2010/4

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    On the Effect of Channel Impairments on VANETs Performance
    (Společnost pro radioelektronické inženýrství, 2010-12) Baltzis, Konstantinos B.
    The primary means of studying the performance of vehicular ad hoc networks (VANETs) are computer simulations. Nowadays, the development of analytical models and the use of hybrid simulations that combine analytical modeling with discrete-event simulation are of great interest due to the significant reduction in computational cost. In this paper, we extend previous work in the area by suggesting an analytical model that includes distance-dependent losses, shadowing and small-scale fading. Closed-form expressions for the packet reception probability and the packet forwarding distance in the absence of simultaneous transmissions are presented. Numerical simulations validate the proposed formulation. The impact of path loss and fading on network throughput is explored. Interesting results that shows the efficacy of the approach are provided. The derived formulation is a useful tool for the modeling and analysis of vehicular communication systems.
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    Estimation of the Radio Channel Parameters using the SAGE Algorithm
    (Společnost pro radioelektronické inženýrství, 2010-12) Mota, Susana; Garcia, Maura Outeiral; Rocha, Armando; Perez-Fontan, Fernando
    This paper presents the problem of estimating the parameters of a given number of superimposed signals, as is the case of the received signal in wireless communications. Based on the description of the received signal in the frequency domain, one version of the SAGE (Space-Alternating Generalized Expectation-Maximization) algorithm is presented, allowing the estimation, for each impinging ray, the delay, azimuth, elevation and complex amplitude. Ray retrieval results are presented in synthetic channels, using data generated with the extended Saleh Valenzuela (ESV) model, and also in real channels.
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    Optimization of the Gaussian Kernel Extended by Binary Morphology for Text Line Segmentation
    (Společnost pro radioelektronické inženýrství, 2010-12) Brodic, Darko; Milivojevic, Zoran
    In this paper, an approach for text line segmentation by algorithm with the implementation of the Gaussian kernel is presented. As a result of algorithm, the growing area around text is exploited for text line segmentation. To improve text line segmentation process, isotropic Gaussian kernel is extended by dilatation. Furthermore, algorithms with isotropic and extended Gaussian kernels are examined and evaluated under different text samples. Results are given and comparative analysis is made for these algorithms. From the obtained results, optimization of the parameters defining extended Gaussian kernel dimension is proposed. The presented algorithm with the extended Gaussian kernel showed robustness for different types of text samples.
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    Simulation and Measurement of the Transmission Distortions of the Digital Television DVB-T/H Part 3: Transmission in Fading Channels
    (Společnost pro radioelektronické inženýrství, 2010-12) Polak, Ladislav; Kratochvil, Tomas
    The paper deals with the third (and last) part of results of the Czech Science Foundation research project that was aimed into the simulation and measurement of the transmission distortions of the digital terrestrial television according to DVB-T/H standards. In this part the transmission of the digital television according to DVB-T/H standard over the fading channels and their models and profiles for fixed, portable and mobile reception is analyzed. Impact of the fading channels and their models on Modulation Error Rate from I/Q constellations and Bit Error Rates before and after Viterbi decoding in DVB-T/H signal decoding is presented.
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    Advanced Fuzzy Logic Based Admission Control for UMTS System
    (Společnost pro radioelektronické inženýrství, 2010-12) Kejik, Petr; Hanus, Stanislav; Blumenstein, Jiri
    The capacity of CDMA (Code Division Multiple Access) systems is interference limited. Therefore radio resources management (RRM) functions are used. They are responsible for supplying optimum coverage, ensuring efficient use of physical resources, and providing the maximum planned capacity. This paper deals with admission control techniques for UMTS (Universal Mobile Telecommunication System). A UMTS system model and four fuzzy logic based admission control algorithms are presented in this paper. Two new versions of fuzzy logic based admission control algorithms are presented there. All algorithms are mutually compared via simulations. Simulations show that the novel advanced fuzzy algorithm outperforms the other simulated algorithms (in terms of blocking probability, dropping probability and the number of active UEs in cell).