Outage capacity estimation of FSO links with pointing errors over gamma turbulence channels

The Free Space Optical (FSO) communication systems, are rapidly gaining popularity as effective, low cost and secure means of transferring data at high rates over relative short distances, with line of sight, through the atmosphere. However, due to the fact that the characteristics of the propagation path do not remain invariable, the systems' performance varies, as well. An important phenomenon which mitigates significantly their performance is the atmospheric turbulence, which causes the scintillation effect and results in fast irradiance fluctuations at the receivers' side, which could be modeled with various statistical distributions depending on the turbulence's strength. Here, we assume weak turbulence conditions and an accurate and with a very compact mathematical expression statistical model is the gamma distribution. Additionally, because of the very narrow optical beam the alignment between the transmitter and the receiver is not perfect and the pointing errors effect should be taken into account. Thus, in this work, we investigate the influence of these effects at the systems' performance, by means of the estimation of their outage capacity, over gamma modeled atmospheric turbulence channels with pointing errors. We derive closed form mathematical expressions for the above mentioned performance metric and we present our results, along with the corresponding simulation outcomes.