2010/2

Browse

Now showing 1 - 5 of 22

Modeling of 830 nm FSO Link Attenuation in Fog or Wind Turbulence
(Společnost pro radioelektronické inženýrství, 2010-06) Pesek, Jiri; Fiser, Ondrej; Svoboda, Jaroslav; Schejbal, Vladimir
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.
PDF 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, Abdul
Terrestrial 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.
Propagation Characteristics and Availability Performance Assessment for Simulated Terrestrial Hybrid 850 nm/58 GHz System
(Společnost pro radioelektronické inženýrství, 2010-06) Kvicera, Vaclav; Grabner, Martin; Fiser, Ondrej
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%.
Transmission Line on Semiconductor Substrate with Distributed Amplification
(Společnost pro radioelektronické inženýrství, 2010-06) Pokorny, Michal; Raida, Zbynek
In order to compensate losses in metal strips, an active microstrip line on a semiconductor substrate is proposed, and its finite element model is presented. The active medium is provided by A3B5 semiconductor in highintensity electric field. The simple model of the active media is developed and used for calculation of the propagation properties of the fundamental mode and for the thermal analysis of the device. The problem of system self-oscillation is discussed and empirical stability criteria are introduced. A proper heat-sink is proposed to provide the operation in a continuous regime.
Electronically Tunable Third-Order Quadrature Oscillator Using CDTAs
(Společnost pro radioelektronické inženýrství, 2010-06) Horng, Jiun-Wei; Lee, Hung; Wu, Jian-Yu
A current/voltage-mode third-order quadrature oscillator based on current differencing transconductance amplifiers (CDTAs) is presented in this paper. Outputs of two current-mode and two voltage-mode sinusoids each with 90o phase difference are available in the quadrature oscillator circuit. The oscillation condition and oscillation frequency are independently controllable. The proposed circuit employs only grounded capacitors and is ideal for integration. Simulation results are included to confirm the theoretical analysis.

Browse

Recent Submissions