Experimental study of atmospheric turbulence effects on RoFSO communication systems

Many existing and emerging broadband wireless services benefit from the Radio on Fiber (RoF) technology offering high speed and large bandwidth over long distance at a low attenuation. Although RoF approach works well in many cases, in fiber not feasible area, free- space optics (FSO) communication techniques have received renewed interest as alternative for Radio-Frequency (RF) signal transmission-concept referred to as Radio on FSO (RoFSO)-because they can offer similar capacity while being cost effective and secure access without extensive installation of copper or fiber infrastructure. We are currently in the development stage of the advanced RoFSO system. On the other hand, atmospheric turbulence manifested as beam wander, intensity fluctuation and beam spreading has significant influence on the performance of conventional FSO as well as RoFSO systems. In order to measure, characterize and quantify the influence of atmospheric turbulence in our system deployment environment, we described in this paper a setup Radio Frequency-FSO (RF-FSO) link to test the basic characteristics of RF signal transmission under various atmospheric and weather conditions e.g., clear weather, clouds, rain, fog and snow. We have attempted to quantify the strength of atmospheric turbulence by calculating the refractive-index structure parameter C_n ² from scintillation index indicating intensity fluctuation caused by atmospheric turbulence. Correlation analysis on carrier-to-noise ratio (CNR) and C _n ² was also made and presented. In addition, a comparative measurement to characterize intensity scintillation and Angle-of-Arrival (AoA) variance has also been presented in this paper. The experimentally derived data and results will be available for antenna design, link margin prediction and evaluation of performance criterion of future RoFSO systems in different deployment environments.