Variation of altitude on the variance of angle of arrival fluctuations for optical beam propagation in free space optical communications

Abstract

Media convergence, endlessly increasing request for adequate bandwidth, fast growing number of mobile subscribers and spectrum congestion have forced the recent advancement in the research of Free Space Optical (FSO) Communication system. This technology has the potential to provide adequate bandwidth and cater for the fast growing number of voice, data and multimedia users. However, the system performance is being impaired by signal fluctuation, scattering and absorption. In addition to these impairments, the distortion of optical beam also contributes to total signal degradations. As it is important to apply several mitigation techniques to combat these challenges, it is also important to do a thorough study on the level of turbulence contributed by the refractive index structure and the height. This paper presents a model study on the atmospheric turbulence effects due to refractive index and height, the effects on the Angle of Arrival (AOA) and its influence on the FSO communication link. In this work, we used the Hufnagel-Valley Boundary (HVB) model and Gamma-Gamma distribution model with a suitable modulation technique to investigate the effects of atmospheric turbulence on the optical beam propagating through free space. Thus, the amplitude and phase fluctuations were investigated and this study demonstrates that variations in height and the refractive index of the propagating medium are major causes of turbulence. The heights of FSO link were varied and the effects of turbulence were simultaneously observed on the FSO link in order to estimate the status of the link performance.