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  • 1.
    Bjurefors, Fredrik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Gold, Richard
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Larzon, Lars-Åke
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Performance of Pastry in a Heterogeneous System2004In: Proceedings of the Fourth IEEE International Conference on Peer-to-Peer computing, 2004Conference paper (Refereed)
    Abstract [en]

    In this paper, we study how Pastry performs in a heterogeneous network environment of varying size. The large traffic overhead for management traffic makes the overlay nonfunctional if it grows too large. This can be circumvented by partitioning the routing tables at the cost of increased path lengths and response times.

  • 2.
    Boano, Carlo Alberto
    et al.
    University of Lübeck.
    Wennerström, Hjalmar
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Zúñiga, Marco Antonio
    TU Delft.
    Brown, James
    Lancaster University.
    Keppitiyagama, Chamath
    Swedish Institute of Computer Science.
    Oppermann, Felix Jonathan
    University of Lübeck.
    Roedig, Utz
    Lancaster University.
    Nordén, Lars-Åke
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Voigt, Thiemo
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Römer, Kay
    University of Lübeck.
    Hot Packets: A systematic evaluation of the effect of temperature on low power wireless transceivers2013In: Proc. 5th Extreme Conference on Communication, New York: ACM Press, 2013, p. 7-12Conference paper (Refereed)
    Abstract [en]

    Temperature is known to have a significant effect on the performance of radio transceivers: the higher the temperature, the lower the quality of links. Analysing this effect is particularly important in sensor networks because several applications are exposed to harsh environmental conditions. Daily or hourly changes in temperature can dramatically reduce the throughput, increase the delay, or even lead to network partitions. A few studies have quantified the impact of temperature on low-power wireless links, but only for a limited temperature range and on a single radio transceiver. Building on top of these preliminary observations, we design a low-cost experimental infrastructure to vary the onboard temperature of sensor nodes in a repeatable fashion, and we study systematically the impact of temperature on various sensornet platforms. We show that temperature affects transmitting and receiving nodes differently, and that all platforms follow a similar trend that can be captured in a simple first-order model. This work represents an initial stepping stone aimed at predicting the performance of a network considering the particular temperature profile of a given environment.

  • 3.
    Girons Lopez, Marc
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Wennerström, Hjalmar
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Nordén, Lars-Åke
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Architecture and Computer Communication.
    Seibert, Jan
    Uppsala University, Disciplinary Domain of Science and Technology, Earth Sciences, Department of Earth Sciences, LUVAL.
    Location and Density of Rain Gauges for the Estimation of Spatial Varying Precipitation2015In: Geografiska Annaler. Series A, Physical Geography, ISSN 0435-3676, E-ISSN 1468-0459, Vol. 97, no 1, p. 167-179Article in journal (Refereed)
    Abstract [en]

    Accurate estimation of precipitation and its spatial variability is crucial for reliable discharge simulations. Although radar and satellite based techniques are becoming increasingly widespread, quantitative precipitation estimates based on point rain gauge measurement interpolation are, and will continue to be in the foreseeable future, widely used. However, the ability to infer spatially distributed data from point measurements is strongly dependent on the number, location and reliability of measurement stations.

    In this study we quantitatively investigated the effect of rain gauge network configurations on the spatial interpolation by using the operational hydrometeorological sensor network in the Thur river basin in north-eastern Switzerland as a test case. Spatial precipitation based on a combination of radar and rain gauge data provided by MeteoSwiss was assumed to represent the true precipitation values against which the precipitation interpolation from the sensor network was evaluated. The performance using scenarios with both increased and decreased station density were explored. The catchment-average interpolation error indices significantly improve up to a density of 24 rain gauges per 1000 km2, beyond which improvements were negligible. However, a reduced rain gauge density in the higher parts of the catchment resulted in a noticeable decline of the performance indices. An evaluation based on precipitation intensity thresholds indicated a decreasing performance for higher precipitation intensities. The results of this study emphasise the benefits of dense and adequately distributed rain gauge networks.

  • 4.
    Heintz, Fredrik
    et al.
    Linköpings Universitet.
    Mannila, Linda
    Linköpings Universitet.
    Nordén, Lars-Åke
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Parnes, Peter
    Luleå Tekniska Universitet.
    Regnell, Björn
    Lunds Universitet.
    Introducing Programming and Digital Competence in Swedish K–9 Education2017In: Informatics in Schools: Focus on Learning Programming, 2017Conference paper (Refereed)
  • 5.
    Hermans, Frederik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Rensfelt, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Gunningberg, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Larzon, Lars-Åke
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Ngai, Edith
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Sensei-UU — a relocatable WSN testbed supporting repeatable node mobility2011In: Testbeds and Research Infrastructures: Development of Networks and Communities, Berlin: Springer-Verlag , 2011, p. 612-614Conference paper (Refereed)
  • 6.
    Hermans, Frederik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Rensfelt, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Larzon, Lars-Åke
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Gunningberg, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    A Lightweight Approach to Online Detection and Classification of Interference in 802.15.4-based Sensor Networks2012In: ACM SIGBED Review, ISSN 1551-3688, Vol. 9, no 3, p. 11-20Article in journal (Refereed)
    Abstract [en]

    With a rapidly increasing number of devices sharing access to the 2.4 GHz ISM band, interference becomes a serious problem for 802.15.4-based, low-power sensor networks. Consequently, interference mitigation strategies are becoming commonplace. In this paper, we consider the step that precedes interference mitigation: interference detection. We have performed extensive measurements to characterize how different types of interferers affect individual 802.15.4 packets. From these measurements, we define a set of features which we use to train a neural network to classify the source of interference of a corrupted packet. Our approach is sufficiently lightweight for online use in a resource constrained sensor network. It does not require additional hardware, nor does it use active spectrum sensing or probing packets. Instead, all information about interferers is gathered from inspecting corrupted packets that are received during the sensor network’s regular operation. Even without considering a history of earlier packets, our approach reaches a mean classification accuracy of 79.8%, with per interferer accuracies of64.9% for WiFi, 82.6% for Bluetooth, 72.1% for microwave ovens, and 99.6% for packets that are corrupted due to insufficient signal strength.

  • 7.
    Hermans, Frederik
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Rensfelt, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Voigt, Thiemo
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Ngai, Edith
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Nordén, Lars-Åke
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Gunningberg, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    SoNIC: Classifying interference in 802.15.4 sensor networks2013In: Proc. 12th International Conference on Information Processing in Sensor Networks, New York: ACM Press, 2013, p. 55-66Conference paper (Refereed)
  • 8. Landström, Sara
    et al.
    Larzon, Lars-Åke
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Reducing the TCP Acknowledgment Frequency2007In: Computer communication review, ISSN 0146-4833, E-ISSN 1943-5819, Vol. 37, no 3, p. 5-16Article in journal (Refereed)
    Abstract [en]

    Delayed acknowledgments were introduced to conserve net-

    work and host resources. Further reduction of the acknowl-

    edgment frequency can be motivated in the same way. How-

    ever, reducing the dependency on frequent acknowledgments

    in TCP is difficult because acknowledgments support reli-

    able delivery, loss recovery, clock out new segments, and

    serve as input when determining an appropriate sending

    rate.

    Our results show that in scenarios where there are no ob-

    vious advantages of reducing the acknowledgment frequency,

    performance can be maintained although fewer acknowledg-

    ments are sent. Hence, there is a potential for reducing the

    acknowledgment frequency more than is done through de-

    layed acknowledgments today. Advancements in TCP loss

    recovery is one of the key reasons that the dependence on

    frequent acknowledgments has decreased.

    We propose and evaluate an end-to-end solution, where

    four acknowledgments per send window are sent. The sender

    compensates for the reduced acknowledgment frequency us-

    ing a form of Appropriate Byte Counting. The proposal also

    includes a modification of fast loss recovery to avoid frequent

    timeouts.

  • 9. Landström, Sara
    et al.
    Larzon, Lars-Åke
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Computer Systems. Datorteknik.
    Bodin, Ulf
    Congestion Control in a High Speed Radio Environment2004In: roceedings of the International Conference on Wireless Networks, 2004Conference paper (Other scientific)
    Abstract [en]

    This paper explores interactions

    between congestion control mechanisms at the

    transport layer and scheduling algorithms at

    the physical layer in the High-Speed Down-link

    Packet Access extension to WCDMA. Two different

    approaches to congestion control – TCP

    SACK and TFRC – are studied. We find that

    TCP SACK and TFRC in most respects perform

    the same way. SIR scheduling give a higher

    system throughput for both protocols than RR

    scheduling, but introduces delay variations that

    lead to spurious timeouts. The no feedback timeout

    of TFRC was shown to exhibit a similar sensitivity

    to delay spikes as the retransmit timeout

    in TCP SACK.

  • 10. Landström, Sara
    et al.
    Larzon, Lars-Åke
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Bodin, Ulf
    Properties of TCP-like congestion control2004In: Proceedings of the Swedish National Computer Networking Workshop, 2004Conference paper (Other academic)
  • 11.
    Larzon, Lars-Åke
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology. Datorteknik. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Degermark, Mikael
    Pink, Stephen
    The Lightweight User Datagram Protocol (UDP-Lite)2004Other (Other (popular science, discussion, etc.))
    Abstract [en]

    This document describes the Lightweight User Datagram Protocol (UDP- Lite), which is similar to the User Datagram Protocol (UDP) (RFC 768), but can also serve applications in error-prone network environments that prefer to have partially damaged payloads delivered rather than discarded. If this feature is not used, UDP-Lite is semantically identical to UDP.

  • 12.
    Nordén, Lars-Åke
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Mannila, Linda
    Linkoping Univ, Dept Comp & Informat Sci, Linkoping, Sweden.
    Pears, Arnold
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Development of a self-efficacy scale for digital competences in schools2017In: 2017 IEEE Frontiers in Education Conference (FIE): Proc. 47th ASEE/IEEE Frontiers in Education Conference, IEEE Press, 2017Conference paper (Refereed)
    Abstract [en]

    As computer science enters the school curricula in an increasing number of countries, teachers must prepare to integrate digital competences into their teaching. This integration is a moving target where new methods, tools and applications appear and disappear at such rates that teachers must have confidence to independently and continuously explore what is new, what is relevant and how to plan their pedagogic activities to include digital competences. In this context approaches which can be used to study self-efficacy in digital competences among school teachers are desperately needed. With such a tool in place, we can make a baseline study and then follow teachers over time to measure changes in their self-efficacy, the cause of these changes and learn how to build their digital competence self-efficacy in different ways. The same tool can also be used to measure the self-efficacy in other populations, e.g., students in teacher training programs to ensure that they obtain an adequate self-efficacy in digital competences during their studies. This paper describes the development of a self-efficacy scale in digital competences, based on the DigiComp 2.0 framework definition of digital competence. The tool focuses predominantly on digital competences relevant for teachers in school years K-9.

  • 13.
    Pears, Arnold
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Larzon, Lars-Åke
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Encouraging Deep Learning Using Student Reflections: A Case Study2006In: Proc. 6th Baltic Sea Conference on Computing Education Research, 2006, p. 38-45Conference paper (Refereed)
    Abstract [en]

    An important aspect in any learning situation is the approach that students to learning. Studies in the 1980's by Prosser, Marton and Säljö as well as Moon and others have built an increasingly convincing case for the existance several different approaches. From this body of literature has emerged three classifications of learning approach adopted by students, deep, surface and achieving. These approaches are not mutually exclusive, and a single student may use any or all of them in combination. A connection has been demonstrated between use of the deep learning and deeper understanding of the material being learned.

    Encouraging deep learning behaviour, however, is a much more complex issue, since choice of learning approach seems to be dependent on the manner in which the student experiences the learning environment. This paper reports on the use of reflections as a part of the educational design of two computing courses. The results describe student's perceptions regarding reflections using analysis of the reflections themselves. Student's perceptions of the utility of reflections as a learning tool are also explored using data collected from interviews with the students in one of the study cohorts.

  • 14.
    Rensfelt, Olof
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Gold, Richard
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Larzon, Lars-Åke
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology. Datorteknik. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    LUNAR over Bluetooth2004In: Proceedings of the 4:th Scandinavian Workshop on Wireless Ad-Hoc Networks, 2004Conference paper (Refereed)
    Abstract [en]

    We describe the porting of the LUNAR ad hoc routing protocol to Bluetooth. LUNAR is an ad hoc routing protocol designed for simplicity, targeting the ad hoc scenario of about a dozen nodes and a maximum of three hops. We believe that within this area, ad hoc networking is currently of most value. Due to the simplicity of LUNAR it is well-suited to a variety of devices where some are very resource constrained. Previously we have ported a version of the LUNAR protocol, called LUNAR, to run on the Lego Mindstorm RCX. This paper describes the process undergone to get LUNAR running over the Bluetooth technology. One of the rationales behind this work is the large amount of Bluetooth-enabled devices such as laptops, PDAs and cell phones. Typically ad hoc routing protocols are run over broadcast based radio technologies such as IEEE 802.11b. Bluetooth, however, contains a large amount of application-speci c functionality in the actual hardware module itself. This functionality does not necessarily lend itself well to the demands of an ad hoc networking protocol. The outline of the paper is as follows: We rst describe the LUNAR protocol and the relevant functionality of Bluetooth and then discuss the issues surrounding the porting process to the Bluetooth technology. The implementation itself is then described and some results presented.We close the paper with some discussions of our experiences.

  • 15.
    Rensfelt, Olof
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Hermans, Frederik
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Ferm, Christofer
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Gunningberg, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Larzon, Lars-Åke
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    An Interactive Test-bed for Heterogeneous Wireless Sensor Networks.2008In: DCOSS demo proceedings, Springer Verlag , 2008Conference paper (Refereed)
  • 16.
    Rensfelt, Olof
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Hermans, Frederik
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Ferm, Christofer
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Larzon, Lars-Åke
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Gunningberg, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Sensei-UU: a flexible testbed for heterogeneous wireless sensor networks2009In: Testbeds and Research Infrastructures for the Development of Networks Communities and Workshops, 2009. TridentCom 2009. 5th International Conference on, 2009, p. 1-2Conference paper (Refereed)
    Abstract [en]

    We present Sensei - a nomadic, relocatable, wireless sensor network (WSN) testbed with support for mobile nodes. The nomadism makes it possible to evaluate a WSN application in different environments ranging from lab environments to in- situ installations to prototype deployments. Other WSN testbeds are often static and can not be easily moved between sites. We also support reproducibility mobility in the testbed, using robots or humans as actuators with movement patterns defined in mobility scripts.

  • 17.
    Rensfelt, Olof
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Hermans, Frederik
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Gunningberg, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Larzon, Lars-Åke
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Repeatable experiments with mobile nodes in a relocatable WSN testbed2010In: Proc. 6th IEEE International Conference on Distributed Computing in Sensor Systems Workshops: DCOSSW 2010, IEEE Computer Society, 2010, p. 1-6Conference paper (Refereed)
    Abstract [en]

    We present Sensei-UU, a testbed that supports mobile sensor nodes. The design objectives are to provide wireless sensor network (WSN) experiments with repeatable mobility and to be able to use the same testbed at different locations, including the target location. The testbed is inexpensive, expandable, relocatable and it is possible to reproduce it by other researchers. Mobile sensor nodes are carried by robots that use floor markings for navigation and localization. The testbed is typically used to evaluate WSN applications when sensor nodes move in meters rather than millimeters, eg. when human carries a mobile data sink (mobile phone) collecting data while passing fixed sensor nodes. To investigate the repeatability of robot movements, we have measured the achieved precision and timing of the robots. This precision is of importance to ensure the same radio link characteristics from one protocol experiment to another. We find that our robot localization is accurate to #x00B1;1 cm and variations in link characteristics are acceptably low to capture fading phenomena in IEEE 802.15.4. In the paper we show repeatable experiment results from three environments, two university corridors and from an anechoic chamber. We conclude that the testbed is relocatable between different environments and that the precision is good enough to capture fading effects in a repeatable way.

  • 18.
    Rensfelt, Olof
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Hermans, Frederik
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Gunningberg, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Larzon, Lars-Åke
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Björnemo, Erik
    Uppsala University, Disciplinary Domain of Science and Technology, Technology, Department of Engineering Sciences, Signals and Systems Group.
    Repeatable experiments with mobile nodes in a relocatable WSN testbed2011In: Computer journal, ISSN 0010-4620, E-ISSN 1460-2067, Vol. 54, no 12, p. 1973-1986Article in journal (Refereed)
    Abstract [en]

    Many sensor network application scenarios include mobile nodes, such as a moving sink. Evaluatingsuch applications in a testbed is challenging since the testbed has to support mobile nodes. Wepresent Sensei-UU, a sensor network testbed that supports mobile sensor nodes. The testbedis inexpensive, relocatable and possible to reproduce by other researchers. Its primary designobjectives are to support experiments with repeatable mobility and to support relocating thetestbed deployment to different locations. Mobile sensor nodes are carried by robots that usefloor markings for navigation and localization. The testbed can be used to evaluate applicationsin which sensor nodes move in the order of meters rather than millimeters, e.g., when a humancarries a mobile phone that collects data while passing stationary sensor nodes. To investigate therepeatability of robot movements, we measure the achieved precision and timing of the robots, andfind that our robot localization is accurate to ±1 cm. Furthermore, we investigate variations inradio signal strengths between mobile and stationary nodes. We study the impact of imprecisemovements, external sources of interference, and environmental influences. We conclude thatSensei-UU supports experiments in which these variations are acceptably low to capture small-scalefading phenomena in IEEE 802.15.4.

  • 19.
    Rensfelt, Olof
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Hermans, Frederik
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Larzon, Lars-Åke
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Gunningberg, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Sensei-UU: a relocatable sensor network testbed2010In: Proc. 5th ACM International Workshop on Wireless Network Testbeds, Experimental Evaluation and Characterization, ACM Press, 2010, p. 63-70Conference paper (Refereed)
  • 20.
    Rensfelt, Olof
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Hermans, Frederik
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Voigt, Thiemo
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Ngai, Edith
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Nordén, Lars-Åke
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Gunningberg, Per
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    SoNIC: Classifying and Surviving Interference in 802.15.4-based Sensor Networks2012Report (Other academic)
  • 21.
    Rensfelt, Olof
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Larzon, Lars-Åke
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    A bandwidth study of a DHT in a heterogeneous environment2006Conference paper (Refereed)
  • 22.
    Rensfelt, Olof
    et al.
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Computer Systems. Datorteknik.
    Larzon, Lars-Åke
    Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology. Uppsala University, Teknisk-naturvetenskapliga vetenskapsområdet, Mathematics and Computer Science, Department of Information Technology, Computer Systems. Datorteknik.
    Addressing heterogeneity in Peer-to-Peer networks2004In: Proceedings of the Swedish National Computer Networking Workshop, 2004Conference paper (Refereed)
  • 23.
    Rensfelt, Olof
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Larzon, Lars-Åke
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Westergren, Sven
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Vendetta – A Tool for Flexible Monitoring and Management of Distributed Testbeds2007In: Proc. 3rd International Conference on Testbeds and Research Infrastructure for the Development of Networks and Communities, Piscataway, NJ: IEEE , 2007, p. 8-Conference paper (Refereed)
  • 24. Sundström, Mikael
    et al.
    Larzon, Lars-Åke
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology. Datorteknik. Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    High-Performance Longest Prefix Matching supporting High-Speed Incremental Updates and Guaranteed Compression2005In: Proceedings of IEEE Infocom 2005, 2005Conference paper (Refereed)
    Abstract [en]

    Longest prefix matching is frequently used for IP forwarding in the Internet. Data structures used must be not only efficient, but also robust against pathological entries caused by an adversary or misconfiguration. In this paper, we attack the longest prefix matching problem by presenting a new algorithm supporting high lookup performance, fast incremental updates and guaranteed compression ratio. High lookup performance is achieved by using only four memory accesses. Guaranteed compression ratio is achieved by combining direct indexing with an implicit tree structure and carefully choosing which construct to use when updating the forwarding table. Fast incremental updates is achieved by a new memory management technique featuring fast variable size allocation and deallocation while maintaining zero fragmentation. An IPv4 forwarding table data structure can be implemented in software or hardware within 2.7 Mb of memory to represent 2^18 routing entries. Incremental updates require only 752 memory accesses in worst case for the current guaranteed compression ratio. For a hardware implementation, we can use 300 MHz SRAM organized in four memory banks and four pipeline stages to achieve a guaranteed performance of 300 million lookups per second, corresponding to ~100 Gbit/s wire speed forwarding, and 400,000 incremental updates per second. In measurements performed on a 3.0 Ghz Pentium 4 machine using a routing table with more than 2^17 entries, we can forward over 27 million IPv4 packets per second, which is equivalent to wire speeds exceeding 10 Gbit/s. On the same machine and with the same routing table, we can perform over 230,000 incremental updates/second.

  • 25.
    Wennerström, Hjalmar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Hermans, Frederik
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Rensfelt, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Rohner, Christian
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Nordén, Lars-Åke
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    A long-term study of correlations between meteorological conditions and 802.15.4 link performance2013In: Proc. 10th International Conference on Sensing, Communications, and Networking, IEEE Communications Society, 2013, p. 221-229Conference paper (Refereed)
  • 26.
    Wennerström, Hjalmar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Hermans, Frederik
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Rensfelt, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Rohner, Christian
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Nordén, Lars-Åke
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    A Long-Term Study on the Effects of Meteorological Conditions on 802.15.4 Links2012In: 8th Swedish National Computer Networking Workshop, Stockholm, June 7-8, 2012Conference paper (Refereed)
    Abstract [en]

    Remote monitoring of natural phenomena using wireless sensor networks requires these networks to successfully operate while being exposed to the surrounding environment. Weather conditions are an essential aspect of the environment, therefore it is important to understand the effects of weather on sensor networks. This understanding is especially important since weather varies strongly over time and affects the communication between sensor nodes. In our ongoing work we study how different meteorological conditions influence radio links in outdoor wireless sensor networks that use IEEE 802.15.4 for communication. We deploy an experimental setup next to a meteorological research station and aim to run experiments over several months in order to capture both short- and long-term changes in the link characteristics. We show some initial measurements of the deployment, highlighting influences on packet reception rate and signal strength.

  • 27.
    Wennerström, Hjalmar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    McNamara, Liam
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Rohner, Christian
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Nordén, Lars-Åke
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    A Study of Packet Errors on Outdoor 802.15.4 Links2013In: The 9th Swedish National Computer Networking Workshop 2013, 2013Conference paper (Refereed)
  • 28.
    Wennerström, Hjalmar
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    McNamara, Liam
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Rohner, Christian
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Nordén, Lars-Åke
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Transmission errors in a sensor network at the edge of the world2013In: Proc. 5th Extreme Conference on Communication, New York: ACM Press, 2013Conference paper (Refereed)
    Abstract [en]

    The performance of an outdoor wireless sensor network for remote monitoring is dictated by its ability to deliver sensed data to a sink. The often isolated location means that radio interference is typically low and with different patterns in transmission errors compared to an indoor deployment. To better understand these processes, we investigate packet errors in such a network. Specically, we study characteristics of decoding errors within 802.15.4 transmissions.

    We describe the experimental deployment of an outdoor sensor network, located above the Arctic circle, where we log both successfully received and broken packets. Results indicate that a substantial amount of received packets contain errors, where the errors in each packet are typically few. We distinguish between transmission errors and payload errors, and find that transmission errors are equally probable over all positions of a packet, whereas bit errors in the payload are not. This results in some bits having a 25% higher risk of being corrupted than others.

  • 29.
    Westergren, Sven
    et al.
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Rensfelt, Olof
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    Larzon, Lars-Åke
    Uppsala University, Disciplinary Domain of Science and Technology, Mathematics and Computer Science, Department of Information Technology, Computer Systems.
    NoteNet2006Conference paper (Refereed)
1 - 29 of 29
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