Analytical performance evaluation of a multiple subcarrier modulated FSO communication system with coherent optical receiver under strong atmospheric turbulence

Optical communication through Free-Space termed as FSO system became popular in recent days as a possible alternative to solve the bottleneck of connectivity problem. But atmospheric turbulence induced fading may severely degrade the performances of FSO communication system. We developed an analytical approach here to evaluate the performances of FSO communication system in respect of carrier to noise ratio and bit error rate with RF subcarrier modulation considering the strong atmospheric turbulence effect and the effect is modeled as gamma-gamma distribution. An analytical expression is developed to find carrier to noise ratio (CNR) by considering the turbulence effect at the coherent optical receiver output. Results are analyzed inform of average CNR, BER and power penalty taking into account the turbulence effect for a certain BER for different system parameters like variance of turbulence, link distance, local oscillator power etc. It is found that at a data rate of 10 Gbps with number of subcarrier 4, the power penalty at a BER of 10
⁻⁹
is 6dB for a link distance of 3.6 Km.