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  • Public defence: 2020-06-09 09:30 C312, Sundsvall
    Bakar, Muhammad Abu
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Electronics Design.
    Wide Range Isolated Power Converters2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Power electronics technology is rapidly growing in most industrialapplications. There is an increasing demand for efficient and low profilepower converters in the industry like automotive, power grids, renewableenergy systems, electric rail systems, home appliances, and informationtechnology. In some applications, there is an increasing demand for powerconverters showing a stable performance over a wide variation in inputvoltage, whereas in others the demand is for converters showing a stableperformance over a wide variation of output voltage. In this regard, not somuch work has been done to combine both requirements into one solution;this is the primary focus of the dissertation. It presents a unique solution tothe industry, which addresses both requirements. The technique can beapplied in a one size fits all solution which not only extends the range of theline voltage and the output voltage but also provides the flexibility to adjustthe required set of line/output voltage. The variation in line voltage severelydegrades the performance of power converters because of the extendedfreewheeling interval, more circulating current, narrow range of zero voltageswitching and increased EMI. To overcome this, the converter consists of tworeconfigurable modes on the input side that can be configured following thevariation in line voltage to maintain a stable performance. In addition, itproposes three reconfigurable steps for the output voltage, which can be usedto adjust the output voltage from base level X to 2X and 4X in discrete stepsand/or from X - 4X volt while showing stable performance. This makes theproposal a 2x3 reconfigurable modes power converter, which means that thegain of the proposed converter can be raised to 4 or 8. Furthermore, theflexibility in the reconfigurable structure simplifies the implementation of theproposed single solution in a range of applications. Each concept proposed inthe thesis is verified analytically, experimentally and modelling it into aSPICE simulation. Then the whole concept is confined into a single entity,which is applied in an example application of a phase shifted full bridgeconverter. The full converter is characterized for input voltage 100-400Vdc, theoutput voltage 24-96Vdc, and up to the load power of 1kW.

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  • Public defence: 2020-06-10 09:00 C312, Sundsvall
    Li, Yongwei
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Systems and Technology.
    Computational Light Field Photography: Depth Estimation, Demosaicing, and Super-Resolution2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The transition of camera technology from film-based cameras to digital cameras has been witnessed in the past twenty years, along with impressive technological advances in processing massively digitized media content. Today, a new evolution emerged -- the migration from 2D content to immersive perception. This rising trend has a profound and long-term impact to our society, fostering technologies such as teleconferencing and remote surgery. The trend is also reflected in the scientific research community, and more intention has been drawn to the light field and its applications.

     

    The purpose of this dissertation is to develop a better understanding of light field structure by analyzing its sampling behavior and to addresses three problems concerning the light field processing pipeline: 1) How to address the depth estimation problem when there is limited color and texture information. 2) How to improve the rendered image quality by using the inherent depth information. 3) How to solve the interdependence conflict of demosaicing and depth estimation.

     

    The first problem is solved by a hybrid depth estimation approach that combines advantages of correspondence matching and depth-from-focus, where occlusion is handled by involving multiple depth maps in a voting scheme. The second problem is divided into two specific tasks -- demosaicing and super-resolution, where depth-assisted light field analysis is employed to surpass the competence of traditional image processing. The third problem is tackled with an inferential graph model that encodes the connections between demosaicing and depth estimation explicitly, and jointly performs a global optimization for both tasks.

     

    The proposed depth estimation approach shows a noticeable improvement in point clouds and depth maps, compared with references methods. Furthermore, the objective metrics and visual quality are compared with classical sensor-based demosaicing and multi-image super-resolution to show the effectiveness of the proposed depth-assisted light field processing methods. Finally, a multi-task graph model is proposed to challenge the performance of the sequential light field image processing pipeline. The proposed method is validated with various kinds of light fields, and outperforms the state-of-the-art in both demosaicing and depth estimation tasks.

     

    The works presented in this dissertation raise a novel view of the light field data structure in general, and provide tools to solve image processing problems in specific. The impact of the outcome can be manifold: To support scientific research with light field microscopes, to stabilize the performance of range cameras for industrial applications, as well as to provide individuals with a high-quality immersive experience.

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    Computational Light Field Photography: Depth Estimation, Demosaicing, and Super-Resolution
  • Public defence: 2020-06-11 09:00 Zoom, Sundsvall
    Beltramelli, Luca
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Systems and Technology.
    Random and Hybrid Medium Access for M2M Communication: Scalability and Energy Analysis2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The term machine-to-machine (M2M) communication identifies any fully automated communication between intelligent devices, autonomous from human intervention. M2M communication is a key enabling technology for the Internet of Things (IoT), where it is used to provide ubiquitous connectivity between a large number of intelligent devices. M2M technologies find applications in numerous emerging use cases, such as smart metering, smart cities, intelligent transportation systems, eHealth monitoring, and surveillance/security. The service requirements placed onM2M communication can vary greatly depending on the intended area of application. In general, M2M applications are characterized by the high number of devices communicating with one another through sporadic and short transmissions. The devices are generally distributed over wide areas without easy access to the power grid, relying for their energy supply on batteries and energy harvesting. Therefore, the design of M2M communication technologies should meet the goal of supporting a large number of connected devices while retaining low energy consumption. One of the obstacles to achieving this goal is the high level of interference that can be present on the channel if a large number of M2M devices decide to transmit within a short period of time. To understand how to overcome this obstacle, it is necessary to explore new and old design options available in the channel access of M2M communication. The aim of this work is to study the performance and propose improvements to the channel access mechanisms of M2M communication technologies operating in the unlicensed frequency spectrum. The two technologies discussed in this thesis are IEEE 802.11ah and LoRaWAN. The performance metrics that have been considered consistently throughout this work are the scalability and energy efficiency of the investigated channel access mechanisms, which are especially critical to massive M2M.The first part of the thesis focuses on the IEEE 802.11ah standard and its medium access mechanism with station grouping. An analytical model of the grouping mechanism of IEEE 802.11ah combined with enhanced distributed channel access (EDCA) is presented to assess the quality of service (QoS) differentiation available in IEEE 802.11ah. The throughput and delay of the access categories of EDCA are investigated for different group size and composition. The results reveal that grouping is effective at increasing the throughput of both high and low priority access categories up to 40% compared to the case without groups. A redesign of the access mechanism of IEEE 802.11ah is proposed to realize a hybrid channel access for energy efficient uplink data transmission.  The numerical results show that fora wide range of contending M2M devices and even for the relatively small frame size of 256 bytes, the use of an hybrid channel access can help reducing the average energy  consumption  of  the  devices  per  successful  uplink  frame  transmission.   In the  considered  scenarios,  the  proposed  MAC  mechanism  was  able  to  reduce  the average  energy  consumption  per  successful  transmission  up  to  55%  compared  to standard approach. The second part of the thesis focuses on LoRa, with an investigation on the performance of alternative random channel access mechanisms in LoRaWAN. The connection between the channel access mechanism and the intensity of interference in LoRa networks is characterized for pure Aloha, slotted Aloha, and CSMA channel access. The results reveal several assisting guidelines on the design and selection of a medium access solution within LoRa’s parameter space: device density, service area, and spreading factor allocation.  An out-of-band synchronization mechanism based on FM-Radio Data System (FM-RDS) is proposed to achieve synchronous channel access in LoRa.  The throughput and fairness results for the proposed communication show the clear advantages of synchronous communication in LoRa, meanwhile, the use of out-of-band synchronization reduces the usage of LoRa channels, improving the scalability.  The timing errors of FM-RDS are evaluated combining experimental approach and analytical methods. The observations reveal that despite the poor absolute synchronization, FM-RDS can effectively be used to realize time-slotted communication in LoRa, with performance similar to those obtained by more accurate but expensive time-dissemination technologies.  Finally, a comprehensive model of the interference in neighboring clusters of LoRa devices is proposed, highlights the disruptive effects of the inter-cluster interference on the transmissions success probability, particularly for the devices using the largest spreading factors.

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  • Public defence: 2020-06-12 10:00 F234, Östersund
    Linnell, Mikael
    Mid Sweden University, Faculty of Human Sciences, Department of Humanities and Social Sciences.
    Scenarios we live by: Theorizing anticipatory practices for societal security2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    This thesis explores and theorizes practices for generating knowledge and experience of possible futures in the present. Often, our unreflected everyday actions are clearly focused on the future. We plan future events into calendars, buy insurances, follow weather forecasts, and practice for performances of various kinds, all to reduce the uncertainties that the future brings. Various societal areas have developed specialized and systematic ways of generating knowledge in order for people to prepare for possible future events. A particular and extensive area is that involving societal security and preparedness for extraordinary events. The thesis explores various aspects of futures-making practices in the overall field of societal security, with a special focus on recent measures to strengthen the public's emergency preparedness. The overall aim is to deepen knowledge about the contemporary use of futures-making practices (such as imagination and enactment) and related techniques (such as scenario writing and simulations). Societal security and emergency preparedness have recently come to be recognized nationally and globally in ways that we have not experienced since the Cold War era. The empirical backdrop of the thesis tells about some major events that occurred during the first five years of the new millennium. During this period, a number of terrorist attacks and natural disasters occurred which greatly affected futures-making practices in areas related to societal security and preparedness. Following the 9/11 attacks in 2001, many actors in the security business began to implement new, or revived, ways of relating to the future. From previously focusing mainly on plausible events, interest now turned to possible and unexpected events. Following the criticized management of hurricane Katrina in 2005, a visionary work was initiated with the aim of creating an inclusive and all-encompassing culture of preparedness, a culture that would involve all sectors and actors of society, including the public. The examples may by from a unilateral American context, however the events can also be perceived as part of a global trend with local variations. A trend that includes new ideas about public participation in societal preparedness, as well as new ways in which we create preliminary representations of possible futures in order to prepare for them. In order to clarify different ways in which we relate to the future, I apply cultural geographer Ben Anderson’s (2010) classification of anticipatory practices. Anderson highlights three principal practices: imagination, calculation, and performance. The thesis explores how futures are imagined and enacted through the techniques of scenario writing and simulation, in four separate studies (articles I-IV). Studies I and II examine how imaginations of future emergencies are articulated in interviews with local safety coordinators and volunteers in Sweden, as well as in institutional exercise scenarios in the US. The first study shows how collaboration between the public and professionals is perceived as an ideal for managing societal stress and, furthermore, how various forms for organizing the voluntary public may facilitate for or interfere with fruitful collaboration. The second study investigates how governmental authorities has popularized emergency preparedness through a campaign aiming to prepare people for a possible zombie invasion. The study shows how the campaign makes use of a dynamic interplay between reality and fiction, realism and irrealism, and affirmation and distancing. Studies III and IV examine the meanings of spatiality, materiality, and affect in large-scale disaster simulations for the public. The studies are based on documents and observations collected and conducted in Japan and Turkey in 2014 and 2015. With the third study, I wish to contribute to existing debates on experience design and affective atmospheres in disaster simulation, while in the fourth study I explore enactment-based exercises and experience design through a lens of Foucauldian governmentality and spatial rationality. The four articles are given a common theoretical framework consisting of sociological perspectives on time and temporality, which highlight how the conditions for futures-making practices has evolved through changes in people’s relation to the future. The overall results in the thesis indicate that possibilities for the public to participate in enactment-based exercises are currently limited. However, when made publicly available, exercises are most often designed as entertaining, sensory, and affective learning experiences. Present imaginaries and enactments of negative futures are thus enmeshed with considerations regarding what is possible and probable, real and unreal, near and distant. Furthermore, facilities for public exercises are part of a complex apparatus involving political, economic, and educational perspectives, as well as aspects of entertainment, urban planning, educational technology, and public space.

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    Scenarios we live by
  • Public defence: 2020-06-12 10:00 C306/Online, Sundsvall
    Lindblom, Terje
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Media and Communication Science.
    Bakom bilderna: Bildjournalister och bildjournalistik i ett marknadsorienterat journalistiskt fält2020Doctoral thesis, monograph (Other academic)
    Abstract [en]

    The restructuring of Swedish newspapers due to technological and economic changes in the last decade has hit journalists, and especially photojournalists, very hard. In 2017, Sweden's 165 daily newspapers only employed a total of 60 photojournalists combined, with 70 newspapers left with no photojournalist on staff at all. However, during the same time period the use of images in Swedish newspapers increased.

    Using Bourdieu’s field theory, the purpose of this dissertation is to analyse the positions of photojournalism and photojournalists in the Swedish journalistic field during a crucial and important time for the media industry, through 40 interviews with respondents in swedish newspaper as well as with freelancers in the field. The actors varied in age, gender and number of years in the field, and most importantly through different amounts of symbolic capital, in accordance with Bourdieu’s theory.

    The study shows that Swedish photojournalists’ ideal was to document the world and produce in-depth visual news stories. However, these time-consuming ideals comes into conflict with emerging market-oriented ideals described by other actors in the Swedish journalistic field. This also meant that although photojournalism itself is described as having an increased importance in the field, the photojournalists hadn’t received a correspondingly higher status.

    The study concludes that the commercial importance of photojournalism to the market-oriented journalistic field, as described by actors in the field, shows how it has become a professional boundary object which in turn exposes an on-going professional boundary work and symbolic power struggles between, on the one side, media managers, reporters and multi-skilled journalists and on the other side, photojournalists, concerning the doxa and ethos of photojournalism which in turn is affecting the professional position of photojournalists in the Swedish journalistic field.

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  • Public defence: 2020-06-16 09:00 Zoom, Sundsvall
    Grimaldi, Simone
    Mid Sweden University, Faculty of Science, Technology and Media, Department of Information Systems and Technology.
    Towards Radio-Environment Aware IoT Networks: Wireless Coexistence Methods for Low-complexity Devices2020Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Wireless technologies for short-range communication play a central role in the massive diffusion of the Internet of Things (IoT) paradigm. Such communication solutions rely extensively on the availability of unlicensed spectrum in the form of bands for industrial, scientific, and medical (ISM) applications. While ISM bands greatly simplify network deployments by avoiding operator-related costs and facilitating worldwide applicability, they present the shortcoming of non-cooperative spectrum usage, which manifests in the form of radio interference. Interference and time-varying environments generate complex and dynamic scenarios for wireless network deployments, endangering communication performance. The problem becomes especially critical when the timeliness and reliability of the communication are subject to stringent requirements, which is the case for several industrial IoT (IIoT) applications.

    This work aims to enhance the reliability and performance of wireless communication in IoT networks by enriching the existing methods for radio-environment analysis. The central idea of this research is that a run-time analysis of the radio channel properties is a crucial element to ensure performance stability in unpredictable radio environments with potentially disruptive interference.An added challenge of this work comes from the hypothesis that such an analysis can be performed even with strongly resource-constrained platforms without hindering routine network functionalities. The employed methodology is heavily reliant on experimental validation, encompassing implementation on IoT radio devices and measurement campaigns. This thesis makes two principal scientific contributions.

    The first contribution is the design of a comprehensive collection of methods for the analysis of the radio environment, designed to operate entirely onboard on IoT radio platforms.The approaches encompass interference detection, classification, spectrum analysis, link-state analysis, and detection of outages in end-to-end communication. The methods are designed to overcome the gap that exists in the related literature between the elaborate signal analysis operated with dedicated hardware and the lightweight, but sub-optimal, analysis methods developed for legacy wireless sensor networks.

    The second contribution of this work is made by showing potential uses of the developed analysis methods to: i) safeguard the performance of wireless communication under interference and ii) enhance the coexistence of co-located wireless networks. To this end, firstly, a proactive method for dynamic blacklisting is designed that exploits real-time signal analysis and significantly improves the communication reliability of an IIoT radio link under heavy radio interference. Secondly, a method for autonomous radio environment mapping (REM) in IoT networks is proposed that employs onboard interference identification and tracks the sources of wireless interference in space, time, and frequency. The approach ensures a dynamic level of REM detail and provides a powerful tool for predicting the IoT network performance and adapting the network parameters at run-time.

    The full text will be freely available from 2020-11-15 00:00