Ändra sökning
Avgränsa sökresultatet
2345678 201 - 250 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.
  • 201.
    Håkansson, Mikael
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Connecting Process Variables to Product Properties in Papermaking: A Multivariate Approach2014Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    In paper-making there are numerous of parameters that control the final outcome of the paper. This thesis examines the connections between paper properties and influential factors in the manufacturing process, by looking at the entire fiber line from the incoming wood chips to the actual finished paper. The analysis is done by studying how important process variables connect to the properties of the paper, and also by investigating the possibilities of modeling how these affect the final product.There are numerous factors that affect the final outcome of a manufactured paper. Five of these; wood type, cooking time, refining energy input, amount of starch and roll pressure in the paper machine, have been investigated in a series of laboratory experiments. A factorial designed experiment was set up to investigate the mentioned factors impact on paper properties. Focus in the study was laid on two aspects. One was to investigate interaction effects among the process variables and the significance of theseinteraction effects as well as the main effects. For the second part it was possible to utilize these interaction effects and deduce which combinations of factor levels that could result in equal output levels of certain paper parameters.Being able to predict the paper quality as accurately as possible is another importantaspect in paper-making. In the second study in the thesis the relation between the paper properties and process variations are charted. Through different multivariate methods prediction models were created based on the data gathered in the designed experiments. The underlying correlation structures in the data could be used in conjunction with the design factors to derive models that connected process parameters to paper properties. With the help of these models it is possible to predict what paper property levels toexpect when altering process variables.

    Ladda ner fulltext (pdf)
    FULLTEXT01
  • 202.
    Håkansson, Mikael
    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.
    Multivariate prediction of key kraft paper properties from designed experiments in a pilot plant2015Ingår i: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 30, nr 2, s. 258-264Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    A two-level factorial design was set up where five factors in a kraft paper process were varied, from wood chip origin to paper machine roll pressure. Nine paper properties were selected for a more in-depth analysis. This paper shows how these 9 responses can be modeled as a function of the experimental factors. The model, a full interaction model, was estimated using Partial Least-Squares Regression. The resulting model shows that there is a strong correlation between the experimental factors and the measured paper properties. The paper also presents a careful analysis of how the uncertainties of the measured values propagate through the model and contribute to the final model uncertainty. Finally, the interpretations and application of the resulting model is discussed. Specifically, having access to a good model enables the plant operators to simulate the effect of changing the process variables, either for training purposes or to test new production scenarios

  • 203.
    Håkansson, Mikael
    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.
    Factorial study of connections between process variables and kraft paper quality properties2014Ingår i: Nordic Pulp & Paper Research Journal, ISSN 0283-2631, E-ISSN 2000-0669, Vol. 29, nr 2, s. 286-293Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    By investigating how properties of a finished paper product are related to different process variables as well as pulp characteristics throughout the fiber line, the understanding of the process will increase. In this paper we investigate the correlation between some key paper quality parameters and five tunable process variables, along the entire fiber production line. A full two-level factorial experiment has been conducted, where five factors were varied. The factor settings were based on a laboratory replica of a specific kraft mill’s paper product. The mill replicate was then used as a center point in the factorial design and appropriate levels of the factors were set based on these center points. Several experimental runs could be simulated via a Monte Carlo approach making it possible to get a reliable estimate of the significance of each factor effect. Analysis of the results shows that there are interaction effects present between variables, and that these interaction effects can be utilized to achieve similar paper properties using different variable settings.

  • 204.
    Håkansson, Mikael
    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.
    Sjölund, Torbjörn
    MoRe Research AB.
    Lambert, François
    MoRe Research AB.
    Experimental study of the kraft paper making process: compilation of reference tests performed at a paper mill and reproduced in a laboratory environment2012Konferensbidrag (Refereegranskat)
    Ladda ner fulltext (pdf)
    FULLTEXT01
  • 205.
    Ibrahim, Emad Farouk
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Selected Topics on Reconfigurable Intelligent Surfaces2022Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Reconfigurable intelligent surface (RIS) is a promising technology for wireless communications applications. A RIS is a thin planar array that consists of multiple reflecting elements, each of which is connected to a tunable chip and can induce a controllable reflection coefficient to the incident signal. The RIS is a nearly passive unit as it only leverages the reflection on its elements and it does not consume any power for transmission. Furthermore, RISs can actively control the propagation channel, by accurately tuning the reflection coefficients of their elements to fit a specific need. The advantage of the RIS arises in creating energy-efficient smart radio environments wherein the wireless channel becomes an optimization variable. In this thesis, we study some of the potential applications and deployments for the RIS in wireless communications. First, the multiple-input multiple-output channel matrix in line-of-sight (LoS) environments turns out to be rank deficient such that spatial multiplexing becomes unattainable. Thus, we exploit the RISs to create additional degrees of freedom by synthesizing a sort of multi-path propagation. Then, we optimize the transmit covariance matrix and the reflection coefficients of the RISs using an alternating optimization algorithm to maximize the achievable rate. Alternatively, we propose different schemes to enhance the composite channel power which would result in an improvement to the achievable rate. Second, we characterize the efficient regions of RIS deployments with single and multiple antenna systems in Rician fading channels. We show that in RIS-aided single antenna systems, near RIS deployments relative to the transmitter or receiver are always better than far deployments. Moreover, we show that in RIS-aided multiple antenna systems, the efficient regions of operations are highly dependent on the propagation environment itself. In LoS environments, both the near and far deployments can result in substantial achievable rate gains. However, as the channel becomes richer with multipath, near deployments gradually become more efficient than the far deployments. Third, we propose the RIS to act as an access point for information transfer by exploiting the polarization control ability of the RIS. In particular, the RIS alternates the polarization state of the reflected waves to perform conventional as well as differential polarization shift keying (PolSK) modulation schemes. In RIS-aided conventional PolSK, two different schemes are proposed. In the first scheme, the receiver corrects for the polarization mismatch loss that occurs in the wireless channel. In the second scheme, the RIS additionally pre-codes the reflected wave to compensate for the polarization mismatch. In RIS-aided differential PolSK, the detection process is independent of the polarization mismatch. Thus, there is no need for a polarization mismatch compensation process by either the receiver or the RIS.

    Ladda ner fulltext (pdf)
    fulltext
  • 206.
    Ibrahim, Emad Farouk
    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.
    Differential Polarization Shift Keying Through Reconfigurable Intelligent Surfaces2022Ingår i: IEEE Communications Letters, ISSN 1089-7798, E-ISSN 1558-2558Artikel i tidskrift (Övrigt vetenskapligt)
    Abstract [en]

    We propose a novel reconfigurable intelligent surface (RIS)-aided differential polarization shift keying modulation scheme for a line-of-sight environment. In this scheme, the RIS exploits the state of polarization (SoP) of the reflected waves over two successive reflection frames to encode the data bit. In particular, the RIS either preserves the SoP of the reflected wave similar to the previous reflection frame or switches it to another orthogonal SoP as a function of the information data bits. The proposed scheme allows non-coherent data detection without the need for polarization mismatch estimation and compensation processes at the receiver.    

    Ladda ner fulltext (pdf)
    fulltext
  • 207.
    Ibrahim, Emad
    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.
    On the Position of Intelligent Reflecting Surfaces2021Ingår i: 2021 Joint European Conference on Networks and Communications & 6G Summit (EuCNC/6G Summit), IEEE, 2021, s. 66-71Konferensbidrag (Refereegranskat)
    Abstract [en]

    We study the positional impact of an intelligent reflecting surface (IRS) on the achievable rate for single and multiple antenna systems. We show that in IRS-aided single antenna systems, it is always best to place the IRS as close as possible to the transmitter or receiver since the large-scale fading for IRS-reflected links is the main factor that characterizes the performance gain. However, for IRS-aided multiple antenna systems, the propagation environment has an important role in characterizing the efficient regions of IRS placement. In the case of a line-of-sight environment, the channel matrix turns out to be rank-deficient. Thus, both far and near IRS placements result in significant achievable rate improvements where the former provides a substantial additional degree-of-freedom, while the latter results in a power gain. Furthermore, as the wireless channel becomes richer with multipath, the rank of the channel matrix increases. Thus, the efficient far placement regions gradually shrink until they disappear in the case of a Rayleigh fading channel where IRS near placements become more efficient than far placements as they result in higher power gains.

    Ladda ner fulltext (pdf)
    fulltext
  • 208.
    Idzikowski, Filip
    et al.
    Poznan University of Technology, Faculty of Electronics and Telecommunications.
    Chiaraviglio, Luca
    University of Rome Tor Vergata.
    Liu, William
    Auckland University of Technology.
    van de Beek, Jaap
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Future internet architectures and sustainability: An overview2018Konferensbidrag (Refereegranskat)
    Abstract [en]

    The Internet Protocol (IP) traffic is constantly growing. The annual global IP traffic is estimated to reach 2.3 Zettabyte per year by 2020 according to the recent Cisco forecasts. New Internet infrastructures are required to handle the emerging Big Data. Several pilot initiatives have proposed Future Internet (FI) architectures. We provide an overview of the FI architectures from the perspective of sustainable development.

  • 209. Isaksson, Mikael
    et al.
    Bengtsson, Daniel
    Deutgren, Petra
    Sandell, Magnus
    Luleå tekniska universitet.
    Sjöberg, Frank
    Luleå tekniska universitet.
    Ödling, Per
    Öhman, Hans
    Zipper: a duplex scheme for VDSL based on DMT1997Rapport (Övrigt vetenskapligt)
    Abstract [en]

    A duplex scheme for DMT-based VDSL systems is presented here. It offers a solution to the problem with NEXT and near-echoes in broadband communications. The scheme has high duplex efficiency, low latency, and attractive transmit power features. However, hardware verification remains.

    Ladda ner fulltext (pdf)
    FULLTEXT01
  • 210.
    Isaksson, Mikael
    et al.
    Telia Research AB.
    Deutgren, Petra
    Luleå tekniska universitet.
    Sjöberg, Frank
    Luleå tekniska universitet.
    Wilson, Sarah Kate
    Luleå tekniska universitet.
    Ödling, Per
    Luleå tekniska universitet.
    Börjesson, Per Ola
    Luleå tekniska universitet.
    Zipper - a flexible duplex method for VDSL1997Ingår i: Proceedings of International Conference on Copper Wire Access Systems: CWAS '97, 1997, s. 95-99Konferensbidrag (Refereegranskat)
    Abstract [en]

    A novel duplex scheme for DMT-based VDSL systems on copper wire pairs is introduced. This method, named Zipper, uses different subcarriers in opposite transmission directions to divide the available bandwidth between the two directions. It provides exceptional versatility when it comes to dividing capacity between up and downstream. The scheme has high duplex efficiency, low latency, and most importantly good coexistence possibilities with other systems such as ADSL.

    Ladda ner fulltext (pdf)
    fulltext
  • 211.
    Isaksson, Mikael
    et al.
    Telia Research.
    Mestdagh, Denis
    Sjöberg, Frank
    Luleå tekniska universitet.
    Nilsson, Rickard
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Ödling, Per
    Bengtsson, Daniel
    Pulse shaping with zipper: spectral compatibility and asynchrony1998Rapport (Övrigt vetenskapligt)
    Abstract [en]

    We have investigated what the effects of adding pulse shaping and windowing to a Zipper-VDSL system would be. By adding short, pulse-shaped wings to the DMT symbol and accepting the, say, 3 % efficiency loss, the spectral sidelobes of the DMT-symbol are reduced. This provides several attractive features including the following: · The pulse shaping in the transmitter reduces the out of band power of the DMT-signal. · The spectral compatibility with other systems such as ADSL and CAP-VDSL is enhanced. · It becomes feasible to use Zipper-VDSL in a time-asynchronous mode, where a VTU-R only synchronizes itself to its VTU-O, while the VTU-R / VTU-O pair may be asynchronous to all other transceiver pairs. · The pulse shaping gives some increase in the depth of spectral notches, for HAM-bands etc. The windowing is a part of a powerful RFI-ingress suppressing method as proposed by John Bingham, Amati.

    Ladda ner fulltext (pdf)
    FULLTEXT01
  • 212.
    Isaksson, Mikael
    et al.
    Telia Research.
    Stefansson, Tomas
    Ödling, Per
    Sjöberg, Frank
    Luleå tekniska universitet.
    Wilson, Sarah Kate
    Luleå tekniska universitet.
    Option for inband POTS and ISDN1997Rapport (Övrigt vetenskapligt)
    Abstract [en]

    We propose an option allowing VDSL to use the spectrum now reserved for narrowband services, such as POTS and ISDN. The main motives for the proposal are: 1) This option will provide lower network complexity and maintenance costs by avoiding duplicate line cards.2) We can increase the number of customers using VDSL for rates below 15 Mbps. This is because when VDSL can use the full spectrum, the reach can be significantly extended. For example, the reach increases by up to 1000 meters for a 2 Mbps symmetric service on TP1 in a central office based scenario.

    Ladda ner fulltext (pdf)
    FULLTEXT01
  • 213.
    Jacobson, Karin
    et al.
    Swerea KIMAB AB, Kista Sweden.
    Carlson, Johan E.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Lindblad, Philip
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Non-Destructive Testing of Plastics and Composites in the Chemical Processing Industry2016Konferensbidrag (Refereegranskat)
    Abstract [en]

    Equipment and components made of plastics and composites are widely used in highly corrosive environments in the processing industry. Examples are the storage tanks, pumps and pipes for chemical transport and stacks in combustion plants. The demand for reliable nondestructive testing of plastic process equipment has increased significantly in recent years. Glass fiber reinforced plastics (GRP) is a common construction material for process equipment in the chemical industry. It can be used both as structural bearing in a dual laminate with a thermoplastic material as a corrosion barrier or as a solid GRP. In the latter case, the laminate is generally built up with a resin rich corrosion barrier (about 2.5 to 5 mm thick) with a low content of glass closest to the chemical. The glass fiber in this layer is usually a surface veil and chopped strand mats (CSM), i.e. it has no general fiber orientation. Outside this is the structural bearing layer with much higher glass content, usually wound fiber and / or woven fiber mats with a preferential fiber direction. The corrosion barrier is not load bearing and corrosion of this layer can be allowed. However, no corrosion can be permitted in the structural support layer. Because of this it is important to measure the thickness of the corrosion barrier for quality control but also to determine how far an attack has reached in the corrosion barrier. Today there is no non-destructive testing method that can answer this. Instead destructive sampling (often a drill core) must be made. This is difficult, expensive and sometimes impossible. There is thus a great interest in a method that, preferably at any time during operation, can provide answers to these questions. Due to the heterogeneity of the GRP material in terms of amount, type and direction of the fibers, conventional algorithm for ultrasound imaging will not work. One aim of our work is thus to develop new signal processing methods to handle this heterogeneity. In addition we are also looking at the possibility to use optical fibers and Fiber Bragg Grating (FBG) sensors for corrosion monitoring of GRP structures

    Ladda ner fulltext (pdf)
    fulltext
  • 214.
    Jafari, Hedyeh
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Mansouri, Sina Sharif
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nikolakopoulos, George
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    On the Fear of Falling Detection by Moving Horizon Estimation2020Ingår i: 21th IFAC World Congress / [ed] Rolf Findeisen, Sandra Hirche, Klaus Janschek, Martin Mönnigmann, Elsevier, 2020, s. 16512-16517Konferensbidrag (Refereegranskat)
    Abstract [en]

    Fear of falling (FoF) is a major health problem, especially in elders, which can lead to falls, injury, loss of independence, and premature needs of nursing and assistance. However, most of the studies have focused on the psychological aspect of the FoF and there is a significant lack of technological assistance and methodology to detect and eliminate the effects of this fear on maintaining balance. In this article, we propose a novel method to detect the FoF as a quantitative signal. In our proposed novel approach, fear is considered as an internal disturbance inside a Central Nervous System (CNS) that can affect the generated output torque to each joint of the psychical body. By assuming the human body in a quiet stance, as an inverted pendulum model, this disturbance signal is estimated by Moving Horizon Estimation (MHE). For this purpose, the body kinetics and kinematics measurements of forty-five subjects during upright stance trails, as well as the psychological FoF falls efficacy test, were collected and utilized for the estimation and validation of the results. The experimental results show that the subjects with FoF present a higher variation in the estimated signal. This method can sufficiently detect the FoF by the posturographic and motion data, which can be utilized on the future assistive devices for prevention and treatment of the FoF and falls.

    Ladda ner fulltext (pdf)
    fulltext
  • 215.
    Jafari, Seyyed Reza
    et al.
    Center of Excellence in Industrial Control, Faculty of Electrical Engineering, K.N. Toosi University of Technology, Seyyed Khandan Bridge, Shariati Ave., Tehran, Iran.
    Khaki-Sedigh, Ali
    Center of Excellence in Industrial Control, Faculty of Electrical Engineering, K.N. Toosi University of Technology, Seyyed Khandan Bridge, Shariati Ave., Tehran, Iran.
    Birk, Wolfgang
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Adaptive multi-objective control allocation with online actuator selection for over-actuated systems2023Ingår i: International Journal of Dynamics and Control, ISSN 2195-268X, E-ISSN 2195-2698, Vol. 11, nr 3, s. 1220-1229Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper presents an adaptive control allocation technique for over-actuated systems. The online actuator selection algorithm is used to select the best group of actuators. Also, a multi-objective cost function is utilized for the allocation unit. The virtual and actual control signals in the control allocation methodologies are linked by the effectiveness matrix. In many practical systems, the elements of the effectiveness matrix may vary due to changing operating conditions, nonlinearities, ageing, disturbances and faults. Hence, an online algorithm for estimation of the entries of the effectiveness matrix is presented in this paper. Estimation of the effectiveness matrix will be used for the proposed adaptive actuator selection strategy, employing the Actuator Effectiveness Index (AEI). The AEI is calculated for all the actuators, and the best group of actuators will be subsequently selected. Finally, simulation results are used to show the effectiveness of the proposed methodology.

  • 216.
    Jensen, Johannes
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Validation of Attitude Determination andControl System on Student CubeSat APTASand Calibration of Coarse Sun Sensors2024Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    In this thesis, a simulation harness is constructed in Simulink for the purpose of validating the Attitude Determination and Control System (ADCS) on the APTAS student CubeSat in support of the upcoming flight readiness review. The simulation results are used to verify the compliance of a subset of the requirements for the ADCS, detailed in table 1. Calibration of the onboard sun sensor array, which is used to find the sun vector for the attitude determination, is performed using a break-out board of sun sensors tested in a sun simulator. The data gathered from this test is used to model the sun sensor system in the simulation and in flight software.

    The results show that the sun sensor system is able to find the sun vector with an average error angle of 5.4 degrees, though the error angle may spike up to 18 degrees in operation. It is found that the complete ADCS is able to guide the spacecraft toward the desired nadir-facing attitude, though not with the accuracy specified in the requirements. The spacecraft is able to detumble much better than required.

    All deficiencies found in the ADCS software have been corrected. These changes arelisted in appendix B. It is concluded that, despite its flaws, the ADCS software is flight ready. 

    Ladda ner fulltext (pdf)
    fulltext
  • 217.
    Jiang, Biao
    Hangzhou Applied Acoustics Research Institute.
    Low-complexity implementation for worst-case optimization-based robust adaptive beamforming2008Ingår i: Sensor Array and Multichannel Signal Processing Workshop, 2008. SAM 2008, Piscataway, NJ: IEEE Communications Society, 2008, s. 311-314Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    In this paper, an efficient low-complexity robust adaptive beamforming method based on worst-case performance optimization is proposed. Lagrangian method was applied to obtain the expression for the robust adaptive weight vector, which is optimized on the boundary of the steering vector uncertainty region, that is to say, in the worst mismatch case. Combining the constraint condition and the eigendecomposition of the array covariance matrix, root-finding method is used to obtain the optimal Lagrange multiplier. Then, the diagonal loading-like robust weight vector is achieved. The implementation efficiency is greatly improved since the main computational burden is the eigendecomposition operator. Numerical results show that the performance of the proposed method is nearly identical to the robust Capon beamforming.

  • 218.
    Jiang, Biao
    Hangzhou Applied Acoustics Research Institute.
    Performance analysis of port-starboard discrimination for towed multi-line array2009Ingår i: Recent Advances in Signal Processing, Rijeka: INTECH, 2009, s. 481-488Kapitel i bok, del av antologi (Refereegranskat)
  • 219.
    Jiang, Biao
    Hangzhou Applied Acoustics Research Institute.
    Robust wideband adaptive beamforming using waveguide invariant focusing method2012Ingår i: Journal of the Acoustical Society of America, ISSN 0001-4966, E-ISSN 1520-8524, Vol. 131, nr 4, s. 3487-Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The waveguide invariant describing the dispersive propagation in underwater environment can provide useful information for signal processing. In this paper, waveguide invariant focusing is exploited to preprocess the received horizontal array signal, such that the moving target is aligned in a single rank-one signal subspace over the bandwidth, results a reduction of the number of the snapshots necessary for the adaptive beamforming, and the diagonal loading is optimized using the robust Capon method to further improve the robustness. Numerical results show that the proposed method can improve the detection performance with limited observation time. Moreover, passive ranging is accomplished when the beamforming output achieves the maximum over a scanned target range limit.

  • 220.
    Jiang, Biao
    SiPLAB, University of Algarve, Campus de Gambelas.
    Vector sensor array processing and geoacoustic inversion with MAKAI'05 sea trial data2013Rapport (Övrigt vetenskapligt)
    Abstract [en]

    Underwater acoustic vector sensor has received much more attentions in recent a few decades. One type of high precise high-frequency vector sensor TV-001, succeeded for several applications in Makai Ex05 sea trial, such as direction-of-arrival (DOA) estimation, geoacoustic inversion, tomography, MIMO communications. In this report, the vector sensor array (VSA) direction finding performance, including the array directivity index (DI), array gain (AG), and Cramér-Rao bound (CRB) are studied. Besides, the main research was focused on the geoacoustic inversion by using various propagation models. One simple inversion method by comparing the downward and upward beams was studied, i.e. bottom reflection coefficient (BRC) matching method, the results showed that the (p+v) processor is the best. The seabed parameter sensitivities were studied, and the compressional velocity was found could be inverted by matched-field inversion (MFI) methods. The CRB's of geoacoustic parameter estimates are derived, which also demonstrated that the (p+v) processing outperforms others. A two-step inversion method was proposed. First, the compressional velocity, along with the receiver range and depth were optimized using genetic algorithm (GA). Secondly, the optimized range and depth information was fed back to improve the accuracy of the replica fields, then the compressional velocity dependent replicas were matched with the real data, giving high resolution and precise results during the period of nearly two hours

  • 221.
    Jiang, Biao
    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.
    Castaño, Miguel
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Lindblad, Philip
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    öhman, Johan
    Luleå tekniska universitet.
    Ultrasonic Imaging Through Thin Reverberating Materials2015Ingår i: Physics Procedia, E-ISSN 1875-3892, Vol. 70, s. 380-383Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Imaging through anisotropic or highly heterogeneous materials is challenging for the existence of strong boundary and volume reverberations. To image small cracks or flaws in a reverberating thin layers, high resolution techniques are needed in both temporal and spatial domain, so that the reverberation can be suppressed to some level. In this paper, the reverberation suppression performance of the total focusing beamforming method (TFM) was evaluated by simulation and real data processing. The results showed that the more the focusing point moves away from the array central line, the more multi-reflections can be suppressed. Furthermore, TFM combined with adaptive processing greatly improves the small flaw detection performance. Test results on real samples confirmed the robustness and reverberation suppression capability of the TFM imaging method.

  • 222.
    Jiang, Biao
    et al.
    Hangzhou Applied Acoustics Research Institute.
    Chen, F.H.
    Hangzhou Applied Acoustics Research Institute.
    High precision time delay estimation using generalised MVDR cross spectrum2007Ingår i: Electronics Letters, ISSN 0013-5194, E-ISSN 1350-911X, Vol. 43, nr 2, s. 130-131Artikel i tidskrift (Refereegranskat)
  • 223.
    Jiang, Biao
    et al.
    Hangzhou Applied Acoustics Research Institute.
    Chen, F.H.
    Hangzhou Applied Acoustics Research Institute.
    Performance analysis of port-starboard discrimination for towed twin-line array2008Ingår i: 16th European Signal Processing Conference: EUSIPCO 2008, Lausanne, Switzerland, August 25-29, 2008, Piscataway, NJ: IEEE Communications Society, 2008Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    The performance of port-starboard discrimination (PSD) for a target detected by a towed twin-line sonar array is presented. The PSD performance is evaluated by a measure referred to as the port-starboard rejection ratio (PSRR), which is defined as the ratio of the output power in the desired signal direction to that in the mirror direction. Analytical expression for the PSRR is derived, in terms of the array separation, signal-to-noise-ratio (SNR), interference-to-noise-ratio (INR), signal-to-interference-ratio (SIR), angular separation and correlation between the desired signal and the interference, array size and finite sample size.

  • 224.
    Jiang, Biao
    et al.
    Hangzhou Applied Acoustics Research Institute.
    Cheng, Qianliu
    Ling, Guomin
    Robust Adaptive Beamforming with SSMUSIC Performance Optimization in the Presence of Steering Vector Errors2007Ingår i: Journal of Digital Information Management, ISSN 0972-7272, Vol. 5, nr 3, s. 107-114Artikel i tidskrift (Refereegranskat)
  • 225.
    Jiang, Biao
    et al.
    Institute of Acoustics, Chinese Academy of Sciences.
    Sun, Changyu
    Institute of Acoustics, Chinese Academy of Sciences.
    Zhu, Ye
    Graduate School Chinese Academy of Sciences.
    Robust Capon estimator for the nominal DOAs and angular spreads of distributed sources2005Ingår i: 2005 International Conference on Communications, Circuits, and Systems: HKUST, Hong Kong, China, May 27-30, 2005, Piscataway, NJ: IEEE Communications Society, 2005Kapitel i bok, del av antologi (Refereegranskat)
    Abstract [en]

    A novel and low complexity estimator based on Capon's minimum variance beamforming method is proposed for the estimation of the nominal (centre) directions of arrival (DOA) and angular spreads of distributed sources. A more reliable array response vector instead of the standard steering vector is put forward according to the incoherently distributed (ID) source model, by which the spread Capon spectrum is obtained. Considering the model mismatch between the new steering vector and the true one, we estimate the parameters not by making the trace of the Capon spectrum matrix minimization but, making the corresponding Frobenius norm minimization. Only a two-dimensional search method is required to optimize the estimates of the nominal angles and angular spreads, so the proposed method is computationally efficient. Numerical results demonstrated its excellent performance in the low SNR case and verified its robustness against some other methods.

  • 226.
    Johansen, H. K.
    et al.
    Luleå tekniska universitet.
    Sørensen, K.
    Laboratory of Geophysics, Finlandsgade 8, DK-8200 Aarhus N, Denmark.
    Fast Hankel-Transforms1979Ingår i: Geophysical Prospecting, ISSN 0016-8025, E-ISSN 1365-2478, Vol. 27, nr 4, s. 876-901Artikel i tidskrift (Refereegranskat)
  • 227.
    Johansson, Gustav
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Borg, Johan
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Johansson, Jonny
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Lundberg Nordenvaad, Magnus
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Wannberg, Gudmund
    Swedish Institute of Space Physics, Kiruna, Sweden.
    Simulation of post-ADC digital beamforming for large aperture array radars2010Ingår i: Radio Science, ISSN 0048-6604, E-ISSN 1944-799X, Vol. 45, nr RS3001Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper presents simulations and methods developed to investigate the feasibility of using a Fractional-Sample-Delay (FSD) system in the planned EISCAT_3D incoherent scatter radar. Key requirements include a frequency-independent beam direction over a 30 MHz band centered around 220 MHz, with correct reconstruction of pulse lengths down to 200 ns. The clock jitter from sample to sample must be extremely low for the integer sample delays. The FSD must also be able to delay the 30 MHz wide signal band by 1/1024th of a sample without introducing phase shifts, and it must operate entirely in baseband. An extensive simulation system based on mathematical models has been developed, with inclusion of performance-degrading aspects such as noise, timing error, and bandwidth. Finite Impulse Response (FIR) filters in the baseband of a band-pass-sampled signal have been used to apply true time delay beamforming. It has been confirmed that such use is both possible and well behaved. The target beam-pointing accuracy of 0.06° is achievable using optimized FIR filters with lengths of 36 taps and an 18 bit coefficient resolution. Even though the minimum fractional delay step necessary for beamforming is ∼13.1 ps, the maximum sampling timing error allowed in the array is found to be σ ≤ 120 ps if the errors are close to statistically independent.

  • 228.
    Johansson, Gustav
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Hägglund, Fredrik
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Carlson, Johan E.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Johansson, Jonny
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Picosecond level error detection using PCA in the hardware timing systems for the EISCAT_3D LAAR2010Ingår i: Radio Science Bulletin, ISSN 1024-4530, nr 333, s. 45-50Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    While developing the timing system for the receiver arrays for the EISCAT_3D system, several approaches to detect and adjust for timing errors within the array have been explored. The demand on the timing error between all elements in the array is to have a standard deviation of less than 120 ps, thus requiring high quality error detection systems to guarantee radar operation. This paper investigates the qualities of a secondary error detection system based on statistical analysis of captured data. The measurements are assembled with a Signal-to-Noise Ratio (SNR) of -30 dB implying that the elements in a 2112 element array need to be grouped into sub-arrays of 48 elements each. The captured data is then evaluated by Principal Component Analysis (PCA) and averaged over 20,000 measurements, or about half a second. Timing errors between sub-arrays of down to ~120 ps and a percentage of faulty sub-arrays of up to 20% are detectable. As a secondary error detection system PCA is cheap to implement since the only need of the analysis is a small amount of computer time. It also provides a valuable detection system for hardware errors in the primary timing system that can otherwise be hard to find.

    Ladda ner fulltext (pdf)
    FULLTEXT01
  • 229.
    Johansson, Jonny
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Borg, Johan
    Larsmark, Mikael
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Lindgren, Tore
    Lundberg Nordenvaad, Magnus
    Luleå tekniska universitet, Institutionen för ekonomi, teknik och samhälle, Industriell Ekonomi.
    Johansson, Gustav
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Ekman, Jonas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Ståbis, Joel
    Sverige.
    Project: EISCAT 3D2007Övrigt (Övrig (populärvetenskap, debatt, mm))
  • 230.
    Johansson, Jonny
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Martinsson, Pär-Erik
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Delsing, Jerker
    Simulation of absolute amplitudes of ultrasound signals using equivalent circuits2007Ingår i: IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, ISSN 0885-3010, E-ISSN 1525-8955, Vol. 54, nr 10, s. 1977-1983Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Equivalent circuits for piezoelectric devices and ultrasonic transmission media can be used to cosimulate electronics and ultrasound parts in simulators originally intended for electronics. To achieve efficient systemlevel optimization, it is important to simulate correct, absolute amplitude of the ultrasound signal in the system, as this determines the requirements on the electronics regarding dynamic range, circuit noise, and power consumption.This paper presents methods to achieve correct, absolute amplitude of an ultrasound signal in a simulation of a pulse-echo system using equivalent circuits. This is achieved by taking into consideration loss due to diffraction and the effect of the cable that connects the electronics and the piezoelectric transducer. 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.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%. The use of a coaxial cable introduces inductance and capacitance that affect the amplitude of a received echo. Amplitude variations of 60% were observed when the cable length was varied between 0.07 m and 2.3 m, with simulations predicting similar variations. The high precision in the achieved results show that electronic design and system optimization can rely on system simulations alone. This will simplify the development of integrated electronics aimed at ultrasound systems.

    Ladda ner fulltext (pdf)
    FULLTEXT01
  • 231. Johnson, Jr., C. Richard
    et al.
    Bennett, P.C.E.
    Leblanc, James
    Krishnamurthy, Vikram
    Blind adaptive equalizer average stationary point stability analysis with admissibility consequences1992Ingår i: Proceedings of the 1992 Conference on Information Sciences and Systems, [March 18, 19, 20, 1992 at Princeton University], Princeton, NJ: Princeton University / Department of Electrical Engineering , 1992Konferensbidrag (Refereegranskat)
  • 232.
    Johnsson, Simon
    Luleå tekniska universitet, Institutionen för system- och rymdteknik.
    Speckle suppression in ultrasound images of heterogeneous materials2023Självständigt arbete på avancerad nivå (yrkesexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Performing non-destructive testing (NDT) on materials is a helpful tool for maintenance and quality control because the materials are not destroyed or disturbed; ultrasound imaging is one type of NDT. Ultrasound imaging of heterogeneous materials contains many echoes from the material itself. These echoes come from changes in the acoustic impedance, i.e. changes in the relation between the density and the sound speed of the material. However, these echoes will show speckle characteristics in images, making it hard to detect any defects in the imaged material. In this work, a method of suppressing this speckle noise is proposed. The proposed method is a 2D Wiener filter, which with the help of an image of the healthy material models changes in the material when a new image is taken later. The filter models the changes of the speckle noise between images of a defected- and healty material and then supresses the speckle from the image with defects. The filter works well on the artificial images used in this work but have yet to be tested on actual data. A version of a weighted moving average filter was also looked into, but this filter did not produce usable results.

    Ladda ner fulltext (pdf)
    fulltext
  • 233. Jr., C. Richard Johnson
    et al.
    Leblanc, James
    Krishnamurthy, Vikram
    Godard blind equalizer misbehavior with correlated sources: two examples1993Ingår i: Journal Marocain d'Automatique, d'Informatique et de Traitement du Signal, Vol. 2, s. 1-39Artikel i tidskrift (Refereegranskat)
  • 234.
    Kadhim, Ali
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Castano, Miguel
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Birk, Wolfgang
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Gustafsson, Thomas
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Relative Gain Array of Weakly Nonlinear Systems using a Nonparametric Identification Approach2015Ingår i: 2015 IEEE International Conference on Control Applications (CCA 2015): Sydney, Australia, September 21-23, Piscataway, NJ: IEEE Communications Society, 2015, s. 1612-1617, artikel-id 7320840Konferensbidrag (Refereegranskat)
    Abstract [en]

    This article presents a procedure to estimate the relative gain array (RGA) matrix for weakly nonlinear systems by means of nonparametric identification of the frequency response matrix (FRM). Specifically, the best linear approximation of nonlinear systems and the covariance of the nonlinear distortions are used in the relative gain array estimation. For the estimation neither process model nor model structure need to be known which is an advantage over methods that require accurate knowledge of a parametric process model. The proposed approach is compared with the original RGA and a nonlinear RGA calculation using the well-known quadruple tank process as a case

  • 235.
    Kallsäby, Mattias
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Datavetenskap.
    Modular MiniTest Tester2017Självständigt arbete på avancerad nivå (yrkesexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    RealTest is a company located in V¨aster˚as, Sweden, that works with embedded systems and test systems. RealTest had a need for a new test system for one of their products, the MiniTester (MT) mk2 that is used to test Drive Control Units (DCUs) used on trains. The problems that had to be solved were, finding out the most common faults of the product, make the test system modifiable and scalable, have a software running on a Windows PC with a working GUI and test logic and design a hardware component measurement unit to generate and measure signals.

    The system described in this report is the software parts of the developed MiniTest tester that runs on a Windows PC as well as the hardware design. The programming of the measurement unit and the testing of that unit is not covered by this report.

    The hardware consist of custom PCBs and Arduino boards. The Windows PC programs implemented a GUI and test logic according to the goals with a few exceptions left for further work. These programs have been evaluated by emulating the hardware. The system is shown to be modifiable in practice by implementation and scalable in theory

    Ladda ner fulltext (pdf)
    fulltext
  • 236.
    Kanwar, John
    Luleå tekniska universitet, Institutionen för system- och rymdteknik.
    Detecting and identifying radio jamming attacks in low-power wireless sensor networks2021Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Wireless sensor networks (WSNs) are used in all kinds of different sectors ranging from agriculture, environment, healthcare and the military. Embedded systems such as sensor nodes are low-power and consist of low memory, which creates a challenge for its security. One of WSN’s worst enemies is interference radio jamming attacks. They are easy to construct and execute, but hard to detect and identify. In this thesis, we tackle the problems of detecting, but most importantly identifying, and distinguishing the most commonly used interference radio jamming attacks. Presenting SpeckSense++, a firmware that makes it possible for low-power embedded systems to detect, identify and distinguish interference radio jamming attacks and unintentional interference such as Bluetooth and WiFi to a certain degree. Showing an accuracy of 96 to 90 % for proactive jammers, 89% for reactive, and 92 to 85 % for unintentional interference.

    Ladda ner fulltext (pdf)
    fulltext
  • 237. Karasalo, I.
    et al.
    Nordenvaad, Magnus Lundberg
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Advanced techniques for active sonar applications2008Ingår i: Conference Proceedings, UDT Pacific 2008: UDT Pacific 2008 : undersea defence technology : conference and exhibition : 4-6 November, SCEC, Sydney, Australia, London: Clarion Defence Ltd , 2008Konferensbidrag (Refereegranskat)
  • 238. Karasalo, Ilkka
    et al.
    Nordenvaad, Magnus Lundberg
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nilsson, Bernt
    Karlsson, Per-Axel
    Parastates, Elias
    Sonar processing methods for reverberation-limited undersea environments2009Rapport (Övrigt vetenskapligt)
    Ladda ner fulltext (pdf)
    FULLTEXT01
  • 239.
    Karvelis, Petros
    et al.
    Laboratory of Knowledge and Intelligent Computing, Department of Computer Engineering, Technological Educational Institute of Epirus, Arta, Greece.
    Röijezon, Ulrik
    Luleå tekniska universitet, Institutionen för hälsovetenskap, Hälsa och rehabilitering.
    Faleij, Ragnar
    Luleå tekniska universitet, Institutionen för hälsovetenskap, Hälsa och rehabilitering.
    Georgoulas, George
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Mansouri, Sina Sharif
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Nikolakopoulos, George
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    A Laser Dot Tracking Method for the Assessment of Sensorimotor Function of the Hand2017Ingår i: 2017 25th Mediterranean Conference on Control and Automation, MED 2017, Piscataway. NJ: Institute of Electrical and Electronics Engineers (IEEE), 2017, s. 217-222, artikel-id 7984121Konferensbidrag (Refereegranskat)
    Abstract [en]

    Assessment of sensorimotor function is crucial during the rehabilitation process of various physical disorders, including impairments of the hand. While moment performance can be accurately assessed in movement science laboratories involving highly specialized personnel and facilities there is a lack of feasible objective methods for the general clinic. This paper describes a novel approach to sensorimotor assessment using an intuitive test and a specifically tailored image processing pipeline for the quantification of the test. More specifically the test relies on the patient being instructed on following a zig-zag pattern using a handled laser pointer. The movement of the pointer is tracked using image processing algorithm capable of automating the whole procedure. The method has potential for feasible objective clinical assessment of the hand and other body parts

  • 240.
    Khattak, Rabiullah
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik.
    Sandberg, Sara
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system. Ericsson Research, Wireless Access Networks, Luleå, 977 53, Sweden.
    Jointly optimized rate-compatible UEP-LDPC codes for half-duplex co-operative relay networks2014Ingår i: EURASIP Journal on Wireless Communications and Networking, ISSN 1687-1472, E-ISSN 1687-1499, Vol. 2014, artikel-id 22Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    This paper addresses the design of low-density parity-check (LDPC) codes for half-duplex co-operative relay networks. Structured rate-compatible codes with unequal error protection (UEP) are designed through joint optimization of the codes for the channels between source and relay and source and destination. The proposed codes clearly outperform simpler LDPC codes which are not optimized for relay channels and puncturing-based rate-compatible LDPC codes, and they show a significant performance improvement over the direct link communication depending on the position of relay. The optimization algorithm for the proposed codes is based on density evolution using the Gaussian approximation and optimal variable node degree distributions are found through iterative linear programming. Interestingly, they anyhow show performance which is almost comparable to the performance of codes optimized through a more complex non-linear optimization algorithm. We analyze the performance of our proposed codes with short, medium and long block lengths, and with low and high rates under realistic assumptions, i.e., imperfect decoding of the codeword at relay and variant signal-to-noise ratio within a single codeword.

  • 241.
    Kinnunen, Tim
    Luleå tekniska universitet, Institutionen för system- och rymdteknik.
    Development and Implementation of Techniques for the Simulation and Processing for Future SAR Systems2023Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Synthetic Aperture Radar (SAR) is a type of radar system that can generate high-resolution images with which one can detect subtle changes on the scale of centimetres from space. It can operate in any weather condition and during both day and night, making it unique compared to optical sensors. SAR is used for applications such as environmental monitoring, surveillance, and earth observation. Its ability to penetrate clouds and, to some extent, vegetation, allows for insights into terrain, vegetation structure, and even subsurface features. The importance of modelling the generated data of a SAR system before initiating the construction and development of it cannot be overstated. This thesis presents the implementation of the Reverse BackProjection Algorithm (RBPA) designed to generate raw SAR data efficiently and accurately. The RBPA stands out with its flexibility, enabling researchers and designers to simulate and gauge the SAR system's effectiveness under diverse scenarios. This provides an easy way of fine-tuning configurations for distinct needs concerning scene geometries, orbits, and radar designs. Two versions of the RBPA were implemented, differing slightly in the theoretical approach of azimuth defocusing. On top of this, a bistatic mode and Terrain Observation by Progressive Scans (TOPS) acquisition mode was also implemented. The inclusion of these two modes were specifically due to their relevance for the upcoming European Space Agency (ESA) SAR mission, Harmony. The addition of the TOPS mode required a comprehensive design of the antenna framework. Moreover, this implementation also paves the way for simpler integration of modes in the future. The two versions of the RBPA were profiled, revealing the optimal system and parameter configurations.

    Ladda ner fulltext (pdf)
    fulltext
  • 242.
    Kleyko, Denis
    et al.
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Datavetenskap.
    Hostettler, Roland
    Department of Electrical Engineering and Automation, Aalto University.
    Lyamin, Nikita
    School of Information Technology, Halmstad University.
    Birk, Wolfgang
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Wiklund, Urban
    Department of Biomedical Engineering and Informatics, Umeå University.
    Osipov, Evgeny
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Datavetenskap.
    Vehicle Classification using Road Side Sensors and Feature-free Data Smashing Approach2016Ingår i: 2016 IEEE 19th International Conference on Intelligent Transportation Systems (ITSC 2016), Piscataway, NJ: Institute of Electrical and Electronics Engineers (IEEE), 2016, s. 1988-1993, artikel-id 7795877Konferensbidrag (Refereegranskat)
    Abstract [en]

    The main contribution of this paper is a study of the applicability of data smashing – a recently proposed data mining method – for vehicle classification according to the “Nordic system for intelligent classification of vehicles” standard, using measurements of road surface vibrations and magnetic field disturbances caused by passing vehicles. The main advantage of the studied classification approach is that it, in contrast to the most of traditional machine learning algorithms, does not require the extraction of features from raw signals. The proposed classification approach was evaluated on a large dataset consisting of signals from 3074 vehicles. Hence, a good estimate of the actual classification rate was obtained. The performance was compared to the previously reported results on the same problem for logistic regression. Our results show the potential trade-off between classification accuracy and classification method’s development efforts could be achieved.

  • 243.
    Kohlbacher, Anton
    et al.
    Luleå tekniska universitet.
    Eliasson, Jens
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, EISLAB.
    Acres, Kevin
    Monash Swarm Robotics Laboratory, Monash University.
    Chung, Hoam
    Monash Swarm Robotics Laboratory, Monash University.
    Barca, Jan Carlo
    Monash Swarm Robotics Laboratory, Monash University.
    A Low Cost Omnidirectional Relative Localization Sensor for Swarm Applications2018Ingår i: IEEE 4th World Forum on Internet of Things, Institute of Electrical and Electronics Engineers (IEEE), 2018, s. 694-699Konferensbidrag (Refereegranskat)
    Abstract [en]

    By enabling coordinated task execution and movement, robotic swarms can achieve efficient exploration of unknown environments. In this paper, we propose a relative localization sensor system using Ultra-wideband (UWB) radio technology for ranging. This system is light-weight and relatively indifferent to the types of surrounding environments. Infrastructure dependency such as the requirement of beacons at known locations is eliminated by making an array of sensors on a swarm agent. In this paper, a novel algorithm is implemented on hardware with limited resources and compared to a more traditional trilateration approach. Both utilize Particle Swarm Optimization (PSO) to be more robust against noise and to achieve similar accuracy. The experimental results show that the proposed algorithm runs up to ten times faster than the existing trilateration approach. The sensor array which forms the localization system weighs only 56g, and achieves around 0.5m RMSE with a 10Hz update rate. Experiments show that the accuracy can be further improved if the rotational bias observed in the UWB devices are compensated for.

    Ladda ner fulltext (pdf)
    fulltext
  • 244.
    Krantz, Elias
    Luleå tekniska universitet, Institutionen för system- och rymdteknik.
    Experiment Design for System Identification on Satellite Hardware Demonstrator2018Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    The subject of this thesis covers the process of online parameter estimation of agile satellites. Accurate knowledge of parameters such as moment of inertia and centre of mass play a crucial role in satellite attitude control and pointing performance. Typically, identification of parameters such as these is performed on-ground using post-processing algorithms. This thesis investigates the potential of performing the identification procedures in real-time on-board operating satellites, using only measurements available from typical satellite attitude sensors.

       The thesis covers the areas of system identification and modelling of spacecraft attitude dynamics. An algorithm based on the Unscented Kalman Filter is developed for online parameter estimation of spacecraft moment of inertia parameters. The proposed method is successfully validated, both through simulation environments, and in practice using Airbus’ satellite hardware demonstrator INTREPID, a three-axis air-bearing table equipped with CMG actuators and typical attitude sensors.

    Ladda ner fulltext (pdf)
    fulltext
  • 245. Krishnamurthy, Vikram
    et al.
    Dey, Subhrakanti
    Leblanc, James
    Blind equalization of IIR channels using hidden Markov models and extended least squares1995Ingår i: IEEE Transactions on Signal Processing, ISSN 1053-587X, E-ISSN 1941-0476, Vol. 43, nr 12, s. 2994-3006Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    In this paper, we present a blind equalization algorithm for noisy IIR channels when the channel input is a finite state Markov chain. The algorithm yields estimates of the IIR channel coefficients, channel noise variance, transition probabilities, and state of the Markov chain. Unlike the optimal maximum likelihood estimator which is computationally infeasible since the computing cost increases exponentially with data length, our algorithm is computationally inexpensive. Our algorithm is based on combining a recursive hidden Markov model (HMM) estimator with a relaxed SPR (strictly positive real) extended least squares (ELS) scheme. In simulation studies we show that the algorithm yields satisfactory estimates even in low SNR. We also compare the performance of our scheme with a truncated FIR scheme and the constant modulus algorithm (CMA) which is currently a popular algorithm in blind equalization.

    Ladda ner fulltext (pdf)
    FULLTEXT01
  • 246.
    Kristoffersson, Tom
    Luleå tekniska universitet, Institutionen för ekonomi, teknik, konst och samhälle.
    Understanding the differences between reverberation and delay on vocals in live music scenarios: A study on the perceptions and preferences of the live concert audience2023Självständigt arbete på grundnivå (kandidatexamen), 10 poäng / 15 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Two common vocal processing techniques in pop- and rock music are the use of artificial reverberation or delay. The differences between these effects have been thoroughly studied in the studio environment (Case, 2007; Henriques & Rietveld, 2018; Ronen, 2015), but research is lacking in the live realm. The purpose of this study was to answer the research question: “Understanding the perceived differences in artificial reverberation and delay (echo) on vocals in a live environment. What differences do listeners hear? What do they prefer?”. This was done through a listening test with two groups of participants, the results of which were then compared to opinions and experiences of live sound engineers working professionally within the field. The results of the study showed that listeners preferred stimuli that had been processed with delay and reverb over stimuli that had only been processed with one of the effects. In one of the listener groups, it could be determined that delay was preferred over reverb, but in the other the results were inconclusive. Overall, listeners seemed to prefer hall reverb above plate reverb, and an eighth-note delay over a quarter-note delay.

    Ladda ner fulltext (pdf)
    fulltext
  • 247.
    Kudrins, Vitalijs
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Rymdteknik.
    Development of Software Library for Open Source GNSS Receiver with Focus on Physical Layer Signal Processing2021Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    In order to directly interface with signal broadcast by global navigation satellite systems (GNSS) – such as GPS or Galileo – for the purpose of calculating location, a potential user is required to extract great amount of information from interface control documents (ICD) as well as build custom software tools to process this information. This is time consuming and inefficient. Instead it would be great if such tools and information was readily available in one single project.

    This thesis addresses this issue by designing a universal data structure which is able to accommodate all necessary information to interface with any GNSS. Universal GNSS data structure is designed in such a way so that software tools can be entirely generic across all GNSS, i.e. do not include any functionality specific to only one GNSS. This is done by embedding certain logic parameters inside data structure itself, which determine how software tools behave.

    The data structure realized in the form of XML file with specific rules and syntax. Data from GPS and Galileo ICDs is scraped and compiled into XML file. A Rust tool-set is created to read XML file and extract information such as pseudo-random noise codes and navigation message structure. Using this information, it is possible to decode a raw bit stream broadcast by GNSS spacecraft, although currently additional tools need to be added to completely automatize this process.

    Ladda ner fulltext (pdf)
    fulltext
  • 248.
    Källström, Elisabeth
    et al.
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling. Volvo Construction Equipment, Eskilstuna, Sweden.
    Lindström, John
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Håkansson, Lars
    Linnaeus University, Växjö, Sweden.
    Karlberg, Magnus
    Luleå tekniska universitet, Institutionen för teknikvetenskap och matematik, Produkt- och produktionsutveckling.
    Öberg, Olof
    Volvo Construction Equipment, Eskilstuna, Sweden.
    Identification of Vibration Properties of Wheel Loader Driveline Parts as a Base for Adequate Condition Monitoring: Bearings2017Ingår i: / [ed] Gibbs B., International Institute of Acoustics and Vibration , 2017Konferensbidrag (Refereegranskat)
    Abstract [en]

    In order to reduce costly downtime, adequate condition monitoring of the automatic transmission components in heavy duty construction equipment is necessary. The transmission in such equipment enables to change the gear ratio automatically. Further, the bearings in an automatic transmission provide low friction support to its rotating parts and act as an interface separating stationary from rotating components. Wear or other bearing faults may lead to an increase in energy consumption as well as failure of other related components in the automatic transmission, and thus costly downtime. In this study, different sensor data (particularly vibration) was collected on the automatic transmission during controlled test cycles in an automatic transmission test rig to enable adequate condition monitoring.

    An analysis of the measured vibration data was carried out using signal processing methods. The results indicate that predictive maintenance information related to the automatic transmission bearings may be extracted from vibrations measured on an automatic transmission. This information may be used for early fault detection, thus improving uptime and availability of heavy duty construction equipment.

    Ladda ner fulltext (pdf)
    fulltext
  • 249.
    Laila, Dina Shona
    et al.
    Engineering Sciences, Faculty of Engineering & the Environment, University of Southampton, Southampton SO17 1BJ, UK.
    Gruenbacher, Engelbert
    Bernecker & Rainer Industrie-Elektronik Ges.m.b.H, 4840 Vöcklabruck, Austria.
    Nonlinear output feedback and periodic disturbance attenuation for setpoint tracking of a combustion engine test bench2016Ingår i: Automatica, ISSN 0005-1098, E-ISSN 1873-2836, Vol. 64, s. 29-36Artikel i tidskrift (Refereegranskat)
  • 250.
    Landström, Anders
    Luleå tekniska universitet, Institutionen för system- och rymdteknik, Signaler och system.
    Adaptive tensor-based morphological filtering and analysis of 3D profile data2012Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    Image analysis methods for processing 3D profile data have been investigated and developed. These methods include; Image reconstruction by prioritized incremental normalized convolution, morphology-based crack detection for steel slabs, and adaptive morphology based on the local structure tensor. The methods have been applied to a number of industrial applications.An issue with 3D profile data captured by laser triangulation is occlusion, which occurs when the line-of-sight between the projected laser light and the camera sensor is obstructed. To overcome this problem, interpolation of missing surface in rock piles has been investigated and a novel interpolation method for filling in missing pixel values iteratively from the edges of the reliable data, using normalized convolution, has been developed.3D profile data of the steel surface has been used to detect longitudinal cracks in casted steel slabs. Segmentation of the data is done using mathematical morphology, and the resulting connected regions are assigned a crack probability estimate based on a statistic logistic regression model. More specifically, the morphological filtering locates trenches in the data, excludes scale regions for further analysis, and finally links crack segments together in order to obtain a segmented region which receives a crack probability based on its depth and length.Also suggested is a novel method for adaptive mathematical morphology intended to improve crack segment linking, i.e. for bridging gaps in the crack signature in order to increase the length of potential crack segments. Standard morphology operations rely on a predefined structuring element which is repeatedly used for each pixel in the image. The outline of a crack, however, can range from a straight line to a zig-zag pattern. A more adaptive method for linking regions with a large enough estimated crack depth would therefore be beneficial. More advanced morphological approaches, such as morphological amoebas and path openings, adapt better to curvature in the image. For our purpose, however, we investigate how the local structure tensor can be used to adaptively assign to each pixel an elliptical structuring element based on the local orientation within the image. The information from the local structure tensor directly defines the shape of the elliptical structuring element, and the resulting morphological filtering successfully enhances crack signatures in the data.

    Ladda ner fulltext (pdf)
    FULLTEXT01
2345678 201 - 250 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