Performance Analysis of Coherent Modulation Schemes in Free-Space Optical Communication Links

Free space optical communication is widely used for long range of distances. Laser beam signals are transmitted through air in coherent free space optical communication. Due to atmospheric turbulence, an optical signal gets affected. This turbulence causes fluctuations in the intensity of the received optical signal. The performance of free space optical communication links is severely degraded due to turbulence. Spatial diversity and coding schemes are used to mitigate the effect of turbulence. The channel parameter is within the range (1,2) and scintillation index is within the range (2,3). The bit error rate of BPSK and 4-QAM is analyzed using closed form moment generating functions under K-distributed turbulence.