# September 2004, Volume 13, Number 3

**J. Novotny, P. Sovka, J. Uhlir**
[references] [full-text]

Study and Application of Silence Model Adaptation for Use in Telephone
Speech Recognition System

This paper addresses the problem of the mismatch between a silence model and background noises which often occurs in a telephone speech recognition system (SRS) application. At first, the use of parallel model combination (PMC) methods is studied with the respect to this application. Secondly, the effective adaptation of a silence model to various background noises is confirmed. Finally, an original method combining log-add PMC with a noise power spectral density estimation based on minimum statistics is proposed. The performed tests prove the benefit of the suggested method to the speech recognition results that is caused by the stability of speech vector selection under the influence of various background noises. The advantages can be seen in no extra voice activity detector and in a relatively low computational load.

- CERNOCKY , J., POLLAK, P., HANZL, V. Czech Recordings andAnnotations on CD's - Documentation on the Czech Database andDatabase Access. Research Report, Prague, CTU, 2000.
- HILGER, F., NEY, H. Noise level normalization and reference adaptationfor robust speech recognition. In Proc. ASR, 2000, p. 64-68.
- RAMAN, V., RAMANUJAM, V. Robustness issues and solutions inspeech recognition based telephony services. In Proc. ICASSP, 1997,p. 1523-1526.
- JUNQUA, J. C., MAK, B., REAVES, B. A robust algorithm for wordboundary detection in the presence of noise. IEEE Trans. on Speech andAudio Processing, 1994, vol. 2, p. 406-412.
- VETH, J., MAUUARY, L., NOE, B., WET, F., SIENEL J., BOVES,L., JOUVET, D. Feature vector selection to improve ASR robustness innoisy conditions. In Proc. Eurospeech, 2001.
- ETSI ES 202 050 V1.1.1. European Telecommunication Standards Institute,2002.
- ACCAINO, S., TSIPORKOVA, E., HAMME, H. Modeling of extraevents for telephony. In Voice operated telecom services: Do they have abright future? workshop proceedings, Ghent, Belgium, 2000, p. 75-78.
- NOVOTNY, J., SOVKA, P., UHL´IR· , J. Analysis and Optimizationof Telephone Speech Command Recognition System Performance inNoisy Environment. Radioengineering, 2004, vol. 13.
- GALES, M. J. F., YOUNG, S.J. HMM recognition in noise using parallelmodel combination. In Proc. Eurospeech, 1993, p. 837-840.
- GALES, M. J. F., YOUNG, S.J. A fast and flexible implementation ofparallel model combination. In Proc. ICASSP, 1995, pp. 133-136.
- GALES, M. J. F. Predictive model-based compensation schemes for robustspeech recognition. Speech Communication, 1998, vol. 25.
- HWANG, T. H., WANG, H. Ch. A fast algorithm for parallel modelcombination for noisy speech recognition. Computer Speech and Language,2000, vol. 14, p. 81-100.
- HUNG, J., SHEN, J., LEE, L. New approaches for domain transformationand parameter combination for improved accuracy in parallel modelcombination (PMC) techniques. IEEE Trans. on Speech and Audio Processing,2001, vol. 9, p. 842-855.
- MARTIN, R. Spectral subtraction based on minimum statistics. In Proc.Eur. Signal Processing Conference, 1994, p. 1182-1185.
- MARTIN, R. Noise power spectral density estimation based on optimalsmoothing and minimum statistics. IEEE Trans. on Speech and AudioProcessing, 2001, vol. 9, p. 504-512.
- YOUNG, S. The HTK Book (for HTK Version 3.1). Cambridge UniversityEngineering Department, December 2001.

**J. Dobes, L. Pospisil**
[references] [full-text]

Enhancing the Accuracy of Microwave Element Models by Artificial Neural
Networks

In the recent PSpice programs, five types of the GaAs FET model have been implemented. However, some of them are too sophisticated and therefore very difficult to measure and identify afterwards, especially the realistic model of Parker and Skellern. In the paper, simple enhancements of one of the classical models are proposed first. The resulting modification is usable for the accurate modeling of both GaAs FETs and pHEMTs. Moreover, its updated capacitance function can serve as an accurate representation of microwave varactors, which is also important. The precision of the updated models can be strongly enhanced using the artificial neural networks. In the paper, both using an exclusive neural network without an analytic model and cooperating a corrective neural network with the updated analytic model will be discussed. The accuracy of the analytic models, the models based on the exclusive neural network, and the models created as a combination of the updated analytic model and the corrective neural network will be compared.

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- DOBES, J. Using modified GaAs FET model functions for the accuraterepresentation of PHEMTs and varactors. In Proceedings of the12th IEEE Mediterranean Electrotechnical Conference, Dubrovnik(Croatia), 2004, p. 35 - 38.
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**J. Pospisil, Z. Kolka, S. Hanus, J. Petrzela, J. Brzobohaty**
[references] [full-text]

Optimized Second-Order Dynamical Systems and Their RLC Circuit Models
with PWL Controlled Sources

Complementary active RLC circuit models with a voltage-controlled voltage source (VCVS) and a current-controlled current source (CCCS) for the second-order autonomous dynamical system realization are proposed. The main advantage of these equivalent circuits is the simple relation between the state model parameters and their corresponding circuit parameters, which leads also to simple design formulas.

- POSPISIL, J., KOLKA, Z., HORSKA, J. Synthesis of optimized piecewise-linear system using similarity transformation - part II: second order systems. Radioengineering. 2001, vol. 10, no. 3, p. 8 - 10.
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**P. Valtr, P. Pechac**
[references] [full-text]

Diffraction Calculations and Measurements in Millimeter Frequency Band

The paper deals with a study of diffraction on dielectric wedge (building corner) in millimeter frequency band, both theoretically and experimentally, to provide knowledge support for ray tracing/launching calculations of MWS interference issues in urban areas. The main motivation was to find balance between reasonably reliable results and necessary demands on calculation complexity and input data accuracy. Verification of Uniform Theory of Diffraction (UTD) was made both for perfectly conducting and dielectric wedge-shaped obstacle. Comparisons of theoretical results and experimental measurement at millimeter waves in anechoic chamber are presented.

- ITU-R P.1410 Propagation data and prediction methods required for design of terrestrial broadband millimetric radio access systems operating in a frequency range about 20-50 GHz. ITU-R. 2000.
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**T. Hult, A. Mohammed**
[references] [full-text]

Suppression of EM Fields using Active Control Algorithms and MIMO
Antenna System

Active methods for attenuating acoustic pressure fields have been successfully used in many applications. In this paper we investigate some of these active control methods in combination with a MIMO antenna system in order to assess their validity and performance when applied to electromagnetic fields. The application that we evaluated in this paper is a model of a mobile phone equipped with one ordinary transmitting antenna and two actuator-antennas which purpose is to reduce the electromagnetic field at a specific area in space (e.g. at the human head). Simulation results show the promise of using the adaptive active control algorithms and MIMO system to attenuate the electromagnetic field power density.

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- HULT, T. Active Suppression of Electromagnetic Fields. Master Thesis, Blekinge Institute of Technology, 2002. [dB]
- HULT, T.; MOHAMMED, A.; NORDEBO, S. Active Suppression of Electromagnetic Fields using a MIMO Antenna System. In 17th Int. Conf. on Appl. Electromagnetics and Commun. ICECom 2003, 2003.

**P. Hanzlik, P. Pata**
[references] [full-text]

Behind the Structure of Video VQ-Coder

This paper introduces an implementation and structure of a video codec (coder-decoder) using Vector Quantization (VQ) in the program Matlab. It also aims on the VQ weak and strong features and it describes an experiment with turning the advantages into concrete profit in video data compression. We would like to aim also on usage in video MPEG 4 (Motion Picture Experts Group) standard or in compressing the scientific (high resolution) images. In conclusion we are comparing our approach with other image compression methods with objective and subjective criteria of image quality perception.

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**V. Sadek, J. Svacina**
[references] [full-text]

Analysis of Homogeneous Coplanar Strip Line

The goal of this work is to introduce a new, maybe complicated but in the final result mathematically simplest model of the coplanar strip line (CPS). In contrast to the usual method based on elliptical integrals the simplest circular inversion is applied. The main advantage is that our solution is mathematically less complicated but its accuracy is a little bit lower. The maximal error of the model described lies within the restricted interval between -3% and 3%. Nevertheless the final formula is useful for the practical engineering application.

- NAVRATIL V., LEONE M. The effect of differential driver asymmetries on common- and differential-mode frequency spectrum with regard to EMC. In Proc. of the 4th International Conference of Ph.D. Students. Miskolc (Hungary), 2003.
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**M. Jelinek, J. Dobes, L. Pousek**
[references] [full-text]

Correlation Analysis in a Pulse Wave Velocity Evaluation

In this paper, methods for a time delay evaluation of phonocardiographic (PCG) signals are presented to estimate a pulse wave velocity (PWV) in a cardiovascular system of a human body, especially in arterial segments of an arterial tree selected. A measuring method used for the pulse wave registration is fully non-invasive. Electronic phonendoscopes pressure/acoustic converters were used as signal transducers. The PWV estimation was carried out using correlation analysis of PCG signals, square of raw PCG signals and the first derivations of PCG signals. Signal processing, i.e. filtration, standardization, etc. was implemented in a Matlab environment using created application. A set of subjects examined in this experiment consists of five young healthy volunteers.

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**P. Cerva, J. Nouza**
[references] [full-text]

MAP Based Speaker Adaptation in Very Large Vocabulary Speech
Recognition of Czech

The paper deals with the problem of efficient adaptation of speech recognition systems to individual users. The goal is to achieve better performance in specific applications where one known speaker is expected. In our approach we adopt the MAP (Maximum A Posteriori) method for this purpose. The MAP based formulae for the adaptation of the HMM (Hidden Markov Model) parameters are described. Several alternative versions of this method have been implemented and experimentally verified in two areas, first in the isolated-word recognition (IWR) task and later also in the large vocabulary continuous speech recognition (LVCSR) system, both developed for the Czech language. The results show that the word error rate (WER) can be reduced by more than 20% for a speaker who provides tens of words (in case of IWR) or tens of sentences (in case of LVCSR) for the adaptation. Recently, we have used the described methods in the design of two practical applications: voice dictation to a PC and automatic transcription of radio and TV news.

- GAUVAIN, J.L., LEE, C.H. Maximum a posteriori estimation for multivariate Gaussian mixture observations of Markov chains. IEEE Trans. SAP. 1994, vol. 2, p. 291 - 298.
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- ZELEZNY, M. Speaker adaptation in continuous speech recognition system of Czech. PhD thesis (in Czech). ZCU Plzen 2001.

**L. Longauer, S. Marchevsky, D. Kocur**
[references] [full-text]

BAMUD Features Demonstration by System View

Direct-sequence code-division multiple access (DS-CDMA) is a frequently used wireless technology in DS-CDMA communications. The conventional DS-CDMA detector follows a single-user detection strategy in which each user is detected separately without regard for the other users. The better strategy is multi-user detection (MUD), where information about multiple users is used to improve detection of each individual user. This paper presents an adaptive multi-user detector converging (for any initialization) to the minimum mean square error (MMSE) detector without requiring training sequences. This blind multi-user detector (BAMUD) requires no more knowledge than does the conventional single-user detector. The structure of adaptive blind detector is simulated by the system design tool SystemView. The aim focus is to verify theoretical knowledge of BAMUD structure using hardware-oriented PC-based model in SystemView.

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