario un consumo con un nivel de asincronías imperceptible. Dicha precisión alcanzada ha resultado en una QoE para el consumidor muy satisfactoria, ofreciéndole al mismo un completo ecosistema de consumo de contenidos que incluye tanto contenido multimedia tradicional, como contenido omnidireccional y mulsemedia. / [CA] Actualment, hi ha una gran varietat de tecnologies de distribució de contingut multimèdia, dispositius de consum, així com tipus de contingut. Pel que fa a les tecnologies de distribució, aquest contingut es pot lliurar a través de xarxes de difusió, com ara xarxes DVB, o a través de xarxes de banda ampla, com les xarxes IP (per exemple, a través d'Internet). La coordinació i convergència entre els dos tipus de tecnologies per distribuir continguts relacionats ofereix un gran potencial als proveïdors de continguts, així com grans beneficis per als consumidors (una prova d'això és l'estàndard Hybrid Broadcast Broadband TV o HbbTV). Tanmateix, la recepció de continguts relacionats des de diferents xarxes híbrides (emissió/banda ampla) comporta una important variabilitat de retard, per la qual cosa s'han de superar una sèrie de reptes importants, com la necessitat de mecanismes que garanteixin el consum sincronitzat d'aquests continguts, ja siga en el mateix dispositiu. o en diferents dispositius (locals o remots). S'han especificat, implementat i evaluat solucions de sincronització per a processos de reproducció de continguts híbrids (xarxes de broadcast i/o de banda ampla) tant en entorns multidispositiu, entre dispositius locals (Inter-Device Synchronization o IDES), com en entorns IDMS (Inter-Destination Media Synchronization o IDMS), incloent la sincronització d'efectes multisensorials. S'ha dissenyat i implementat una plataforma d'extrem a extrem per a la generació, distribució (adaptativa) i consum de contingut híbrid relacionat, tant en un sol dispositiu com en múltiples locals (p. ex., escenari multipantalla) o remots (p. ex., Social TV). dispositius. S'han generat i preparat contingut multimèdia tradicional (2D) i omnidireccional (360), enriquit amb efectes multisensorials que milloren el grau de realisme i immersivitat dels usuaris. La plataforma és compatible amb l'estàndard HbbTV i, a més, inclou solucions eficients per a aspectes clau que no s'especifiquen en aquest estàndard, però que són necessaris per a la implantació amb èxit de serveis de televisió híbrids i multidispositiu en el mateix, com ara: la necessitat per a un buffer per a continguts de difusió (existent i opcional fins a HbbTV 2. 0.2); mecanismes de senyalització, associació i descripció dels continguts disponibles i relacionats amb el contingut principal; mecanismes de coordinació i interacció entre dispositius de consum; o solucions de sincronització per alinear en el temps el consum de continguts de manera satisfactòria. Els resultats obtinguts en l'avaluació realitzada mostren que el nivell de sincronització adquirit entre els processos de reproducció dels diferents tipus de continguts disponibles a través de diferents tecnologies de transmissió assoleix valors suficients per proporcionar a l'usuari un consum amb un nivell d'asincronies imperceptibles. La precisió aconseguida ha donat com a resultat una QoE molt satisfactòria per al consumidor, oferint-li un ecosistema complet de consum de continguts que inclou tant contingut multimèdia tradicional com contingut omnidireccional i mulsemedia. / [EN] Currently, there is a wide variety of multimedia content distribution technologies, consumer devices, as well as types of content. In terms of distribution technologies, such content can be delivered either over broadcast networks, such as DVB networks, or over broadband networks, such as IP networks (e.g. over the Internet). The coordination and convergence between the two types of technologies to distribute related content offers great potential to content providers, as well as great benefits to consumers (a proof of this is the Hybrid Broadcast Broadband TV or HbbTV standard). However, the reception of related content from different hybrid networks (broadcast/broadband) entails significant delay variability, so a number of important challenges must be overcome, such as the need for mechanisms to ensure synchronized consumption of such content, either on the same device or on different devices (local or remote). We have specified, implemented and evaluated synchronization solutions for hybrid content playback processes (broadcast and/or broadband networks) both in multi-device environments, between local devices (Inter-Device Synchronization or IDES), and in multi-user environments, between distributed network recipients (Inter-Destination Media Synchronization or IDMS), including the synchronization of multi-sensory effects. An end-to-end platform has been designed and implemented for the generation, distribution (adaptive) and consumption of related hybrid content, both on a single device and on multiple local (e.g., multiscreen scenario) or remote (e.g., Social TV) devices. Traditional (2D) and omnidirectional (360) multimedia content has been generated and prepared, enriched with multisensory effects that enhance the degree of realism and immersiveness for users. The platform is compatible with the HbbTV standard and, in addition, includes efficient solutions for key aspects that are not specified in that standard, but are necessary for the successful implementation of hybrid and multi-device TV services on it, such as: the need for a buffer for broadcast content (existing and optional up to the HbbTV 2. 0.2); mechanisms for signaling, association and description of content available and related to the main content; coordination and interaction mechanisms between consumption devices; or synchronization solutions to align in time the consumption of content in a satisfactory way. The results obtained in the evaluation carried out show that the level of synchronization acquired between the reproduction processes of the different types of content available through different transmission technologies reaches sufficient values to provide the user with a consumption with an imperceptible level of asynchronies. The accuracy achieved has resulted in a very satisfactory QoE for the consumer, offering him a complete content consumption ecosystem that includes traditional multimedia content as well as omnidirectional and mulsemedia content. / Marfil Reguero, D. (2022). Especificación, implementación y evaluación de soluciones de sincronización multimedia híbrida (broadcast/broadband) e inter-destinatario para posibilitar nuevas experiencias televisivas enriquecidas, personalizadas, inmersivas y compartidas [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/185746

In recent years, the subject of wide-area synchronized measurements has gained a significant amount of attention from the power system researchers. All of this started with the introduction of the Phasor Measurement Unit (PMU), which added a new perspective in the field of wide-area measurement systems (WAMS). With the ever evolving technologies over the years and the need for a more cost effective solution for synchronized frequency measurements, the Frequency Monitoring Network (FNET) was developed and introduced by the Power IT laboratory at Virginia Tech. The FNET is comprised of many Frequency Disturbance Recorders (FDR) geographically distributed throughout the United States. The FDR is a dedicated data acquisition device deployed at the distribution level, which allows for a lower cost and easily deployable WAMS solution. With Internet connectivity and GPS timing synchronization, the FDR provides high accuracy frequency, voltage magnitude and voltage angle data to the remote servers. Although the current FDR design is up to the standard in terms of the measurement accuracy and portability, it is of interest to further the research into alternative architectures and leverage the ever advancing technologies in high speed computing. One of the purposes of this dissertation is to present novel design options for a new generation of FDR hardware design. These design options will allow for more flexibility and to lower reliance on some vendor specific components. More importantly, the designs seek to allow for more computation processing capabilities so that more accurate frequency and angle measurements may be obtained. Besides the fact that the accuracy of frequency and angle measurement is highly dependent on the hardware and the algorithm, much can be said about the role of timing synchronization and its effects on accurate measurements. Most importantly, the accuracy of the frequency and angle estimation is highly dependent on the sampling time of local voltage angles. The challenges to accurate synchronized sampling are two folds. One challenge has to do with the inherent fallbacks of the GPS receiver, which is relatively high cost and limited in availability when the satellite signal is degraded. The other challenge is related to the timing inaccuracies of the sampling pulses, which is attributed to the remainder that results from the imperfect division of the processor counter. This dissertation addresses these issues by introducing the implementation of the high sensitivity (indoor) GPS and network timing synchronization, which aims to increase the availability of frequency measurements in locations that would not have been possible before. Furthermore, a high accuracy timing measurement system is introduced to characterize the accuracy and stability of the conventional crystal oscillator. To this end, a new method is introduced in close association with some prior work in generating accurate sampling time for FDR. Finally, a new method is introduced for modeling the FDR based on the sampling time measurements and some results are presented in order to motivate for more research in this area. / Ph. D.

An important phenomenon of systems driven far-from-equilibrium is spatiotemporal chaos where the dynamics are aperiodic in both time and space. We explored this numerically for three systems: the Lorenz-96 model, the Swift-Hohenberg equation, and Rayleigh-Bénard convection. The Lorenz-96 model is a continuous in time and discrete in space phenomenological model that captures important features of atmosphere dynamics. We computed the fractal dimension as a function of system size and external forcing to estimate characteristic length and time scales describing the chaotic dynamics. We found extensive chaos with significant deviations from extensivity for small changes in system size and also the power-law growth of the dimension with increasing forcing. The Swift-Hohenberg equation is a partial differential equation for a scalar field, which has been widely used as a model for the study of pattern formation. We found that the magnitude of the mean flow in this model must be sufficiently large for spiral defect chaos to occur. We also explored the spatiotemporal chaos in experimentally accessible Rayleigh-Bénard convection using large-scale numerical simulations of the Boussinesq equations and the corresponding tangent space equations. We performed a careful study analyzing the impact of variations in the domain size, Rayleigh number, and Prandtl number on the system dynamics and fractal dimension. In addition, we quantified the dynamics of the spectrum of Lyapunov exponents and the leading order Lyapunov vector in an effort to connect directly with the dynamics of the flow field patterns. Further, we numerically studied the synchronization of chaos in convective flows by imposing time-dependent boundary conditions from a principal domain onto an initially quiescent target domain. We identified a synchronization length scale to quantify the size of a chaotic element using only information from the pattern dynamics. We also explored the relationship of this length scale with the pattern wavelength. Finally, we analyzed bioconvection which occurs as the result of the collective behavior of a suspension of swimming microorganisms. We developed a series of simulations to capture the gyrotactic pattern formation of the swimming algae. The results can be compared with the corresponding trend of pattern instabilities observed in the experimental studies. / Ph. D.