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  • 101.
    Segerström, Mikael
    et al.
    Karlstads universitet, Institutionen för informationsteknologi.
    Kristiansson, Jörgen
    Karlstads universitet, Institutionen för informationsteknologi.
    Dokumentation av elsystem vid Kvaerner Kamfab AB, Karlstad2006Independent thesis Basic level (professional degree), 10 poäng / 15 hpOppgave
    Abstract [sv]

    Detta projekt är utfört vid Kvaerner Kamfab AB i Karlstad och beskriver hur strukturering av företagets elsystem har utförts i form av uppmärkning och dokumentation. Detta skall ligga till grund för en effektivisering vid ombyggnation av ställverket.

  • 102.
    Siripi, Vishnu Vardhan
    Karlstads universitet, Institutionen för informationsteknologi.
    Investigation of an optimal utilization of Ultra-wide band measurements for position purposes2006Independent thesis Advanced level (degree of Magister), 20 poäng / 30 hpOppgave
    Abstract [en]

    Ultra wideband (UWB) communication systems refers to systems whose bandwidth is many times greater than the “narrowband” systems (refers to a signal which occupies only small amount of space on the radio spectrum). UWB can be used for indoor, communications for high data rates, or very low data rates for substantial link distances because of the extremely large bandwidth, immune to multi-path fading, penetrations through concrete block or obstacles. UWB can also used for short distance ranging whose applications include asset location in a warehouse, position location for wireless sensor networks, and collision avoidance.

    In order to verify analytical and simulation results with real-world measurements, the need for experimental UWB systems arises. The Institute of Communications Engineering [IANT] has developed a low-cost experimental UWB positioning system to test UWB based positioning concepts. The mobile devices use the avalanche effect of transistors for simple generation of bi-phase pulses and are TDMA multi-user capable. The receiver is implemented in software and employs coherent cross-correlation with peak detection to localize the mobile unit via Time-Difference-Of-Arrival (TDOA) algorithms. Since the power of a proposed UWB system’s signal spread over a very wide bandwidth, the frequencies allocated to multiple existing narrowband systems may interfere with UWB spectrum. The goal of the filters discussed in this project is to cancel or suppress the interference while not distort the desired signal. To investigate the interference, we develop a algorithm to calculate the interference tones. In this thesis, we assume the interference to be narrowband interference (NBI) modeled as sinusoidal tones with unknown amplitude, frequency and phase. If we known the interference tones then it may be removed using a simple notched filter. Herein, we chose an adaptive filter so that it can adjust the interference tone automatically and cancel. In this thesis I tested adaptive filter technique to cancel interference cancellation (ie) LMS algorithm and Adaptive Noise Cancellation (ANC) technique. In this thesis performance of the both filters are compared.

  • 103.
    Strömberg, Daniel
    Karlstads universitet, Institutionen för informationsteknologi.
    Analys av BI-system och utveckling av BI-applikationer2006Independent thesis Basic level (professional degree), 20 poäng / 30 hpOppgave
    Abstract [sv]

    Detta examensarbete på D-nivå beskriver skapandet av BI-applikationer och analys av tre

    olika BI-system. Projekten har givits av Cederroth International AB som är ett av Sveriges

    största företag inom dagligvaruhandeln. Uppsatsen ger en inblick i vad BI är och hur BI

    fungerar i företagsvärlden. Det ges även en stegvis beskrivning i hur en applikation skapas

    med hjälp av BI-systemet QlikView och analyser av BI-systemen QlikView, SQL Server 2005

    och BusinessObjects XI om huruvida dessa uppfyller de funktionella kraven på ett BI-verktyg.

    Bakgrundsinformation om Cederroth och dess system för affärsdatahantering ges också i

    uppsatsen.

    Den BI-applikation som beskrivs i denna uppsats involverar finsk återförsäljningsdata.

    Stegen från grunddata till färdig applikation beskrivs och förklaras ingående i uppsatsen.

    Analysen av de tre BI-systemen som därefter gjorts har beskrivits i en del där

    grundinformation följs av en analys med hänsyn till de funktionella aspekterna i BI-systemen.

    Denna analys resulterade i ett likvärdigt resultat för de tre BI-systemen. BI-systemen hade

    dock olika lösningar på de funktionella delarna.

  • 104. Sundén, Susanne
    et al.
    Wicander, Gudrun
    Karlstads universitet, Institutionen för informationsteknologi.
    Bridging the Digital Divide: ICT Solutions Supporting Economic and Social Development for the Unseen Majority2003Inngår i: HumanIT 2003 / [ed] John Sören Pettersson, Karlstad: Karlstads universitet, 2003, Vol. 2003:26Kapittel i bok, del av antologi (Fagfellevurdert)
    Abstract [en]

    Although we are now in the 21st century the majority of the global population has still never used or even touched information and communication technologies (ICTs). Having the opportunity to use ICT becomes a question of equality between continents, nations, races, gender etc. if ICT is seen as a development instrument which can create opportunities for the 4 billion poor people all over the world. The majority of the poor live in rural and often isolated areas and have next to no contact with the world beyond their nearest neighbours. From our own fieldwork in rural Zambia we can easily provide examples where even the simplest kinds of ICT would have been of tremendous help in daily life.The aim of HumanITs research programme Bridging the Digital Divide (BDD) is to identify key factors which underlie the use of information and communication technologies when this use becomes a mechanism for sustainable economic development in rural areas in developing countries. In order to establish what these key factors are it is necessary to identify variables which can make visible the benefits and disadvantages of different kinds of ICT use

  • 105.
    Udatsjen, Klas
    et al.
    Karlstads universitet, Institutionen för informationsteknologi.
    Lind, Michael
    Karlstads universitet, Institutionen för informationsteknologi.
    Konstruktion av LAN-anslutet moduluppbyggt styrsystem2006Independent thesis Basic level (professional degree), 10 poäng / 15 hpOppgave
    Abstract [sv]

    Vår uppgift från Special-Elektronik var att konstruera en moduluppbyggd produkt för styrning via LAN. Den skulle kunna användas till att styra lampor och kontrollera strömbrytare i ett hus, via befintligt TCP/IP-nätverk som eliminerar viss del av kabeldragningen.

    För att lösa denna uppgift använde vi oss av en enchipsdator, en Xport från Lantronix och en kontrollserver. Xporten fungerar som mastermodul och översätter kommunikationen från TCP/IP till seriell och tvärt om.

    Som slavmodul valde vi att använda oss av en enchipsdator av typen ATMEGA8, där vi utnyttjar 8 digitala in- och utgångar.

  • 106.
    Ulfhake, Louise
    Karlstads universitet, Institutionen för informationsteknologi.
    A model for systems development to produce pedagogical software: multimedia for business or pleasure2001Inngår i: On methods for systems development in professional organisations: the Karlstad University approach to information systems and its role in society / [ed] Anders G Nilsson, John Sören Pettersson, Lund: Studentlitteratur, 2001, s. 142-164Kapittel i bok, del av antologi (Fagfellevurdert)
    Abstract [en]

    Freshly produced or newly purchased software should increase the productivity in our business operations. The program should be functional, usable and able to fulfil our need of information. This is particularly important if it is to be used in education, as a means to learn new material. Developing software for education purposes is a complicated process, requiring knowledge of how we think and learn, and of the possibilities and limitations that affect a computer. In this chapter a structured and systematic model for systems development is presented, designed during the process of developing pedagogical software. Currently some pedagogical software applications are used in distance education, for courses in the subject of Information Systems. One of these, entitled "Systems development", is introduced and used as a recurring example in this chapter

  • 107.
    Wennström (Klockar), Annika
    Karlstads universitet, Institutionen för informationsteknologi.
    A Measurement Based Performance Study of TCP over GSM/GPRS2004Licentiatavhandling, med artikler (Annet vitenskapelig)
    Abstract [en]

    In this thesis, the performance of the wireless Internet is studied with a focus on TCP over GSM/GPRS. To this end, we have developed a GSM/GPRS test bed for TCP measurements. We present measurements conducted in the test bed with TCP over both GSM and GPRS. The GSM measurements show that TCP interacts efficiently with the radio link layer in GSM, also under very poor radio conditions. The only cases when some inefficiency is detected occur due to sudden variations in delay. In GPRS, delay is, among other things, caused by buffering in intermediate nodes and by dynamic resource sharing. The GPRS measurements indicate that if the buffers in intermediate nodes are reduced, then the delay can be decreased significantly with almost retained throughput. Dynamic resource sharing is often configured to give preemptive priority to voice calls, which implies that all GPRS resources may be lost. Measurements with preemptive priority indicate that TCP performance is degraded more than necessary due to inefficient buffer management. The situation would improve if data was buffered during preemption and if the data was transmitted immediately as GPRS resources become available again

  • 108.
    Wennström (Klockar), Annika
    et al.
    Karlstads universitet, Institutionen för informationsteknologi.
    Alfredsson, Stefan
    Karlstads universitet, Institutionen för informationsteknologi.
    Brunstrom, Anna
    Karlstads universitet, Institutionen för informationsteknologi.
    TCP over Wireless Networks2004Rapport (Annet vitenskapelig)
    Abstract [en]

    This report provides an overview of common wireless network technologies used today, with emphasis on data transmission. Wireless networks are becoming increasingly used for Internet communications. As discussed in the report, the TCP protocol may experience performance degradations over wireless networks, due to non-congestion related packet loss and varying round trip times. To this end, many enhancements for TCP to the link and transport layer have been proposed. A selection of these are presented and discussed in relation to the wireless network technologies.

  • 109.
    Wennström (Klockar), Annika
    et al.
    Karlstads universitet, Institutionen för informationsteknologi.
    Brunstrom, Anna
    Karlstads universitet, Institutionen för informationsteknologi.
    Garcia, Johan
    Karlstads universitet, Institutionen för informationsteknologi.
    Gustafsson, Jan H.
    Telia Mobile AB, Karlstad, Sweden.
    A GSM/GPRS Testbed for TCP Performance Evaluation2002Inngår i: Proceedings of International Workshop on Wired/Wireless Internet Communications / [ed] Hamid R. Arabnia, Youngsong Mun, CSREA Press, 2002, s. 19-26Konferansepaper (Annet vitenskapelig)
    Abstract [en]

    Investigating the wireless Internet is a nontrivial task dueto the complexity of wireless systems and the many protocolinteractions that appear. In this paper we present a measurementtestbed that allows us to investigate the performanceof Internet traffic over a real GSM network but witha controlled radio environment and traffic load. A detailedperformance evaluation of TCP over GSM is presented. Arange of radio conditions are considered with a focus on theinteraction between TCP and the GSM link layer. With respectto efficient protocol layer interaction, the results showthat high variability in round trip times is more problematicthan poor radio conditions. How the testbed has been extendedfor GPRS and planned measurements for this systemare also discussed.

  • 110.
    Wennström (Klockar), Annika
    et al.
    Karlstads universitet, Institutionen för informationsteknologi.
    Brunström, Anna
    Karlstads universitet, Institutionen för informationsteknologi.
    TCP over GPRS: The Effect of Preemption2003Konferansepaper (Fagfellevurdert)
    Abstract [en]

    GPRS extends the widely deployed GSM system with a more efficient wireless Internet access. In this paper we present measurements of GPRS traffic when preempted by circuit-switched calls. The results indicate that TCP performance is degraded more than necessary, as buffered data is flushed immediately when the GPRS traffic is preempted. The time required for error recovery is considerable also for very short preemtion periods.

  • 111.
    Wennström (Klockar), Annika
    et al.
    Karlstads universitet, Institutionen för informationsteknologi.
    Brunström, Anna
    Karlstads universitet, Institutionen för informationsteknologi.
    Rendón, Juan
    Impact of GPRS buffering on TCP performance2004Inngår i: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911X, IEE Electronics Letters Volume 40, Issue 20, 30 Sept. 2004 Page(s): 1279-1281, Vol. 40, nr 20, s. 1279-1281Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    GPRS networks, excessive buffering has a negative effect on TCP as the round trip times become very long. Measurements with different buffer settings indicate that the queueing delay can be reduced by orders of magnitude with a smaller buffer, without significantly degrading TCP throughput. The measurements are conducted in a GPRS testbed consisting of real network nodes.

  • 112.
    Wennström (Klockar), Annika
    et al.
    Karlstads universitet, Institutionen för informationsteknologi.
    Brunström, Anna
    Karlstads universitet, Institutionen för informationsteknologi.
    Rendón, Juan
    Technology Dept., Pompeu Fabra University, Barcelona, Spain.
    Gustafsson, J. H.
    Telia Mobile AB, Karlstad, Sweden.
    The Impact of Preemptive Priority in GPRS on TCP Performance: A Measurement Study2004Inngår i: The first International Workshop on TCP and MAC Protocols in Wireless and Wired Networks, 2004, s. 430-436Konferansepaper (Fagfellevurdert)
    Abstract [en]

    GPRS extends the widely deployed GSM system with a more effecient wireless Internet access. In this paper we investigate how a TCP transmission over GPRS is affected when it loses all its resources due to preemption by circuit-switched calls with higher priority. The results indicate that TCP performance is degraded more than necessary, as buffered data is flushed immediately when the GPRS traffic is preempted. The time required for error recovery is considerable also for very short preemption periods. The situation would improve if data was buffered during preemption and if the data was transmitted immediately as GPRS resources become available again.

  • 113.
    Wennström (Klockar), Annika
    et al.
    Karlstads universitet, Institutionen för informationsteknologi.
    Brunström, Anna
    Karlstads universitet, Institutionen för informationsteknologi.
    Rendón, Juan
    Technology Dept., Pompeu Fabra University, Barcelona, Spain.
    Gustafsson, Jan H.
    Telia Mobile, Karlstad, Sweden.
    A GPRS Testbed for TCP Performance Measurements2002Inngår i: 4th International Workshop on Mobile and Wireless Communications Network, IEEE conference proceedings, 2002, s. 320-324Konferansepaper (Fagfellevurdert)
    Abstract [en]

    In this paper a GPRS measurement testbed for TCP performance evaluation is presented. Unlike simulations and live measurements, the testbed combines the use of real network equipment and protocol implementations with a precise control over radio channel conditions. Some initial TCP measurements obtained with the GPRS testbed are also presented. The effect of varying numbers of PDCH and of buffering in the GPRS system is investigated.

  • 114.
    Wennström (Klockar), Annika
    et al.
    Karlstads universitet, Institutionen för informationsteknologi.
    Brunström, Anna
    Karlstads universitet, Institutionen för informationsteknologi.
    Rendón, Juan
    Gustafsson, Jan H.
    The Impact of GPRS Buffering on TCP Performance2003Rapport (Fagfellevurdert)
    Abstract [en]

    Wireless Internet access over GPRS, the packet-oriented extension to GSM, provides for higher data rates and more efficient network utilization compared to circuit-switched access. The performance of the Internet protocols in GPRS is dependent not only on the quality of the radio link, but also on the buffering in the GPRS network. In this paper we investigate the impact of buffering on TCP performance. Measurements are conducted in a GPRS testbed consisting of real network nodes with real protocol implementations. When the buffer between the fixed and the wireless networks is large, then the round trip times may become very long. Measurements with different buffer settings indicate that the buffer could be decreased in order to reduce the queuing delay, without degrading the throughput. Measurements of concurrent packet- and circuit-switched traffic show that buffered data is flushed immediately as the GPRS traffic is preempted by circuit-switched calls. When resources are available again, the lost data must be retransmitted. In many cases this could be avoided by guarding the data with a timer

  • 115.
    Wennström (Klockar), Annika
    et al.
    Karlstads universitet, Institutionen för informationsteknologi.
    Garcia, Johan
    Karlstads universitet, Institutionen för informationsteknologi.
    Brunström, Anna
    Karlstads universitet, Institutionen för informationsteknologi.
    Gustafsson, Jan H.
    Telia Mobile AB, Karlstad, Sweden.
    TCP and GSM Link Layer Interactions: Implications for the Wireless Internet2001Inngår i: IEEE VTS 53rd Vehicular Technology Conference, 2001, IEEE conference proceedings, 2001, s. 2198-2202Konferansepaper (Fagfellevurdert)
    Abstract [en]

    The demand for wireless access to the Internet has grown rapidly making the performance of TCP in wireless environments an important issue. We present experimental measurements of the performance of TCP over GSM. The measurements were captured over a real GSM network connected to a controlled radio environment. A range of radio conditions were considered with a focus on the interaction between TCP and the GSM link layer. Even for very poor radio conditions, only neglible negative interaction effects were found.

  • 116.
    Wicander, Gudrun
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Centrum för HumanIT. Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för informatik och projektledning.
    Sundén, Susanne
    Karlstads universitet, Institutionen för informationsteknologi.
    ICT Use in a Rural Zambian Context - Local Conceptions Expressed as Critical Success Factors2004Inngår i: Proceedings of the IFIP WG 9.2, 9.6/11.7 Summer School on Risks and Challenges of the Network Society / [ed] Duquennoy, P., Fischer-Hübner, S., Holvast, J., Zuccato, A, Karlstad: Karlstads universitet, 2004, Vol. 2004:35Kapittel i bok, del av antologi (Annet vitenskapelig)
    Abstract [en]

    The objective of this study is to contribute to the analysis of the ICT situation in rural Zambia. The study aims to identify Critical Success Factors essential for ICT implementation and use within a district in Zambia. Data was collected during a two-month field study in the eastern part of Zambia. We carried out interviews with people from different areas of activities. The study provides a characterization of the ICT situation in a rural Zambian context based on conceptions expressed in interviews with local people. The factors range from national to local level. Notably, the Critical Success Factors are not limited to technology. In fact, most Critical Success Factors in our study relate to socio-cultural and governmental issues, which need to be addressed before and parallel to technological solutions

  • 117.
    Zhang, Ge
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Fischer-Hübner, Simone
    Karlstads universitet, Institutionen för informationsteknologi.
    A survey on anonymous voice over IP communication: attacks and defenses2019Inngår i: Electronic Commerce Research, ISSN 1389-5753, E-ISSN 1572-9362, ISSN 1389-5753, Vol. 19, nr 3, s. 655-687Artikkel i tidsskrift (Fagfellevurdert)
    Abstract [en]

    Anonymous voice over IP (VoIP) communication is important for many users, in particular, journalists, human rights workers and themilitary. Recent research work has shown an increasing interest in methods of anonymous VoIP communication. This survey starts by introducing and identifying the major concepts and challenges in this field. Then we review anonymity attacks on VoIP and the existing work done to design defending strategies. We also propose a taxonomy of attacks and defenses. Finally, we discuss possible future work.

  • 118.
    Zhang, Ge
    et al.
    Karlstads universitet, Fakulteten för ekonomi, kommunikation och IT, Avdelningen för datavetenskap.
    Pallares, Jordi Jaen
    Rebahi, Yacine
    Fischer-Hübner, Simone
    Karlstads universitet, Institutionen för informationsteknologi.
    SIP Proxies: New Reflectors in the Internet2010Inngår i: Communications and Multimedia Security: 11th IFIP TC 6/TC 11 International Conference, CMS 2010, Linz, Austria, May 31 – June 2, 2010. Proceedings, Springer, 2010, s. 142-153Konferansepaper (Fagfellevurdert)
    Abstract [en]

    To mitigate identity theft in SIP networks, an inter-domain authentication mechanism based on certificates is proposed in RFC 4474 [10]. Unfortunately, the design of the certificate distribution in this mechanism yields some vulnerabilities. In this paper, we investigate an attack which exploits SIP infrastructures as reflectors to bring down a web server. Our experiments demonstrate that the attacks can be easily mounted. Finally, we discuss some potential methods to prevent this vulnerability.

123 101 - 118 of 118
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