BER performance improvement of FSO links with aperture averaging and receiver diversity technique under various atmospheric conditions

The performance of terrestrial free space optical (FSO) links is degraded by the presence of atmospheric turbulence and weather conditions. In this paper, it is proposed to evaluate the bit error rate (BER) of a FSO link by modeling the turbulence as a gamma-gamma distribution and incorporating the effect of weather by the Beer-Lambert's law. Results show that BER increases as the turbulence strength goes from weak to strong. The presence of weather conditions such as fog, haze, drizzle, etc., cause a degradation in the link performance, with fog having the worst effect followed by haze, drizzle and very clear weather conditions over all turbulence regimes. Further, the performance enhancement brought about by using receiver diversity schemes, namely aperture averaging and array receivers is studied and compared. With an increase in the aperture diameter, BER decreases irrespective of the turbulence strength and weather conditions. Also, as the number of direct detection receivers in the array are increased, BER decreases. However, it is seen that in strong turbulence regime or in presence of fog, diversity receivers become the preferred choice in comparison to the aperture averaging technique.