Mitigation of Atmospheric Attenuations in Hybrid Fiber-optical and Free-space Optical Channel for Last-mile Communication System

Abstract

The aim of this research is to investigate the performance of a hybrid fiber-optical (FO) and free-space optical (FSO) communication system to reach the last mile, as well as to propose a technique to overcome atmospheric attenuation. Installing transmission cables between buildings is costly and difficult, but FSO technology can be implemented where fiber-optic cables cannot be installed. This work considers attenuation effects in weather conditions such as haze, thin fog, thick fog, and heavy fog. A single FSO channel (1*1), dual FSO channels (2*2), and four FSO channels (4*4) are cascaded in a fiber optic channel to reach the last mile and to mitigate attenuation in signal transmission over free space. The Q-factor, bit error rate (BER) at the receiver, and eye diagrams were analyzed for all cases. This system is demonstrated up to 3.5km FSO channel range for haze and thin fog conditions and 2.2km and 1.7km range for thick and heavy fog conditions. The system results show improvement in BER as 4.93e-040 for 1*1 FSO channel, 1.07e-078 for 2*2 FSO channel, and 1.28e-154 for 4*4 FSO channel in case of 22dB/km atmospheric attenuation for 1.4km range with minimum power penalty. A data stream of 10 Gbps was transmitted under four attenuation conditions, and the results show that 4*4 FSO channels have a better Q-factor and BER than other systems.