Photonics Laboratory, Physics Department, Iran University of Science and Technology, Tehran, Iran
In this paper, the effects of scintillation phenomena on Bit Error Rate (BER) and Signal to Noise Ratio (SNR), which are essential characteristics in Free Space Optical (FSO) communication system, are studied. Until now various methods have been introduced to decrease BER and increase the link's reliability. Optimizing SNR is one of the fundamental methods to decrease BER value. Intensity fluctuations variance of laser beam on the receiver optics due to propagation through turbulent atmosphere which is called Scintillation Index is an effective parameter in SNR. Thus, due to the importance of this index in FSO systems, to study the effects of source and turbulence parameters on BER, first the scintillation index of incoherent flat-topped laser beam propagating through turbulent atmosphere is calculated (using Kolmogorov spectrum model). Then, an analytical formula for SNR and so BER based on Log-Normal irradiance distribution function is expressed. With the help of this formula, results of investigations are shown by graphs. Simulations show that scintillation index and source parameters such as modulation methods and order of beam's flatness have a strong effect on SNR and BER.