Investigation of PSK/Qam Modulated Hybrid Fiber Optic and Free Space Optic System Under Various Atmospheric Losses

Abstract

This research aims to investigate how effectively digital modulation performs to transfer data via hybrid fiber optic and free space optic (FO-FSO) channels for last-mile communication systems. Digital modulation techniques investigated are phase-shift keying (PSK) 8-PSK, 16-PSK, quadrature amplitude modulation (QAM) 4-QAM, 16-QAM, and 64-QAM. FSO is line-of-sight technology being a solution to a last-mile communication system for the challenge of fiber optic cables installation. Combining FSO with fiber optic technology avoids bending losses and the implementation challenges of fiber optic cables in metropolitan areas and between buildings. But atmospheric challenges such as haze, fog, and rain cause signal loss while transmitting data in free space. Also, atmospheric turbulence and antenna misalignments lead to signal error. This paper proposed the models of QAM and PSK digital modulated signal transmission over FO-FSO and compared the results to better fiber optic-FSO links to achieve a last-mile communication network. This fiber optic and FSO model is analyzed for the distance up to 100 km of fiber optic channel and 0.4-1.5 km of FSO channel. Constellation diagrams and error-vector magnitude (EVM) concerning received power at the receiver are compared to analyze FSO channel capacity for various weather attenuations.