Resilience of long range free space optical link under a tropical weather effects

Abstract

Free-Space Optics (FSO) can transmit high data rate from several meters to kilometers. They are potential candidates in overcoming high data rate and longer last miles connection needs in the context of development of mobile broadband networks in many countries. The optical signal is generally affected by weather conditions which still being a major issue on the performances and availability of FSO systems. Studies are developed on the optimizations of FSO systems but most of them do not take into consideration the overall external effects on the signal. In another hand, there are new investigations and models established under laboratory conditions and not verified deeply in real environments. In that paper we investigate on the reliability and resilience of a 5 km FSO link simulated by using visibilities data recorded from Dakar city. The Percentages of availabilities, the power margins, optimal relays placement, and architecture are proposed when operating conditions vary from clear atmosphere to heavy rain or in presence of heavy dust. During these bad weather conditions, often occurred in tropical climate, the effect of turbulence induced irradiance fluctuations, varying beam divergence angle and misalignment issues were analyzed and estimated. In addition lognormal distributions established will allow easy use of channel modeling and survey of FSO systems in similar physical environments. Keywords: FSO link margin, Link availability, Rain losses, Scintillation effects, Dust losses, resilience