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Modeling and estimation of scattering attenuation and scintillation effects on optical wireless communication systems in South Africa.

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Optical wireless communication (OWC) is a viable complementary solution for next-generation communication networks saddled with meeting the great demands of high data rates and fast internet connectivity. Its numerous advantages include: high data throughput; secure transmission; license-free spectrum; relative low cost of deployment; flexible network connectivity; etc. However, OWC system performance is severely degraded by atmospheric conditions such as fog and scintillation. Most of the proposed FSOC and hybrid FSOC systems in the literature are limited in their capacity to predict the extent to which atmospheric disturbances will impact on the performance of FSOC links in each location where they are to be deployed. This is because of the complexities involved in accessing and analyzing the information on the unique meteorological and climatic characteristics of the locations of interest prior to FSOC link deployment. This important information is necessary for determining the fade margin required by FSOC systems to withstand atmospheric disturbances in various locations of deployment. The effects of other atmospheric conditions such as gas absorption, molecular scattering, and aerosol absorption on the transmission wavelengths of interest (850 and 1550 nm) are negligible, and as such, were not considered in this study. This research, therefore, focuses on the investigation and modeling of scattering attenuation and irradiance fluctuations based on the unique climatic peculiarities of nine major cities in each of the provinces of South Africa where OWC links are to be deployed. These cities are Bloemfontein, Cape Town, Durban, Johannesburg, Kimberley, Mafikeng, Mbombela, Polokwane, and Port Elizabeth. Meteorological data of visibility, wind speed, relative humidity, temperature, fractional sunshine, and atmospheric pressure from 1st January 2010 till 30th June 2018, for each of the locations of interest, are statistically processed and used in the investigation, estimation, and modeling of atmospheric phenomena affecting the performance of OWC signals. To achieve this, visibility modeling and prediction for OWC systems are performed using regression analysis. The results obtained show that various simple and multiple linear regression models reliably forecast visibility from other meteorological parameters considered in this study. The model's selection may be influenced not only by its performance but also by the parameters' availability. While caution is taken to avoid model over-specification, multiple linear regression models are preferable over simple regression models. The significance of the results obtained is the validated alternatives the simple and multiple linear regression models provide while saving costs and avoiding the complexities of measuring FSO visibility in the investigated locations. The relationship between atmospheric visibility and aerosol scattering attenuation has been established by various aerosol scattering models based on the Mie scattering theory. This is made possible because the radii of aerosol particles in the atmosphere are approximately equal to the infra-red wavelengths of optical signals. Thus, the cumulative distribution of visibility and aerosol scattering attenuations based on the Ijaz fog and Kim models for transmission wavelengths of 850 and 1550 nm in nine cities in South Africa are presented. The Ijaz fog and Kim models are also used in computing the probabilities of exceedance, deceedance, and encountering of different aerosol scattering attenuations for 850 and 1550 nm. The impact of these specific attenuations on free space optical communication (FSOC) link performance are investigated for all the various locations of interest. The results show that during foggy weather, the optical signals transmitted at 1550 nm encounter more scattering attenuation than those transmitted at the 850 nm wavelength. The reverse is the case during clear weather periods. Modeling of the minimum required visibility cumulative distribution functions (CDF) during foggy and clear weather conditions for both optical wavelengths is also presented. These CDFs are employed in evaluating the FSOC link availabilities in various cities in South Africa.


Doctoral Degree. University of KwaZulu-Natal, Durban.