2002/3

Browse

Recent Submissions

Now showing 1 - 5 of 9
  • Thumbnail Image
    Item
    A Comparison of Selected GBN ARQ Schemes for Variable-Error-Rate Channel Using QAM
    (Společnost pro radioelektronické inženýrství, 2002-09) Alexova, P.; Kosut, P.; Polec, J.; Kotuliakova, K.
    In non-stationary channels, error rates vary considerably. The paper compares Yao's Adaptive Go-back-N (GBN) Automatic-Repeat-Request (ARQ) scheme with Adaptive go-back-N with sliding window mechanism which both estimate the channel state in a simple manner, and adaptively switch their operation mode. The throughput of these schemes is compared in conditions of Additive White Gauss Noise (AWGN) channel with independent errors using 16-QAM modulation.
  • Thumbnail Image
    Item
    Walsh - Hadamard Transformation of a Convolution
    (Společnost pro radioelektronické inženýrství, 2002-09) Usakova, A.; Kotuliakova, J.; Zajac, M.
    A convolution is mathematical operation used in signal processing, in the homomorphous signal processing and digital image processing (e.g. image interpolation). In regard of computational complexity of the convolution in the time domain, it used to calculate in the other domain. Exp. x(n) * h(n) R X(W) × H(W), resp. X(W) × H(W), shows that a convolution in the time domain corresponds to multiplication in the Z domain, respectively frequency domain. This paper shows utilization of Walsh-Hadamard orthogonal transformations for convolution.
  • Thumbnail Image
    Item
    3-D Center-Weighted Vector Directional Filters for Noisy Color Sequences
    (Společnost pro radioelektronické inženýrství, 2002-09) Lukac, R.
    This paper focuses on a noise filtering in color image sequences, where a new class of center-weighted vector directional filters is provided. According to high dimensionality of color image sequences, where besides the spatial frequencies in the frames it is necessary to consider the temporal correlation of an image sequence and the correlation between color channels too, the processing of color image sequences represents very important and interesting problem. Clearly, the color image sequences represent three-dimensional (3-D) vector-valued image signals and thus, the 3-D vector filters provide optimal approach, only. Novelty of this paper lies in the impulse noise suppression by a new class of center-weighted vector directional filters, where the influence of the filter parameter to filter performance is analyzed. The interesting behavior of a new filter class is illustrated by a number of experimental results and comparisons with the well-known filtering algorithms for color image sequences.
  • Thumbnail Image
    Item
    Design of Planar Reflector Antennas
    (Společnost pro radioelektronické inženýrství, 2002-09) Gona, S.; Raida, Zbyněk
    A design of single and folded reflector antennas is presented. We focus in the use of an optimization during the design process. In comparison to existing papers, possibility of realization of folded antenna at X band frequencies is demonstrated. Further more, an original procedure of phase center extraction of antennas and scatters is described. The procedure is applied in the design of simple reflector antenna incorporating a non-hyperbolic, electrically small reflector.
  • Thumbnail Image
    Item
    Use of the Analog Neural Networks in the Adaptive Antenna Control Systems
    (Společnost pro radioelektronické inženýrství, 2002-09) Tobes, Z.; Raida, Zbyněk
    In the paper, original control system of adaptive antennas, which is based on Kalman filter, is presented and compared with earlier approaches to this problem. The designed control circuit eliminates some disadvantages of the control circuits based on the classical Kalman neural network and the Wang one, and enables a real time processing of quickly changing signals processed by adaptive antennas. Especially, the dependence of the convergence rate on ratio of eigenvalues and the risk of instability are significantly reduced.