Recent Submissions

Now showing 1 - 5 of 7
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    FDTD Stability: Critical Time Increment
    (Společnost pro radioelektronické inženýrství, 2003-06) Pauk, Lukas; Skvor, Zbynek
    A new approach suitable for determination of the maximal stable time increment for the Finite-Difference Time-Domain (FDTD) algorithm in common curvilinear coordinates, for general mesh shapes and certain types of boundaries is presented. The maximal time increment corresponds to a characteristic value of a Helmholz equation that is solved by a finite-difference (FD) method. If this method uses exactly the same discretization as the given FDTD method (same mesh, boundary conditions, order of precision etc.), the maximal stable time increment is obtained from the highest characteristic value. The FD system is solved by an iterative method, which uses only slightly altered original FDTD formulae. The Courant condition yields a stable time increment, but in certain cases the maximum increment is slightly greater [2].
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    A New Quasi-Optimum Power Control Scheme for Downlink in W-CDMA Macro Cellular System
    (Společnost pro radioelektronické inženýrství, 2003-06) Taha Ahmed, Bazil; Calvo Ramon, Miguel; de Haro Ariet, Leandro
    The downlink power control problem in W-CDMA is studied using a new proposed model. The downlink cell capacity is given for the old model given by Gejji and our new model. A capacity increase of 16 % for the special case = 0 (no orthogonality between users) and a generalization of the old model in terms of the propagation exponent and orthogonality factor is introduced.
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    Analysis and Simulation of Frost's Beamformer
    (Společnost pro radioelektronické inženýrství, 2003-06) Strupl, Miroslav; Sovka, Pavel
    Sensor arrays are often used for a signal separation from noises using the information about the direction of arrival. The aim of this paper is to analyze Frost's beamformer with respect to the speech preprocessing for the hearing impaired people. The frequency response of the system including the background noise attenuation are derived as functions of the direction of arrival. The derivation supposes a uniform linear array of sensors and plane waves. It is shown that the number of possible configurations can be decreased by using some symmetries. The impact of the used algorithm constraint on the frequency response and subsequently on the directional noise suppression is derived analytically.
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    Microwave-Circuit Optimization with Parallel Enhanced Fast Messy Genetic Algorithm (pefmGA)
    (Společnost pro radioelektronické inženýrství, 2003-06) Kostka, Pavel; Skvor, Zbynek
    Fast messy genetic optimization is found suitable for complex microwave circuit design. Increase in computation speed is achieved using several ordinary computers connected to a network. Calculations are running on background so that computers can be used for other purposes at the same time. Dynamic change of bounds, search space segmentation and gradient incorporation have significantly improved convergence rate. The new method has found global minimum in each run, while classic methods failed for some starting points.
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    Throughput Analysis of an Adaptation Rule in the HARQ Environment
    (Společnost pro radioelektronické inženýrství, 2003-06) Goga, Stefan; Polec, Jaroslav; Kotuliakova, Kvetoslava
    In this paper we analyze the adaptation rule, which estimates the channel state and switches between hybrid ARQ (automatic-repeat-request) and pure ARQ. Convolutional code was chosen as FEC (forward-error-correction) in hybrid ARQ part and go-back-N ARQ scheme is used in both cases. The adaptation rule is based on counting ACKs and NAKs and its throughput analysis is made.