Analysis of a free space optical (FSO) link under the influence of spatial widening effect from propagation through clouds

Abstract

Free Space Optical communication is a line of sight technology that transmits light between two points through atmosphere as the channel of propagation. Clouds as a part of the communication channel cause signal power attenuation and spatial widening due to the inter symbol interference. These effects decrease the received signal power and increase the bit error rate (BER). The main objective of this thesis is to find out the bit error rate (BER) and signal to interference and noise ratio (SINR) in presence of cloud in different system parameters including cloud thickness, bit rate and wavelength. The transfer function of cloud is used to determine the spatial widening due to the inter symbol interference effect. The results are presented in terms of signal to interference and noise ratio (SINR), bit error rate (BER) and power penalty using the intensity modulation direct detection (IM/DD) system. It is noticed that cloud has a great effect on signal transmission due to the spatial widening. Analytical results show that the shorter wavelength region of 0.532 m is the preferred wavelength region for optical communication according to criteria of least power transmission and least spatial widening. It is also found that with the increase of bit rate, the spatial widening increases and consequently BER increases.