April 2000, Volume 9, Number 1
Electrical Activity of a human brain measured on the skull (electroencephalogram, EEG) contains in the sleep period many transients (sleep spindles, spike-like structures or vertex waves), i. e. bursts of EEG activity of limited duration, having random occurrence and may be coupled with specific sleep stages. A computer-based detector was designed that detects a transient called K-complex. The detector is based on linear matched filtering and its nonlinear modifications. The linear and nonlinear approaches are compared and evaluated with respect to the detection efficiency.
The paper describes the design of an electronic-lock system which was completed as part of the Basic VHDL course in the Department of Control and Measurement Faculty of Electrical Engineering and Informatics, Technical University of Ostrava, Czech Republic in co-operation with the Department if Electronic Engineering, University of Hull, Great Britain in the frame of TEMPUS project no. S_JEP/09468-95.
In this paper is presented a new design of LUM smoother. The LUM smoother, a subclass of lower-upper-middle (LUM) filters is used in smoothing image and signal applications. This filter very well can suppress impulsive noise and preserve signal details, simultaneously. It is achieved by simply varying the filter parameter for smoothing. However, the tuning parameter for smoothing is fixed for the whole image. A new design is based on adaptive controlled level of the smoothing. The analysis of new methods is presented. Performance of the proposed methods is evaluated through subjective and objective criteria and compared with the traditional LUM smoother and the well known median.
This paper treats of compression of digital video signals and the main aim is to probe the possibility of using several discrete transforms besides well-known discrete cosine transform (DCT). Mathematical description of these transforms is presented in the article. DCT and other orthogonal transforms are described here. Matrix notation of computation of two-dimensional transform is also presented. The comparison of the results obtained by application of the transforms on pictures is introduced.
Echo cancellation system used in mobile communications is analyzed. Convergence behavior and misadjustment of several LMS algorithms are compared. The misadjustment means errors in filter weight estimation. The resulting echo suppression for discussed algorithms with simulated as well as rela speech signals is evaluated. The optional echo cancellation configuration is suggested.
Anechoic and EMC chamber at the CTU in Prague was designed and used for a variety of antenna measurements and EMI testing. Due to different measurement methods (near field, far field, compact range, and EMI measurement) applied in the laboratory, different simulations were performed during the design process.
Two problems arising in the real-life application of echo cancellation systems are analysed.The first, simultaneous activity of both telephone users (double talk) deteriorates the echo suppression. The second, environmental noise is the crucial point in echo cancellation system applications. Experimental evaluation of the influence of both phenomena is given together with possible solution.
Indoor propagation modelling is demanded for the design and maintenance of indoor wireless services. Empirical modelling seems to be the most efficient approach. Even so there are many studies dealing with empirical models for indoor propagation, the results can be hardly used for local buildings without modifications. There are several specific architecture styles and used materials. The indoor propagation measurement campaigns in the frequency range of 900 MHz were done in two typical multi-storey university buildings in Prague. Based on the measurement results, the easy-to-use empirical propagation prediction were derived for both of the buildings with satisfactorily accuracy. variations of the models were studied. The models are being implemented into a CAD software tool for complex design of indoor cellular systems. The project continues using a similar approach for other frequency bands. In the same time, other novel ways of semi-empirical modeling of indoor propagation are investigated.
In this paper, a new method of hybrid coding of image sequences by using wavelet transform is proposed. The basic MPEG scheme with DCT has been modificated in sense of replacement DCT by wavelet transform. In the proposed method, the motion estimation and compensation are used for motion vectors calculation and different frame between current frame and compensated frame is coded by using wavelet transform. Some experimental results of image sequences coding by using a new method are presented.
Four types of second-generation current conveyors are shown. The realisation of the above conveyors using differential voltage current conveyors (VDCC) is presented. Two examples illustrate the building of adjoint networks containing second-generation current conveyors.
Variables and functions for expressing quality of the prediction of the chaotic signal can serve as tools for simplified but useful description of the chaotic signal. In this paper, the known generation mechanism of chaos is used as a predictor but using the perturbed signal as an input. Prediction performance of the predictor is compared with the estimate of the predictability based on a mutual information between known quantities and a predicted value. mentioned two methods of investigation have different requirements for a priori knowledge of chaos. Certain constraints are given in consequence of an imperfection of numerical calculations and computer simulations.