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  • 301.
    Thota, Neena
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Berglund, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    A structured approach to master thesis writing2015In: Conference for University Pedagogical Development, Uppsala, Sweden: Uppsala University, 2015Conference paper (Other academic)
  • 302.
    Thota, Neena
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Berglund, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Integrating international students into CS programs2015In: Proc. 1st Al Baha University and Uppsala University Symposium on Quality in Computing Education, 2015, p. 6-8Conference paper (Refereed)
    Abstract [en]

    In recent years there has been a rapid increase in the intake of international students at universities. Integrating foreign students into the disciplinary and social culture prevalent at the university is a challenging task. In this paper, first, we summarize the findings of three of our studies on the experiences of Chinese students studying computer science at the Department of Information Technology, Uppsala University, Sweden. Then, based on our findings we make recommendations on how to integrate international students into academic life at Computer Science departments. We focus on the program and course levels, and also at the level of individual students in their new social and cultural environment.

  • 303.
    Thota, Neena
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Berglund, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Learning Computer Science: Dimensions of variation within what Chinese students learn2016In: ACM Transactions on Computing Education, ISSN 1946-6226, E-ISSN 1946-6226, Vol. 16, no 3, article id 10Article in journal (Refereed)
  • 304.
    Thota, Neena
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Estadieu, Gerald
    Ferrao, Antonio
    Wong, Kai Meng
    Engaging school students with tangible devices: Pilot project with .NET gadgeteer2015In: Proc. 3rd International Conference on Learning and Teaching in Computing and Engineering, Los Alamitos, CA: IEEE Computer Society, 2015, p. 112-119Conference paper (Refereed)
  • 305.
    Thota, Neena
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems. University of Saint Joseph, Macau, China.
    Negreiros, João G. M.
    Introducing Educational Technologies to Teachers: Experience Report2015In: Journal of University Teaching and Learning Practice, ISSN 1449-9789, E-ISSN 1449-9789, Vol. 12, no 1, p. 5:1-13Article in journal (Refereed)
  • 306. Tian, Ye
    et al.
    Li, Xiong
    Sangaiah, Arun Kumar
    Ngai, Edith
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Song, Zheng
    Zhang, Lanshan
    Wang, Wendong
    Privacy-preserving scheme in social participatory sensing based on Secure Multi-party Cooperation2018In: Computer Communications, ISSN 0140-3664, E-ISSN 1873-703X, Vol. 119, p. 167-178Article in journal (Refereed)
    Abstract [en]

    Social participant sensing has been widely used to collect location related sensory data for various applications. In order to improve the Quality of Information (QoI) of the collected data with constrained budget, the application server needs to coordinate participants with different data collection capabilities and various incentive requirements. However, existing participant coordination methods either require participants to reveal their trajectories to the server which causes privacy leakage, or tradeoff the location accuracy of participants for privacy, thereby leading to lower QoI. In this paper, we propose a privacy-preserving scheme, which allows application server to provide quasi-optimal QoI for social sensing tasks without knowing participants’ trajectories and identity. More specifically, we first suggest a Secure Multi-party Cooperation (SMC) based approach to evaluate participant’s contribution in terms of QoI without disclosing each individual’s trajectory. Second, a fuzzy decision based approach which aims to finely balance data utility gain, incentive budget and inferable privacy protection ability is adopted to coordinate participant in an incremental way. Third, sensory data and incentive are encrypted and then transferred along with participant-chain in perturbed way to protect user privacy throughout the data uploading and incentive distribution procedure. Simulation results show that our proposed method can efficiently select appropriate participants to achieve better QoI than other methods, and can protect each participant’s privacy effectively.

  • 307. Tian, Ye
    et al.
    Wang, Wendong
    Wu, Jie
    Kou, Qinli
    Song, Zheng
    Ngai, Edith C.-H.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Privacy-preserving social tie discovery based on cloaked human trajectories2017In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 66, no 2, p. 1619-1630Article in journal (Refereed)
  • 308.
    Tran, Kim-Anh
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Jimborean, Alexandra
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Carlson, Trevor E.
    National University of Singapore, Singapore.
    Koukos, Konstantinos
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Själander, Magnus
    NTNU, Norway.
    Kaxiras, Stefanos
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    SWOOP: software-hardware co-design for non-speculative, execute-ahead, in-order cores2018In: Proceedings of the 39th ACM SIGPLAN Conference on Programming Language Design and Implementation, Association for Computing Machinery (ACM), 2018, p. 328-343Conference paper (Refereed)
    Abstract [en]

    Increasing demands for energy efficiency constrain emerging hardware. These new hardware trends challenge the established assumptions in code generation and force us to rethink existing software optimization techniques. We propose a cross-layer redesign of the way compilers and the underlying microarchitecture are built and interact, to achieve both performance and high energy efficiency.

    In this paper, we address one of the main performance bottlenecks — last-level cache misses — through a software-hardware co-design. Our approach is able to hide memory latency and attain increased memory and instruction level parallelism by orchestrating a non-speculative, execute-ahead paradigm in software (SWOOP). While out-of-order (OoO) architectures attempt to hide memory latency by dynamically reordering instructions, they do so through expensive, power-hungry, speculative mechanisms.We aim to shift this complexity into software, and we build upon compilation techniques inherited from VLIW, software pipelining, modulo scheduling, decoupled access-execution, and software prefetching. In contrast to previous approaches we do not rely on either software or hardware speculation that can be detrimental to efficiency. Our SWOOP compiler is enhanced with lightweight architectural support, thus being able to transform applications that include highly complex control-flow and indirect memory accesses.

  • 309.
    Tshering, Phurpa
    et al.
    Royal University of Bhutan, Bhutan.
    Lhamo, Dekar
    Royal University of Bhutan, Bhutan.
    Yu, Lu
    Tongji University, China.
    Berglund, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    How do first year students learn C programming in Bhutan?2017In: Proc. 5th International Conference on Learning and Teaching in Computing and Engineering, IEEE Computer Society, 2017, p. 25-29Conference paper (Refereed)
  • 310.
    Tsiftes, Nicolas
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Computer Systems. SICS.
    Storage-Centric System Architectures for Networked, Resource-Constrained Devices2016Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    The emergence of the Internet of Things (IoT) has increased the demand for networked, resource-constrained devices tremendously. Many of the devices used for IoT applications are designed to be resource-constrained, as they typically must be small, inexpensive, and powered by batteries. In this dissertation, we consider a number of challenges pertaining to these constraints: system support for energy efficiency; flash-based storage systems; programming, testing, and debugging; and safe and secure application execution. The contributions of this dissertation are made through five research papers addressing these challenges.

    Firstly, to enhance the system support for energy-efficient storage in resource-constrained devices, we present the design, implementation, and evaluation of the Coffee file system and the Antelope DBMS. Coffee provides a sequential write throughput that is over 92% of the attainable flash driver throughput, and has a constant memory footprint for open files. Antelope is the first full-fledged relational DBMS for sensor networks, and it provides two novel indexing algorithms to enable fast and energy-efficient database queries.

    Secondly, we contribute a framework that extends the functionality and increases the performance of sensornet checkpointing, a debugging and testing technique. Furthermore, we evaluate how different data compression algorithms can be used to decrease the energy consumption and data dissemination time when reprogramming sensor networks.

    Lastly, we present Velox, a virtual machine for IoT applications. Velox can enforce application-specific resource policies. Through its policy framework and its support for high-level programming languages, Velox helps to secure IoT applications. Our experiments show that Velox monitors applications' resource usage and enforces policies with an energy overhead below 3%.

    The experimental systems research conducted in this dissertation has had a substantial impact both in the academic community and the open-source software community. Several of the produced software systems and components are included in Contiki, one of the premier open-source operating systems for the IoT and sensor networks, and they are being used both in research projects and commercial products.

    List of papers
    1. Efficient Sensor Network Reprogramming through Compression of Executable Modules
    Open this publication in new window or tab >>Efficient Sensor Network Reprogramming through Compression of Executable Modules
    2008 (English)In: Proceedings of Fifth Annual IEEE Communications Society Conference on Sensor, Mesh and Ad Hoc Communications and Networks (SECON 2008): June 16-20, 2008, San Francisco, California, USA. 2008, 2008Conference paper, Published paper (Refereed)
    National Category
    Computer Engineering
    Identifiers
    urn:nbn:se:uu:diva-142776 (URN)
    Conference
    Fifth Annual IEEE Communications Society Conference on Sensor, Mesh and Ad Hoc Communications and Networks (SECON 2008): June 16-20, 2008, San Francisco, California, USA. 2008
    Projects
    wisenet
    Available from: 2011-01-17 Created: 2011-01-17 Last updated: 2018-01-12
    2. Enabling Large- Scale Storage in Sensor Networks with the Coffee File System
    Open this publication in new window or tab >>Enabling Large- Scale Storage in Sensor Networks with the Coffee File System
    2009 (English)In: Proceedings of the 8th ACM/IEEE International Conference on Information Processing in Sensor Networks (IPSN 2009), San Francisco, USA, April 2009, 2009Conference paper, Published paper (Refereed)
    Identifiers
    urn:nbn:se:uu:diva-142686 (URN)
    Conference
    8th ACM/IEEE International Conference on Information Processing in Sensor Networks (IPSN 2009), San Francisco, USA, April 2009
    Projects
    wisenet
    Available from: 2011-01-14 Created: 2011-01-14 Last updated: 2016-02-12
    3. A Database in Every Sensor
    Open this publication in new window or tab >>A Database in Every Sensor
    2011 (English)Conference paper, Published paper (Refereed)
    Keywords
    Antelope, database, energy-efficiency, sensor network
    National Category
    Computer Sciences
    Research subject
    Computer Science with specialization in Database Technology
    Identifiers
    urn:nbn:se:uu:diva-267634 (URN)
    Conference
    The 9th ACM Conference on Embedded Networked Sensor Systems (SenSys 2011)
    Funder
    EU, FP7, Seventh Framework Programme, FP7-ICT-224282EU, FP7, Seventh Framework Programme, FP7-2007-2-224053Swedish Foundation for Strategic Research
    Available from: 2015-11-25 Created: 2015-11-25 Last updated: 2018-01-10
    4. Efficient and Flexible Sensornet Checkpointing
    Open this publication in new window or tab >>Efficient and Flexible Sensornet Checkpointing
    2014 (English)In: Wireless Sensor Networks, volume 8354, 2014, p. -65Conference paper, Published paper (Refereed)
    Abstract [en]

    Developing sensornet software is difficult partly because ofthe limited visibility of the system state of deployed nodes. Sensor-net checkpointing is a method that allows developers to save and restore full system state of nodes. We present four extensions to sensornetcheckpointing—compression, binary diffs, selective checkpointing, and checkpoint inspection—that reduce the time required for checkpointing operations considerably, and improve the granularity at which system state can be examined and manipulated down to the variable level. We show through an experimental evaluation that the checkpoint sizes can be reduced by 70%-93%, and the time can be reduced by at least 50% because of these improvements. The reduced time and increased granularity benefits multiple checkpointing use cases, including automated testing, network visualization, and software debugging.

    National Category
    Computer Systems
    Identifiers
    urn:nbn:se:uu:diva-211145 (URN)0.1007/978-3-319-04651-8_4 (DOI)000340395900004 ()978-3-319-04650-1 (ISBN)978-3-319-04651-8 (ISBN)
    Conference
    EWSN 2014: The European Conference on Wireless Sensor Networks; 17-19 February 2014; University of Oxford; Oxford, UK
    Projects
    ProFuN
    Available from: 2013-11-20 Created: 2013-11-20 Last updated: 2016-02-12Bibliographically approved
    5. Velox: A Virtual Machine for IoT Software Security and Resource Protection
    Open this publication in new window or tab >>Velox: A Virtual Machine for IoT Software Security and Resource Protection
    (English)Manuscript (preprint) (Other academic)
    National Category
    Computer Sciences
    Research subject
    Computer Science
    Identifiers
    urn:nbn:se:uu:diva-268870 (URN)
    Funder
    VINNOVAKnowledge Foundation
    Available from: 2015-12-10 Created: 2015-12-10 Last updated: 2018-01-10
  • 311.
    Tsiftes, Nicolas
    et al.
    RISE SICS, Box 1263, SE-16429 Kista, Sweden.
    Voigt, Thiemo
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication. RISE SICS, Box 1263, SE-16429 Kista, Sweden.
    Velox VM: A safe execution environment for resource-constrained IoT applications2018In: Journal of Network and Computer Applications, ISSN 1084-8045, E-ISSN 1095-8592, Vol. 118, p. 61-73Article in journal (Refereed)
    Abstract [en]

    We present Velox, a virtual machine architecture that provides a safe execution environment for applications in resource-constrained IoT devices. Our goal with this architecture is to support developers in writing and deploying safe IoT applications, in a manner similar to smartphones with application stores. To this end, we provide a resource and security policy framework that enables fine-grained control of the execution environment of IoT applications. This framework allows device owners to configure, e.g., the amount of bandwidth, energy, and memory that each IoT application can use. Velox's features also include support for high-level programming languages, a compact bytecode format, and preemptive multi-threading. In the context of IoT devices, there are typically severe energy, memory, and processing constraints that make the design and implementation of a virtual machine with such features challenging. We elaborate on how Velox is implemented in a resource-efficient manner, and describe our port of Velox to the Contiki OS. Our experimental evaluation shows that we can control the resource usage of applications with a low overhead. We further show that, for typical I/O-driven IoT applications, the CPU and energy overhead of executing Velox bytecode is as low as 1-5% compared to corresponding applications compiled to machine code. Lastly, we demonstrate how application policies can be used to mitigate the possibility of exploiting vulnerable applications.

  • 312.
    Tsiftes, Nicolas
    et al.
    RISE SICS.
    Voigt, Thiemo
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Velox VM: A safe execution environment for resource-constrained IoT applications2018In: Journal of Network and Computer Applications, ISSN 1084-8045, E-ISSN 1095-8592, Vol. 18, p. 61-73Article in journal (Refereed)
    Abstract [en]

    We present Velox, a virtual machine architecture that provides a safe execution environment for applications in resource-constrained IoT devices. Our goal with this architecture is to support developers in writing and deploying safe IoT applications, in a manner similar to smartphones with application stores. To this end, we provide a resource and security policy framework that enables fine-grained control of the execution environment of IoT applications. This framework allows device owners to configure, e.g., the amount of bandwidth, energy, and memory that each IoT application can use. Velox's features also include support for high-level programming languages, a compact bytecode format, and preemptive multi-threading.

    In the context of IoT devices, there are typically severe energy, memory, and processing constraints that make the design and implementation of a virtual machine with such features challenging. We elaborate on how Velox is implemented in a resource-efficient manner, and describe our port of Velox to the Contiki OS. Our experimental evaluation shows that we can control the resource usage of applications with a low overhead. We further show that, for typical I/O-driven IoT applications, the CPU and energy overhead of executing Velox bytecode is as low as 1–5% compared to corresponding applications compiled to machine code. Lastly, we demonstrate how application policies can be used to mitigate the possibility of exploiting vulnerable applications.

  • 313.
    Tu, Wei
    et al.
    Wuhan Univ, Coll Comp, Wuhan, Peoples R China..
    Wei, Lei
    Hunan Univ, Coll Comp Sci & Elect Engn, Changsha, Hunan, Peoples R China..
    Hu, Wenyan
    Carnegie Mellon Univ, Sch Comp Sci, Pittsburgh, PA 15213 USA..
    Sheng, Zhengguo
    Univ Sussex, Dept Engn & Design, Brighton, E Sussex, England..
    Nicanfar, Hasen
    Univ British Columbia, Dept Elect & Comp Engn, Vancouver, BC, Canada..
    Hu, Xiping
    Univ British Columbia, Dept Elect & Comp Engn, Vancouver, BC, Canada..
    Ngai, Edith C.-H.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Leung, Victor C. M.
    Univ British Columbia, Dept Elect & Comp Engn, Vancouver, BC, Canada..
    A Survey on Mobile Sensing Based Mood-Fatigue Detection for Drivers2016In: SMART CITY 360 / [ed] LeonGarcia, A Lenort, R Holman, D Stas, D Krutilova, V Wicher, P Caganova, D Spirkova, D Golej, J Nguyen, K, SPRINGER INT PUBLISHING AG , 2016, p. 3-15Conference paper (Refereed)
    Abstract [en]

    The rapid development of the Internet of Things (IoT) has provided innovative solutions to reduce traffic accidents caused by fatigue driving. When drivers are in bad mood or tired, their vigilance level decreases, which may prolong the reaction time to emergency situation and lead to serious accidents. With the help of mobile sensing and mood-fatigue detection, drivers' moodfatigue status can be detected while driving, and then appropriate measures can be taken to eliminate the fatigue or negative mood to increase the level of vigilance. This paper presents the basic concepts and current solutions of moodfatigue detection and some common solutions like mobile sensing and cloud computing techniques. After that, we introduce some emerging platforms which designed to promote safe driving. Finally, we summarize the major challenges in mood-fatigue detection of drivers, and outline the future research directions.

  • 314.
    Ulander, David
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Software Architectural Metrics for the Scania Internet of Things Platform: From a Microservice Perspectiv2017Independent thesis Advanced level (professional degree), 20 credits / 30 HE creditsStudent thesis
    Abstract [en]

    There are limited tools to evaluate a microservice architecture and no common definition of how the architecture should be designed. Moreover, developing systems with microservices introduces additional complexity to the software architecture. That, together with the fact the systems are becoming more complex has led to a desire for architecture evaluation methods.

    In this thesis a set of quality attributes measured by structural metrics are used to evaluate Scania's IoT Offboard platform. By implementing a metrics evaluation program the quality of the software architecture can be improved. Also, metrics can assist developers and architects while they are becoming more efficient since they better understand how performance is measured, i.e. which quality attributes are the most important and how these are measured.

    For Scania's IoT Offboard platform the studied quality attributes are listed in decreasing importance: flexibility, reusability and understandability. All the microservices are loosely coupled in the platform, which results in a loosely coupled architecture. This indicates a flexible, reusable and understandable system, in terms of coupling. Furthermore, the architecture is decentralized, i.e. the system is unflexible and difficult to change. The other metrics were lacking a reference scale, hence they will act as a point of reference for future measurements as the architecture evolves.

    To improve the flexibility, reusability and understandability of the architecture the large microservices should be divided into several smaller microservices. Also aggregators should be utilized more to make the system more flexible.

  • 315.
    Van den Steen, Sam
    et al.
    Univ Ghent, Dept Elect & Informat Syst, B-9000 Ghent, Belgium..
    De Pestel, Sander
    Univ Ghent, Dept Elect & Informat Syst, B-9000 Ghent, Belgium..
    Mechri, Moncef
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Eyerman, Stijn
    Univ Ghent, Dept Elect & Informat Syst, B-9000 Ghent, Belgium..
    Carlson, Trevor
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Black-Schaffer, David
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Hagersten, Erik
    Eeckhout, Lieven
    Univ Ghent, Dept Elect & Informat Syst, B-9000 Ghent, Belgium..
    Micro-Architecture Independent Analytical Processor Performance and Power Modeling2015In: 2015 IEEE International Symposium on Performance Analysis and Software (ISPASS), 2015, p. 32-41Conference paper (Refereed)
    Abstract [en]

    Optimizing processors for specific application(s) can substantially improve energy-efficiency. With the end of Dennard scaling, and the corresponding reduction in energy-efficiency gains from technology scaling, such approaches may become increasingly important. However, designing application-specific processors require fast design space exploration tools to optimize for the targeted application(s). Analytical models can be a good fit for such design space exploration as they provide fast performance estimations and insight into the interaction between an application's characteristics and the micro-architecture of a processor. Unfortunately, current analytical models require some micro-architecture dependent inputs, such as cache miss rates, branch miss rates and memory-level parallelism. This requires profiling the applications for each cache and branch predictor configuration, which is far more time-consuming than evaluating the actual performance models. In this work we present a micro-architecture independent profiler and associated analytical models that allow us to produce performance and power estimates across a large design space almost instantaneously. We show that using a micro-architecture independent profile leads to a speedup of 25x for our evaluated design space, compared to an analytical model that uses micro-architecture dependent profiles. Over a large design space, the model has a 13% error for performance and a 7% error for power, compared to cycle-level simulation. The model is able to accurately determine the optimal processor configuration for different applications under power or performance constraints, and it can provide insight into performance through cycle stacks.

  • 316.
    Van den Steen, Sam
    et al.
    Univ Ghent, Dept Elect & Informat Syst, Ghent, Belgium..
    Eyerman, Stijn
    Intel, Kontich, Belgium..
    De Pestel, Sander
    Univ Ghent, Dept Elect & Informat Syst, Ghent, Belgium..
    Mechri, Moncef
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Carlson, Trevor E.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Black-Schaffer, David
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Hagersten, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Eeckhout, Lieven
    Univ Ghent, Dept Elect & Informat Syst, Ghent, Belgium..
    Analytical Processor Performance and Power Modeling Using Micro-Architecture Independent Characteristics2016In: I.E.E.E. transactions on computers (Print), ISSN 0018-9340, E-ISSN 1557-9956, Vol. 65, no 12, p. 3537-3551Article in journal (Refereed)
    Abstract [en]

    Optimizing processors for (a) specific application(s) can substantially improve energy-efficiency. With the end of Dennard scaling, and the corresponding reduction in energy-efficiency gains from technology scaling, such approaches may become increasingly important. However, designing application-specific processors requires fast design space exploration tools to optimize for the targeted application(s). Analytical models can be a good fit for such design space exploration as they provide fast performance and power estimates and insight into the interaction between an application's characteristics and the micro-architecture of a processor. Unfortunately, prior analytical models for superscalar out-of-order processors require micro-architecture dependent inputs, such as cache miss rates, branch miss rates and memory-level parallelism. This requires profiling the applications for each cache and branch predictor configuration of interest, which is far more time-consuming than evaluating the analytical performance models. In this work we present a micro-architecture independent profiler and associated analytical models that allow us to produce performance and power estimates across a large superscalar out-of-order processor design space almost instantaneously. We show that using a micro-architecture independent profile leads to a speedup of 300x compared to detailed simulation for our evaluated design space. Over a large design space, the model has a 9.3 percent average error for performance and a 4.3 percent average error for power, compared to detailed cycle-level simulation. The model is able to accurately determine the optimal processor configuration for different applications under power or performance constraints, and provides insight into performance through cycle stacks.

  • 317.
    Vasilchenko, Anna
    et al.
    Newcastle Univ, Open Lab, Newcastle, England.
    Cajander, Åsa
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computerized Image Analysis and Human-Computer Interaction.
    Daniels, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Balaam, Madeline
    KTH Royal Inst Technol, Dept Media Technol & Interact Design, Stockholm, Sweden.
    The self-flipped classroom concept: Underlying ideas and experiences2018In: Proc. 48th ASEE/IEEE Frontiers in Education Conference, Piscataway, NJ: IEEE Press, 2018Conference paper (Refereed)
    Abstract [en]

    In the modern fast changing world no formal education is able to provide learners with a complete set of knowledge, skills and competences that they would need to successfully compete on tomorrow's job market. Therefore, the role of universities is increasingly shifting towards provision of an environment where students have a chance to acquire lifelong learning skills. This paper presents underlying ideas of, and practical experiences with, an innovative pedagogy that addresses the lifelong learning skills acquisition along with additional benefits for science and technology students. The proposed approach, called self-flipped classroom (SFC), is built on a synergy of two pedagogies: learning through making and flipped classroom. To unveil the construct of the SFC, we discuss each of its components individually presenting appropriate theoretical grounding. We also report on our experiences from self-flipped classroom implementations in two countries, UK and Sweden, and in three different educational settings. From our work with the SFC concept we have identified four different roles the students can assume in a SFC scenario: creators, collaborators, communicators, and learners. We present our observations regarding the identified roles that have been found in the studied settings. We also outline some implications for teaching using the SFC concept and future research directions in this space.

  • 318.
    Vo, Huu-Phuc
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computing Science.
    Berglund, Anders
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Daniels, Mats
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    A perspective from Vietnamese students on teaching of soft skills2017In: Proc. 5th International Conference on Learning and Teaching in Computing and Engineering, IEEE Computer Society, 2017, p. 23-24Conference paper (Refereed)
    Abstract [en]

    Soft skills are significant to the engineering labour market, especially in Information Technology where demands are high on for instance communication skill, teamwork skill, presentation skill, etc. Despite their importance, educating students in using those skills is not fully included in the bachelor education programmes, especially in developing countries. This project aims to gain insights in how soft skills are taught in Vietnamese universities, and which skills are missing in their bachelor education programmes. The findings are intended to support education in order to develop the teaching of soft skills for Vietnamese students, and decrease the unemployment rate of Vietnamese graduates. In this project, semi-structured interviews, by e-mail, have been used to collect the data. There are eight Vietnamese interviewees who have experiences from various education programmes. The interview transcripts were then analysed and categorised into themes. The results of our work are a preliminary identification of missing skills in the undergraduate programmes, and a set of proposed skills that could be considered to improve the education programmes.

  • 319.
    Voogt, Marianne
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Chen, Chuan Sheng
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Thota, Neena
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Academics' Experience of Teaching Open Ended Group Projects A phenomenographic study2016In: 2016 IEEE FRONTIERS IN EDUCATION CONFERENCE (FIE), 2016Conference paper (Refereed)
    Abstract [en]

    An Open Ended Group Project (OEGP) is a distinguishable pedagogical tool, used by teachers in computing, engineering, and information technology courses. The tool contributes to the development of 'soft' skills essential for students' future career needs. This paper reports on a phenomenographic study that investigates the research question: What are the ways in which academics teaching Open Ended Group Projects experience teaching the course? Previous studies, using the phenomenographic research approach, have offered insights into academics' conceptions of science learning and teaching. However, there are no studies that investigate the experiences of teachers who use OEGP in their classes. This is the first study, that asks academics using an OEGP how they experience teaching these courses. Students enrolled in a course on computing education research conducted the small-scale study at Uppsala University, Sweden. In order to answer the research question, a theoretical sample was selected with a wide range of relevant population characteristics (e.g. background, prior experience, gender, and age). The semi -structured interview questions focused on understanding of OEGP, the learning objectives of OEGP, strategies for teaching these learning objectives, and the teacher's experience in teaching through OEGP. The results indicate that teachers see their role within OEGP as a coach and that the variation between experiences lies in what is intended to be coached. This variation is presented in a hierarchy (the outcome space). Categories focus on: the team, discipline, problem solving skills, learning and motivation. We also look at the first-hand experience of a student in an OEGP course and discuss the teachers' perceptions of students' experiences of OEGP. The implication for teaching is that a teacher needs to reconsider the way he or she teaches more often in OEGP than in regular courses. There are two reasons for this. First, teaching OEGP is based less on teaching content knowledge and more on teaching skills. Secondly, OEGP deals with a 'real problem', and aspects of the problem continuously change. Teachers are recommended to aim for reaching a higher category, indicating a deeper level of experience, and to use the experience of coaching OEGP in other courses as well. The importance of metacognition (reflection on action) and discussion with other teachers who have experience in teaching OEGP is highlighted.

  • 320.
    Wang, Wendong
    et al.
    Beijing Univ Posts & Telecommun, State Key Lab Networking & Switching Technol, XiTuCheng Rd 10, Beijing 100876, Peoples R China.
    Xi, Teng
    Beijing Univ Posts & Telecommun, State Key Lab Networking & Switching Technol, XiTuCheng Rd 10, Beijing 100876, Peoples R China.
    Ngai, Edith C.-H.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Song, Zheng
    Virginia Tech, Dept Comp Sci, Blacksburg, VA 24060 USA.
    Energy-efficient collaborative outdoor localization for participatory sensing2016In: Sensors, ISSN 1424-8220, E-ISSN 1424-8220, Vol. 16, no 6, article id 762Article in journal (Refereed)
    Abstract [en]

    Location information is a key element of participatory sensing. Many mobile and sensing applications require location information to provide better recommendations, object search and trip planning. However, continuous GPS positioning consumes much energy, which may drain the battery of mobile devices quickly. Although WiFi and cell tower positioning are alternatives, they provide lower accuracy compared to GPS. This paper solves the above problem by proposing a novel localization scheme through the collaboration of multiple mobile devices to reduce energy consumption and provide accurate positioning. Under our scheme, the mobile devices are divided into three groups, namely the broadcaster group, the location information receiver group and the normal participant group. Only the broadcaster group and the normal participant group use their GPS. The location information receiver group, on the other hand, makes use of the locations broadcast by the broadcaster group to estimate their locations. We formulate the broadcaster set selection problem and propose two novel algorithms to minimize the energy consumption in collaborative localization. Simulations with real traces show that our proposed solution can save up to 68% of the energy of all of the participants and provide more accurate locations than WiFi and cellular network positioning.

  • 321. Wang, Wenqi
    et al.
    Wei, Yangjie
    Guan, Nan
    Yi, Wang
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    The automatic detection and analysis of electrocardiogram based on Lorenz plot2015In: Proc. 12th International Conference on Robotics and Biomimetics, Piscataway, NJ: IEEE, 2015, p. 644-649Conference paper (Refereed)
  • 322.
    Wang, Xiaojie
    et al.
    NeuSoft Corp, Shenyang, Liaoning, Peoples R China; Dalian Univ Technol, Sch Software, Dalian, Peoples R China.
    Ning, Zhaolong
    Dalian Univ Technol, Sch Software, Dalian, Peoples R China; Kyushu Univ, Fukuoka, Fukuoka, Japan.
    Hu, Xiping
    Chinese Acad Sci, Shenzhen Inst Adv Technol, Beijing, Peoples R China.
    Ngai, Edith
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems. Imperial Coll London, London, England.
    Wang, Lei
    Dalian Univ Technol, Sch Software, Dalian, Peoples R China; Bell Labs Res China, Shanghai, Peoples R China; Samsung, Seoul, South Korea; Washington State Univ, Vancouver, WA USA.
    Hu, Bin
    Lanzhou Univ, Sch Informat Sci & Engn, Lanzhou, Gansu, Peoples R China; Tsinghua Univ, Beijing, Peoples R China; Swiss Fed Inst Technol, Zurich, Switzerland; ACM China, Beijing, Peoples R China.
    Kwok, Ricky
    Univ Hong Kong, Hong Kong, Hong Kong, Peoples R China; HKIE, Hong Kong, Hong Kong, Peoples R China; IET, Hong Kong, Hong Kong, Peoples R China.
    A City-Wide Real-Time Traffic Management System: Enabling Crowdsensing in Social Internet of Vehicles2018In: IEEE Communications Magazine, ISSN 0163-6804, E-ISSN 1558-1896, Vol. 56, no 9, p. 19-25Article in journal (Refereed)
    Abstract [en]

    As an emerging platform based on ITS, SIoV is promising for applications of traffic management and road safety in smart cities. However, the end-to-end delay is large in store-carry-and-forward-based vehicular networks, which has become the main obstacle for the implementation of large-scale SIoV. With the extensive applications of mobile devices, crowdsensing is promising to enable real-time content dissemination in a city-wide traffic management system. This article first provides an overview of several promising research areas for traffic management in SIoV. Given the significance of traffic management in urban areas, we investigate a crowdsensing-based framework to provide timely response for traffic management in heterogeneous SIoV. The participant vehicles based on D2D communications integrate trajectory and topology information to dynamically regulate their social behaviors according to network conditions. A real-world taxi trajectory analysis-based performance evaluation is provided to demonstrate the effectiveness of the designed framework. Furthermore, we discuss several future research challenges before concluding our work.

  • 323.
    Wang, Yang
    et al.
    Northeastern Univ, Shenyang, Liaoning, Peoples R China..
    Guan, Nan
    Hong Kong Polytech Univ, Hong Kong, Hong Kong, Peoples R China..
    Sun, Jinghao
    Northeastern Univ, Shenyang, Liaoning, Peoples R China..
    Lv, Mingsong
    Northeastern Univ, Shenyang, Liaoning, Peoples R China..
    He, Qingqiang
    Northeastern Univ, Shenyang, Liaoning, Peoples R China..
    He, Tianzhang
    Northeastern Univ, Shenyang, Liaoning, Peoples R China..
    Wang, Yi
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems. Northeastern Univ, Shenyang, Liaoning, Peoples R China..
    Benchmarking OpenMP Programs for Real-Time Scheduling2017In: 2017 IEEE 23Rd International Conference On Embedded And Real-Time Computing Systems And Applications (RTSCA), IEEE Computer Society, 2017Conference paper (Refereed)
    Abstract [en]

    Real-time systems are shifting from single-core to multi-core processors. Software must be parallelized to fully utilize the computation power of multi-core architecture. OpenMP is a popular parallel programming framework in general and high-performance computing, and recently has drawn a lot of interests in embedded and real-time computing. Much recent work has been done on real-time scheduling of OpenMP-based parallel workload. However, these studies conduct evaluations with randomly generated task systems, which cannot well represent the structure features of OpenMP workload. This paper presents a benchmark suite, ompTGB, to support research on real-time scheduling of OpenMP-based parallel tasks. ompTGB does not only collect realistic OpenMP programs, but also models them into task graphs so that the real-time scheduling researchers can easily understand and use them. We also present a new response time bound for a subset of OpenMP programs and use it to demonstrate the usage of ompTGB.

  • 324.
    Wang, Yi
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Towards Customizable CPS: Composability, Efficiency and Predictability2017In: Formal Methods and Software Engineering / [ed] Duan, Z Ong, L, Springer, 2017, p. 3-15Conference paper (Refereed)
    Abstract [en]

    Today, many industrial products are defined by software, and therefore customizable by installing new applications on demand - their functionalities are implemented by software and can be modified and extended by software updates. This trend towards customizable products is extending into all domains of IT, including Cyber-Physical Systems (CPS) such as cars, robotics, and medical devices. However, these systems are often highly safety-critical. The current state-of-practice allows hardly any modifications once safety-critical systems are put in operation. This is due to the lack of techniques to preserve crucial safety conditions for the modified system, which severely restricts the benefits of software. This work aims at new paradigms and technologies for the design and safe software updates of CPS at operation-time - subject to stringent timing constraints, dynamic workloads, and limited resources on complex computing platforms. Essentially there are three key challenges: Composability, Resource-Efficiency and Predictability to enable modular, incremental and safe software updates over system life-time in use. We present research directions to address these challenges: (1) Open architectures and implementation schemes for building composable systems, (2) Fundamental issues in real-time scheduling aiming at a theory of multi-resource (inc. multiprocessor) scheduling, and (3) New-generation techniques and tools for fully separated verification of timing and functional properties of real-time systems with significantly improved efficiency and scalability. The tools shall support not only verification, but also code generation tailored for both co-simulation (interfaced) with existing design tools such as Open Modelica (for modeling and simulation of physical components), and deployment on given computing platforms.

  • 325. Wei, Yangjie
    et al.
    Wu, Chengdong
    Yi, Wang
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Dong, Zaili
    Efficient shape reconstruction of microlens using optical microscopy2015In: IEEE transactions on industrial electronics (1982. Print), ISSN 0278-0046, E-ISSN 1557-9948, Vol. 62, no 12, p. 7655-7664Article in journal (Refereed)
  • 326. Wei, Yangjie
    et al.
    Wu, Chengdong
    Yi, Wang
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Wang, Wenxue
    Diffusion-based three-dimensional reconstruction of complex surface using monocular vision2015In: Optics Express, ISSN 1094-4087, E-ISSN 1094-4087, Vol. 23, no 23, p. 30364-30378Article in journal (Refereed)
  • 327. Wei, Yangjie
    et al.
    Yi, Wang
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Dynamic blind source separation based on source-direction prediction2016In: Neurocomputing, ISSN 0925-2312, E-ISSN 1872-8286, Vol. 185, p. 73-81Article in journal (Refereed)
  • 328.
    Winblad, Kjell
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computing Science.
    Sagonas, Konstantinos
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computing Science.
    Jonsson, Bengt
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computing Science. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Lock-free Contention Adapting Search Trees2018In: The 30th ACM Symposium on Parallelism in Algorithms and Architectures, SPAA 2018, New York, NY, USA, 2018, Vol. 30Conference paper (Refereed)
  • 329.
    Xi, Teng
    et al.
    Beijing Univ Posts & Telecommun, State Key Lab Networking & Switching Technol, Beijing, Peoples R China..
    Ngai, Edith
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Song, Zheng
    Virginia Tech, Dept Comp Sci, Blacksburg, VA USA..
    Tian, Ye
    Beijing Univ Posts & Telecommun, State Key Lab Networking & Switching Technol, Beijing, Peoples R China..
    Gong, Xiangyang
    Beijing Univ Posts & Telecommun, State Key Lab Networking & Switching Technol, Beijing, Peoples R China..
    Wang, Wendong
    Beijing Univ Posts & Telecommun, State Key Lab Networking & Switching Technol, Beijing, Peoples R China..
    Collaborative Localization in Participatory Sensing with Load Balancing2015In: 2015 IEEE 23Rd International Symposium On Quality Of Service (IWQOS), 2015, p. 61-62Conference paper (Refereed)
    Abstract [en]

    The increasingly popular smartphones enable participatory sensing systems to collect location-based sensing data for different tasks. However, GPS positioning is very energy consuming, which could drain a mobile device's battery quickly. High energy consumption may threaten the participants and reduce the sustainability of the participatory sensing systems. In this paper, we propose a collaborative localization strategy with load balancing. Simulations with real traces showed that our proposed solution can save more than 80% of the energy consumption for localization in the entire network with load balancing.

  • 330.
    Xi, Teng
    et al.
    Beijing Univ Posts & Telecommun, State Key Lab Networking & Switching Technol, Beijing, Peoples R China.
    Wang, Wendong
    Beijing Univ Posts & Telecommun, State Key Lab Networking & Switching Technol, Beijing, Peoples R China.
    Ngai, Edith C-H
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Liu, Xiuming
    Uppsala Univ, Div Comp Syst, Dept Informat Technol, Uppsala, Sweden.
    Spatio-Temporal Aware Collaborative Mobile Sensing with Online Multi-Hop Calibration2018In: Proceedings of the 2018 the Nineteenth International Symposium on Mobile Ad Hoc Networking and Computing (MOBIHOC '18), Association for Computing Machinery (ACM), 2018, p. 310-311Conference paper (Refereed)
    Abstract [en]

    Real-time accurate air quality data is very important for pollution exposure monitoring and urban planning. However, there are limited high-quality air quality monitoring stations (AQMS) in cities due to their high equipment costs. To provide real-time and accurate data covering large area, this paper proposes a novel scheme that jointly considers online multi-hop calibration and spatio-temporal coverage in route selection for mobile sensors. A novel sensor carrier selection problem (SCSP) is formulated, which aims to maximize the spatio-temporal coverage ratio and guarantee the accuracy of measurements through sensor calibration. An online Bayesian based collaborative calibration (OBCC) scheme is proposed to relax the multi-hop calibration constraint in the SCSP. Based on the OBCC, a multi-hop calibration judgment algorithm (MCJA) is proposed to decide whether the data accuracy of a given set of routes can be guaranteed through collaborative calibration. Furthermore, a heuristic sensor route selection algorithm (SRSA) is then developed to solve the SCSP.

  • 331. Xu, Gang
    et al.
    Ngai, Edith C.-H.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Liu, Jiangchuan
    Ubiquitous transmission of multimedia sensor data in Internet of Things2018In: IEEE Internet of Things Journal, ISSN 2327-4662, Vol. 5, no 1, p. 403-414Article in journal (Refereed)
    Abstract [en]

    The Internet of Things (IoT) enables environmental monitoring by collecting data from sensing devices, including cameras and microphones. The popularity of smartphones enables mobile users to communicate and collect data from their surrounding sensing devices. The mobile devices can obtain useful environmental data from nearby sensors through short-range communication such as Bluetooth. Nevertheless, the limited contact time and the wireless capacity constrain the amount of data to be collected. With the increasing amount of multimedia big data such as videos and pictures from cameras, it is crucial for mobile users to collect prioritized data that can maximize their data utility. In this paper, we propose a distributed algorithm to provide information-centric ubiquitous data collection of multimedia big data by mobile users in the IoT. The algorithm can handle transmissions of multimedia big data recorded by the surrounding cameras and sensors, and prioritize the transmissions of the most important and relevant data. The mobile users construct data collection trees adaptively according to their dynamic moving speeds and the value of information carried by the multimedia and sensor data. The distributed algorithm can support smooth data collection and coordination of multiple mobile users. We provide both numerical analysis and extensive simulations to evaluate the information value, energy efficiency and scalability of our solution. The results showed that our distributed algorithm can improve the value of information up to 50% and reduce energy consumption to half compared with existing approach. Our algorithm also scales perfectly well with increasing number of mobile users and dynamic moving speeds.

  • 332.
    Yan, Wenqing
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Flinta, Christofer
    Ericsson Res, Stockholm, Sweden.
    Johnsson, Andreas
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems. Ericsson Res, Stockholm, Sweden.
    Machine-Learning Based Active Measurement Proxy for IoT Systems2019In: 2019 IFIP/IEEE Symposium On Integrated Network And Service Management (IM), IEEE, 2019, p. 198-206Conference paper (Refereed)
    Abstract [en]

    Network operators are accustomed to using IP-layer active measurements for assessing end-to-end network performance and expect that new technology, such as IoT, provides similar means. Unfortunately, active measurements in IoT systems are associated with both energy and network overhead. This paper presents and evaluates a novel active-measurement proxy approach, based on machine learning, that enables reduction of active measurement overhead in IoT systems. The paper describes the approach and its implementation. Further, the approach is evaluated in a IEEE 802.15.4 testbed, and the results show high-performing and accurate modeling.

  • 333. Yang, Y.
    et al.
    Tian, Y.
    Ngai, Edith
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Zhang, L.
    Teng, Y.
    Wang, W.
    Vulnerable Friend Identification: Who Should You Beware of Most in Online Social Networks2015In: 2015 IEEE Global Communications Conference (Globecom), 2015Conference paper (Refereed)
    Abstract [en]

    Web users are immersed in their roles as information producers and propagation pushers. They are unaware of being potential threats to privacy-protection towards themselves and their friends. It is necessary to know who they should beware of most in their friend-networks once their privacy information is divulged inadvertently. In this paper, we aim to identify the vulnerable friend who maximizes the dissemination of privacy information. First we develop a Privacy Receiving-Disseminating (PRD) model to simulate the iterative course of privacy information dissemination within social graph. The subgraph constituted of those users who are involved in the dissemination, called Ultimate Circle of Disseminating (UCD), is then detected by an iterative algorithm. The contribution of each direct friend could be evaluated by comparing the disseminating intensities of detected UCDs before and after unfriending himself. The performance of our work has been validated empirically with the comparison of different unfriending strategies.

  • 334.
    Zeljic, Aleksandar
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Computer Systems. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Approximations and abstractions for reasoning about machine arithmetic2016Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Safety-critical systems rely on various forms of machine arithmetic to perform their tasks: integer arithmetic, fixed-point arithmetic or floating-point arithmetic. The problem with machine arithmetic is that it can exhibit subtle differences in behavior compared to the ideal mathematical arithmetic, due to fixed-size representation in memory. Failure of safety-critical systems is unacceptable, because it can cost lives or huge amounts of money, time and effort. To prevent such incidents, we want to formally prove that systems satisfy certain safety properties, or otherwise discover cases when the properties are violated. However, for this we need to be able to formally reason about machine arithmetic. The main problem with existing approaches is their inability to scale well with the increasing complexity of systems and their properties. In this thesis, we explore two alternatives to bit-blasting, the core procedure lying behind many common approaches to reasoning about machine arithmetic.

    In the first approach, we present a general approximation framework which we apply to solve constraints over floating-point arithmetic. It is built on top of an existing decision procedure, e.g., bit-blasting. Rather than solving the original formula, we solve a sequence of approximations of the formula. Initially very crude, these approximations are frequently solved very quickly. We use results from these approximations to either obtain a solution, obtain a proof of unsatisfiability or generate a new approximation to solve. Eventually, we will either have found a solution or a proof that solution does not exist. The approximation framework improves the solving time and can solve a number of formulas that the bit-blasting cannot.

    In the second approach, we present a novel method to reason about the theory of fixed-width bit-vectors. This new decision procedure is called mcBV and it is based on the model constructing satisfiability calculus (mcSAT). The procedure uses a lazy representation of bit-vectors and attempts to avoid bit-blasting altogether. It is able to reason about bit-vectors on both bit- and word-level, leveraging both Boolean constraint propagation and native arithmetic reasoning. It also features a greedy explanation generalization mechanism and is capable of more general learning compared to existing approaches. mcBV is able to reason about bit-vectors with sizes that significantly exceed the usual 32, 64 and 128 bits. Evaluation of mcBV shows an improvement in performance (compared to bit-blasting) on several classes of problems.

    List of papers
    1. An approximation framework for solvers and decision procedures
    Open this publication in new window or tab >>An approximation framework for solvers and decision procedures
    2017 (English)In: Journal of automated reasoning, ISSN 0168-7433, E-ISSN 1573-0670, Vol. 58, no 1, p. 127-147Article in journal (Refereed) Published
    National Category
    Computer Sciences
    Identifiers
    urn:nbn:se:uu:diva-305180 (URN)10.1007/s10817-016-9393-1 (DOI)000392387400006 ()
    Projects
    UPMARC
    Available from: 2016-11-10 Created: 2016-10-12 Last updated: 2018-01-14Bibliographically approved
    2. Deciding bit-vector formulas with mcSAT
    Open this publication in new window or tab >>Deciding bit-vector formulas with mcSAT
    2016 (English)In: Theory and Applications of Satisfiability Testing: SAT 2016, Springer, 2016, p. 249-266Conference paper, Published paper (Refereed)
    Place, publisher, year, edition, pages
    Springer, 2016
    Series
    Lecture Notes in Computer Science, ISSN 0302-9743 ; 9710
    National Category
    Computer Sciences
    Identifiers
    urn:nbn:se:uu:diva-305182 (URN)10.1007/978-3-319-40970-2_16 (DOI)000387430600016 ()978-3-319-40969-6 (ISBN)
    Conference
    SAT 2016, July 5–8, Bordeaux, France
    Projects
    UPMARC
    Available from: 2016-06-11 Created: 2016-10-12 Last updated: 2018-01-14Bibliographically approved
  • 335.
    Zeljic, Aleksandar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Backeman, Peter
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Wintersteiger, Christoph M.
    Microsoft Research, Cambridge, UK.
    Rümmer, Philipp
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Exploring Approximations for Floating-Point Arithmetic using UppSAT2018In: Automated Reasoning / [ed] Didier Galmiche, Stephan Schulz, Roberto Sebastiani, Springer, 2018, p. 246-262Conference paper (Refereed)
    Abstract [en]

    We consider the problem of solving floating-point constraints obtained from software verification. We present UppSAT—an new implementation of a systematic approximation refinement framework as an abstract SMT solver. Provided with an approximation and a decision procedure (implemented in an off-the-shelf SMT solver), UppSAT yields an approximating SMT solver. Additionally, UppSAT includes a library of predefined approximation components which can be combined and extended to define new encodings, orderings and solving strategies. We propose that UppSAT can be used as a sandbox for easy and flexible exploration of new approximations. To substantiate this, we explore encodings of floating-point arithmetic into reduced precision floating-point arithmetic, real-arithmetic, and fixed-point arithmetic (encoded into the theory of bit-vectors in practice). In an experimental evaluation we compare the advantages and disadvantages of approximating solvers obtained by combining various encodings and decision procedures.

  • 336.
    Zeljic, Aleksandar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Wintersteiger, Christoph M.
    Rümmer, Philipp
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    An approximation framework for solvers and decision procedures2017In: Journal of automated reasoning, ISSN 0168-7433, E-ISSN 1573-0670, Vol. 58, no 1, p. 127-147Article in journal (Refereed)
  • 337.
    Zeljic, Aleksandar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Wintersteiger, Christoph M.
    Rümmer, Philipp
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Deciding bit-vector formulas with mcSAT2016In: Theory and Applications of Satisfiability Testing: SAT 2016, Springer, 2016, p. 249-266Conference paper (Refereed)
  • 338.
    Zhang, Cong
    et al.
    Simon Fraser Univ, Sch Comp Sci, Burnaby, BC V5A 1S6, Canada..
    Liu, Jiangchuan
    Simon Fraser Univ, Sch Comp Sci, Burnaby, BC V5A 1S6, Canada..
    Chen, Fei
    Jiangnan Univ, Sch Digital Media, Wuxi, Peoples R China..
    Cui, Yong
    Tsinghua Univ, Dept Comp Sci, Beijing, Peoples R China..
    Ngai, Edith C.-H.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Dependency-Aware Caching for HTTP Adaptive Streaming2016In: 2016 Digital Media Industry And Academic Forum (DMIAF), 2016, p. 89-93Conference paper (Refereed)
    Abstract [en]

    There has been significant interest in the use of HTTP adaptive streaming for live or on-demand video over the Internet in recent years. To mitigate the streaming transmission delay and reduce the networking overhead, an effective and critical approach is to utilize cache servers between the origin servers and the heterogeneous clients. As the underlying protocol for web transactions, HTTP has great potentials to explore the resources within state-of-the-art CDNs tor caching; yet distinct challenges arise in the HTTP adaptive streaming context. After examining a long-term and large-scale adaptive streaming dataset as well as statistical analysis, we demonstrate that the switching requests among the different qualities frequently emerge and constitute a significant portion in a per-day view. Consequently, they have substantially affected the performance of cache servers and Quality-of-Experience (QoE) of viewers. In this paper, we propose a novel cache model that captures the dependency among the segments in the cache server for adaptive HTTP streaming. Our work does not assume any specific selection algorithm on the client's side and hence can be easily incorporated into existing streaming cache system. Its centralized nature is also well accommodated by the latest DASH specification. The performance evaluation shows our dependency-aware strategy can significantly improved the cache hit-ratio and QoE of HTTP streaming as compared to previous methods.

  • 339. Zhang, Cong
    et al.
    Liu, Jiangchuan
    Chen, Fei
    Cui, Yong
    Ngai, Edith C.-H.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Hu, Yuemin
    Dependency- and similarity-aware caching for HTTP adaptive streaming2018In: Multimedia tools and applications, ISSN 1380-7501, E-ISSN 1573-7721, Vol. 77, no 1, p. 1453-1474Article in journal (Refereed)
    Abstract [en]

    There has been significant interest in the use of HTTP adaptive streaming for live or on-demand video over the Internet in recent years. To mitigate the streaming transmission delay and reduce the networking overhead, an effective and critical approach is to utilize cache services between the origin servers and the heterogeneous clients. As the underlying protocol for web transactions, HTTP has great potentials to explore the resources within state-of-the-art CDNs for caching; yet distinct challenges arise in the HTTP adaptive streaming context. After examining a long-term and large-scale adaptive streaming dataset as well as statistical analysis, we demonstrate that the switching requests among the different qualities frequently emerge and constitute a significant portion in a per-day view. Consequently, they have substantially affected the performance of cache servers and Quality-of-Experience (QoE) of viewers. In this paper, we propose a novel cache model that captures the dependency among the segments in the cache server for adaptive HTTP streaming. Our work does not assume any specific selection algorithm on the client's side and hence can be easily incorporated into existing streaming cache systems. Its centralized nature is also well accommodated by the latest DASH specification. Moreover, we extend our work to the multi-server caching context and present a similarity-aware allocation mechanism to enhance the caching efficiency. The performance evaluation shows our dependency- and similarity-aware strategy can significantly improve the cache hit-ratio and QoE of HTTP streaming as compared to previous approaches.

  • 340. Zhang, Jiao
    et al.
    Hu, Xiping
    Ning, Zhaolong
    Ngai, Edith C.-H.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Zhou, Li
    Wei, Jibo
    Cheng, Jun
    Hu, Bin
    Energy-latency tradeoff for energy-aware offloading in mobile edge computing networks2018In: IEEE Internet of Things Journal, ISSN 2327-4662, Vol. 5, no 4, p. 2633-2645Article in journal (Refereed)
  • 341.
    Zhang, Jiao
    et al.
    Natl Univ Def Technol, Coll Elect Sci, Changsha 410073, Hunan, Peoples R China;Chinese Acad Sci, Shenzhen Inst Adv Technol, Shenzhen 518055, Peoples R China.
    Hu, Xiping
    Chinese Acad Sci, Shenzhen Inst Adv Technol, Shenzhen 518055, Peoples R China.
    Ning, Zhaolong
    Dalian Univ Technol, Key Lab Ubiquitous Network & Serv Software Liaoni, Sch Software, Dalian 116620, Peoples R China.
    Ngai, Edith
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computing Science.
    Zhou, Li
    Natl Univ Def Technol, Coll Elect Sci, Changsha 410073, Hunan, Peoples R China.
    Wei, Jibo
    Natl Univ Def Technol, Coll Elect Sci, Changsha 410073, Hunan, Peoples R China.
    Cheng, Jun
    Chinese Acad Sci, Shenzhen Inst Adv Technol, Shenzhen 518055, Peoples R China.
    Hu, Bin
    Lanzhou Univ, Sch Informat Sci & Engn, Lanzhou 410073, Gansu, Peoples R China.
    Leung, Victor C. M.
    Univ British Columbia, Dept Elect & Comp Engn, Vancouver, BC V6T 1Z4, Canada.
    Joint Resource Allocation for Latency-Sensitive Services Over Mobile Edge Computing Networks With Caching2019In: IEEE Internet of Things Journal, ISSN 2327-4662, Vol. 6, no 3, p. 4283-4294Article in journal (Refereed)
    Abstract [en]

    Mobile edge computing (MEC) has risen as a promising paradigm to provide high quality of experience via relocating the cloud server in close proximity to smart mobile devices (SMDs). In MEC networks, the MEC server with computation capability and storage resource can jointly execute the latency-sensitive offloading tasks and cache the contents requested by SMDs. In order to minimize the total latency consumption of the computation tasks, we jointly consider computation offloading, content caching, and resource allocation as an integrated model, which is formulated as a mixed integer nonlinear programming (MINLP) problem. We design an asymmetric search tree and improve the branch and bound method to obtain a set of accurate decisions and resource allocation strategies. Furthermore, we introduce the auxiliary variables to reformulate the proposed model and apply the modified generalized benders decomposition method to solve the MINLP problem in polynomial computation complexity time. Simulation results demonstrate the superiority of the proposed schemes.

  • 342.
    Zhang, Jiao
    et al.
    Natl Univ Def Technol, Coll Elect Sci, Changsha 410073, Hunan, Peoples R China.
    Zhou, Li
    Natl Univ Def Technol, Coll Elect Sci, Changsha 410073, Hunan, Peoples R China.
    Tang, Qi
    Natl Univ Def Technol, Coll Elect Sci, Changsha 410073, Hunan, Peoples R China.
    Ngai, Edith
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Hu, Xiping
    Chinese Acad Sci, Shenzhen Inst Adv Technol, Shenzhen 518055, Peoples R China.
    Zhao, Haitao
    Natl Univ Def Technol, Coll Elect Sci, Changsha 410073, Hunan, Peoples R China.
    Wei, Jibo
    Natl Univ Def Technol, Coll Elect Sci, Changsha 410073, Hunan, Peoples R China.
    Stochastic Computation Offloading and Trajectory Scheduling for UAV-Assisted Mobile Edge Computing2019In: IEEE Internet of Things Journal, ISSN 2327-4662, Vol. 6, no 2, p. 3688-3699Article in journal (Refereed)
    Abstract [en]

    Unmanned aerial vehicle (UAV) has been witnessed as a promising approach for offering extensive coverage and additional computation capability to smart mobile devices (SMDs), especially in the scenario without available infrastructures. In this paper, a UAV-assisted mobile edge computing system with stochastic computation tasks is investigated. The system aims to minimize the average weighted energy consumption of SMDs and the UAV, subject to the constraints on computation offloading, resource allocation, and flying trajectory scheduling of the UAV. Due to nonconvexity of the problem and the time coupling of variables, a Lyapunov-based approach is applied to analyze the task queue, and the energy consumption minimization problem is decomposed into three manageable subproblems. Furthermore, a joint optimization algorithm is proposed to iteratively solve the problem. Simulation results demonstrate that the system performance obtained by the proposed scheme can outperform the benchmark schemes, and the optimal parameter selections are concluded in the experimental discussion.

  • 343. Zhang, Lei
    et al.
    Fu, Di
    Liu, Jiangchuan
    Ngai, Edith C.-H.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Zhu, Wenwu
    On energy-efficient offloading in mobile cloud for real-time video applications2017In: IEEE transactions on circuits and systems for video technology (Print), ISSN 1051-8215, E-ISSN 1558-2205, Vol. 27, no 1, p. 170-181Article in journal (Refereed)
  • 344.
    Zhang, Sizhuo
    et al.
    MIT CSAIL.
    Vijayaraghavan, Muralidaran
    MIT CSAIL.
    Wright, Andrew
    MIT CSAIL.
    Alipour, Mehdi
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Mithal, Arvind
    MIT CSAIL.
    Constructing a Weak Memory Model2018Conference paper (Refereed)
    Abstract [en]

    Weak memory models are a consequence of the desire on part of architects to preserve all the uniprocessor optimizations while building a shared memory multiprocessor. The efforts to formalize weak memory models of ARM and POWER over the last decades are mostly empirical - they try to capture empirically observed behaviors - and end up providing no insight into the inherent nature of weak memory models. This paper takes a constructive approach to find a common base for weak memory models: we explore what a weak memory would look like if we constructed it with the explicit goal of preserving all the uniprocessor optimizations. We will disallow some optimizations which break a programmer's intuition in highly unexpected ways. The constructed model, which we call General Atomic Memory Model (GAM), allows all four load/store reorderings. We give the construction procedure of GAM, and provide insights which are used to define its operational and axiomatic semantics. Though no attempt is made to match GAM to any existing weak memory model, we show by simulation that GAM has comparable performance with other models. No deep knowledge of memory models is needed to read this paper.

  • 345. Zhang, Tianyu
    et al.
    Guan, Nan
    Deng, Qingxu
    Yi, Wang
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Start time configuration for strictly periodic real-time task systems2016In: Journal of systems architecture, ISSN 1383-7621, E-ISSN 1873-6165, Vol. 66–67, p. 61-68Article in journal (Refereed)
  • 346. Zhou, Li
    et al.
    Hu, Xiping
    Ngai, Edith C.-H.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Zhao, Haitao
    Wang, Shan
    Wei, Jibo
    Leung, Victor C. M.
    A dynamic graph-based scheduling and interference coordination approach in heterogeneous cellular networks2016In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 65, no 5, p. 3735-3748Article in journal (Refereed)
  • 347.
    Zhou, Li
    et al.
    Natl Univ Def Technol, Coll Elect Sci & Engn, Changsha, Hunan, Peoples R China..
    Hu, Xiping
    Univ British Columbia, Dept Elect & Comp Engn, Vancouver, BC, Canada..
    Zhu, Chunsheng
    Univ British Columbia, Dept Elect & Comp Engn, Vancouver, BC, Canada..
    Ngai, Edith C. -H.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Wang, Shan
    Natl Univ Def Technol, Coll Elect Sci & Engn, Changsha, Hunan, Peoples R China..
    Wei, Jibo
    Natl Univ Def Technol, Coll Elect Sci & Engn, Changsha, Hunan, Peoples R China..
    Leung, Victor C. M.
    Univ British Columbia, Dept Elect & Comp Engn, Vancouver, BC, Canada..
    Green Small Cell Planning in Smart Cities under Dynamic Traffic Demand2015In: 2015 IEEE Conference on Computer Communications Workshops (INFOCOM WKSHPS), 2015, p. 618-623Conference paper (Refereed)
    Abstract [en]

    In smart cities, cellular network plays a crucial role to support connectivity anywhere and anytime. However, the communication demand brought by applications and services is hard to predict. Traffic in cellular networks might fluctuate heavily over time to time, which causes burden and waste under different traffic states. Recently, small cell was proposed to enhance spectrum efficiency and energy efficiency in cellular networks. However, how green the small cell network can be is still a question because of the accompanying interference. To meet this challenge, new green technologies should be developed. In this paper, we propose a green small cell planning scheme considering dynamic traffic states. First, we predefine a set of candidate locations for base stations (BSs) in a geographical area and generate a connection graph which contains all possible connections between BSs and user equipments (UEs). Then we adopt a heuristic to switch off small cell BSs (s-BSs) and update BS-UE connections iteratively. Finally we obtain a cell planning solution with energy efficiency without reducing spectrum efficiency and quality-of-service (QoS) requirements. The simulation results show that our dynamic small cell planning scheme has low computational complexity and achieves a significant improvement in energy efficiency comparing with the static cell planning scheme.

  • 348.
    Zhu, Chunsheng
    et al.
    Univ British Columbia, Dept Elect & Comp Engn, Vancouver, BC V5Z 1M9, Canada..
    Leung, Victor C. M.
    Univ British Columbia, Dept Elect & Comp Engn, Vancouver, BC V5Z 1M9, Canada..
    Ngai, Edith C. -H.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Yang, Laurence T.
    St Francis Xavier Univ, Dept Comp Sci, Antigonish, NS, Canada..
    Shu, Lei
    Guangdong Univ Petrochem Technol, Guangdong Prov Key Lab Petrochem Equipment Fault, Maoming, Peoples R China..
    Li, Xiuhua
    Univ British Columbia, Dept Elect & Comp Engn, Vancouver, BC V5Z 1M9, Canada..
    Pricing Models for Sensor-Cloud2015In: 2015 IEEE 7Th International Conference On Cloud Computing Technology And Science (Cloudcom), 2015, p. 454-457Conference paper (Refereed)
    Abstract [en]

    Incorporating ubiquitous wireless sensor networks (WSNs) and powerful cloud computing (CC), Sensor-Cloud (SC) is attracting growing attention from both academia and industry. However, pricing for SC is barely explored. In this paper, filling this gap, five SC pricing models (i.e., SCPM1, SCPM2, SCPM3, SCPM4 and SCPM5) are proposed first. Particularly, they charge a SC user, based on 1) the lease period of the user; 2) the required working time of SC; 3) the SC resources utilized by the user; 4) the volume of sensory data obtained by the user; 5) the SC path that transmits sensory data from the WSN to the user, respectively. Further, analysis is also presented to study and demonstrate the performance of the proposed SCPMs. We believe that the pricing designs and analysis performed in this work could be a very valuable guidance for future researches regarding pricing in SC.

  • 349. Zhu, Chunsheng
    et al.
    Leung, Victor C. M.
    Shu, Lei
    Ngai, Edith C.-H.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Green Internet of Things for Smart World2015In: IEEE Access, E-ISSN 2169-3536, Vol. 3, p. 2151-2162Article in journal (Refereed)
    Abstract [en]

    Smart world is envisioned as an era in which objects (e.g., watches, mobile phones, computers, cars, buses, and trains) can automatically and intelligently serve people in a collaborative manner. Paving the way for smart world, Internet of Things (IoT) connects everything in the smart world. Motivated by achieving a sustainable smart world, this paper discusses various technologies and issues regarding green IoT, which further reduces the energy consumption of IoT. Particularly, an overview regarding IoT and green IoT is performed first. Then, the hot green information and communications technologies (ICTs) (e.g., green radio frequency identification, green wireless sensor network, green cloud computing, green machine to machine, and green data center) enabling green IoT are studied, and general green ICT principles are summarized. Furthermore, the latest developments and future vision about sensor cloud, which is a novel paradigm in green IoT, are reviewed and introduced, respectively. Finally, future research directions and open problems about green IoT are presented. Our work targets to be an enlightening and latest guidance for research with respect to green IoT and smart world.

  • 350.
    Zhu, Yunyun
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Division of Computer Systems.
    Caches, Transactions and Memories: Models, Coherence and Consistency2018Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Computers have brought us inestimable convenience in recent years. We have become dependent on them and more sensitive to their performance. During the past decades, we have been trying to improve program efficiency. The invention of multi-core systems is regarded as the new era of boosting performance of computer programs. When we focus on improving program efficiency, we also need to pay attention to program correctness. In some specific areas, errors, aka bugs, of programs can cause disastrous consequences. The dominant approach to bug detection is testing, which is conducted by executing a program against test cases generated based on scenarios. A bug is found when the output of the program does not match the expected output defined in the test case. One main drawback of testing is that it only shows the presence of bugs. An alternative approach is formal verification, which is a method that can exhaustively analyze the program executions and therefore show the absence of bugs. This thesis focuses on one of the main areas of formal verification - model checking. Model checking analyzes a mathematical model extracted from a program and automatically checks if it satisfies the desired properties.

    In this thesis, we first consider verifying safety and liveness properties for transactional memories. In particular, we consider the FlexTM hybrid transactional memory. We build a formal model of FlexTM, and apply a small model theorem that restricts the number of threads and variables in the model. This allows us to reduce the problem of verifying safety and liveness properties of FlexTM to checking language inclusion between the automata of FlexTM and a reference transactional memory. Second, we present a method for automatic verification of cache coherence protocols in the presence of transactional memories. We build a formal model containing a filter that represents the conflict resolution strategies of the transactional memory. We also apply a small model theorem which limits the number of cache lines of the protocol. To check cache coherence, we extend a backward reachability algorithm for infinite state systems, by removing the traces not allowed by the filter. Using this technique, we verify two cache protocols under different transactional memories respectively and conclude that they both maintain coherence.  Finally, we consider verification of safety properties of programs running over Self-Invalidate and Self-Downgrade cache coherence protocols. To that end, we define a formal model which captures the weak memory model induced by such protocols. We design an algorithm for inserting a set of optimal fences in the program, which guarantees the safety property while still maintaining the efficiency of a maximal degree.

    List of papers
    1. Verifying safety and liveness for the FlexTM hybrid transactional memory
    Open this publication in new window or tab >>Verifying safety and liveness for the FlexTM hybrid transactional memory
    Show others...
    2013 (English)Conference paper, Published paper (Refereed)
    Abstract [en]

    We consider the verification of safety (strict serializability and abort consistency) and liveness obstruction and livelock freedom) for the hybrid transactional memory framework FlexTM. This framework allows for flexible implementations of transactional memories based on an adaptation of the MESI coherence protocol. FlexTM allows for both eager and lazy conflict resolution strategies. Like in the case of Software Transactional Memories, the verification problem is not trivial as the number of concurrent transactions, their size, and the number of accessed shared variables cannot be a priori bounded. This complexity is exacerbated by aspects that are specific to hardware and hybrid transactional memories. Our work takes into account intricate behaviours such as cache line based conflict detection, false sharing, invisible reads or non-transactional instructions. We carry out the first automatic verification of a hybrid transactional memory and establish, by adopting a small model approach, challenging properties such as strict serializability, abort consistency, and obstruction freedom for both an eager and a lazy conflict resolution strategies. We also detect an example that refutes livelock freedom. To achieve this, our prototype tool makes use of the latest antichain based techniques to handle systems with tens of thousands of states.

    Place, publisher, year, edition, pages
    Grenoble, France: , 2013
    National Category
    Computer Systems
    Identifiers
    urn:nbn:se:uu:diva-213232 (URN)978-1-4503-2153-2 (ISBN)
    Conference
    Design, Automation and Test in Europe, DATE 13, Grenoble, France, March 18-22, 2013
    Projects
    UPMARC
    Available from: 2013-12-19 Created: 2013-12-19 Last updated: 2018-04-09
    2. Verification of Cache Coherence Protocols wrt. Trace Filters
    Open this publication in new window or tab >>Verification of Cache Coherence Protocols wrt. Trace Filters
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    2015 (English)In: Proc. 15th Conference on Formal Methods in Computer-Aided Design, Piscataway, NJ: IEEE , 2015, p. 9-16Conference paper, Published paper (Refereed)
    Place, publisher, year, edition, pages
    Piscataway, NJ: IEEE, 2015
    National Category
    Computer Sciences
    Identifiers
    urn:nbn:se:uu:diva-272322 (URN)978-0-9835678-5-1 (ISBN)
    Conference
    FMCAD 2015, September 27–30, Austin, TX
    Projects
    UPMARC
    Available from: 2015-09-30 Created: 2016-01-13 Last updated: 2018-04-09
    3. Fencing programs with self-invalidation and self-downgrade
    Open this publication in new window or tab >>Fencing programs with self-invalidation and self-downgrade
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    2016 (English)In: Formal Techniques for Distributed Objects, Components, and Systems, Springer, 2016, p. 19-35Conference paper, Published paper (Refereed)
    Place, publisher, year, edition, pages
    Springer, 2016
    Series
    Lecture Notes in Computer Science, ISSN 0302-9743 ; 9688
    National Category
    Computer Engineering
    Identifiers
    urn:nbn:se:uu:diva-300663 (URN)10.1007/978-3-319-39570-8_2 (DOI)000379297600002 ()978-3-319-39569-2 (ISBN)
    Conference
    FORTE 2016, June 6–9, Heraklion, Greece
    Projects
    UPMARC
    Available from: 2016-05-24 Created: 2016-08-10 Last updated: 2018-04-09Bibliographically approved
    4. Mending fences with self-invalidation and self-downgrade
    Open this publication in new window or tab >>Mending fences with self-invalidation and self-downgrade
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    2018 (English)In: Logical Methods in Computer Science, ISSN 1860-5974, E-ISSN 1860-5974, Vol. 14, no 1, article id 6Article in journal (Refereed) Published
    National Category
    Computer Sciences
    Identifiers
    urn:nbn:se:uu:diva-347675 (URN)000426512000004 ()
    Available from: 2018-01-16 Created: 2018-04-06 Last updated: 2018-05-17Bibliographically approved
4567 301 - 350 of 350
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