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  • 151. Nordebo, Sven
    et al.
    Claesson, Ingvar
    Nordholm, Sven
    Adaptive Beamforming: Spatial Filter Designed Blocking Matrix1994In: IEEE journal of oceanic engineering : a journal devoted to the application of electrical and electronics engineering to the oceanic environment , ISSN 0364-9059 , Vol. 19, no 14, p. 583-590Article in journal (Refereed)
    Abstract [en]

    Controlling the resolution in adaptive beamformers is often crucial. A simple method that works for both narrowband and broad-band arrays is presented. This method is based on the normalized leaky LMS algorithm in conjunction with a generalized sidelobe canceller (GSC) structure, where the GSC is designed using a spatial filtering approach. In essence, the suppression of the spatial filters and the implicit noise of the leaky LMS algorithm together determine the adaptive beamformer. Analytical expressions are given for the Wiener filters and the output spectrum versus frequency and point source location. These expressions are employed in the design specification of the spatial filters and to obtain conditions for a controlled quiescent beamformer response. Simulation results are presented to illustrate the behavior of the array.

  • 152. Nordebo, Sven
    et al.
    Claesson, Ingvar
    Nordholm, Sven
    An Adaptive Microphone Array Employing Calibration Signals Recorded On-Site1994Conference paper (Refereed)
    Abstract [en]

    This paper presents an adaptive microphone array, which facilitates a simple built-in calibration to the environment and the electronic equipment used. The method is well-suited for speech enhancement in handsfree mobile telephones as well as for speech enhancement in speech recognition devices.

  • 153. Nordebo, Sven
    et al.
    Claesson, Ingvar
    Nordholm, Sven
    An Adaptive Microphone Array Employing Calibration Signals Recorded On-Site1994Conference paper (Refereed)
    Abstract [en]

    This paper presents an adaptive microphone array, which facilitates a simple built-in calibration to the environment and the electronic equipment used. The method is well-suited for speech enhancement in handsfree mobile telephones as well as for speech enhancement in speech recognition devices.

  • 154. Nordebo, Sven
    et al.
    Claesson, Ingvar
    Nordholm, Sven
    Design of Broadband Adaptive Beamformers using Spatial Filters1993Report (Other academic)
  • 155. Nordebo, Sven
    et al.
    Claesson, Ingvar
    Nordholm, Sven
    FIR Approximation of the Spatial Filter Designed Generalized Sidelobe Canceller1991Report (Other academic)
  • 156. Nordebo, Sven
    et al.
    Claesson, Ingvar
    Nordholm, Sven
    Quadratic Programming for the Design of Two--Dimensional Weighted Chebyshev FIR Filters with Incomplete Specifications1997In: Nonlinear Analysis, Theory, Methods \& Applications, ISSN 0362-546X , Vol. 30, no 7, p. 4345-4355Article in journal (Refereed)
  • 157. Nordebo, Sven
    et al.
    Claesson, Ingvar
    Nordholm, Sven
    Quadratic Programming for the Design of Two-Dimensional Weighted Chebyshev FIR Filters with Incomplete Specifications1996Conference paper (Refereed)
  • 158. Nordebo, Sven
    et al.
    Claesson, Ingvar
    Nordholm, Sven
    Robust beamforming with respect to model imperfections and channel mismatch1994Conference paper (Refereed)
  • 159. Nordebo, Sven
    et al.
    Claesson, Ingvar
    Nordholm, Sven
    Robust Beamforming with Respect to Model Imperfections and Channel Mismatch1994Conference paper (Refereed)
  • 160. Nordebo, Sven
    et al.
    Claesson, Ingvar
    Nordholm, Sven
    Semi-Infinite Linear Programming for Signal Processing Applications1998Conference paper (Refereed)
  • 161. Nordebo, Sven
    et al.
    Claesson, Ingvar
    Nordholm, Sven
    Spatial Filter Designed Generalized Sidelobe Canceller for Broadband Implementations1992Conference paper (Refereed)
    Abstract [en]

    A novel design procedure for the signal blocking matrix in the broadband generalized sidelobe canceller, is proposed. A 1-dimensional spatial filter is devised in order to prevent the target signal from reaching the cancelling adaptive filters. Simulations and calculations have been performed in order to verify the design

  • 162. Nordebo, Sven
    et al.
    Claesson, Ingvar
    Nordholm, Sven
    Spatial Filter Designed Generalized Sidelobe Canceller for Broadband Implementations1992Conference paper (Refereed)
    Abstract [en]

    A novel design procedure for the signal blocking matrix in the broadband generalized sidelobe canceller, is proposed. A 1-dimensional spatial filter is devised in order to prevent the target signal from reaching the cancelling adaptive filters. Simulations and calculations have been performed in order to verify the design.

  • 163. Nordebo, Sven
    et al.
    Claesson, Ingvar
    Nordholm, Sven
    Weighted Chebyshev Approximation for the Design of Broadband Beamformers using Quadratic Programming1994In: IEEE Signal Processing Letters, ISSN 1070-9908 , Vol. 1, no 7, p. 103-105Article in journal (Refereed)
    Abstract [en]

    A method to solve a general broadband beamformer design problem is formulated as a quadratic program. As a special case, the minimax near-field design problem of a broadband beamformer is solved as a quadratic programming formulation of the weighted Chebyshev approximation problem. The method can also be applied to the design of multidimensional digital FIR filters with an arbitrarily specified amplitude and phase. For linear phase multidimensional digital FIR filters, the quadratic program becomes a linear program. Examples are given that demonstrate the minimax near-field behavior of the beamformers designed.

  • 164. Nordebo, Sven
    et al.
    Claesson, Ingvar
    Nordholm, Sven
    Bengtsson, Bengt
    In Situ Calibrated Adaptive Microphone Array1994Report (Other academic)
  • 165. Nordebo, Sven
    et al.
    Gustavsson, Jan-Olof
    On the Application of Linear Programming to Channel and Symbol Maximum Likelihood Estimation1997Conference paper (Refereed)
  • 166. Nordebo, Sven
    et al.
    Nordholm, Sven
    Bengtsson, Bengt
    Claesson, Ingvar
    Noise Reduction Using an Adaptive Microphone Array in a Car- A Speech Recognition Evaluation1993Conference paper (Refereed)
    Abstract [en]

    This paper describes an evaluation of an adaptive microphone array with respect to speech recognition performance in a car. The microphone array is compared to two conventional microphones of different types. The speech recognition device is aimed to be a part of a man/machine-interface between the driver and car information services

  • 167. Nordebo, Sven
    et al.
    Nordholm, Sven
    Claesson, Ingvar
    Broadband Adaptive Beamforming for Noise Suppression1992Conference paper (Refereed)
  • 168. Nordebo, Sven
    et al.
    Zang, Zhuquan
    Application of Infinite Dimensional Linear Programming to IIR Filter Design with Time Domain Constraints1999In: IEEE Transactions on Signal Processing, ISSN 1053-587X , Vol. 47, no 7, p. 2060-2063Article in journal (Refereed)
  • 169. Nordebo, Sven
    et al.
    Zang, Zhuquan
    Application of Infinite Dimensional Linear Programming to IIR Filter Design with Time Domain Constraints1998Conference paper (Refereed)
    Abstract [en]

    Recently developed infinite dimensional linear programming techniques are used for the design of recursive filters with complex Chebyshev error criteria and time-domain constraints. The approach is applied to a numerical example which deals with the design of a Laguerre network as an equalization filter for a digital transmission channel.

  • 170. Nordholm, Sven
    A Sensitivity Analysis of a Spatial Filter Adaptive Beamforming Structure1991Report (Other academic)
  • 171. Nordholm, Sven
    Adaptive Microphone Array Employing Calibration Signals. An Analytical Evaluation1995Report (Other academic)
    Abstract [en]

    This report evaluates an adaptive microphone array which facilitates a simple built-in calibration to the environment and instrumentation. The method has been suggested for use in hands-free mobile telephones for both speech enhancement and acoustic echo-cancellation as well as speech recognition. The scheme has several advantages such as a simple calibration procedure, directed jammer suppression, versatile robust beamforming and reduced target signal distortion. The analysis employs noncausal Wiener filters yielding compact and effective theoretical suppression limits.

  • 172. Nordholm, Sven
    Broadband Adaptive Beamforming with Applications in Acoustic Signal Processing1992Doctoral thesis, comprehensive summary (Other academic)
  • 173. Nordholm, Sven
    et al.
    Claesson, Ingvar
    Analytical evaluation of a self-calibrating microphone array1997Conference paper (Refereed)
    Abstract [en]

    This paper gives an analytical description of an adaptive microphone array which facilitates a simple built-in calibration to the environment and instrumentation. The scheme offers several advantages, such as a simple calibration procedure and reduced target signal distortion. The analysis employs noncausal Wiener filters yielding compact and effective theoretical suppression limits.

  • 174. Nordholm, Sven
    et al.
    Claesson, Ingvar
    Preventing Target Cancellation in Adaptive Broadband Microphone Arrays1991Conference paper (Refereed)
  • 175. Nordholm, Sven
    et al.
    Claesson, Ingvar
    Preventing Target Cancellation in Adaptive Broadband Microphone Arrays1991Conference paper (Refereed)
  • 176. Nordholm, Sven
    et al.
    Claesson, Ingvar
    Bengtsson, Bengt
    Adaptive Array Noise Suppression of Handsfree Speaker Input in Cars1993In: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 42, no 4, p. 514-518Article in journal (Refereed)
    Abstract [en]

    Handsfree speaker input of mobile telephones is most desirable today in order to enable safe operation in cars. This is also a prerequisite for voice control of car devices. This paper presents an ''on the road'' evaluation of the performance of an adaptive microphone array for speech enhancement in cars. The results show a signal-to-noise ratio (SNR) improvement in the range of 10-15 dB over the telephone frequency range with a slight favour for higher frequencies when driving at normal speeds.

  • 177. Nordholm, Sven
    et al.
    Claesson, Ingvar
    Bengtsson, Bengt
    Implementation of a Griffith-Jim Adaptive Microphone Array on a TMS320C25 Multi-DSP1990Conference paper (Refereed)
  • 178. Nordholm, Sven
    et al.
    Claesson, Ingvar
    Bengtsson, Bengt
    Near Field Performance Evaluation of a Spatial Filtering Adaptive Microphone Array1991Report (Other academic)
  • 179. Nordholm, Sven
    et al.
    Claesson, Ingvar
    Bengtsson, Bengt
    Eriksson, Per
    On the road: Evaluation of an Adaptive Array for Handsfree Mobile Telephones1991Conference paper (Refereed)
  • 180. Nordholm, Sven
    et al.
    Claesson, Ingvar
    Bengtsson, Bengt
    Eriksson, Per
    On-the-Road Evaluation of an Adaptive Array for Handsfree Mobile Telephones1991Conference paper (Refereed)
  • 181. Nordholm, Sven
    et al.
    Claesson, Ingvar
    Bengtsson, Bengt
    Eriksson, Per
    Signalprocessor-Implementering av en Adaptiv Mikrofon-Array1990Conference paper (Refereed)
  • 182. Nordholm, Sven
    et al.
    Claesson, Ingvar
    Dahl, Mattias
    Adaptive Microphone Array Employing Calibration Signals. An Analytical Evaluation1999In: IEEE transactions on speech and audio processing, ISSN 1063-6676, E-ISSN 1558-2353, Vol. 7, no 3, p. 241-52Article in journal (Refereed)
    Abstract [en]

    This paper gives an analytical description of an adaptive microphone array that facilitates a simple built-in calibration to the environment and instrumentation. This method, suggested for use in hands-free mobile telephones and speech recognition systems for cars, provides speech enhancement and acoustic echo-cancellation. The scheme offers several advantages, such as a simple calibration procedure, suppression of directional sources, versatile robust beamforming, and reduced target signal distortion. The analysis employs noncausal Wiener filters yielding compact and effective theoretical suppression limits

  • 183. Nordholm, Sven
    et al.
    Claesson, Ingvar
    Eriksson, Per
    Superresolution effects in Broadband Antenna Arrays1990Conference paper (Refereed)
    Abstract [en]

    The problem of finding the angular 3-dB beamwidth for a wideband Griffiths-Jim adaptive beamformer is discussed. Approximate analytic expressions are presented and their relation to the Cramer-Rao bound (CRB) is considered. Results on the CRB in direction of arrival estimation for a sinusoidal signal are extended to narrowband and broadband signals, together with simple interpretations of their behavior. Superresolution results with a five-element array for three target signal bandwidths (400-2000, 800-1600, and 1120-1280 Hz) are presented.

  • 184. Nordholm, Sven
    et al.
    Claesson, Ingvar
    Eriksson, Per
    Superresolution Effects in Broadband Antenna Arrays1990Conference paper (Refereed)
    Abstract [en]

    The problem of finding the angular 3-dB beamwidth for a wideband Griffiths-Jim adaptive beamformer is discussed. Approximate analytic expressions are presented and their relation to the Cramer-Rao bound (CRB) is considered. Results on the CRB in DOA (director of arrival) estimation for a sinusoidal signal are extended to narrowband and broadband signals, together with simple interpretations of their behavior. Superresolution results with five-element array for three target signal bandwidths (400-2000, 800-1600, and 1120-1280 Hz) are presented.

  • 185. Nordholm, Sven
    et al.
    Claesson, Ingvar
    Eriksson, Per
    The Broadband Wiener Solution for Griffiths-Jim Beamformers1992In: IEEE Transactions on Signal Processing , ISSN 1053-587X , Vol. 40, no 2, p. 474-478Article in journal (Refereed)
    Abstract [en]

    This correspondence treats the problem of finding the Wiener filters for a wide-band adaptive beamformer. Explicit expressions are given for the filte rs and error power spectrum in the frequency domain. The expressions are si mple to program and give the possibility of investigating superresolution f or wide-band signals and of determining sufficient lengths of the FIR filte rs in adaptive arrays. Further, approximative analytic expressions of the 3 -dB resolution of broad-band arrays are presented.

  • 186. Nordholm, Sven
    et al.
    Claesson, Ingvar
    Grbic, Nedelko
    Performance Limits in Subband Beamforming2003In: IEEE transactions on speech and audio processing, ISSN 1063-6676, E-ISSN 1558-2353, Vol. 11, no 3, p. 193-203Article in journal (Refereed)
    Abstract [en]

    This paper analyzes subband beamforming schemes mainly aimed at speech enhancement and acoustic echo suppression applications such as hands-free telephony for both mobile and office environments, internet telephony and video conferencing. Analytical descriptions of both causal finite-length and noncausal infinite-length subband microphone array structures are given. More specifically, this paper compares finite Wiener filter performance with the noncausal Wiener solution, giving a comprehensive theoretical suppression limit. It is shown that even short filters will yield a good approximation of the infinite solution, provided that the element spacing and temporal sampling is matched to the frequency band of interest. Typically, 10-20 FIR taps are sufficient in each subband.

  • 187. Nordholm, Sven
    et al.
    Claesson, Ingvar
    Nordebo, Sven
    Hands-free Mobile Telephony by Means of an adaptive Microphone Array1994Conference paper (Refereed)
  • 188. Nordholm, Sven
    et al.
    Claesson, Ingvar
    Nordebo, Sven
    Dahl, Mattias
    Hands-free mobile telephony by means of an adaptive microphone array1994Conference paper (Refereed)
  • 189. Nordholm, Sven
    et al.
    Dahl, Mattias
    Claesson, Ingvar
    Adaptive Microphone Array: Analytical and Measurement Results1997Conference paper (Refereed)
  • 190. Nordholm, Sven
    et al.
    Leung, Ye Hong
    Performance of Broad-band Generalized Sidelobe Cancellers in Isotropic Noise Field2000In: Journal of Acoustical Society of America, ISSN 0001-4966 , Vol. 107, no 2, p. 1057-60Article in journal (Refereed)
    Abstract [en]

    In acoustic applications, the signal source of interest is generally broadband and the background noise field is predominantly isotropic. In this letter, the performance of the broadband generalized sidelobe canceller, optimized with respect to an isotropic noise field, is analyzed and compared against the performance of the conventional summing beamformer. The comparison is based on an ideal continuous-time infinite-length generalized sidelobe canceller with the aim of determining the performance limits of this beamforming structure. ©2000 Acoustical Society of America.

  • 191. Nordholm, Sven
    et al.
    Nordberg, Jörgen
    Delayless Subband Echo Cancellation1997Conference paper (Refereed)
    Abstract [en]

    Echo suppression is a vital part of every communications system. The use of hands-free communication in cars, computer applications and video conferencing have created further demands for high-quality acoustic echo cancellation. In these applications the acoustic channel has, typically, a long impulse response in the order of 100 ms. Typical lengths of adaptive FIR-filters are 500-1500 taps, assuming a 12 kHz sampling frequency. In order to reduce the computational load and also to improve the convergence rate, sub-band processing schemes have been suggested. This paper presents a study of a delayless sub-band adaptive filter. The study shows a possible echo suppression of about 30 dB and also an improved convergence rate when compared to a fullband LMS-filter. The main issues discussed are filter bank design and a simple speech detector that gives a drastic performance improvement.

  • 192. Nordholm, Sven
    et al.
    Nordberg, Jörgen
    Nordebo, Sven
    Sub-band Acoustic Echo Cancellation1997Report (Other academic)
    Abstract [en]

    Echo suppression is a vital part of every communications system. The use of handsfree communication in cars, computer applications and video conferencing have created further demands for high-quality acoustic echo cancellation. In these applications the acoustic channel has, typically, a long impulse response in the order of 100ms. Typical lengths of adaptive FIR-filters are 500-1500 taps, assuming a 12 kHz sampling frequency. In order to reduce the computational load and also to improve the convergence rate, subband processing schemes have been suggested. This paper presents a study of a delayless sub-band adaptive filter. The study shows a possible echo suppression of about 30 dB and also an improved convergence rate when compared to a fullband LMS-filter. The main issues discussed are filter bank design and a simple speech detector that gives a drastic performance improvement

  • 193. Nordholm, Sven
    et al.
    Nordberg, Jörgen
    Skoog, Joakim
    An Acoustic Echo Canceller Using Subband Adaptive Filters1996Conference paper (Refereed)
    Abstract [en]

    The use of hands-free communication in cars, computer applications and video-conferencing has created a demand for high-quality acoustic echo cancellation. In these applications have the acoustic channel typically a long impulse response in the order of 100ms. Typical lengths of adaptive FIR-filters can be 500-1500 taps. In order to reduce the complexity and also improve the convergence rate have subband processing schemes been suggested. This paper presents an implementation of a delayless subband adaptive filter. The study shows a possible suppression of about 30 dB and also a more rapid convergence than a fullband LMS-filter.

  • 194. Nordholm, Sven
    et al.
    Rehbock, Volke
    Teo, Kok Ley
    Nordebo, Sven
    Chebyshev Optimization for the Design of Broadband Beamformers in the Near Field1998In: IEEE transactions on circuits and systems. 2 : Analog and digital signal processing, ISSN 1057-7130 , Vol. 45, no 1, p. 141-143Article in journal (Refereed)
    Abstract [en]

    The use of microphone arrays for video conferences, hands-free mobile telephony and computer applications has created the demand for near-field broadband beamformer design methods. Here, a general broadband beamformer design problem is formulated as a weighted Chebyshev optimization problem, and a method to solve the resulting functionally-constrained problem is presented. The formulation can also be applied to the design of multidimensional digital finite-impulse response (FIR) filters with an arbitrarily specified amplitude and phase. Numerical results that demonstrate the minimax near-field behavior of the designed beamformers are given.

  • 195. Persson, Per
    et al.
    Nordebo, Sven
    Claesson, Ingvar
    A multimode mean field annealing technique to design recursive digital filters2001In: IEEE transactions on circuits and systems. 2, Analog and digital signal processing (Print), ISSN 1057-7130, E-ISSN 1558-125X, p. 1151-1154Article in journal (Refereed)
    Abstract [en]

    The multi-mode mean field annealing (MM-MFA) approach to combinatorial optimization is introduced as a tool to design recursive infinite-impulse response (IIR) digital filters with discrete coefficients. As an application example demonstrating the potential of the method we consider the design of structurally passive IIR digital filters realized as the sum of two all-pass functions. The new design technique facilitates the solution of nontrivial filter design problems such as satisfying a general frequency specification by solving a combinatorial optimization problem over discrete coefficients and a max-norm cost. The final solution is not guaranteed to be a globally optimal solution but the convergence time is short enough to allow interactive design even for large problems.

  • 196. Persson, Per
    et al.
    Nordebo, Sven
    Claesson, Ingvar
    Blekinge Institute of Technology, Department of Signal Processing.
    Design of Digital Filters with General Hardware Constraints by Mean Field Annealing2001Conference paper (Refereed)
    Abstract [en]

    The mean field annealing (MFA) algorithm is presented as an efficient tool to design digital filters with discrete coefficients and hardware constraints. As an application example the algorithm is used to design a finite wordlength digital filter with a simple hardware constraint. The ability of the deterministic MFA algorithm to approximate the mean behavior of the stochastic simulated annealing algorithm is indicated by numerical results.

  • 197. Sattar, Farook
    et al.
    Floreby, Lars
    Salomonsson, Göran
    Lövström, Benny
    Blekinge Institute of Technology, Department of Signal Processing.
    Image Enhancement based on a Nonlinear Multiscale Method1997In: IEEE Transactions on Image Processing, ISSN 1057-7149, E-ISSN 1941-0042, Vol. 6, no 6, p. 888-895Article in journal (Refereed)
    Abstract [en]

    An image enhancement method that reduces speckle noise and preserves edges is introduced. The method is based on a new nonlinear multiscale reconstruction scheme that is obtained by successively combining each coarser scale image with the corresponding modified interscale image. Simulation results are included to demonstrate the performance of the proposed method.

  • 198. Sjösten, Per
    Active Engine Mount for Marine Applications1994Conference paper (Refereed)
  • 199. Sjösten, Per
    Active Noise Control: An Overview and a Short Description of the Project at CTH1990Conference paper (Refereed)
  • 200. Sjösten, Per
    Noise Shaping of Multitone Spectra Using the LMS Adaptive Algorithm1990Conference paper (Refereed)
12345 151 - 200 of 220
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