Change search
Refine search result
891011121314 501 - 550 of 1407
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf
Rows per page
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sort
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
  • Standard (Relevance)
  • Author A-Ö
  • Author Ö-A
  • Title A-Ö
  • Title Ö-A
  • Publication type A-Ö
  • Publication type Ö-A
  • Issued (Oldest first)
  • Issued (Newest first)
  • Created (Oldest first)
  • Created (Newest first)
  • Last updated (Oldest first)
  • Last updated (Newest first)
  • Disputation date (earliest first)
  • Disputation date (latest first)
Select
The maximal number of hits you can export is 250. When you want to export more records please use the Create feeds function.
  • 501. Hossfeld, Tobias
    et al.
    Binzenhöfer, Andreas
    Fiedler, Markus
    Tutschku, Kurt
    Measurement and Analysis of Skype VoIP Traffic in 3G UMTS Systems2006Conference paper (Refereed)
    Abstract [en]

    Voice-over-IP (VoIP) telephony becomes more and more popular in the wired Internet because of easy-to-use applications with high sound quality like Skype. UMTS operators promise to offer large data rates which should also make VoIP possible in a mobile environment. However, the success of those application strongly depends on the user perceived voice quality. In this paper, we therefore analyze the achievable and the actual quality of IP-based telephony calls using Skype. This is done performing measurements in both a real UMTS network and a test environment. The latter is used to emulate rate control mechanisms and changing system conditions of UMTS networks. The results show whether Skype over UMTS is able to keep pace with existing mobile telephony systems and how it reacts to different network characteristics. The investigated performance measures comprise the Perceptual Evaluation of Speech Quality (PESQ) to evaluate the voice quality, the packet loss, the inter-packet delay, and the throughput to capture networkbased factors. In this context, the concept of the Network Utility Function (NUF) is applied to describe the impact of the network on the voice quality as perceived by the end-user.

  • 502. Hossfeld, Tobias
    et al.
    Hock, David
    Tran-Gia, Phuoc
    Tutschku, Kurt
    Blekinge Institute of Technology, School of Engineering, Department of Telecommunication Systems.
    Fiedler, Markus
    Blekinge Institute of Technology, School of Engineering, Department of Telecommunication Systems.
    Testing the IQX Hypothesis for Exponential Interdependency between QoS and QoE of Voice Codecs iLBC and G.7112008Conference paper (Refereed)
    Abstract [en]

    Given the growing importance of quantitative relationships between user-perceived Quality of Experience (QoE) and network Quality of Service (QoS), this paper investigates the IQX hypothesis for two voice codecs, iLBC and G.711. This hypothesis expresses QoE as an exponential function of QoS degradation. The experiments are carried out in a controlled environment using the softphone SJPhone, the network emulator NIST Net, and a tool calculating the PESQ (Perceptual Evaluation of Speech Quality) from sent and received audio files. The IQX hypothesis is confirmed exactly for disturbances perceived on applications level, packet loss and packet reordering, which clearly correlate to the main sensitivities of the used softphone to packet-level disturbances such as loss, jitter and reordering. So, besides of providing a unified relationship between QoE and QoS, the IQX also proved to be capable of identifying the QoS parameters of relevance for QoE degradations. The study also points out interesting tracks for future work in terms of QoS degradations and related QoE evaluations.

  • 503. Hu, Ganglan
    et al.
    Aurum, Aybüke
    Wohlin, Claes
    Adding Value to Software Requirements? An Empirical Study in the Chinese Software Industry2006Conference paper (Refereed)
  • 504. Hult, Tommy
    Novel Applications of Space-Time Processing for Wireless Systems2006Licentiate thesis, comprehensive summary (Other academic)
    Abstract [en]

    Space-time processing techniques have emerged as one of the most promising areas of research and development in wireless communications. Space-time processing signifies the signal processing performed on a system consisting of several antenna elements, whose signals are processed adaptively in order to exploit both the spatial (space) and temporal (time) dimensions of the radio channel. Space-time processing techniques can be applied at the transmitter, the receiver or both. The use of space-time signal processing can significantly improve average signal power, mitigating fading, and reduce inter-symbol interference and co-channel interference. This can significantly improve capacity, coverage and quality of wireless systems. In this thesis we expand the scope of space-time processing by proposing novel applications in wireless communications. These include the reduction of possibly harmful electromagnetic radiation from mobile phones, enhancing link quality for Bluetooth links in indoor office environments, and increasing the spectral efficiency of satellite communication systems. Several studies have been conducted on the effects of radiation from hand held mobile phones. The amount of radiation emitted from most mobile phones is minute, but given the close proximity of the phone to the head it might be possible for the radiation to cause harm. In Part I, we suggest the use of adaptive signal processing algorithms combined with a MIMO (multiple-input multiple output) antenna system to decrease the electromagnetic radiation inside a certain volume in space (e.g. the the human head). In addition, we investigate the impact of MIMO antenna parameters, carrier frequency and power constraint on the performance of the system. Over the last decade there has been an explosive growth in the use of wireless mobile communications. Today we find users with mobile phones, wireless PDA's, MP3 players, and wireless headphones to connect to these devices. In Part II, we investigate the wave propagation effects of a short-range wireless device, such as the Bluethooth technology. Specifically, we assess the fading phenomenon for Bluetooth link in indoor office environment by simulation of different propagation scenarios, and use measurement results to confirm our findings. In addition, we investigate the improvement in performance resulting from receiver diversity gain of a system employing multiple receive antennas with various combining techniques. The need for high-speed, high-quality bandwidth efficient mobile communications is constantly increasing. In Part III, we address the potential gain of using MIMO antenna system in combination with OFDM (orthogonal frequency division multiplexing) in order to increase the bandwidth efficiency in satellite communication systems. In particular, we consider the increase in channel capacity that is possible by exploiting satellite and polarization diversity. In addition we investigate the effect of using different compact MIMO polarization antenna configurations and power control on the information theoretic capacity of the total transmission channel of the satellite system.

  • 505. Hult, Tommy
    Space-Time Processing Applications for Wireless Communications2008Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    Wireless mobile communication networks are rapidly growing at an incredible rate around the world and a number of improved and emerging technologies are seen to be critical to the improved economics and performance of these networks. The technical revolution and continuing growth of mobile radio communication systems has been made possible by extraordinary advances in the related fields of digital computing, high-speed circuit technology, the Internet and, of course, digital signal processing. Improved third generation (3G) and future generation wireless communication systems must support a substantially wider and enhanced range of services with respect to those supported by second generation and basic 3G systems. The never-ending quest for such personal and multimedia services, however, demands technologies operating at higher data rates and broader bandwidths. This combined with the unpredictability and randomness of the mobile propagation channel has created many new technically challenging problems for which innovative, adaptive and advanced signal processing techniques may offer new and better solutions. Space-time processing techniques have emerged as one of the most promising areas of research and development in wireless communications for the efficient utilization of the physical mobile radio propagation channel. Space-time processing signifies the signal processing performed on a system consisting of several antenna elements, whose signals are processed adaptively in order to exploit both the spatial (space) and temporal (time) dimensions of the radio channel. This can significantly improve the capacity, coverage, quality and energy efficiency of wireless systems. This thesis expands the scope of space-time processing by proposing novel applications in wireless communication systems. These include the reduction of possibly harmful electromagnetic radiation from mobile phones, enhancing the quality of Bluetooth links in indoor office environments, increasing the spectral efficiency of satellite and the novel high altitude platforms (HAPs) communication systems, enhancing the coverage and capacity of integrated multiple-HAP 3G systems, and improving the energy efficiency of cooperative wireless sensor networks. The performance of these systems is assessed by theoretical analysis, by computer simulations under a range of propagation environments including realistic channel models, advanced commercial electromagnetic modeling software, and a proposed novel multi-channel simulator suitable for various space-time applications.

  • 506. Hult, Tommy
    WCDMA Uplink Interference Assessment from Multiple High Altitude Platform Configurations2008In: EURASIP Journal on Wireless Communications and Networking, ISSN 1687-1472, E-ISSN 1687-1499, Vol. vol. 2008, no Special Issue on Advanced Communication Techniques and Applications for High-Altitude PlatformsArticle in journal (Refereed)
    Abstract [en]

    We investigate the possibility of multiple high altitude platform (HAP) coverage of a common cell area using a wideband code division multiple access (WCDMA) system. In particular, we study the uplink system performance of the system. The results show that depending on the traffic demand and the type of service used, there is a possibility of deploying 3-6 HAPs covering the same cell area. The results also show the effect of cell radius on performance and the position of the multiple HAP base stations which give the worst performance.

  • 507. Hult, Tommy
    et al.
    Falletti, Emanuela
    Mohammed, Abbas
    Sellone, Fabrizio
    Multi-antenna Channel Model for Space-Polarization Systems2007Conference paper (Refereed)
  • 508. Hult, Tommy
    et al.
    Falletti, Emanuela
    Mohammed, Abbas
    Sellone, Fabrizio
    The Impact of Depolarizing Effects on a Multiple HAP System Employing Polarization Diversity2007Conference paper (Refereed)
  • 509. Hult, Tommy
    et al.
    Grace, David
    Mohammed, Abbas
    WCDMA Capacity and Coverage Enhancement from Multiple High Altitude Platform Configuration2007Conference paper (Refereed)
  • 510. Hult, Tommy
    et al.
    Mohammed, Abbas
    A Combined Satellite Diversity and Compact MIMO Antenna Configurations for High Data Rate Communications2007Conference paper (Refereed)
  • 511. Hult, Tommy
    et al.
    Mohammed, Abbas
    Active Signal Processing Algorithms for Controlling Electromagnetic Fields: a Tutorial2008Conference paper (Refereed)
  • 512. Hult, Tommy
    et al.
    Mohammed, Abbas
    Active Suppression of Electromagnetic Fields2004Conference paper (Refereed)
  • 513. Hult, Tommy
    et al.
    Mohammed, Abbas
    Assessment of a HAP Diversity System Employing Compact MIMO-Tetrahedron Antenna2007Conference paper (Other academic)
  • 514. Hult, Tommy
    et al.
    Mohammed, Abbas
    Assessment of Multipath Propagation for a 2.4 GHz Short-Range Wireless Communication System2007Conference paper (Refereed)
    Abstract [en]

    In this paper we assess the multipath propagation effects of a short-range wireless device operating at 2.4 GHz in an indoor office environment. The investigations are carried out using FEM simulations and measurement trials for NLOS and LOS propagation scenarios. The FEM simulations will also be used for assessing the influence on propagation when doors are opened or closed. Finally, we investigate a single-input multiple-output (SIMO) antenna receive diversity system utilizing different combining techniques to improve the performance over a fading radio channel in a NLOS propagation environment. Simulation results show that a substantial diversity gain would be achieved by using this system. © 2007 IEEE

  • 515. Hult, Tommy
    et al.
    Mohammed, Abbas
    CAPACITY OF A SATELLITE DIVERSITY SYSTEM EMPLOYING MULTIPLE POLARIZATIONS2006Conference paper (Refereed)
    Abstract [en]

    In this paper we address the potential gain of using compact MIMO antenna array configurations in conjunction with satellite diversity techniques in order to increase the data rates in satellite communication systems. Simulation results show that by exploiting the additional multiple polarization channels and satellite diversity we can achieve considerable capacity gain compared to the single satellite case.

  • 516. Hult, Tommy
    et al.
    Mohammed, Abbas
    CAPACITY OF MULTIPLE HAP SYSTEM EMPLOYING MULTIPLE POLARIZATIONS2006Conference paper (Refereed)
    Abstract [en]

    In this paper we investigate the potential increase in capacity of HAP (High Altitude Platforms) communication systems using compact MIMO antenna array configurations in conjunction with HAP diversity techniques. In addition, we evaluate the system performance for different separation angles between HAPs. Simulation results show that the HAP diversity system provides superior performance compared to the single HAP case.

  • 517. Hult, Tommy
    et al.
    Mohammed, Abbas
    COMBINED POLARIZATION AND SATELLITE DIVERSITY FOR HIGH DATA RATE COMMUNICATIONS2006Conference paper (Refereed)
    Abstract [en]

    This paper addresses the potential gain of using multiple-input multiple-output (MIMO) principle in order to increase the bandwidth efficiency in satellite communication systems. In particular, we consider the increase in channel capacity that is possible by exploiting satellite and polarization diversity. In addition, we investigate the effect of using different compact MIMO polarization antenna configurations and power control on the information theoretic capacity of the total transmission channel of the satellite system.

  • 518. Hult, Tommy
    et al.
    Mohammed, Abbas
    Compact MIMO Antennas and HAP Diversity for Enhanced Data Rate Communications2007Conference paper (Refereed)
    Abstract [en]

    In this paper we address the potential gain of using various compact MIMO antenna array configurations in conjunction with HAP (High Altitude Platforms) diversity techniques in order to enhance the data rates in HAP communication systems. We will also investigate the effects of spatial correlation and mutual coupling between the separate antenna elements on system performance. Simulation results show that although the capacity is degraded by correlation and mutual coupling, we still achieve significant capacity gain compared to the single HAP case. Simulations also show the existence of an optimum separation angle between HAPs that maximizes capacity. © 2007 IEEE.

  • 519. Hult, Tommy
    et al.
    Mohammed, Abbas
    Cooperative Beamforming for Wireless Sensor Networks2007Conference paper (Refereed)
  • 520. Hult, Tommy
    et al.
    Mohammed, Abbas
    Estimation of the TOA performance of Loran-C2004Conference paper (Refereed)
    Abstract [en]

    Loran-C is a navigational aid that relies on the ability to make correct estimates of the Times of Arrival (TOAs) of signals received over a noisy radio channel. How good is the performance of Loran-C in this respect? Is it close to optimal? Are there perhaps better estimation techniques available than we currently employ? In this paper we use Estimation Theory to find the optimal limit of the accuracy of TOA estimates, for a given signal-to-noise ratio (SNR). Specifically, we compute the Cramer-Rao Lower Bound (CRLB) which specifies the absolute minimum error variance that can be achieved by an unbiased estimator. From the CRLB we can estimate the best repeatable accuracy that can be attained using a set of TOAs. We compute here the CRLBs for the TOA of a Loran-C signal with both Additive White Gaussian Noise (AWGN) and Additive Coloured Gaussian Noise (ACGN). We then employ the Maximum Likelihood Estimator (MLE) and compare its results with that of CRLB. Simulation results show that the MLE approaches the minimum variance obtained by CRLB for SNR values of practical and reliable Loran-C operation.

  • 521. Hult, Tommy
    et al.
    Mohammed, Abbas
    HAP Diversity and Compact MIMO Antennas for High Data Rate Communications2006Conference paper (Refereed)
    Abstract [en]

    In this paper we address the potential gain of using compact MIMO antenna array configurations in conjunction with HAP diversity and OFDM techniques in order to increase the data rates in HAP communication systems. Simulation results show that the MIMO system provides superior performance as compared to the single HAP case.

  • 522. Hult, Tommy
    et al.
    Mohammed, Abbas
    Indoor Propagation Simulation using FEM for Short-Range Wireless Communication Systems Operating at 2.4 GHz2005Conference paper (Refereed)
    Abstract [en]

    In this paper we investigate the wave propagation effects of a short-range wireless device, like the Bluetooth, in an indoor office environment. Specifically, we investigate line of sight (LOS) and non line of sight (NLOS) propagation scenarios and verify the theoretical statistics of the fading using real measurements and finite element method (FEM) simulations of the environment. The simulations are also used for assessing the impact on propagation when doors are opened or closed. In addition, we also investigate the improvement in performance resulting from receive diversity gain of a system employing multiple receive antennas with various combining techniques.

  • 523. Hult, Tommy
    et al.
    Mohammed, Abbas
    MIMO ANTENNA APPLICATIONS FOR HIGH ALTITUDE PLATFORMS2006Conference paper (Refereed)
    Abstract [en]

    In this paper we address the potential gain of using compact MIMO antenna array configurations in conjunction with HAP (High Altitude Platforms) diversity techniques in order to increase the data rates in HAP communication systems. Simulation results show that the MIMO system provides superior performance as compared to the single HAP case.

  • 524. Hult, Tommy
    et al.
    Mohammed, Abbas
    MIMO Antenna Applications for LEO Satellite Communications2005Conference paper (Refereed)
    Abstract [en]

    This paper addresses the potential gain of using multiple antennas and MIMO-OFDM techniques in order to increase the bandwidth efficiency in satellite communication systems. In particular, we consider the increase in channel capacity that is possible by exploiting satellite and polarization diversity. In addition, we investigate the effect of using different compact MIMO polarization antenna configurations and power control on the information theoretic capacity of the total transmission channel of the satellite system.

  • 525. Hult, Tommy
    et al.
    Mohammed, Abbas
    MIMO for HAPs: an idea whose time has come2006Conference paper (Refereed)
    Abstract [en]

    In this paper we address the potential gain of using compact MIMO antenna array configurations in conjunction with HAP diversity techniques in order to increase the data rates in HAP communication systems. Simulation results show that the MIMO system provides superior performance as compared to the single HAP case

  • 526. Hult, Tommy
    et al.
    Mohammed, Abbas
    MULTIPATH PROPAGATION ASSESSMENT FOR A 2.4 GHZ SHORT-RANGE WIRELESS COMMUNICATION SYSTEM2006Conference paper (Refereed)
    Abstract [en]

    In this paper we assess the effects of multipath propagation on the link performance of a short-range wireless device, like the Bluetooth, in an indoor office environment. Specifically, we analyze the non line of sight (NLOS) propagation scenario and confirm the theoretical statistics of the fading using real measurements and finite element method (FEM) simulations of the environment. The simulations are also used for assessing the impact of multipath propagation when doors are opened or closed. In addition, we also investigate the improvement in performance resulting from receive diversity gain of a system employing multiple receive antennas with various combining techniques.

  • 527. Hult, Tommy
    et al.
    Mohammed, Abbas
    Novel Applications of MIMO Antenna System for Active Suppression of Electromagnetic Fields2005Report (Other academic)
    Abstract [en]

    Active suppression of noise and vibrations is a well established field of research with many applications in acoustic and mechanical industries. In this report we test some of these active control methods combined with MIMO antenna system in order to assess their validity and performance when applied to electromagnetic fields. The application that we evaluated is a model of a mobile phone equipped with one ordinary transmitting antenna and a number of actuator-antennas which purpose is to cancel out the electromagnetic field at a specific volume in space (e.g. at the human head) while maintaining a predefined level of the overall output power of the system. This power control is achieved through the use of a quadratic constraint on the active control algorithm. In addition, we will also investigate the impact of MIMO antenna parameters and carrier frequency on the performance of the system. Simulation results show the promise of using the adaptive control algorithms and MIMO system to attenuate the electromagnetic field power density.

  • 528. Hult, Tommy
    et al.
    Mohammed, Abbas
    Performance Evaluation of Adaptive Signal Processing and MIMO Antenna System for the Reduction of Electromagnetic Field Density2007Conference paper (Refereed)
  • 529. Hult, Tommy
    et al.
    Mohammed, Abbas
    Power Constrained Active Suppression of Electromagnetic Fields Using MIMO Antenna System2004Conference paper (Refereed)
  • 530. Hult, Tommy
    et al.
    Mohammed, Abbas
    Power Constrained Space-Time Processing for Suppression of Electromagnetic Fields2005In: Journal of Communication Software and Systems, ISSN 1845-6421, E-ISSN 1846-6079, Vol. 1, no 1Article in journal (Refereed)
    Abstract [en]

    Active suppression of noise and vibrations is a well established field of research with many applications in acoustic and mechanical industries. In this paper we investigate the possibility of applying these adaptive active control methods with the aim of lowering the electromagnetic power density at a specific volume in space using the superposition principle and space-time processing employing the full MIMO (Multiple Input Multiple Output) antenna system setup. The application that we evaluated is a model of a mobile phone equipped with one ordinary transmitting antenna and two actuator-antennas which purpose is to cancel out the electromagnetic field at the human head while maintaining a predefined level of the overall output power of the system. This power control is achieved through the use of a quadratic constraint on the active control algorithm. Simulation results show the promise of using the adaptive control algorithms and MIMO system to attenuate the electromagnetic field power density

  • 531. Hult, Tommy
    et al.
    Mohammed, Abbas
    Suppression of EM Fields using Active Control Algorithms2004In: Radioengineering, ISSN 1210-2512, E-ISSN 1805-9600, Vol. 13, no 3, p. 22-25Article in journal (Refereed)
    Abstract [en]

    Active methods for attenuating acoustic pressure fields have been successfully used in many applications. In this paper we investigate some of these active control methods in combination with a MIMO antenna system in order to assess their validity and performance when applied to electromagnetic fields. The application that we evaluated in this paper is a model of a mobile phone equipped with one ordinary transmitting antenna and two actuator-antennas which purpose is to reduce the electromagnetic field at a specific area in space (e.g. at the human head). Simulation results show the promise of using the adaptive active control algorithms and MIMO system to attenuate the electromagnetic field power density.

  • 532. Hult, Tommy
    et al.
    Mohammed, Abbas
    THE IMPACT OF MIMO ANTENNA SYSTEM AND CARRIER FREQUENCYON ACTIVE CONTROL SUPPRESSION OF ELECTROMAGNETIC FIELD2004Conference paper (Refereed)
    Abstract [en]

    There have been several studies done, with conflicting results, on the effects of cell-phone radiation on the human body. The amount of radiation emitted from most cell phones is very minute. However, given the close proximity of the phone to the head, it is entirely possible for the radiation to cause harm. If you want to be on the safe side, the easiest way to minimize the radiation you are exposed to is to position the antenna as far from your head as possible. Utilizing a hands-free kit, a car-kit antenna or a cell phone whose antenna is even a couple of inches farther from the head can do this most effectively. This paper makes a contribution to that discussion by proposing a new approach by employing adaptive active control algorithms combined with a Multiple-Input Multiple-Output (MIMO) antenna system to suppress the electromagnetic field at a certain area in space. We will also investigate the effects of the size and number of MIMO antenna elements and test the algorithms at different carrier frequencies (e.g., other GSM bands and UMTS).

  • 533. Hult, Tommy
    et al.
    Mohammed, Abbas
    Theoretical Analysis and Assessment of Depolarization Effects on the Performance of High Altitude Platforms2008Conference paper (Refereed)
  • 534. Hult, Tommy
    et al.
    Mohammed, Abbas
    Falletti, Emanuela
    Sellone, Fabrizio
    Analysis of Depolarizing Effects and Impact on the Performance of a Multiple Satellite System Employing Polarization Diversity2007Conference paper (Refereed)
  • 535. Hult, Tommy
    et al.
    Mohammed, Abbas
    Falletti, Emanuela
    Sellone, Fabrizio
    Multi-Antenna Multi-HAP Channel Model for Space-Polarization2008Conference paper (Refereed)
  • 536. Hult, Tommy
    et al.
    Mohammed, Abbas
    Grace, David
    WCDMA Coverage Enhancement from Multiple High Altitude Platforms2008Conference paper (Refereed)
  • 537. Hult, Tommy
    et al.
    Mohammed, Abbas
    Grace, David
    Yang, Zhe
    Performance of a Multiple HAP System Employing Multiple Polarization2006Conference paper (Refereed)
  • 538. Hultgren, Anders
    et al.
    Nilsson, Magnus
    Kulesza, Wlodek
    Walther, Björn
    Integration av matematik och teknik på ingenjörsutbildningar2008Conference paper (Other academic)
    Abstract [sv]

    I detta bidrag presenterar vi en uppläggning av integrerade kurser i matematik och tillämpningar, vilken använts inom högskoleingenjörsutbildningen vid Högskolan i Kalmar. Kursverksamheten, som bedrivs inom ramen för kurspaketet ingenjörsvetenskap, tillgodoser såväl behovet av att betona matematikens roll som ett generellt och abstrakt verktyg för problemlösning som behovet av att ge studenterna bra baskunskaper i matematik i anslutning till möjliga tillämpningsområden.

  • 539.
    Husain, Rashid
    et al.
    Blekinge Institute of Technology, School of Engineering, Department of Interaction and System Design.
    Kazmi, Syed Muhammad Husnain
    Blekinge Institute of Technology, School of Engineering, Department of Interaction and System Design.
    Comparative Analysis of Static Recovery Schemes for Distributed Computing2008Independent thesis Advanced level (degree of Master (One Year))Student thesis
    Abstract [en]

    The primary objective of this thesis is to evaluate how grid computing works with their infrastructure. It also provides study to recognize the cases in which dynamic scheduler is preferable, how can the static recovery schemes play an effective role in large distributed system where load balancing is a key element and how can we get optimality in maximum number of crash computers using dynamic or static recovery schemes. This thesis consists of two parts: construction of Golomb and Trapezium modules, and performance comparison of Golomb and Trapezium recovery schemes with dynamic recovery scheme. In the first part we construct two modules that generate the recovery list of n computers, one for Golomb and one for Trapezium. In second part we make three schedulers, two for static recovery scheme and one for dynamic recovery scheme. In static recovery scheme we compare the performance of Golomb and Trapezium recovery scheme then we compare this performance with dynamic recovery scheme by using GridSim.

  • 540.
    Hussain, Musharrif
    et al.
    Blekinge Institute of Technology, School of Engineering, Department of Interaction and System Design.
    Mahmood, Sulman
    Blekinge Institute of Technology, School of Engineering, Department of Interaction and System Design.
    Secure Software and Communication on Handheld Devices2007Independent thesis Advanced level (degree of Master (One Year))Student thesis
    Abstract [en]

    Some applications on mobile handheld devices are involved in exchanging critical information e. g. sending positioning data of heavy-good vehicles as a basis for road toll. This information must not be accessed or modified illegitimately; however, there is the risk that can be accessed or modified by modifying the application or during communication of the handheld device with its counterpart. This thesis report investigates concepts to shelter software from modification and how the communication of these applications running on a handheld device over public mobile network can be made more secure. This work was performed by carefully identifying relevant literature and developing the concept that how a smart card can enhance the security of the software running on it particularly for handheld devices. It also discusses the issues and threats to smart cards. Furthermore it proposes a solution based on the specified scenario. The security of the software comprises on two layers; one layer is for analysis prevention, making it hard to understand the behaviour of the program both at static and dynamic levels. The other layer is responsible for verifying the integrity of the software to ensure that it is not modified. The software is installed on smart card which acts as an extra security layer. The communication relies on the security features of the public mobile network with some enhancement. In order to shelter the communication via public Internet, a border based VPN solution is deployed between the public mobile network and the remote server using the network assisted approach. This thesis will serve as basis for designing a secure communication path for Swedish road toll system.

  • 541.
    Hussain, Rizwan
    Blekinge Institute of Technology, School of Engineering, Department of Signal Processing.
    ADAPTIVE POWER CONTROL BY USING THE RECEIVED SNR AS A PROXY FOR DISTANCE TO OPTIMIZE THE SPECTRUM USAGE IN A COGNITIVE RADIO SYSTEMADAPTIVE POWER CONTROL BY USING THE RECEIVED SNR AS A PROXY FOR DISTANCE TO OPTIMIZE THE SPECTRUM USAGE IN A COGNITIVE RADIO SYSTEM2009Independent thesis Advanced level (degree of Master (Two Years))Student thesis
    Abstract [en]

    In this thesis work we have proposed an Adaptive Power Transmission scheme for Cognitive Radio. The proposed scheme estimates the distance between the primary user and the Cognitive Radio, using the SNR as proxy for distance, also utilizing the information of IT (Interference Temperature). On the basis of these information the Cognitive radio adaptively changes its transmit power to prevent the primary user from harmful interference. The most challenging problem of cognitive radio is the interference which occurs when a cognitive radio accesses a licensed band but fails to notice the presence of the licensed user. Another challenge is to compute the correct distance between the cognitive radio and the primary user. To allow the cognitive radio to access the same spectrum band where the primary user is operating creates a problem, in such case; the cognitive radio may interfere with the primary system, hence degrading the quality of service for the primary receiver. The Primary goal of this work is to propose Adaptive power control based on the estimated distance R_cr^pr between the cognitive radio and primary user. We will discuss the transmit power being controlled on the basis of distance. But there is no such method to calculate the exact distance between the cognitive radio and the primary user, so that we interpret distance in terms of SNR. We will propose a method to make the CR so intelligent that it can determine the maximum level of the transmission power which does not cause any harmful interference to the primer user’s quality of service.

  • 542.
    Hussain, Sajid
    Blekinge Institute of Technology, School of Engineering, Department of Signal Processing.
    Dynamic Radio Resource Management in 3GPP LTE2009Independent thesis Advanced level (degree of Master (Two Years))Student thesis
    Abstract [en]

    Orthogonal Frequency Division Multiple Access (OFDMA) is specified as downlink multiple access scheme in 3GPP LTE which divides the available bandwidth into multiple narrow orthogonal frequency bands. Thus, there is no ISI (Inter Symbol Interference) within the cell boundary. As the whole frequency spectrum is available in a cell site there would be greater chance of ICI (Intercell Interference) among the cell edge users of adjoining cells if frequency bands are allocated without any arrangement. This ICI can be mitigated with the help of different arrangements of frequency bands allocations and possibly with different transmission power distinguishing between the cell centre users and cell edge users. In this thesis work different ICI mitigation techniques are analyzed with different frequency allocation schemes and transmission power, and also different radio resource scheduling algorithms are analysed to enhance bandwidth efficiency and throughput.

  • 543. Hussain, Sajid
    et al.
    Grahn, Håkan
    Fast kd-Tree Construction for 3D-rendering Algorithms like Ray Tracing2007Conference paper (Refereed)
    Abstract [en]

    Many computer graphics rendering algorithms and techniques use ray tracing for generation of natural and photo-realistic images. The efficiency of the ray tracing algorithms depends, among other techniques, upon the data structures used in the background. kd-trees are some of the most commonly used data structures for accelerating ray tracing algorithms. Data structures using cost optimization techniques based upon Surface Area Heuristics (SAH) are generally considered to be best and of high quality. During the last decade, the trend has been moved from off-line rendering towards real time rendering with the introduction of high speed computers and dedicated Graphical Processing Units (GPUs). In this situation, SAH-optimized structures have been considered too slow to allow real-time rendering of complex scenes. Our goal is to demonstrate an accelerated approach in building SAH-based data structures to be used in real time rendering algorithms. The quality of SAH-based data structures heavily depends upon split-plane locations and the major bottleneck of SAH techniques is the time consumed to find those optimum split locations. We present a parabolic interpolation technique combined with a golden section search criteria for predicting kd-tree split plane locations. The resulted structure is 30% faster with 6% quality degradation as compared to a standard SAH approach for reasonably complex scenes with around 170k polygons.

  • 544. Hussain, Sajid
    et al.
    Grahn, Håkan
    Ranking Journals, Conferences and Authors in Computer Graphics: A Fuzzy Reasoning2008Conference paper (Refereed)
    Abstract [en]

    Rankings of different research bodies are of particular interest for academia and bibliometrics is used to measure the quality of these research bodies. Different factors affecting this quality have been proposed. In this paper, we have demonstrated a new approach based on fuzzy models and taken into account different proposed factors to access the overall quality. Our model actually refines the ranking by adding more factors which affects this quality. Thus, improving the information retrieval system based on human reasoning. A dimensionless index called Fuzzy Index (FI) has been proposed and used to shuffle the previously ranked research bodies. We have successfully demonstrated the application of our FI in ranking journals, conferences and authors in the field of computer graphics in particular and computer science in general.

  • 545. Hussain, Sajid
    et al.
    Grahn, Håkan
    Tracking Data Structures Coherency in Animated Ray Tracing for Real-Time 3D-Rendering2008Conference paper (Refereed)
    Abstract [en]

    Ray tracing is a well known method for photorealistic image synthesis, volume visualization and rendering. Over the last decade the method is being adopted throughout the research community around the world. With the advent of the high speed processing units, the method has been emerging from offline rendering towards real time rendering. The success behind ray tracing algorithms lies in the use of acceleration data structures and modern processing power of CPUs and GPUs. kd-tree is one of the most widely used data structures based on surface area heuristics (SAH). The major bottleneck in kd-tree construction is the time consumed to find optimum split locations. In this paper, we propose a prediction algorithm for animated ray tracing based on Kalman filtering. The algorithm successfully predicts the split locations for the next consecutive frame in the animation sequence. Thus, giving good initial starting points for one dimensional search algorithms to find optimum split locations – in our case parabolic interpolation combined with golden section search. With our technique implemented, we have reduced the “running kd-tree construction” time by between 78% and 87% for dynamic scenes with 16.8K and 252K polygons respectively.

  • 546. Hussain, Sajid
    et al.
    Grahn, Håkan
    Tracking Data Structures Coherency in Animated Ray Tracing: Kalman and Wiener Filters Approach2008Conference paper (Refereed)
    Abstract [en]

    The generation of natural and photorealistic images in computer graphics, normally make use of a well known method called ray tracing. Ray tracing is being adopted as a primary image rendering method in the research community for the last few years. With the advent of todays high speed processors, the method has received much attention over the last decade. Modern power of GPUs/CPUs and the accelerated data structures are behind the success of ray tracing algorithms. kd-tree is one of the most widely used data structures based on surface area heuristics (SAH). The major bottleneck in kd-tree construction is the time consumed to find optimum split locations. In this paper, we propose a prediction algorithm for animated ray tracing based on Kalman and Wiener filters. Both the algorithms successfully predict the split locations for the next consecutive frame in the animation sequence. Thus, giving good initial starting points for one dimensional search algorithms to find optimum split locations – in our case parabolic interpolation combined with golden section search. With our technique implemented, we have reduced the “running kd-tree construction” time by between 78% and 87% for dynamic scenes with 16.8K and 252K polygons respectively.

  • 547. Hussain, Sajid
    et al.
    Grahn, Håkan
    Persson, Jan A.
    A Minimum Vertex Cover Feature-Preserving Mesh Simplification2008Conference paper (Refereed)
    Abstract [en]

    The complexity of meshes in computer graphics rendering algorithms like ray tracing hinders the performance of these algorithms. Therefore, the need arises for reduced and approximated mesh quality and at the same time preserving the salient features of the shape. Mesh simplification problem in some cases can be considered as initial value problem where the quality of simplified mesh heavily depends on initial selection of vertices for contraction. In this short paper, we present an ongoing work in mesh simplification that uses a greedy algorithm for minimum vertex cover problem in order to select vertex contraction pairs to preserve salient features in the simplified mesh. Initial experiments show promising results with preserved salient features.

  • 548. Hussain, Sajid
    et al.
    Grahn, Håkan
    Persson, Jan A.
    Feature-preserving Mesh Simplification: A Vertex Cover Approach2008Conference paper (Refereed)
    Abstract [en]

    In computer graphics image synthesis algorithms like ray tracing, the mesh complexity decreases the performance of these algorithms. Therefore, the need arises to reduce the complexity of these meshes and at the same time preserving the salient features of the shape. Initial selection of vertices for mesh simplification heavily relates with the quality of the simplified meshes. In this paper, we present a greedy approach to select initial vertex contraction pairs to preserve salient features in the simplified meshes. The greedy algorithm exploits the property of meshes where vertices forming small features contain less number of edges. The technique selects vertices connected with large number of edges and makes them potential candidates for contraction according to a given cost function. The purpose is to first simplify those regions which are enriched with number of triangles and preserve small details of the shape constructed with small number of triangles. Our technique preserves very small details in the shape even after considerable simplification as compared to other existing techniques. Initial experiments show promising results with preserved salient features.

  • 549.
    Hussain, Shahid
    et al.
    Blekinge Institute of Technology, School of Engineering, Department of Systems and Software Engineering.
    Shabbir, Hassan
    Blekinge Institute of Technology, School of Engineering, Department of Systems and Software Engineering.
    Directory scalability in multi-agent based systems2008Independent thesis Advanced level (degree of Master (Two Years))Student thesis
    Abstract [en]

    Simulation is one approach to analyze and model the real world complex problems. Multi-agent based systems provide a platform to develop simulations based on the concept of agent-oriented programming. In multi-agent systems, the local interaction between agents contributes to the emergence of the global phenomena by getting the result of the simulation runs. In MABS systems, interaction is one common aspect for all agents to perform their tasks. To interact with each other the agents require yellow page services from the platform to search for other agents. As more and more agents perform searches on this yellow page directory, there is a decrease in the performance due to a central bottleneck. In this thesis, we have investigated multiple solutions for this problem. The most promising solution is to integrate distributed shared memory with the directory systems. With our proposed solution, empirical analysis shows a statistically significant increase in performance of the directory service. We expect this result to make a considerable contribution to the state of the art in multiagent platforms.

  • 550. Huzar, Zbigniew
    et al.
    Kuzniarz, Ludwik
    Reggio, Gianna
    Sourrouille, JL
    Consistency problems in UML-based software development2005Conference paper (Refereed)
    Abstract [en]

    This survey of the workshop series Consistency Problems in UML-based Software Development aims to help readers to find the guidelines of the papers. First, general considerations about consistency and related problems are discussed. Next, the approaches proposed in the workshop papers to handle the problems are categorized and summarized. The last section includes extended abstracts of the papers from the current workshop.

891011121314 501 - 550 of 1407
CiteExportLink to result list
Permanent link
Cite
Citation style
  • apa
  • harvard1
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Other style
More styles
Language
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Other locale
More languages
Output format
  • html
  • text
  • asciidoc
  • rtf