Long-Term Propagation Statistics and Availability Performance Assessment for Simulated Terrestrial Hybrid FSO/RF System
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Research Article Long-Term Propagation Statistics and Availability Performance Assessment for Simulated Terrestrial Hybrid FSO/RF System Vaclav Kvicera,1 Martin Grabner,1 and Ondrej Fiser2 1
Czech Metrology Institute, Hvozdanska 3, 148 00 Prague 4, Czech Republic of Atmospheric Physics, The Academy of Sciences of the Czech Republic, Bocni II/1401, 141 31 Prague 4, Czech Republic
2 Institute
Correspondence should be addressed to Vaclav Kvicera, [email protected] Received 1 November 2010; Accepted 7 February 2011 Academic Editor: Fabrizio Granelli Copyright © 2011 Vaclav Kvicera et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Long-term monthly and annual statistics of the attenuation of electromagnetic waves that have been obtained from 6 years of measurements on a free space optical path, 853 meters long, with a wavelength of 850 nm and on a precisely parallel radio path with a frequency of 58 GHz are presented. All the attenuation events observed are systematically classified according to the hydrometeor type causing the particular event. Monthly and yearly propagation statistics on the free space optical path and radio path are obtained. The influence of individual hydrometeors on attenuation is analysed. The obtained propagation statistics are compared to the calculated statistics using ITU-R models. The calculated attenuation statistics both at 850 nm and 58 GHz underestimate the measured statistics for higher attenuation levels. The availability performance of a simulated hybrid FSO/RF system is analysed based on the measured data.
1. Introduction Free space optical communication systems are becoming a more and more important part of the telecommunication infrastructure. Terrestrial free space optical (FSO) links operating in the atmosphere are cost effective and easy to deploy [1, 2]. Furthermore, they can provide a much larger transmission capacity than most of the currently available terrestrial microwave communication links. There are commercially-available FSO systems providing transmission bit rates above 1 Gb/s, something that is difficult to achieve with current radio-frequency (RF) technologies. What is considered to be the single most important disadvantage of FSO links is the fact that their operational availability may be strongly degraded by adverse propagation effects caused by specific atmospheric conditions between the transmitter and receiver. An especially unpleasant role from this point of view is played by atmospheric hydrometeors and aerosols such as fog, snow, rain, or dust. The scattering of light on hydrometeors may result in significant attenuation of the received optical power. When planning FSO systems, a pragmatic approach is usually adopted to estimate the availability performance
from the link parameters. Attenuation statistics are then derived from the local statistics of atmospheric visibility using some of th
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