Ändra sökning
Avgränsa sökresultatet
45678910 301 - 350 av 603
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf
Träffar per sida
  • 5
  • 10
  • 20
  • 50
  • 100
  • 250
Sortering
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
  • Standard (Relevans)
  • Författare A-Ö
  • Författare Ö-A
  • Titel A-Ö
  • Titel Ö-A
  • Publikationstyp A-Ö
  • Publikationstyp Ö-A
  • Äldst först
  • Nyast först
  • Skapad (Äldst först)
  • Skapad (Nyast först)
  • Senast uppdaterad (Äldst först)
  • Senast uppdaterad (Nyast först)
  • Disputationsdatum (tidigaste först)
  • Disputationsdatum (senaste först)
Markera
Maxantalet träffar du kan exportera från sökgränssnittet är 250. Vid större uttag använd dig av utsökningar.
  • 301. Lundberg, Magnus
    et al.
    Brown, C. L.
    Modelling of occluded signatures with application to optical detection of surface laid land mines2003Ingår i: Proceedings of the International Conference on Requirements and Technologies for the Detection, Removal and Neutralization of Landmines and UXO (EUDEM2-SCOT): Brussels, Belgium, September 2003., 2003Konferensbidrag (Refereegranskat)
  • 302.
    Lundberg, Magnus
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Brown, Christopher L
    Technische Universität, Darmstadt.
    Uppsäll, Magnus S.
    Swedish Defence Research Agency.
    Spatial modeling of occlusion patterns applied to the detection of surface-laid mines2004Ingår i: Detection and Remediation Technologies for Mines and Minelike Targets IX, 2004, s. 799-810Konferensbidrag (Refereegranskat)
    Abstract [en]

    Images recorded in ground areas potentially containing surface laid land mines are considered. The first hypothesis is that the image is of clutter (grass) only, while the alternative is that the image contains a partially occluded (covered) land mine in addition to the clutter. In such a scenario, the occlusion pattern is unknown and has to be treated as a nuisance parameter. In a previous paper it was shown that deterministic treatment of the unknown occlusion pattern, in companion with the applied model, renders a substantial increase in detector performance as compared to employment of the traditional additive model. However, a deterministic assumption ignores possible correlation and additional gains could be possible by taking the spatial properties into account. In order to incorporate knowledge regarding the occlusion, the spatial distribution is characterized in terms of an underlying Markov Random Field (MRF) model. A major concern with MRF models is their complexity. Therefore, in addition to this, a less computationally demanding technique to accommodate the occlusion behavior is also proposed. The main purpose of this paper is to investigate if significant gains are possible by acknowledging the spatial dependence. Evaluation on data using real occluded targets however indicates that the gain seem to be marginal.

  • 303.
    Lundberg, Magnus
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Eliasson, Jens
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Allan, Jason
    Luleå tekniska universitet.
    Johansson, Jonny
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Lindgren, Per
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Power characterization of a bluetooth-equipped sensor node2005Ingår i: REALWSN 2005: proceedings of the First Workshop on Real-World Wireless Sensor Network : Stockholm, Sweden, 20-21 June 2005, Kista: Swedish Institute of Computer Science , 2005Konferensbidrag (Refereegranskat)
    Abstract [en]

    Wireless Sensor Networks (WSNs) consist of small, autonomous devices with wireless networking capabilities. In order to further increase the applicability of WSNs in real world ap- plications, minimizing energy consumption and size are im- portant research topics. A WSN node itself is a complex system consisting of numerous components, and the energy consumption of the node depends heavily on the interac- tion between its components and their respective operation modes. To develop a power consumption model, we have investigated the power characteristics of a Bluetooth(BT)- equipped node based on COTS (commercial o®-the-shelf) components running standardized protocols for communica- tion. The characterization captures the transient behavior of the individual components as well as the dynamic behav- ior of the system as a whole. Although the parameters of the model are derived for a speci¯c node, the model and our conclusions can be applied to WSN nodes in general. Based on our model the estimated lifetime of a battery powered BT-equipped node can range from a couple of days to sev- eral months depending on battery and usage. This result indicates that COTS based sensor nodes can be used in a wide range of applications.

    Ladda ner fulltext (pdf)
    FULLTEXT01
  • 304.
    Lundberg, Magnus
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Eliasson, Jens
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Svensson, Linus
    Lindgren, Per
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Context aware power optimizations of wireless embedded Internet systems2004Ingår i: From the electrometer to the networked instruments: giant step toward a deeper knowledge : proceedings of the 21th IEEE Instrumentation and Measurement Technology Conference, Como, Italy, May 18 - 20, 2004 / [ed] Serge Demidenko, Piscataway, NJ: IEEE Communications Society, 2004, s. 91-95Konferensbidrag (Refereegranskat)
    Abstract [en]

    A key issue in research around embedded Internet systems (EIS) is to reduce power consumption. We envision EIS devices with lifetimes in the range of months or even years. This calls for developing aggressive power management techniques with a high degree of context awareness. As a first step towards this goal we introduce a design methodology for making context aware power optimizations of EIS. The presented design methodology which is verified by experimental results is a promising first step in prolonging operating time of battery powered wireless EIS.

    Ladda ner fulltext (pdf)
    FULLTEXT01
  • 305. Lundberg, Magnus
    et al.
    Gu, Irene Y. H.
    Chalmers University of Technology.
    3D matched filter for detection of land mines using spatio-temporal thermal modeling2000Ingår i: Detection and Remediation Technologies for Mines and Minelike Targets V, 2000Konferensbidrag (Refereegranskat)
    Abstract [en]

    Shallowly buried object sand the background soil have different specific heat and heat conductivity. Thus, the thermal alternation over day and night produces a thermal contrast on the soil surface that can be detected by an IR sensor. We present a simple model for the spatio-temporal temperature signature of a buried land mine by means of a 3D Gaussian function. Such a mode is appropriate since both measured data and simulations based on the finite element method show a spatio-temporal behavior that strongly resembles a 3D Gaussian shape. An advantage of modeling the signature as a Gaussian shape is that objects with approximately the same size but with different physical properties can be obtained simply from a scaled version of the original model.

  • 306. Lundberg, Magnus
    et al.
    Muhammad, Khurram
    Texas Instruments, Dallas.
    Roy, Kaushik
    Purdue University.
    Wilson, Sarah Kate
    A novel approach to high-level switching activity modeling with applications to low-power DSP system synthesis2001Ingår i: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 49, nr 12, s. 3157-3167Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    We address high-level synthesis of low-power digital signal processing (DSP) systems by using efficient switching activity models. We present a technology-independent hierarchical scheme that can be easily integrated into current communications/DSP CAD tools for comparing the relative power/performance of two competing DSP designs without specific knowledge of transistor-level details. The basic building blocks considered for such systems are a full adder, a half adder, and a one-bit delay. Estimates of the switching activity at the output of these primitives are used to model the activity in more complex building blocks of DSP systems. The presented hierarchical method is very fast and simple. The accuracy of estimates obtained using the proposed approach is shown to be within 4% of the results obtained using extensive bit-level simulations. Our approach shows that the choice of multiplier/multiplicand is important when using array multipliers in a datapath. If the input signal with smaller mean square value is chosen as the multiplicand, almost 20% savings in switching activity can be achieved. This observation is verified by an analog simulation using a 16 × 16 bit array multiplier implemented in a 0.6-μ process with 3.3 V supply voltage.

  • 307.
    Lundberg, Magnus
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Muhammad, Khurram.
    School of Electrical and Computer Engineering, Purdue University, West Lafayette.
    Roy, Kaushik
    School of Electrical and Computer Engineering, Purdue University, West Lafayette.
    Wilson, Sarah Kate
    Luleå tekniska universitet.
    High-level modeling of switching activity with application to low-power DSP system synthesis1999Ingår i: Proceedings / 1999 IEEE International Conference on Acoustics, Speech, and Signal Processing: ICASSP 99 ; March 15 - 19, 1999, Civic Plaza, Hyatt Regency, Phoenix, Arizona, U.S.A., Piscataway, NJ: IEEE Communications Society, 1999, s. 1877-1880Konferensbidrag (Refereegranskat)
    Abstract [en]

    We address the issue of high-level synthesis of low-power digital signal processing (DSP) systems by proposing switching activity models. In particular, we present a technology independent hierarchical scheme to compare relative power performance of two competing DSP systems. The basic building blocks considered for such system are a full-adder and a one-bit delay. Estimates of switching activity at the output of these building blocks is used to model the activity in different architectural primitives used for building DSP systems. This method is very fast and simple and simulations show accuracy within 4% of extensive bit-level simulations. Therefore, it can easily be integrated into current communications/DSP CAD tools for low-power applications. The models show that the choice of multiplier/multiplicand is important when using array multipliers in a data-path. If the input signal with smaller variance is chosen as the as the multiplicand, up to 20% savings in switching activity can be achieved. This observation is verified by analog simulation

  • 308. Lundberg, Magnus
    et al.
    Scharf, Louis L.
    Colorado State University.
    Pezeshki, Ali
    Colorado State University.
    Multi-rank Capon beamforming2004Ingår i: Conference Record of the Thirty-Eighth Asilomar Conference on Signals, Systems and Computers, IEEE Communications Society, 2004, Vol. 2, s. 2335-2339Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents a multi-rank extension of the Capon beamformer. By expanding the rank of the beamformer it is possible to fully exploit situations in which signals lie in multi-dimensional subspaces, as opposed to the standard point source case. Such situations are commonly caused by array mismatches and scattered or distributed sources. The extension involves the design of a constraint matrix which can be interpreted in terms of signal power. Three possible choices for the constraint are proposed. These correspond to one non-adaptive choice, one choice that is dependent on the signal covariance structure only, and one choice that is both signal and data adaptive. Simulation examples are presented that show the promise of the idea of multi-rank Capon beamforming. Especially the signal- and data adaptive constraint appears very promising.

  • 309.
    Lundberg, Magnus
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Svensson, Lennart
    Chalmers University of Technology, Department of Signals and Systems.
    The Haar measure and the generation of random unitary matrices2004Ingår i: 2004 IEEE Sensor Array and Multichannel Signal Processing Workshop: 18 - 21 July 2004, Barcelona, Spain, Piscataway, NJ ;: IEEE Communications Society, 2004, s. 114-118Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper derives the Haar measure over the set of unitary matrices. The Haar measure is essential when studying the statistical behavior of complex sample covariance matrices in terms of their eigenvalues and eigenvectors. The characterization is based on Murnaghans parameterization of unitary matrices which can be seen as a generalization of the representation of orthogonal matrices using Givens rotations. In addition to deriving the Haar measure, an efficient method to obtain samples from it is also presented

  • 310.
    Lundberg, Magnus
    et al.
    Chalmers Univ. of Technology, Sweden; Swedish Defense Research Agency, Sweden.
    Svensson, Lennart B.M.
    Chalmers University of Technology, Sweden.
    Gu, Irene Y.H.
    Chalmers University of Technology, Sweden.
    Infrared detection of buried landmines based on texture modeling2001Ingår i: Detection and Remediation Technologies for Mines and Minelike Targets VI, 2001, Vol. 4349, s. 199-206Konferensbidrag (Refereegranskat)
    Abstract [en]

    A parametric model for the infrared signature caused by a buried land mine is presented. Further, two ways of modeling the colored background noise, is proposed. In the first, it is assumed the noise can be approximated by an autoregressive process, while in the second, the statistics of the noise is described using recent development in texture modeling, the so called FRAME method. Given an a priori distribution of the mine parameters in combination with a trained noise distribution, a Bayesian detector is derived. Experiments indicate that significant gains in performance can be achieved as compared to the standard detector used, which correlates the infrared image with the known mine shape and thresholds the square of the output.

  • 311.
    Lundqvist, Erik
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Kriging radio environment map construction2022Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    With the massive increase in usage of some parts of the electromagnetic spectrum during the last decades, the ability to create real time maps of signal coverage is now more important than ever before. This Masters project is designed to test two different methods of generating such maps with a one second limit to processing time. The interpolation methods under consideration are known as inverse distance weighting and kriging. Several different variants of kriging are considered and compared some of which were implemented specif cally for the project and one variant designed by a third party.The data used is acquired from an antenna array inside a laboratory room at LTU rather than being simulated. The data collection is done with the transmitter at several different positions in the room to make sure the interpolation works consistently.

    The results show only small differences in both the mean and median of the absolute error when comparing inverse distance weighting and kriging and the variations between transmitter positions are signifcant enough that no single variant is consistently the best using that metric. Using a resolution with 25cm2 pixel size there were no problems reaching significantly lower than the 1sec time limit. If the resolution is increased to apixel size of 1cm2 neither method is able to consistently update the map at the required pace. Kriging however showed that it can generate values outside the range of observed values which could make the extra effort required to implement it worth it since such a characteristic might be very useful for  finding the transmitter.

    Ladda ner fulltext (pdf)
    fulltext
  • 312. Lycksam, Henrik
    et al.
    Sjödahl, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Strömningslära och experimentell mekanik.
    Gren, Per
    Leblanc, James
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Wiener filtering of interferometry measurements through turbulent air using an exponential forgetting factor2008Ingår i: Applied Optics, ISSN 1559-128X, E-ISSN 2155-3165, Vol. 47, nr 16, s. 2971-2978Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The problem of imaging through turbulent media has been studied frequently in connection with astronomical imaging and airborne radars. Therefore most image restoration methods encountered in the literature assume a stationary object, e.g., a star or a piece of land. In this paper the problem of interferometric measurements of slowly moving or deforming objects in the presence of air disturbances and vibrations is discussed. Measurement noise is reduced by postprocessing the data with a digital noise suppression filter that uses a reference noise signal measured on a small stationary plate inserted in the field of view. The method has proven successful in reducing noise in the vicinity of the reference point where the size of the usable area depends on the degree of spatial correlation in the noise, which in turn depends on the spatial scales present in the air turbulence. Vibrations among the optical components in the setup tend to produce noise that is highly correlated across the field of view and is thus efficiently reduced by the filter. © 2008 Optical Society of America.

  • 313.
    Löfgren, Isabelle
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap. Energy Engineering, Dalarna University, Falun, Sweden.
    Ravindran, Vineetha
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Rönnberg, Sarah
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Interharmonics under Fundamental Frequency Variations2021Ingår i: CIRED 2021 - The 26th International Conference and Exhibition on Electricity Distribution, IEEE, 2021, s. 658-662, artikel-id 0048Konferensbidrag (Refereegranskat)
  • 314.
    Lööv, Camilla
    et al.
    Department of Neuroscience, Uppsala University.
    Mitchell, Claire H.
    Department of Anatomy and Cell Biology, University of Pennsylvania.
    Simonsson, Martin
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Erlandsson, Anna
    Department of Neuroscience, Uppsala University.
    Slow degradation in phagocytic astrocytes can be enhanced by lysosomal acidification2015Ingår i: Glia, ISSN 0894-1491, E-ISSN 1098-1136, Vol. 63, nr 11, s. 1997-2009Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Inefficient lysosomal degradation is central in the development of various brain disorders, but the underlying mechanisms and the involvement of different cell types remains elusive. We have previously shown that astrocytes effectively engulf dead cells, but then store, rather than degrade the ingested material. In the present study we identify reasons for the slow digestion and ways to accelerate degradation in primary astrocytes. Our results show that actin-rings surround the phagosomes for long periods of time, which physically inhibit the phago-lysosome fusion. Furthermore, astrocytes express high levels of Rab27a, a protein known to reduce the acidity of lysosomes by Nox2 recruitment, in order to preserve antigens for presentation. We found that Nox2 colocalizes with the ingested material, indicating that it may influence antigen processing also in astrocytes, as they express MHC class II. By inducing long-time acidification of astrocytic lysosomes using acidic nanoparticles, we could increase the digestion of astrocyte-ingested, dead cells. The degradation was, however, normalized over time, indicating that inhibitory pathways are up-regulated in response to the enhanced acidification.

  • 315.
    Maeder, Anthony
    et al.
    Monash University, Melbourne, VIC.
    Thurley, Matthew
    Progressive regional compression of digital images1992Ingår i: International Symposium on Signal Processing and Its Applications: proceedings, August 16-21, 1992, ANA Hotal, Gold Coast, Queensland, Australia / [ed] D.A. Gray, Edgecliff, N.S.W: IREE Australia , 1992Konferensbidrag (Refereegranskat)
  • 316.
    Malmelöv, Tomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik.
    Implementation and Evaluation of Encoder Tools for Multi-Channel Audio2019Självständigt arbete på avancerad nivå (yrkesexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    The increasing interest for immersive experiences in areas such as augmented and virtual reality makes high quality 3D sound more important than ever before. A technique for capturing and rendering 3D audio which has received more attention during the last twenty years are Higher Order Ambisonics (HOA). Higher Order Ambisonics is a scene based audio format which has a lot of advantages compared to other standard formats. Hovever, one problem with HOA is that it requires a lot of bandwidth. For example, sending an uncoded high quality HOA signal requires 49 channels to be transmitted at the same time which requires a bandwidth of about 40 Mbps. A lot of effort has been made in the last ten years on coding HOA signals. In this thesis, two different approaches are taken on coding HOA signals. In one approach, called Sound Field Rotation (SFR) in this thesis, the microphone that records the sound field is virtually rotated to see if it is possible to make some of the channels zero. The second approach, called Sound Field Decomposition (SFD) in this thesis, use Principal component analysis to decompose a sound field into a foreground and background component. The Sound Field Decomposition approach is inspired by the emerging MPEG-H 3D Audio standard for coding HOA signals. The result shows that the Sound Field Rotation method only works for very simple sound scenes. It has also been shown that a 49 channels HOA signal can be reduced to as little as 7 channels if the sound scene consists of a point source. The Sound Field Deomposition method worked for more complex sound scenes. It was shown that a MPEG similar system could be improved. Result from MUSHRA (Multiple stimuli with hidden reference and anchor) listening tests showed that an improved MPEG similar system reached a MUSHRA score about 78 while the MPEG similar system reached 55 at a bitrate of 256 kbps. Without coding each monochannels with the 3GPP EVS (Enhanced voice services) codec, the improved MPEG similar system reached the MUSHRA score 85. At 256 kbps, the improved MPEG similar system coded the HOA signal into six channels instead of 49 for the uncoded signal. From objective results, it was shown that the improved MPEG similar system had largest effect at low bitrates.

    Ladda ner fulltext (pdf)
    fulltext
  • 317. Marquet, D.
    et al.
    Leblanc, James
    RAMO: management network for telecommunications environment equipment1993Ingår i: 27-30 September 1993, Palais des Congres de Paris, France, 15ieme Conférence Internationale sur l'Énergie dans les Télécommunications, 15th International Telecommunications Energy Conference INTELEC '93, Paris: Sitecmo Dieppe , 1993, s. 173-177Konferensbidrag (Refereegranskat)
    Abstract [en]

    The RAMO network is the fundamental tool for operating the technical environment equipment of telecommunications centres which concern the power supply, cooling system, building surveillance, access control, security, EMC and electrostatic environment. It implements functions which make it possible to analyse the quality of the equipment's performance in operation, to precisely identify equipment failures to reduce their mean time to repair. The type of equipment included in this network varies depending on the size of the centre which houses it. It comprises the power supply systems, consisting of an electrical generator, an AC distribution cabinet, a conversion and power storage cabinet from the Alfatel range, catering for all power requirements from 2.5 kVA to 60 kVA, and from the Geode range for power greater than 100 kVA, together with the cooling systems and uninterruptible power supplies. The networking of all these items of equipment on an X.25 protocol using France Telecom's operating architecture comprises the RAMO network.

    Ladda ner fulltext (pdf)
    FULLTEXT01
  • 318.
    Martinez Arenas, Julia
    et al.
    Ecole National Superieure de Telecommunications, Site de Toulouse.
    Landström, Daniel
    Luleå tekniska universitet. Lund Institute of Technology, Lund University, Sweden.
    van de Beek, Jaap
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Börjesson, Per Ola
    Lund Institute of Technology, Department of Applied Electronics.
    Boucheret, Marie-Laure
    Ecole Nationale Supérieure des Télécommunications.
    Ödling, Per
    Department of Electrosciences, Lund Institute of Technology.
    Synchronization in OFDM systems: Sensitivity to the choice of pulse shape1997Konferensbidrag (Refereegranskat)
  • 319.
    Martinsson, Jesper
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Compensating distortion effects in repeated measurements under non-stationary conditions2009Ingår i: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 20, nr 2Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper a compensation technique is presented for applications using repeated measurements under moderate non-stationary measurement conditions. The assumption is that the measurement conditions are stationary during a single repeated measurement but non-stationary over the entire measurement time. The objective with repeated measurements is often to retrieve an estimate of the (noise reduced) signal and its uncertainties. In order to obtain accurate estimates of these two quantities, stationary measurement conditions must be guaranteed under the measurement time. A condition that in many situations is difficult to achieve, e.g., during long measurement times or in a rapidly changing environment. The proposed method compensates for linear dynamic changes during the measurement time, where the dynamical changes, the underlying signal waveform and the noise covariance are considered unknown. The theoretical effect of moderate non-stationary conditions on repeated measurements is analyzed and experimentally validated. Estimation results using the proposed technique are presented for repeated ultrasonic measurements under non-stationary temperature conditions. The results show accurate signal estimation and noise characterization with uncorrelated normally distributed residuals, in contrast to standard synchronization techniques

  • 320.
    Martinsson, Jesper
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Estimating the underlying signal waveform, noise covariance and synchronization jitter from unsynchronized measurements2008Ingår i: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 19, nr 2Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper a new synchronization technique is presented for applications using repeated measurements or experiments with periodically excited signals. The objective with repeated or periodic measurements is often to retrieve an estimate of the (noise reduced) signal and its uncertainties. However, these measurements need to be synchronized to obtain accurate estimates. Existing synchronization techniques are limited to specific signal and noise conditions, such as white Gaussian noise or narrowband signals, to achieve good performance. The proposed method, not limited by these conditions, extracts statistical information regarding the underlying signal and the noise contained in the measurements, to obtain good synchronization (asymptotically optimal). The Cramér-Rao lower bound (CRLB) is derived for the synchronization problem, including bounds for the underlying signal waveform and the covariance of the measurement noise, both considered unknown. The method, which is shown to be the maximum-likelihood estimator (MLE) in both white and colored Gaussian noise, is compared with the CRLB along with standard sub-sample estimation and aligning techniques using Monte Carlo simulations. The results show significant mean square error (MSE) improvements compared to standard synchronization techniques. Synchronization results using the proposed technique are presented for repeated ultrasonic measurements, to validate the method in a real measurement situation, and to experimentally support theoretical results.

    Ladda ner fulltext (pdf)
    fulltext
  • 321.
    Martinsson, Jesper
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Statistical tools for ultrasonic analysis of dispersive fluids2006Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    This thesis focuses on the possibility of using ultrasonic measurement techniques for energy gas characterization. The idea is to combine both on-line flow measurements with non-invasive fluid characterization in the same measurement setup using the same sensor(s). The long-term goal of the project is to develop measurement methods based on ultrasonic techniques that can measure; the flow rate, the energy content, detect impurities, and estimate the composition. In this thesis different problems concerning gas characterization and modeling are addressed. The information obtained from ultrasonic measurements are limited to spectral variations in the attenuation and phase velocity. Hence, part of the research is focused on estimating these quantities accurately with low uncertainty. Another area is parametric modeling and identification of the bulk modulus, where a new model structure for gas mixtures with complex dynamic behavior and/or unknown components is presented, capable of handling the combined effect of the absorption mechanisms. Finally, the problem of estimating the composition of a gas mixture is considered. The results show that it is possible to estimate the composition of processed and upgraded biogas, with high accuracy and precision, by combining the developed estimation techniques with multiple linear regression methods. The thesis consists of two parts. The first part includes an introduction to the research area together with a short summary of the contributions. The second part contains a collection of four papers describing the research.

    Ladda ner fulltext (pdf)
    FULLTEXT01
  • 322. Martinsson, Jesper
    et al.
    Carlson, Johan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Parametric estimation of ultrasonic phase velocity and attenuation in dispersive media2006Ingår i: Ultrasonics, ISSN 0041-624X, E-ISSN 1874-9968, Vol. 44, nr Supplement 1, s. e991-e994Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In ultrasonic characterization of liquids, gases, and solids, accurate estimation of frequency dependent attenuation and phase velocity is of great importance. Non-parametric methods, such as Fourier analysis, suffers from noise sensitivity, and the variance of the estimated quantities is limited by the signal-to-noise ratio. In this paper we present a parametric method for estimation of these properties. Pulse echo experiments in ethane, oxygen and mixtures of the two show that the proposed method can estimate phase velocity and attenuation with up to 50 times lower variance than standard non-parametric methods.

    Ladda ner fulltext (pdf)
    FULLTEXT01
  • 323. Martinsson, Jesper
    et al.
    Carlson, Johan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Parametric modeling of wave propagation in gas mixtures: a system identification approach2005Ingår i: 2005 IEEE Ultrasonics Symposium: 18 - 21 September 2005, Rotterdam, the Netherlands, Piscataway, NJ: IEEE Communications Society, 2005, s. 2288-2292Konferensbidrag (Refereegranskat)
    Abstract [en]

    In ultrasonic pulse-echo systems, the observable properties are restricted to frequency dependent attenuation and phase velocity, which in turn are related to the material properties of the investigated media. In this paper we present a parametric model of the bulk modulus, composed of the basic physical building blocks of absorption (relaxation blocks). The parametric model is capable of handling the combined effect of the absorption mechanisms present in a gas or gas mixture and captures the experimental variation in the observation. The performance of the parametric model is demonstrated with pulse-echo experiments in oxygen, ethane and mixtures of the two. Compared to standard Fourier analysis techniques, the parametric model gives higher accuracy when estimating attenuation and phase velocity, and physical parameters such as relaxation strengths and relaxation frequencies can be extracted from it.

    Ladda ner fulltext (pdf)
    FULLTEXT01
  • 324.
    Martinsson, Jesper
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Carlson, Johan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system. Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Niemi, Jan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Model-based phase velocity and attenuation estimation in wideband ultrasonic measurement systems2007Ingår i: IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, ISSN 0885-3010, E-ISSN 1525-8955, Vol. 54, nr 1, s. 138-146Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A parametric method to estimate frequencydependent phase velocity and attenuation is presented in this paper. The parametric method is compared with standard nonparametric Fourier analysis techniques using numerical simulations as well as real pulse-echo experiments. Approximate standard deviations are derived for bothmethods and validated with numerical simulations. Compared to standard Fourier analysis, the parametric model gives considerably lower variance when estimating attenuation and phase velocity. In contrast to nonparametric techniques, the proposed estimator avoids the phase unwrapping problem because analytical expressions for thecontinuous phase velocity and attenuation can be derived.

    Ladda ner fulltext (pdf)
    fulltext
  • 325. Martinsson, Jesper
    et al.
    Hägglund, Fredrik
    Carlson, Johan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Estimating the underlying signal waveform and synchronization jitter from repeated measurements2006Ingår i: Proceedings: 2006 IEEE Ultrasonics Symposium : Vancouver, Canada, 3 - 6 October 2006, Piscataway, NJ: IEEE Communications Society, 2006, s. 440-443Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper we present a synchronization technique, for applications using repeated or periodically excited measurements. The problem with existing techniques is their limitations to specific signal and noise conditions, such as white Gaussian noise or narrowband signals. The proposed method extracts statistical information about the underlying signal and noise in the measurements to obtain good synchronization (asymptotically optimal). The Cramér-Rao lower bound (CRLB) is derived for the synchronization problem, including bounds for the underlying signal waveform and the covariance of the noise. The method, which is the maximum-likelihood estimator for both white and colored Gaussian noise, is compared with standard sub-sample estimation and aligning techniques using Monte Carlo simulations. The results show significant improvements compared to standard synchronization techniques.

    Ladda ner fulltext (pdf)
    FULLTEXT01
  • 326. Martinsson, Jesper
    et al.
    Hägglund, Fredrik
    Carlson, Johan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Separation of dispersive coinciding signals by combining hard and soft modeling2008Ingår i: Proceedings of the International Congress on Ultrasonics: Vienna, April 9-13, 2007, Paper ID 1563, Session R17, 2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    In some ultrasonic measurement situations, an adequate signal separation is difficult to achieve. A typical situation is material characterization of thin media, relative to the emitted signal's time support. In this paper a new method is proposed that enables accurate signal separation of measured coinciding signals in the postprocessing stage. The method is based on a combination of hard physical and soft empirical models, which allows for a description of both known and unknown dynamics making the separation possible. The proposed technique is verified using real measurements on thin dispersive samples and validated with residual analysis.

    Ladda ner fulltext (pdf)
    FULLTEXT01
  • 327. Martinsson, Jesper
    et al.
    Hägglund, Fredrik
    Carlson, Johan E.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Complete post-separation of overlapping ultrasonic signals by combining hard and soft modeling2008Ingår i: Ultrasonics, ISSN 0041-624X, E-ISSN 1874-9968, Vol. 48, nr 5, s. 427-443Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In some ultrasonic measurement situations, an adequate signal separation is difficult to achieve. A typical situation is material characterization of thin media using pulse-echo or through-transmission techniques, when the time-of-flight in the media is shorter than the emitted signal's time support. Separated signals are necessary to obtain accurate estimates of material properties and transit times. In this paper a new method is proposed that enables complete post separation of measured coinciding signals. The method is based on a combination of hard physical and soft empirical models, which allows for a description of both known and unknown properties making a complete separation possible. The validity and limitations of the model and the separation results are thoroughly addressed. The proposed technique is verified using real measurements on thin dispersive samples and validated using residual analysis. The experimental results show a complete separation with uncorrelated and normally distributed residuals. The method enables characterization and/or flow analysis in difficult overlapping situations.

    Ladda ner fulltext (pdf)
    FULLTEXT01
  • 328.
    Martinsson, Pär-Erik
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Calculation of temperature dependency of acoustic properties of diatomic gases using spectroscopic data2003Ingår i: Proceedings, 2003 IEEE Ultrasonics Symposium: October 5 - 8, 2003, Hilton Hawaiian Village, Honolulu, Hawaii ; an international symposium / [ed] Donald E. Yuhas, Piscataway, NJ: IEEE Communications Society, 2003, Vol. 2, s. 1471-1474Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper describes how optical spectroscopic constants can be used to calculate the speed of sound as a function of temperature in diatomic gases. A general expression for the speed of sound is derived by using the vibrational partition function of the gas. The presented method was evaluated for oxygen and nitrogen. The results are in good agreement with the measured data.

  • 329.
    Martinsson, Pär-Erik
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Characterization of energy gases by ultrasound: theory and experiments2004Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The long-term goal with the research presented in this thesis has been to develop an ultrasonic sensor capable of measuring the energy content of energy gases such as natural- and biogas. The energy content can be calculated if the concentration of each constituent of a gas mixture is known. The acoustic properties of a gas mixture are dependent on its composition and by measuring, for example, the speed of sound it is possible to draw conclusions about the composition of the gas mixture. This feature could for instance be built into an ultrasonic flow meter. Natural gas manufactured from a single well is usually very consistent in its composition. However, the gas composition might vary between different wells and therefore also the energy content of the gas. This has the consequence that the quality of a gas might fluctuate if gases from different sources are mixed together. Therefore, the energy content of the gas mixture needs to be monitored in order to assure the quality of the gas. The physical principal that makes ultrasound suitable for gas measurements is called molecular relaxation. At certain frequencies this is the dominating source of acoustic attenuation and dispersion in gases. The frequency region at which the relaxation occurs differs between gases. This feature makes it possible to extract information about the composition of a gas from an ultrasonic pulse that has propagated through the gas. In a gas the molecules are constantly in motion. The molecules have also rotational and vibrational energy levels excited and the temperature determines the equilibrium between external and internal motion. An ultrasonic pulse transmitted trough the gas disturbs the equilibrium between the external and internal modes. This is due to the fact that a pressure pulse locally increases the velocity of the gas molecules, which is equivalent to an increase in temperature. This generates a flow of energy from the translational mode to the internal modes and the pulse is therefore attenuated. In order to design an ultrasonic energy meter there is number of problems that has to be considered. The frequency region where the relaxation effect is dominant has to be determined in order to maximize the variation of measured parameters as function of gas composition. These frequency regions can be found from theoretical predictions or by performing experiments. Many external factors will affect the performance of an energy meter situated \textit{in-situ}. It is important to be able to differ between effects generated by actual variations in gas composition from variations generated by other factors, for example, temperature variations and contamination in the flow. Before an energy meter can be manufactured, simulations has to be done \textit{a priori} in order to design the meter. Such a simulation must consider the electronics of the measurement system and the physics of the acoustic wave propagation through the gas. Much of the useful information wanted is found as variations in the frequency spectra of speed and attenuation of sound. Hence, the ability to measure the frequency dependent speed and attenuation accurate from pulses must be mastered. Further more, ultrasonic pulses are attenuated rapidly in many gases. Therefore, the signal-to-noise ratio can be very low. Is it still possible to extract the useful information even for such pulses? In the thesis different problems concerning gas measurements and modeling is addressed. The research has resulted in a model for temperature dependency of the speed of sound in gases. The model that is applicable to ideal gases has been derived by statistical thermodynamics. Measurement results of the frequency dependency of acoustic properties of gases are presented. Diffraction effects present in the ultrasonic measurement system have been simulated with equivalent circuits. It is shown how pulse shape distortions between pulses that have traveled through different samples of gas can be used as a mean for statistical gas classification. A method for calculating the speed of sound from noisy measurements has been derived. The thesis consists of two parts. The second part contains seven papers that describe the research. The first part serves as an introduction, and a survey, to some of the research problems described in Part II.

    Ladda ner fulltext (pdf)
    FULLTEXT01
  • 330.
    Martinsson, Pär-Erik
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Improved modeling of ultrasonic systems: feasible for industrial applications2002Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    In this thesis tree aspects of ultrasonic measurement and modelling techniques have been investigated. Namely, transducer diffraction modelling using equivalent circuits, wave propagation in multi phase flow, and wave propagation in gases. The work is relevant both from an scientific point of view and from an engineering point of view. It is of importance in all fields of science and engineering to accurately understand, and create simple and yet physically significant models and methods, of complex systems. The goal with the research have been to create a deeper understanding of complex ultrasonic systems, including transducers and wave propagation. This is a prerequisite when designing and constructing ultrasonic measurement systems.

  • 331.
    Martinsson, Pär-Erik
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Carlson, Johan
    Investigating the feasibility of using principal component analysis for ultrasonic classification of gas mixtures2003Ingår i: Proceedings, 2003 IEEE Ultrasonics Symposium: October 5 - 8, 2003, Hilton Hawaiian Village, Honolulu, Hawaii ; an international symposium / [ed] Donald E. Yuhas, Piscataway, NJ: IEEE Communications Society, 2003, s. 1396-1399Konferensbidrag (Refereegranskat)
    Abstract [en]

    On-line measurement of the energy content of natural gas is of interest for both industry and customers, since the energy content determines its monetary value. Experiments with pulsed ultrasound show that, in addition to changes in speed of sound and acoustic attenuation, there is also a change in the shape of the sound waveform. In this paper, we investigate the feasibility of using principal component analysis (PCA) to quantify this change in pulse shape. The principle is evaluated for pure oxygen, pure ethane, and mixtures of the two, for different pressures. The results show that by using PCA, it is possible to distinguish between pulses that have propagated through oxygen from pulses in ethane and mixtures of the two.

    Ladda ner fulltext (pdf)
    FULLTEXT01
  • 332.
    Martinsson, Pär-Erik
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Carlson, Johan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Carlson, R.E.
    Tromsø University.
    Ultrasonic classification of gases using principal component analysis2003Ingår i: 5th world congress on ultrasonics WCU 2003, Paris: Institut Biomedical des Cordeliers, Université Pierre et Marie Curie , 2003, s. 1129-1132Konferensbidrag (Refereegranskat)
    Abstract [en]

    On-line measurement of the energy content of natural gas is of interest for both industry and customers, since the energy content determines its monetary value. Experiments with pulsed ultrasound show that, in addition to changes in speed of sound and acoustic attenuation, there is also a change in the shape of the sound waveform. In this paper we investigate the feasibility of using Principal Component Analysis (PCA) to quantify this change in pulse shape. The principle is evaluated for Oxygen and Ethane, for different pressures and different temperatures. The results show that by using PCA, it is possible to distinguish between pulses that have propagated through Oxygen from pulses in Ethane.

    Ladda ner fulltext (pdf)
    fulltext
  • 333.
    Martinsson, Pär-Erik
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Delsing, Jerker
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Ultrasonic measurements of molecular relaxation in ethane and carbon monoxide2002Ingår i: Proceedings: 2002 IEEE Ultrasonics Symposium : October 8 - 11, 2002, Forum Hotel, Munich, Germany; an international symposium / [ed] Donald E. Yuhas, Piscataway, NJ: IEEE Communications Society, 2002, s. 511-516Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper describes how molecular relaxation can be measured using ultrasound. The velocity and absorption of sound varies with frequency due to molecular relaxation. By measuring these variation the relaxation strength and the effective relaxation time for singular relaxations can be calculated. This paper describes initial measurements performed in order to survey the sound properties in gases both experimentally and theoretically.

    Ladda ner fulltext (pdf)
    fulltext
  • 334.
    Martinsson, Pär-Erik
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Johansson, Jonny
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Incorporation of diffraction effects in simulations of ultrasonic systems using PSpice models2001Ingår i: Proceedings: 2001 IEEE Ultrasonics Symposium : October 7 - 10, 2001, Omni Hotel, Atlanta, Georgia ; an international symposium / [ed] Donald E. Yuhas, Piscataway, NJ: IEEE Communications Society, 2001, s. 405-410Konferensbidrag (Refereegranskat)
    Abstract [en]

    The use of PSpice models for piezoelectric devices and ultrasonic transmission media is of major importance in the design of electronics for ultrasonic systems. Today, these models include viscoelastic loss but disregard loss due to diffraction, i.e. beam spreading. This paper presents a method to include diffraction loss in PSpice simulations of ultrasonic systems. The conductive loss in the transmission line, that models the propagation media of the ultrasound pulse, is used to model the loss due to diffraction. Parameter variations for the piezoelectric device can affect the result greatly. Thus, a sensitivity analysis for the simulation model is presented. Measurements and simulations have been performed using a pulse echo system in water. Maximum distance to the reflector was 200 mm. The piezoelectric devices used were PZ-27 crystals with diameters 6 mm and 12 mm, with a center frequency of 4 MHz. Results show that the simulated amplitude of the echo follows measured values well in both near and far fields, with an offset of about 10%.

    Ladda ner fulltext (pdf)
    fulltext
  • 335.
    Moghaddam, Sadegh
    et al.
    Institute of Geophysics, University of Tehran, Tehran, Iran.
    Oskooi, Behrooz
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geovetenskap och miljöteknik. Institute of Geophysics, University of Tehran, Tehran, Iran.
    Goudarzi, Alireza
    Graduate University of Advanced Technology, Kerman, Iran.
    Azadi, Asghar
    Payam Noor University of Parand, Tehran, Iran.
    The comparative sense of sparse deconvolution and least-squares deconvolution methods in increasing the temporal resolution of GPR data2019Ingår i: Arabian Journal of Geosciences, ISSN 1866-7511, E-ISSN 1866-7538, Vol. 12, nr 20, artikel-id 627Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Improving the temporal resolution of ground-penetrating radar (GPR) data is a fundamental factor in presenting the characteristics of the underground structures. The advantages of sparse signal processing using the majorization-minimization (MM) method in GPR signal compression are investigated. In this method, minimizing the cost function is determined with L1 and L2 norms; also, the banded structures of matrices resulting from the sparse deconvolution problem are regarded. Then, the MM algorithm has been implemented with least-squares deconvolution (LSQR) on the synthetic and real data collected by a system with dual-frequency antennas of 300 and 800 MHz. The compression process has resulted in a high-resolution image from the subsurface layers and anomalies. Analysis of the outputs reported that the reflection coefficient improved significantly by application of the MM algorithm to the synthetic and real data compared with the least-squares deconvolution which only filters the data. The power spectrum after using the MM algorithm shows acceptable compression. Moreover, this algorithm leads to a considerable improvement on the amplitudes so that the hidden anomalies are better restored.

  • 336.
    Mohamad, Medhat
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Activity: An SDR-based prototype of spectrally precoded OFDM2016Konferensbidrag (Övrig (populärvetenskap, debatt, mm))
    Abstract [en]

    OFDM scheme possesses high OOB emission which degrades the spectral efficiency of OFDM systems. Poor spectral efficiency limits the validity of OFDM as a candidate for 5G. Spectrally precoded OFDM is a recent approach that treats the OFDM signal to suppress the out of band (OOB) emission. Although the theoretical results of spectral precoding show very efficient OOB emission suppression (more than 50 dB reduction compared to plain OFDM), practically, hardware impairments limit its performance.We, at Luleå University of Technology, examine the practicality of the suggested approach and show for the first time through this demonstration that despite the hardware impairments, implemented spectral precoded OFDM has OOB emission tens of decibels less than that of plain OFDM. We set up and examine a communication link through which we approve that communication systems are less vulnerable to interference coming from spectrally precoded OFDM signals than to interference coming from plain OFDM signals.

  • 337.
    Mohamad, Medhat
    Luleå tekniska universitet, Institutionen för system- och rymdteknik.
    Design, Analysis and Prototyping of Spectrally Precoded OFDM2016Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Despite shifting towards mm-wave bands, the sub 6-GHz band will continue tobe a fundamental spectral band in 5G. Yet, the severe crowdedness of this bandmakes a well constrained spectrum one of the critical 5G requirements. A wellconstrained spectrum means that the communications regimes should dwell politelywithin their dedicated spectral bands and not interfere with other systems workingon neighboring bands. Consequently, communications community seeks convenientmodulation schemes.Accordingly, high Out Of Band (OOB) emission phenomenon in Orthogonal Fre-quency Division Multiplexing (OFDM) is unfavorable for some regimes operating in5G. Therefore, to legitimize OFDM with all 5G regimes, we need to suppress OFDMOOB emission.Since the discontinuous nature of the OFDM signal is the main reason for the highOOB emission, one solution is to render the discontinuous OFDM signal continuous.Two factors control this discontinuity: the physical shape of the modulated signaland the correlation property of the data symbols that modulate the OFDM signal.While most of the traditional approaches focus on reshaping the OFDM signalto render it continuous, in this work we give our attention to the spectral precod-ing approaches. These approaches manipulate the correlation property of the datasymbols to control the high OOB emission in OFDM.On the other hand, tweaking the correlation property of the modulating datasymbols will violate their orthogonality. This violation will yield in-band interfer-ence within the OFDM signal which would degrade the bit error performance of thereceived data.The thesis explains the spectral precoding techniques from conceptual and math-ematical point of view. We discuss the OOB emission suppression capability of theprecoding techniques and study their drawbacks and limitations. We provide ana-lytical trade o study between precoding approaches and classical OFDM treatmentapproaches at the level of OOB emission suppression and in-band interference. Weshow that the in-band interference in precoding techniques is independent on thecommunications channel behavior contrary to that of classical techniques. More-over, we dene the optimal precoder that minimizes the in-band interference. Con-sequently, we design a novel practical precoder that approaches the performanceof the optimal precoder. Furthermore, we analyze the complexity of the precodingapproaches and study the implementation computational requirements.Finally, we test the real time performance of these precoding techniques usingSoftware Designed Radio (SDR) Universal Software Radio Peripherals (USRPs). Wespotlight the hardware limitations and show that despite these limitations, the spec-tral precoder is able to suppress the OOB emissions by tens of decibels. We check the reliability of spectral precoding in practical over air communications systems bysetting up the rst spectral precoding proof of concept prototype. The prototypeproves that precoded OFDM systems cause less OOB interference on neighboringcommunications systems.

    Ladda ner fulltext (pdf)
    fulltext
  • 338.
    Mohamad, Medhat
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Spectrally Precoded OFDM-Design and Analysis2019Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Despite shifting towards mm-wave bands, the sub-6 GHz band will continue to be a fundamental spectral band in 5G. However, the severe congestion in this band makes a well-constrained spectrum a critical requirementof 5G. A well-constrained spectrum means that the communications regimes should dwell within their dedicated spectral bands and do not interfere with other systems working on neighboring bands. Consequently, the communi-cations community seeks convenient modulation schemes.

    The 5G standards have already defined cyclic prefix orthogonal frequency division multiplexing (CP-OFDM) as the modulation scheme for most of the sub-6 GHz band. However, the high out-of-band (OOB) emission phe-nomenon in OFDM is unfavorable for some regimes operating in 5G. Therefore, to legitimize OFDM in all 5G regimes, we need to suppress the OFDM OOB emission.

    Since the discontinuous nature of the OFDM signal is the main reason forthe high OOB emission, one solution is to render the discontinuous OFDM signal continuous. Two factors control this discontinuity: the physical shape of the modulated signal and the correlation of the data symbols that modulate the OFDM signal.

    While most traditional approaches focus on reshaping the OFDM signal to render it continuous, in this work, we give our attention to the spectral precoding approaches. These approaches manipulate the correlation of the data symbols to control the high OOB emission in OFDM.

    After almost ten years of analytical and theoretical study of the spectralprecoding approaches in the literature, we believe it is time to investigate the practicality and ability of spectral precoding methods to compete with traditional approaches. Consequently, we check whether spectral precoding satisfies the spectral requirements of LTE measures. We analyze the precoders' implementation complexity and provide methodologies to reduce it. We design practical spectral precoders that match with the practical OFDM transmitters, and we study spectral precoding extensibility toward MIMO (and massive MIMO) systems.

    Moreover, in this work, we introduce the first proof-of-concept prototype of spectrally precoded OFDM. In the prototype, we use software-defined radios (SDRs) to perform a real-time examination of how spectral precoding improves the spectral containment of OFDM systems.

    Ladda ner fulltext (pdf)
    fulltext
  • 339.
    Mohamad, Medhat
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nilsson, Rickard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    van de Beek, Jaap
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    A Novel Transmitter Architecture for Spectrally-Precoded OFDM2018Ingår i: IEEE Transactions on Circuits and Systems Part 1: Regular Papers, ISSN 1549-8328, E-ISSN 1558-0806, Vol. 65, nr 8, s. 2592-2605Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Frequency nulling spectral precoding is an approachthat suppresses the out-of-band emission in OFDM systems.In this paper, we discuss the transmitter architecture of thespectrally precoded OFDM systems. We design a novel precoderthat matches the practical implementation of the OFDM modulator.We show that spectral precoding can relax the analog lowpass filtering requirements of the OFDM system transmitter. Weexamine the effect of spectral precoding on the PAPR as wellas the effect of the PA on the spectral precoding suppressionperformance. We also study the compliance of the spectrallyprecoded OFDM transmitter with the 3GPP standardizationmeasures and analyze its computation complexity. At the receiverside, we analyze the in-band interference and BER performanceof the suggested precoding approach.

    Ladda ner fulltext (pdf)
    fulltext
  • 340.
    Mohamad, Medhat
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nilsson, Rickard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    van de Beek, Jaap
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    An analysis of out-of-band emission and in-band interference for precoded and classical OFDM systems2015Ingår i: European Wireless 2015: 21th European Wireless Conference, 20-22 May 2015, Budapest, Hungary, Piscataway, NJ: IEEE Communications Society, 2015, artikel-id 7147703Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper we present analytical expressions for the out-of-band (OOB) emission and in-band interference of two different OOB suppressed OFDM-systems; classical low-pass filtered and precoded. Then, we analytically compare their performance in terms of OOB emission suppression and introduced level of in-band interference. We analyse the fact that the in-band interference introduced by the filter depends on the length of the cyclic prefix as well as the behavior of the channel while that of the precoded OFDM does not. The analysis confirms that edged subcarriers suffer higher in-band interference than central subcarriers. Moreover, frequency precoders, for a specific choice of notching frequencies, can outperform time precoders.

    Ladda ner fulltext (pdf)
    fulltext
  • 341.
    Mohamad, Medhat
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nilsson, Rickard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    van de Beek, Jaap
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    An SDR-based prototype of spectrally-precoded OFDM2017Ingår i: EuCNC 2017: European Conference on Networks and Communications, Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2017, artikel-id 7980758Konferensbidrag (Refereegranskat)
    Abstract [en]

    Spectrally precoded OFDM is a recent approach that aims for the suppression of the OOB, as well as the in-band gap, emissions in OFDM systems. Theoretically, the technique shows High suppression of the OOB and the in-band gap emissions. Although, practically hardware impairments may limit the precoder's performance. Yet, this demonstration shows that despite the hardware impairments, implemented spectrally precoded OFDM generates emissions tens of decibels less than that of plain OFDM. Therefore, the demonstration proves that communications links are less vulnerable to interference coming from spectrally precoded OFDM signals than to interference coming from plain OFDM signals

  • 342.
    Mohamad, Medhat
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nilsson, Rickard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    van de Beek, Jaap
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Minimum-EVM N-continuous OFDM2016Ingår i: 2016 IEEE International Conference on Communications (ICC): Kuala Lumpur, 22-27 May 2016, Piscataway, NJ: IEEE Communications Society, 2016, artikel-id 7511164Konferensbidrag (Refereegranskat)
    Abstract [en]

    The N-continuous precoder for the suppression ofOOB emission in OFDM systems that minimizes the EVM isintroduced. We show that the minimum in-band interference dueto the introduced precoding approach is 3 dB less than the inbandinterference of existing N-continuous precoders. Moreover,we introduce a novel practical block precoder that approachesthe performance of the suggested optimal precoder. We analyzethe spectrum of the OFDM signal after block precoding, the inbandinterference due to block precoding and the effect of blockprecoding on the BER. The price to pay for block precoding isthe computational complexity that grows linearly with the blocksize.

  • 343.
    Mohamad, Medhat
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nilsson, Rickard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    van de Beek, Jaap
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    N-smooth OFDMIngår i: Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper introduces a new multicarrier system - a practical alternative for N-continuous OFDM: N-smooth OFDM. N-smooth OFDM improves the spectral compactness of practical OFDM systems by suppressing OOB emission. The higher spectral compactness of N-smooth OFDM allows the system to relax requirements of the digital to analog converter (DAC) construction filter. Moreover, it decreases the signal's self interference that results from spectral precoding as well as precoder's computational complexity. 

  • 344.
    Mohamad, Medhat
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nilsson, Rickard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    van de Beek, Jaap
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Spectrally-Precoded OFDM for 5G Wideband Operation in Fragmented sub-6GHz SpectrumArtikel i tidskrift (Refereegranskat)
    Abstract [en]

    We consider spectrally-precoded OFDM waveforms for 5G wideband transmission in sub-6GHz band. In this densely

    packed spectrum, a low out-of-band (OOB) waveform is a critical 5G component to achieve the promised high spectral

    efficiency. By precoding data symbols before OFDM modulation, it is possible to achieve extremely low out-of-band

    emission with very sharp spectrum transition enabling an efficient and flexible usage of frequency resources. Spectrallyprecoded

    OFDM shows promising results for reaching 5G targets in high-data rate enhanced mobile broadband and ultrareliable

    low-latency communications use cases. Spectral precoding is particularly efficient for wideband transmission

    enabling short-time transmission, which will often require flexible fragmented spectrum usage.

  • 345.
    Mohamad, Medhat
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Taheri, Tayebeh
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nilsson, Rickard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    van de Beek, Jaap
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Subspace-precoded OFDM with low Out-of-Band Emissions:it will workManuskript (preprint) (Övrigt vetenskapligt)
    Abstract [en]

    Today’s multicarrier transmitters, deployed in essentially all communications radio equipment we use(phones, TV’s, computers, etc.), contain means to avoid undesired out-of-band power emissions. Standards and regulations typically restrict the levels of these emissions in order to allow for an efficient use of the radio spectrum. Radio vendors deploy well-established algorithms such as low-pass filtering or windowing to satisfy these regulations. A new approach, specifically applicable to OFDM systems, known as spectralprecoding, has been studied during the last decade. In particular, subspace precoding has attracted theinterest of academia, for its elegance, and despite a few adamant disadvantages. Recent advances now provide a breakthrough: subspace precoding is now a viable alternative to today’s algorithms.

  • 346.
    Mousavi, Milad
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Effects of Distributed Flexibility Resources on Hosting Capacity2022Övrigt (Övrigt vetenskapligt)
    Abstract [en]

    Flexibility resources are an integral part of the solutions to the intermittency associated with the unprecedented increase in variable renewable energy sources (VRES). In this regard, not only can distributed flexibility resources (DFRs) provide grid and system services, but also can offer opportunities to improve the hosting capacity (HC) of the distribution systems. Therefore, it is essential to consider the effects of DFRs on novel techniques of HC studies and the challenges ahead. Some questions arise on the matter: How do DFRs affect the HC studies’ characteristics and assessment? Subsequently, how can the affected HC studies improve the integration of distributed VRES?

    Ladda ner fulltext (pdf)
    fulltext
  • 347.
    Mukherjee, Moumita
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Platform-Agnostic Resilient Decentralized Multi-Sensor Fusion for Pose Estimation2024Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    This thesis presents an innovative decentralised sensor fusion framework with significant potential to improve navigation accuracy in autonomous vehicles. Its applicability is especially noteworthy in demanding scenarios, such as adverse weather conditions and intricate urban environments. In general, sensor fusion is a crucial method for integrating signals from various sources, extracting and integrating information from multiple inputs into a unified signal or data set. Frequently, sources of information are from sensors or devices designed for the perception and measurement of dynamic environmental changes. The collected data from diverse sensors undergoes processing through specialised algorithms, commonly referred to as "sensor fusion" or "data fusion" algorithms. This thesis describes sensor fusion's significance in processing data from multiple sources. It highlights the classification of fusion algorithms, demonstrating the versatility and applicability of sensor fusion across a range of redundant sensors. Moreover, various creative strategies for sensor fusion, including fault detection and isolation and methods for addressing non-Gaussian noise through smoothing filter techniques, are collectively introduced as part of a comprehensive navigation framework. The contributions of this thesis are summarized in the following. First, it introduces a decentralised two-layered fusion architecture for pose estimation, emphasising fault resilience. In a decentralised fashion, it utilises distributed nodes equipped with extended Kalman filters in the initial tier and optimal information filters in the subsequent tier to amalgamate pose data from multiple sensors. The design is named the Fault-Resilient Optimal Information Fusion (FR-OIF) architecture in this thesis, which guarantees reliable pose estimation, even in cases of sensor malfunctions. Secondly, this work proposes an Auto-encoder-based fault detection framework for a multi-sensorial distributed pose estimation. In this framework, auto-encoders are applied to detect anomalies in the raw signal measurements. At the same time, a fault-resilient optimal information filter (FROIF) approach is incorporated with the auto-encoder-based detection to improve estimation accuracy. The effectiveness of these methods is demonstrated through experimental results involving a micro aerial vehicle and is compared to a novel classical detection approach based on the Extended Kalman filter. Furthermore, it introduces an integrated multi-sensor fusion architecture enhanced by centralised Auto-encoder technology and an EKF framework. This approach effectively removes sensor data noise and anomalies, ensuring reliable data reconstruction, even when faced with time-dependent anomalies. The assessment of the framework's performance using actual sensor data collected from the onboard sensors of a micro aerial vehicle demonstrates its superiority compared to a centralised Extended Kalman filter without Auto-encoders. The next part of the thesis discusses the increasing need for resilient autonomy in complex space missions. It emphasises the challenges posed by interactions with non-cooperative objects and extreme environments, calling for advanced autonomy solutions.  Furthermore, this work introduces a decentralised multi-sensor fusion architecture for resilient satellite navigation around asteroids. It addresses challenges such as dynamic illumination, sensor drift, and momentary sensor failure. The approach includes fault detection and isolation methods, ensuring autonomous operation in adverse conditions. Finally, the last part of the thesis focuses on accurate localisation and deviation identification in multi-sensor fusion with Millimeter-Wave Radars. It presents a flexible, decentralised smoothing filter framework that effectively handles unwanted measurements and enhances Ego velocity estimation accuracy.  Overall, this thesis plays a significant role in advancing the field of decentralised sensor fusion, encompassing anomaly avoidance mechanisms, fault detection and isolation frameworks, and robust navigation algorithms applicable across a range of domains, covering everything from robotics to space exploration. In the initial section of this thesis, we delve into the backdrop, reasons behind the research, existing challenges, and the contributions made. Conversely, the subsequent section comprises the complete articles linked to the outlined contributions and a bibliography.

    Ladda ner fulltext (pdf)
    fulltext
  • 348.
    Mukherjee, Moumita
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Banerjee, Avijit
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Koval, Anton
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nikolakopoulos, George
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Decentralized Fusion-Based Ego Velocity Estimation Using Multiple FMCW Radars2023Ingår i: 2023 21st International Conference on Advanced Robotics (ICAR), IEEE, 2023, s. 244-251Konferensbidrag (Refereegranskat)
  • 349.
    Mwakyanjala, Moses B.
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Emami, Reza
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik. University of Toronto.
    van de Beek, Jaap
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Software-defined radio baseband system for satellite management services2017Ingår i: AIAA SPACE and Astronautics Forum and Exposition, Aerospace Research Central (ARC) , 2017, artikel-id 2017-5244Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents functional analysis and system specifications of a baseband system based on software-defined radio (SDR) technology. The analysis is primarily based on the latest blue-book standards from the Consultative Committee for Space Data Systems(CCSDS). It covers telemetry, telecommand, ranging, and Doppler measurements, as well as some specifications of the associated physical layers. The SDR-based baseband system can support satellite management in the form of a software-as-a-service (SaaS) private cloud.

  • 350.
    Mörck, Mikael
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik.
    Speed Limit Information Function2018Självständigt arbete på grundnivå (yrkesexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
45678910 301 - 350 av 603
RefereraExporteraLänk till träfflistan
Permanent länk
Referera
Referensformat
  • apa
  • ieee
  • modern-language-association-8th-edition
  • vancouver
  • Annat format
Fler format
Språk
  • de-DE
  • en-GB
  • en-US
  • fi-FI
  • nn-NO
  • nn-NB
  • sv-SE
  • Annat språk
Fler språk
Utmatningsformat
  • html
  • text
  • asciidoc
  • rtf