Wi-Fi Offload: Tragedy of the Commons or Land of Milk and Honey?

Fueled by its recent success in provisioning on-site wireless Internet access, Wi-Fi is currently perceived as the best positioned technology for pervasive mobile macro network offloading. However, the broad transitions of multiple collocated operators towards this new paradigm may result in fierce competition for the common unlicensed spectrum at hand. In this light, our paper game-theoretically dissects market convergence scenarios by assessing the competition between providers in terms of network performance, capacity constraints, cost reductions, and revenue prospects. We will closely compare the prospects and strategic positioning of fixed line operators offering Wi-Fi services with respect to competing mobile network operators utilizing unlicensed spectrum. Our results highlight important dependencies upon inter-operator collaboration models, and more importantly, upon the ratio between backhaul and Wi-Fi access bit-rates. Furthermore, our investigation of medium- to long-term convergence scenarios indicates that a rethinking of control measures targeting the large-scale monetization of unlicensed spectrum may be required, as otherwise the used free bands may become subject to tragedy-of-commons type of problems.Comment: Workshop on Spectrum Sharing Strategies for Wireless Broadband Services, IEEE PIMRC'13, to appear 201

Engaging Users in the Behavior Change Process With Digitalized Motivational Interviewing and Gamification : Development and Feasibility Testing of the Precious App

Background: Most adults do not engage in sufficient physical activity to maintain good health. Smartphone apps are increasingly used to support physical activity but typically focus on tracking behaviors with no support for the complex process of behavior change. Tracking features do not engage all users, and apps could better reach their targets by engaging users in reflecting their reasons, capabilities, and opportunities to change. Motivational interviewing supports this active engagement in self-reflection and self-regulation by fostering psychological needs proposed by the self-determination theory (ie, autonomy, competence, and relatedness). However, it is unknown whether digitalized motivational interviewing in a smartphone app engages users in this process. Objective: This study aimed to describe the theory- and evidence-based development of the Precious app and to examine how digitalized motivational interviewing using a smartphone app engages users in the behavior change process. Specifically, we aimed to determine if use of the Precious app elicits change talk in participants and how they perceive autonomy support in the app. Methods: A multidisciplinary team built the Precious app to support engagement in the behavior change process. The Precious app targets reflective processes with motivational interviewing and spontaneous processes with gamified tools, and builds on the principles of self-determination theory and control theory by using 7 relational techniques and 12 behavior change techniques. The feasibility of the app was tested among 12 adults, who were asked to interact with the prototype and think aloud. Semistructured interviews allowed participants to extend their statements. Participants’ interactions with the app were video recorded, transcribed, and analyzed with deductive thematic analysis to identify the theoretical themes related to autonomy support and change talk. Results: Participants valued the autonomy supportive features in the Precious app (eg, freedom to pursue personally relevant goals and receive tailored feedback). We identified the following five themes based on the theory-based theme autonomy support: valuing the chance to choose, concern about lack of autonomy, expecting controlling features, autonomous goals, and autonomy supportive feedback. The motivational interviewing features actively engaged participants in reflecting their outcome goals and reasons for activity, producing several types of change talk and very little sustain talk. The types of change talk identified were desire, need, reasons, ability, commitment, and taking steps toward change. Conclusions: The Precious app takes a unique approach to engage users in the behavior change process by targeting both reflective and spontaneous processes. It allows motivational interviewing in a mobile form, supports psychological needs with relational techniques, and targets intrinsic motivation with gamified elements. The motivational interviewing approach shows promise, but the impact of its interactive features and tailored feedback needs to be studied over time. The Precious app is undergoing testing in a series of n-of-1 randomized controlled trials. KEYWORDS health app; mHealth; human-computer interaction; prevention; service design; usability design; intrinsic motivation; reflective processes; spontaneous processes; engagement; self-determination theory; autonomous motivation; gamification; physical activityPeer reviewe

Phylogeography and epidemic history of hepatitis C virus genotype 4 in Africa

HCV genotype 4 is prevalent in many African countries, yet little is known about the genotype׳s epidemic history on the continent. We present a comprehensive study of the molecular epidemiology of genotype 4. To address the deficit of data from the Democratic Republic of the Congo (DRC) we PCR amplified 60 new HCV isolates from the DRC, resulting in 33 core- and 48 NS5B-region sequences. Our data, together with genotype 4 database sequences, were analysed using Bayesian phylogenetic approaches. We find three well-supported intra-genotypic lineages and estimate that the genotype 4 common ancestor existed around 1733 (1650-1805). We show that genotype 4 originated in central Africa and that multiple lineages have been exported to north Africa since ~1850, including subtype 4a which dominates the epidemic in Egypt. We speculate on the causes of the historical intra-continental spread of genotype 4, including population movements during World War 2

Graphical debugging of QVT relations using transformation nets

Zsfassung in dt. SpracheModelltransformationen (MT) übernehmen eine Schlüsselrolle im Model Driven Engineering (MDE) Paradigma, welche zur Standardisierung der Modelltransformationssprache Query / View / Transformation (QVT) von der Object Management Group (OMG) führte. Allerdings konnte diese Sprache bislang nicht das gleiche Interesse wie die Unified Modeling Language (UML) wecken, da ein immanenter Mangel an adequaten Debugging Mechanismen besteht. Folgende drei Problembereiche wurden dabei identifiziert: Erstens offerieren deklarative Sprachen wie QVT Relations (QVT-R) keine operative Sicht des Transformationsprozesses. Nur die Informationen, die von den Interpretern zur Verfügung gestellt werden, sowie die vorhandenen Ein- und Ausgabedaten, können für die Beobachtung der Transformationsumsetzung genutzt werden. Sogar die Reihenfolge der Transformationsausführung wird durch den MT engine als Black-box-System verschleiert. Dies kann zum Problem der Diskrepanz zwischen Design- und Laufzeit führen. Zweitens verfügt der QVT-R Code über ein höheres Abstraktionslevel als die Ausführung und das Debugging des Codes. Dies beeinträchtigt die Möglichkeit von Schlussfolgerungen aus produziereten Ergebnissen. Drittens sind die Informationen der Durchführung der Modelltransformationen über mehrere Artefakte -- einschließlich des Source-Modells, des resultierenden Ziel-Modells und des umfassenden QVT-R Codes -- zerstreut. Daraus folgend sind die Gründe für ein bestimmtes Ergebnis für den Benutzer nicht nachvollziehbar.Zur Lösung der genannten Probleme wird in dieser Diplomarbeit die Visualisierung von QVT-R in Transformationsnetzen mittels des MT Frameworks ``Transformation On Petri Nets In Color'' (TROPIC), das auf Colored Petri Nets (CPN) aufbaut, erörtert. Diese kann als explizite Definition der operationalen Semantik für die Fehlersuche auf hoch abstraktem Level interpretiert werden. Die vorliegende Arbeit formuliert einen konzeptionellen Ansatz mit protoypischer Umsetzung zur Überwindung der bestehenden Kluft zwischen den verwendeten Paradigmen. Dies erfolgt durch die Abbildung der QVT-R Konzepte auf TROPIC. Konkret werden drei Kontributionen präsentiert: (i) ein Lösungsansatz für unidirektionale Transformationen welche ein Zielmodell aus einem bestehenden Quellmodell erstellen, (ii) die Unterstützung von Modelvererbung, und (iii) Synchronisationsansätze für zeitliche und versionsbedingte inkrementelle Änderungen.Model transformations (MT) play a key role in the Model Driven Engineering (MDE) paradigm, leading to the standardization of the Query/View/Transformation (QVT) model transformation language by the Object Management Group (OMG). Until now, however, this language did not attract the same interest as the Unified Modeling Language (UML), because of the lack of adequate debugging facilities which are necessary regarding the following three problem areas: First, declarative languages like QVT Relations (QVT-R) hides the operational semantics of transformations. Only the information provided by the interpreter, as well as the tendered inputs and returned outputs are available for tracking the progress of transformations. Furthermore, the ordering of transformation application is hidden by the MT engines providing only a black-boxes view to the users. This can lead to the problem of impedance mismatches between design and runtime. These characteristics of QVT-R are assets for developing, but are handicaps for debugging. Second, QVT-R code is specified on higher abstraction level than its execution and state-of-the-art debugging. This deteriorates the ability to deduce causes from produced results. Third, the information content responsible for operating MTs is spread over several artifacts including the input model, a resulting target model and the QVT-R code. As a consequence, the reasons for a particular outcome are hard to be derived from the involved artifacts. This severely harms the ease of debugging.Therefore, this master thesis tackles the mentioned problems by visualizing QVT-R as Transformations Nets, using the MT framework ``Transformations On Petri Nets In Color'' (TROPIC) based on Colored Petri Nets (CPN). This can be seen as explicit definition of operational semantics on a high abstraction level providing a white-box view for debugging QVT-R. This thesis proposes a procedure model formulated in a conceptual approach and in a prototypic implementation striving for bridging the existing gap between these two different paradigms by mapping the concepts of QVT Relations to such nets. In this thesis three particular contributions are provided: (i) a solution approach for unidirectional mappings producing target models from an existing source model, (ii) the support for model inheritance, (iii) and synchronization approaches for timely and version-based incremental changes.10

Visual design and analysis support for answer set programming : VIDEAS

Zsfassung in dt. SpracheIn the last decade, logic programming experienced new impetus by the growth of Answer Set Programming (ASP) as one of the key drivers in the academic world. However, ASP could not attract the same interest as other declarative programming languages in practice so far. This lack of interest in ASP may be explained by the absence of a sufficiently supported software engineering methodology resulting in a difficulty of designing and developing ASP programs. No tools supporting the development of ASP programs are available. So far, no modeling environment has been introduced in the context of software development based on the ASP paradigm, which offers valuable abstraction and visualization support during the development process.This thesis aims at establishing a novel method for visually designing and analyzing ASP programs. Therefore, a graphical approach for the visualization of ASP is proposed, which is based on concepts presented in literature for other declarative approaches. Moreover, concepts of model engineering are combined with the field of logic programming.Following an Model Driven Engineering approach, an ASP-specific modeling language is established which is able to visualize important facets of ASP. The modeling language is applied within a graphical editor for the model creation. The resulting models are transformed to textual ASP programs by a code generator. The model engineering approaches are used to define the metamodel, a graphical editor, and to generate the ASP program code from models. Therefore, the link between the formalism of ASP and the graphical representation has to be established. Due to the close connection between ASP and deductive databases-databases with logical reasoning capabilities-the widely used Entity Relationship diagram is applied as initial visualization method for ASP programs.Im letzten Jahrzehnt erlebte die Logikprogrammierung durch die Verbreitung von Answer Set Programmierung (ASP) als eine der treibende Kräfte neuen Auftrieb in der akademischen Welt. Jedoch konnte ASP in der Praxis bislang nicht das gleiche Interesse hervorrufen wie andere deklarative Programmiersprachen. Dieses fehlende Interesse könnte durch die Absenz geeigneter Methodologien des Software Engineerings erklärt werden, welche die Entwicklung von ASP Programmen erschwert. Tools, die den Entwicklungsprozess von ASP Programmen unterstützen, sind nicht verfügbar. Bislang wurde keine Modellierungsumgebung für die ASP Softwareentwicklung vorgestellt, die eine wertvolle Abstraktions- und Visualisierungsunterstützung bietet.Diese Arbeit zielt darauf ab, eine neuartige Methode für die Erstellung und Analyse von ASP Programmen zu etablieren. Dies wird durch die Vorstellung eines graphischen Ansatzes für die Visualisierung von ASP erreicht, welche auf Konzepten aus der Literatur für andere deklarative Sprachen basiert. Darüber hinaus werden Konzepte des Model Engineerings mit dem Bereich der Logikprogrammierung verknüpft. Aufbauend auf einem Model-Driven Engineering Ansatz wird eine ASP-spezifische Modellierungssprache erstellt, welche wichtige Facetten von ASP darstellen kann. Diese Modellierungssprache wird durch die Erstellung von Modellen mittels eines graphischen Editors angewandt. Damit erzeugte Modelle können mit einem Code Generator zurück in ASP Programme transformiert werden. Die Model Engineering Konzepte werden eingesetzt um ein Metamodel, einen graphischen Editor und einen Code Generator zu erstellen. Infolgedessen muss eine Verbindung zwischen den ASP Formalismen und der graphischen Repräsentation definiert werden.Aufgrund der engen Verknüpfung zwischen ASP und deduktiven Datenbanken-Datenbanken mit Inferenz-Fähigkeiten-wird das weit verbreitete Entity Relationship Diagramm als initiale Visualisierungsmethode für ASP Programme eingesetzt.12

A Fixed-Point Model for QoE-based Charging

International audienceWithin the current paradigm change from Quality-of-Service (QoS) towards Quality-of-Experience (QoE), the question of how to charge for QoE is widely neglected in the research community despite of its obvious importance. In this paper, we present and analyze a fixed point model which specifically reflects the double role of prices, i.e. as regulating factor for demand size and at the same time as part of the QoE-based user context. The model is validated through comprehensive user trial results which allow interesting insights into the temporal behavior of end users who are confronted with a fine-grained scale of choices on video quality and corresponding tariffs

What you pay is what you get?

International audienceComplementing the current paradigm change from QoS to QoE, we address fundamental QoE charging issues for Internet services from an end user perspective. Here, key issues arise from gaps of different information contexts involved, which have to be managed when introducing a QoE product. Hence, this paper analyzes the double role of prices for quality perception as well as the impact of QoE on user demand with the help of a fxed point model. Our model is consistent with real-world user behavior that we have observed during comprehensive user trials on quality perception for video on demand services. Based on these results, we propose a simple approach for convergence-based user classifcation, and discuss the complementarity of willingness-to-pay vs. subjective quality perception in service purchasing situations

On the Fixpoint Problem of QoE-based Charging

International audienceWhile with traditional QoS-based charging the pricing structure mainly reflects the delivered QoS in order to regulate the demand, the role of service prices in a Quality of Experience (QoE) context is more complex. Amongst others, the charged price may in addition have a direct impact on the user's quality perception. In this paper, we analyze the structure of the resulting fixpoint problem and discuss the corresponding equilibrium. Based on recent user trials, additional insight into the characteristics of the related feedback loops is provided, before we conclude with outlining some consequences for future QoE-based charging mechanisms

How Paradoxical is "the Paradox of Side Payments" ? : Notes from a Network Interconnection Perspective

International audienceThe world of content provisioning over IP-based networks is currently undergoing a significant change, as Content Providers (CPs) have started to connect directly to Network Service Providers (NSPs) or even operate networks on their own. The resulting novel network architectures pose several fundamental economical challenges, for instance with respect to incentives for traditional network operators to offer Internet access to large Over-The-Top (OTT) providers. In this paper, we discuss these challenges from a techno-economic perspective, with an emphasis on new business and charging models. We focus on the so-called "Paradox of Side Payments", an important property for charging frameworks enabling more sophisticated cooperation with OTTs. After briefly revisiting the paradox itself, we critically discuss its underlying assumptions. Based on a numerical analysis, we point out limitations of the model, including aspects of applicability for commercial scenarios and future business models. A summary of the main results concludes the paper