Investigation of optimum FSO communication link using different modulation techniques under fog conditions

The FSO communication system offers high data rate investigated over the last few decades because of extraordinary advantages like unlicensed frequency and bandwidth at low power consumption, simple design, hasty, and minimal installation cost, including no right of way. It is essential to investigate solutions against degrading factors like absorption and scattering caused by fog, dust, rain, smog, and uncertain temperature variation of environmental channels. In this work various modulation techniques (AM, CS-NRZ, CS-RZ, DB-NRZ, MDB-NRZ, MDB-RZ, RZ, NRZ) are simulated and used to mitigate the weather attenuation of the specific airfield of Lahore, Pakistan under fog conditions, to provide a reliable FSO communication link for high data rate up to 40 Gbps over a link distance from 1.2 to 1.8 km at transmitted power up to 34 dBm in congested region. The real-time visibility data was taken metrological department for the estimation of attenuation under fog conditions and simulated using Optisys software for further investigation. To choose an FSO communication link, analysis for data rate, link distance, SNR, BER and Q-factor are performed under fog conditions using eight different modulation techniques. An increase in signal channel loss has been observed under fog conditions and performance of the FSO communication system is degraded consequently. The 3 R's (range, rate, and reliability) depend on each other if the link range is tarnished in a foggy condition that will also degrade the data rate and subsequently, reliability of the FSO system. It is observed that for maximum link distance, the performance parameters of AM modulation technique are prominent and more efficient, offering better Q-factor value at 6.08 dB, lower bit error rate at 7.03 × 10^-10, and better SNR of 4.29 dB. The results also show that AM modulation technique offers better signal-to-noise power and has good SNR due to well-received signal power as compared to all other modulation techniques. This research will be helpful to design and implement an FSO communication system under foggy conditions in a metropolitan city to provide a high data communication link among different national institutions.