V. Kvicera, M. Grabner, M. Hlavaty [references] [full-text] [Download Citations]
Rain Intensity Statistical Processing and Comparison with ITU-R Recommendations

Rain intensities have been measured since February 1992 by means of a heated siphon raingauge. Rain intensity data gathered over 11-year period were statistically processed, cumulative distributions of rain intensities obtained, and relations between them were compared with ITU-R recommendations.

1. Rec. ITU-R P.837-3 Characteristics of precipitation for propagation modelling. ITU, Geneva, March 2003.
2. Rec. ITU-R P. 841-2 Conversion of annual statistics to worst-month statistics. ITU, Geneva, March 2003.

Z. Raida, Z. Lukes, V. Otevrel [references] [full-text] [Download Citations]
Modeling Broadband Microwave Structures by Artificial Neural Networks

The paper describes the exploitation of feed-forward neural networks and recurrent neural networks for replacing full-wave numerical models of microwave structures in complex microwave design tools. Building a neural model, attention is turned to the modeling accuracy and to the efficiency of building a model. Dealing with the accuracy, we describe a method of increasing it by successive completing a training set. Neural models are mutually compared in order to highlight their advantages and disadvantages. As a reference model for comparisons, approximations based on standard cubic splines are used. Neural models are used to replace both the time-domain numeric models and the frequency-domain ones.

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R. Tkadlec [references] [full-text] [Download Citations]
S-Parameter Measurements in the Time Domain

The paper provides a basic overview of the theory of time-domain measurements. Results of the use time-domain techniques to obtain S-parameter are here presented. Advantages and disadvantages of this technique compared to frequency-domain measurements are mentioned.

1. DE JONGH, R. V., HAJIAN, M., LIGTHART, L. P. Antenna time-domain measurement techniques. IEEE Transactions on Antennas and Propagation. 1997, vol. 39, no.5, p. 7 - 11.
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V. Stofanik, I. Balaz [references] [full-text] [Download Citations]
Frequency Stability Improvement in Direct Digital Frequency Synthesis

The paper describes a digital frequency synthesizer that incorporates a novel method of the clock signal frequency versus temperature dependency compensation. The clock signal is derived directly from a dual mode crystal oscillator (DMXO). With introducing the method, synthesized signal frequency versus temperature instability below a0.15ppm can be obtained over a wide temperature range (between 45°C and +85°C). Since a temperature information is obtained directly from a crystal itself rather than from an external sensor, temperature offset and lag effects are eliminated.

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J. Petrzela, V. Pospisil [references] [full-text] [Download Citations]
Nonlinear Resistor with Polynomial AV Characteristics and Its Application in Chaotic Oscillator

This paper shows the realization of two terminal devices with an arbitrary polynomial nonlinearity up to the fifth order. The proposed design procedure is completely systematic using minimum of components. The very heart of our conception is four-channel four-quadrant analog multiplier MLT04. The implementation of synthesized nonlinear resistor as a general nonlinearity in chaotic oscillator is also presented and experimentally verified.

1. PETRZELA, J. Obvodova realizace konzervativniho chaotickeho oscilatoru. Elektrorevue. 2004.
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Z. Peric, S. Bogosavljevic [references] [full-text] [Download Citations]
Asymptotic Analysis of Optimal Piecewise Uniform Polar Quantization

In this paper, a simple and complete asymptotical analysis is given for a mean square error (MSE) piecewise uniform polar quantizer (PUPQ). We show that PUPQ has the same performance as the asymptotic nonuniform polar quantizer (NPQ) and has implementation complexity between complexities of NPQ and uniform polar quantization. The goal of this paper is solving the quantization problem in case of PUPQ and finding the corresponding support region.

1. ARSLAN, F. T. Adaptive Bit Rate Allocation in Compression of SAR Images with JPEG2000. University of Arizona, 2001.
2. PERIC, Z. H., JOVKOVIC, J. Application of the optimal uniform polar quantization on complex reflectivity function. Advances in Electrical and Computer Engineering. 2002, vol. 9, no. 1, p. 80 - 86.
3. PERIC, Z. H., STEFANOVIC, M. Asymptotic analysis of optimal uniform polar quantization. International Journal of Electronics and Communications. 2002, vol. 56, no. 5, p. 345 - 347.
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5. NA, S., NEUHOFF, D. L. On the support of MSE-optimal, fixed-rate scalar quantizers. IEEE Transactions of Information Technology. 2001, vol. 47, no. 7, p. 2972 - 2982.
6. PERIC, Z. H. Piecewise uniform product two-dimensional Laplace source quantization. Electronics and Electrical Engineering. 2003, vol. 44, no. 2, p. 13 - 17.
7. POPAT, K., ZEGER, K. Robust quantization of memoryless sources using dispersive FIR filters. IEEE Transactions on Communication. 1992, vol. 40, no. 11, p. 1670 - 1674.

J. Vojtko [references] [full-text] [Download Citations]
Reduction of Elastomagnetic Sensor Errors by Using Neural Networks

This article deals with possibilities of reduction of elastomagnetic sensor errors. Elastomagnetic sensors are used for measuring of massive pressure force (of range about 200 kN). At the same time with demands on sensor accuracy, a filter can be added to the measuring set. The function of this filter is to regulate the basic metrological characteristics of sensor in order to achieve the smallest deviation from an ideal transfer characteristic. The using of exactly defined algorithm of reducing sensor errors is not appropriate in this case. So, the unconventional solution is using of the neural networks.

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B. Taha-Ahmed, M. Calvo-Ramon, L. de Haro-Ariet [references] [full-text] [Download Citations]
On the High Altitude Platform (HAP) W-CDMA System Capacity

The performance of a downlink power control model, based on a n-th power distance law, is evaluated for high altitude platform station (HAPS) W-CDMA systems. The downlink capacity using this model is compared with the uplink capacity. It is shown that the uplink capacity is higher than the downlink capacity.

1. DJUNNIC, G. M., FREDENFELDS, J. Establishing wireless communications services via high-altitude aeronautical platforms: a con-cept whose time has come? IEEE Communication Magazine. 1997, no. 9, p. 128 - 135.
2. GEJJI, R. R. Forward-link power control in CDMA cellular systems. IEEE Transactions on Vehicular Technology. 1992, vol. 41, no. 11, p. 532 - 536.
3. FOO, Y. C., LIM, W. L., TAFAZOLLI, R., BARCLAY, L. W. For-ward link power control for high altitude platform stations W-CDMA system. In Proceedings of the 54th Vehicular Technology Conference 2001 Fall. 2001, p. 625 - 629.
4. TAHA-AHMED, B., CALVO-RAMON, M., HARO-ARIET, L. On the downlink capacity of high altitude platform W-CDMA system. In Proceedings of IST 2003. Aviero (Portugal) 2003, p. 765 - 768.