2008/1

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    Wavelet Based Hilbert Transform with Digital Design and Application to QCM-SS Watermarking
    (Společnost pro radioelektronické inženýrství, 2008-04) Maity, Santi Prasad; Maity, Seba
    In recent time, wavelet transforms are used extensively for efficient storage, transmission and representation of multimedia signals. Hilbert transform pairs of wavelets is the basic unit of many wavelet theories such as complex filter banks, complex wavelet and phaselet etc. Moreover, Hilbert transform finds various applications in communications and signal processing such as generation of single sideband (SSB) modulation, quadrature carrier multiplexing (QCM) and bandpass representation of a signal. Thus wavelet based discrete Hilbert transform design draws much attention of researchers for couple of years. This paper proposes an (i) algorithm for generation of low computation cost Hilbert transform pairs of symmetric filter coefficients using biorthogonal wavelets, (ii) approximation to its rational coefficients form for its efficient hardware realization and without much loss in signal representation, and finally (iii) development of QCM-SS (spread spectrum) image watermarking scheme for doubling the payload capacity. Simulation results show novelty of the proposed Hilbert transform design and its application to watermarking compared to existing algorithms.
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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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    Ultra-Wideband Coplanar-Fed Monopoles: A Comparative Study
    (Společnost pro radioelektronické inženýrství, 2008-04) Jilkova, Jana; Raida, Zbynek
    The paper provides an experimental comparison of four types of ultra-wideband coplanar-fed planar monopole antennas. Parameters of the open stub completed by an L-shaped monopole and the cross monopole were adopted from the literature. The forked monopole and the coplanar monopole were fabricated and measured. Monopoles were compared from the viewpoint of the impedance bandwidth, gain, directivity patterns and dimensions.
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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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    Design of Primary Feeds for 32m KDDI Antenna System IBA-4 in Cassegrain Configuration
    (Společnost pro radioelektronické inženýrství, 2008-04) Galuscak, Rastislav; Watanabe, Michiaki; Hazdra, Pavel; Takeda, Shigeru; Seki, Kouichi; Prochazka, Miroslav; Uchiyama, Yoosuke
    Physically large dimensional dish antennas in Cassegrain configuration have played an important role in satellite communications during the past several decades. Recently, however, emerging new technologies have begun to displace these elegant antennas in professional telecommunication service due to their lower operating costs. A beneficial aspect of this transitional situation is that it has created opportunities for amateur radio enthusiasts to use these soon-to-be-retired dish antenna systems for limited experimental testing. Adaptation of these professionally designed antennas to bands allocated for amateur radio service presents excellent educational opportunities in using antenna engineering skills and the use of modern electromagnetic simulation software provides a novel perspective for these antenna design and transformation tasks.