2010/2
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Recent Submissions
- ItemModeling of 830 nm FSO Link Attenuation in Fog or Wind Turbulence(Společnost pro radioelektronické inženýrství, 2010-06) Pesek, Jiri; Fiser, Ondrej; Svoboda, Jaroslav; Schejbal, VladimirThis 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.
- ItemPDF Estimation and Liquid Water Content Based Attenuation Modeling for Fog in Terrestrial FSO Links(Společnost pro radioelektronické inženýrství, 2010-06) Muhammad, Sajid Sheikh; Awan, Muhammad Saleem; Rehman, AbdulTerrestrial Free-space optical communication (FSO) links have yet to achieve a mass market success due to the ever elusive 99.999% availability requirement. The terrestrial FSO links are heavily affected by atmospheric fog. To design systems which can achieve high availability and reliability in the presence of fog, accurate and better models of fog attenuation need to be developed. The current article puts forth appropriate probability density function estimates for received signal strength (hereafter RSS) under fog conditions, where variations in the RSS during foggy events have been statistically characterized. Moreover, from the surface observations of fog density, liquid water content (hereafter LWC) of fog is estimated. The actual measured optical attenuations are then compared with the optical attenuations estimated from LWC. The results presented suggest that fog density measurements carried out are accurate representation of the fog intensity and the attenuation predictions obtained by the LWC estimate match the actual measured optical attenuations. This suggests that the LWC is a useful parameter besides visibility range to predict optical attenuations in the presence of hydrometeors.
- ItemComparison of Constant and Temperature Dependent Blood Perfusion in Temperature Prediction for Superficial Hyperthermia(Společnost pro radioelektronické inženýrství, 2010-06) Drizdal, Tomas; Togni, Paolo; Visek, Lukas; Vrba, JanThe purpose of this study was to determine whether prediction of the 3D temperature profile for superficial hyperthermia using constant blood perfusion model could be matched to one with a temperature dependent blood perfusion. We compared three different constant blood perfusion scenarios with one temperature dependent blood perfusion using a layered model of biological tissue consisting of skin (2 mm), fat (10 mm) and muscle (108 mm). For all four scenarios the maximum temperature of 43 °C was found in the muscle tissue in the close proximity (1 – 3 mm) of fat layer. Cumulative histograms of temperature versus volume were identical for the region of 100x100x40 mm3 under the applicator aperture for the three constant blood perfusion models. For temperature dependent blood perfusion model, 85 % of the studied region was covered with the temperature equal or higher than 40 °C in comparison with 43 % for the constant blood perfusion models. Hence this study demonstrates that constant blood perfusion scenarios cannot be matched to one with a temperature dependent blood perfusion.
- ItemEstimation of Accessible Probability in a Low Earth Orbit Satellite to Ground Laser Communications(Společnost pro radioelektronické inženýrství, 2010-06) Takayama, Yoshihisa; Toyoshima, Morio; Kura, NobuhiroThe accessible probability of a low-orbit satellite from ground is estimated by using images taken by a meteorological satellite and by analyzing visible passes of the satellite. The study indicates that the blockage by clouds in satellite-ground laser communications is almost avoidable by properly distributing several optical ground stations. For the calculation, we use an orbit information of a low-earth orbit satellite, the Optical Inter-orbit Communications Engineering Test Satellite (OICETS), as the counterpart of the optical ground stations. The calculation of the cumulative accessible probability shows the required time to achieve over 99% accessibility between the low orbit satellite and the optical ground stations.
- ItemA Novel OFDM Channel Estimation Algorithm with ICI Mitigation over Fast Fading Channels(Společnost pro radioelektronické inženýrství, 2010-06) Tao, Cheng; Qiu, Jiahui; Liu, LiuOrthogonal frequency-division multiplexing (OFDM) is well-known as a high-bit-rate transmission technique, but the Doppler frequency offset due to the high speed movement destroys the orthogonality of the subcarriers resulting in the intercarrier interference (ICI), and degrades the performance of the system at the same time. In this paper a novel OFDM channel estimation algorithm with ICI mitigation based on the ICI self-cancellation scheme is proposed. With this method, a more accurate channel estimation is obtained by comb-type double pilots and then ICI coefficients can be obtained to mitigate the ICI on each subcarrier under the assumption that the channel impulse response (CIR) varies in a linear fashion. The theoretical analysis and simulation results show that the bit error rate (BER) and spectral efficiency performances are improved significantly under high-speed mobility conditions (350 km/h – 500 km/h) in comparison to ZHAO’s ICI self-cancellation scheme.