June 2003, Volume 12, Number 2
Sensor arrays are often used for a signal separation from noises using the information about the direction of arrival. The aim of this paper is to analyze Frost's beamformer with respect to the speech preprocessing for the hearing impaired people. The frequency response of the system including the background noise attenuation are derived as functions of the direction of arrival. The derivation supposes a uniform linear array of sensors and plane waves. It is shown that the number of possible configurations can be decreased by using some symmetries. The impact of the used algorithm constraint on the frequency response and subsequently on the directional noise suppression is derived analytically.
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- FROST, O. L. An algorithm for linearly constrainedadaptive array processing. In Proceedings of IEEE,1972, vol. 60, no. 8, p. 926-934.
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- GANNOT, S.,BRUSHTEIN, D., WEINSTEIN, E.Beamforming for multichannel speech enhancement.In Proceedings of IWAENC'99, 1999, p. 96-99.
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Fast messy genetic optimization is found suitable for complex microwave circuit design. Increase in computation speed is achieved using several ordinary computers connected to a network. Calculations are running on background so that computers can be used for other purposes at the same time. Dynamic change of bounds, search space segmentation and gradient incorporation have significantly improved convergence rate. The new method has found global minimum in each run, while classic methods failed for some starting points.
- KNJAZEW, D. Application of the Fast Messy Genetic Algorithm to Permutation and Scheduling Problems. Illigal Report 2000022, University of Illinois, May 2000.
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- The search for Extraterrestrial Intelligence, http://setiat-home.ssl.berkley.edu
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A new approach suitable for determination of the maximal stable time increment for the Finite-Difference Time-Domain (FDTD) algorithm in common curvilinear coordinates, for general mesh shapes and certain types of boundaries is presented. The maximal time increment corresponds to a characteristic value of a Helmholz equation that is solved by a finite-difference (FD) method. If this method uses exactly the same discretization as the given FDTD method (same mesh, boundary conditions, order of precision etc.), the maximal stable time increment is obtained from the highest characteristic value. The FD system is solved by an iterative method, which uses only slightly altered original FDTD formulae. The Courant condition yields a stable time increment, but in certain cases the maximum increment is slightly greater .
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This contribution addresses the problem of additive noise reduction in speech picked up by a microphone in a noisy environment. Two systems belonging to the family of coherence-based noise cancellers are presented. Suggested systems have the modular structure using 2 or 4 microphones and suppress non-stationary noises in the range of 4 to 17 dB depending on the chosen structure and noise characteristics. The common properties are acceptable noise suppression, low speech distortion and residual noise.
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- DORBECKER, M.: Speech enhancement using small microphone arrays with optimized directivity. IWAENC 97, 1997, pp. 100-103.
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- DORBECKER, M., ERNST, S. Combination of two-channel spectral subtraction and adaptive Wiener post filtering for noise reduction and deverberation. IWAENC 97, 1997.
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The FDSS macrocell downlink capacity is evaluated for macrocells that operate at the same frequency of the Digital TV station (DTV) and that are nearby the DTV installations. It has been founded that the cell capacity is not affected when the distance between the DTV installations and the macrocell is more than 25 km. For lower distance, the effect is high and the downlink vanishes at a distance less than 2.1 km.
- KALEH, G. Frequency Diversity Spread Spectrum Communications to Counter Bandlimited Gaussian Interference. IEEE Transactions on Communications. 1996, vol. 44, no. 7, p. 886 - 893.
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- CALVO-RAMON, M. Third Generation IMT-2000 (UMTS) Mobile Communication Systems. Fundacion Airtel Vodafone, 2002. In Spanish.
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The downlink power control problem in W-CDMA is studied using a new proposed model. The downlink cell capacity is given for the old model given by Gejji and our new model. A capacity increase of 16 % for the special case = 0 (no orthogonality between users) and a generalization of the old model in terms of the propagation exponent and orthogonality factor is introduced.
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In this paper we analyze the adaptation rule, which estimates the channel state and switches between hybrid ARQ (automatic-repeat-request) and pure ARQ. Convolutional code was chosen as FEC (forward-error-correction) in hybrid ARQ part and go-back-N ARQ scheme is used in both cases. The adaptation rule is based on counting ACKs and NAKs and its throughput analysis is made.
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- KOSUT, P. Analyza priepustnosti adaptivnych Go-Back-N schem. PhD thesis, Slovak University of Technology Bratislava, 2001.
- CHOI, S., SHIN, K.G. A Class of Adaptive Hybrid ARQ Schemes for Wireless Links. IEEE Trans. on Vehicular Techn., 2001, vol.50, no.3, pp. 777-790.
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- POLEC, J., KARLUBIKOVA, T., Stochasticke modely v telekomunikaciach 1. FABER 1999, Bratislava.