Analysing The Effect Of Visibility And Scintillation On Free Space Optical Communication: A Case Of Dodoma And Dar Es Salaam

ABSTRACT

Free space optical communication (FSO) is receiving a lot of attention as an alternative last mile wireless communication system. This is because of its high data rate, large bandwidth and easy installation than the traditional radio frequency (RF) and fiber optic communication systems. However the medium through which the signal travels is the atmosphere. This medium is affected by the prevailing weather conditions. FSO is prone to hash atmospheric conditions such as wind, temperature, humidity which induce scintillation. Rain, fog, snow, aerosols are the other conditions which induce visibility and affects the communication channel. In order to establish the feasibility of the technology while taking into account these impediments this study calculated visibility and scintillation attenuation for Dar es Salaam and Dodoma based on data obtained from Tanzania Meteorological Agency (TMA) and weather underground (WU). The attenuation coefficients were also calculated and input into the simulation package called OptiSystem 7 to simulate the bit error, Q factor and eye diagrams. The results of the simulation have shown that Dar es Salaam has higher FSO attenuation that Dodoma. It has also been shown that Dodoma weather conditions provide better FSO communication than Dar es Salaam. The transmission using the study parameters shows that one can transmit for a distance of eight (8) km for Dar es salaam and above twelve (12) kilometre for Dodoma. A comparison of the two modulation schemes has shown that NRZ is the best modulation scheme that could be used for the two cities and October is best month for transmission in Dodoma. This technology is feasible under the parameters that were used in this study and therefore is recommended for adoption.