Titel Deelnemers "Korte inhoud" "Scalability analysis of the OpenAM access control system with the Universal Scalability Law" "Thomas Heyman, Davy Preuveneers, Wouter Joosen" "© 2014 IEEE. The scalability of a software system is greatly impacted by the scalability of the underlying access control system, which makes analyzing the scalability of that access control system paramount. However, this is not trivial, as contemporary access control systems have a myriad of architectural deployment variations, each of which has a potentially large impact on overall system throughput. There is a need for a systematic approach to map these architectural variations to a reference model which allows to make comparisons and to identify trade-offs. This work provides a piece of the puzzle by demonstrating how this can be achieved by systematically applying the Universal Scalability Law (USL). We illustrate our approach by performing a rigorous scalability analysis of the OpenAM access control system for various deployment alternatives in the domain of authentication. We conclude that the approach is able to provide both qualitative and quantitative results which can be translated into practical operational recommendations for the envisioned types of system deployments." "Scalar: Systematic scalability analysis with the Universal Scalability Law" "Thomas Heyman, Davy Preuveneers, Wouter Joosen" "© 2014 IEEE. Analyzing the scalability and quality of service of large scale distributed systems requires a highly scalable benchmarking framework with built-in communication and synchronisation functionality, which are features that are lacking in current load generation tools. This paper documents Scalar, our distributed, extensible scalability analysis tool that can generate high request volumes using multiple communicating, coordinated nodes. We show how Scalar offers analytics capabilities that support the Universal Scalability Law. We illustrate Scalar on an electronic payment case study, and find that the framework supports complex work flows and is able to characterize and give predictive insights into the quality of service and relative capacity of the system under test in function of the user load." "Analysis of the scalability of UWB indoor localization solutions for high user densities" "Matteo Ridolfi, Samuel Van de Velde, Heidi Steendam, Eli De Poorter" "Radio frequency (RF) technologies are often used to track assets in indoor environments. Among others, ultra-wideband (UWB) has constantly gained interest thanks to its capability to obtain typical errors of 30 cm or lower, making it more accurate than other wireless technologies such as WiFi, which normally can predict the location with several meters accuracy. However, mainly due to technical requirements that are part of the standard, conventional medium access strategies such as clear channel assessment, are not straightforward to implement. Since most scientific papers focus on UWB accuracy improvements of a single user, it is not clear to which extend this limitation and other design choices impact the scalability of UWB indoor positioning systems. We investigated the scalability of indoor localization solutions, to prove that UWB can be used when hundreds of tags are active in the same system. This paper provides mathematical models that calculate the theoretical supported user density for multiple localization approaches, namely Time Difference of Arrival (TDoA) and Two-Way Ranging (TWR) with different MAC protocol combinations, i.e., ALOHA and TDMA. Moreover, this paper applies these formulas to a number of realistic UWB configurations to study the impact of different UWB schemes and settings. When applied to the 802.15.4a compliant Decawave DW1000 chip, the scalability dramatically degrades if the system operates with uncoordinated protocols and two-way communication schemes. In the best case scenario, UWB DW1000 chips can actively support up to 6171 tags in a single domain cell (no handover) with well-selected settings and choices, i.e., when adopting the combination of TDoA (one-way link) and TDMA. As a consequence, UWB can be used to simultaneously localize thousands of nodes in a dense network. However, we also show that the number of supported devices varies greatly depending on the MAC and PHY configuration choices." "Influencing factors in the scalability of distributed stream processing jobs" "Giselle van Dongen, Dirk Van den Poel" "Fast mode decision algorithm for H.264/AVC-to-SVC transcoding with temporal scalability" "Rosario Garrido-Cantos, Jan De Cock, Sebastiaan Van Leuven, Pedro Cuenca, Antonio Garrido, Rik Van de Walle" "Scalable Video Coding (SVC) uses a notion of layers within the encoded bitstream for providing temporal, spatial and quality scalability, separately or combined. By truncating layers the bitstream can be adapted to devices with different characteristics and to varying network constraints. Since the majority of the existing video content is encoded using H.264/AVC without scalability, they cannot benefit from these scalability tools, so a transcoding process should be applied to provide scalability to this existing encoded content. In this paper, an algorithm based on Machine Learning techniques for temporal scalability transcoding from H.264/AVC to SVC focusing on mode decision task is discussed. The results show that when our technique is applied, the complexity is reduced by 82% while maintaining coding efficiency." "Multi-loop quality scalability based on high efficiency video coding" "Glenn Van Wallendael, Jan De Cock, Rik Van de Walle, Marta Mrak" "Scalable video coding performance largely depends on the underlying single layer coding efficiency. In this paper, the quality scalability capabilities are evaluated on a base of the new High Efficiency Video Coding (HEVC) standard under development. To enable the evaluation, a multi-loop codec has been designed using HEVC. Adaptive inter-layer prediction is realized by including the lower layer in the reference list of the enhancement layer. As a result, adaptive scalability on frame level and on prediction unit level is accomplished. Compared to single layer coding, 19.4% Bjontegaard Delta bitrate increase is measured over approximately a 30dB to 40dB PSNR range. When compared to simulcast, 20.6% bitrate reduction can be achieved. Under equivalent conditions, the presented technique achieves 43.8% bitrate reduction over Coarse Grain Scalability of the SVC - H.264/AVC-based standard." "Scalability of the parallel MLFMA" "Jan Fostier, Femke Olyslager" "This paper investigates the scalability of the parallel multilevel fast multipole algorithm (MLFMA). The scalability of a parallel algorithm is its ability to handle a larger problem on a proportionally larger parallel environment without loss of efficiency. It is demonstrated that this is closely related to the distribution of the workload among the different nodes: conventional spatial and hybrid partitioning techniques do not lead to a scalable algorithm, as opposed to the recently introduced hierarchical partitioning scheme. The repartitioning requirements for both the two- and three-dimensional case are investigated. It is shown how the hierarchical partitioning scheme can be combined with an asynchronous implementation that is suitable for scattering at multiple dielectric objects. A scalable open-source implementation in two dimensions is presented and the accurate scattering at a perfect electric conduction cylinder with a diameter of 1.2 million wavelengths is presented." "Sustainability and Scalability in Educational Technology Initiatives: Research-Informed Practice" "Dale S. Niederhauser, Sarah K. Howard, Joke Voogt, Douglas D. Agyei, Therese Laferriere, Jo Tondeur, Margaret J. Cox" "Although a positive impact of technology interventions on educational practice and student outcomes has been shown in many previous research settings, the use of technology in classrooms and schools is still often superficial and not meeting the potential of technology as envisioned by education reformers and researchers in the field. However, when technology projects have been implemented successfully in educational practice and shown valuable impacts, sustainability within similar contexts is not guaranteed—let alone scaling the initiative to other broader contexts. This article builds on the discussions of the EDUsummIT 2017 Thematic Working Group 9 (TWG9) and the summary report that captured the outcome of those discussions. The goal of TWG9 was to help inform policy and practice by providing insights into key factors that contribute to scalability and sustainability of educational technology integration and impact." "Scalability issues in optimal assignment for carpooling" "Luk KNAPEN, Irith Ben-Arroyo Hartman, Daniel Keren, Ansar YASAR, Sungjin CHO, Tom BELLEMANS, Davy JANSSENS, Geert WETS" "Carpooling for commuting can save cost and helps in reducing pollution. An automatic Web based Global CarPooling Matching Service (GCPMS) for matching commuting trips has been designed. The service supports carpooling candidates by supplying advice during their exploration for potential partners. Such services collect data about the candidates, and base their advice for each pair of trips to be combined, on an estimate of the probability for successful negotiation between the candidates to carpool. The probability values are calculated by a learning mechanism using, on one hand, the registered person and trip characteristics, and on the other hand, the negotiation feedback. The problem of maximizing the expected value of carpooling negotiation success was formulated and was proved to be NP-hard. In addition, the network characteristics for a realistic case have been analyzed. The carpooling network was established using results predicted by the operational FEATHERS activity based model for Flanders (Belgium)." "LoRa scalability : a simulation model based on interference measurements" "Jetmir Haxhibeqiri, Floris Van den Abeele, Ingrid Moerman, Jeroen Hoebeke"