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  • 101. Hasslinger, Gerhard
    et al.
    Fiedler, Markus
    Analysis of deterministic servers with Ornstein-Uhlenbeck input process for voice traffic multiplexing2001Conference paper (Refereed)
    Abstract [en]

    Traffic models with a rate varying according to a Gaussian distribution are commonly used to evaluate statistical multiplexing in telecommunication systems. The Ornstein-Uhlenbeck process (OUP) is a Markovian and Gaussian process closely related to a first order autoregressive process (AR(1)). The superposition of voice or other homogeneous traffic sources asymptotically approaches an OUP in continuous time or an AR(1) in discrete time models, respectively. Performance results for a multiplexer with OUP input (OUP/D/1) are obtained based on functions of a single system parameter, We use fluid flow analysis and an approach for discrete time semi-Markovian systems to analyze the OUP/D/1 queueing system. A comparison of waiting time quantiles for input from a limited number of voice sources with the OUP/D/1 results indicates rather small deviations already for a moderate number of sources.

  • 102. Hasslinger, Gerhard
    et al.
    Fiedler, Markus
    Why buffers in switching systems do not essentially improve QoS: An analytical case study for aggregated On-off traffic2002Conference paper (Refereed)
    Abstract [en]

    Traffic models with a rate varying according to a Gaussian distribution are commonly used to evaluate statistical multi-plexing in telecommunication systems. The superposition of a sufficient large number of homogeneous Markovian On-Off sources asymptotically approaches an Ornstein-Uhlenbeck process (OUP) which represents a Gaussian process with ex-ponential autocorrelation function. We derive a simple expression for the bandwidth demand under QoS constraints which is close to numerical OUP/D/1 analysis results over the entire parameter region with relevance to applications. In com-parison, results of the fluid flow method for fixed aggregation level are used to verify the OUP/D/1 asymptotics and to estimate its accuracy depending on the number of aggregated flows. Moreover, the OUP/D/1 asymptotics provides a useful check of the accuracy of bounds and approximations proposed in the literature in order to improve the effective bandwidth principle. Based on analytical evaluation, the efficiency of buffers for voice traffic is finally shown to be very limited, i.e. no more than 2% of bandwidth can be saved owing to buffers with regard to real time constraints and a predefined loss probability as QoS demands for voice.

  • 103. Hasslinger, Gerhard
    et al.
    Hartleb, Franz
    Fiedler, Markus
    The relevance of the bufferless analysis for traffic management in telecommunication networks2000Conference paper (Refereed)
    Abstract [en]

    We study the analysis of switches or routers in a network to determine sufficient link capacities that can guarantee small loss probabilities as a main quality of service requirement. The bufferless case is considered, motivated by far simpler analysis as compared to queueing models but also by the proven inefficiency of buffering to achieve low cell or packet loss rates in the presence of real-time constraints and/or long range dependencies in the development of the traffic load, whereas statistical multiplexing can provide quality of service at reasonable bandwidth utilization even without buffering.

  • 104. Hult, Tommy
    et al.
    Mohammed, Abbas
    Nordebo, Sven
    Active Suppression of Electromagnetic Fields Using a MIMO Antenna System2003Conference paper (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 test some of these active control methods in order to assess their validity and performance when applied to electromagnetic fields. The application that we evaluated is a model of a mobile telephone equipped with one ordinary transmitting antenna and two actuator-antennas which purpose is to cancel out the electromagnetic field at a specific point in space (e.g. at your head).

  • 105. Håkansson, Lars
    et al.
    Brandt, Anders
    Lagö, Thomas L
    Claesson, Ingvar
    Modal Analysis and Operating Deflection Shapes of a Boring Bar2003Conference paper (Refereed)
    Abstract [en]

    In the manufacturing industry, the internal turning or boring operation is a common metal working process that is usually associated with vibration problems. Vibration in boring operations is usually inevitable. This necessitates extra care being taken in production planning and preparation. Thus, the vibration problems in internal turning considerably influence important factors such as productivity, production costs, etc. In order to gain further understanding of the dynamic behaviour of clamped boring bars in the metalcutting process experimental methods may be utilized. Two experimental methods have been used in order to investigate dynamic properties of a clamped boring bar: an experimental modal analysis and an operating deflection shape analysis. The results indicate a correlation between the shapes of the deflection shapes and/or mode shapes produced by the two different analysis methods. On the other hand, the orientation of the forced deflection shapes and/or mode shapes and the resonance frequencies demonstrates differences between the two methods. During continuous cutting, it is demonstrated that the bending motion of the first two resonance frequencies is to a large extent in the cutting speed direction.

  • 106. Håkansson, Lars
    et al.
    Claesson, Ingvar
    Lagö, Thomas L
    Active Control of Machine Tool Chatter1999Conference paper (Refereed)
    Abstract [en]

    In the turning operation chatter or vibration is a frequent problem, which affects the result of the machining, and, in particular, the surface finish. Tool life is also influenced by vibration. Severe acoustic noise in the working environment frequently occurs as a result of dynamic motion between the cutting tool and the workpiece. By proper machine design, e.g. improved stiffness of the machine structure, the problem of relative dynamic motion between cutting tool and workpiece may be partially solved. However, by active control of machine-tool vibration, a further reduction of the dynamic motion between cutting tool and workpiece can be achieved. It was found that adaptive feedback control based on the filtered-x LMS-algorithm, enables a reduction of the vibration by up to 40 dB at 1.5 kHz and by approximately 40 dB at 3 kHz. The active control performed a broadband attenuation of the sound pressure level by up to 35 dB. A significant improvement of the workpiece surface was also observed.

  • 107. Håkansson, Lars
    et al.
    Claesson, Ingvar
    Pettersson, Linus
    Lagö, Thomas L
    Active Control Machine Tool Chatter Embedded Piezo Ceramic Actuators in Tool Holder Shank1999Conference paper (Refereed)
    Abstract [en]

    In the turning operation chatter or vibration is a frequent problem, which affects the result of the machining, and, in particular, the surface finish. Tool life is also influenced by vibration. Severe acoustic noise in the working environment frequently occurs as a result of dynamic motion between the cutting tool and the workpiece. These problems can be reduced by active control of machine-tool vibration. Adaptive feedback control based on the filtered-x LMS-algorithm, enables a reduction of the vibration by up to 40 dB at 1.5 kHz and by approximately 40 dB at 3 kHz. The active control performed a broadband attenuation of the sound pressure level by up to 35 dB . A significant improvement of the workpiece surface was also observed. In the active control of tool vibration a tool holder construction based on integrated high magnetostrictive actuators was used. However, both the physical features and properties of an active tool holder construction based on high magnetostrictive actuators and the fact that this type of actuators generally have a non-linear behaviour highly reduce its applicability to the general lathe and turning operation. Therefor, a new generation embedded active tool holder shanks based on piezo ceramic actuators have been developed. Based on spectrum estimates, both coherence spectrum and frequency response function estimates has been calculated for both the old tool holder construction and the new generation active tool holder shank. From the results it follows that the phase delay is smaller and the linearity of the new generation active tool holder shank are superior compared to the old technology. It is also obvious that physical features and properties of new generation embedded active tool holder shanks based on piezo ceramic actuators fits the general lathe application.

  • 108. Håkansson, Lars
    et al.
    Claesson, Ingvar
    Pettersson, Linus
    Lagö, Thomas L
    Embedded Piezoceramic Actutaors in a Tool Holder Shank for the Active Control of Machine-tool Vibration1999Conference paper (Refereed)
    Abstract [en]

    In the turning operation chatter or vibration is a frequent problem, which affects the result of the machining, and, in particular, the surface finish. Tool life is also influenced by vibration. Severe acoustic noise in the working environment frequently occurs as a result of dynamic motion between the cutting tool and the workpiece. These problems can be reduced by active control of machine-tool vibration based on high magnetostrictive actuators. However, both the physical features and properties of a active tool holder construction based on high magnetostrictive actuators and the fact that this type of actuators generally have a non-linear behaviour highly reduce its applicability to the general lathe and turning operation. Therefor, a new generation embedded active tool holder shanks based on piezo ceramic actuators have been developed. Based on spectrum estimates, both coherence spectrum and frequency response function estimates has been calculated for both the old tool holder construction and the new generation active tool holder shank. From the results it follows that the phase delay is smaller and the linearity of the new generation active tool holder shank are superior compared to the old technology. It is also obvious that physical features and properties of new generation embedded active tool holder shanks based on piezo ceramic actuators fits the general lathe application.

  • 109. Håkansson, Lars
    et al.
    Claesson, Ingvar
    Sturesson, Per-Olof
    Lagö, Thomas L
    Active Control of Chatter in Turning: The Origine of Chatter1999Conference paper (Refereed)
    Abstract [en]

    In the turning operation chatter or vibration is a frequent problem, which affects the result of the machining, and, in particular, the surface finish. Tool life is also influenced by vibration. Severe acoustic noise in the working environment frequently occurs as a result of dynamic motion between the cutting tool and the workpiece. By proper machine design, e.g. improved stiffness of the machine structure, the problem of relative dynamic motion between cutting tool and workpiece may be partially solved. To achieve a further reduction of the dynamic motion between cutting tool and workpiece one solution is the active control of machine-tool vibration. However, to successfully apply active control of tool vibration in the external turning operation the response of the tool holder shank has to be investigated in order to enable the proper introduction of secondary vibration in the tool holder shank and to select a suitable controller. The investigation of the dynamic response of the tool holder shank relies on a stochastic approach while the structural dynamic properties have been evaluated by a normal mode analysis. This resulted in active control of tool vibration in a lathe that enables a reduction of the vibration by up to 40 dB at 1.5 kHz and by approximately 40 dB at 3 kHz.

  • 110. Håkansson, Lars
    et al.
    Johansson, Sven
    Dahl, Mattias
    Sjösten, Per
    Claesson, Ingvar
    NOISE CANCELLING HEADSETS FOR SPEECH COMMUNICATION2002In: Noise Reduction in Speech Applications / [ed] Davis, Gillian M., Boca Raton, Florida: CRC Press , 2002, p. 305-327Chapter in book (Other academic)
    Abstract [en]

    Headsets for speech communication are used in a wide range of applications. The basic idea is to allow hands-free speech communication, leaving both hands available for other tasks. One typical headset application is aircraft pilot communication. The pilot must be able to communicate with personnel on the ground and at the same time use both hands to control the aircraft. Communication headsets usually consist of a pair of headphones and a microphone attached with an adjustable boom. Headphone design varies widely between different manufacturers and models. In its simplest form, the headphone has an open construction providing little or no attenuation of the environmental noise. In headsets designed for noisy environments, the headphones are mounted in ear cups with cushions that provide some attenuation. The microphone is primarily designed to pick up the speech signal, but if the headset is used in a noisy environment, the background noise will also be picked up and transmitted together with the speech. As a consequence, speech intelligibility at the receive end will be reduced, possibly to zero. To increase the speech-to-noise ratio, it is common to use a directional microphone that has a lower sensitivity to sound incident from other directions than the frontal direction. In addition to this, the microphone electronics are usually equipped with a gate function that completely shuts off the microphone signal if its level drops below a threshold value. The purpose of the gate is to open the channel for transmission only when a speech signal is present. Headsets are frequently used in noisy environments where they suffer from problems of speech intelligibility. Even if an ear-cup type headset is used, the attenuation is relatively poor for low frequencies. Low frequency noise has a masking effect on speech, which significantly reduces the speech intelligibility. Several cases have been reported in which the sound level of the communication signal was increased to hazardous levels by the user to overcome this low frequency masking effect [1,2]. Ear exposure to the communication system resulted in hearing damage, such as hearing loss, tinnitus and hyperacusis.

  • 111.
    Jansson, Henrik
    et al.
    Blekinge Institute of Technology, Department of Telecommunications and Signal Processing.
    Åkesson, Benny
    Blekinge Institute of Technology, Department of Telecommunications and Signal Processing.
    Video Stabilisering för Mobil Utrustning2003Independent thesis Advanced level (degree of Master (One Year))Student thesis
    Abstract [en]

    This master thesis covers a solution to the image stabilization problem that does not require accelerators or gyros. The use of a fast and simple feature based algorithm to remove unwanted video motion makes it suitable for use in mobile equipment. The algorithm estimates the camera motion from the incoming video stream and compensates for unwanted translation and rotation. Experimental results are included from real life situations. The proposed algorithm can be used in real time applications, due to the low memory usage and low computational complexity.

  • 112. Jena, Ajit K.
    et al.
    Popescu, Adrian
    End-User Performance of WWW Services2001Conference paper (Refereed)
    Abstract [en]

    The global Internet has seen tremendous growth in terms of nodes and user base as well as of types of applications. One of the most important consequences of this growth is related to an increased complexity of the traffic models experienced in the networks. Each application has a set of unique characteristics in terms of the way it performs its transactions as well as the way transaction processing profile maps onto unique network resource requirements. In order to support Internet applications effectively, it is therefore important to understand and to characterize the application level transactions and also to investigate their scaling properties. Recent advances in high resolution traffic monitoring and analyzing capabilities have enabled us to build up realistic models for the TCP/IP protocol stack with diverse network applications. In this paper we report investigations of classical applications such as FTP, SMTP, and HTTP to evaluate end-to-end performance requirements and accordingly to assess end-user performance like Service Level Agreement (SLA) for WWW. Our results show the presence of a robust correlation structure in the traffic streams that has a fundamental bearing on the user perceived quality of the applications.

  • 113. Jena, Ajit K.
    et al.
    Popescu, Adrian
    Modeling of Internet Applications2000Conference paper (Refereed)
    Abstract [en]

    The global Internet has seen tremendous growth in terms of nodes and user base as well as of types of applications. One of the most important consequences of this growth is related to an increased complexity of the traffic experienced in these networks. Each application has a set of unique characteristics in terms of performance characteristics, transactions as well as the way the transaction processing profile maps onto unique network resource requirements. In order to support Internet applications effectively, it is therefore important to understand and to characterize the application level transactions as well as the effect of different TCP/IP control mechanisms on application-level parameters. It is the goal of this paper to model and to evaluate the characteristics of World Wide Web traffic. Results are reported on measuring, modeling and analysis of specific Hyper Text Transfer Protocol traffic collected from different (classes of) sites together with methodologies used for capturing HTTP flows as well as for modeling. The paper concludes with a discussion on the structure of Web pages and a model for the generation of the number of embedded pages in a Web page is suggested.

  • 114. Jena, Ajit K.
    et al.
    Popescu, Adrian
    Traffic Engineering for Internet Applications2001Conference paper (Refereed)
    Abstract [en]

    The focus of the paper is on resource engineering for supporting Service Level Agreements (SLAs) in IP networks. SLA at both link level and application level are considered. Using an object-oriented simulation model a case study is presented for client-server interactions generated by mixed traffic conditions in a Frame Relay (FR) WAN. Performance issues of Short Range Dependence (SRD) and Long Range Dependence (LRD) traffic under different resource control regimes are compared. The results show that major portion of the end-to-end delay comes from the queueing delay at the WAN ingress points, which is due to the significant bandwidth differences that may exist between LAN and WAN link layers. The results also highlight the role TCP window size and FR PVC control mechanisms play in the provision of delay performance for Internet services.

  • 115. Jena, Ajit K.
    et al.
    Popescu, Adrian
    Traffic Engineering for Internet Services2001Other (Other academic)
    Abstract [en]

    The focus of the paper is on resource engineering for supporting Service Level Agreements (SLAs) in IP networks. SLA at both link level and application level are considered. Using an object-oriented simulation model a case study is presented for client-server interactions generated by mixed traffic conditions in a Frame Relay (FR) WAN. Performance issues of Short Range Dependence (SRD) and Long Range Dependence (LRD) traffic under different resource control regimes are compared. The results show that major portion of the end-to-end delay comes from the queueing delay at the WAN ingress points, which is due to the significant bandwidth differences that may exist between LAN and WAN link layers. The results also highlight the role TCP window size and FR PVC control mechanisms play in the provision of delay performance for Internet services.

  • 116. Jena, Ajit K.
    et al.
    Popescu, Adrian
    Nilsson, Arne A.
    Application Layer Tracing for Performance Evaluation2002Conference paper (Refereed)
    Abstract [en]

    The paper reports on a set of non-intrusive tools that can be used for the performance evaluation of "classical" Internet applications such as Email, WWW, and FTP. At the application layer, key factors influencing the events are stochastic aspects of user behavior, protocol characteristics and sizes of contents transferred. A multi pronged approach involving application log analysis, direct probe of the WWW pages, and network flow analysis has been used. The measurement infrastructure is presented and diverse software tools for gathering of application layer properties are described in detail. The motivation is to build stochastic models for the key elements of application layer that can be further used to build up an integrated end-to-end performance testbed for conducting traffic engineering experiments.

  • 117. Jena, Ajit K.
    et al.
    Popescu, Adrian
    Nilsson, Arne A.
    Modeling and Evaluation of Internet Applications2002Report (Other academic)
    Abstract [en]

    The paper presents a modeling and evaluation study of the characteristics of several "classical" Internet applications (SMTP, HTTP and FTP) in terms of user behavior, nature of contents transferred and application layer protocol exchanges. Results are reported on measuring, modeling and analysis of application layer traces collected, at both the client and the server end, from different environments such as university networks and commercial Frame Relay networks. The methodologies used for capturing traffic flows as well as for modeling are reported. Statistical models have been developed for diverse parameters of applications (e.g., HTTP document sizes, FTP file sizes, and SMTP message sizes), which can be useful for building synthetic workloads for simulation and benchmarking purposes. All three applications possess a session oriented structure. Within each session, a number of transactions are performed. For the above mentioned applications, the number of transactions that may occur during a session has been also modeled.

  • 118. Jena, Ajit K.
    et al.
    Popescu, Adrian
    Nilsson, Arne A.
    Resource Engineering for Internet Applications2002Report (Other academic)
    Abstract [en]

    The focus of the paper is on resource engineering for supporting Service Level Agreements (SLAs) in IP networks. We review some of the recent developments in Internet service architecture and protocol developments as well as some of the most important challenges still to be considered. An important performance metrics that must be considered in developing the new Internet is regarding the delay and the delay variation/jitter. Connected with this, a case-study is reported on end-to-end delay performance in a best-effort Internet. Performance issues of Short Range Dependence (SRD) and Long Range Dependence (LRD) traffic under different resource control regimes are compared. The results show that a major portion of the end-to-end delay comes from the queueing delay at the WAN ingress point, which is due to the significant bandwidth differences that may exist between LAN and WAN link layers. The results also highlight the role TCP window size and Frame Relay Permanent Virtual Channel (FR PVC) control mechanisms play in the provision of delay performance for Internet services.

  • 119. Jena, Ajit K.
    et al.
    Popescu, Adrian
    Pruthi, Parag
    Modeling and Analysis of HTTP Traffic2000Conference paper (Refereed)
    Abstract [en]

    The global Internet has seen tremendous growth in terms of nodes and user base as well as of types of applications. One of the most important consequences of this growth is related to an increased complexity of the traffic experienced in these networks. Each application has a set of unique characteristics in terms of performance characteristics, transactions as well as the way the transaction processing profile maps onto unique network resource requirements. In order to support Internet applications effectively,it is therefore important to understand and to characterize the application level transactions as well as the effect of different TCP/IP control mechanisms on application-level parameters. It is the goal of this paper to model and to evaluate the characteristics of World Wide Web traffic. Results are reported on measuring, modeling and analysis of specific Hyper Text Transfer Protocol traffic collected from different (classes of) sites together with methodologies used for capturing HTTP flows as well as for modeling. The paper concludes with a discussion on the structure of Web pages and a model for the generation of the number of embedded pages in a Web page is suggested.

  • 120. Jena, Ajit K.
    et al.
    Pruthi, Parag
    Popescu, Adrian
    Modeling and Evaluation of Network Applications and Services1999Conference paper (Refereed)
    Abstract [en]

    The global Internet has seen tremendous growth in terms of nodes and user base as well as of types of applications. One of the most important consequences of this growth is related to an increased complexity of the traffic experienced in these networks. Each application has a set of unique characteristics in terms of its performance characteristics, its transactions as well as the way the transaction processing profile maps onto unique network resource requirements. In order to support Internet applications effectively, it is therefore important to understand and to characterise the application level transactions. Recent advances in high resolution traffic monitoring and analysis capabilities have enabled us to build up realistic models for diverse network applications. In this paper we report investigations of classical applications such as FTP, SMTP, and HTTP to evaluate end-to-end network performance requirements. Our results show the presence of a robust correlation structure in the traffic streams that has a fundamental bearing on the user perceived quality of the applications.

  • 121. Jena, Ajit K.
    et al.
    Pruthi, Parag
    Popescu, Adrian
    Resource Engineering for Internet Applications1999Conference paper (Refereed)
    Abstract [en]

    Recent measurements on LAN, MAN and WAN traffic have demonstrated that Long-Range Dependence (LRD) is an invariant property irrespective of network technology being employed. As a consequence, the performance of the network is dominated by the property of LRD in the network traffic. Latency in information access is one of the most important factors in the user perceived Quality of Service (QoS) in network applications. Almost all the applications follow the client-server paradigm to transfer information entities which are typically files or typed-in messages. The distribution of the sizes of these information entities are best described by heavy-tailed distributions and results in LRD. This fundamental property impacts all the aspects of application layer performance (e.g., response time) and the network layer performance (e.g., packet loss and delay). In the traditional traffic models, the network resource management is aimed at capturing the timescales at which bursts occur and dimensioning the network for the burst sizes occuring at that timescale. This management paradigm has proven to be ineffective for the traffic having significant level of LRD. Because of LRD, bursts of all possible sizes occur at timescales spanning over several orders of magnitude. Engineering of network resources to protect application layer QoS is therefore an important task. In this paper heavy-tailed distributions are used to model the information contents transferred by some of the classical network applications such as FTP, SMTP and HTTP. The parameters of these models are based on high resolution non-intrusive monitoring of busy periods in live networks. The clients and the servers are modelled as ON-OFF sources producing LRD phenomena at the packet level through aggregation. The user level quality for these applications is investigated (in terms of end-to-end delay performance) and preliminary results are reported showing how the quality is affected by the bandwidth and buffer allocation schemes.

  • 122. Johansson, Anders
    et al.
    Grbic, Nedelko
    Nordholm, Sven
    Speaker localisation using the far-field SRP-PHAT in conference telephony2002Conference paper (Refereed)
    Abstract [en]

    This paper describes a robust algorithm for sound source localization in conference rooms. The method used is a modi¯ed steered response power phase alignment transform algorithm. The results are obtained by processing real data recorded in a typical conference room, and they are compared to data obtained from a simple free-field model. The algorithm demonstrates good accuracy for ¯nding the correct angle of arrival for the dominant speaker in the room and works well for speech sources. The algorithm integrates well with subband decomposition and is suited for realtime applications.

  • 123. Johansson, Sven
    Active Control of Lateral Vibrations in a High-Speed Train2003Conference paper (Refereed)
    Abstract [en]

    As trains are continually designed for higher and higher speeds the problems of railway carriage vibration are on the increase. Lateral vibrations in a railway carriage are noticeable to passengers if the vibration frequencies are lower than approximately 20 Hz. Below this frequency discomfort is a common problem for the passengers and below approximately 1 Hz motion sickness is a problem. The passive solution of stiffening the carriage chassis to shift the vibrational frequencies higher up results in inflated manufacturing and running costs, and opposes higher travel speeds due to increased weight. Semi-passive solutions such as modifying the structural dynamics of the carriage body by decoupling heavy under-floor equipment does not come with a weight penalty, but do not reduce the vibrations sufficiently. However, by using an active vibration control system it is possible to improve the attenuation of the lateral train vibrations. This paper addresses two simple active vibration control systems for reducing lateral vibrations: one feedforward system and one feedback. Computer simulations based on signals derived from a dynamic computer model of a train indicates that the incorporation of an active control system, in addition to the semi-passive approach, is likely to introduce an improved attenuation of the low-frequency lateral vibrations. Active control results illustrate an attenuation of the lateral carriage vibration by up to 15 dB.

  • 124. Johansson, Sven
    Active Control of Propeller-Induced Noise in Aircraft: Algorithms & Methods2000Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    In the last decade acoustic noise has become more and more regarded as a problem. In cars, boats, trains and aircraft, low-frequency noise reduces comfort. Lightweight materials and more powerful engines are used in high-speed vehicles, resulting in a general increase in interior noise levels. Low-frequency noise is annoying and during periods of long exposure it causes fatigue and discomfort. The masking effect which low-frequency noise has on speech reduces speech intelligibility. Low-frequency noise is sought to be attenuated in a wide range of applications in order to improve comfort and speech intelligibility. The use of conventional passive methods to attenuate low-frequency noise is often impractical since considerable bulk and weight are required; in transportation large weight is associated with high fuel consumption. In order to overcome the problems of ineffective passive suppression of low-frequency noise, the technique of active noise control has become of considerable interest. The fundamental principle of active noise control is based on secondary sources producing ``anti-noise.'' Destructive interference between the generated and the primary sound fields results in noise attenuation. Active noise control systems significantly increase the capacity for attenuating low-frequency noise without major increase in volume and weight. This doctoral dissertation deals with the topic of active noise control within the passenger cabin in aircraft, and within headsets. The work focuses on methods, controller structures and adaptive algorithms for attenuating tonal low-frequency noise produced by synchronized or moderately synchronized propellers generating beating sound fields. The control algorithm is a central part of an active noise control system. A multiple-reference feedforward controller based on the novel actuator-individual normalized Filtered-X Least-Mean-Squares algorithm is introduced, yielding significant attenuation of such period noise. This algorithm is of the LMS-type, and owing to the novel normalization it can also be regarded as a Newton-type algorithm. The new algorithm combines low computational complexity with high performance. For that reason the algorithm is suitable for use in systems with a large number of control sources and control sensors in order to reduce the computional power required by the control system. The computational power of the DSP hardware is limited, and therefore algorithms with high computational complexity allow fewer control sources and sensors to be used, often with reduced noise attenuation as a result. In applications, such as controlling aircraft cabin noise, where a large multiple-channel system is needed to control the relative complex interior sound field, it is of great importance to keep down the computational complexity of the algorithm so that a large number of loudspeakers and microphones can be used. The dissertation presents theoretical work, off-line computer experiments and practical real-time experiments using the actuator-individual normalized algorithm. The computer experiments are principally based on real-life cabin noise data recorded during flight in a twin-engine propeller aircraft and in a helicopter. The practical experiments were carried out in a full-scale fuselage section from a propeller aircraft.

  • 125. Johansson, Sven
    et al.
    Claesson, Ingvar
    Active Noise Control in Propeller Aircraft2001Conference paper (Refereed)
    Abstract [en]

    A noisy environment dominated by low frequency noise can often be improved through the use of active noise control. This situation arises naturally in propeller aircraft where the propellers induce periodic low frequency noise inside the cabin. The cabin noise is typically rather high, and the passenger flight comfort could be improved considerably if this level were significantly reduced. This paper addresses same design aspects for multiple-reference active noise control systems based on the feedforward strategy. The paper also discusses the operation of narrowband feedforward active noise control system and presents results from experiments.

  • 126. Johansson, Sven
    et al.
    Claesson, Ingvar
    Nordebo, Sven
    Sjösten, Per
    Evaluation of Multiple Reference Active Noise Control Algorithms on Dornier 328 Aircraft Data1999In: IEEE transactions on speech and audio processing, ISSN 1063-6676 , Vol. 7, no 4, p. 473-477Article in journal (Refereed)
    Abstract [en]

    This correspondence presents an evaluation of multiple-reference adaptive algorithms. Two LMS-types and a Newton-type algorithm are considered. The special structure of the adaptive filtering problem implies that the Newton-type algorithm can be implemented with the same numerical complexity as LMS-type algorithms. The concept of a fast filtered-x Newton algorithm is thus introduced.

  • 127. Johansson, Sven
    et al.
    Håkansson, Lars
    Persson, Per
    Claesson, Ingvar
    Active Control Methods for Reducing Lateral Vibrations in High-Speed Trains2002Conference paper (Refereed)
    Abstract [en]

    The problem of low-frequency lateral train-car vibration is an important issue surrounding the design of high-speed trains. Passive vibration control solutions such as stiffening the car chassis are impractical because of the weight increase, and modifying the structural dynamics of the carboy through nonrigid coupling of heavy underfloor equipment does not come with a weight penalty, but do not sufficiently reduce the vibrations. This paper addresses two simple active vibration control systems for reducing lateral vibrations: one feedforward system and one feedback. Computer simulations based on signals derived from a dynamic computer model of a train car indicates that the incorporation of an active control system, in addition to the passive approach, is likely to introduce an improved attenuation of the low-frequency lateral vibrations. Active control results illustrate an attenuation of the lateral train-car vibration by up to 14 dB.

  • 128. Johansson, Sven
    et al.
    Håkansson, Lars
    Persson, Per
    Claesson, Ingvar
    Active Control of Lateral Vibrations in a Railway Carriage2002In: International Journal of Acoustics and Vibration, ISSN 1027-5851, Vol. 7, no 4, p. 195-210Article in journal (Refereed)
    Abstract [en]

    As trains are continually designed for higher and higher speeds the problems of railway carriage vibration are on the increase. Lateral vibrations in a railway carriage are noticeable to passengers if the vibration frequencies are lower than approximately 20 Hz. Below this frequency discomfort is a common problem for the passengers and below approximately 1 Hz motion sickness is a problem. The passive solution of stiffening the carriage chassis to shift the vibrational frequencies higher up results in inflated manufacturing and running costs, and opposes higher travel speeds due to increased weight. Semi-passive solutions such as modifying the structural dynamics of the carriage body by decoupling heavy underfloor equipment do not reduce the vibrations sufficiently. However, by appending a multi-reference feedforward active vibration control system, one way expect a substantial reduction in the lateral vibration level. Using a dynamic computer model of a railway carriage simulating the lateral vibration, and using as input bogie acceleration data measured on a running train, multiple-input/single-output coherence spectra were shown to constitute a suitable set of reference signals for an active control system. Control simulations based on the Feedforward Multiple-Input/Single-Output Filtered-x LMS Algorithm are carried out using different reference signal combinations. The control results indicate lateral vibration attenuation on the order of 15dB at the objective frequency of 10Hz.

  • 129. Johansson, Sven
    et al.
    Håkansson, Lars
    Persson, Per
    Claesson, Ingvar
    THE MULTIPLE-INPUT/SINGLE-OUTPUT FEEDFORWARD CONTROL OF LATERAL VIBRATION IN A HIGH-SPEED TRAIN CAR2002Conference paper (Refereed)
    Abstract [en]

    The problem of low- frequency lateral train-car vibration is an important issue surrounding the design of high-speed trains. Passive solutions such as stiffening the car chassis are impractical because of the weight increase. Semi-passive solutions, such as modifying the structural dynamics of the carboy through non-rigid coupling of heavy underfloor equipment does not come with a weight penalty, but do not sufficiently reduce the vibrations. However, computer simulations based on signals derived from a dynamic computer model of a train car indicates that the incorporation of a feedforward active control system, is likely to introduce a substantial reduction in the lateral vibration level. A simple controller structure is used and it is based on the multiple- input/single-output filtered-x LMS algorithm. Active control results illustrate an attenuation of the lateral train-car vibration by up to 14 dB.

  • 130. Johansson, Sven
    et al.
    Håkansson, Lars
    Persson, Per
    Claesson, Ingvar
    The Multiple-input/Single-output Feedforward Control of Lateral Vibration in a High-speed Train Car2002Conference paper (Refereed)
    Abstract [en]

    The problem of low- frequency lateral train-car vibration is an important issue surrounding the design of high-speed trains. Passive solutions such as stiffening the car chassis are impractical because of the weight increase. Semi-passive solutions, such as modifying the structural dynamics of the carboy through non-rigid coupling of heavy underfloor equipment does not come with a weight penalty, but do not sufficiently reduce the vibrations. However, computer simulations based on signals derived from a dynamic computer model of a train car indicates that the incorporation of a feedforward active control system, is likely to introduce a substantial reduction in the lateral vibration level. A simple controller structure is used and it is based on the multiple- input/single-output filtered-x LMS algorithm. Active control results illustrate an attenuation of the lateral train-car vibration by up to 14 dB.

  • 131. Johansson, Sven
    et al.
    Lagö, Thomas L
    Claesson, Ingvar
    PERFORMANCE OF A SINGLE- VERSUS A TWIN-REFERENCE CONTROLLER IN A NARROWBAND ACTIVE NOISE CONTROL APPLICATION1999Conference paper (Refereed)
    Abstract [en]

    In many applications of noise control, the greatest annoyance is caused by periodic low frequency noise. Successful reduction of such noise can often be achieved by using an Active Noise Control (ANC) system with narrowband feedforward control. If several noise sources contribute to the sound field, a multiple--reference control system is usually required. This allows the reference signals from each noise source to be processed individually within the controller, thereby enabling individual control of the sound field from each noise source. The present paper addresses the problem of controlling noise from two sources that are more or less synchronized. A typical application is the control of propeller-generated noise within a twin propeller aircraft. To find out whether a multiple-reference controller is necessary, or if a single--reference controller can do the job, the performance of a single- versus twin-tacho control algorithm was evaluated in a comparative study. The study is a computer simulation using real life data recorded in a Dornier 328 under different flight conditions. The results demonstrate that the twin-tacho algorithm performs better than the single-tacho whenever there is a slight deviation in the rotational speed of the two propellers.

  • 132. Johansson, Sven
    et al.
    Lagö, Thomas L
    Nordebo, Sven
    Claesson, Ingvar
    CONTROL APPROACHES FOR ACTIVE NOISE CONTROL OF PROPELLER-INDUCED CABIN NOISE EVALUATED FROM DATA FROM A DORNIER 328 AIRCRAFT1999Conference paper (Refereed)
    Abstract [en]

    In many applications of noise control, the greatest annoyance is caused by periodic low frequency noise. Successful reduction of such noise can often be achieved by using an Active Noise Control (ANC) system with narrowband feedforward control. If several noise sources contribute to the sound field, a multiple-reference control system is usually required. This system allows the reference signals from each noise source to be processed individually within the controller, thereby enabling individual control of the sound field from each noise source. This paper presents a mukiple-reference control algorithm and addresses the problem of controlling noise from two sources that are more or less synchronized. A typical application is the control of propeller-generated noise within a twin propeller aircraft. To find out whether a multiple-reference controller is necessary, or if a single-reference controller can do the job, the performance of a single- versus twin-tacho control algorithm was evaluated in a comparative study. The study is a computer simulation using real life data recorded in a Domier 328 under different flight conditions. The results demonstrate that the twin-tacho controller performs better than the single-tacho whenever there is a slight deviation in the rotational speed of the two propellers.

  • 133. Johansson, Sven
    et al.
    Nordebo, Sven
    Claesson, Ingvar
    Convergence Analysis of a Twin-Reference Complex Least-Mean-Squares Algorithm2002In: IEEE transactions on speech and audio processing, ISSN 1063-6676, E-ISSN 1558-2353, Vol. 10, no 4, p. 213-221Article in journal (Refereed)
    Abstract [en]

    In many noise control applications, the noise is dominated by low frequencies and generated by several independent periodic sources. In such situations the tonal noise may be suppressed by using a narrowband multiple-reference feedforward controller. The performance characteristics of the control system, e.g., the convergence behavior and noise reduction are directly related to the controller adaptation rate as well as the frequency separation of the tonal components in the noise, i.e., the beat frequency. This paper treats the convergence performance of a complex least-mean-squares (LMS) algorithm using two reference signals. An analysis of its convergence behavior is presented as well as the results from computer simulations validating the convergence behavior. The convergence of the filter weights and the decrease rate of the squared error (the learning curve) for noise control applications are also discussed.

  • 134. Johansson, Sven
    et al.
    Nordebo, Sven
    Sjösten, Per
    Claesson, Ingvar
    A Novel Multiple-Reference Algorithm for Active Control of Propeller-Induced Noise in Aircraft Cabins2000Report (Other academic)
    Abstract [en]

    The cabin noise inside propeller aircraft is essentially dominated by strong tonal components at harmonics of the blade passage frequency of the propellers. In order to achieve an efficient reduction of such a periodic low frequency noise, it is advisable to use an active noise control system based on adaptive narrowband feedforward techniques. The feedforward controller presented in this paper exploits narrowband assumptions by using complex-valued filtering and complex modeling of control paths. This paper introduces a multiple reference controller based on the novel actuator-individual normalized Filtered-X Least-Mean-Squares (FX LMS) algorithm. This algorithm combines low computational complexity with high performance. The algorithm is of the LMS-type. However, owing to the novel normalization of the algorithm it can also be regarded as a Newton-type algorithm. A comparison between the actuator-individual normalized FX LMS algorithm and the ordinary normalized FX LMS algorithm is presented. The results demonstrate better performance in terms of convergence rate and tracking properties when the Newton-like actuator-individual normalized FX LMS algorithm is used as compared with the conventional normalized LMS algorithm. The evaluation was performed using noise signals recorded inside the cabin of a twin engine propeller aircraft during flight. The paper also discusses variants of the actuator-individual normalized FX LMS algorithm.

  • 135. Johansson, Sven
    et al.
    Nordebo, Sven
    Sjösten, Per
    Winberg, Mathias
    Claesson, Ingvar
    Active Control of Sound using the Actuator-Individual Normalized Filtered-X LMS Algorithm2001Conference paper (Refereed)
    Abstract [en]

    The control algorithm is a central part of an active noise control system. The computational power of the DSP hardware is limited, and therefore algorithms with high computational complexity allow fewer control sources and sensors to be used, often with reduced noise attenuation as a result. This paper presents results from practical experiments using an ANC system based on the actuator-individual normalized Filtered-X LMS algorithm. The algorithm combines low computational complexity with high performance. For that reason the algorithm is suitable for use in large multi-channel systems in order to reduce the computional power required by the control system.

  • 136. Johansson, Sven
    et al.
    Persson, Per
    Claesson, Ingvar
    ACTIVE CONTROL OF PROPELLER-INDUCED NOISE IN AN AIRCRAFT MOCK-UP1999Conference paper (Refereed)
    Abstract [en]

    A noisy environment dominated by low frequency noise can often be improved through the use of active noise control. This situation arises naturally in propeller aircraft where the propellers induce periodic low frequency noise inside the cabin. The overall interior sound pressure level inside a turboprop aircraft is typically rather high, and the passenger flight comfort could be improved considerably if this level was significantly reduced. This paper discusses the behaviour and robustness of a narrowband twin--reference feedforward active noise and vibration control system in a SAAB 340 mock-up. The resulting sound pressure level were recorded and is presented as the narrowband attenuation versus time. The spatial distribution of the sound pressure level is also presented. The results show that the twin-reference controller exhibits good performance with respect to attenuation and robustness for both stationary and non-stationary conditions.

  • 137. Johansson, Sven
    et al.
    Persson, Per
    Claesson, Ingvar
    Lagö, Thomas L
    Evaluation of the Performance of an Active Noise Control System in an Aircraft Mock-up2000Conference paper (Refereed)
    Abstract [en]

    This paper treats the convergence behavior and robustness of a narrowband twin-reference feedforward active control system using different kinds of actuators and control sensors, and various actuator/sensor configurations. Results from a practical experiment carried out in a fuselage section of a SAAB 340 aircraft, using beating and non-beating sound fields, are presented. The results show that the proposed multiple-reference controller based on the actuator-individual normalizedjfiltered-x LMS algorithm exhibits high performance with respect to robustness and noise suppression, for the different configurations as well as for beating and non-beating sound fields. A slight degradation of the performance was noticed for beating sound fields.

  • 138. Johansson, Sven
    et al.
    Sjösten, Per
    Nordebo, Sven
    Claesson, Ingvar
    Comparison of Multiple- and Single-Reference MIMO Active Noise Control Approaches Using Data Measured in a Dornier 328 Aircraft2000In: International Journal of Acoustics and Vibration, ISSN 1027-5851, Vol. 5, no 4, p. 77-88Article in journal (Refereed)
    Abstract [en]

    In many applications of noise control, the greatest annoyance is caused by periodic low frequency noise. Successful reduction of such noise can often be achieved by using an active noise control system with narrowband feedforward control. If several noise sources contribute to the sound field, a multiple-reference control system is usually required. This type of system allows the reference signals from each noise source to be processed individually within the controller, thereby enabling individual control of the sound field from each noise source. The present paper addresses the problem of controlling noise from two sources that are more or less synchronized. A typical application is the control of propeller-generated noise within a twin propeller aircraft. To find out whether a multiple-reference controller is necessary, or if a single-reference controller is sufficient, the performance of a single- versus twin-reference control algorithm is evaluated in a comparative study. The study is performed as a computer simulation (off-line evaluation) using real-life data recorded in a Dornier 328 under different flight conditions. The results demonstrate that the twin-reference controller performs better than the single-reference whenever there is a slight deviation in the rotational speed of the two propellers. The paper also treats the generation of reference signals. The approach presented is based on a fixed sampling rate and uses a sliding FFT filtering technique.

  • 139. Johansson, Sven
    et al.
    Sjösten, Per
    Persson, Per
    Claesson, Ingvar
    Experimental Performance Evaluation of a Multi-Reference Algorithm for Active Control of Propeller-Induced Cabin Noise2000Report (Other academic)
    Abstract [en]

    A noisy environment dominated by low frequency noise can often be improved through the use of active noise control. This situation arises naturally in propeller aircraft where the propellers induce periodic low frequency noise inside the cabin. The cabin noise is typically rather high, and the passenger flight comfort could be improved considerably if this level were significantly reduced. This paper discusses the operation and robustness of a narrowband feedforward active noise control system in a practical installation. The ANC system used 8 control sources and 11 control microphones, and the control algorithm was the multi-reference actuator-individual normalized filtered-x least mean squares algorithm. The experiment was performed in a full-scale fuselage section of a SAAB 340 aircraft. To produce the propeller noise, loudspeakers mounted in a ring around the fuselage were used. Results are presented from a series of experiments on the active control of propeller-induced cabin noise. Among the ``flight" conditions evaluated were: conditions where the ``propellers" were completely synchronized, and conditions with constant as well as time-varying frequency beat between ``left and right propellers."

  • 140. Johansson, Sven
    et al.
    Winberg, Mathias
    Claesson, Ingvar
    A New Passive/Active Hybrid Headset for a Helicopter Application1999Conference paper (Refereed)
    Abstract [en]

    In helicopters, the low frequency noise generated by the rotors and engines often masks and jeopardizes safe communication. In addition, pilots are likely to suffer from damage to their hearing due to the high sound levels in the headset produced in compensating for the noise caused by increased loudspeaker levels. A feasible approach is to reduce the low frequency noise by using active techniques combined with a method for reducing the noise in the intercom microphone signal, with lower loudspeaker levels as a result. In order to achieve an efficient attenuation of the primary noise inside the headset, a combination of a digital feedforward controller and an analog feedback controller is employed. Spectral Subtraction is used to suppress the background noise in speech signals. This paper evaluates a combination of the techniques and their application to real data.

  • 141. Johansson, Sven
    et al.
    Winberg, Mathias
    Claesson, Ingvar
    Svensson, Börje
    Lönn, Jan
    Active Control of Interior Noise in a Fork-Lift Truck2003Conference paper (Refereed)
    Abstract [en]

    Modern fork-lift trucks incorporate a wide range of sophisticated passive techniques to reduce the noise inside the cabin. By using a combination of passive and active noise control technologies it may be possible to further reduce the noise level, thereby improving the comfort for the truck driver. The purpose of the work presented in this paper is to examine whether it is possible to reduce the low-frequency cabin noise by using active noise control technology. The noise situation inside the truck cabin is discussed as well as the active noise control strategy for a practical fork-lift truck installation. The paper presents sound field plots of the cabin noise and preliminary active noise control results from computer experiments based on recorded cabin noise.

  • 142. Johansson, Sven
    et al.
    Winberg, Mathias
    Sjösten, Per
    Claesson, Ingvar
    ACTIVE HEADSET FOR ENHANCED SPEECH INTELLIGIBILITY IN INTERCOM SYSTEMS2001Conference paper (Refereed)
    Abstract [en]

    Low frequency noise has a masking effect on speech, which significantly reduces the speech intelligibility. Usually, in order to overcome the masking effect the sound level of the communication signal is increased. Exposure to the communication system then causes hearing damage. A feasible approach is to reduce the low frequency noise by using active techniques combined with a method for reducing the noise in the intercom microphone signal. In order to achieve an efficient low frequency noise attenuation inside the headset an active hybrid headset is proposed, and in order to suppress the background noise in speech signals spectral subtraction is used. Improved low frequency noise attenuation enables lower communication levels and reduces the risk for hearing damage.

  • 143. Johnson, Henric
    Security in Lightweight Ad Hoc Networks2002Conference paper (Refereed)
    Abstract [en]

    The focus of my research is on security in wireless lightweight ad hoc networks. So far, much research has been concentrated primarily on making ad hoc networks feasible and useful and not on issues of security. However, ad hoc networks are highly vulnerable to attacks. In my research, I will present the requirements of making an ad hoc network secure and scalable, and also provide solutions as to how to authenticate the identity of the nodes by only adding one authentication bit to each packet. This will dramatically reduce the bandwidth and power consumption in the ad hoc network.

  • 144. Johnson, Henric
    Security Issues in Wireless Networks2001Conference paper (Refereed)
    Abstract [en]

    In this paper I describe my research project in the area of wireless network security. Since in the area of wireless communication, information is propagated through the air instead of through wires, a number of new security risks occur when using the new wireless technologies. Research dealing with these risks and vulnerabilities is, however, rarely seen. Reports about hacker attacks against wireless networks is almost non-existent, but it is only a matter of time before serious attacks will target these systems. Therefore, security aspects of mobile networks 3G and 4G systems and wireless standards like Wireless Application Protocol (WAP), HiperLAN, Bluetooth and wireless LAN standard IEEE 802.11b are central standards of investigation in my research. The main questions, which my research project is concerned with, are whether it is possible to achieve end-to-end security in a wireless network, and, if so, to what costs.

  • 145. Johnson, Henric
    et al.
    Nilsson, Arne A.
    Fiedler, Markus
    Wireless Network Security2001Conference paper (Refereed)
    Abstract [en]

    In this paper we describe and give an overview of the various security aspects and problems that have emerged in the area of wireless communications during the last few years. Wireless Application Protocol (WAP), HiperLAN, Bluetooth and wireless LAN standard IEEE 802.11b are central standards of investigation in this paper. In conclusion, we believe that future wireless network systems will probably consist of many different wireless systems linked together, therefore there will be a need for how to harmonize the differences in their security solutions.

  • 146. Johnson, Henric
    et al.
    Nilsson, Arne A.
    Fu, Judy
    Wu, Felix
    Chen, Albert
    Huang, He
    SOLA: A One-bit Identity Authentication Protocol for Access Control in IEEE 802.112002Conference paper (Refereed)
    Abstract [en]

    Given the wide deployment of IPSec/VPN (Virtual Private Networks) technology, there might be a redundancy in security protection in some configurations. Various commercial companies have replaced 802.11 security with IPSec/VPN to protect the wireless LAN (Local Area Network). How to do it in an efficient and lightweight way is a challenging research problem. This paper introduces a new lightweight identity authentication protocol, SOLA (Statistical One-bit Lightweight Authentication), for access control well suited for IEEE 802.11 networks with IP connections. This protocol prevents unauthorized access on a per packet basis. Since SOLA only adds one identity bit to each packet it will have a low impact on the network bandwidth and power consumption. The performance and efficiency of the SOLA protocol together with IEEE 802.11 is analyzed and evaluated via simulation.

  • 147.
    Karlsson, Andreas
    Blekinge Institute of Technology, Department of Telecommunications and Signal Processing.
    WOSP: Wireless Open Source Platform2001Independent thesis Advanced level (degree of Master (One Year))Student thesis
    Abstract [en]

    The hot spot in the market of embedded systems today are opening up the systems so the world around can communicate with it. The idea of this Master Thesis is to show a way to wirelessly open up an embedded system to the world. The goal of the project is to build a prototype for machine-to-machine applications. This project clarifies the practical issues that rise when the idea is implemented. In this project an embedded WAP-server has been developed. All software components used are open source even the development environment. This means that there will be no license costs at all. The server runs on top of Axis? Bluetooth communication stack. The operating system used is eCos, which is open source and shipped by Red Hat. The system runs on an evaluation board equipped with an ARM7 processor, 256 KB RAM and 256 KB ROM. The report can be found at http://www.combitechsystems.com/node2866.asp

  • 148.
    Karlsson, Andreas
    et al.
    Blekinge Institute of Technology, Department of Telecommunications and Signal Processing.
    Thelandersson, Fredrik
    Blekinge Institute of Technology, Department of Telecommunications and Signal Processing.
    Application of Formal Verification Techniques1999Independent thesis Basic level (degree of Bachelor)Student thesis
    Abstract [en]

    Today there are electrical circuits everywhere, e.g. telephones, TVs, cars and computers. The big problem with the rapidly-growing complexity in today's machines is, however, that since they are so complex it is impossible to check all combinations of events before the products are sent to the market. This lack of testing can lead to defective products. There are two well-known examples: Intel’s Pentium-processor, which failed on complex mathematical problems, and the European spaceprogram’s Ariane-rocket that exploded after take-off due to an error in an electrical circuit. For a long time simulation was the only way to verify a design’s behaviour. But simulation cannot check all possible cases within reasonable time for larger circuits. Therefore, the existence of software that performs equivalence checking between two circuits or between a circuit and its specification is justified. This software typically uses some kind of tree structure, e.g. binary decision diagram. Since this market is still rather young the best solution has not yet been found. There are two goals of this diploma work. The first is to find a new structure that uses less time than binary decision diagrams and is able to verify multipliers, which is impossible with binary decision diagrams. The second goal is to provide the results for the user in a manageable way without any unnecessary expressions, and make it possible for the user to influence the expression by setting variables to zero or one.

  • 149.
    Karlsson, Christian
    et al.
    Blekinge Institute of Technology, Department of Telecommunications and Signal Processing.
    Sellberg, Erik
    Blekinge Institute of Technology, Department of Telecommunications and Signal Processing.
    LCD Optimized Image Enhancement2002Independent thesis Advanced level (degree of Master (One Year))Student thesis
    Abstract [en]

    With the increased bandwidth in 3G terminals, the possibilities to make new exciting multimedia applications are enormous. Mobile devices generally uses small LCD:s with only a few gray-scales or colors. The goal for this master thesis will be to find ways to enhance and correct the images before they are shown on the LCD. Could this be done with algorithms who enhance the images automatically depending on which information the images have? It will also be necessary to consider the LCDs characteristic before enhancement of the images. In this master thesis work it was discovered that sharpened and enhanced images with histogram modifications clearly improves the quality when displayed on the LCD. But it is also important to enhance the colors in the image, not only with color correction but also with dithering and quantization technique. Combining techniques like sharpening, color saturation and histogram modification gave clearly an improvement to the quality of the image and the result from the survey also pointed in this direction, the survey is published in appendix A. Some of the algorithms in histogram modification were used in an automatic enhancement and one of the algorithms worked with satisfaction. This histogram modification algorithm has been the basis for a patent application and we suggest a new outstanding performance histogram-modification method. The method cannot be described in this master thesis because the patent process is not finished.

  • 150.
    Krejstrup, Richard
    et al.
    Blekinge Institute of Technology, Department of Telecommunications and Signal Processing.
    Fredriksson, Andreas
    Blekinge Institute of Technology, Department of Telecommunications and Signal Processing.
    Databashanterare i Visual C++ för flygradiostationer1998Independent thesis Basic level (degree of Bachelor)Student thesis
    Abstract [sv]

    Examensarbetet som är utfört för SAS Flight Academy innebär att modernisera hanteringen av flygradiostationer för en flygsimulator från 1968. Detta görs med hjälp en PC som kopplas till det nuvarande datorsystemet med ett parallellkort. I PC:n finns en Microsoft Access databas där all data lagras om världens alla flygradiostationer. Informationen om flygradiostationerna finns lagrade på en CD-ROM som uppdateras ett antal gånger per år. Klienten till databasen är programmerad i Visual C++ och använder Microsofts programbibliotek MFC för hantering av databasen. Klienten har två uppgifter dels sköta hanteringen och dels uppdateringar av databasen. Sedan skall även filer kunna genereras med information till flygsimulatorn.

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