2008/1

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    Resource Planning for Voice over Wireless Both-Way Transmission Media
    (Společnost pro radioelektronické inženýrství, 2008-04) Tsankov, Boris; Pachamanov, Radostin; Pachamanova, Dessislava
    The medium in IEEE 802.11- and IEEE 802.16-based networks for voice communications can be considered “both-way” - for transmission and reception. Therefore, the packet arrivals for voice dialogue services in such networks are not strictly independent. In this paper, we discuss the traffic capacity in the call (network) layer and suggest accounting for the impact of the correlated nature of two-way voice conversations on performance estimation. We present analytical results and numerical examples.
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    Common Virtual Path and Its Expedience for VBR Video Traffic
    (Společnost pro radioelektronické inženýrství, 2008-04) Chromy, Erik; Baronak, Ivan
    The paper deals with utilization of common Virtual Path (VP) for variable bit rate (VBR) video service. Video service is one of the main services for broadband networks. Research is oriented to statistical properties of common and separate VPs. Separate VP means that for each VBR traffic source one VP will be allocated. Common VP means that for multiple VBR sources one common VP is allocated. VBR video traffic source is modeled by discrete Markov chain.
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    Time-Frequency Decomposition of an Ultrashort Pulse: Wavelet Decomposition
    (Společnost pro radioelektronické inženýrství, 2008-04) Khelladi, Mounir; Seddiki, Omar; Bendimerad, Fethi Tarik
    An efficient numerical algorithm is presented for the numerical modeling of the propagation of ultrashort pulses with arbitrary temporal and frequency characteristics through linear homogeneous dielectrics. The consequences of proper sampling of the spectral phase in pulse propagation and its influence on the efficiency of computation are discussed in detail. The numerical simulation presented here is capable of analyzing the pulse in the temporal-frequency domain. As an example, pulse propagation effects such as temporal and spectral shifts, pulse broadening effects, asymmetry and chirping in dispersive media are demonstrated for wavelet decomposition.
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    Broadband Measurement of Complex Permittivity Using Reflection Method and Coaxial Probes
    (Společnost pro radioelektronické inženýrství, 2008-04) Zajicek, Radim; Oppl, Ladislav; Vrba, Jan
    This paper describes and evaluates a method for determining complex permittivity, and presents results of permittivity measurement of some substances. Complex permittivity of a phantom of biological muscle tissue, of some industrial chemicals and dielectrics is found. A non-destructive and non-invasive method based on reflection coefficient measurement of an open-ended coaxial line attaching the material under test is used. Two coaxial probes are under investigation. Vector measurement of the reflection coefficient on the interface between probes and measured samples is performed with the aid of network analyzer in the frequency range from 300 kHz to 3 GHz. Numerical modeling (FDTD) is compared with measurement. The results indicate that using the coaxial probe with dimensions of N connector the method is suitable in the frequency range approximately from 30 MHz to 1 GHz and using the probe with dimensions of SMA connector in range approximately from 30 MHz to 3 GHz.
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    Recognition of OFDM Modulation Method
    (Společnost pro radioelektronické inženýrství, 2008-04) Ulovec, Karel
    This contribution deals with asynchronous noncoherent recognition of modulation types. The main aim is to recognize OFDM modulation method from some other single-carrier analog and digital modulation types in the presence of AWGN noise. The described solution of recognizer uses key features of the received signal. The signal amplitude is observed at the output of the quadrature intermediate-frequency stage. The properties of the recognizer are verified by simulations using Matlab.