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1
Content available Suitable Spreading Sequences for Asynchronous MC-CDMA Systems
Addad M., Djebbari A.
Journal of Telecommunications and Information Technology
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2018
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nr 3
9--13
EN
In order to meet the demand of high data rate transmission with good quality maintained, the multi-carrier code division multiple access (MC-CDMA) technology is considered for the next generation wireless communication systems. However, their high crest factor (CF) is one of the major drawbacks of multi-carrier transmission systems. Thus, CF reduction is one of the most important research areas in MC-CDMA systems. In addition, asynchronous MC-CDMA suffers from the effect of multiple access interference (MAI), caused by all users active in the system. Degradation of the system’s bit error rate (BER) caused by MAI must be taken into consideration as well. The aim of this paper is to provide a comparative study on the enhancement of performance of an MC-CDMA system. The spreading sequences used in CDMA play an important role in CF and interference reduction. Hence, spreading sequences should be selected to simultaneously ensure low CF and low BER values. Therefore, the effect that correlation properties of sequences exert on CF values is investigated in this study. Furthermore, a numerical BER evaluation, as a function of the signal-to-noise ratio (SNR) and the number of users, is provided. The results obtained indicate that a trade-off between the two criteria is necessary to ensure good performance. It was concluded that zero correlation zone (ZCZ) sequences are the most suitable spreading sequences as far as the satisfaction of the above criteria is concerned.
2
Content available Bearing estimation using double frequency reassignment for a linear passive array
Czarnecki K., Leśniak W.
Polish Maritime Research
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2017
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nr 3
26--35
EN
The paper demonstrates the use of frequency reassignment for bearing estimation. For this task, signals derived from a linear equispaced passive array are used. The presented method makes use of Fourier transformation based spatial spectrum estimation. It is further developed through the application of two-dimensional reassignment, which leads to obtaining highly concentrated energy distributions in the joint frequency-angle domain and sharp graphical imaging. The introduced method can be used for analysing, a priori, unknown signals of broadband, nonstationary, and/or multicomponent type. For such signals, the direction of arrival is obtained based upon the marginal energy distribution in the angle domain, through searching for arguments of its maxima. In the paper, bearing estimation of three popular types of sonar pulses, including linear and hyperbolic frequency modulated pulses, as well as no frequency modulation at all, is considered. The results of numerical experiments performed in the presence of additive white Gaussian noise are presented and compared to conventional digital sum-delay beamforming performed in the time domain. The root-mean-square error and the peak-to-average power ratio, also known as the crest factor, are introduced in order to estimate, respectively, the accuracy of the methods and the sharpness of the obtained energy distributions in the angle domain.
3
Content available remote Wpływ współczynnika szczytu na błędy przetworników RMS-DC typu ELIN o potęgowych funkcjach przetwarzania
Pilśniak A., Topór-Kamiński L., Holajn P., Guzik J., Kumor A.
Prace Naukowe Politechniki Śląskiej. Elektryka
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2014
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z. 2-3
95--101
PL
Producenci przetworników wartości skutecznej zazwyczaj ograniczają się do określenia maksymalnego błędu dla swojego produktu. Wynika on z dwóch składników: multiplikatywnego – zależny od badanej wartości oraz addytywnego, którego powodem są szumy i napięcie offsetu.
EN
Usually a maximum error is defined in data sheets of True RMS analog converters. It includes two components. One of them is a multiplication error which depends of actual voltage value. The second is an additional error, caused by a noise and offset voltage.
4
Content available remote Sposób oceny wpływu przekładnika prądowego na współczynniki określające jakość energii elektrycznej
Kaczmarek M.
Przegląd Elektrotechniczny
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2013
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R. 89, nr 3a
83--85
PL
Przedstawiony w artykule sposób oceny wpływu przekładników prądowych pracujących, w układach pośrednich, na wartości współczynników określających jakość energii elektrycznej umożliwia obliczenie maksymalnych wartości błędów wyznaczania wybranych współczynników charakteryzujących odkształcenie prądu określonych dla strony wtórnej zastosowanego przekładnika prądowego.
EN
Presented in the paper method for determine the influence of current transformers on estimated power quality factors enable calculation of the maximal changes in values of selected factors used for characterization of signals distortion caused by usage of the current transformer.
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