Modeling of Pointing Errors in Terrestrial FSO Links Caused by Building Sway Under Wind Loads

Abstract

With their high data rate capacity, free space optical (FSO) communication systems can be used for last mile access, backhauling and fiber optic replacement. Terrestrial FSO links are typically installed on building roofs and are prone to building sways due to dynamic wind loads. In this paper, we provide a realistic modeling of the pointing errors in terrestrial FSO links relating them to the underlying physical phenomena. Towards this end, we use a civil engineering software for multi-story building analysis and design in conjunction with a wind simulator. We conduct extensive simulations to characterize the behaviour of various building sizes under wind loads. Statistical analysis of the building sway motion due to wind demonstrates that the motion is Gaussian in each axis and is in good agreement with current literature. However, it is also observed that the sway motion is dominated by the major axis (horizontal) while the other two are negligible in amplitude when the building is directly facing the wind. This leads to a zero mean single-sided Gaussian distribution. Through non-linear regression, we propose a closed-form expression for the standard deviation as a function of building height, width and wind speed. Afterwards, we present a closed-form expression of the error probability as a function of these environmental parameters and confirm its accuracy through numerical computations.