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  • 401. Vu, Viet Thuy
    et al.
    Sjögren, Thomas
    Pettersson, Mats
    Fast detection of moving targets by focusing in Ultra-wideband SAR2009Conference paper (Refereed)
    Abstract [en]

    Moving target detection in Ultra-Wideband (UWB) SAR is associated with long integration time and has to handle azimuth focusing for reliable detection. This paper presents the theory and simulation results of the Fast Detection of Moving Targets by Focusing method (FDMTF) which is understood as the Detection of Moving Targets by Focusing method (DMTF) incorporating fast time-domain algorithms in the process. Two fast time-domain algorithms Fast Backprojection (PBP) and Fast Factorized Backprojection (FFBP) are considered. The results show that FDMTF performs very efficiently and still retains the ability of detection.

  • 402. Vu, Viet Thuy
    et al.
    Sjögren, Thomas
    Pettersson, Mats
    Moving target detection by focusing for frequency-domain algorithms in UWB low frequency SAR2008Conference paper (Refereed)
    Abstract [en]

    Moving target detection at low radar frequencies is associated with long integration time and has to handle azimuth focusing for reliable detection. The detection by focusing in which time-domain is the basis for the focusing approach has been proposed and successfully experimented in reality. The main objective of this paper is to apply and evaluate the detection method for frequency-domain algorithms. Range Migration Algorithm (RM) is chosen as a candidate for this study due to the accuracy of the algorithm with very wide integration angles. The simulated SAR data, which is used in this study, is based on the parameters of an airborne UWB low frequency system such as CARABAS-II.

  • 403.
    Vu, Viet Thuy
    et al.
    Blekinge Institute of Technology, School of Engineering, Department of Signal Processing.
    Sjögren, Thomas
    Blekinge Institute of Technology, School of Engineering, Department of Signal Processing.
    Pettersson, Mats
    Blekinge Institute of Technology, School of Engineering, Department of Signal Processing.
    On Apodization Techniques for Ultra-wideband SAR Imaging2009Conference paper (Refereed)
    Abstract [en]

    Ultra-wideband (UWB) SAR imaging suffers from a number of inherent problems in which the apodization has not been investigated appropriately. This paper presents a discussion on apodization techniques and possibilities to apply these techniques in UWB SAR imaging.

  • 404. Vu, Viet Thuy
    et al.
    Sjögren, Thomas
    Pettersson, Mats
    Gustavsson, Anders
    Definition on SAR image quality measurements for UWB SAR2008Conference paper (Refereed)
    Abstract [en]

    Analyses in this study show that measurements under currently used definitions on SAR image quality measurement may be unsuitable for UWB SAR. The main objective of this paper is therefore to propose a definition based on the shape of a single point target in a SAR image which is more suitable for UWB SAR. We use both real and simulated data based on the airborne UWB low frequency SAR CARABAS-II in experiments. The time-domain algorithm Global Backprojection (GBP) is selected for the image formation in this study.

  • 405. Vu, Viet Thuy
    et al.
    Sjögren, Thomas
    Pettersson, Mats
    Zepernick, Hans-Jürgen
    Gustavsson, Anders
    Experimental Results on Moving Targets Focusing in UWB Low Frequency SAR2007Conference paper (Refereed)
    Abstract [en]

    The main objective of this paper is to present and evaluate a method to detect moving targets in Ultra Wideband (UWB) low frequency Synthetic Aperture Radar (SAR). Moving target detection at low radar frequencies is associated with long integration time and has to handle azimuth focusing for reliable detection. The examined method tests different hypotheses on relative speeds in the area of interest. The optimum step size between the hypotheses is found from a point target approximation. Experimental results show that the ability to detect moving targets increases significantly. In this study, the improvement of the Signal-to-Clutter Noise Ratio (SCNR) is up to approximately 20dB using a single antenna. The focusing method allows initial estimates in speed of moving targets. The SAR data, which is used in our experiments, was collected by the airborne UWB low frequency CARABAS-II system.

  • 406.
    Waheed, Abdul-Mohammed
    Blekinge Institute of Technology, School of Engineering, Department of Signal Processing.
    Optimization on H.264 De-blocking Filter2008Independent thesis Advanced level (degree of Master (Two Years))Student thesis
    Abstract [en]

    H.264/AVC is the state-of-the-art video coding standard which promises to achieve same video quality at about half the bit rate of previous standards (H.263, MPEG-2). This tremendous achievement in compression and perceptual quality is due to the inclusion of various innovative tools. These tools are highly complex and data intensive as a result poses very heavy computational burden on the processors. De-blocking filter is one among them, it is the most time consuming part of the H.264/AVC reference decoder. In this thesis, a performance analysis of the de-blocking filter is made on Intel Pentium 4 processor and accordingly various optimization techniques have been studied and implemented. For some techniques statistical analysis of video data is done and according to the results obtained optimization is performed and for other techniques SIMD instructions has been used to achieve the optimization. Comparison of optimized techniques using SIMD with the reference software has shown significant speedup thus contributing to the real time implementation of the de-blocking filter on general purpose platform.

  • 407. Wang, Feng
    et al.
    Zepernick, Hans-Jürgen
    Autocorrelation Analysis for Reduced-Reference Mobile Video Quality Assessment2009Conference paper (Refereed)
    Abstract [en]

    Due to the growing use of mobile video services, monitoring of perceived video quality in live systems becomes of high interest. For this purpose, it is required to capture video quality consistent with the principles behind the operation of the human visual system and to accommodate some suitable quality reference to the transmission of the mobile video service. This can be achieved by extracting structural information in terms of a finite number of spatial features from a video sequence and utilize these features as foundation of a reduced-reference design of a perceptual video quality metric. In this paper, we examine the dynamics of such spatial features with respect to their progression over time by applying an autocorrelation analysis that reveals the coherence time over which the individual features can be considered as constant. As prerequisite of the analysis, we have conducted subjective tests to categorize a set of standard videos into the classes of slow, median, and fast motion. The coherence times deduced from the autocorrelation analysis show that the dynamic behavior of certain spatial features is independent from the video content while statistics of other spatial features are dependent on the video categories. These findings allow us to reduce not only the computational load for capturing dynamics of spatial features in video sequences at the mobile device but also the amount of information to be carried as reduced-reference to the receiver.

  • 408. Wang, Feng
    et al.
    Zepernick, Hans-Jürgen
    Autocorrelation Analysis of Spatial Features for Mobile Video Services2008Conference paper (Refereed)
    Abstract [en]

    The growing deployment of mobile video applications is calling for new methods to measure quality as perceived by humans. The suitable quality metrics may explore spatial and temporal video features that quantify the presence of related artifacts in an examined mobile video service. Considering a video as a sequence of images, computation of spatial features for each involved image would pose significant strain on system resources such as battery power and potentially induce large computational load in the mobile terminal. In this paper, we therefore examine the progression of spatial features in mobile videos over time using an autocorrelation approach. This enables us to reveal the duration over which spatial feature values of a mobile video may be considered as constant. In analogy to the characterization of mobile radio channels, we refer to this duration as the coherence time of an examined spatial feature for a given video. The provided numerical results illustrate that large reductions in the frequency of computing spatial features in mobile videos may be obtained. This in turn reduces the consumption of resources in the mobile terminal.

  • 409. Westerlund, Nils
    Counteracting Acoustic Disturbances in Human Speech Communication2006Doctoral thesis, comprehensive summary (Other academic)
    Abstract [en]

    A signal can be said to be any information bearing unit or action carrying a message from a sender to a receiver. This definition covers a vast number of human and non-human actions, ranging from flirtation to satellite communication. This thesis deals with increasing the quality of one of the most ubiquitous human-to-human signals: Speech. Surrounding noise is a severe obstacle to relaxed speech communication. Cars, industry and many everyday machines emit high noise levels that render personal communication difficult, degrade our mental and physical ability and may cause nausea, vertigo, fatigue and temporary or permanent hearing loss. Indeed, exposure to noise of a high sound pressure level is a major contributor to often irreversible sensorineural hearing impairment, i.e. Noise Induced Hearing Loss (NIHL). This doctoral thesis deals with three different approaches for facilitating human speech communication. First, methods for adaptively controlling acoustic feedback — commonly denoted "howling" — in hearing aids are developed and subsequently evaluated. Howling is a very common problem in hearing aids and a stable and robust feedback eliminator would serve many hearing aid users. The proposed method detects tonal components, i.e. howling, in the signal path of the hearing aid. If such a component is detected, the feedback control system invokes different countermeasures to adaptively cancel the howling. Second, a method for speech quality and intelligibility enhancement is described. Instead of focusing on noise suppression, the method acts as a speech booster: Frequency bands containing a usable amount of speech energy are boosted. All other frequency bands remain unchanged. This results in an increased Signal-to-Noise Ratio (SNR) and the elimination of background artefacts which may be present in some other noise reduction algorithms. Furthermore, speech distortion is kept to a negligible level. Finally, a compact receiver unit, based on bone conduction, is designed and evaluated. The unit is placed inside the external auditory canal of a user and picks up bone conducted speech from the user's speech organ. This solution, in combination with a pair of active hearing protectors, yields several advantages and allows the user to reliably communicate in environments where extremely high sound pressure levels are present.

  • 410. Westerlund, Nils
    et al.
    Dahl, Mattias
    Claesson, Ingvar
    In-Ear Microphone Techniques for Severe Noise Situations2005Report (Other academic)
    Abstract [en]

    Today, noise reduction methods are nearly ubiquitous although often not noticed by laymen. Cellular phones, some hands-free headsets and ear-phones offered by some airlines during long haul flights all utilize noise reduction algorithms. However, there are some situations in everyday life where ordinary noise reduction algorithms do not suffice; situations where the surrounding noise sound pressure level is too high to be efficiently attenuated by ordinary algorithms. Personal communication is then partly or totally prohibited by this noise. Examples of such situations may be motorcycle riding or attending a concert. In addition, many occupations, foremost industrial work, expose people to very high sound pressure levels. Still, these people need to be able to communicate safely. This report describes a technique where an ear-mic, i.e. a small microphone for communication purposes, is placed inside the auditory canal where it picks up bone conducted speech from the user's speech organ. The report describes three different approaches and usage areas: First, a basic approach where combination effects of an ear-mic and a pair of Active Noise Control (ANC) equipped ear-muffs are investigated. Second, this approach is used to improve a speech recognition system. The third approach is to connect a well-known noise reduction algorithm - the spectral subtraction - in cascade with the previously described ear-mic/ANC-solution in order to achieve extreme noise suppression.

  • 411. Westerlund, Nils
    et al.
    Dahl, Mattias
    Claesson, Ingvar
    Speech Enhancement by Non-Stationary Tonal Disturbance Cancellation using Subband Zero Crossing Measures2004Conference paper (Refereed)
    Abstract [en]

    A time domain based method for rejection of tonal disturbances in speech signals is presented. Tonal disturbances in personal communication arise in a variety of situations such as environmental sounds from rotating machinery, acoustic feedback in PA-systems or hearing aids and internal circuitry of some personal communication devices. The method is based on the zero crossings of subband signals. After splitting the disturbed signal into subbands, the distances between zero crossings in the subband signals are measured. A low distance spread indicates that a tonal component is dominating the subband signal. This distance spread is then used to steer a gain function that adaptively and continuously attenuates subbands in which tonal components are dominant. The method has proven to be effective on stationary as well as non-stationary disturbances with reasonable amount of speech signal distortion.

  • 412. Westerlund, Nils
    et al.
    Dahl, Mattias
    Claesson, Ingvar
    Speech Enhancement for Personal Communication Using an Adaptive Gain Equalizer2005In: Signal Processing, ISSN 0165-1684 , Vol. 85, no 6, p. 1089-1101Article in journal (Refereed)
    Abstract [en]

    An increasing part of our daily personal communication takes place in various noisy environments. Ever since the broad introduction of cellular phones, we tend to communicate using these phones in cars, streets and other noisy places. Noise has a negative effect on both speech intelligibility and quality; a poor Signal-to-Noise Ratio (SNR) may indeed result in a complete lack of speech intelligibility. This paper presents a speech enhancement method for personal communication, where the input signal is divided into a number of subbands that are individually and adaptively weighted in time domain according to a short term SNR estimate in each subband at every time instant. Hence the name Adaptive Gain Equalizer. The signal disassembly into narrow subbands is performed using computationally effective Infinite Impulse Response (IIR) filters with low group delay. The method is focused on speech enhancement, acting as a \emph{speech booster}, and remains idle when the SNR in a particular subband is low. Hence, background artifacts are eliminated. In addition, the method has proven to be advantageous since it offers low complexity and low delay. It is stand-alone and works regardless of speech coding schemes and other surrounding adaptive systems.

  • 413. Westerlund, Nils
    et al.
    Dahl, Mattias
    Claesson, Ingvar
    Speech Enhancement using an Adaptive Gain Equalizer with Frequency Dependent Parameter Settings2004Conference paper (Refereed)
    Abstract [en]

    This paper presents an enhanced noise reduction method for speech communication where the input signal is divided into a number of subbands that are individually weighted in time domain according to the short time Signal-to-Noise Ratio estimate (SNR) in each subband at every time instant. Instead of focusing on suppression the noise, the method is focusing on speech enhancement. The subband based method is extended with frequency dependent parameter settings, equipping the user with further tweaking possibilities. Hence, making the algorithm even more versatile and applicable in different noise situations. The method has proven to be advantageous since it offers low complexity, low delay and low distortion. Also, there is no need for a Voice Activity Detector (VAD). The method is stand-alone and works regardless of speech coding schemes and other surrounding adaptive systems.

  • 414. Westerlund, Nils
    et al.
    Dahl, Mattias
    Grbic, Nedelko
    Detection And Attenuation of Feedback Induced Howling in Hearing Aids Using Subband Zero-Crossing Measures2005Conference paper (Refereed)
    Abstract [en]

    A modern hearing aid should be aesthetically appealing as well as offer sufficient and adequate signal amplification. Due to the small physical size of these devices, acoustical feedback (howling) is a major problem. Apart from the annoyance and potential hearing damaging effects that howling implies, it also reduces the supplied maximum Real Ear Aided Gain (REAG). This paper proposes a novel method for subband feedback detection and cancellation, based on the zero-crossing rate measure. After splitting the hearing aid input signal into subbands, the distances between subband zero-crossings are measured. A low distance variance in a particular subband indicates that howling has arisen. The variance measure is then used to adaptively and continuously steer subband gain functions which attenuate tonal infested subbands. The method has proven to be robust and simulation indicates that it offers additional REAG of about 15 dB.

  • 415. Westerlund, Nils
    et al.
    Grbic, Nedelko
    Dahl, Mattias
    Subband Adaptive Feedback Control in Hearing Aids with Increased User Comfort2006Report (Other academic)
    Abstract [en]

    This report describes important physiological and anatomical aspects of human hearing, including instruments for hearing improvements, i.e. hearing aids. One common problem with hearing aids is acoustic feedback (howling). A new subband Adaptive Feedback Control (AFC) system for hearing aids is proposed. This system detects howling by calculating distances between zero crossings in the subband input signal. A stable subband zero crossing distance measure indicates that howling is present in a particular subband. This triggers an adaptation to estimate and attenuate the feedback channel. The adaptation is driven by a probe noise sequence constrained in both time and frequency. This constraint implies increased signal quality and that user discomfort due to emitted probe noise is reduced. Also, an effective and reliable adaptation is achieved. The method has proven to operate well in computer simulations, with speech as well as music as signal input. Initial simulations indicate that an increased hearing aid gain of at least 15 dB is possible.

  • 416. Wiklunda, Kenneth
    et al.
    Lindström, Fredric
    Claesson, Ingvar
    EVALUATION OF A HANDS-FREE UNIT DURING DOUBLE-TALK2005Conference paper (Refereed)
    Abstract [en]

    The double-talk performance of a handsfree speech communication system is crucial to the overall quality. This paper presents a method to evaluate double-talk performance of conference phones and speakerphones. The method measures loudness, clipping and the amount of echo during double-talk.

  • 417. Winberg, Mathias
    et al.
    Johansson, Sven
    Claesson, Ingvar
    INERTIAL MASS ACTUATORS, UNDERSTANDING AND TUNING2004Conference paper (Refereed)
    Abstract [en]

    The actuators, the error sensors and the control system are central components in active noise and vibration control systems. The actuators produce the secondary forces acting on the structure while the error sensors measure the quantity to be minimized. Inertial mass actuators are used frequently in a variety of applications, e.g. boat engine mounts and airplane fuselages. To tune the inertial mass actuator to fit a certain application or just to understand the manufactures specification it is important to have an understanding of the construction of the actuator and the equations describing it. This paper presents a mathematical model of the mechanical and electrical system for the inertial mass actuator. A mobility analogy is introduced in order to determine how the inertial mass and the spring constant of the suspension effect the resonance frequency of the actuator as well as the output force. Does the mobility of the structure, the actuator is mounted on, effect the produced output force in relationship to the rated force of the actuator? Practical measurement results are presented in order to determine the resonance frequency and output force of an inertial mass actuator manufactured by Metravib in France.

  • 418. Winberg, Mathias
    et al.
    Johansson, Sven
    Håkansson, Lars
    Claesson, Ingvar
    Lagö, Thomas L
    Active Vibration Isolation in Ships: A Pre-Analysis of Sound and Vibration Problems2005In: International Journal of Acoustics and Vibration, ISSN 1027-5851, Vol. 10, no 4, p. 175-196Article in journal (Refereed)
    Abstract [en]

    Engine-induced sound and vibration levels in boats for professional and leisure use are in many cases unacceptably high in terms of comfort and environmental disturbance. Classical methods for passive treatment are normally less efficient due to the low frequency content and often lead to a substantial increase in weight. The requirements for lower weight which would increase the maximum speed of the boat as well as improve fuel economy have to be considered. More efficient vibration damping methods must therefore be found. With, for example, active engine mounts, it is possible to achieve a decrease in the vibrations even for cases when the hull is not very stiff. This is especially important in marine applications, since the engines are usually mounted on flexible and light structures. The project Active Vibration Isolation In Ships (AVIIS) aims at investigating the effects of using a type of Active Noise and Vibration Control system (ANVC) in this type of marine application. This article presents the analysis of the sound and vibration problems in one particular leisure boat from an ANVC point of view. A very thorough investigation is carried out, the main noise and vibration sources are established as well as the transmission paths of the noise into the boat. Answers are found from this investigation as to where the actuators should be positioned, which kind of ANVC approach that would be preferable to use and the expected interior noise reduction. This is the kind of pre-analysis that is needed for a complex structure such as found in a marine vessel for the successful implementation of ANVC. An optimized engine mount was also designed and evaluated resulting in a 10 dBA saloon sound level reduction compared to the standard engine mounts. Additionally, with the optimized engine mounts, the vibration levels at the hull were also reduced by up to 15 dB at the main harmonic components. This paper also presents a feasible way to estimate the performance of a potential active control system based on feedforward narrowband control of engine and propeller harmonics. Secondary sources inertial mass actuators are proposed and for error sensors, accelerometers or microphones or a combination of the two are used. In the low frequency range, below 300 Hz, a further reduction of engine orders and propeller BPFs in the order of 5-10 dB are predicted.

  • 419. Winberg, Mathias
    et al.
    Johansson, Sven
    Lagö, Thomas L
    SPEAKING PANELS: NEW ACTUATORS FOR ACTIVE NOISE CONTROL2005Conference paper (Refereed)
    Abstract [en]

    Abstract Different actuators have been developed for active noise control. A broadband linear actuator, typically a loudspeaker, is often used. However, this is not an absolute necessity, the important issue is that the performance is “good” in the frequency band where the actuator should work, and that the actuator can produce the volume displacement needed. A speaking panel is a lightweight actuator, intended to be applied in propeller aircraft where the weight consideration is of great importance. The dimension of the used speaking panel is 200x600 mm. The panel is based on piezo ceramic materials embedded in a thin carbon fiber plate, resulting in a lightweight and more flexible actuator for trim panel mounting in an aircraft, as compared to a normal loudspeaker. A disadvantage, though, is that the actuator shows a nonlinear behavior, that cannot be overlooked when designing the controller. The cabin noise inside a propeller driven aircraft consists essentially of tonal components originating from the propellers as well as broadband boundary layer noise. However, it is only the tonal components that will be targeted by the controller therefore a narrowband controller has been used in this application. With this in mind the nonlinear characteristics are evaluated in terms of frequency response functions and harmonic distortion. An evaluation of the speaking panels together with a MIMO complex filtered-X LMS algorithm, is presented. The setup consists of four speaking panels, mounted in a test mock-up, four control microphones and two monitor microphones. The controller is implemented on a Texas Instruments C31 signal processor.

  • 420. Winberg, Mathias
    et al.
    Åkesson, Henrik
    Lagö, Thomas L
    Claesson, Ingvar
    Acoustical Measurements Using a Virtual Microphone Technique2008Conference paper (Refereed)
    Abstract [en]

    Virtual sensing is the art of measuring a quantity at a certain spatial position without having a physical sensor placed at that exact same position. In practical applications, this technique is sometimes very useful, when it is not feasible to put the sensor at the position where the physical quantity should be measured. For example, a virtual microphone could be considered in the following scenario: The sound level, preliminary school environment, should be studied at the different students head positions. In order to get statistical relevant data, the measurement has to be carried out over a period of time. However, it is not a feasible approach to use a large number of microphones hanging from the ceiling at the students head level, over a longer period of time for obvious reasons. One thoughtful solution in such a situation is to put microphones at the walls and close to the ceiling and using the virtual technique to calculate the noise level at the students head positions based on the measure data. An advantage in such large setup is that it often requires less physical sensors than the number of virtual measurement positions and at the same time features a better validation and sanity check of the data. The most popular application area, though, are active noise control (ANC) or active structural acoustic control (ASAC), where the aim is to move the zone of quietness away from the physical error microphones to the desired location of maximum attenuation. This paper presents a virtual microphone concept for a sound measurement in a closed cavity.

  • 421. Wirandi, Jenny
    et al.
    Chen, Jiandan
    Kulesza, Wlodek
    An Adaptive Model of the Fuzzy Variable: Quality Index2007Conference paper (Refereed)
  • 422. Wirandi, Jenny
    et al.
    Chen, Jiandan
    Kulesza, Wlodek
    An Adaptive Quality Assessment System-Aspect of Human Factor and Measurement Uncertainty2009In: IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT, IEEE , 2009, Vol. 58, no 1, p. 68-75Conference paper (Refereed)
    Abstract [en]

    In this paper, we discuss a model of quality that makes use of the fuzzily defined variable approach to better understand the concept and, thus, enables the further development of this variable. We propose a general method that may estimate a quality index (QI) that handles both qualitative and quantitative issues. The system further uses a neural network since the system learns how to integrate human factors into a quantitative QI. In our case study, we have examined the measurement of image quality and proposed a theoretical model of pulp quality.

  • 423. Wirandi, Jenny
    et al.
    Kulesza, Wlodek
    Lauber, Alexander
    Human Factor Validation in an Industrial Measurement System2008In: Measurement, ISSN 0263-2241, E-ISSN 1873-412X, Vol. 41, no 6, p. 705-718Article in journal (Refereed)
    Abstract [en]

    The object of this study is to determine how people interpret measurement data; which factors influence their interpretation and which do not. This study forms part of an investigation series undertaken at the paper pulp company Södra Cell in Sweden (N = 1200 employees), the investigated parameter being "paper pulp quality". The findings presented in the study are the outcomes of a questionnaire that was repeated four times (n1 = 54, n2 = 53, n3 = 43, n4 = 38), an interview (ni = 32) and regular group discussions that included 10 people (nd = 10) and that took place once a month over a three-year period. In order to quantify the quality of the product - paper pulp - different measurements must be combined. This study reveals that different employees prefer different parameters for the quantification of paper pulp quality. This study furthermore shows that there is a correlation between the employees' choice of parameters and their belonging to a particular pulp mill within the company. We also found that external factors, e.g. the opinion of authorities, affected which parameters were favoured when product quality was determined. Furthermore, the data analysis indicates that there is a correlation between the job-position of employees and the way they interpret measurement data related to product quality. Controllers and operators make similar judgments, with the exception of chemists whose opinions appear to deviate. However, the greatest variation found in the study is related to the individual person - independently of education or physical or psychological condition. The study finally proposes a number of preventive measures to improve the uniformity and reliability of measurements conducted at a process company, the most important of which is improved education of all employees who are in a position to influence product quality. © 2007 Elsevier Ltd. All rights reserved.

  • 424. Wirandi, Jenny
    et al.
    Kulesza, Wlodek
    Lauber, Alexander
    The problem of applying modern uncertainty concepts to the measurement of instrument specific parameters2006In: IEEE Transactions on Instrumentation and Measurement, ISSN 0018-9456, E-ISSN 1557-9662, Vol. 55, no 3, p. 700-705Article in journal (Refereed)
    Abstract [en]

    This paper presents a number of problems that occur when applying the Guide to the Expression of Uncertainty in Measurement (GUM) to modern instruments. These instruments are often automatic, which makes it complicated to evaluate the uncertainty components in each measurement step because it is difficult to control and analyze them. Many of these instruments try to quantify instrument-specific parameters, which are difficult to compare with others that have the same dimension but are measured using other techniques. Often, these parameters lack traceable calibration, which may result in a large uncertainty component. This paper also considers the human aspect of the measurement process.

  • 425. Wu, Felix
    et al.
    Johnson, Henric
    Nilsson, Arne A.
    SOLA: Lightweight Security for Access Control in IEEE 802.112004In: IT Professional Magazine, ISSN 1520-9202, E-ISSN 1941-045X, Vol. 6, no 3, p. 10-16Article in journal (Refereed)
    Abstract [en]

    The IEEE 802.11 wireless standard provides little support for secure access control. As a result, access control in IEEE 802.11 on a per packet basis requires a new and robust identity authentication protocol. The SOLA (Statistical One-Bit Lightweight Authentication) protocol is well suited in a wireless constrained environment because this protocol's communication overhead is extremely low: only one bit. Furthermore, SOLA fulfills the requirements of being secure, useful, cheap, and robust. The synchronization algorithm performs very well. SOLA also makes it easy to develop a framework to detect and respond to, for instance, denial-of-service attacks or an adversary who tries to guess the identity authentication bit for successive packets.

  • 426.
    Xiao, Kai
    Blekinge Institute of Technology, School of Engineering, Department of Signal Processing.
    Analysis and sound synthesis for human echolocation2008Independent thesis Advanced level (degree of Master (Two Years))Student thesis
    Abstract [en]

    Human echolocation is the way in which people use information in echoes to detect objects and locate themselves. Previous research were done in order to investigate this complex processing. One on-going research is based on empirical results of both blind and sighted people, and tries to set up the relations between behavioral data and physical analysis. Repetition pitch and loudness are two of the mechanisms which human echolocation is based on. People’s perception of repetition pitch and loudness has been found to be strongly related to autocorrelation and the root mean square value of the sound signal respectively. This thesis project was conducted in order to analyze the relevant information in previously made sound recordings. By comparing theoretical results, some important sound properties were identified. Colorations in the original sound recordings were found to be able to influence participants’ judgments on echoes. An acoustic model was set up in order to synthesize sound recordings with pre-defined properties. Physical results of autocorrelation and root mean square value of the synthesized sound signals were validated to follow the theoretical expectations. Discussions and proposals were made in order to further improve the sound syntheses’ correspondence to physical recordings. The main achievements in this thesis project were to provide analysis from signal processing’s point of view in order to identify sound properties, to investigate relations between physical results and empirical results of human echolocation and to propose an acoustic model to synthesis sound.

  • 427.
    Xing, Ye
    Blekinge Institute of Technology, School of Engineering, Department of Signal Processing.
    Detection of Speed Signs2006Independent thesis Advanced level (degree of Master (One Year))Student thesis
    Abstract [en]

    This report describes an efficient methodology of speed sign detection which constitutes of several steps to extract speed signs from frames of video recorded from a web-camera mounted in the front of a car. The most difficult implementation issues that are encountered in this task are the angle of the speed sign, the illumination of the image, the size of the speed sign and the calculation speed. In the proposed detection framework several detection decisions are presented, several of those are conducted by utilizing the k-means clustering algorithm. The detector is evaluated on a database with images recorded from a real scenario. The proposed detection system exhibits relatively good performance with a True Positive Rate (TPr) = 0.9875 and a False Positive Rate (FPr) = 1.03*10^-7 on this database.

  • 428. Yang, Zhe
    et al.
    Grace, David
    Mohammed, Abbas
    Optimizing Antenna Performance for Improving Coexistence Performance of Providing WiMAX Servicefrom High Altitude Platforms and Terrestrial WiMAX Deployments2006Conference paper (Refereed)
  • 429. Yang, Zhe
    et al.
    Kamit, Saltanat
    Mohammed, Abbas
    Larson, Peter
    An Investigation of the Business Model in Karlskrona Municipal Wireless Network in Sweden2008Conference paper (Refereed)
    Abstract [en]

    In this paper, an investigation on an emerging operational "business model" for the municipal wireless network in the city of Karlskrona in Sweden is explored. We inquire into the association between of different actors involved in the business model implemented by Karlskrona municipality in our selected case study, and identify a number of key considerations in the business model and wireless city services for municipality when it is initializing and deploying the municipal wireless network as a business driven and public-utility driven service.

  • 430. Yang, Zhe
    et al.
    Mohammed, Abbas
    A Comparative Study on Business Models of Municipal Wireless Cities in US and Sweden2008Conference paper (Refereed)
    Abstract [en]

    In this paper, we will explore the existing operational "business models" for municipal wireless networks in US and Sweden. Based on the current paradigms of the North-American public wireless networks, we will investigate an emerging wireless city concept in Sweden to analysis this new business concept in the existing field. We will look into the relationship of different actors in various business models of the wireless cities in our selected case studies. This paper will aim to demonstrate a number of key considerations when designing and managing the business model of Municipal wireless networks as business-driven and public utility-driven services.

  • 431. Yang, Zhe
    et al.
    Mohammed, Abbas
    A Study of Multiple Access Schemes for Wireless Sensor Network Applications via High Altitude Systems2009Conference paper (Refereed)
    Abstract [en]

    In this paper, we investigate the performance of a multiple access scheme based on orthogonal frequency-division multiplexing (OFDM) in High Altitude Platform (HAP) system for Wireless Sensor Network (WSN) applications. In our study, HAPs are used to replace the traditional gateway deployed on the ground and collect data from sensor nodes. Two scenarios of OFDM schemes with different subcarrier spacing are simulated in Rayleigh and Ricean fading environment. Results show the multiple access scheme based on OFDM for WSN can improve the performance against multipath transmission.

  • 432. Yang, Zhe
    et al.
    Mohammed, Abbas
    A Study of Multiple Access Schemes for Wireless Sensor Network Applications via High Altitude Systems2009Conference paper (Other academic)
  • 433. Yang, Zhe
    et al.
    Mohammed, Abbas
    Broadband Communication Services from Platform and Business Model Design2008Conference paper (Refereed)
  • 434. Yang, Zhe
    et al.
    Mohammed, Abbas
    Business model design for capacity-driven services from High Altitude Platforms2008Conference paper (Refereed)
    Abstract [en]

    In this paper, we will discuss the business model design for the deployment of capacity-driven services from High Altitude Platforms (HAPs). Key factors of successfully delivering the HAP services will be investigated in terms of coexisting with current major wireless broadband and cellular network operators in a long term perspective. A partnership-based business model will be proposed and demonstrated to be effective. We will mainly concentrate on describing how HAP wireless network operator could establish its network and cooperate with other actors being in the proposed business model.

  • 435. Yang, Zhe
    et al.
    Mohammed, Abbas
    Coexistence Performance Evaluation of WiMAX Uplink Broadband Services via High Altitude Platforms2008Conference paper (Refereed)
  • 436. Yang, Zhe
    et al.
    Mohammed, Abbas
    Evaluation of WiMAX Uplink Performance in High Altitude Platforms Cellular System2007Conference paper (Refereed)
  • 437. Yang, Zhe
    et al.
    Mohammed, Abbas
    Evaluation of WiMAX Uplink Performance in High Altitude Platforms Cellular System2008Conference paper (Refereed)
  • 438. Yang, Zhe
    et al.
    Mohammed, Abbas
    High Altitude Platforms for Sensor Network Applications2009Conference paper (Refereed)
  • 439. Yang, Zhe
    et al.
    Mohammed, Abbas
    High Altitude Platforms for Wireless Sensor Applications2009Conference paper (Other academic)
  • 440. Yang, Zhe
    et al.
    Mohammed, Abbas
    High Altitude Platforms for Wireless Sensor Network Applications2008Conference paper (Refereed)
  • 441. Yang, Zhe
    et al.
    Mohammed, Abbas
    On the Cost-Effective Wireless Broadband Service Delivery from High Altitude Platforms with an Economical Business Model Design2008Conference paper (Refereed)
  • 442. Yang, Zhe
    et al.
    Mohammed, Abbas
    Wireless Broadband Access and Applications from High Altitude Platforms2008Conference paper (Refereed)
    Abstract [en]

    In this paper, we give an overview of using High Altitude Platforms (HAPs) for providing wireless telecommunication and broadband communication services. Comparisons of HAPs, satellite and terrestrial systems are shown to illustrate unique characteristics of the system. Three architectures for HAP systems are discussed in terms of cooperation with terrestrial and satellite systems. Telecommunication, broadband and disaster applications of HAPs are showed based on system scenarios.

  • 443. Yang, Zhe
    et al.
    Mohammed, Abbas
    Wireless Broadband Services for Suburban and Rural Applications from High Altitude Platforms with an Economical Business Model Design2008Conference paper (Refereed)
  • 444. Yang, Zhe
    et al.
    Mohammed, Abbas
    Awoniyi, Oluwaseyi
    Oladipo, Andrew Oluseyi
    Hult, Tommy
    Salomonsson, Maria
    Comparative Analysis of Channel Models for Stratospheric Propagation2007Conference paper (Refereed)
  • 445. Yang, Zhe
    et al.
    Mohammed, Abbas
    Grace, David
    Optimizing Download Coexistence Performance of Providing WiMAX Service from HAPS and Terrestrial Deployment2006Conference paper (Refereed)
  • 446. Yang, Zhe
    et al.
    Mohammed, Abbas
    Hult, Tommy
    Modelling and Optimizing Downlink Coexistence Performance of WiMAX Services in HAP and Terrestrial Deployments in Shared Frequency Bands2007Conference paper (Refereed)
  • 447. Yang, Zhe
    et al.
    Mohammed, Abbas
    Hult, Tommy
    Performance Evaluation of WiMAX Broadband from High Altitude Platform Cellular System and Terrestrial Coexistence Capability2008In: EURASIP Journal on Wireless Communications and Networking, ISSN 1687-1472, E-ISSN 1687-1499, Vol. 2008Article in journal (Refereed)
    Abstract [en]

    The performance obtained from providing worldwide interoperability for microwave access (WiMAX) from high altitude platforms (HAPs) with multiple antenna payloads is investigated, and the coexistence capability with multiple-operator terrestrial WiMAX deployments is examined. A scenario composed of a single HAP and coexisting multiple terrestrial WiMAX base stations deployed inside the HAP coverage area (with radius of 30 km) to provide services to fixed users with the antenna mounted on the roof with a directive antenna to receive signals from HAPs is proposed. A HAP cellular configuration with different possible reuse patterns is established. The coexistence performance is assessed in terms of HAP downlink and uplink performance, interfered by terrestrial WiMAX deployment. Simulation results show that it is effective to deliver WiMAX via HAPs and share the spectrum with terrestrial systems.

  • 448. Yang, Zhe
    et al.
    Mohammed, Abbas
    Hult, Tommy
    Grace, David
    Assessment of Coexistence Performance for WiMAX Broadband in High Altitude Platform Cellular System and Multiple-Operator Terrestrial Deployments2007Conference paper (Refereed)
    Abstract [en]

    In this paper, performance of providing WiMAX from High Altitude Platforms (HAPs) with multiple antenna payload will be investigated as well as considering the coexistence capability with multiple-operator terrestrial deployments. A scenario of a HAP and terrestrial WiMAX base stations deployed inside a HAP coverage area with a radius at 30 km will be proposed. HAP cellular formation with different reuse patterns will be established. Coexistence performance will be assessed in terms of HAP downlink signal interfered by terrestrial WiMAX deployment. This paper will show it is effective to deliver WiMAX via HAPs and can efficiently share the spectrum with terrestrial WiMAX systems.

  • 449. Yang, Zhe
    et al.
    Mohammed, Abbas
    Hult, Tommy
    Grace, David
    Downlink Coexistence Performance Assessment and Techniques for WiMAX Services from High Altitude Platform and Terrestrial Deployments2008In: EURASIP Journal on Wireless Communications and Networking, ISSN 1687-1472, E-ISSN 1687-1499, Vol. 2008Article in journal (Refereed)
    Abstract [en]

    We investigate the performance and coexistence techniques for worldwide interoperability for microwave access (WiMAX) delivered from high altitude platforms (HAPs) and terrestrial systems in shared 3.5 GHz frequency bands. The paper shows that it is possible to provide WiMAX services from individual HAP systems. The coexistence performance is evaluated by appropriate choice of parameters, which include the HAP deployment spacing radius, directive antenna beamwidths based on adopted antenna models for HAPs and receivers. Illustrations and comparisons of coexistence techniques, for example, varying the antenna pointing offset, transmitting and receiving antenna beamwidth, demonstrate efficient ways to enhance the HAP system performance while effectively coexisting with terrestrial WiMAX systems.

  • 450. Yang, Zhe
    et al.
    Mohammed, Abbas
    Hult, Tommy
    Grace, David
    Optimizing Downlink Coexistence Performance of WiMAX Services in HAP and Terrestrial Deployments in Shared Frequency Bands2007Conference paper (Refereed)
678910 401 - 450 of 491
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