Performance Evaluation of Free Space Optical Communication in Dar es Salaam: Impact of Scintillation and Modulation Schemes

Abstract

Free space optical communication (FSO) holds significant relevance in the modern communication system as it offers high and unlimited data rates, enhanced security, rapid deployment, and low cost for installation. However, the performance of FSO transmission is greatly affected by harsh atmospheric conditions such as wind, temperature, and humidity, which induce scintillation. With the rapid growth of internet users and Dar es Salaam being a business city in Tanzania, higher and unlimited bandwidth for communication is highly demanded. This study primarily aims to evaluate the performance of FSO transmission in Dar es Salaam, Tanzania, by investigating the impact of atmospheric conditions particularly scintillation on link availability and transmission quality. We evaluated link availability and the effect of scintillation in terms of eye diagrams, Bit Error Rate (BER), and two modulation schemes (i.e. Return-to-Zero (RZ) and Non-Return-to-Zero (NRZ) schemes) in the Dar es Salaam region. Our work used weather data, including temperature, relative humidity, and wind speed average data, collected from January 2014 to December 2017 by the Tanzania Meteorological Authority (TMA) in the Dar es Salaam region for link availability and performance analysis. The simulation was performed to determine the FSO link availability, and the scintillation effect was analyzed using the Hufnagel Valley (HV) day prediction model. Results analysis indicates that link availability is significantly influenced by atmospheric conditions, with the simulation results showing that Dar es Salaam has higher FSO attenuation and that the transmission can sustain link availability up to a distance of two kilometers. A comparison of the two modulation schemes has shown that NRZ is the best modulation scheme that could be used, and January is the best month for transmission in Dar es Salaam. This technology is feasible and therefore is recommended for adoption.