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Sökning: WFRF:(Nordholm Sven)

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  • Dahl, Mattias, et al. (författare)
  • Acoustic Echo and Noise Cancelling using Microphone Arrays
  • 1996
  • Konferensbidrag (refereegranskat)abstract
    • This paper presents a new method to simultaneously perform 20 dB acoustic echo cancellation and 10 dB speech enhancement utilizing an adaptive microphone array. The system is based on a fast and efficient on-site calibration. Primarily intended for handsfree telephones in automobiles, the microphone array system simultaneously emphasizes the near-end talker and suppresses the handsfree loudspeaker and car noise. The method can also be used in other situations such as conventional speaker phones.
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  • Nordberg, Jörgen, et al. (författare)
  • Acoustic Echo Cancellation Employing Delayless Subband Adaptive Filters
  • 1996
  • Konferensbidrag (refereegranskat)abstract
    • 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 these acoustic channel has 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 to improve the convergence rate, subband processing schemes have 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 compared to a fullband LMS-filter.
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  • Nordberg, Jörgen, et al. (författare)
  • Digital Beamforming as a Means for Interference Cancellation
  • 1997
  • Konferensbidrag (refereegranskat)abstract
    • The increasing demand for user capacity is one of the major challenges to network operators today. In order to increase the capacity in a mobile radio network, it is desirable to exploit the spatial domain in an efficient way. An array adds spatial domain selectivity in order to improve the Carrier-to-Interference ration (C/I). An adaptive antenna ray can further improve the Carrier-to-Interference ratio (C/I) by suppressing interfering signals. The proposed circular array consists of M elements and combines fixed beamformers with interference cancellors. The fixed beamformers use a weight matrix to form multiple beams. The radius of the circular array is assumed to be half the wavelenght of the signal. The interference cancellor suppresses undesired signals, so called jammers, leaking into the desired beam. The desired signal is filtered out by the fixed beamforming structure. Due to the sidelobes, interfering signals will also, however, be present in this beam. Two alternative strategies may be chosen to cancel these interferers; use the other fixed beam outputs as inputs to an adaptive interference canceller, or demodulate the outputs from the other fixed beams and regenerate clean signals which are used as inputs to adaptive interference cancellers. Results are presented using beamformer weights obtained from an LS minimization as well as minimax.
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  • Resultat 1-10 av 117

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