On the derivation of exact analytical FSO link attenuation model

The development of semiconductor technology has led to an increase of the usable bandwidth of light-emitting diodes (LED), which are suitable for indoor high-speed communications or free-space optical (FSO) communications over a relatively short distance. The high-speed long-distance FSO links, where turbulence effects are considerably high, are a domain of laser sources. Hence, the paper covers the study of an exact analytical model of FSO link attenuation and the benefits of using an elliptically symmetrical Gaussian beam rather than a circularly symmetrical one.The paper further generalises the study to the FSO link misalignment and the pointing error analysis. The main contribution is in the derivation of an exact laser beam attenuation model, which is further used to analyse the geometrical losses in FSO systems as well as a general misalignment of an elliptically symmetrical beam in any direction from a circular receiver aperture. The challenging mathematical part includes two and six expressions of the general laser beam attenuation model for FSO communications taking into consideration circular and elliptical beams, respectively. The paper concludes with an analysis of advantages of using elliptical beams in FSO systems and a discussion on optimal orientation of the major beam axis with respect to the maximisation of the link availability.The paper summarises some previous results of the team of authors to further extend the model's applicability into more general terms towards a unified model. Copyright (c) 2014 John Wiley & Sons, Ltd.