Analysis of 25 Gbps 4-QAM-modulated coherent OFDM-FSO link employing LDPC channel coding across diverse atmospheric scenarios

Abstract Atmospheric turbulence and different environmental conditions severely reduce the performance and reliability of free-space optical (FSO) links. This paper describes a simulation-based analysis of signal quality of the proposed FSO link under various climatic conditions. It specifically examines the performance of a 25 Gbps 4-quadrature amplitude modulation (QAM)-based coherent optical OFDM (CO-OFDM) FSO system that is with and without the deployment of low-density parity-check (LDPC) channel coding. Several key performance indicators, such as bit error rate (BER), signal-to-noise ratio (SNR), received power, distance of the link and general reliability are considered. Simulation outcomes confirm that the use of LDPC channel coding makes the system resist atmosphere attenuation and turbulence by a much higher margin; that is, lower BER, higher SNR, good amount of received power, and more extended reliable communication distance. These enhancements reflect the practical advantages of LDPC coding in FSO link performance in adverse environmental conditions.