2009/2
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- ItemA Simple Signal Shaper for GMSK/GFSK and MSK Modulator Based on Sigma-Delta Look-up Table(Společnost pro radioelektronické inženýrství, 2009-06) Svedek, Tomislav; Herceg, Marijan; Matic, TomislavDue to wide power spectrums of rectangular data streams, it is important for base-band signals to be heavily band limited before modulation. That can be achieved by pulse shaping of rectangular bits. Some of the most common are a half-sine pulse shaper and a Gaussian pulse shaper which are used in Minimum Shift Keying (MSK), Gaussian Minimum Shift Keying (GMSK) and Gaussian Frequency Shift Keying (GFSK) modulations, respectively. The most common solutions of such shapers use PCM based look-up-table (LUT), which requires an nbit D/A converter. We proposed the use of a 1-bit Sigma Delta Modulation (SDM) LUT, which results in smaller ROM capacity, a 1-bit wide output word, and a simple1-bit D/A converter realized as an out-of-chip first-order lowpass RC filter, or an in-chip charge pump. This article describes a simple, but efficient SDM LUT-based half-sine and Gaussian shaper that can be used for generation of MSK and GMSK/GFSK modulated signals. Oscillograms and power spectrums are measured on SDM LUT realized in FLEX AlteraTM PLD, for a 10-bit pseudo-noise sequence test input signal.
- ItemInfluence of EBG Structures on the Far-Field Pattern of Patch Antennas(Společnost pro radioelektronické inženýrství, 2009-06) Horak, Jiri; Raida, ZbynekIn this paper, the influence of the EBG structures on the far-field pattern of patch antennas is investigated. As a reference model, a conventional rectangular patch antenna on a high-permittivity substrate is used. The reference model is consequently equipped by an EBG substrate (instead of the conventional one), and by an EBG cover (so called EBG superstrate). The changes in the farfield radiation patterns are discussed. In the second part of the paper, the substrate is perturbed by two different EBG structures designed for the coverage of two operation bands.
- ItemSPICE Model of Memristor with Nonlinear Dopant Drift(Společnost pro radioelektronické inženýrství, 2009-06) Biolek, Zdenek; Biolek, Dalibor; Biolkova, VieraA mathematical model of the prototype of memristor, manufactured in 2008 in Hewlett-Packard Labs, is described in the paper. It is shown that the hitherto published approaches to the modeling of boundary conditions need not conform with the requirements for the behavior of a practical circuit element. The described SPICE model of the memristor is thus constructed as an open model, enabling additional modifications of non-linear boundary conditions. Its functionality is illustrated on computer simulations.
- ItemDistribution of Video-on-Demand Service over Cable Television Networks(Společnost pro radioelektronické inženýrství, 2009-06) Jordanova, Lidia T.; Nenkov, Jordan I.The paper deals with investigations carried out to increase the effectiveness of video-on-demand (VoD) systems when cable television networks are used. A comparative analysis of the existing VoD architectures is made with respect to the equipment cost and the traffic load over the central transport network. Through statistical studies the main characteristics of a particular hybrid VoD are determined (such as twenty-four-hour distribution of the video traffic, average inter-arrival time of the VoD requests, average duration of video streams demanded, movies distribution according to the subscribers’ preferences). An algorithm for the videocontent flexible distribution among the distribution hubs is suggested. Thus a higher effectiveness of the system is achieved without significantly increasing the equipment cost.
- ItemUWB System Performance Improvement Using Smart Interference Rejection Filter(Společnost pro radioelektronické inženýrství, 2009-06) Dimitrijevic, Bojan; Milosevic, Nenad; Nikolic, Zorica; Petrovic, PredragIn this paper we proposed a smart interference rejection filter in TH-PPM UWB system, which improves the system\'s error probability for an order of magnitude in case of high power OFDM interference. The smart filter is based on an adaptive transversal filter. Based on the fulfillment of certain conditions, the filter activates or deactivates some parts of it.