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  • 151.
    Eriksson, Håkan B.
    et al.
    Luleå tekniska universitet.
    Ödling, Per
    Luleå tekniska universitet.
    Multiple-antenna reception and reduced-state Viterbi detection for block transmission systems1995Ingår i: Gateway to the 21st century : record: 1995 Fourth IEEE International Conference on Universal Personal Communications, Meiji Kinenkan, Tokyo, Japan, November 6 - 10, 1995., Piscataway, NJ: IEEE Communications Society, 1995, s. 37-41Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents a receiver structure employing multiple receiving antennas and reduced-state Viterbi detection. The presentation is couched in terms of matrices representing a discrete-time, symbol-sampled system with frequency-selective, slow fading and additive Gaussian noise. The receiver design involves determining two matrices: one matrix defining the metric of the reduced-state Viterbi detector and one representing a pre-processor operating on the output from a maximal-ratio combiner. The presented receiver is a generalization of those used earlier in single-antenna, combined linear-Viterbi equalizers for continuous transmission systems. Performance comparisons are made with the minimum mean-square error (MMSE) linear equalizer and the MMSE decision-feedback equalizer for block transmission systems, indicating that the presented class of receivers offers superior performance

  • 152.
    Eriksson, Håkan B.
    et al.
    Luleå tekniska universitet.
    Ödling, Per
    Luleå tekniska universitet.
    Börjesson, Per-Ola
    Luleå tekniska universitet.
    Simultaneous time of flight and channel estimation using a stochastic channel model1993Ingår i: Radiovetenskaplig konferens på Lunds tekniska högskola 5-7 april 1993: sammanfattning av posters och föredrag / RVK-93, Lund: Lunds tekniska högskola , 1993, s. 43-46Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper we address the problem of estimating the Time-of-Flight of a transmitted signal when the shape of the received waveform is stochastic. Specifically, we examine the case when the transmission system model is stochastic, linear and time discrete, with additive Gaussian noise, and where the transmitted waveform is known to the receiver. The joint estimation is couched in terms of Maximum a Posteriori (MAP) and Maximum Likelihood estimation. When deriving the MAP estimator we assume a priori knowledge of the probability density of the transmission system impulse response. The MAP estimator is then compared to estimators derived using less a priori information and lower order system models. The ordinary correlation based Time-of-Flight estimator assumes knowledge of the received waveform, that is has a one-dimensional transmission system model. This investigation indicates that a more complex model structure is worthwhile when distortion in excess of low additive noise is present.

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  • 153.
    Eriksson, Håkan B.
    et al.
    Luleå tekniska universitet.
    Ödling, Per
    Luleå tekniska universitet.
    Koski, Timo
    Kungliga tekniska högskolan, KTH.
    Börjesson, Per Ola
    Luleå tekniska universitet.
    A genie-aided detector with a probabilistic description of the side information1995Ingår i: Proceedings: 995 IEEE International Symposium on Information Theory, Whistler, British Columbia, Canada, 17 - 22 September, 1995, Piscataway, NJ: IEEE Communications Society, 1995, s. 332-Konferensbidrag (Refereegranskat)
    Abstract [en]

    Building on Forney's concept of the genie (1972), and introducing the idea of an explicit statistical description of the side information provided to the genie-aided detector, we develop a generic tool for derivation of lower bounds on the bit-error rate of any actual receiver. With this approach, the side information statistics become design parameters, which may be chosen to give the resulting bound a desired structure. To illustrate this, we choose statistics in order to obtain a special case: the lower bound derived by Mazo (1975). The statistical description of the side information makes the lower bounding a transparent application of Bayesian theory

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  • 154.
    Eriksson, Håkan
    et al.
    Luleå tekniska universitet.
    Börjesson, Per Ola
    Luleå tekniska universitet.
    Ödling, Per
    Luleå tekniska universitet.
    Holmer, Nils-Gunnar
    Department of biomedical engineering, Lund university.
    A robust correlation receiver for distance estimation1994Ingår i: IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, ISSN 0885-3010, E-ISSN 1525-8955, Vol. 41, nr 5, s. 596-603Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Many methods for distance estimation, such as the ultrasonic pulse-echo method, involve the estimation of a time-of-flight (TOF). In this paper, a signal model is developed that, apart from the TOF, accounts for an unknown, linear frequency dependent distortion as well as for additive noise. We derive a TOF estimator for this model based on the criteria of maximum likelihood. The resulting receiver can be seen as an extension or generalization of the well known cross-correlation, or "matched filter", estimator described, e.g., by Nilsson. The novel receiver is found to be more robust against unknown pulse shape distortion than the cross-correlation estimator, giving less biased TOF estimates. Also, bias versus noise sensitivity can be controlled by proper model order selection

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  • 155.
    Eriksson, Mats
    et al.
    Arctos Labs Scandinavia AB.
    van de Beek, Jaap
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Rural 5G: Oxymoron or Opportunity?2015Ingår i: IEEE ComSoc Technology News, nr NovemberArtikel i tidskrift (Övrig (populärvetenskap, debatt, mm))
  • 156.
    Ethaib, Saleem
    et al.
    Department of Civil Engineering, College of Engineering, University of Thi-Qar, 64001 Al-Nassiriya, Iraq.
    Zubaidi, Salah L.
    Department of Civil Engineering, College of Engineering, Wasit University, Iraq.
    Al-Ansari, Nadhir
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Geoteknologi.
    Evaluation water scarcity based on GIS estimation and climate-change effects: A case study of Thi-Qar Governorate, Iraq2022Ingår i: Cogent Engineering, E-ISSN 2331-1916, Vol. 9, nr 1, artikel-id 2075301Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This work aims to evaluate water scarcity in Thi-Qar governorate, Iraq, based on GIS estimation, environmental data, climate-change effects, and detection of the changes in marshes over the last three decades (1991–2021). The methodology process included collecting and analysing the related data sets such as water quality indicators, surface water quantity, climatic data, and Landsat’s images. GIS-based data and spatial data were acquired from the USGS website. Arc GIS 10.4.1 software was used to create a hydrological analysis. The results showed that generally, in Iraq, the annual volume of water available per person is 1,390.95 m3/cap/year, which is lower than the threshold for water scarcity (1700 m3/cap/year). The average daily potable water per person in Thi-Qar governorate was 284 L/cap/day, lower than the general average daily potable water per person of Iraq (340 L/cap/day). Meanwhile, 6% of the months along 1998–2018 did not meet the water demands. Water quality tests exhibited some high amounts of pollutants in drinking water, e.g., biological pollution was recorded in 55% of the total number of annual samples. Landsat’s images illustrated a high variation in water areas of marshes over the selected period, whereas the highest marshes area was 1548.21 km2 in 1991 compared to the lowest area, 65.45 km2 found in 1999. To sum up, the research outcomes revealed that the study area faced a serious water scarcity, which had a negative impact on the local people. Also, this research offered a scientific view for the decision-makers to mitigate and manage the water scarcity problem.

  • 157.
    Farooq, Umer
    et al.
    Department of Cyber Security, National University of Computer and Emerging Sciences, Islamabad 44000, Pakistan.
    Asim, Muhammad
    Department of Cyber Security, National University of Computer and Emerging Sciences, Islamabad 44000, Pakistan.
    Tariq, Noshina
    Department of Computer Science, Shaheed Zulfikar Ali Bhutto Institute of Science and Technology, Islamabad 44000, Pakistan.
    Baker, Thar
    Department of Computer Science, College of Computing and Informatics, University of Sharjah, Sharjah P.O. Box 27272, United Arab Emirates.
    Awad, Ali Ismail
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Digitala tjänster och system. College of Information Technology, United Arab Emirates University, Al Ain P.O. Box 17551, United Arab Emirates; Faculty of Engineering, Al-Azhar University, Qena P.O. Box 83513, Egypt; Centre for Security, Communications and Network Research, University of Plymouth, Plymouth PL4 8AA, UK.
    Multi-Mobile Agent Trust Framework for Mitigating Internal Attacks and Augmenting RPL Security2022Ingår i: Sensors, E-ISSN 1424-8220, Vol. 22, nr 12, artikel-id 4539Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Recently, the Internet of Things (IoT) has emerged as an important way to connect diverse physical devices to the internet. The IoT paves the way for a slew of new cutting-edge applications. Despite the prospective benefits and many security solutions offered in the literature, the security of IoT networks remains a critical concern, considering the massive amount of data generated and transmitted. The resource-constrained, mobile, and heterogeneous nature of the IoT makes it increasingly challenging to preserve security in routing protocols, such as the routing protocol for low-power and lossy networks (RPL). RPL does not offer good protection against routing attacks, such as rank, Sybil, and sinkhole attacks. Therefore, to augment the security of RPL, this article proposes the energy-efficient multi-mobile agent-based trust framework for RPL (MMTM-RPL). The goal of MMTM-RPL is to mitigate internal attacks in IoT-based wireless sensor networks using fog layer capabilities. MMTM-RPL mitigates rank, Sybil, and sinkhole attacks while minimizing energy and message overheads by 25–30% due to the use of mobile agents and dynamic itineraries. MMTM-RPL enhances the security of RPL and improves network lifetime (by 25–30% or more) and the detection rate (by 10% or more) compared to state-of-the-art approaches, namely, DCTM-RPL, RBAM-IoT, RPL-MRC, and DSH-RPL. 

  • 158.
    Fitz, Kelly
    et al.
    Department of Electrical Engineering, Washington State University, United States.
    Haken, Lippold
    CERL Sound Group, Univ. Illinois at Urbana-Champaign, United States.
    Lefvert, Susanne
    Luleå tekniska universitet. Department of Computer Science, University of Chicago, United States.
    Champion, Corbin
    Department of Electrical Engineering, Washington State University, United States.
    O'Donnell, Mike
    Department of Computer Science, University of Chicago, United States.
    Cell-Utes and Flutter-Tongued Cats: Sound Morphing Using Loris and the Reassigned Bandwidth-Enhanced Model2003Ingår i: Computer music journal, ISSN 0148-9267, E-ISSN 1531-5169, Vol. 27, nr 3, s. 44-65Artikel, forskningsöversikt (Refereegranskat)
    Abstract [en]

    An account of sound manipulation and transformation modeling based on the usage of Loris and the reassigned bandwidth-enhanced additive sound model was presented. The bandwidth enhancement technique combined sinusoidal energy and noise energy into single partial. The single partial contained time-varying frequency, amplitude, noisiness parameters.

  • 159.
    Gasson, J. R.
    et al.
    University of Bergen, Department of Chemistry.
    Carlson, Johan E.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Eide, I.
    Statoil Research Centre, Trondheim.
    Barth, T.
    University of Bergen, Department of Chemistry.
    Extracting homologous series from fingerprint mass spectrometry data of bio-oils: a complement to PCA2012Konferensbidrag (Refereegranskat)
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  • 160.
    Gasson, James R.
    et al.
    Department of Chemistry, University of Bergen.
    Carlson, Johan E.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Eide, Ingvar
    Statoil Research Centre, Trondheim.
    Barth, Tanja
    Department of Chemistry, University of Bergen.
    Deciphering complex bio-oil mass spectra with the help of chemometrics2011Konferensbidrag (Refereegranskat)
  • 161.
    Gasson, James R.
    et al.
    Department of Chemistry, University of Bergen.
    Carlson, Johan E.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Eide, Ingvar
    Statoil Research Centre, Trondheim.
    Barth, Tanja
    Department of Chemistry, University of Bergen.
    Extracting homologous series from fingerprint bio-oil mass spectra: a complement to PCA2012Konferensbidrag (Refereegranskat)
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  • 162.
    Gavrilovska, Liljana M.
    et al.
    Ss. Cyril and Methodius University, Skopje.
    van de Beek, Jaap
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Xie, Yong
    Huawei Technologies, Chengdu.
    Lidström, Erik
    Huawei Technologies, Stockholm.
    Riihijärvi, Janne
    RWTH Aachen University.
    Mähönen, Petri H.
    RWTH Aachen University.
    Atanasovski, Vladimir M.
    Ss. Cyril and Methodius University, Skopje, Faculty of Electrical Engineering, Ss. Cyril and Mehtodius, Skopje.
    Denkovski, Daniel
    Faculty of Electrical Engineering, Ss. Cyril and Mehtodius, Skopje.
    Rakovic, Valentin
    Faculty of Electrical Engineering, Ss. Cyril and Mehtodius, Skopje.
    Enabling LTE in TVWS with radio environment maps: From an architecture design towards a system level prototype2014Ingår i: Computer Communications, ISSN 0140-3664, E-ISSN 1873-703X, Vol. 53, s. 62-72Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper reports recent prototyping efforts that show the feasibility of the radio environmental map to enable efficient exploitation of TV white spaces by a cellular LTE system. We describe a flexible REM backend implementation, fully integrated with standard-compliant operational LTE base station equipment. Simulations results indicate that REMs enhance white-space detection by their means to incorporate accurate and local channel propagation information, while experimental laboratory results illustrate the feasibility and performance of transmitter localization capabilities in a REM.

  • 163. Ge, Hongya
    et al.
    Lundberg, Magnus
    Scharf, Louis L.
    Colorado State University.
    Warp convergence in conjugate gradient Wiener filters2004Ingår i: 2004 IEEE Sensor Array and Multichannel Signal Processing Workshop: 18 - 21 July 2004, Barcelona, Spain, Piscataway, NJ: IEEE Communications Society, 2004, s. 109-113Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this work, we present interesting case studies that lead to new and deeper results on fast convergence of reduced-rank conjugate gradient (RRCG) Wiener filters (WF), for applications in communications and sensor array signal processing. We discover that for signal modes with a specially structured Gram matrix, which induces L groups of distinct eigenvalues in the data covariance matrix, a fast and predictable convergence, in at most L steps, can be achieved when the RRCG WF is used to detect, and/or to focus on, the desired signal mode. For such applications, given knowledge of the repeated eigenstructure of the Gram matrix of signal modes or of the measurement covariance matrix, a RRCG Wiener filter, of at most rank L, delivers the same performance as the full-rank Wiener filter. Typically L is much less than the rank of the Gram matrix.

  • 164. Ge, Hongya
    et al.
    Scharf, L.L.
    Lundberg, Magnus
    Reduced-rank multiuser detectors based on vector and matrix conjugate gradient Wiener filters2004Ingår i: 2004 IEEE 5th Workshop on Signal Processing Advances in Wireless Communications: Lisbon, Portugal, 11 - 14 July, 2004, Piscataway, NJ: IEEE Communications Society, 2004, s. 189-193Konferensbidrag (Refereegranskat)
    Abstract [en]

    Using the notion of expanding subspace and the framework of reduced-rank signal processing, we present our latest discovery on applying the vector and matrix conjugate gradient (CG) methods to design reduced-rank linear MMSE multiuser detectors (MUD) for code division multiple access (CDMA) systems. We show that for a synchronous CDMA system with K users, each using a distinct length N spreading code, the vector CG method converges to the full-rank linear MUD in at most K steps (K≤N).The matrix CG method converges to the full-rank linear MUD in one step. Furthermore, when the Gold codes are used as spreading codes in combination with a groupwise power control scheme, early convergence in the vector CG Wiener filter can be reached in just L steps (L≪K≤N), typically L=2∼4 independent of the user number K and the spreading length N.

  • 165.
    Georgoulas, Georgios
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Karvelis, Petros
    Laboratory of Knowledge and Intelligent Computing, Department of Computer Engineering, Technological Educational Institute of Epirus, Arta.
    Spilka, Jiří
    CIIRC, Czech Technical, University in Prague.
    Chudáček, Václav
    CIIRC, Czech Technical, University in Prague.
    Stylios, Chrysostomos D.
    Laboratory of Knowledge and Intelligent Computing, Department of Computer Engineering, TEI of Epirus, Artas, Kostakioi.
    Lhotská, Lenka
    CIIRC, Czech Technical, University in Prague.
    Investigating pH based evaluation of fetal heart rate (FHR) recordings2017Ingår i: Health and Technology, ISSN 2190-7188, E-ISSN 2190-7196, Vol. 7, nr 2/3, s. 241-254Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Cardiotocography (CTG) is a standard tool for the assessment of fetal well-being during pregnancy and delivery. However, its interpretation is associated with high inter- and intra-observer variability. Since its introduction there have been numerous attempts to develop computerized systems assisting the evaluation of the CTG recording. Nevertheless these systems are still hardly used in a delivery ward. Two main approaches to computerized evaluation are encountered in the literature; the first one emulates existing guidelines, while the second one is more of a data-driven approach using signal processing and computational methods. The latter employs preprocessing, feature extraction/selection and a classifier that discriminates between two or more classes/conditions. These classes are often formed using the umbilical cord artery pH value measured after delivery. In this work an approach to Fetal Heart Rate (FHR) classification using pH is presented that could serve as a benchmark for reporting results on the unique open-access CTU-UHB CTG database, the largest and the only freely available database of this kind. The overall results using a very small number of features and a Least Squares Support Vector Machine (LS-SVM) classifier, are in accordance to the ones encountered in the literature and outperform the results of a baseline classification scheme proving the utility of using advanced data processing methods. Therefore the achieved results can be used as a benchmark for future research involving more informative features and/or better classification algorithms.

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  • 166. Grennberg, Anders
    Measuring subsample time delay differences in narrowband ultrasonic echoes1994Ingår i: Norsig 94: Nordic Signal Processing Symposium ; Ålesund, Norway, June 2 - June 4 1994 / [ed] John M. Leirvik; Anders Wahlin, Trondheim: Norsk forening for signalbehandling , 1994, s. 290-293Konferensbidrag (Refereegranskat)
    Abstract [en]

    In many areas the time delay of arrival (TDOA) is desired. In the case of narrowband signals we us a new fast and simple method to estimate small time delays. This method has good accuracy for delays on the order of fractions of the sample interval. It is based on forming the scalar product of the signal and its Hilbert transform. The method can be applied to narrowband signals where the measurements are repeatable, such as ultrasonic imaging. In ultrasonic applications, due to fluctuations in the insonified media, especially in the air, a small random time shift may be present. By placing a wire at a fixed distance from the transducer, so small that it does not disturb the main echo from the surface but still gives a reference echo strong enough to use our method, we make corrections to the arrival time of the main echo.

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  • 167. Grennberg, Anders
    et al.
    Almquist, Lars-Olof
    Lunds universitet.
    Holmner, Nils-Gunnar
    Lunds universitet.
    Olsson, Lennart
    Luleå tekniska universitet.
    Secondary sound classification for the assessment of focus positioning in shock-wave lithotripsy1993Ingår i: IX Nordic Meeting on Medical and Biological Engineering: abstracts ; regional meeting of the IFMBE., Lund: Medicinsk Teknik , 1993Konferensbidrag (Övrigt vetenskapligt)
    Abstract [en]

    A problem encountered when using acoustic shock-waves for kidney stone disintegration is that the positioning of the focus relative to a stone, for the best possible fragmenting effect, is crtitical. The standard methods for focus positioning are ultrasound or x-ray imaging. These methods are, however, not always sufficient and a better indication of a well positioned focus would be valuable. The secondary sound emitted as a result of each shock-wave has been found to contain valuable information. A skilled operator is able to hear from the timbre of these sound pulses when the positioning of the focus is adequate. A method for the automatic evaluation of secondary sounds, using a computer, is developed in this work.

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  • 168. Grennberg, Anders
    et al.
    Sandell, Magnus
    Luleå tekniska universitet.
    Estimation of subsample time delay differences in narrowband ultrasonic echoes using the Hilbert correlation1994Rapport (Övrigt vetenskapligt)
    Abstract [en]

    In many areas the time delay of arrival (TDOA) is desired. Conventional estimators usually have the property of breaking down for low SNR. In the case of narrowbanded signals we propose a fast and simple method to estimate the small time delays. The method is shown to have the same accuracy as conventional methods for small delays and high SNR while it performs better for low SNR. It is based on using the Hilbert transform in correlation between two signals. Apart from using it for better resolution in TDOA, it may also be used in applications with narrowbanded signals where the measurements are repeatable, such as ultrasonic imaging and ECG. In ultrasonic applications, due to fluctuations in the insonified media, a small random time shift may be present causing the signals to be misaligned in time. Averaging signals under these conditions will result in a distortion of the signal shape. We propose an averaging method to avoid this and to accomplish a higher SNR without the distortion. Simulations and experiments from ultrasonic applications are presented.

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  • 169. Grennberg, Anders
    et al.
    Sandell, Magnus
    Luleå tekniska universitet.
    Estimation of subsample time delay differences in narrowband ultrasonic echoes using the Hilbert transform correlation1994Ingår i: IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, ISSN 0885-3010, E-ISSN 1525-8955, Vol. 41, nr 5, s. 588-595Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In many areas the time delay of arrival (TDOA) is desired. In the case of narrowband signals we propose a fast and simple method to estimate small time delays. This method is shown to have the same or better accuracy as the cross correlation methods for small delays in the order of fractions of the sample interval. It is based on using the Hilbert transform in correlation between two signals and consists of only one scalar product, which makes it fast. It may also be used in applications with narrowband signals where the measurements are repeatable, such as ultrasonic imaging and nondestructive testing. In ultrasonic applications, due to fluctuations in the insonified media, a small random time shift may be present causing the signals to be misaligned in time. Averaging signals under these conditions will result in a distortion of the signal shape. We propose an averaging method to avoid this and to accomplish a higher SNR without the distortion. Simulations and experiments from ultrasonic applications are presented.

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  • 170. Grennberg, Anders
    et al.
    Sandell, Magnus
    Luleå tekniska universitet.
    Experimental determination of the single point echo of an ultrasonic transducer using a tomographic approach1992Ingår i: Proceedings of the Annual International Conference of the IEEE Engineering in Medicine and Biology Society: Paris, France, October 29-November 1, 1992, Piscataway, NJ: IEEE Communications Society, 1992, Vol. 5, s. 2151-2152Konferensbidrag (Refereegranskat)
    Abstract [en]

    The impulse response method is often used to study the ultrasonic field radiated by planar or gently curved transducers. This, however, requires one transmitting and one receiving transducer which has to be placed with great accuracy in the ultrasonic field. Here we propose a measuring method with only one transducer which acts both as transmitter and receiver. Echoes from sliding halfplanes are registered and by using tomographic methods, the echo from a single point in the same plane as the halfplanes can then be calculated. Beside the ultrasonic field, these calculations will yield us the transducer's characteristics. These can be used to extract further information from an echo of an arbitrary surface, such as the gradient of the surface

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  • 171.
    Grennberg, Anders
    et al.
    Luleå tekniska universitet.
    Sandell, Magnus
    Luleå tekniska universitet.
    Experimental determination of the ultrasonic echo from a pointlike reflector using a tomographic approach1992Ingår i: Proceedings: IEEE 1992 Ultrasonics Symposium ; October 20 - 23, 1992, Holiday Inn Broadway, Tucson, Arizona / [ed] Bruce R. McAvoy, Piscataway, NJ: IEEE Communications Society, 1992, Vol. 2, s. 639-642Konferensbidrag (Refereegranskat)
    Abstract [en]

    One important parameter for an ultrasonic transducer is the echo it yields from a pointlike reflector. It can be measured directly but there are however certain problems connected with this. This reflector must have such a size that it can be considered a point, which results in a very weak echo and consequently a low SNR. We propose an alternative method to calculate the echo from a pointlike reflector by measuring the echoes from sliding halfplanes. Using a tomographic way of reasoning, we can calculate the single point echo from these measurements. Our approach was to find basis functions that are suitable for the inversion of the measurements. These basis functions depend on which norm and weight function you choose. Numerical solutions are given for chosen weight functions and the inversion is shown for the measurements.

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  • 172.
    Gupta, Payal
    et al.
    Centre of Applied Research in Electronics, Indian Institute of Technology, New Delhi, India.
    Agrawal, Monika
    Centre of Applied Research in Electronics, Indian Institute of Technology, New Delhi, India.
    Improved resolving capabilities of linear array using 2 q th order non‐circular statistics2021Ingår i: IET Signal Processing, ISSN 1751-9675, E-ISSN 1751-9683, Vol. 15, nr 2, s. 61-79Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Resolving more sources than sensors is always of interest to researchers. For this purpose, generation of the virtual array from the non-uniform linear array has recently gathered a lot of attention. The covariance/cumulant lags of the array output define virtual sensors and thereby virtual array. The aperture of the designed virtual array is much more than the aperture of physical array. This large aperture provides highest degrees of freedom to solve the underdetermined system. In the case of non-circular signals, pseudo-covariances/cumulants are significant, and this additional information can further be used to increase the virtual array aperture. Herein, a framework is proposed to extend the virtual array aperture by additionally using pseudo-/non-circular cumulants along with the circular cumulants of the array output for non-circular signals. The suggested framework not only increases the resolvability but also improves the DoA estimation accuracy. With fourth-order statistics, the virtual array aperture becomes almost double, and the increment is much more with further higher order statistics. Numerical simulations demonstrate the efficacy of the claims.

  • 173.
    Gupta, Payal
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Carlson, Johan E.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Deep Learning for Modeling of Sound Pressure Fields of Real-World Ultrasound Transducers2022Ingår i: 2022 IEEE International Ultrasonics Symposium (IUS), IEEE, 2022Konferensbidrag (Refereegranskat)
    Abstract [en]

    There are several freely available toolboxes for modeling the sound pressure field of ultrasound transducers and transducer arrays (e.g., Field II, k-Wave, and DREAM, etc.). These model the beam patterns, or how the ultrasound pulse changes depending on where we observe it, i.e., they model the spatial impulse response of the transducers. Normally, the transmitted pulse is not modeled using these toolboxes, but instead it is assumed that this pulse shape is known. Also, the models are based on assumption of an ideal behavior of the transducers, which is not necessarily the case for a real-world transducers. As a consequence, fitting these models to real measurement data, in order for them to mimic the individual transducer available in the lab, is not generally not possible with any numerical accuracy. In this paper we show, instead, how a deep learning approach can be adopted to train a model that with numerical accuracy models an transducer individual. We compare the proposed technique with real measurements and models using the Field II toolbox and show that for the actual transducer at hand, the deep learning approach outperforms the results from Field II.

  • 174.
    Gustavsson, Jan-Olof
    Luleå tekniska universitet.
    Analysis of receivers based on a generalized matched filter in non-gaussian noise environments1997Rapport (Övrigt vetenskapligt)
  • 175.
    Gustavsson, Jan-Olof
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Estimation in non-gaussian noise and classification of welding signals1991Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
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  • 176.
    Gustavsson, Jan-Olof
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Project work for course in median and morphological filtering in signal and image processing1990Rapport (Övrigt vetenskapligt)
  • 177.
    Gustavsson, Jan-Olof
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Börjesson, Per Ola
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    A generalized matched filter1991Rapport (Övrigt vetenskapligt)
  • 178. Gustavsson, Jan-Olof
    et al.
    Börjesson, Per Ola
    Luleå tekniska universitet.
    A simultaneous maximum likelihood estimator based on a generalized matched filter1994Ingår i: ICASSP-94: 1994 IEEE International Conference on Acoustics, Speech and Signal Processing, April 19 - 22, 1994, Adelaide Convention Centre, Adelaide, South Australia; [proceedings], Piscataway, NJ: IEEE Communications Society, 1994, Vol. 4, s. 481-484Konferensbidrag (Refereegranskat)
    Abstract [en]

    The paper discusses parameter estimation and detection in Laplace distributed noise. The received signal is modeled as r(·)=As(·,&thetas;)+n(·), where A is an unknown amplitude, &thetas; is the parameter vector to be estimated and n(·) is independent Laplace distributed noise. The simultaneous maximum likelihood estimator of (A,&thetas;) is derived. The derived estimator is based on a combination of a weighted median filter [Astola and Nuevo, 1992] and a generalized form of the ordinary matched filter [Gustavsson and Borjesson, 1992]. Examples of performance for four different detectors are given for a case of binary detection, when the amplitude A or the signal shape s(·,&thetas;) are varied. Simulations indicate that the performance of detectors based on the generalized matched filter is not particularly dependent on either the estimate of the amplitude A or the signal shape

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  • 179.
    Gustavsson, Jan-Olof
    et al.
    Luleå tekniska universitet.
    Börjesson, Per-Ola
    Luleå tekniska universitet.
    A generalized matched filter1992Ingår i: International Symposium on Signal Processing and Its Applications: proceedings, August 16-21, 1992, ANA Hotal, Gold Coast, Queensland, Australia / [ed] D. Gray, Edgecliff, N.S.W, 1992, s. 16-22Konferensbidrag (Refereegranskat)
    Abstract [en]

    Parameter estimation in additive independent identically distributed noise is treated. It is shown that there exists a generalized form of the matched filter which can be used for an arbitrary noise distribution to make e.g. ML-, MAP- or MMSE-estimates of a parameter vector. Simulations are presented to illustrate the performance.

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  • 180.
    Gustavsson, Jan-Olov
    Luleå tekniska universitet.
    Detection of signals corrupted by non-gaussian disturbances1997Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The detection of signals in additive, non-Gaussian disturbances is the main theme of this thesis. The disturbances are modeled either by non-Gaussian noise or by Gaussian noise in combination with intersymbol or co-channel interference. The maximum likelihood (ML) approach is adopted in the design of receivers, which leads to a generalized form of the conventional matched filter. The most prominent feature of the resulting ML receivers is that the multipliers of the conventional matched filter are replaced by non-linearities. Receiver performance is found to be mainly governed by the characteristics of the non-linearities and the amount of impulsive noise in the observed signal. The performance is not very sensitive to mismatch in the receiver design parameters, although the choice of these parameter values becomes more critical as the noise becomes more impulsive. Furthermore, receiver performance appears to be strongly dependent on the signal shape, especially in impulsive noise. A simultaneous ML detector and channel estimator is derived for noise characterized by the Laplacian or the uniform distributions. For uniform noise it is found that the ML receiver is not unique due to the special character of this noise distribution. Therefore, the effect of different channel estimators and decision rules are studied and it is found that the performance is sensitive to how these are chosen. A novel ML receiver structure is presented for the case when the disturbance consists of Gaussian noise in combination with either co-channel interference (CCI) in multiuser systems or intersymbol interference (ISI) in time-dispersive communication systems. The relation of detection problems in CCI systems to detection problems in ISI systems is considered, as is the relation of their corresponding receivers. Moreover, this new receiver structure illustrates the relationship between the ML receiver and three other commonly recognized receivers. The final part ot the thesis deals with the problem of arrival time estimation of narrowband signals in Gaussian noise. The minimum-mean square eror (MMSE) estimator is investigated and its performance is compared to that of the maximum a posteriori (MAP) estimator. The performance of the estimators is demonstrated by some examples of three-dimensional ultrasonic imaging.

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  • 181. Gustavsson, J-O
    et al.
    Nordebo, S.
    Börjesson, Per Ola
    Luleå tekniska universitet.
    Simultaneous channel and symbol maximum likelihood estimation in Laplacian noise1998Ingår i: ICSP' 98: 1998 Fourth International Conference on Signal Processing : October 12-16, 1998, Beijing, China / [ed] Yuan Baozong; Tang Xiaofang, Piscataway, NJ: IEEE Communications Society, 1998, s. 81-84Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper treats channel estimation and signal detection in Laplacian noise. The received signal is assumed to be a transmitted signal which has been corrupted by an unknown channel, modeled as a FIR filter, the output being further disturbed by additive independent Laplacian noise. The transmitted signal is assumed to depend on an unknown parameter belonging to a known finite set. The simultaneous maximum likelihood (ML) estimator of the unknown parameter, as well as of the FIR filter coefficients, is derived. The ML estimate of the channel can be obtained by using a linear programming approach and the decision about the parameter is based on the output from a set of generalized matched filters. Simulation results are included in order to illustrate the performance of the proposed receivers

  • 182.
    Gutierrez Ballesteros, Elena
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Rönnberg, Sarah
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Energivetenskap.
    Gil-de-Castro, Aurora
    Departamento de Ingeniería Electrónica y de Computadores, Universidad de Córdoba, Córdoba, Spain.
    Spectrum Analysis Of Transients Using The Short-Time Fourier Transform2021Ingår i: CIRED 2021 - The 26th International Conference and Exhibition on Electricity Distribution, Institution of Engineering and Technology, 2021, s. 663-667, artikel-id 0049Konferensbidrag (Refereegranskat)
    Abstract [en]

    The aim of this paper is to analyse the spectrum of real transients from a LV network. The spectrum is obtained using the Short-Time Fourier Transform (STFT). The MATLAB function spectrogram is used to obtain the STFT. The STFT is tested with different configurations and applied to several waveforms lengths. Forty transients have been recorded from random devices in an apartment in south Spain. The transients are mostly notches or with minor oscillations. Thirty-three transients with an oscillatory characteristic have been recorded from an induction stove, as well as an oscillatory transient from a PV panel. The spectrum of these transients has been obtained using the STFT and analysed.

  • 183.
    Hanquist, Carl-Henrik
    Luleå tekniska universitet, Institutionen för system- och rymdteknik.
    Airborne Radar Ground Clutter Suppression Using Multitaper Spectrum Estimation & Choosing DPSS Parameters2018Självständigt arbete på avancerad nivå (yrkesexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [sv]

    En av de största utmaningarna i ett flygburet radarsystem är att urskilja ett mål från markekot. Problem uppstår eftersom markekot, kallat markklotter, kan vara upp emot en miljon gånger starkare än svaret från målet i fråga. I dagsläget används flera olika filtreringmetoder i flyburna radarsystem för att urskilja målet från markklottret, alla har sina fördelar och nackdelar. I en ideal värld skulle det optimala filtret filtrera ut markklottret fullständigt och endast bevara målsignalen. Eftersom dessa filter inte existerar i verkligheten eftersträvas istället ett filter med låga sidlober och minimal förlust i signal-till-interferens ration. En typ av filter som uppvisar detta beteende är diskreta prolata sfäroid sekvenser (DPSS).

    Denna uppsats undersöker ifall DPSS kan användas som viktfunktioner i multitaper spektralestimering för att filtrera ut markklotter i en radarsignal. En enkel klottermodell utvecklades för generering av simulerat markklotter som sedan filtrerades ut med multitaper metoden och en traditionell metod. Resultatet visade att det var möjligt att använda DPSS i multitaper spektralestimering och att metodens prestanda överstiger den traditionella meteoden, så länge parametrar som bandbredd och antal använda sekvenser väljs korrekt. Prestandaförbättringen mot den traditionella metoden uppstår mot en kostnad i beräkningstid som ökar med varje DPSS ordning som används.

    Ett full factorial experiment utfördes också för att undersöka vilka parametrar som hade störst påverkan för att maximera förbättringsfaktorn och minsta detekterbara hastighet. Resultated visade att låg bandbredd vid generering av DPSS var att föredra, samt att ett stort antal använda DPSS och tidssamples ökade prestandan. Resultaten visade också att för ett ökat antal tisdssamples så måste bandbredd och antal sekvenser som används justeras för att bibehålla samma nivå av förbättringsfaktorn.

    Slutligen rekommenderades det att framtida arbete borde fokusera på validering med mer avancerade klottermodeller och MTI filter i simuleringar, samt validering mot verklig radar data. Om detta visar sig framgångsrikt bör optimering av beräkningstid och implementation av ett adaptivt val av DPSS bandbredd göras före implementering i ett radarsystem.

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  • 184.
    Hansson Lagerberg, Joel
    Luleå tekniska universitet, Institutionen för konst, kommunikation och lärande.
    The Impact of the Difference Signal on the Perceived Loudness of a Piece of Stereo Rock Music: A Comparison Between Headphones and Loudspeakers2019Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    The purpose of this study was to evaluate how the BS.1770 Loudness Standard is affected by the amount of difference signal present in the signal being measured, and if this affection is different between the two playback systems Headphones and Loudspeakers. The study was restricted to rock music productions in a stereo format. The results obtained from the study might provide useful information to mixing and mastering engineers, as it evaluates the correlation between spatial information and subjective loudness. The study consisted of an active listening test, containing six stimuli with different Sum and Difference Ratio (SDR). The test was done in both headphones and loudspeakers, and the difference in volume as set by the subjects were noted. The results from the headphone version and the loudspeaker version were then compared in a paired t-test to see if there was a significant difference between the two formats. The results pointed to the factors of Playback System and SDR to have non- significant effect on the results. After analyzing the possible error sources, it became apparent that other factors had a far greater effect on the results. The results imply that the BS.1770 Loudness Standard can accurately measure the loudness of a given stereo rock music material, despite the fact that it does not consider the differences between the channels when conducting the measurement. Whether or not the effect being studied is significant in other conditions is not verified, due to the restrictions of the study. Further studies would be needed in order to verify the findings of this study, preferably with more attention to detail since there were apparent flaws in the method used.

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  • 185.
    Henkel, Werner
    et al.
    School of Engineering and Science, Jacobs University Bremen, 28759 Bremen, Germany.
    Hassan, Khaled
    School of Engineering and Science, Jacobs University Bremen, 28759 Bremen, Germany.
    von Deetzen, Neele
    Silver Atena Electronic Systems Engineering GmbH, Hamburg, Germany.
    Sandberg, Sara
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Sassatelli, Lucile
    University of Nice, Sophia-Antipolis, BP 2135, 06103 Nice, France.
    Declercq, David
    ETIS ENSEA/UCP/CNRS, 95014 Cergy-Pontoise, France.
    UEP concepts in modulation and coding2010Ingår i: Advances in Multimedia, ISSN 1687-5680, E-ISSN 1687-5699, Vol. 2010Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    First unequal error protection (UEP) proposals date back to the 1960's (Masnick and Wolf; 1967), but now with the introduction of scalable video, UEP develops to a key concept for the transport of multimedia data. The paper presents an overview of some new approaches realizing UEP properties in physical transport, especially multicarrier modulation, or with LDPC and Turbo codes. For multicarrier modulation, UEP bit-loading together with hierarchical modulation is described allowing for an arbitrary number of classes, arbitrary SNR margins between the classes, and arbitrary number of bits per class. In Turbo coding, pruning, as a counterpart of puncturing is presented for flexible bit-rate adaptations, including tables with optimized pruning patterns. Bit- and/or check-irregular LDPC codes may be designed to provide UEP to its code bits. However, irregular degree distributions alone do not ensure UEP, and other necessary properties of the parity-check matrix for providing UEP are also pointed out. Pruning is also the means for constructing variable-rate LDPC codes for UEP, especially controlling the check-node profile.

  • 186.
    Holmström, Caroline
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Modeling and Compensation of Nonlinear Distortion in High Efficient Electrodynamic Loudspeakers2020Självständigt arbete på avancerad nivå (yrkesexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Loudspeakers transform electrical energy into acoustic waves but most of the electrical energy is lost as heat. It is possible to increase the electro-acoustic efficiency by changing the electrical, mechanical or acoustical design of the loudspeaker but with these changes come unwanted side effects. An efficient loudspeaker exhibits strongly nonlinear behavior, but the nonlinear effects can be reduced by the means of implementing an algorithm on a digital signal processor. This is of great interest for Axis Communications since it makes it possible to increase the efficiency in their products without loss of sound quality.

    The purpose of this thesis was to investigate nonlinear distortion in high efficient electrodynamic loudspeakers using a simulation software, COMSOL Multiphysics, and to model the nonlinear response of the loudspeaker behavior. The simulations were conducted in order to get an understanding of the nonlinear behavior but also to estimate data for the theoretical model. Further, a nonlinear model describing the voice coil excursion was investigated with the purpose of constructing a nonlinear filter able to reduce nonlinear distortion.

    The result of the simulation showed it was possible to estimate the force factor as a function of voice coil displacement and that it also should be possible, according to the magnetic fields and streamlines, to obtain the function that describes the voice coil inductance from the same simulation of the loudspeaker. The numerical implementation of the voice coil excursion showed the voice coil was operating in the wrong domain when it was driven with a real input signal. Hence, the Volterra series need further work before a nonlinear filter can be derived.

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  • 187.
    Hoseinie, Hadi
    et al.
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Ghodrati, Behzad
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Galar, Diego
    Luleå tekniska universitet, Institutionen för samhällsbyggnad och naturresurser, Drift, underhåll och akustik.
    Juuso, Esko
    University of Oulu, Control Engineering Group, Faculty of Technology, University of Oulu.
    Optimal Preventive Maintenance Planning for Water Spray System of Drum Shearer2015Ingår i: IFAC-PapersOnLine, E-ISSN 2405-8963, Vol. 48, nr 17, s. 166-170Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Water spray system is one of the most important parts of rock cutting machines, especially the drum shearer. Field data shows that the maintenance of this system is time-consuming and causes major downtimes in the coal mines’ production process. Therefore, it is essential to find an optimum preventive maintenance task and intervals, to reduce the downtime and minimize the associated costs of the machine. In this paper, in order to suggest an optimum preventive maintenance plan, a parametric failure and reliability analysis was done on available data from an Iranian longwall coal mine over the two years. A reliability-based cost modelling was implemented to identify the optimum maintenance interval and frequencies of restoration for the water spray system. In the study, a cost rate function was introduced in which an as-good-as-new effectiveness for restoration actions is considered. The results of the analysis showed that the minimum maintenance cost per unit of time for the studied machine, $19.54/hour, will be achieved within a range of intervals i.e. T=136 hours to T=142 hours.

  • 188.
    Hostettler, Roland
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik.
    Birk, Wolfgang
    Nordenvaad, Magnus Lundberg
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Feasibility of road vibrations-based vehicle property sensing2010Ingår i: IET Intelligent Transport Systems, ISSN 1751-956X, E-ISSN 1751-9578, Vol. 4, nr 4, s. 356-364Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This article discusses a novel approach to vehicle property sensing based on traffic-induced road surface vibrations and investigates the feasibility of this approach. Road surface vibrations from real-life experiments are acquired using three-axis accelerometers and the data are analysed. Based on the assessment of the data, a first coarse scheme for axle detection of passing vehicles is developed. The scheme is then evaluated using measurement data from a highway with moderate traffic intensity but diverse traffic. It is found that the proposed approach is feasible and the estimation scheme yields promising results. Furthermore, delimitations, encountered problems and identified research challenges are discussed and future research directions are given.

  • 189. Hostettler, Roland
    et al.
    Birk, Wolfgang
    Luleå tekniska universitet, Institutionen för system- och rymdteknik.
    Nordenvaad, Magnus Lundberg
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Surface mounted vehicle property sensing for cooperative vehicle infrastructure systems2009Ingår i: 16th World Congress and Exhibition on Intelligent Transport Systems 2009: 16th ITS World Congress ; Stockholm, Sweden, 21 - 25 September 2009, Red Hook: Curran Associates, Inc., 2009Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper presents first results for vehicle detection and vehicle property estimation based on the assessment of traffic induced vibrations in the road surface. A surface mounted 3D accelerometer device is used to register the vibrations in the surface. Acquired data from experiments on roads are used to design methods that are able to detect vehicle passages, estimate the number of axles of a vehicle and also deduce the wheel-base for passenger cars. Evaluation of the methods indicate that the accelerometer based approach is feasible and should be further developed in order to deduce vehicle properties like vehicle speed and distance to sensing device from one device. Moreover, results for the vehicle detection on real-life traffic data from the E4 in northern Sweden are summarized.

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  • 190.
    Hostettler, Roland
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nordenvaad, Magnus Lundberg
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Birk, Wolfgang
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    A system identification approach to modeling of wave propagation in pavements2012Ingår i: 16th IFAC Symposium on System Identification, IFAC, International Federation of Automatic Control , 2012, s. 292-297Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, modeling of the pavement as a wave propagation medium and estimation of the corresponding model parameters is approached from a system identification perspective. A model based on the physical background is proposed and the corresponding parameters are then estimated from measurement data. In order to achieve the latter, two estimators are proposed, their performance evaluated, and then applied to the measurement data. It is found that the proposed methods are applicable and the results show that different eigenmodes of the structure are excited.

  • 191.
    Hui, Dennis
    et al.
    Ericsson Res, Santa Clara, CA 95054 USA.
    Sandberg, Sara
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system. Ericsson Res, Lulea, Sweden.
    Blankenship, Yufei
    Ericsson, Chicago, IL USA.
    Andersson, Mattias
    Ericsson Res, Stockholm, Sweden.
    Grosjean, Leefke
    Ericsson Res, Stockholm, Sweden.
    Channel Coding in 5G New Radio: A Tutorial Overview and Performance Comparison with 4G LTE2018Ingår i: IEEE Vehicular Technology Magazine, ISSN 1556-6072, E-ISSN 1556-6080, Vol. 13, nr 4, s. 60-69, artikel-id 8477009Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Fifth-generation (5G) new radio (NR) holds promise in fulfilling new communication requirements that enable ubiquitous, low-latency, high-speed, and high-reliability connections among mobile devices. Compared to fourth-generation (4G) long-Term evolution (LTE), new error-correcting codes have been introduced in 5G NR for both data and control channels. In this article, the specific low-density parity-check (LDPC) codes and polar codes adopted by the 5G NR standard are described. The purpose of each key component in these codes and the associated operations are explained. Performance and implementation advantages of these new codes are compared with those of 4G LTE.

  • 192.
    Hägglund, Fredrik
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Tools for ultrasonic characterization of layered media2007Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Many industries are dealing with composite materials and multi-layered structures of various materials. Errors in the manufacturing process may lead to defects in the final product, and hence, avoiding imperfections is crucial. The importance of repeated quality assurance online is therefore essential during the process. For quality assurance the industry needs accurate and cost-effective diagnostic methods. Ultrasonic measurement techniques are familiar to most people from their medical applications, such as looking for the fetus in the mother's womb or imaging tissue anomalies in order to detect e.g. tumours. However, applications for ultrasound are widely used in the industry today, as a nondestructive evaluation technique for many different media. In the aircraft industry for example, components are inspected before they are assembled into the aircraft and also periodically inspected throughout their useful life, by using for example ultrasonic techniques. Ultrasonic inspection is extensively used to locate tiny cracks and to measure the thickness of the aircraft skin from the outside. The objectives of this thesis is to address the advancement of methods for ultrasonic characterization of layered media. The research problem addressed is stated as: How can methods for Nondestructive Evaluation of layered media using ultrasound be developed or improved? To easier approach this question it can be divided into smaller parts which are addressed separately and in combinations. The approach to answer the research question and the project objectives is chosen to be in the field of ultrasound, because of its superior penetrating properties in solid materials. When using ultrasound and ultrasonic measurement techniques we are restricted to measure frequency dependent phase velocity and attenuation. However, these properties can be used to calculate material properties of interest in the investigated medium. The focus of the work in this thesis is on the development of a parametric model for multi-layered materials. The model is used to describe ultrasonic signals reflected from a multi-layered structure in a successive way. Results show that the proposed model can be used to deal with the research problem in this thesis. The thesis is divided into two parts. The first part contains an introduction to the research area together with a summary of thecontributions, and the second part is a collection of four papers describing the research.

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  • 193. Hägglund, Fredrik
    et al.
    Carlson, Johan E.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Andersson, Tobias
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Ultrasonic classification of thin layers within multi-layered structures2010Ingår i: Measurement science and technology, ISSN 0957-0233, E-ISSN 1361-6501, Vol. 21, nr 1Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Methods for non-destructive inspection of layered materials are becoming more and more popular as a way of assuring product integrity and quality. In this paper, we present a model-based technique using ultrasonic measurements for classification of thin bonding layers within three-layered materials. This could be, for example, an adhesive bond between two thin plates, where the integrity of the bonding layer needs to be evaluated. The method is based on a model of the wave propagation of pulse-echo ultrasound that first reduces the measured data to a few parameters for each measured point. The model parameters are then fed into a statistical classifier that assigns the bonding layer to one of a set of predefined classes. In this paper, two glass plates are bonded together with construction silicone, and the classifiers are trained to determine if the bonding layer is intact or if it contains regions of air or water. Two different classification methods are evaluated: nominal logistic regression and discriminant analysis. The former is slightly more computationally demanding but, as the results show, it performs better when the model parameters cannot be assumed to belong to a multivariate Gaussian distribution. The performance of the classifiers is evaluated using both simulations and real measurements.

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  • 194. Hägglund, Fredrik
    et al.
    Martinsson, Jesper
    Carlson, Johan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Flaw detection in layered media based on parametric modeling of overlapping ultrasonic echoes2006Ingår i: Proceedings: 2006 IEEE Ultrasonics Symposium : Vancouver, Canada, 3 - 6 October 2006, Piscataway, NJ: IEEE Communications Society, 2006, s. 136-139Konferensbidrag (Refereegranskat)
    Abstract [en]

    In materials consisting of several thin layers, multiple reflections within the structure give rise to received ultrasonic signals composed of overlapping echoes. In this paper we present a parametric model that can be used to decompose such signals into the individual reflections. We derive a Maximum Likelihood Estimator for the the model parameters, which are then used in a Generalized Likelihood Ratio Test (GLRT) to detect flaws in multi-layered structures. We show with simulations how the presence of a thin bonding layer in a three-layer structure can be detected. The probability of detection is shown to be ≈ 96%, for a signal-to-noise ratio (SNR) of 15 dB and a probability of false alarm of 5%.

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  • 195. Hägglund, Fredrik
    et al.
    Martinsson, Jesper
    Carlson, Johan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Carlander, Carl
    D-Flow Technology AB.
    Model-based characterization of thin layers using pulse-echo ultrasound2008Ingår i: Proceedings of the International Congress on Ultrasonics: Vienna, April 9-13, 2007, Paper ID 1562, Session R17, 2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    Measurements performed on a thin multilayered structure will imply a received signal waveform consisting of reverberant overlapping echoes. In this paper the multi-layered structure is modeled by a physical model and the Maximum Likelihood Estimator (MLE) is derived for the model parameters. A general recursive expression for the model is given. The model is evaluated using measurements on a thin three-layered structure, where two glass layers are bonded together. We show that measured signal waveforms can be reconstructed using the estimated parameters, and that physical properties can be extracted from the estimated model parameters. Simulations also show that physical parameters can be estimated for thicknesses of the bonding layer down to 50 μm for a wavelength of 200 μm of the ultrasonic pulse.

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  • 196. Hägglund, Fredrik
    et al.
    Martinsson, Jesper
    Carlson, Johan E.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Model-based classification of thin layers in multi-layered materials using nondestructive ultrasonic testing2008Ingår i: Paper summaries CD-ROM, ASNT fall conference & quality testing show 2008: Charleston, SC, November 10 - 14, 2008, Columbus, Ohio: American Society for Nondestructive Testing , 2008, s. 213-220Konferensbidrag (Refereegranskat)
  • 197. Hägglund, Fredrik
    et al.
    Martinsson, Jesper
    LKAB, Research & Development, 983 81 Malmberget.
    Carlson, Johan E.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Model-based estimation of thin multi-layered media using ultrasonic measurements2009Ingår i: IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, ISSN 0885-3010, E-ISSN 1525-8955, Vol. 56, nr 8, s. 1689-1702Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In ultrasonic measurement situations, when dealing with media of multi-layered structures consisting of 1 or more thin layers, analysis of the measured ultrasonic waveform can be difficult because of overlapping and reverberant echoes. Information from the individual layers is then difficult to extract because the individual echoes cannot be detected. In this study, we use a parametric layer model to analyze the multi-layered material in a system identification approach. The parameters of the model are connected to physical properties of the investigated material, e.g., the reflection coefficients, the time-of-flight, and the attenuation. The main advantage using this model is that the complexity of the model is connected to the number of layers rather than the number of observable echoes in the received ultrasonic waveform. A system of linear equations is presented, giving the opportunity to find the model for both pulse-echo and through-transmission measurements. A thorough effort is made on the parameter estimation and optimization algorithm. The model is validated with practical measurements on a 3-layered structure using both pulse-echo and through-transmission techniques. The 3-layered material consists of a thin embedded middle layer with the time-of-flight in that layer shorter than the emitted signal¿s time support, giving rise to overlapping echoes. Finally the relation between the model parameters and physical properties of the material is established.

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  • 198. Hägglund, Fredrik
    et al.
    Martinsson, Jesper
    Carlson, Johan E.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Ultrasonic imaging of thin layers within multi-layered structures2008Ingår i: 2008 IEEE International Ultrasonics Symposium: IUS ; Beijing, China, 2 - 5 November 2008, New York: IEEE Communications Society, 2008, s. 828-831Konferensbidrag (Refereegranskat)
    Abstract [en]

    In the area of process control, non-destructive testing (NDT) using ultrasound is valuable due to its noninvasive properties. In process control, imaging of surface profiles is used to locate defects or problematic areas in order to quickly steer the manufacturing process on track again. This paper presents a method for imaging of parallel thin layers within multi-layered structures. Due to the application in process control a parametric model is used, and all subsequent analysis is performed on the model parameters rather than on the signal waveforms, resulting in a necessary data reduction. The parameters in the model are directly connected to physical properties, such as the reflection coefficients, time-of-flights, and attenuation coefficients. Experimental results shows that the estimated model parameters can be used in imaging of thin layer properties within the material structure. Images of embedded layers with a thickness about the wavelength is shown. Result also show that flaws can be detected in such structures. The results are verified by comparing the images to visual inspections of photographs.

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  • 199.
    Hägglund, Kristoffer
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Symmetric alpha-Stable Adapted Demodulation and Parameter Estimation2018Självständigt arbete på avancerad nivå (yrkesexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Transmission and reception of signals in wireless communication systems is affected by additive interference corrupting the signal. Traditionally, the interference is assumed to be AWGN and the system designs are usually based on that assumption. Modern military platforms consists of many electrical components and systems and as such the noise affecting the signals is often a product of interference between the components and systems. This type of noise tend to be very impulsive in nature. The standard AWGN model is not suited for impulsive noise which leaves an opportunity to investigate the performance of a demodulation scheme adapted to the current interference environment in order to increase the performance gain. To properly analyze the performance of an interference-adapted demodulator, knowledge about the characteristic parameters of the chosen noise model is required to perform the necessary calculations. 

    This project combines the aspect of adaptive demodulation with parameter estimation evaluation. Four different parameter estimation techniques specifically customized for Symmetric alpha-Stable distributed noise were implemented and examined. The four methods were the Empirical Characteristic Function (ECF) method, Fractional Lower-Order Moments (FLOM) method, Extreme-Order Statistics (EOS) method as well as the Quantiles method. The effectiveness and performance of the methods were investigated in two Symmetric alpha-Stable processes of varying level of impulsiveness as well as two Class A processes in order to monitor the performance in noise not specifically distributed according to the intended model, functioning as an arbitrary representation of non-Gaussian interference. The results were evaluated using the measure of Kullback-Leibler Divergence. The demodulator was designed for Symmetric alpha-Stable distributed noise and implemented using an LLR-algorithm. The simulations were performed using an LDPC-coding protocol and the experiment was conducted in both Class A and Symmetric alpha-Stable distributed noise. The modulation schemes were 4-QAM and BPSK.

    The simulations showed that ECF was the most consistent parameter estimation method overall, regardless of distribution model or number of available samples. FLOM performed well in alpha-Stable noise but struggled in Class A processes. EOS and Quantiles shared the struggles of fewer available samples.

    The experiments show that an alpha-Stable adapted demodulator coupled with a parameter estimation technique based on the empirical characteristic function (ECF) is a very competitive and viable option in impulsive interference environments regardless of the origin of the noise distribution. The performance gain vis-a-vis demodulation using the standard AWGN option exceeded thresholds of upwards 25 dB for impulsive noise processes.

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  • 200.
    Häggman, Evert
    Luleå tekniska universitet, Institutionen för system- och rymdteknik.
    Development, Modelling and Investigation of a Robotic Exoskeleton for Astronaut Back Support2021Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Musculoskeletal disorders, specifically low back pain, has been well documented andreported by astronauts throughout the space exploration era. Statistics from astronautmemoirs states that 52-68% of astronauts experience moderate to severe lower backpain after prolonged spaceflights. The main cause is atrophy in the paraspinal musclesof the lumbar region. No sufficient countermeasure exists in-flight currently and therehabilitation programs remain ineffective. This thesis presents the first attempt to designand develop a prototype robotic exoskeleton, actuated by pneumatic artificial muscles, asan active countermeasure in-flight where it will be utilised as an equipment for muscularhypertrophy and a supporting device for rehabilitation programs on Earth. It will bemanufactured by additive manufacturing methods for adaptability while remaining lowin weight.A thorough analysis of the spine and lumbar region as a biomechanical system wasmade. Appropriate assumptions was made to simplify the understanding of the complexsystem that is the human spine. The targeted muscles were: multifidus, erector spinaeiliocostalis and erector spinae longissimus. A force analysis of the human torso bendingin the sagittal plane was made, finding that the torques of the torso reaches 244 Nm.The complete exoskeleton design is presented with the parts that will be 3D-printed andthe working principle of the system. Thereafter an extensive model of the exoskeletonis established using Denavit-Hartenberg representation of manipulators as a serial linksystem. The model provides a fundamental understanding of exoskeleton and enablesthe possibility to simulate it accurately. The evaluation protocol for the validation testsis then presented. Active pressure will be tested at 0, 3 and 6 bar and loads of 5 and 11kg will be lifted.Subsequently the assembly, with all the hardware and software selected for the prototypeis demonstrated. Thereafter the results of the evaluation tests are presented followed bya discussion of the results; anomalies, faults and challenges are subjects discussed. Thediscussion concludes that the exoskeleton shows potential for both supporting the motionin a rehabilitation use and enabling muscular hypertrophy in the lumbar region for theresistive tests. Although an extensive heavy-duty evaluation needs to be performed totruly validate the exoskeleton.

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