Fiser O

Publications (9)0 Total impact

• Source

  Available from: Schejbal Vladimir

  Article: Modeling of 830 nm FSO Link Attenuation in Fog or Wind Turbulence

  Pesek J, Fiser O, Svoboda J, Schejbal V
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  ABSTRACT: This study is focused on the experimental research of the atmosphere impact on FSO link attenuation. Experiment is performed on a mountain observatory Milesovka of severe weather conditions. The empirical relationships on 830 nm only between FSO attenuation A on one hand and atmospheric visibility V or wind turbulent energy ET on the other hand are presented and discussed. In the fog case it was found A= 401.4V-0.5738- 1.462 dB/60m (V in meters) while for the attenuation due to the wind turbulence ET it holds A = 2.112 - 2.213 exp(-0.2867ET) dB/60m (ET in m2s-2, it was derived for 830 nm wave length). A discussion concerning problems of the “clear air attenuation,” atmospheric turbulences and sun shine impact, which was observed as a maximum 2 dB attenuation for a few minutes with a period of 24 hours is added.
  Radioengineering. 01/2010;
• Source

  Available from: V. Kvicera

  Article: Propagation Characteristics and Availability Performance Assessment for Simulated Terrestrial Hybrid 850 nm/58 GHz System

  Kvicera V, Grabner M, Fiser O
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  ABSTRACT: Results of a propagation study on a free space optical link at 850 nm on a path 853 meters long and on a parallel 58 GHz radio link obtained over a 3-year period of observation are presented. The cumulative distributions of attenuation due to all of the hydrometeors combined as well as due to individual hydrometeors were obtained for both paths. The availability performances of the FSO link, the RF link and the simulated hybrid FSO/RF system were assessed. Significantly higher availability performance was achieved for the simulated hybrid FSO/RF system than for the FSO link alone. The diversity improvement factor reached significant values for attenuation greater than 5 dB and a significant diversity gain was obtained for the percentages of time smaller than 2%.
  Radioengineering. 01/2010;
• Source

  Available from: V. Kvicera

  Article: BER and Availability Measured on FSO Link

  Kvicala R, Kvicera V, Grabner M, Fiser O
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  ABSTRACT: The BER and the availability belong among the basic qualitative parameters of free space optical (FSO) links. The BER parameter is usually mentioned by FSO manufacturers, but it is not defined what conditions a certain value of BER stands for. This article deals with problems of measuring the BER of free space optical link and with questions how to determine the probability of unavailability of a certain link. The implementation of bit error rate tester with the E1 interface system is presented. In the article the statistics of the meteorological optical range for the year 2006 are shown. Using these data one can determine the probability of a certain value of atmospheric attenuation that influences the link unavailability.
  Radioengineering. 01/2007;
• Source

  Available from: Schejbal Vladimir

  Article: Multipath Propagation of UWB Through-Wall Radar and EMC Phenomena

  Schejbal V, Cermak D, Nemec Z, Pidanic J, Konecny J, Bezousek P, Fiser O
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  ABSTRACT: The UWB (ultra wide band) radar output signals can be substantially affected due to electromagnetic wave propagation through obstacles (such as walls) and multipath effects, too. Multipath effects are analyzed and simulated numerically for various cases with several antenna heights and distances. Delays (due to propagation through walls and various paths of direct and reflected rays) and the ringing (similar to UWB propagation through wall) can be clearly observed and analyzed. Moreover, frequency spectra analyses can demonstrate both UWB interferences and susceptibility from electromagnetic compatibility (EMC) viewpoint.
  Radioengineering. 01/2006;
• Source

  Available from: Schejbal Vladimir

  Article: UWB Propagation through Walls

  Schejbal V, Bezousek P, Cermak D, Nemec Z, Fiser O, Hajek M
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  ABSTRACT: The propagation of ultra wide band (UWB) signals through walls is analyzed. For this propagation studies, it is necessary to consider not only propagation at a single frequency but in the whole band. The UWB radar output signal is formed by both transmitter and antenna. The effects of antenna receiving and transmitting responses for various antenna types (such as small and aperture antennas) are studied in the frequency as well as time domain. Moreover, UWB radar output signals can be substantially affected due to electromagnetic wave propagation through walls and multipath effects.
  Radioengineering. 01/2006;
• Source

  Available from: radioeng.cz

  Article: Statistics of Radio Refractivity Derived from Prague Radiosounding Data

  Rezacova D, Fiser O, L. Ramon Saez
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  ABSTRACT: Vertical gradient of radio refractivity in the lowest 100 m isderived from the meteorological radio-sounding data of the Prague-Libusstation. The data cover the measurements at the terms 00, 06, 12, and18UTC, and the extent of data is 20 years. Diurnal, monthly, and annualdistributions are presented and the relative role of the dry and wetcomponents of the refractivity gradient is discussed. The b0 values,expressing the percentage of the time with the refractivity gradientbelow -100 km-1, are presented. This work should enable the effectiveradio-relay link design with respect to the radiowave bending.
  Radioengineering. 01/2003;
• Source

  Available from: doaj.org

  Article: Diurnal and Seasonal Variations of Water Vapour and Cloud Water Attenuation in Microwave Frequency Bands

  Fiser O, Rezacova D
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  ABSTRACT: 20 years of radiosonde data from the aerological station Prague-Libus were analysed to evaluate integrated values of water vapour content and cloud water content. Both parameters are proportional to the attenuation in microwave frequency bands. The soundings from 00, 06, 12, and 18 UTC were taken into account to discuss diurnal as well as seasonal variations. The methods available to compute the cloud and the water vapour attenuation are presented.
  Radioengineering. 01/1997;
• Source

  Available from: radioeng.cz

  Article: Prediction of Rain and Water Vapour Attenuation at Frequencies 10-30 GHz

  Fiser O
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  ABSTRACT: This contribution discusses the attenuation of microwaves in the atmosphere and applies the results to the conditions in the Czech Republic. The simple CCIR method predicting the rain attenuation is described and the relevant rain intensity as the only meteorological parameter required is presented on a map. Five methods of evaluation of the water vapour attenuation are discussed and compared . Included is also the computation of the zenith water vapour attenuation and its distribution based on the statistical evaluation of real four-year vertical profiles of important meteorological parameters from the Prague station.
  Radioengineering. 01/1996;
• Article: A Simple Generator of Forward Scattering Functions on Spherical Dielectrics

  Fiser O
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  ABSTRACT: The described program generates the forward scattering functions of dielectrics of spherical shape, while the input parameters are: frequency, radius of the sphere and complex refractive index. The part enabling to evaluate the complex refractive index of water in the dependence on frequency and temperature is added.
  Radioengineering. 01/1993;