Effect of Visibility Variation on Free Space Optical Communication System over the Eastern Coast of South Africa Using Climatic Data

Existing wired and wireless communication systems do not favor communication systems that require high performance characteristics, license-free spectrum with high bandwidth access, high security and cheap installation cost. In recent years, it has been demonstrated that the Free Space Optical (FSO) communication system has characteristics that match the above benefits over other forms of communication systems. However, a significant degrading component that considerably impacts its propagation is the occurrence of atmospheric fog, which greatly diminishes its quality when it propagates over an atmospheric scattering medium. This paper evaluates the degree of the effects of various atmospheric conditions within the eastern coast of South Africa: Durban as a case study, using different approaches available for Free Space Optical communications. This work also classified the entire visibility range into different classes, to properly account for all the atmospheric conditions in this location. The collected visibility data were used to estimate the specific optical attenuation magnitude and the received optical power over Durban for the entire year 2011. The results obtained showed that there are several occurrences of severe atmospheric attenuation especially during the worst-case scenarios, reaching as high as 169.81 dB/km which can cause optical link failure or outage. The results of the computed link margin also showed that during situations of thick, moderate and light fog conditions with expected atmospheric attenuations as high as 340 dB/km, 85 dB / km and 34 dB / km, the optical link cannot transmit further than 0.34 km, 0.70 km and 1.24 km respectively.