Prediction of drop size distribution parameters for optical wireless communications through moderate continental fog

International Journal of Satellite Communications and Networking (Impact Factor: 0.74). 01/2011; 29:97-116. DOI: 10.1002/sat.950
Source: DBLP


Wireless optical communication links (OCL), or free space optics links involving optical ground stations are highly influenced by the earth atmosphere due to the interaction of the optical wave with particles of different size and shape. Fog, clouds, rain and snow cause significant signal attenuation, thus limiting the performance of OCL. In this paper, we consider the behavior of OCL in the troposphere under moderate continental fog conditions, which are important for both ground–ground and ground–space OCL. The impact of the droplet size distribution (DSD) of fog is investigated, by processing laser attenuation measurements carried out in Milan (Italy) and Graz (Austria). Significant differences are observed between measured and predicted attenuation when using standard values for the DSD parameters. Hence, new sets of DSD parameters are proposed to model peak, mean and median values of measured attenuation for moderate continental fog. These, in turn, can be useful to make accurate link availability predictions, thus improving the quality of service design for OCL. Copyright © 2010 John Wiley & Sons, Ltd.

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Available from: László Csurgai-Horváth,
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    • "Fog is characterized by several physical parameters such as liquid water content, particle size distribution, temperature and humidity. Since the size of fog particles is comparable to the transmission wavelength of optical and near infrared waves, Mie scattering applies and results in high attenuation [13]. Fog comprises of fine water droplets, ice crystals or smoke particles suspended in the atmosphere. "
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    ABSTRACT: The error characteristics of a free-space optical (FSO) channel are significantly different from the fiber based optical links and thus require a deep physical understanding of the propagation channel. In particular different fog conditions greatly influence the optical transmissions and thus a channel model is required to estimate the detrimental fog effects. In this paper we shall present the probabilistic model for radiation fog from the measured data over a 80 m FSO link installed at Graz, Austria. The fog events are classified into thick fog, moderate fog, light fog and general fog based on the international code of visibility range. We applied some probability distribution functions (PDFs) such as Kumaraswamy, Johnson SB and Logistic distribution, to the actual measured optical attenuations. The performance of each distribution is evaluated by Q-Q and P-P plots. It is found that Kumaraswamy distribution is the best fit for general fog, while Logistic distribution is the optimum choice for thick fog. On the other hand, Johnson SB distribution best fits the moderate and light fog related measured attenuation data. The difference in these probabilistic models and the resultant variation in the received signal strength under different fog types needs to be considered in designing an efficient FSO system.
    Radioengineering 09/2010; 19(3):460-465. · 0.65 Impact Factor
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    • "Fog, having very low densities, contains very small amount of water and thus results in lower values of LWC around 0.05 g/m 3 for a moderate fog (visibility range around 300 m). Much higher values of LWC (around 0.5 g/m 3 ) usually mean formation of thick or dense fog (visibility range of about 50 m) [20]. Similarly, clouds may have LWC value of 0.06405 g/m 3 and 1-3 g/m 3 for Cirrus and Cumulonimbus clouds, respectively measured in the same amount of space [22]. "
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    ABSTRACT: 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.
    Radioengineering 06/2010; 19(2). · 0.65 Impact Factor
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    ABSTRACT: Line of sight optical wireless or free space optics (FSO) plays an increasingly important role in our communication infrastructure as they offer gigabit per second data rates and low system complexity. The biggest disadvantage of terrestrial FSO links is that low clouds, dry snow and especially dense fog conditions entail heavy losses to the optical beam transmitted in the terrestrial free-space. We address here the effect of fog on optical wireless signals theoretically and experimentally and analyse measured fog attenuations in terms of its temporal and spatial variability. Attenuation data presented and discussed here is collected in Graz, Austria, in the winter months of year 2004-05 and year 2005-06. It is shown that continental fog attenuations vary spatially and temporally in case of terrestrial FSO link and has very distinct seasonal and diurnal dependence during the fog life cycle of continental fog.
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